Underfloor Air Distribution (UFAD) Design Guide
Underfloor Air Distribution (UFAD) Design Guide
Underfloor Air Distribution (UFAD) Design Guide
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This publication was prepared under ASHRAE Research Project RP-1064
in cooperation with TC 5.3, Room Air Distribution.
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Underfloor
Air Distribution (UFAD)
Design Guide
Fred S. Bauman
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ISBN 1-931862-21-4
ASHRAE has compiled this publication with care, but ASHRAE has not investi-
gated, and ASHRAE expressly disclaims any duty to investigate, any product, ser-
vice, process, procedure, design, or the like that may be described herein. The
appearance of any technical data or editorial material in this publication does not
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process, procedure, design, or the like. ASHRAE does not warrant that the informa-
tion in the publication is free of errors, and ASHRAE does not necessarily agree with
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mation in this publication is assumed by the user.
ASHRAE STAFF
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Contents
Acknowledgments xi
Chapter 1Introduction 1
1.1 Purpose of Guide 1
1.2 System Description 2
1.3 Background 7
1.4 Benefits 11
1.4.1 Improved thermal comfort 11
1.4.2 Improved ventilation efficiency
and indoor air quality 12
1.4.3 Reduced energy use 12
1.4.4 Reduced life-cycle building costs 13
1.4.5 Reduced floor-to-floor height
in new construction 14
1.4.6 Improved productivity and health 14
1.5 Technology Needs 14
1.5.1 New and unfamiliar technology 15
1.5.2 Lack of information and
design guidelines 15
1.5.3 Gaps in fundamental understanding 15
1.5.4 Perceived higher costs 16
1.5.5 Limited applicability to retrofit
construction 16
1.5.6 Problems with applicable
standards and codes 17
1.5.7 Cold feet and draft discomfort 17
1.5.8 Problems with spillage and dirt entering
UFAD systems 18
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CONTENTS
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2.3.3 Stratification Height 36
2.3.4 Controlling Stratification 37
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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CONTENTS
viii
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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CONTENTS
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14.1.5 Ventilation Performance 186
14.1.6 Field Studies 187
14.1.7 Productivity Studies 187
14.1.8 Cost Studies 187
14.2 Design Tools 187
14.3 Standards and Codes 188
14.4 Building Industry Developments 188
14.5 Technology Transfer 188
Glossary 189
Index 237
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Acknowledgments
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ACKNOWLEDGMENTS
mann and Blaevoet), Ralph Hockman (Tate Access Floors), Eric Horn
(Webcor Builders), Dan Int-Hout (Krueger), Tim Irvin (York Interna-
tional), Blair McCarry (Keen Engineering), Jim Reese (York Interna-
tional), Dennis Stanke (Trane), Steve Taylor (Taylor Engineering),
Dave Troup (HOK), Mark Vranicar (Critchfield Mechanical), and
David Wyon (Technical University of Denmark).
Several graduate student researchers in the Department of Archi-
tecture at UC Berkeley assisted me on this project. I would like to thank
Rachel Bannon for her writing and editorial skills, and Jane Lin, Amiee
Lee, and Susie Douglas, who produced the majority of the graphics.
Many of my research colleagues at UC Berkeley have made valu-
able contributions through their critical reviews, interest, and enthusi-
astic support of our UFAD research program. In particular, I would like
to thank Tom Webster, my primary co-researcher within the CBE
UFAD research program, for our many discussions of UFAD issues
that improved our collective understanding of UFAD technology and
guided our research directions. I would also like to express my warm
appreciation to Ed Arens, Gail Brager, Charlie Huizenga, Cliff Feder-
spiel, Zhang Hui, and David Lehrer, all with CBE. In addition, my
thanks go to William Fisk, David Faulkner, and Doug Sullivan of the
Indoor Environment Department at Lawrence Berkeley National Lab-
oratory for their technical advice and interest.
Finally, I give my love and thanks to Jenny and Rocko for all their
support and understanding during the many days, nights, and long
hours that I worked on the design guide.
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Chapter 1
Introduction
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CHAPTER 1INTRODUCTION
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
regularly occupied work space). Typically, the occupant can control the
perceived temperature of the local environment by adjusting the speed
and direction, and in some cases the temperature, of the incoming air
supply, much like the dashboard of a car. Although not a requirement,
the design of a large majority of TAC systems has involved the use of
underfloor air distribution (UFAD). For purposes of presentation in
this guide, TAC systems are distinguished from standard UFAD sys-
tems by their higher degree of personal comfort control provided by the
localized supply outlets. TAC supply outlets use direct velocity cooling
to achieve this level of control and are therefore most commonly con-
figured as fan-driven (active) jet-type diffusers that are located as part
of the furniture or partitions. Active floor diffusers are also possible.
Throughout this guide, use of the term TAC system will refer to a
UFAD system featuring active supply outlets with the above-described
individual control capabilities. TAC systems that do not employ UFAD,
such as desktop systems ducted down from an overhead system, are not
covered by this guide. For further information on a complete range of
TAC systems, see Bauman and Arens (1996) and Loftness et al. (2002).
Figures 1.1, 1.2, and 1.3 present and compare schematic diagrams
of a conventional overhead system, UFAD system, and UFAD with
TAC system, respectively, for a cooling application in an open-plan
office building. Some of the most important advantages of UFAD sys-
tems over ceiling-based systems occur for cooling conditions, which
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CHAPTER 1INTRODUCTION
Figure 1.3 Cutaway of typical office work space showing UFAD with
TAC system.
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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CHAPTER 1INTRODUCTION
nal units, either used alone or in combination with one another; (2)
zero-pressure plenum with air delivered into the conditioned space
through local fan-powered (active) supply outlets in combination
with the central air handler; and (3) in some cases, ducted air supply
through the plenum to terminal devices and supply outlets. The use
of pressurized underfloor plenums appears to be the focus of cur-
rent practice, although zero-pressure plenums pose no risk of
uncontrolled air leakage to the conditioned space, adjacent zones,
or the outside.
Within the plenum, air flows freely in direct contact with the ther-
mally massive slab and floor panels and enters the workspace
through diffusers at floor level or as part of the furniture or parti-
tions. Because the air is supplied directly into the occupied zone,
floor supply outlet temperatures should be maintained no lower
than in the range of 61-65F (16-18C) to avoid uncomfortably cool
conditions for the nearby occupants. For TAC supply outlets located
closer to the occupant (e.g., furniture- or partition-based diffusers)
where the occupant is exposed to diffuser velocity cooling, even
warmer supply temperatures may be advisable.
UFAD systems are generally configured to have a relatively larger
number of smaller supply outlets, many in closer proximity to the
building occupants, as opposed to the larger diffusers and spacing
used in conventional overhead systems. Outlets that are located
within workstations or otherwise near occupants at their work loca-
tions are typically adjustable or thermostatically controlled, provid-
ing an opportunity for adjacent individuals to at least have some
amount of control over their perceived local thermal environment.
Fan-driven TAC diffusers can more directly influence local thermal
comfort by using increased air movement to provide occupant cool-
ing.
Air is returned from the room at ceiling level, or at the maximum
allowable height above the occupied zone. This produces an overall
floor-to-ceiling airflow pattern that takes advantage of the natural
buoyancy produced by heat sources in the office and more efficiently
removes heat loads and contaminants from the space, particularly for
cooling applications. In contrast to the well-mixed room air condi-
tions of the conventional overhead system, during cooling conditions,
UFAD system operation can be optimized to promote some amount
of stratification in the space, with elevated temperatures and higher
levels of pollutants above head height where their effect on occupants
is reduced.
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
1.3 BACKGROUND
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CHAPTER 1INTRODUCTION
indoor air, the acoustics, and the quality of the building man-
agements service.
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CHAPTER 1INTRODUCTION
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
1.4 BENEFITS
What are the potential advantages that UFAD systems have over
traditional overhead air distribution systems? Well-engineered systems
can provide the following.
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pant) provide personal control of an occupants microclimate over a
sizable rangeup to 13F (7C) for desktop outlets and up to 9F (5C)
for floor-based outlets [Tsuzuki et al. 1999]. These tests measured only
sensible cooling rates; total cooling (including latent effects) would be
even higher. This amount of control is more than enough to allow the
full range of individual thermal preferences to be accommodated. Pas-
sive diffusers (diffusers that do not rely on local fans), such as the com-
monly used swirl floor diffusers in UFAD systems, will not provide this
same magnitude of control. However, by being accessible to the occu-
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CHAPTER 1INTRODUCTION
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CHAPTER 1INTRODUCTION
underfloor plenum, floor diffusers along with all power, voice, and data
outlets can be placed almost anywhere on the raised floor grid. In-house
maintenance personnel can carry out these reconfigurations at signifi-
cantly reduced expense using simple tools and modular hardware.
Firms that are more likely to install underfloor systems are also, for the
very same reasons, more likely to churn at a higher rate. For further dis-
cussion, see Chapter 10.
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CHAPTER 1INTRODUCTION
2002a, 2002b; Lin and Linden 2002; Yamanaka et al. 2002]. For fur-
ther discussion, see Chapter 2.
1.5.3.2 Underfloor air supply plenum. An important differ-
ence between conventional and UFAD system design is the heat
exchange between the concrete slab, raised floor panels, and the sup-
ply air as it flows through the underfloor plenum. If the slab has
absorbed heat, particularly from warm return air flowing along the
underside of the slab, then supply temperature will increase with dis-
tance from the plenum inlet. Energy and operating cost savings,
including peak shaving, can be achieved by using the concrete slab in
a thermal storage strategy, but further research is still needed to opti-
mize and quantify this effect. For further discussion, see Chapter 4.
1.5.3.3 Whole-building performance. There currently does
not exist a whole-building energy simulation program capable of
accurately modeling UFAD systems, a subject discussed by Addison
and Nall (2001). This is one of the top technology needs identified by
system designers. Additionally, whole-building performance data are
needed from completed UFAD projects in the form of energy use,
indoor environmental quality, occupant satisfaction, comfort, health,
and performance, and first and life-cycle (operating) costs to quantify
the relative benefits of the technology.
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CHAPTER 1INTRODUCTION
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
1.6 APPLICATIONS
UFAD systems are well suited for all office buildings, especially
those with open office plans in which adjustable diffusers can allow
occupants to individually control their local workstation environments.
In high-tech offices and other businesses with extensive use of infor-
mation technologies and typically high churn rates (e.g., dot-com
offices, call centers, trading floors), the flexibility provided by service
delivery systems, including cable management, is a great benefit.
Because of the significant savings in life-cycle costs for UFAD sys-
tems, owner-occupied buildings are strong candidates for application.
Other buildings suitable for UFAD systems include schools, television
studios, and light manufacturing installations that dont involve spill-
age of liquids.
Any building that already is using a raised floor system for cable
distribution or other purposes should consider a UFAD system. An
exception would be clean room applications that are designed to return
air at floor level. There are other areas in buildings where raised floors
and underfloor air distribution are generally not appropriate. These
areas include those in which spillage has the potential to occur, such as
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CHAPTER 1INTRODUCTION
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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UFAD and TAC technology. In addition, a description of the LEED
(Leadership in Energy & Environmental Design) Rating System is
provided.
Chapter 12, Design Methodology, presents a summary of recom-
mended design procedures for UFAD systems. In particular, those
areas where UFAD design differs from conventional overhead air
distribution design are discussed.
Chapter 13, UFAD Project Examples, presents a list of web sites,
references and other sources describing examples of UFAD and
TAC system configurations.
Chapter 14, Future Directions, describes ongoing research and
standards development work, as well as recommended future direc-
tions within the building industry, addressing UFAD and TAC tech-
nology needs.
Glossary, defines terminology related to UFAD and TAC technol-
ogy specifically and to HVAC design in general.
References and Annotated Bibliography, provides a complete list
of references for all sections as well as other publications related to
UFAD and TAC technology for readers seeking additional informa-
tion. Brief descriptions of the contents of key references are pro-
vided.
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Chapter 2
Room Air Distribution
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CHAPTER 2ROOM AIR DISTRIBUTION
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CHAPTER 2ROOM AIR DISTRIBUTION
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CHAPTER 2ROOM AIR DISTRIBUTION
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feed the entrainment. These plumes will expand and rise until they
encounter equally warm air in the upper regions of the space. The upper
zone above the stratification height is characterized by low-velocity
recirculation, which produces a fairly well mixed layer of warm air
whose contaminant concentration exceeds that in the lower levels of the
space.
A key feature of the stratification height in a true DV system is that
vertical air motion across the level is due only to the effects of buoy-
ancy. In an idealized configuration in which only heat sources are
present, only thermal plumes of sufficient strength will rise into the
upper zone. The net result will be that once the warmer and more pol-
luted air enters the upper zone, it will never reenter the lower zone. This
principle is the basis for the improved ventilation effectiveness and heat
removal efficiency associated with DV systems. In some practical
applications (e.g., morning start-up, winter), there will also be sources
of cooling present in the space, such as a cold perimeter window. In this
situation, the resulting cold downdraft may transport some air from the
upper zone back down into the lower zone. Figure 2.4 shows these basic
elements in a simplified schematic of a DV system. In the figure, q0 rep-
resents the supply airflow into the room from a low side-wall diffuser,
q1 is the upward moving airflow contained in thermal plumes that form
above heat sources, and q2 is the downward moving airflow resulting
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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Figure 2.5 Vertical profiles of pollutant concentrations in a room
with displacement ventilation.
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CHAPTER 2ROOM AIR DISTRIBUTION
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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an UFAD system in an office environment. The diagram identifies the
two characteristic heights in the room that define the three zones in the
room: (1) the throw height (TH) of the floor diffusers and (2) the strat-
ification height (SH), similar to that found in DV systems. As shown in
the figure, UFAD diffusers typically create clear zones in their imme-
diate vicinity, representing regions within which long-term occupancy
is not recommended due to excessive draft and cool temperatures.
However, when under direct individual control by the occupanta fea-
ture of UFAD and especially TAC systemsthese local thermal con-
ditions may be acceptable and even desirable for short-term occupancy.
There is a price for improving comfort conditions (at high load) as the
increased mixing in the occupied zone diminishes the ventilation per-
formance compared to DV systems. In any case, the control and opti-
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CHAPTER 2ROOM AIR DISTRIBUTION
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CHAPTER 2ROOM AIR DISTRIBUTION
air movement in this zone is entirely buoyant, driven by the rising ther-
mal plumes around convective space heat sources. The formation of
these thermal plumes is uninhibited in this region, as air movement is
not affected by supply air jets. The vertical temperature gradient in this
zone tends to be greatest, approaching that for DV systems. The middle
stratified zone only exists when the throw height of the supply outlets
is below the stratification height, or upper boundary of the room,
whichever is lower.
2.3.1.3 Upper (Mixed) Zone. The upper mixed zone is com-
posed of warm (contaminated) air deposited by the rising heat plumes
within the space. Although its average air velocities are generally quite
low, air within this zone is relatively well mixed as a result of the
momentum of thermal plumes penetrating its lower boundary. This
zone is analogous to the upper zone found in spaces served by DV sys-
tems (compare Figures 2.2 and 2.6). Its bottom boundary, the stratifi-
cation height, is primarily a function of the ratio of the space heat load
to the supply airflow rate. As discussed below, if jets from the supply
outlets penetrate into this zone, its depth (or even existence) may be
affected, although if properly controlled this may be a secondary effect
(Figure 2.8).
In cases where the supply airflow rate is equal to or greater than the
volume of the heat plumes generated within the space, the upper mixed
zone will not form and the space may be modeled as a two-zone model,
consisting only of the lower mixed and middle stratified zones.
34
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CHAPTER 2ROOM AIR DISTRIBUTION
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tage that UFAD systems have over DV systems when trying to maintain
comfort at higher heat loads. For the same room airflow rate, DV sys-
tems will need to use a higher supply air temperature than UFAD sys-
tems to avoid overly cool temperatures near the floor. Assuming all
conditions are the same (heat load, supply airflow, and temperature),
DV systems will produce higher stratification in the occupied zone
compared to UFAD systems. The only way for DV systems to avoid
excessive stratification at high heat loads is to increase the room airflow
rate, a subject discussed by Yuan et al. (1999). While suggesting that
cooling loads as high as 40 Btu/h-ft2 (120 W/m2) can be handled by DV
systems, Yuan et al. also state that this requires sufficient space for large
supply diffusers (often impractical in office configurations), and that
the energy consumption will increase significantly.
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CHAPTER 2ROOM AIR DISTRIBUTION
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Figure 2.10 Effect of room airflow variation at constant heat input,
swirl diffusers, interior zone.
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
3.2F (1.8C). The difference between the middle and first profiles also
demonstrates that despite a 40% reduction in airflow rate, the temper-
ature in the space only increases by about 1F (0.5C) up to a height of
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nearly 4 ft (1.2 m).
Figure 2.11 shows test results from Webster et al. [2002b] where
supply air temperature (SAT) was varied over the range of 60-67F (16-
19C) for constant heat input (19 Btu/h-ft2 [59 W/m2]) and room air-
flow rate (0.5 cfm/ft2 [2.7 L/s/m2]) for a simulated interior space. As
shown, the temperatures of the profiles increase or decrease with the
change in supply air temperature but retain approximately the same
shape. Resetting SAT may be advisable in combination with adjust-
ments in total room airflow to achieve optimal comfort conditions
throughout the occupied zone.
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Chapter 3
Thermal Comfort
and Indoor Air Quality
Thermal comfort and indoor air quality are two of the leading fac-
tors in determining the success of a buildings HVAC system perfor-
mance. As described in Chapter 2, the traditional design solution in the
vast majority of commercial buildings has been to use an overhead air
distribution system that attempts to maintain close to uniform temper-
atures and ventilation air throughout the conditioned space. In this
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CHAPTER 3THERMAL COMFORT AND INDOOR AIR QUALITY
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CHAPTER 3THERMAL COMFORT AND INDOOR AIR QUALITY
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as individual preferences can be accommodated. In every work envi-
ronment, there are significant variations in individual comfort prefer-
ences due to differences in clothing, activity level (metabolic rate),
body weight and size, and individual preferences. In terms of clothing
variations, if a person reduced their level of clothing from a business
suit (0.9 clo) to slacks and a short-sleeved shirt (0.5 clo), the room tem-
perature could be increased by approximately 4F (2C) and still main-
tain equivalent comfort. As an example of the variations in activity
level that commonly occur, a person walking around continuously in an
office (1.7 met) will experience an effective temperature of the envi-
ronment that is approximately 3F to 5F (2C to 3C) warmer than that
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Figure 3.3 Test configuration for manikin experiments of local cool-
ing from TAC diffusers (D = desktop, U = underdesk, F
= floor); perspective view.
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CHAPTER 3THERMAL COMFORT AND INDOOR AIR QUALITY
Figure 3.4 Sensible whole-body cooling rates, EHT (F), for two
desktop jet diffusers blowing air toward a person seated
in front of desk. Results applicable to average room tem-
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direction toward the person seated at the desk. Note that occupants can
typically adjust the cooling rate from TAC diffusers such as these by
changing both the airflow rate and supply air direction. All three mod-
els provide good fits to the test data with R2 in the range of 0.85-0.88.
EHT, or the change in equivalent homogeneous temperature [Wyon
1989], represents the amount of whole-body cooling provided by a dif-
fuser, compared to still-air conditions at the same average room tem-
perature. By presenting results in terms of the air velocity measured
where the diffuser air jet hits the person, the results can also be applied
to supply outlets that deliver air from generally the same direction
(desktop, underdesk, or floor). The results indicate that for the range of
test conditions investigated, these outlets can provide personal cooling
control of equivalent whole-body temperature over a sizable range: up
to 13F (7C) of sensible cooling for desktop-mounted outlets, up to
7F (4C) of sensible cooling for underdesk outlets, and up to 9F (5C)
of sensible cooling for floor-based outlets. This amount of control is
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CHAPTER 3THERMAL COMFORT AND INDOOR AIR QUALITY
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Figure 3.6 Sensible whole-body cooling rates, EHT (F), for fan-
powered floor jet diffuser blowing air toward a person
seated approximately 1 m (3 ft) to the side. Results appli-
cable to average room temperatures of 72F to 79F
(22C to 26C), room-supply temperature differences of
0F to 13F (0C to 7C), and supply velocities of 50 to 240
fpm (0.25 to 1.21 m/s). Velocity measured near arm of
test manikin on side toward diffuser.
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an underfloor air-conditioning system on one floor was compared to
the performance of a ceiling-based air-conditioning system on another
floor of the same building. In this field study, airborne particle concen-
trations were significantly lower for the underfloor air conditioning
system. Laboratory experiments with desktop-based diffusers have
shown that the ventilation efficiency can be improved significantly in
comparison to mixing-type air distribution at the workers breathing
level in the occupied zone when the percent of outside air is high and
when supply air is directed towards the work location at a low velocity
to reduce mixing [Faulkner et al. 1993, 1999]. Faulkner et al. [2002]
found that the air change effectiveness at breathing level produced by
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CHAPTER 3THERMAL COMFORT AND INDOOR AIR QUALITY
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Figure 3.7 Local air motion improves the perceived air quality.
3.5 PRODUCTIVITY
Research evidence suggests that occupant satisfaction and produc-
tivity can be increased by giving individuals greater control over their
local environment. In one of the first widely publicized productivity
studies of TAC systems, Kroner et al. (1992) analyzed routinely col-
lected worker performance data for an insurance company both before
and after moving from an older conventional office building into a new
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Chapter 4
Underfloor
Air Supply Plenums
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4.1 DESCRIPTION
An underfloor plenum is the open service distribution space
between a structural concrete slab and the underside of a raised, or
access, floor system (Figure 4.1a). As shown in the photo in Figure
4.1b, the raised floor platform is made up of 2 ft 2 ft (0.6 m 0.6 m)
steel panels filled with concrete-like material (other compositions and
finishes are available). The floor panels are attached and supported at
each corner with a screw into the head of an adjustable pedestal that is
glued to the concrete slab. Although not shown in Figure 4.1, horizontal
stringers between pedestals and sometimes additional diagonal seismic
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CHAPTER 4UNDERFLOOR AIR SUPPLY PLENUMS
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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CHAPTER 4UNDERFLOOR AIR SUPPLY PLENUMS
will focus on the first two approaches, as guidelines for fully ducted air
distribution systems are well established.
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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plenum, this savings will be offset by the energy consumed by the large
number of small local fans. However, if a pressurized plenum leaks at
a high rate, this can also lead to excessive fan energy use. Another con-
sideration with local fan-driven units is the possibility of increased
noise levels, although underfloor systems are generally rated as being
quieter than conventional overhead systems.
Zero-pressure plenums share many of the same thermal perfor-
mance issues as pressurized plenums. See Section 4.4 for further dis-
cussion.
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CHAPTER 4UNDERFLOOR AIR SUPPLY PLENUMS
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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The maximum practical distance between the point where condi-
tioned air is injected into the open underfloor plenum and its point of
discharge into the space is generally determined by:
1. The degree of thermal decay experienced by the air as it moves to
the supply outlet.
2. The residence time of the conditioned air within the open floor
cavity.
While resident within the underfloor plenum, the conditioned air is
subject to heat transfer from the building slab, as well as the room (by
means of the raised floor panels). This thermal transfer rate, discussed
in greater detail in Section 4.4, generally limits the distance through
which the conditioned air may travel according to its maximum allow-
able temperature rise. Although additional research is needed in this
area, designers familiar with underfloor system design typically
employ as a guideline a 0.05-0.15F temperature gain per linear foot of
travel (0.1-0.3C/m), resulting in a maximum practical distance of 50-
60 ft (15-18 m) between the plenum inlet and point of discharge into the
space.
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CHAPTER 4UNDERFLOOR AIR SUPPLY PLENUMS
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
Table 4.1:
Air Leakage Through Gaps Between
Floor Panels (cfm/ft2) [L/(s.m2)]
nections to the slab, interior walls, along pipe chases, stair landings,
elevators, and HVAC shaft walls during the construction phase of the
project. Even if this is done, the integrity of a well-sealed underfloor
plenum must be preserved over the lifetime of the building, as subse-
quent work can easily lead to new penetrations. If this is not done care-
fully, these types of leaks will be the most difficult to locate and fix later
in the project. In most cases, designers can expect to encounter leakage
losses of 10% to 30%, depending on quality of construction. See Sec-
tion 8.2 for further discussion of this construction issue.
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CHAPTER 4UNDERFLOOR AIR SUPPLY PLENUMS
gaps in the plenum were sealed during the tests. Measured data are
shown for a plenum pressure of 0.05 in. H2O (12.5 Pa) and for three dif-
ferent modes of floor covering: none (bare floor panels), aligned carpet
tiles, and offset carpet tiles. No adhesive was used to install the carpet
tiles during these tests so reported leakage values will be slightly con-
servative. As shown in Figure 4.7, aligned carpet tiles occur when the
size and edges of the carpet tile match those of the floor panel (2 ft
2 ft [0.6 m 0.6 m]). Offset carpet tiles occur when the carpet tile is
shifted over so that the edges are not aligned. The floor panels tested
represent a design that is known to have the lowest leakage of most
commercially available models. Experiments have shown that air leak-
age will vary approximately as the square root of plenum pressure
[ASTM 2000]. Based on this relationship, the air leakage values for a
plenum pressure of 0.1 in. H2O (25 Pa) can be estimated and are listed
in Table 4.1. Please refer to manufacturers test data for more precise
data on air leakage rates for specific raised floor configurations.
The magnitude of air leakage from a pressurized plenum shown in
Table 4.1 is surprisingly high. The results indicate that the layer of car-
peting plays an important role by significantly reducing air leakage
rates between floor panels. The performance of a UFAD system with
bare floor panels would be severely compromised if no additional
means of sealing between panels were installed. Placing carpet tiles
across the gaps between floor panels (offset mode) reduces the air leak-
age rate by 50% compared to aligned carpet tiles. Even with carpeting
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in place, the results suggest that minimizing leakage from other parts
of the underfloor plenum should have a high priority.
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CHAPTER 4UNDERFLOOR AIR SUPPLY PLENUMS
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Figure 4.9 Plan view of plenum airflow patterns: (a) without inlet
vanes, (b) with inlet vanes.
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CHAPTER 4UNDERFLOOR AIR SUPPLY PLENUMS
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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Chapter 5
Underfloor
Air Distribution (UFAD)
Equipment
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CHAPTER 5UNDERFLOOR AIR DISTRIBUTION (UFAD) EQUIPMENT
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
Figure 5.2 Cutaway photo of passive swirl floor diffuser [Trox 2002].
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included in this design guide. Please refer to Loftness et al. [2002] for
information on these products.
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CHAPTER 5UNDERFLOOR AIR DISTRIBUTION (UFAD) EQUIPMENT
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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hole through the carpet tile and raised floor panel with a trim ring on
top and a retainer, or mounting ring, below. Two grille designs are
shown in Figure 5.4. The one on the right with radial slots produces the
standard swirl discharge pattern. The two on the left feature a combi-
nation grille with part (radial slots) producing the same swirl discharge
pattern and part (circular slots) producing more of an inclined jet dis-
charge pattern. The directional characteristics of the jet discharge allow
an occupant to control the amount of air blowing toward them (for
increased cooling) or away from them by rotating the grille.
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CHAPTER 5UNDERFLOOR AIR DISTRIBUTION (UFAD) EQUIPMENT
Figure 5.7 VAV floor boot for swirl diffuser [Price 2002].
74
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CHAPTER 5UNDERFLOOR AIR DISTRIBUTION (UFAD) EQUIPMENT
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Figure 5.9 Photo and schematic of linear floor grille with VAV cool-
ing and CAV heating (Price 2002).
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
or some other means of minimizing heat gain from the slab and warm
faade. Linear grilles typically have multi-blade dampers that are not
designed for frequent adjustment by individuals and are therefore not
used in densely occupied office space where some amount of occupant
control is desirable.
Figure 5.9 shows a recently introduced linear floor grille for perim-
eter zone applications. The heating inlet (shown) is designed for ducted
fan-powered supply air when there is a call for heating. The inlet also
features a backdraft damper to prevent air supply when the fan is turned
off. On the opposite side of the unit (not shown) is the cooling inlet.
Cooling air supply is delivered directly from a pressurized plenum and
is modulated in VAV mode by a control damper. The control damper
closes down to the minimum opening on a call for heating. Control
power is required for the VAV operation of the unit. The unit delivers
up to 200 cfm (94 L/s) at 0.1 in. H2O (25 Pa).
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CHAPTER 5UNDERFLOOR AIR DISTRIBUTION (UFAD) EQUIPMENT
is supplied from a mixing box that is hung in the back or corner of the
knee space of the desk and connected to the two desktop supply noz-
zles. The mixing box uses a small variable-speed fan to pull air from the
underfloor plenum and deliver a free-jet-type airflow from the nozzles.
The unit can supply a total of 12-150 cfm (6-70 L/s) through its two
nozzles. See Chapter 3 for occupant cooling performance data for this
diffuser. Recirculated air is also drawn from the knee space through a
mechanical prefilter. Both primary supply air and recirculated room air
are drawn through an electrostatic air filter. As shown in Figure 5.11,
the unit has a desktop control panel containing adjustable sliders that
allow the occupant to control the speed of the air emerging from the
nozzles, its temperature, the temperature of a 200-watt radiant heating
panel located in the knee space, the dimming of the occupants task
light, and a white noise generator for acoustical masking. The control
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panel also contains an infrared occupancy sensor that shuts the unit off
when the workstation has been unoccupied for a few minutes.
Figure 5.12 shows an active (fan-driven) underdesk TAC diffuser
consisting of a panel attached to the underside of a conventional desk,
connected by a flexible duct to a portable filter and fan unit placed next
to the desk (shown) or in the underfloor plenum. Airflow from two
adjustable outlets at the front edge of the desk is used to condition the
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
air directly upward into the occupants breathing zone. The other deliv-
ers air toward the occupants body for cooling purposes. The maximum
airflow from the unit is only 15 cfm (7 L/s) because the air is concen-
trated directly on the occupant. Heating of the lower part of the body
can be provided by a controllable radiant heating panel under the desk.
Figure 5.13 shows a schematic diagram of another active (fan-
driven) underdesk TAC diffuser consisting of five 4-way adjustable
grilles, similar to a car's dashboard. A fan unit located in the underfloor
plenum delivers air through a flexible duct to two outlet locations: (1)
the supply grilles (jet-type) mounted just below and even with the front
edge of the desk, and (2) in this example, a supply grille located on the
backside of the desk. This configuration permits a true task/ambient
control strategy to be employed. The total air supply delivered to both
supply outlets is thermostatically controlled to maintain overall com-
fort conditions in the ambient space. The amount of air supplied
through the underdesk diffuser can be adjusted by occupants using a
damper lever just behind the supply grilles to satisfy their personal
comfort preferences. The underdesk diffuser is nominally designed to
deliver 0-70 cfm (0-33 L/s) of supply air. See Chapter 3 for occupant
cooling performance data for this diffuser. Other configurations using
this same TAC control strategy are available (Figure 5.14).
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CHAPTER 5UNDERFLOOR AIR DISTRIBUTION (UFAD) EQUIPMENT
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CHAPTER 5UNDERFLOOR AIR DISTRIBUTION (UFAD) EQUIPMENT
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
Figure 5.18 Perimeter solution using heating fan terminal with VAV
diffusers [York 2002].
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CHAPTER 5UNDERFLOOR AIR DISTRIBUTION (UFAD) EQUIPMENT
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Figure 5.19 Perimeter zone installation of fan terminal unit with VAV
cooling and reheat [Trox 2002].
the plenum. Under thermostatic control, room air provides the first
stage of heating followed by activation and modulation of the heating
coil. This perimeter solution requires no underfloor partitions.
Figure 5.19 shows a photo of another possible underfloor fan ter-
minal installation serving a perimeter zone. The fan operates only dur-
ing periods of reheat and peak cooling demand. Under normal cooling
operation, the VAV damper (on the left side of the unit) controls the
amount of cooling from a pressurized plenum. The first stage of reheat
occurs by closing the VAV damper so that the main source of air is recir-
culated room air entering through the floor grille at the lower left in the
photo. Ventilation air is assumed to enter the space from adjacent over-
ventilated spaces. Under peak heating conditions, an integral (hot water
or electric) coil is energized. The terminal discharge at the top of the
photo enters a small partitioned plenum zone containing typically 4-6
swirl diffusers (linear grilles could also be used). It is recommended
that you contact the equipment manufacturers directly to obtain the
most up-to-date information on fan terminal units and applications.
Also, see Chapter 9 for further discussion of perimeter and special zone
solutions.
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CHAPTER 5UNDERFLOOR AIR DISTRIBUTION (UFAD) EQUIPMENT
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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Figure 5.22 Non-adhesive carpet tile that is held in place with dim-
ples indexed to matching holes on top of floor panel
[Tate Access Floors 2002a].
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Chapter 6
Controls, Operation,
and Maintenance
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CHAPTER 6CONTROLS, OPERATION, AND MAINTENANCE
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However, even with proper design that promotes stratification at
peak conditions, CAV operation can result in a changing environment
in the occupied region as load changes. In CAV spaces, constant supply
air temperature with decreasing load causes the space temperature pro-
file to shift toward cooler temperatures and become less stratified. In
this case, the average occupied zone temperature tends to be a few
degrees cooler than the peak load thermostat temperature. Thus, supply
air temperature (SAT) reset is recommended. However, the system
response time during SAT reset can be significant due to the important
impact of the temperature of the thermally massive concrete slab on
supply air temperatures. CAV systems become progressively more
over-aired as loads decrease from peak conditions, eventually virtually
eliminating stratification. If the system is over-designed in the first
place, stratification is likely never to be experienced in actual opera-
tion, which may explain why many projects in operation today report
lack of stratification.
Many projects use CAV systems for large interior zones where the
perimeter zones are served by supply air passing through the plenum of
the interior zone. If these interior systems were conservatively sized
compared to actual loads and zone airflow is not properly adjusted dur-
ing system balancing, then the zone will be over-aired. As discussed in
Chapter 4, air leakage from pressurized plenums plus the additional
heat loss through the floor surface can provide a substantial portion of
the required cooling under part-load conditions. If part-load conditions
or over-airing in the interior lead to a significant increase in the SAT,
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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CHAPTER 6CONTROLS, OPERATION, AND MAINTENANCE
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Figure 6.1 Example sequence for controlling thermal stratification.
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
before being delivered directly into the underfloor plenum. The face
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CHAPTER 6CONTROLS, OPERATION, AND MAINTENANCE
and bypass dampers are controlled to achieve the desired supply air
temperature as load changes. To save energy, the coil temperature can
be varied to control humidity so a greater coil leaving temperature can
be used when entering humidity conditions are low. If desired, this con-
figuration also allows a range of coil temperatures to be utilized,
including low-temperature air systems with or without ice storage.
94
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
tion shaft decreases rapidly, it indicates that the demand for air supply
through the floor supply units has been reduced (i.e., fan units have
been turned down or off), resulting in the overpressurization of the
underfloor plenum. The central air handler can then be throttled down
until the reversal in flow direction through the induction shaft is elim-
inated. A minimum setpoint at the air handler can be used to ensure that
sufficient airflow is always supplied to the space.
Another task/ambient control strategy described in Section 5.1.5
(Figures 5.13 and 5.14) allows individuals to choose the amount of air
from an underdesk diffuser for personal comfort without influencing
the total amount of air being delivered to the space [Levy 2002]. A fan
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unit located in the underfloor plenum delivers air to two outlet loca-
tions, one under the desk for personal control and one farther away for
control of the ambient space. The total air supply delivered to both sup-
ply outlets is thermostatically controlled to maintain overall comfort
conditions in the room. The individual controls simply divert a portion
of this total air quantity to the underdesk diffuser, as desired. A CAV-
VT strategy for controlling the central AHU would be the simplest
approach with this system. Of course, VAV control strategies could also
be applied.
TAC system configurations using fan-powered supply outlets pro-
vide a convenient means of allowing direct feedback from occupant
control actions to improve overall system operation. Advances in direct
digital control systems and monitoring capabilities allow this type of
solution to be implemented. By monitoring fan speed settings, adjust-
ments can be made to the setpoints for primary supply air temperature,
ambient space temperature, and central supply air volume. For exam-
ple, when a large enough percentage of occupants in the same zone of
the building select low fan speeds, indicating that they are too cool, the
primary air supply temperature to that zone could be raised.
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CHAPTER 6CONTROLS, OPERATION, AND MAINTENANCE
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
the underfloor plenum where it will mix with the air supply stream and
be distributed throughout the occupied space. Experience has shown
that if the plenum area is thoroughly cleaned at the end of construction,
the amount of dust buildup on the slab is not excessive and can be han-
dled through cleaning scheduled as part of normal plenum reconfigu-
ration work. The required frequency of this type of cleaning is
estimated to be two to three years depending on the observed rate of
buildup. Dirt and particulates that do fall into floor diffusers will be col-
lected by the catch basins beneath the diffusers. These basins should be
cleaned as part of the regular maintenance schedule, depending on rate
of build-up.
Two important considerations are that (1) except near the plenum
inlets, air speeds within the underfloor plenum are so low that they do
not entrain any dirt or other contaminants from the plenum surfaces into
the supply air, and (2) if a spill or other accidental contamination, such
as fire, arises that does require cleaning, the accessibility of the under-
floor plenum makes this process far simpler and more effective than in
the case of overhead ductwork.
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Chapter 7
Energy Use
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CHAPTER 7ENERGY USE
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
Table 7.1:
Comparison of Fan Power for Overhead (Option 1)
vs. UFAD (Option 2) Systems
Option 1: Central Fan Only
Total Airflow 20,000 cfm
Fan Type Airfoil
Fan Wheel Size 30 in.
Design Static Pressure 3.0 in.
Motor Size 15 hp
Operating Power 13.4 bhp
Fan Efficiency 76%
Motor Efficiency 92.0%
Combined Efficiency 70%
Option 2: Central Fan + 4 Perimeter Fans
Total Airflow 20,000 cfm
Fan Type Airfoil
Fan Wheel Size 30 in.
Design Static Pressure 2.5 in.
Motor Size 15 hp
Operating Power 11.7 bhp
Fan Efficiency 73%
Motor Efficiency 92.0%
Combined Efficiency 67%
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CHAPTER 7ENERGY USE
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
Table 7.2:
Comparison of Sensible Cooling Coil Energy Use
for Overhead vs. UFAD Systems
Cooling
Cooling Coil
CFMsupply Qroom OAT SAT Qx RAT OA% MAT Coil T Sensible
[ft3/min] [Btu/h] [F] [F] [Btu/h] [F] [-] [F] [F] [Btu/h]
1,180 22,000 55 65 1946 85.0 67% 65.0 0 0
2,167 22,000 55 65 3576 75.0 50% 65.0 0 0
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1,084 22,000 55 55 3576 75.0 100% 55.0 0 0
1,180 22,000 64 65 1946 85.0 95% 65.0 0 0
2,167 22,000 64 65 3576 75.0 91% 65.0 0 0
1,084 22,000 64 55 3576 75.0 100% 64.0 -9 10, 729
1,180 22,000 66 65 1946 85.0 100% 66.0 -1 1, 298
2,167 22,000 66 65 3576 75.0 100% 66.0 -1 2,384
1,084 22,000 66 55 3576 75.0 100% 66.0 -11 13, 113
1,180 22,000 74 65 1946 85.0 100% 74.0 -9 11,678
2,167 22,000 74 65 3576 75.0 100% 74.0 -9 21,458
1,084 22,000 74 55 3576 75.0 100% 74.0 -19 22,650
1,180 22,000 76 65 1946 85.0 100% 76.0 -11 14,273
2,167 22,000 76 65 3576 75.0 15% 75.2 -10.2 24,200
1,084 22,000 76 55 3576 75.0 15% 75.2 -20.2 24,021
1,180 22,000 84 65 1946 85.0 100% 84.0 -19.0 24,654
2,167 22,000 84 65 3576 75.0 15% 76.4 -11.7 27,061
1,084 22,000 84 55 3576 75.0 15% 76.4 -21.7 25,452
1,180 22,000 86 65 1946 85.0 15% 85.2 -20.2 26,146
2,167 22,000 86 65 3576 75.0 15% 76.7 -11.7 27,776
1,084 22,000 86 55 3576 75.0 15% 76.7 -21.7 25,809
1,180 22,000 90 65 1946 85.0 15% 85.8 -20.8 26,925
2,167 22,000 90 65 3576 75.0 15% 77.3 -12.3 29,207
1,084 22,000 90 55 3576 75.0 15% 77.3 -22.3 26,525
1,180 22,000 96 65 1946 85.0 15% 86.7 -21.7 28,093
2,167 22,000 96 65 3576 75.0 15% 78.2 -21.7 28,093
1,084 22,000 96 55 3576 75.0 15% 78.2 -23.2 27, 598
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CHAPTER 7ENERGY USE
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Figure 7.1 Example of sensible cooling energy as a function of out-
side air temperature.
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
Coil Sensible indicates the net sensible cooling load provided by the
HVAC system.
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CHAPTER 7ENERGY USE
oped between the SAT and the RAT75F (24C) RAT minus 55F
(13C) SAT. In the UFAD case without stratification, only a 10F (6C)
room temperature difference was developed. In this case twice as much
air is needed to remove the load. In the UFAD case with stratification,
again the system was able to generate and maintain a 20F (11C)
degree room-air temperature difference.
However, as the stratified temperature difference across a room
develops, so also develops a temperature difference from the bottom to
the top of the occupied zone. This occupied zone temperature gradient
can adversely affect occupant comfort. As described in Chapter 3, only
a 5F (3C) variation from ankle to neck is allowed by ASHRAE Stan-
dard 55.
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CHAPTER 7ENERGY USE
The potential benefits from this approach are real, but a proven
implementation has yet to be studied. More research is needed to
address thermal storage performance and support the development of
design and implementation guidance.
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Chapter 8
Design, Construction,
and Commissioning
and provides a stable and level walking surface. The physical dimen-
sions of the raised floor system should be considered early in the design
process. These include:
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CHAPTER 8DESIGN, CONSTRUCTION, AND COMMISSIONING
building components that will be placed within the plenum, the place-
ment and requirements for other building services not located within
the underfloor plenum (e.g., elevators, access ramps, HVAC shafts), the
operating characteristics of the UFAD system, and the requirements for
their particular building-related concern. Engaging contractors with
some degree of experience in installing and commissioning UFAD sys-
tems will be conducive to a smooth installation.
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8.2 CONSTRUCTION
Although the number of projects using underfloor air distribution
has increased noticeably in the past five years, experience with the
installation of this technology is still rather limited within the U.S.
building industry. As guidelines have not been available, designers and
installers working on these projects have largely developed their own
methods and approaches. It is generally accepted that an underfloor air
supply plenum can provide benefits during the construction process.
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CHAPTER 8DESIGN, CONSTRUCTION, AND COMMISSIONING
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tomed to paying close attention to the sealing of the air distribution
path. For example, the sealing of edge details all around the underfloor
plenum should address window-wall connections to the slab, stair land-
ings, and HVAC shaft walls. At these locations, other members of the
construction team, including the general contractor, may become
involved. It is important that the responsible contractors recognize and
perform the critical role that proper sealing plays in the effective oper-
ation of a pressurized UFAD system.
In addition to initial installation, the integrity of a well-sealed
underfloor plenum or air highway must be preserved over the course of
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CHAPTER 8DESIGN, CONSTRUCTION, AND COMMISSIONING
all subsequent work within the plenum, even after building occupancy.
Sheet metal underfloor partitions used to define separate control zones
or air highways can be easily and repeatedly penetrated during instal-
lation of other services, such as cabling and plumbing. Seismic bracing,
sometimes required for plenums of greater depth (generally higher than
18 in. [0.45 m]), can lead to unsealed openings, and penetrations
through exterior walls and along interior structural elements are also
commonplace. Specifications should be put in place for the lifetime of
the building requiring all such penetrations to be carefully repaired and
sealed. Another approach that has been used to reduce uncontrolled
penetrations is to pre-install access channels or sealable ports across air
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CHAPTER 8DESIGN, CONSTRUCTION, AND COMMISSIONING
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8.5 COMMISSIONING
A carefully conducted commissioning of a UFAD installation will
go a long ways toward ensuring that all building systems are properly
applied, installed, and operated, despite the novelty of this technology
to some members of the design and construction teams. Commission-
ing is a systematic process that begins in the design phase and extends
through occupancy and the warranty period for the building and uses
documentation and verification methods to make sure that the facility
meets the design intent and the expectations of the owner and occupants
[ASHRAE 1996; Dasher et al. 2002; PECI 2002]. Because UFAD tech-
nology is classified as being energy-efficient and green, well-designed
systems will tend to be right-sized, not the more common over-
sized [York 1998]. With less of a safety margin, correct system oper-
ation, as verified by commissioning, takes on added importance.
Recent research has shown that promoting and maintaining room
air stratification is critical to successful design and operation (under
cooling conditions) of UFAD systems [Webster et al. 2002a, 2002b].
Overall room air stratification is primarily driven by room airflow rate
relative to load. As room airflow is reduced for constant heat input,
stratification will increase. On the other hand, if room airflow is
increased relative to load, stratification will be reduced, approaching
the well-mixed constant temperature profile characteristic of overhead
air distribution systems. The objective is to determine the operating
point that minimizes energy use (reduced room airflow) while main-
taining comfort (acceptable temperatures and stratification in the occu-
pied zone).
Because of the important balance between room airflow and heat
input to the space, proper and complete commissioning of a UFAD sys-
tem will require operation and adjustment of the system under peak (or
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Chapter 9
Perimeter and
Special Systems
119
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CHAPTER 9PERIMETER AND SPECIAL SYSTEMS
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grams in Figure 9.1 illustrate a two-pipe overhead fan-coil at left and
a two-pipe underfloor fan-coil at right. In Figure 9.1 and all subsequent
figures in this section, T refers to the room thermostat being used to
control the indicated equipment.
In both systems illustrated in Figure 9.1, ventilation and cooling air
is provided by the central air system. In the case of the overhead two-
pipe fan coil, the damper under the floor is connected to a segregated
portion of the plenum located below a perimeter zone. Cooling and
ventilation air is controlled to the zone through an underfloor modu-
lating, pressure-dependent damper. In heating mode, the damper goes
to minimum position and the fan in the fan-coil is engaged, recirculat-
ing return air to the space. If more heating is required, then the heating
coil is engaged.
In the underfloor two-pipe diagram, the fan-box intake is fitted with
a damper that allows air to be taken from the room in heating mode or
from the plenum in cooling mode. As cooling demand varies, either
room air or hot-water reheat is used to temper the cooling supply air
delivered to the space. In heating mode, the intake damper goes to a
minimum position to allow minimum ventilation while the remaining
air comes from recirculated room air. Heat is added via the reheat coil
as needed.
The constant-volume operation of this fan-coil option makes its
operation relatively energy inefficient. This system option is also
expensive compared to others. Care must be taken in design to address
the noise created by these fans.
Another variation on the underfloor constant-speed fan-coil ducts
55F (13C) air directly to the cooling inlet of the box. The fan-coil then
mixes 55F (13C) air and room air as needed to maintain comfortable
space conditions. The advantages of this option include an ability to
deal with high loads and minimized shaft area requirements. A disad-
vantage is that significant amounts of equipment and ductwork are
required under the floor.
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(a)
(b)
Figure 9.1 (a) Two-pipe overhead fan coil; (b) two-pipe underfloor
fan coil.
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CHAPTER 9PERIMETER AND SPECIAL SYSTEMS
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Figure 9.2 VAV diffusers with heating-only fan coil.
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CHAPTER 9PERIMETER AND SPECIAL SYSTEMS
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
damper varies the amount of air introduced to the zone based on a space
temperature sensor. In heating, the damper goes to minimum position
and a convector in a trench that is not open to the plenum, or a baseboard
heater located above the raised floor, engages to add heat to the zone.
125
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CHAPTER 9PERIMETER AND SPECIAL SYSTEMS
Figure 9.5 Control sequence for variable-speed fan coil with reheat.
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Figure 9.7 Perimeter fan coil units ducted to linear bar grilles.
Figure 9.7 shows a plan view of typical perimeter fan coils ducted
to supply grilles located at the perimeter of a zone.
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One variation on this approach uses a small partitioned perimeter
plenum instead of ducted supply grilles. This variation is illustrated
both schematically (Figure 9.8) and in plan (Figure 9.9).
One caution to bear in mind with this approach is that the perimeter
plenum becomes pressurized because of the fans and, because it is
located directly adjacent to the exterior wall of the building, can poten-
tially become a major source of air leaks to the outdoors. Care must be
exercised in thoroughly detailing and sealing the slab and exterior wall
connections. Also, the plenum dividers reduce system flexibility.
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CHAPTER 9PERIMETER AND SPECIAL SYSTEMS
Figure 9.9 Plan view of fan coil unit serving partitioned perimeter
plenum.
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CHAPTER 9PERIMETER AND SPECIAL SYSTEMS
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When compared to the VAV underfloor fan-coil approach, the VAV
change-over system has the following disadvantages. It requires larger
mechanical rooms for the central equipment. It requires additional
small shafts at the building perimeter. It can create conflicts with oper-
able windows. It cannot heat and cool simultaneously. Finally, it
requires complex control logic that needs careful commissioning.
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CHAPTER 9PERIMETER AND SPECIAL SYSTEMS
CO2 sensors can be used effectively to save energy and reduce sub-
cooling in special zones like these as well.
The use of plenum partitions for thermal zoning reduces the flexi-
bility of the underfloor space.
Using underfloor fans to condition perimeter spaces typically
erodes some of the energy benefits of UFAD systems as described
in Chapter 7. The maintenance and noise impacts of underfloor fans
must also be addressed in a well-designed UFAD system.
As described in Chapter 7, some UFAD systems employ reheat in
their designs. In most designs, reheat energy losses are small rela-
tive to overhead systems because of the warm supply air tempera-
ture and the ability to use very low minimum volume setpoints due
to the warm air supply from the floor. Still, strategies to reduce or
eliminate reheat, such as fan-powered boxes supplying room air
rather than plenum air, can be applied effectively to UFAD systems.
Take advantage of the natural thermal plume at the skin due to solar
radiation, conduction, and infiltration during cooling to reduce sup-
ply air requirements. Use blinds and light shelves wherever possible
to capture the solar load at the skin.
Using the same diffusers for heating and cooling is an effective
strategy to reduce cost and floor penetrations.
When designing perimeter and special systems, consider the ease
and cost of system and equipment reconfiguration.
Due to the chimney effect of skin loads and solar with blinds or light
shelves plus cooling transmission of the floor, the underfloor system
can require the same or even less air to cool the perimeter space with
63-65F (17-18C) air than an overhead system with 55F (13C) air.
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Chapter 10
Cost Considerations
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Table 10.1a: Cost Considerations for the Addition of Raised Floor and UFAD Systems: First Costs
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tained nate need for false ceiling
Cost of the raised floor and premium
for carpet tiles (vs. rolled carpet)
Power/Voice/Data Service Costs: Power/Voice/Data Service Costs: Power/Voice/Data Power/Voice/Data Service Costs:
134
Power wiring uses homerun power mod- Service Costs:
CHAPTER 10COST CONSIDERATIONS
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required connection time for PVD services
Installation costs are reduced due to the
HVAC System Costs: HVAC System Costs: HVAC System Costs: HVAC System Costs:
Thorough sealing of Reduction (or elimination) of hori-
components/sur- zontal (branch) ductwork feeding
faces that compose terminal units
the underfloor sup- Reduction of (rectangular and flexi-
ply plenum ble) discharge ductwork and damp-
Addition of ducts or ers
air highways to Reduction of required thermal insu-
ensure proper deliv- lation as supply air passes through
ery of the condi- an already conditioned plenum
tioned air through Reduced outlet balancing require-
the underfloor ple- ments as most diffusers allow occu-
num pant adjustment
135
Higher diffuser cost Elimination of radiation dampers on
due to increased supply outlets
quantity and rela- Reduction in the number of required
tively higher cost terminal units (especially in interior
($/cfm) of the out- zones)
lets Reduced number of space thermo-
Additional smoke stats and associated wiring as the
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detectors for under- number of terminal units are reduced
floor plenum Potential reduction in return outlets
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Table 10.1b: Cost Considerations for the Addition of Raised Floor and UFAD Systems: Life-Cycle Costs
136
resulting from use of replaceable carpet reduction of terminal units
CHAPTER 10COST CONSIDERATIONS
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Cash Flow Related Cash Flow Related Intangibles: Cash Flow Related Cash Flow Related Intangibles:
Intangibles: Possible accelerated depreciation on Intangibles: Possible reduction in installation time of
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
building. As discussed below, normally not all of the total floor plate
area will be covered by an access floor system on any given floor of an
office building.
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CHAPTER 10COST CONSIDERATIONS
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CHAPTER 10COST CONSIDERATIONS
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sioning costs between UFAD systems and traditional systems should
also be considered. It may be difficult to obtain long-term maintenance
cost data for UFAD systems since experience with these systems is lim-
ited in U.S. buildings. Some engineers believe that equipment mainte-
nance costs for raised floor-based systems will be slightly higher than
those for conventional systems. However, research suggests that the
frequency of occupant complaints will be reduced when occupants are
given some individual control over their local environment [Bauman et
al. 1998]. Most practicing engineers agree that UFAD systems have the
potential to save energy in comparison to traditional designs. To date,
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CHAPTER 10COST CONSIDERATIONS
tial by comparison.
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Chapter 11
Standards, Codes,
and Ratings
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Since UFAD technology is relatively new to the building industry,
its characteristics may require consideration of unfamiliar code
requirements and, in fact, may be in conflict with the provisions of
some existing standards and codes. Applicable standards should be
reviewed carefully; revisions and exceptions that are more compatible
with UFAD technology will likely be forthcoming as additional
research results are obtained. Local building codes and the interpreta-
tions of local officials should be considered early in the design process
of a building using underfloor air supply plenums. Experience has
shown that the first UFAD project in an area governed by an unfamiliar
jurisdiction will usually end up establishing the ground rules for code
interpretations on future projects.
Listed below are brief discussions of the applicable building stan-
dards and codes that have important provisions related to the design,
installation, and operation of UFAD systems. In addition, a brief
description of the LEED (Leadership in Energy & Environmental
Design) Rating System is provided.
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CHAPTER 11STANDARDS, CODES, AND RATINGS
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CHAPTER 11STANDARDS, CODES, AND RATINGS
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CHAPTER 11STANDARDS, CODES, AND RATINGS
result, the integration between the local and central controls should be
carefully considered. The effects of individual thermal preferences on
overall air quality and comfort should also be taken into account.
Although the current version of Title 24 does not specifically
address underfloor air distribution, if enough supporting energy- and
cost-saving data can be obtained, UFAD systems could be added to the
subsequent revision (three-year cycle).
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
satisfy the intent of the code language to ensure a clean air distribution
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system, regular vacuuming of the dust/dirt collection devices should be
included in the maintenance schedule.
In terms of the combustibility of diffusers, Sections 2-3.6.2 and 2-
3.7.2 state that air outlets and inlets shall be constructed of non-com-
bustible material or a material that has a maximum flame spread index
of 25 and a maximum smoke developed index of 50. There has been
considerable debate about the acceptability of diffusers made from
polycarbonate materials, which appear to violate the intent of NFPA
90A. For nearly 20 years several established diffuser models have been
regularly used in UFAD system installations and yet are made from a
plastic material that satisfies the required flame spread index but cannot
comply with the smoke index of 50. One argument commonly put for-
ward in defense of plastic diffusers is that the smoke test protocol
(ASTM E 84, NFPA 255requiring that a large 25-ft [7.6-m] sample
of the material be burned) cannot reasonably be applied to polycarbon-
ate material. In any event, metal diffusers fully comply with NFPA
90A, and designers should proceed cautiously with the use of plastic
materials unless specific exception has been granted by the local build-
ing code authority.
The combustibility of material in the underfloor plenum is also gov-
erned by NFPA 90A in Section 2-3.10.6.
The space between the top of the finished floor and the underside
of a raised floor shall be permitted to be used to supply air to the
occupied area, or return or exhaust air from the occupied area,
provided that the following conditions are met:
1. All materials exposed to the airflow shall be noncombusti-
ble or limited combustible and shall have a maximum smoke
developed index of 50.
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CHAPTER 11STANDARDS, CODES, AND RATINGS
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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Chapter 12
Design Methodology
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CHAPTER 12DESIGN METHODOLOGY
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UNDER FLOOR AIR DISTRIBUTION DESIGN GUIDE
Figure 12.1 Comparison of typical floor-to-floor heights for ceiling-based and underfloor air distribution systems.
155
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Table 12.1: Comparison of Typical Floor-to-Floor Heights
Building Steel Beam Construction with Steel Beam Construction with Concrete Flat Slab Construction
Element Overhead Air Distribution Underfloor Air Distribution with Underfloor Air Distribution
Structure Concrete 2.5 in. (65 mm) Concrete 2.5 in. (65 mm) Concrete 8 in. (200 mm)
Metal deck 2.5 in. (65 mm) Metal deck 2.5 in. (65 mm) floor
Steel beam 21 in. (530 mm) Steel beam 21 in. (530 mm) Concrete 12 in. (305 mm)
Fireproofing 2 in. (50 mm) Fireproofing 2 in. (50 mm) beam
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Ceiling 21-26 in. (530-660 mm) 8-12 in. (200-305 mm) 8-12 in. (200-305 mm)
plenum
Floor-to- 9 ft (2.70 m) 9 ft (2.70 m) 9 ft (2.70 m)
ceiling
Underfloor 12-18 in. (305-460 mm) 12-18 in. (305-460 mm)
156
plenum
CHAPTER 12DESIGN METHODOLOGY
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Underfloor plenums accommodating both cable/electrical distribu-
tion and an UFAD system are often deeper than those employed solely
for cable management purposes. However, the additional height
required for acceptable airflow performance is not large, based on
recent research results [Bauman et al. 1999a]. Underfloor plenum
heights are usually determined by
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CHAPTER 12DESIGN METHODOLOGY
can be a relatively dry process, once the concrete structural slab has
been adequately sealed, minimizing damage to other building ele-
ments.
where
Q = heat loads in a room, Btu/h,
CFM = airflow moving through a room, ft3/min, and
T = temperature difference between the room setpoint temperature
and the supply air temperature, F.
The validity of this equation relies on two assumptionsthat the
room is at steady state and that the room is fully mixed. The assumption
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that a room is fully mixed is not valid for UFAD systems, and, as such,
this simple room energy balance equation cannot be applied here.
Consider this example of a room in cooling mode, which sheds
some light on the common question asked of UFAD systems, Do
UFAD systems need more air than OH systems? In fact, current
research indicates that airflow rates are very comparable to overhead
systems [Webster et al. 2002a].
12.3.1.2 How UFAD Stratification Affects Loads. Under-
standing how air becomes stratified in spaces employing UFAD is key
to developing a correct cooling load calculation model. As discussed in
Chapter 2, the floor-to-ceiling air flow pattern driven by rising thermal
plumes in UFAD systems produces a vertical temperature gradient in
the space. Unless air supply quantities are exceedingly high, a stratifi-
cation height is established in the room that divides the room into an
upper zone and one or two lower zones (depending on diffuser throw
height). In general, the fact that once room air has risen above this strat-
ification height it will not reenter the lower zones represents a funda-
mental difference from the fully mixed room assumed in OH system
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CHAPTER 12DESIGN METHODOLOGY
tion of the room will be called the occupied zone. Air above the
occupied zone can be allowed to warm up beyond what would other-
wise be comfortable temperatures. The zone above the occupied zone
will be called the unoccupied zone.
12.3.1.3 Assigning Heat Gains to Occupied and Unoc-
cupied Zones. Heat loads are physically located in either the occu-
pied or unoccupied zone. For example, a ceiling pendant-mounted light
fixture is located in the unoccupied zone. A computer sitting on a desk
is located in the occupied zone. Figure 12.2 is a schematic diagram
showing some typical loads in an office.
The heat from a load is not necessarily allocated only to the occu-
pied or unoccupied zone where the load physically resides. Heat
sources must be analyzed based on their convective and radiant com-
ponents, a subject addressed by Hosni et al. [1999]. Both the location
and the convective/radiant split characterizing a specific type of heat
load determine where the heat from a load needs to be assigned. Lou-
dermilk [1999] has described a space heat gain analysis using this
approach based on empirical estimates. Unfortunately, no research-
based guidance exists to guide the assignment of loads to the occupied
and unoccupied zones. This is particularly true for heat sources located
near the stratification height (e.g., most desktop computers and equip-
ment). Using the same examples as above, the convective portion of the
light fixture can logically be assigned to the unoccupied zone, but a
good deal of the radiant portion of that energy needs to be assigned to
the occupied zone. In the case of the computer, some amount of both
the convective and radiant portions of the load can likely be assumed
to be in the unoccupied as well as the occupied zones. Table 12.2 doc-
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Figure 12.2 Typical loads in an office showing convective and radiant
split.
Radiant Convective
Heat Source Portion Portion
[%] [%]
Transmitted solar, no inside shade 100 0
Window solar, with inside shade 63 37
Absorbed (by fenestration) solar 63 37
Fluorescent lights, suspended, unvented 67 33
Fluorescent lights, recessed, vented to return air 59 41
Fluorescent lights, recessed, vented to return air and 19 81
supply air
Incandescent lights 80 20
People, moderate office work 38 62
Conduction, exterior walls 63 37
Conduction, exterior roof 84 16
Infiltration and ventilation 0 100
Machinery and appliances 20 to 80 80 to 20
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CHAPTER 12DESIGN METHODOLOGY
Figure 12.3 Definition of two zones for simplified UFAD load calcu-
lation model.
uments the radiant and convective splits of some typical office heat
loads [ASHRAE 2001a, chapter 29].
The designer needs to use his or her judgment based on an under-
standing of the physical properties of the loads and room to assign these
properly. As discussed in Section 12.3.1.1, being overly conservative
and assigning too much load to the occupied zone has the disadvantage
of requiring more air than is needed in a zone. This results in more
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equipment and higher minimum air flow quantities for VAV systems
than would otherwise be needed.
12.3.1.4 Simplified Two-Zone UFAD Load Calculation
Model. Instead of modeling a single mixed zone as with OH load cal-
culations, the simplified UFAD model uses the assumption of two dis-
tinct mixed zones, one below the stratification height and a second one
above the stratification height, as illustrated in Figure 12.3.
In the two-step procedure below, Qoccupied and Qunoccupied are cal-
culated based on guidance from Section 12.3.1.3. Other terms are
defined as illustrated in Figure 12.3. In step 1, the supply air quantity
(CFM) is calculated based on the heat load and temperature difference
across the lower occupied zone only. Note that if the temperature
near the top of this lower zone is higher than the average setpoint tem-
perature (Tset) due to stratification, this higher temperature can be sub-
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stituted for Tset, resulting in a lower supply air quantity. In step 2, the
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return air temperature (Treturn) is calculated based on the heat load in
the upper unoccupied zone, the supply air quantity from step 1, and
the temperature near the top of the lower zone (Tset or other), as used
in step 1.
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CHAPTER 12DESIGN METHODOLOGY
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building envelope where heat loss to the outdoors can cool spaces and
may cause discomfort. Heating may also be needed in some top floor
interior zones and during periods of low occupancy (e.g., nights and
weekends).
In operation, delivering warm air from rapidly mixing diffusers
near floor level is very effective at providing heat to the conditioned
space. Due to buoyancy effects, the characteristic thermal stratification
obtained in cooling operation is replaced with a well-mixed, uniform
temperature distribution. The calculation of heating loads can therefore
use the same methods as for conventional overhead air distribution sys-
tems.
Effective heating systems isolate the source of warm air from the
thermal lag effect of the concrete slab (which is usually slightly cooler
than room temperature). This can be done, for example, by ducting
from an underfloor fan coil unit or by using baseboard radiation or con-
vection units. Quick response on heating can be very important during
morning start-up, particularly if a nighttime setback strategy is used.
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CHAPTER 12DESIGN METHODOLOGY
to operate. In this case the active diffusers will continue to provide local
air motion and cooling due to the thermal inertia of the concrete slab.
The greater ability of zero-pressure systems using active diffusers
to provide localized cooling [Tsuzuki et al. 1999] suggests their suit-
ability in projects involving high and diversified heat loads. In fact, this
is why fan-driven solutions are frequently applied in perimeter zones
and special zones with rapidly changing loads.
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that plenum pressures and airflow are quite uniform in pressurized
plenums as shallow as 8-in. (200-mm) over a distance of up to 80 ft
(24 m) [Bauman et al. 1999a].
Provide an acceptable degree of thermal decay (temperature varia-
tion) as the supply air passes through the open plenum (see Section
12.7 for more details).
Deliver supply air to terminals supplying (partitioned) control
zones.
Isolate heated air (typically from fan coil units) from the cooler slab
and other surfaces in the plenum, and allow fan-driven supply air to
quickly respond to changes in load (perimeter diffusers are usually
ducted from these terminals). In all cases it is recommended to min-
imize ductwork and partitioning in order to reduce costs and con-
flicts with other trades and to maintain an open and highly flexible
underfloor service plenum.
If multiple vertical shafts are used in the building, horizontal duct-
work in the plenum can be reduced or eliminated.
Coordinate with wiring, conduit, and piping distribution needs in the
plenum.
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The design and layout of main ducts from the central plant to ple-
num inlet locations is similar to that of conventional overhead systems
except that access must be provided for the ducts to reach the under-
floor plenum. The amount of main ductwork can be reduced in designs
using medium to small-sized air handlers (floor-by-floor units) that are
located closer to the point of use. However, ductwork for ventilation air
is still required and must be sized accordingly in climates where the use
of an outside-air economizer will be an important operating strategy.
At plenum inlets, it is recommended to limit discharge velocities to
about 1,500 fpm (7.6 m/s) for acoustical purposes. Although not an
issue of the same magnitude as it is in computer room applications with
much larger air delivery rates, to avoid reentry of room air through dif-
fusers it is recommended to place floor diffusers at least about 6 ft (2
m) away from major plenum inlet locations.
The largest distribution ducts in the underfloor plenum can be stan-
dard rectangular or round ducts, but they must have a maximum width
of 22 in. (560 mm) to fit between raised floor pedestals and a maximum
height of at least 2 in. (50 mm) less than the finished floor height to
account for the thickness of the floor panels. Wider ducts can be accom-
modated, but this adds complexity and cost to the raised floor installa-
tion, requiring special bridging to span across the ductwork.
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In recent years, air highways have been introduced, which are
fabricated rectangular ducts that use the underside of the floor panel as
the top, concrete slab as the bottom, and sealed sheet metal partitioning
for the sides. Air highways are often designed to be two floor panels in
width (4 ft [1.2 m]).
The advantages of using air highways instead of single or multiple
standard ducts running between floor pedestals in the plenum include
lower costs due to less sheet metal and lower labor rates for floor install-
ers; lower pressure drop because they provide larger effective duct area;
and reduced coordination and conflicts.
In practice, built projects are finding that actual cost savings are
questionable due to the lack of familiarity of construction by floor con-
tractors and the general contractor. Other issues that need to be con-
sidered are the code equivalence to a duct when it comes to crossing
corridors. Construction coordination can be impacted because the
ducts are not complete until floor tiles installed. The air highways are
also susceptible to damage by other trades. Finally, although the goal
is a leak-free installation, the air highways have only limited pressure
capability, and overpressurized air-highways can lead to substantial air
leakage.
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
50 ft (15 m) from the closest supply point into the plenum. It is also pos-
sible under suitable weather conditions to reduce thermal decay by
employing a nighttime precooling strategy of thermal mass in the
underfloor plenum (see Section 12.11).
Other considerations in selecting a minimum plenum air tempera-
ture include avoiding excessively cool floor surfaces and preventing
condensation on cool surfaces in the plenum. Current recommenda-
tions are to control plenum air temperature to be no colder than in the
range of 61-65F (16-18C).
Cooling air quantities for UFAD systems should be carefully deter-
mined. Higher supply air temperatures would suggest that higher sup-
ply air volumes are required, but the higher return temperatures created
by stratification reduce the required increase in volume. As previously
described in Section 12.3.1, properly controlled stratification in the
space allows cooling air quantities for UFAD systems to be very similar
to those required under the same conditions using overhead air distri-
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CHAPTER 12DESIGN METHODOLOGY
bution. Daly [2002] discusses this issue and notes that in many com-
pleted UFAD projects, measured return air temperatures are not as high
as anticipated. This evidence suggests that over-airing is a common
problem, leading to reduced stratification and higher fan energy use. If
a designer conservatively assigns too large a fraction of the heat sources
to the lower occupied zone, excessive air quantities will be supplied
to the space. In a constant-air-volume (CAV) zone, as many interior
zones are designed for simplicity, high air supply volumes will lead to
overcooling.
In pressurized plenums, another factor affecting air supply quanti-
ties is the additional cooling effect provided by air leakage through the
raised floor combined with the heat transferred from the room through
the raised floor panels to the underfloor plenum. Recent testing has
measured air leakage rates for one type of floor panel with offset carpet
tiles (covering the gaps between panels) in the range of 0.1-0.2 cfm/ft2
(0.5-1.0 L/(s.m2)). Accounting for the additional heat loss through the
floor, this amount can be a substantial fraction (approaching 50%) of
the total required cooling in the zone. Unless this is considered, even
more overcooling may develop. Zero-pressure plenum designs are not
impacted by air leakage, although heat transfer through the floor will
still be an issue.
Floor diffusers are most commonly used and offer the widest selec-
tion of products to the designer. Due to growing interest in UFAD sys-
tems in the U.S., several new designs have been introduced in the last
five years and this trend is expected to continue. Floor diffusers can be
passive or active, depending on the plenum configuration and mode of
operation (see below). TAC supply outlets that provide a wider range
of control by the occupant are typically fan-driven (active) and may be
located in the floor, furniture, partitions, or ceiling. Please see Chapter
5, UFAD Equipment, for a more detailed discussion of diffuser
options.
Passive diffusers are defined as air supply outlets that rely on a pres-
surized underfloor plenum to deliver air from the plenum through the
diffuser into the conditioned space of the building. Active diffusers are
defined as air supply outlets that rely on a local fan to deliver air from
the plenum through the diffuser into the conditioned space of the build-
ing. Passive diffusers can generally be converted to active diffusers by
simply attaching a fan-powered outlet box to the underside of the dif-
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fuser or grille. Most manufacturers provide both passive and active dif-
fusers.
Three types of floor diffusers currently in use are:
1. Swirl diffuser: This is the most commonly installed type of dif-
fuser in UFAD systems; more models are commercially available
than for any other design. The swirling air flow pattern of air dis-
charged from this round floor diffuser provides rapid mixing of
supply air with the room air in the occupied zone. Occupants may
have limited control of the amount of air being delivered by rotat-
ing the face of the diffuser or by opening the diffuser and adjust-
ing a volume control damper. Designs are also available with
integral automatic volume control.
2. Variable-area diffuser: This diffuser is designed for variable-air-
volume operation. It uses an automatic internal damper to main-
tain close to a constant discharge velocity as air flow is reduced.
Air is supplied through a slotted square floor grille in a jet-type
air flow pattern. Occupants can adjust the direction of the supply
jets by changing the orientation of the grille. Supply volume may
be controlled by a thermostat on a zone basis or, if available, as
adjusted by an individual user.
3. Linear floor grille: Linear grilles have been used for many years
in underfloor applications where occupant control is not an issue.
Air is supplied in a jet-type planar sheet, making them well
matched for ducted applications in perimeter zones adjacent to
exterior windows. Although linear grilles often have multi-blade
dampers, they are not designed for frequent adjustment by indi-
viduals and are therefore not typically used in densely occupied
interior office space.
In addition to the three types of floor diffusers described above for
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passive diffusers, several other types of active diffusers are available.
See Chapter 3 for data on effective cooling rates for three of the fol-
lowing fan-driven diffusers:
1. Floor supply module: Multiple discharge grilles (jet-type) are
mounted in a single raised floor panel. Fixed vanes in the grilles
are inclined at 40 so that air flow direction can be adjusted by
rotating the grilles. Integral fan speed control allows the air sup-
ply volume to be controlled.
2. Desktop air supply pedestals: Two supply pedestals located near
the back of the desk surface allow adjustment of air flow direction
and flow rate. Air is supplied from a mixing box that is typically
hung in the back or corner of the knee space of the desk and con-
nected by flexible duct to the two desktop supply nozzles. The
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CHAPTER 12DESIGN METHODOLOGY
mixing box uses a small variable-speed fan to pull air from the
underfloor plenum and deliver a free-jet-type air flow from the
nozzles.
3. Underdesk diffuser: One or more fully adjustable (for air flow
direction) grilles, similar to a car's dashboard, are mounted just
below and even with the front edge of the desk surface (other
positions are possible). A fan unit located either adjacent to the
desk or in the underfloor plenum delivers air through flexible duct
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to the grilles.
4. Partition-based diffuser: Grilles are mounted in the partitions
immediately adjacent to the desk. Air is delivered through pas-
sageways that are integrated into the partition design to controlla-
ble supply grilles that may be located just above desk level or just
below the top of the partition.
It is recommended that you contact the diffuser manufacturers
directly to obtain the most up-to-date product information on the afore-
mentioned TAC diffusers.
The flexibility of mounting supply diffusers in movable raised floor
panels is a major advantage for UFAD systems. The inherent ability to
easily move diffusers to more closely match the distribution of loads in
the space makes the placement of diffusers a much easier task. In open
plan offices, it is highly desirable to install one local task diffuser in
each workstation, thereby providing the potential for individual control
by each occupant. After initial placement of the diffusers during the
final stages of construction, final adjustments can take place after the
location of furniture and loads, as well as the preferences of individual
occupants, are more accurately determined.
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
into the plenum through open floor grilles can also serve as makeup air
for zero pressure plenum designs when local fan-powered outlets
require more air than that being supplied from the central AHU.
If recirculation takes place directly in the underfloor plenum, the
supply and return air streams must be well mixed within the underfloor
plenum before delivery to the conditioned space. This can usually be
achieved by distributing the primary air at regularly spaced intervals
throughout the plenum and/or employing fan-powered local supply
units to aid mixing of primary supply air with the return air.
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CHAPTER 12DESIGN METHODOLOGY
cool primary air to produce supply air of the proper temperature and
humidity before being delivered directly into the underfloor plenum. In
this configuration, a range of coil temperatures can be utilized, includ-
ing low-temperature air systems with or without ice storage. The only
adjustment would be the required amount of bypassed return air to mix
and produce the desired plenum inlet temperature. This and other
equipment selection challenges are discussed by Int-Hout [2001].
It is recommended that in designs with both UFAD and overhead air
distribution systems, separate AHU and mechanical cooling systems
be selected with each type of system. If the same chiller and AHU are
used, this can lead to system inefficiencies for the UFAD system. For
example, during mild weather, a single cooling plant would need to be
operated to serve the colder supply air requirements of the overhead
system, even though the UFAD system (using a warmer supply air tem-
perature) would need no cooling. For further discussion of this subject,
see AEC [2001].
Consideration must also be given to the need for a heating coil at the
AHU. Such a coil may be needed for morning warm-up or to produce
the required higher supply air temperatures during cold weather at min-
imum outdoor air.
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Chapter 13
UFAD Project
Examples
One of the best ways to educate the engineering and design com-
munity on how to apply UFAD technology is to review the work of oth-
ers as described in case studies and other reports on completed
installations. This section presents a list of references, web sites, and
other sources describing examples of UFAD and TAC system designs.
Inclusion of a particular project, designer, or product in the following
list does not constitute an endorsement but rather is intended to dem-
onstrate the range of possible solutions that have been applied in prac-
tice.
ArchitectureWeek. 2000. Building for Harmony with nature. Archi-
tectureWeek, June 14, http://www.architectureweek.com/2000/
0614/building_1-1.html.
Arnold, D. 1990. Raised floor air distributiona case study. ASHRAE
Transactions, Vol. 96, Pt. 2.
Barker, C.T., G. Anthony, R. Waters, A. McGregor, and M. Harrold. 1987.
Lloyd's of London. Air Conditioning: Impact on the Built Environ-
ment. New York: Nichols Publishing Company.
Bauman, F., K. Powell, R. Bannon, A. Lee, and T. Webster. 2000. Under-
floor air technology web site: http://www.cbe.berkeley.edu/under-
floorair. Center for the Built Environment, University of California,
Berkeley, December.
Beck, P. 1993. Intelligent design passes IQ test. Consulting-Specifying
Engineer, January.
Cornell University. 1999. Case study: 901 Cherry Gap Headquarters.
http://dea.human.cornell.edu/Ecotecture/Case%20Studies/Gap/
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CHAPTER 13UFAD PROJECT EXAMPLES
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Diagnostics, Carnegie Mellon University, Pittsburgh, PA.
Matsunawa, K., H. Iizuka, and S. Tanabe. 1995. Development and appli-
cation of an underfloor air conditioning system with improved out-
lets for a smart building in Tokyo. ASHRAE Transactions, Vol.
101, Pt. 2.
McCarry, B. 1998. Innovative underfloor system. ASHRAE Journal,
Vol. 40, No. 3, March, pp. 76-79.
McQuillen, D. 2001. 3 case studies for improved IAQ. Environmental
Design + Construction, posted 1/24/2001, http://www.edc-
mag.com.
Portland General Electric. 2002. Earth Advantage/Building Profile:
CNF Information Technology Center. http://www.earthadvan-
tage.com/commercial/projects.asp. Portland General Electric,
Commercial and Industrial Energy Efficiency Programs, Portland,
OR.
Shute, R.W. 1992. Integrated access floor HVAC. ASHRAE Transac-
tions, Vol. 98, Pt. 1.
Tuddenham, D. 1986. A floor-based approach. ASHRAE Journal (July).
Warson, A. 1990. The pin-striped office. Canadian Building, March.
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
Six project profiles and two case studies are provided for the fol-
lowing projects: (1) BC Hydro, Burnaby, British Columbia; (2)
California State Automobile Association (CSAA), Livermore, CA;
(3) First National Bank of Omaha (FNBO) Technology Center,
Omaha, NE; (4) Sacramento Municipal Utility District (SMUD)
Customer Service Center (CSC), Sacramento, CA; (5) Teledesic
Broadband Center, Bellevue, WA; and (6) Telus, Vancouver, British
Columbia.
Webster, T., R. Bannon, and D. Lehrer. 2002. Teledesic Broadband Cen-
ter. Center for the Built Environment, University of California,
Berkeley, CA, April.
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Chapter 14
Future Directions
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CHAPTER 14FUTURE DIRECTIONS
14.1 RESEARCH
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
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As discussed in Chapter 11, since UFAD and TAC systems are rel-
atively new to the building industry, some features and performance
characteristics of these systems may be interpreted to be in conflict
with applicable standards and codes. Efforts are now underway within
ASHRAE to revise some of these standards to make them more com-
patible with UFAD and TAC technology [e.g., ASHRAE 1990, 1992].
It is highly likely that other standards and code language (for example,
NFPA, 90A, UBC, etc.) may need revisions and/or new sections spe-
cifically addressing UFAD and TAC applications.
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Glossary
access floor
A platform structure typically consisting of 0.6 m 0.6 m (2 ft 2
ft) concrete-filled steel floor panels supported on pedestals 0.2 to 0.46
m (8 in. to 18 in.) above the concrete structural floor slab. Each panel
can be independently removed for easy access to the underfloor plenum
created below and can include openings for electrical outlets, grilles, or
any other floor accessory in its thickness. In most office installations,
carpet tiles are laid on top to provide a finished floor surface. Raised
floor systems provide maximum flexibility and significantly lower
costs associated with reconfiguring building services.
active diffuser
Any air supply outlet that relies on a local fan to deliver air from the
plenum through the diffuser into the conditioned space of the building.
air change effectiveness (ACE)
Air change effectiveness describes the ability of an air distribution
system to provide ventilation (outside) air at the breathing zone (where
occupants breathe). ACE is defined as the age of air that would occur
throughout the space if the air were perfectly mixed, divided by the
average age of air where occupants breathe.
air changes per hour (ACH)
A measure of the air exchange rate of a building, or space, that gives
the time unit in hours.
air exchange rate
A measure of the rate at which the volume of air contained within
a space is replaced by supply (outside, conditioned, or recirculated) air.
This is expressed in terms of air changes per hour (ACH) and found by
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GLOSSARY
dividing the airflow rate (volume per hour) by the volume of the space
or building.
airflow
The movement of airtypically defined as that within a defined
volume such as a room, duct, or plenum.
air-handling unit (AHU)
The component of an HVAC system that is responsible for condi-
tioning and delivering air through the system. Within the AHU, a por-
tion of the return air from the conditioned space is recirculated and
mixed with incoming outside air for conditioning and delivery to the
space, and the remainder is exhausted to the outside. The AHU typi-
cally contains one or more supply and return fans for maintaining air
movement and heating/cooling coils and filters to condition the air. The
cooling coil and other equipment, as necessary, are used to control the
moisture content of the air.
air inlet (see also air outlet)
Inlets are apertures through which air is intentionally drawn from
a conditioned space. Grilles, diffusers, and louvered openings can all
serve as inlets. Examples are return inlets at ceiling level and floor dif-
fusers that become return inlets for specially designed perimeter heat-
ing solutions for open plenum designs.
air outlet (see also air inlet)
Outlets are apertures through which air is intentionally delivered
into a conditioned space. Grilles, diffusers, and louvered openings can
all serve as outlets. Examples are floor and ceiling diffusers.
air supply volume
The volume of supply air flowing through a cross-sectional plane
of a duct per unit time. Found by multiplying air velocity by the cross-
sectional area of the duct, measured in cubic feet per minute (cfm) or
liters per second (L/s).
air velocity
The rate at which air travels in a given direction, measured as a dis-
tance per unit time. The units used vary according to the scale of the
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
ASHRAE
American Society of Heating, Refrigerating and Air-Conditioning
Engineers, Inc.
cable management
Addresses the distribution, routing, and overall organization of
cable networks installed in underfloor plenums. Raised floors came
into widespread use as a means of containing and concealing the exten-
sive cabling of typical voice, power, and data systems and are now a
common feature in contemporary office buildings. In this respect, con-
cerns that the installation of a UFAD system will entail additional con-
struction costs can be mitigatedthe decision to install a raised floor
system is often made for communications purposes, regardless of the
type of HVAC system chosen.
ceiling-based systems
A ceiling-based air distribution system supplies air to, and removes
air from, a conditioned space at ceiling level. Both supply and return
grilles are located in the ceiling plane, above which there will be a ceil-
ing plenum of sufficient depth to accommodate the extensive supply
ductwork, as well as other building services. Relying on the principle
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GLOSSARY
term occupancy, and when under direct individual control by the occu-
pant, air velocities may be too high and temperatures too low (under
cooling conditions) within clear zones to satisfy the thermal comfort
preferences of a large majority of occupants (> 80%). Diffuser place-
ment should take this into consideration and maintain a distance of at
least half the diameter of the clear zone between occupants' seating and
their diffusers.
conditioned air
Air that has been treated, typically in an air-handling unit, by alter-
ing one or more of the following properties: temperature, humidity,
cleanliness (filtering), or mixture of outside and recirculated air.
conditioned space
A space within a building served by an HVAC system supplying
conditioned air in order to achieve acceptable thermal comfort and
indoor air quality conditions.
constant air volume, variable temperature (CAV-VT)
A control strategy of an air supply system in which varying heating
and cooling loads are met by adjusting the temperature of the supply air,
keeping the airflow volume constant. Alternatively a variable-air-vol-
ume (VAV) system can be employed in which the airflow volume is var-
ied, while the temperature remains constant.
conventional systems
A typical, conventional air distribution system supplies air to, and
removes air from, a conditioned space at ceiling level. Both supply and
return grilles are located in the ceiling plane, above which there will be
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GLOSSARY
aim to minimize mixing of supply air with room air, instead maintain-
ing conditions in the occupied zone as close as possible to that of the
conditioned supply air, leading to an improved air change effective-
ness.
draft
Movement of air causing undesirable local cooling of a body due to
one or more of the following factors: low air temperature, high velocity,
or inappropriate airflow direction.
dry-bulb temperature
The air temperature indicated by an ordinary thermometer.
duct
A duct is an encased conduit, usually constructed of sheet metal and
having a round, square, or rectangular cross section through which air
moves around an HVAC system. Other types of duct construction
include fibrous glass ducts (rigid fiberglass with aluminum facing) and
flexible ducts (used to connect diffusers, mixing boxes, and other ter-
minal units to the air distribution system).
ductwork
The network of ducts comprising an HVAC system, typically con-
necting the AHU to supply, return, intake, and exhaust grilles and
underfloor and ceiling plenums. Ductwork can be exposed or con-
cealed within floor or ceiling plenums, services zones, and plant rooms.
economizer (see outside air economizer)
energy use
A term referring to the energy used by a system or component in the
course of its operation. In the context of HVAC, this would include
energy used by components such as fans, refrigeration and heating
equipment, cooling towers, and pumps.
entrainment (see also secondary air motion)
Air discharged from an outlet creates a swirling, jet, or other air
motion that pulls (entrains) the surrounding air into its path where it
mixes with the supply air.
exfiltration (see also infiltration)
The uncontrolled, unintentional flow of inside air out of a building.
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exhaust air
The air extracted from a space and discharged to the outdoors. This
is distinct from air extracted from one space and sent to another or recir-
culated within the HVAC system.
exhaust opening, or inlet
Any opening, a grille for example, through which air is removed
from a space.
fan coil unit
A fan terminal unit with a heating (electric or hot water) and/or
cooling (chilled water) coil on the discharge of the unit.
fan-powered mixing box
A compartment containing an integral fan that mixes two air sup-
plies before being discharged. In underfloor applications, these boxes
may be configured as having one ducted inlet supplying room or return
air, for example, to be mixed with plenum air entering the box through
an unducted opening. A reheat coil can be added to the discharge of the
unit.
fan terminal unit
A compartment containing an integral fan that delivers a constant
or variable volume of air to the space. These units are often used in
perimeter and other special zones where large and rapid changes in
cooling and/or heating load requirements occur.
first costs
The initial costs involved in a building project, typically incurred
during the construction and installation stages.
floor-to-floor height
The vertical height between the finished-floor level of a space in a
multi-story building and that of the floor immediately above or below
it.
forced ventilation
A term used to describe the use of fans and intake and exhaust vents
to mechanically distribute ventilation and other conditioned air
throughout a building. Buildings operating forced ventilation systems
are generally pressurized to reduce infiltration. This term is often con-
trasted with natural ventilation.
grille
A perforated or louvered covering on any area that air passes
through. Grilles can be placed in the ceiling, floor, or wall and can be
fixed, or adjustable.
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GLOSSARY
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those estimated over the lifetime of the building (e.g., long-term oper-
ation and maintenance). Considerations of life-cycle costs are impor-
tant when making decisions at the initial design stage.
localized ventilation (see also underfloor air distribution
[UFAD] system)
Air distribution systems that supply air to a number of localized
areas within the occupied zone, typically at floor or desktop level, are
termed localized ventilation. Underfloor air distribution systems oper-
ate on the principles of localized ventilation.
lower zone
The volume of a conditioned space below the stratification height
produced by a DV or UFAD system.
mechanical ventilation
A term used to describe the use of fans and intake and exhaust vents
to mechanically distribute ventilation and other conditioned air
throughout a building. Buildings operating mechanical ventilation sys-
tems are generally pressurized to reduce infiltration. This term is often
contrasted with natural ventilation.
mixing systems (also known as mixing-type air distribution)
In mixing systems, conditioned air is delivered to the space at veloc-
ities much greater than those acceptable to occupants. Conventional
overhead air distribution is an example of a mixing system. Supply air
temperature may be above, below, or equal to the air temperature in the
occupied zone. The incoming high-velocity air mixes rapidly with the
room air by entrainment so that by the time it enters the occupied zone
its temperature and velocity are within an acceptable range. Mixing
systems are designed to maintain the entire volume of air in the space
(floor to ceiling) at a relatively uniform temperature, humidity, and air
quality condition.
natural ventilation
When air moves into and out of a building through intentional or
planned routes, without the assistance of mechanical equipment, this is
termed natural ventilation. Generally driven by pressure differences,
inlets and outlets include windows, doors, grilles, roof openings, and
other designed apertures. This is often contrasted with forced or
mechanical ventilation.
occupant control
Used to describe a system incorporating individual, or occupant,
control in which occupants are able to adjust the operating parameters
according to their personal preferences. In the context of HVAC, under-
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GLOSSARY
floor systems can include grilles designed for easy occupant adjust-
ment of the direction and volume of supply air serving their workspace.
occupied zone
The volume of a conditioned space containing the occupants of the
space. Typically this is taken as extending from floor level up to a height
of 1.8 m (6 ft), and sometimes considered as set in 0.6 m (2 ft), on plan,
from external walls.
outside air
This term can denote either the air outside a building or air taken
into a building that has not previously been circulating through the
HVAC system.
outside air economizer
An HVAC control strategy that uses outside air under suitable cli-
matic conditions to reduce or eliminate the required mechanical cool-
ing. When the outside air temperature is less than the required supply
air temperature during cooling periods, the economizer allows a build-
ings mechanical ventilation system to use up to 100% outside air,
thereby reducing the energy required to cool the mixture of outside air
and warm recirculated air under normal operating conditions. This
method of cooling, often described as free cooling, is widely used in
temperate climates where outside air temperatures rarely go above 21-
24C (70-75F) during most days and periodically will be less than the
supply air temperatures (nighttime economizer cycles are frequently
employed, for example). As UFAD systems supply air at a higher tem-
perature than that for ceiling-based systems (typically 18C (65F) for
UFAD, 13C (55F) for ceiling HVAC), many North American tem-
perate climates will have a significantly larger number of daytime
hours during which the economizer can be used. Some method of vari-
able-volume relief must be provided to exhaust the extra outside air to
the outside. In addition, enthalpy-based economizer control is recom-
mended to maintain proper humidity levels (particularly during night-
time) and protect against condensation in the plenum. See Chapter 7 for
more discussion.
overhead systems
A typical, overhead air distribution system supplies air to, and
removes air from, a conditioned space at ceiling level. Both supply and
return grilles are located in the ceiling plane, above which there will be
a ceiling plenum of sufficient depth to accommodate the extensive sup-
ply ductwork, as well as other building services. Relying on the prin-
ciple of mixing-type air distribution, ceiling-based supply and return
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
systems are designed to condition the entire volume of the space (floor
to ceiling), thereby providing a single uniform thermal and ventilation
environment. This control strategy provides no opportunity to satisfy
different thermal preferences among the building occupants.
passive diffuser
Any air supply outlet that relies on a pressurized underfloor plenum
to deliver air from the plenum through the diffuser into the conditioned
space of the building. Passive diffusers have no local fans associated
with them, although they can be converted to an active diffuser by
attaching a fan-powered outlet box to the underside of the diffuser.
perimeter zone
This is the zone immediately adjacent to, and within 5 m (15 ft) of,
the external faade, which is affected by weather and outside condi-
tions. Perimeter spaces require special consideration in terms of their
heating and cooling loads, which are significantly different from and
change much more frequently than those of internal/core zone areas.
This is due to the influence of factors such as solar gain and heat gain/
loss through the building envelope.
plenum (see also service plenum)
Any defined space, typically above a suspended ceiling or beneath
a raised floor, through which supply air and/or voice, power, and data
cabling and other building services can be distributed.
plenum height
The vertical distance between the top surface of a structural floor
slab and the top surface of the raised floor system above it, which con-
tains, and defines, the underfloor plenum. Accounting for the typical
thickness of raised floor panels, the clear space within the underfloor
plenum will be 33 mm (1.3 in.) less than the plenum height.
plenum inlet
Any location in an underfloor plenum where conditioned air that
has been ducted from the air handler is discharged into the plenum.
plenum partition
A partition, typically formed from vertically oriented sheet metal,
erected within the plenum in order to divide up the plan of a conditioned
space and create separate zones within the underfloor area.
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pressurized plenum
In this system configuration, the underfloor plenum is under a pos-
itive static pressure produced by the central AHU that drives the air
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GLOSSARY
along the plenum and up through the diffusers. Typical pressures are
quite low (12.5-25 Pa [0.05-0.1 in. H2O]).
psychrometric
Relating to psychrometry, the study of atmospheric conditions
particularly the level of moisture in air. In terms of HVAC systems, psy-
chrometric charts are useful for illustrating the relationship between
properties such as wet- and dry-bulb temperatures and absolute and rel-
ative humidities when determining the desired supply air conditions.
raised floor
A platform structure typically consisting of 0.6 m 0.6 m (2 ft 2
ft) concrete-filled steel floor panels supported on pedestals 0.2 to 0.46
m (8 in. to 18 in.) above the concrete structural floor slab. Each panel
can be independently removed for easy access to the underfloor plenum
created below and can include openings for electrical outlets, grilles, or
any other floor accessory in its thickness. In most office installations,
carpet tiles are laid on top to provide a finished floor surface. Raised
floor systems provide maximum flexibility and significantly lower
costs associated with reconfiguring building services.
recirculated air
Return air that is diverted from the exhaust route, mixed with
incoming outside air (in some systems, recirculated air bypasses the
cooling coil and is mixed with the cool air leaving the coil to produce
the warmer supply air temperatures used in UFAD designs), passed
through the AHU for conditioning, and delivered to the conditioned
spaceessentially a means of recycling the air circulating through an
HVAC system for energy-saving purposes.
return air
The air extracted from a conditioned space (typically at ceiling
level) and returned to the air-handling unit (AHU), where a portion is
recirculated and the remainder is exhausted to the outside.
secondary air motion (see also entrainment)
Air discharged from an outlet creates a swirling, jet, or other air
motion that pulls (entrains) the surrounding air into its path where it
mixes with the supply air.
sensor
A device that can detect and measure a variable, for example, air
temperature, velocity, humidity, or light levels.
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service plenum
Any defined space, typically above a suspended ceiling or beneath
a raised floor, through which supply air and/or voice, power, and data
cabling and other building services can be distributed.
stagnant zone
A volume of a space in which there is low air velocity and the poten-
tial for increased stratification and poorer air quality.
static pressure (see also total pressure; velocity pressure)
Pressure is the force exerted per unit area by a gas or liquid. In air
distribution systems, static pressure is equal to the total pressure minus
velocity pressure and represents the pressure exerted by the air at rest.
Air distribution pressures are typically measured in inches of water (in.
H2O) or pascals (Pa).
stratification (see also thermal stratification)
The creation of a series of horizontal layers of air with different
characteristics (e.g., temperature, pollutant concentration) within a
conditioned space. UFAD systems, and other displacement ventilation-
based systems, rely on the upward convection of air driven by thermal
plumes to remove heat loads and contaminants from a space. This
results in both thermal and pollutant stratification in which a layer of
warmer, more polluted air forms above the occupied zone where it will
not affect the occupants.
stratification height (see also displacement ventilation)
In a displacement ventilation (DV) system, a horizontal interface,
known as the stratification height, is established at the height in the
room where the airflow rate in the thermal plumes equals the total sup-
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ply air volume entering the room at or near the floor level. The strati-
fication height divides the room into two zones (upper and lower)
having distinct airflow conditions. The lower zone below the stratifi-
cation height has no recirculation and is close to displacement flow.
The upper zone above the stratification height is characterized by recir-
culating flow producing a fairly well-mixed region. In a properly
designed displacement ventilation system, the stratification height is
maintained near the top of the occupied zone (1.8 m [6 ft]). In UFAD
systems, a stratification height similar to that found in DV systems is
formed, but the airflow conditions in the lower zone are changed due
to the greater mixing provided by the turbulent floor diffusers.
supply air
The air entering a space through an outlet, diffuser, or grille, having
been delivered from the air-handling unit (AHU).
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GLOSSARY
supply duct
Any duct through which supply air is delivered to the conditioned
space from the AHU, local fan, or other air movement device.
task/ambient conditioning (TAC) system
Any space conditioning system that allows occupants to individu-
ally control the thermal environment in the localized zone of their work
space while still maintaining acceptable environmental conditions in
the buildings ambient spaces (circulation and open-use spaces, for
example). This is typically achieved by enabling occupants to adjust
the volume and direction of the air supply serving their workspace,
according to their personal preferences. TAC systems, therefore, gen-
erally include a large number of supply diffusers throughout a building,
many located in close proximity to the occupants. Although not a
requirement, most TAC systems are integrated with the use of under-
floor air distribution.
thermal comfort
That condition of mind that expresses satisfaction with the thermal
environment. Thermal comfort is influenced by both subjective and
objective factors. Heat transfer between the human body and the envi-
ronment, and hence acceptance of the thermal environment, is influ-
enced by a combination of environmental factors (air temperature,
radiant temperature, air velocity, humidity) and personal factors (cloth-
ing and activity level). There is also evidence that people who know
they have control over their local thermal environment are more toler-
ant of temperature variations, making it easier to satisfy their comfort
preferences.
thermal plume
The upward movement of warm air due to buoyancy forces above
a heat source (e.g., person, computer, lights) in a room. The air volume
in a rising thermal plume increases with height as the plume entrains
ambient air.
thermal stratification (see also stratification)
The creation of a series of horizontal layers of air having increasing
temperature with height within a conditioned space. UFAD systems,
and other displacement ventilation-based systems, rely on the upward
convection of air driven by thermal plumes to remove heat loads and
contaminants from a space. This results in both thermal and pollutant
stratification in which a layer of warmer, more polluted air forms above
the occupied zone where it will not affect the occupants.
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thermostat
An automatic control device that is responsive to temperature and
used to control temperature in a conditioned space or zone. In the con-
text of UFAD systems, thermostats located in an office space (typically
installed on walls) register changes in ambient air temperature. These
devices communicate information to the HVAC control unit, which
adjusts the temperature, or airflow volume, of the supply air to maintain
the temperature measured at the thermostat within a pre-programmed
comfort range around a setpoint temperature.
thermostatic control
A means of automatically controlling the operation of an HVAC
system component, collection of components, or complete system in
response to information about air temperatures as registered by one or
more thermostats located within the conditioned space.
total pressure (see also static pressure; velocity pressure)
Pressure is the force exerted per unit area by a gas or liquid. In air
distribution systems, total pressure is equal to the sum of static pressure
and velocity pressure. Air distribution pressures are typically measured
in inches of water (in. H2O) or pascals (Pa).
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GLOSSARY
underfloor plenum
The open space between a structural concrete slab and the under-
side of a raised access floor system. Commonly used as the access route
for telecommunications cabling, in underfloor systems the supply air is
also delivered through this space.
upper zone
The volume of a conditioned space above the stratification height
produced by a DV or UFAD system.
variable air volume (VAV)
A control strategy of an air supply system in which varying heating
and cooling loads are met by adjusting the airflow volume, keeping the
temperature of the air constant. Alternatively, a constant air volume,
variable temperature (CAV-VT) system can be employed in which the
temperature of the airflow is varied, while the volume is kept constant.
VAV box
A variable-air-volume control box. Typically, a VAV box is ducted
on its inlet and uses dampers to control the volume of air discharged
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from the unit.
velocity pressure (see also static pressure; total pressure)
Pressure is the force exerted per unit area by a gas or liquid. In air
distribution systems, velocity pressure is the pressure due to the veloc-
ity and density of the moving air. Air distribution pressures are typi-
cally measured in inches of water (in. H2O) or pascals (Pa).
ventilation
The process of intentionally supplying outside air to a building
achieved by either natural or mechanical (forced) means.
ventilation effectiveness
Ventilation effectiveness describes the systems ability to remove
pollutants generated by internal sources in a space, zone, or building.
In comparison, air change effectiveness describes the ability of an air
distribution system to ventilate a space, zone, or building.
zero-pressure plenum
In this system configuration, the underfloor plenum is maintained
at very nearly the same static pressure as that of the conditioned space.
Supply air is delivered to the plenum by the central AHU, and small
fan-powered air outlets are used to discharge air from the plenum into
the conditioned space. Some systems may create a slight negative pres-
sure in the plenum to draw recirculated air (typically directly from the
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room through open floor grilles, or down from the ceiling through
shafts) into the plenum where it is mixed with the supply air from the
AHU.
zone
Also known as a control zone for an HVAC system, a zone is
defined as a space or group of spaces in a building having similar heat-
ing and cooling requirements throughout its occupied area so that com-
fort conditions may be controlled by a single thermostat.
zoning (see also interior zone; perimeter zone)
The practice of dividing a building into smaller zones for control of
the HVAC system. For example, buildings may be zoned into individ-
ual floors, rooms, or spaces with distinct loads, such as perimeter and
interior zones.
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References and
Annotated Bibliography
Addison, M., and D. Nall. 2001. Cooling via underfloor air distribution:
Current design issues and analysis options. From: Cooling Fron-
tiers: The Advanced Edge of Cooling Research and Applications in
the Built Environment. College of Architecture and Environmental
Design, Arizona State University.
AEC. 2000. Design Brief: Underfloor air distribution and access floors.
Energy Design Resources web site, http://www.energydesignre-
sources.com. Architectural Energy Corporation, Boulder, CO.
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This design brief is an introduction to underfloor air and access
floor systems and addresses the following topics: displacement
ventilation and hybrid underfloor systems, energy savings and
indoor air quality improvement, access floor system design and
construction, economics of combined underfloor air and access
floor systems, comfort and productivity issues, and applications of
underfloor air and access floor systems.
Akimoto, T., T. Nobe, and Y. Takebayashi. 1995. Experimental study on
the floor-supply displacement ventilation system. ASHRAE
Transactions, Vol. 101, Pt. 2.
Akimoto, T., T. Nobe, S.Tanabe, and K. Kimura. 1996. Experimental
study on indoor thermal environment and air quality of the floor-
supply displacement ventilation system. Proceedings, Indoor Air
1996, Nagoya, Japan, July 21-26.
Architectural Institute of Japan. 1993. Proceedings, Symposium on Floor-
Based Air Supply HVAC Systems, Tokyo, October 1 (in Japanese).
Useful for its brief outline of a wide range of subjects contained
within nine presentations on floor-based systems, covering general
energy conservation, indoor conditions, design and operation fun-
damentals, and specific examples of different installations.
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REFERENCES AND ANNOTATED BIBLIOGRAPHY
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Phase I. Center for Environmental Design Research, University of
California, Berkeley, June, 81 pp.
Bauman, F.S., G. Brager, E. Arens, A. Baughman, H. Zhang, D. Faulkner,
W. Fisk, and D. Sullivan. 1992. Localized thermal distribution for
office buildings, Final reportPhase II. Center for Environmental
Design Research, University of California, Berkeley, December,
220 pp.
This report presents the results of research in five key areas: (1)
survey of industry perspective on task conditioning systems, (2)
laboratory experiments, (3) recommendations to improve localized
thermal distribution system performance, (4) whole building
energy simulations, and (5) building standards and codes.
Bauman, F.S., and M. McClintock. 1993. A study of occupant comfort
and workstation performance in PG&Es advanced office systems
testbed. Center for Environmental Design Research, University of
California, Berkeley, May, 135 pp.
Bauman, F.S., H. Zhang, E. Arens, and C. Benton. 1993. Localized com-
fort control with a desktop task conditioning system: Laboratory
and field measurements. ASHRAE Transactions, Vol. 99, Pt. 2.
210
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This paper presents the results of both laboratory and field mea-
surements investigating the thermal performance of desktop task
conditioning systems. Interesting for its consideration of the ther-
mal conditions resulting from a range of nozzle sizes.
Bauman, F., E. Arens, M. Fountain, C. Huizenga, K. Miura, T. Xu, T.
Akimoto, H. Zhang, D. Faulkner, W. Fisk, and T. Borgers. 1994.
Localized thermal distribution for office buildings, Final report
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Phase III. Center for Environmental Design Research, University
of California, Berkeley, July, 115 pp.
This report presents the results of research completed during
phase III of the localized thermal distribution (LTD) project, cov-
ering three task areas: (1) whole-building energy simulations, (2)
field studies, and (3) LTD engineering applications guide outline.
Includes comprehensive field studies on two buildings, located in
Phoenix, Arizona, and San Ramon, California.
Bauman, F.S., E.A. Arens, S. Tanabe, H. Zhang, and A. Baharlo. 1995.
Testing and optimizing the performance of a floor-based task con-
ditioning system. Energy and Buildings, Vol. 22, No. 3, pp. 173-
186.
A comprehensive report of controlled environmental chamber
experiments studying the thermal performance of a floor-based
TAC system. Discussion includes a summary of research to date,
use of the latest thermal manikin model, analysis involving the
effect of supply volume, grille direction and Archimedes number of
air supply jets, and concise design recommendations for improving
TAC system performance.
Bauman, F., ed. 1995. Proceedings: Workshop on task/ambient condition-
ing systems in commercial buildings, San Francisco, CA, 4-5 May
1995. Center for Environmental Design Research, University of
California, Berkeley, October.
A collection of literature from contributors to this workshop. A
broad range of industry interests are represented, from manufactur-
ers to commercial and academic research organizations.
Bauman, F., and T. Akimoto. 1996. Field study of a desktop task condi-
tioning system in PG&Es advanced office systems testbed. Cen-
ter for Environmental Design Research, University of California,
Berkeley.
Bauman, F.S. 1996. Task/ambient conditioning systems: Engineering
and application guidelines. Proceedings, 3rd International Con-
ference on Energy and Environment: Towards the Year 2000. Capri,
Italy.
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This article looks at the current status of underfloor systems in
the marketplace. Crockett discusses reasons why underfloor is still
not commonly used, some of its benefits, and available web
resources.
Croome, D.J., and D. Rollason. 1988. Freshness, ventilation and tem-
perature in offices. Proceedings of CIB Conference on Healthy
Buildings 88, 5-8 September, Stockholm.
Daly, A. 2002. Underfloor air distribution: Lessons learned. ASHRAE
Journal, Vol. 44, No. 5, May, pp. 21-24.
Presents three strategies for capturing as many benefits of under-
floor air distribution as possible while keeping the initial cost to a
minimum: minimize the ductwork in the plenum, prevent plenum
leakage, and dont oversize airflows.
Dasher, C., A. Potter, and K. Stum. 2002. Commissioning to meet
green expectations. Portland Energy Conservation, Inc. web
site: http://www.peci.org.
David, J. 1984. Under floor air conditioning. Journal of the Chartered
Institution of Building Services, August.
de Dear, R., and G.S. Brager. 1998. Developing an adaptive model of
thermal comfort and preference. ASHRAE Transactions, Vol. 104,
Pt. 1.
Under the hypothesis that contextual factors and past thermal
history modify building occupants thermal expectations and pref-
erences, a worldwide thermal comfort database was compiled
examining thermal sensation, acceptability, and preference from
observations in 160 buildings. The results formed the basis of a pro-
posal for a variable indoor temperature standard.
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REFERENCES AND ANNOTATED BIBLIOGRAPHY
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terns with a floor-based task ventilation system discusses relation-
ships between average age of air, the supply-airs piston-like flow
pattern, and height. Experimental variables include intra-room
transport of tobacco smoke particles (produced mechanically), sup-
ply-air flow rate, temperature, direction, and internal heat loads,
measured using a tracer gas procedure.
Faulkner, D., W.J. Fisk, D.P. Sullivan, and D.P. Wyon. 1999 Ventilation
efficiencies of desk-mounted task/ambient conditioning systems.
Indoor Air, No. 9, pp. 273-281.
Outlines required outdoor air content and supply airflow rate and
direction for optimum values of air exchange effectiveness and pol-
216
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national Conference on Air Distribution in Rooms, ROOMVENT
1996, Yokohama, Japan.
A study of the characteristics of air flow velocities and temper-
ature distributions around the human body using typical audito-
rium/theater seats fed with supply air from below the seat. Of
interest for highlighting alternative applications of personal condi-
tioning underfloor air supply systems.
Krepchin, I. 2001. Underfloor air systems gain foothold in North Amer-
ica. E Source Report, ER-01-1. Boulder, Colo.: Financial Times
Energy, Inc., January.
Presents market information. Report includes sections with
headings on The Market Expands, Why Is the Market Grow-
ing? What Challenges Remain? as well as an appendix of man-
ufacturers and buildings using underfloor air.
Kroll, K. 2001. Customer driven real estate: Fisher Properties wants to
find better ways to serve tenants need for speed and flexibility.
One step is to let them leave on 30 days notice. Building Operating
Management, May.
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Underfloor air distribution is cited as a way in which buildings
can be flexible to accommodate different tenants.
Kroner, W., J. Stark-Martin, and T. Willemain. 1992. Using advanced
office technology to increase productivity: The impact of environ-
mentally responsive workstations (ERWs) on productivity and
worker attitude. The Center for Architectural Research, Rensse-
laer, Troy, NY.
An in-depth case study on the ERWs with individualized con-
trols, installed in the new West Bend Mutual Insurance Headquar-
ters, Wisconsin. Useful as a reference for its range of subjective
assessment and measurement techniques and means of internal val-
idation.
Lee, H., and F. Bauman. Development of an air leakage test methodology
for underfloor plenums. To be submitted to ASHRAE Transac-
tions.
Levy, H. 2002. Individual control by individual VAV. Proceedings,
ROOMVENT 2002, Copenhagen, Denmark, 8-11 September 2002.
This paper presents a study on sensible cooling by varying air
velocity (VAV) through personal air outlets adjustable by occu-
pants. The paper concludes that the system tested and described in
the paper will air condition individual people instead of the build-
ing and will eliminate dissatisfaction with thermal conditions.
Lin, Y.-J., and P.F. Linden. 2002. Modeling an underfloor air distribu-
tion system. Proceedings, ROOMVENT 2002, Copenhagen, Den-
mark, 8-11 September 2002.
Livchak, A., and D. Nall. 2001. Displacement ventilation Application
for hot and humid climate. Proceedings, Clima 2000/Napoli 2001
World Congress, Naples, Italy, 15-18 September 2001.
Loftness, V., P. Mathew, G. Gardner, C. Mondor, T. Paul, R. Yates, and M.
Dellana. 1999. Sustainable development alternatives for specula-
tive office buildings: A case sudy of the Soffer Tech Office Build-
ing. Final report. Center for Building Performance and
Diagnostics, Carnegie Mellon University, Pittsburgh, Pa.
This 38-page report documents the analysis of sustainable
design alternatives for the Tech Office Building. Raised floor for
HVAC and networking is included along with 13 other sustainable
alternatives such as faade glazing and shading, roof insulation,
lighting, energy recovery, etc.
Loftness, V., R. Brahme, M. Mondazzi, E. Vineyard, and M. MacDonald.
2002. Energy savings potential of flexible and adaptive HVAC
distribution systems for office buildings Final report. Air Con-
ditioning and Refrigeration Technology Institute 21-CR Research
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REFERENCES AND ANNOTATED BIBLIOGRAPHY
Sodec, F., and R. Craig. 1991. Underfloor air supply system: Guidelines
for the mechanical engineer. Report No. 3787A. Aachen, West
Germany: Krantz GmbH & Co., January.
Although covering issues relevant for all designers, the language
used, and level of knowledge assumed of the reader, is targeted
toward mechanical engineers. Discussion ranges from technical
data for twist outlets to control zones to maintenance of room
humidity and underfloor air as a fire or smoke hazard.
Spoormaker, H.J. 1990. Low-pressure underfloor HVAC system.
ASHRAE Transactions, Vol. 96, Pt. 2.
This paper presents a case study of the development and opera-
tion of a low-pressure underfloor air-conditioning system installed
in a South African office building in the early 1980s. Includes use-
ful classifications of levels of flexibility, durability, reliability, and
maintainability for HVAC systems and a schematic description of
a low-pressure underfloor HVAC system.
Stanke, D., and B. Bradley. 2001. Turning air distribution upside down:
Underfloor air distribution. TRANE engineers newsletter, Vol. 30,
No. 4.
An overview for those not familiar with underfloor air, this arti-
cle touches on floor choices, air distribution options, approaches to
design, potential advantages, and growing pains.
Suwa, T., 1991. Installation example of an underfloor air conditioning
system, Toyo-cho building of Meiji Life Insurance Co. Journal of
the Society of Heating, Air-conditioning and Sanitary Engineers of
Japan, Vol. 65, No.7.
Case study of an underfloor system application featuring custom
designed floor outlets, each equipped with a 50 W fan unit and con-
trol mechanisms (manual and automatic).
Svensson, A.G.L. 1989. Nordic experiences of displacement ventilation
systems. ASHRAE Transactions, Vol. 95, Pt. 2.
TAK and Takenaka Corporation. 1993. Design and practice of under-
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floor air conditioning systems. Tokyo: Gijutsu Shoin (in Japa-
nese).
Tamblyn, R.T. 1995. Toward zero complaints for office air condition-
ing. Heating/Piping/Air Conditioning, March.
This article cites 100% outside air systems and personal control
of air temperature and motion as two possibilities for reducing
occupant dissatisfaction with their office environments and dis-
cusses the means by which both can be operated without undue
increase in initial or operating costs. The hypothetical design of an
office building with these systems is used to illustrate the report.
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REFERENCES AND ANNOTATED BIBLIOGRAPHY
Trox. 1998. Economics of raised access floors with underfloor air for
office space environments. Trox Technik Technical Bulletin
TB080498, Trox USA, Alpharetta, Ga.
A comprehensive cost analysis of underfloor versus conven-
tional (poke through and cellular deck) systems covering issues
within constructional, operational, and relocation costs.
Trox. 2002. Product information. Trox USA, Alpharetta, Ga, http://
www.troxusa.com.
TRW FAA SETA. 1995. FAA SETA raised floor trade study. Draft Pre-
pared for the Federal Aviation Authority (FAA). This report com-
pares single-layer and triple-layer raised floor systems to determine
the optimum type for FAA facilities. A comprehensive study cov-
ering many issues from implications for electrical layouts to life-
cycle costing to environmental control. A good source of informa-
tion on an alternative raised floor configuration about which little
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
has been published despite examples of use cited dating from the
report (1995) back to 1984.
Tsuzuki, K., E.A. Arens, F.S. Bauman, and D.P. Wyon. 1999. Individual
thermal comfort control with desk-mounted and floor-mounted
task/ambient conditioning (TAC) systems. Proceedings of Indoor
Air 99, Edinburgh, Scotland, 8-13 August.
This paper outlines experiments comparing three TAC systems
(two desk-based, one floor-based) in terms of their effect on heat
loss from a thermal mannequin at various room temperatures.
Results indicate such systems are capable of considerably influenc-
ing control over the heat balance of an occupant.
Tuddenham, D. 1986. A floor-based approach. ASHRAE Journal, July.
Vranicar, M. 2002. Personal communication. Critchfield Mechanical,
Inc., Menlo Park, Calif.
Warson, A. 1990. The pin-striped office. Canadian Building, March.
Webster, T., et al. 1999-2002. UFAD Project Profiles. http://
www.cbe.berkeley.edu/underfloorair/whereHasItBeenDone.htm.
Underfloor air technology web site, Center for the Built Environ-
ment, University of California, Berkeley.
Webster, T., E. Ring, and F. Bauman. 2000. Supply fan energy use in
pressurized underfloor plenum systems. Center for the Built Envi-
ronment, University of California, Berkeley.
This preliminary study examines the impact of various design
assumptions on the fan energy consumption of pressurized under-
floor plenum systems, compared to traditional overhead constant-
air-volume and variable-air-volume systems.
Webster, T., F. Bauman, and J. Reese. 2002a. Underfloor air distribu-
tion: Thermal stratification. ASHRAE Journal, Vol. 44, No. 5,
May, pp. 28-36.
This article describes the idea of stratification, the control and
optimization of which is crucial for system design of underfloor
systems. This article focuses on practical implications of room air
stratification testing results for the control and operation of con-
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Index
A
access flooring 9
See also raised floor system
acoustic performance 97, 140
air change effectiveness 49, 147
air highway 66, 171
air leakage 6062, 113, 114, 168, 169, 174
air velocity 43, 4648, 143
air-handling unit 168, 177
VAV change-over 127
ANSI/ASHRAE Standard 113-1990 146
ANSI/ASHRAE Standard 55-1992 43, 44, 49, 143
ANSI/ASHRAE Standard 62-2001 145
ANSI/ASHRAE/IESNA Standard 90.1-2001 146
ASHRAE Standard 129-1997 147
C
cable management 9, 13, 55, 85, 139, 149, 157
carpet tile 8587, 114
ceiling plenum 14, 154, 155
chiller 12, 178
churn 13, 141
cleaning 96, 111, 138
clear zone 31, 48
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INDEX
D
dehumidification 18
design phase 109, 138, 153
design tools 187
diffusers
active 3, 70, 77, 81, 130, 174
combustibility of 149
fan-powered 11, 45, 48, 7881, 174
floor 1, 5, 6, 48, 69, 71, 73, 81, 174, 175
furniture-based 3, 5, 6, 4547, 49, 77, 78, 81, 175
jet 4548, 78, 79
low side-wall 28, 30
passive 11, 70, 71, 174
swirl 35, 37, 38, 47, 71, 73, 81, 175
TAC 12, 45, 49, 69, 77, 79, 145, 174
variable-area 35, 73, 122, 175
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E
economizer 12, 102, 105, 164
integrated 105
efficiency, cooling-system 106
electronically commutated motor (ECM) 100, 125
energy use 12, 99, 116, 146, 147, 169
air distribution 99
central fan 100, 102
fan 13, 100
perimeter fan 100
equivalent homogenous temperature 4548
F
fan coil unit
constant-speed 120
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heating-only 122
variable-speed 125
fan pressure 99
fan terminal 81, 84, 130
fire safety 138
floor panel 53
heat transfer through 65, 174
floor-to-floor height 14, 17, 115, 140, 154
G
grille, linear floor 75, 121, 124, 127129, 175
H
health 142
heat gain
convective 160
radiant 160
heat load 30, 34, 36
See also heat gain
heat pump 122
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INDEX
--`,`,`,,,`,`,,,```,,``,,`,`,`,-`-`,,`,,`,`,,`---
HVAC design 5, 7
HVAC equipment, primary 177
I
individual control 3, 6, 31, 44, 48, 51, 95
indoor air quality 12, 30, 41, 50, 145
induction shaft 94, 172
L
LEED rating system 150
load
air-side 160
space cooling 158
space heating 158, 164
load calculation 158, 162164
M
mixing-type air distribution 5, 12, 23, 24, 33, 158
morning warm-up 107, 164, 179
N
noise 120, 122, 125, 132
O
occupancy sensor 78, 130
occupant control 78, 79, 143
occupant cooling 6, 44, 45, 144
evaporative 47
sensible 4548
occupied zone 160
office building 9, 19, 30, 97
operation
cooling 116
heating 82, 107
part-load 90
operation and maintenance 96, 167
240
Copyright ASHRAE
Provided by IHS under license with ASHRAE Licensee=Australia/5940240024
No reproduction or networking permitted without license from IHS Not for Resale, 09/28/2010 02:18:33 MDT
--`,`,`,,,`,`,,,```,,``,,`,`,`,-`-`,,`,,`,`,,`---
P
personal control 44, 46, 48, 145
pollutants 29
productivity 14, 50, 142, 187
property value 142
R
raised concrete core 137
raised floor system 5, 85, 97, 153, 157, 167
costs 137
installation of 111
reconfiguring building services 97, 141
reheat 120, 122, 125, 126, 132
return air 6, 176
return air bypass 177
room air distribution 23, 31, 146
room air distribution model 3134
room airflow rate 28, 34, 3638, 159
S
space planning 115
standards
thermal comfort 43, 44, 143
Title-24 147
stratification 6, 15, 33, 36, 37, 49, 107, 146, 159, 186
controlling 37, 91, 92, 116
stratification height 26, 2834, 36, 159
structural slab 5, 6, 178
nighttime precooling of 66, 107, 178
supply air 31
supply air volume 13, 28, 92, 94, 162, 173
241
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No reproduction or networking permitted without license from IHS Not for Resale, 09/28/2010 02:18:33 MDT
INDEX
systems
perimeter 119
special 119, 130
--`,`,`,,,`,`,,,```,,``,,`,`,`,-`-`,,`,,`,`,,`---
task/ambient conditioning (TAC) 2, 8, 10, 31, 41, 94
tax savings 142
temperature
return air 102, 163, 173
supply air 38, 39, 89, 93, 102, 172
temperature difference
head-foot 37
room-supply 4548
temperature gradient 30, 34, 92, 106
temperature near the floor 35
temperature profile 30, 33, 37
thermal bypass in perimeter zones 163
thermal comfort 6, 11, 41, 44, 48, 106, 143, 186
thermal plume 27, 34, 163
thermal storage 107, 178
thermostat height 93
thermostat setpoint 93, 162
throw height 31, 34, 37
Title-24 147
U
underfloor air distribution (UFAD) 2, 810, 31, 153
benefits 1114
underfloor plenum 2, 5, 16, 53, 167, 186
dirt entering 18, 96
ducting within 59, 66, 139, 170
height of 57, 157
obstructions within 59
pressurized 5, 56, 57, 89, 168
sealing of 113, 138
thermal decay in 59, 63, 65, 66, 173
thermal performance of 63, 178
zero-pressure 6, 56, 94, 123, 169
242
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UNDERFLOOR AIR DISTRIBUTION DESIGN GUIDE
V
variable volume and temperature (VVT) 127
variable-air-volume (VAV) 7, 13, 70, 73, 91, 94, 122
VAV box 129
ventilation 49, 145, 164, 186
ventilation effectiveness 12, 24, 50, 145, 147, 164
ventilation efficiency 12
W
whole-building energy simulation 16, 186
whole-building performance 16, 187
window blinds 132
Z
zones
interior 90, 165
perimeter 81, 82, 119, 163, 165, 166
special 119, 166
zoning 165
243
Copyright ASHRAE
Provided by IHS under license with ASHRAE Licensee=Australia/5940240024
No reproduction or networking permitted without license from IHS Not for Resale, 09/28/2010 02:18:33 MDT