MB Passive Active Floors Jan17

Concrete floor solutions for
passive and active cooling
Design options for low energy buildings

2 CONCRETE FLOOR SOLUTIONS FOR PASSIVE AND ACTIVE COOLING
Contents
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Fabric Energy Storage (FES) and thermal mass. . . . . . . . . . . . . . . . 4
How much thermal mass do you need? . . . . . . . . . . . . . . . . . . . . . . . . . 5
Other design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Passive and active floor options
Exposed slab, naturally ventilated building.

Case study: Cambridge Federation
of Women’s Institute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Exposed slab, underfloor mechanical ventilation.
Case study: PowerGen Headquarters . . . . . . . . . . . . . . . . . . . . . . 12
Exposed hollowcore slab with cores supplied by
mechanical ventilation.
Case study: Innovate Green Office . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Exposed in-situ or lattice girder slab with embedded

air ducts supplied by mechanical ventilation.
Case study: 4 West Building, University of Bath. . . . . . . . . 16
Exposed slab with embedded cooling/heating pipework.

Case study: CAFOD Headquarters (Romero House) . . . . . . 18
Exposed hollowcore slab with embedded heating/

cooling pipework.
Case study: Vanguard House. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Exposed composite lattice girder soffit slab with

embedded pipework.
Case study: Manchester Metropolitan University
Business School. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Chilled beams with an exposed

or partially exposed soffit.
Case study: Conquest House. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Cover images
CAFOD Headquarters (Romero House), London, features exposed, in-situ

slabs with embedded water cooling pipes and mixed-mode ventilation. See
page 19. Photo: courtesy of Black Architecture
Top insert: A coffered slab with underfloor ventilation
Bottom insert: 4 West Building, University of Bath, which uses the Concretcool
system, see pages 16 and 17. Photo: courtesy of Cowlin Construction Ltd.
This page: 160 Tooley Street, London uses the thermal mass provided by the
concrete to help optimise the building's passive cooling performance. See
page 26.
CONCRETE FLOOR SOLUTIONS FOR PASSIVE AND ACTIVE COOLING 3
Introduction About this publication

Since this guide was first published in 2005 existing FES techniques have
The last few years have seen low energy, high thermal evolved and new systems developed. This updated guide details all the
mass office construction make a decisive move into the various systems currently available, from the simple passive approach to
mainstream market. What was once largely the preserve the more sophisticated active systems.
of the one-off, owner occupier client has matured
Case studies are included to highlight recent projects featuring the various
to become an increasingly common approach for
systems covered. This guide focuses on issues including cooling capacity,
minimising the cooling load in speculative offices. system control, visual appearance and buildability/spans etc. and aims to
assist designers select the best floor option to meet specific project needs.
Growth is largely the result of three key drivers:
At one end of the spectrum is the entirely passive approach, which uses
1. Tougher Part L energy/CO2 targets and a significant increase in the
natural ventilation in combination with a flat soffit to meet the cooling
efficiency requirements for mechanical cooling plant.
needs of fairly undemanding environments, for which close control is not
2. Rising energy costs which, more than anything else, is driving demand critical. At the other end of the spectrum is the high load environment,
among occupiers1. This has significantly strengthened the business requiring the use of active slabs with water and/ or mechanical ventilation
case for investment in low energy buildings, particularly offices. Many as the cooling medium to provide greater cooling output and control.
investment institutions now accept low energy designs as the best These options and the others that sit between share many design features,
way of future proofing their property assets2 and avoiding climatic but also offer qualities of their own, all of which are summarised in
obsolescence as temperatures continue to rise3. the guide.
3. A growing appreciation of visual concrete and the role it can play in the
‘fabric first’ approach to energy efficient design.
The use of thermal mass to optimise fabric performance centres on the

principle of Fabric Energy Storage (FES), which uses concrete floor slabs to
absorb unwanted heat, helping stabilise the internal temperature and cut
the CO2 emissions associated with mechanical cooling, see Figure 1. This is
achieved either passively or in combination with a more active approach
such as mechanical ventilation or chilled water to augment performance
(sometimes referred to as a Thermally Active Building System or TABS).
Using floors in this way makes good sense, as they typically provide the
greatest source of thermal mass in non-residential buildings. The overall
ability of concrete floors to provide thermal mass whilst also fulfilling
structural and aesthetic roles, make it a hard working material, capable of
saving significant capital and operating costs over the life of the building.
0 25 50 75 100 125 150 175 200
Kg CO2 /m2/year
Figure 1: Benchmark CO2 emissions from office buildings4. Bermondsey Square, London, which features exposed hollowcore slabs.
Photo: courtesy of Igloo Regeneration Limited.
Fabric Energy Storage (FES)

and thermal mass
How FES works during the daytime How FES works during the
The way FES works is quite simple. Concrete floor slabs have a high level
night time
of thermal mass, in other words they can store a lot of heat. This means
As the evening approaches and the working day comes to an end, heats
that on warm days an exposed concrete soffit will soak up much of the
gains from the sun, internal equipment and occupants start to diminish.
unwanted heat in a building, helping to maintain a comfortable, stable
During the night, particularly the early hours of the morning, the heating/
temperature and reduce the energy used in air-conditioned environments.
cooling cycle goes into reverse and stored heat is given up by the floor
The main way in which the soffit absorbs heat is by radiation from adjacent
slab. The simplest way of facilitating this is by ventilating the building with
surfaces i.e. objects and people at a higher temperature radiate heat to the
cool night air, which can be achieved with either natural and/or mechanical
comparatively cool concrete. Comfort is determined by a combination of
ventilation. The purging of accumulated heat ensures the floor slab is ready
radiant temperature, air temperature and air movement, so the presence of
to repeat the cycle the following day.
a comparatively cool soffit makes a significant contribution to summertime
performance. The radiant cooling effect will continue throughout the
This process is quite effective in the UK, as the variation in diurnal
day even though a significant amount of heat may be absorbed. This is a
temperature (difference between day and night) is rarely less than five
consequence of the high level of thermal mass (i.e. heat capacity) provided
degrees, and is usually much higher, making night cooling an effective
by the slab which ensures the surface temperature increases very little
means of removing heat. However, the urban heat island effect in the
across the day, maintaining the beneficial temperature difference between
centre of large cities can reduce the effectiveness of night time cooling. An
soffit and occupants.
alternative or addition to night ventilation uses water to provide a more
active approach to cooling. This offers greater flexibility and control of the
The proximity of the soffit to the occupants makes it particularly suitable for
process, since the amount of heat removed is not solely determined by
radiant cooling because, to be effective, occupants need to be within line
night time temperatures.
of sight of a comparatively cool surface that is nearby and cannot become
obscured in the same way that walls and floors often are e.g. by furniture,
carpets etc. Floor slabs also provide some convective cooling i.e. to air that
comes into contact with the surface. This is more significant where floors
form part of a mechanical ventilation system (e.g. underfloor ventilation or
the TermoDeck system, see page 14).
In addition to stabilising the internal temperature an exposed concrete

floor can delay its peak by around six hours, which in an office environment,
will typically occur in the early evening when the occupants have left for
the day, see Figure 2.
Peak temperature
Up to 8 degrees difference
delayed by up to
between peak external
six hours
and internal temperature
Internal temperature
30oC with high thermal mass
Internal temperature
with low thermal mass
External
temperature
15oC
Day Night Day
Figure 2: Stabilising effect of thermal mass on the internal temperature

How much thermal mass

do you need?
The significance of heat capacity with a simple 24 hour heating and cooling cycle. However, in addition to
a building’s daily cycle, there are also longer cycles related to a typical hot
and heat flow spell (usually three to five days) and also the weekly cycle of five working
days, from which heat will reach different depths within the available
thermal mass. For example, in a non-air-conditioned building the greater
Concrete floors of all types have the ability to store heat, but the degree to
the slab depth, the longer the time period it responds to; the core of a
which this can be usefully exploited largely depends on two key factors:
300mm thick concrete slab responds to the monthly average condition
The level of thermal mass – the greater the thermal mass, the greater a and draws heat in deeper over an extended period of hot weather. For
floor’s potential for storing heat; the question is whether the volume/depth longer time periods these factors are important because it is the longer-
of concrete will be sufficient to handle the building’s cooling demand and term average room temperatures that define the thermal storage core
the range of external conditions experienced over a typical summer? temperature and hence the temperature gradient that draws heat in5. So,
whilst 100mm of concrete offers some useful thermal mass, thicker slabs
The rate of heat flow - i.e. the rate at which the floor slab can absorb provide greater temperature stability and increased cooling performance
and release heat. This needs to be sufficiently high to make a worthwhile across a range of conditions including hot periods.
contribution to the daily cooling needs of the building.
To help visualise what this means in practice, Figure 3 shows how the soffit
These two factors are intrinsically linked since increased heat flow allows temperature of exposed 100mm and 300mm concrete floors in a naturally
more thermal mass to be utilised resulting in greater cooling potential, ventilated office respond to the onset of hot weather. This was produced
whilst poor heat flow has the opposite effect. What this means in practical using finite difference modelling6 to calculate the heat transfer at the soffit
terms is explained below, firstly for naturally ventilated buildings and then and through the floor slab over the course of several days, during which
for air-conditioned buildings. there is an increase in the external temperature7.
In the case of the 300mm slab, it can be seen that the soffit temperature
Thermal mass in naturally ventilated slowly increases over the course of several days in response to the onset
buildings of hot weather, during which it continues to provide a useful amount of

cooling by virtue of its comparatively low soffit temperature. In contrast,
the 100mm floor warms up more rapidly, offering less resilience to the
A question often asked by architects and designers is “how much thermal hotter conditions, resulting in a greater risk of overheating. It is also less
mass do you need?” The answer largely depends on the extent to which effective at delaying and moderating the daily peak internal temperature.
you want to optimise the building design. It is sometimes suggested that The 300mm slab will of course take longer to cool down when conditions
100mm of concrete is sufficient, but this does not take into account the moderate, although as the external temperature drops windows can be
way buildings respond to real weather patterns. For example, a naturally opened more freely to optimise comfort, something that is best avoided
ventilated office with exposed 100mm floors (e.g. steel decking/soffit with during the preceding hot weather.
in-situ concrete topping) should have sufficient heat capacity to cope
26
25
Start of hot weather
24 Exposed 100mm lightweight floor

Soffit temperature (oC)
(steel decking with concrete topping)

23
Exposed 300mm concrete floor
22
21 The 300mm floor stays around two

degrees cooler than the 100mm
floor for several days and then
20
stabilises at a lower temperature
during the day time.
19
18
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Day
Figure 3: Change in soffit temperature in response to a period of hot weather

Thermal mass in air-conditioned Surface emissivity –

buildings why this matters
In air-conditioned buildings the heating/cooling cycle is generally limited For heat to be stored or released from an exposed soffit it must of course
to 24 hours. This is because the tighter control of temperature should pass between the concrete slab and occupied space below. Although
ensure there is no build up of heat in the fabric over periods much longer heat moves relatively quickly through concrete, the rate is generally much
than a day. This might suggest that 100mm of concrete would provide slower at its surface, which tends to act as a thermal bottle neck. Where
the optimal level of thermal mass needed to reduce the air conditioning possible, encouraging turbulent air flow across the soffit will improve the
load. Whilst this is true for a concrete floor slab exposed on one side (i.e. convective heat flow. However, the rate at which the radiant heat flow
the soffit), in practice, slabs are often exposed on multiple surfaces i.e. occurs is determined by a different property called surface emissivity. This
combinations of top, bottom and internal surfaces formed by cores running relates to how reflective or dull/matt a surface is, and is measured by a
through the slab. This greatly increases the surface area for heat absorption factor ranging between 0 and 1. Emissivity matters because matt surfaces,
and the effective depth of concrete that can be utilised in a 24 hour period, such as that of concrete, have a high emissivity level of between 0.85-0.95,
which in turn, significantly increases the cooling output of the slab, see making them very good at absorbing and emitting radiant heat. In contrast,
Figure 6 on page 9. comparatively reflective surfaces such as floors with steel decking forming
the soffit, have a much lower emissivity of around 0.22-0.28, which limits
A doubling of surface area is commonly achieved by combining an radiant heat flow. Since the overall heat flow at the soffit is typically about
exposed soffit with underfloor mechanical ventilation, enabling heat two thirds radiant and one third convective, a low surface emissivity will
transfer from top and bottom surfaces. Similarly, another option is to have have a significant impact on the already limited movement of heat to and
an exposed soffit in conjunction with hollowcores through which air is from the surface.
channelled, greatly increasing the heat transfer area and cooling output.
The use of mechanical ventilation also enables the air passing over the In practical terms, low surface emissivity restricts the FES performance of
concrete to be made relatively turbulent, significantly increasing the rate exposed floors with steel decking, which is further reduced if permeable
of heat transfer at the surface and, as a consequence, the depth heat will ceiling tiles are used to visually screen the steel decking. This can be seen
penetrate in the limited time available12; it is worth noting that the 100mm in the cooling output of around 10-14 W/m2, dropping to around 4-9 W/m2
benchmark often quoted assumes the use of natural ventilation when a permeable ceiling is used. This contrasts with a value of around 15-
i.e. smooth/laminar air flow across a single surface. 25 W/m2 for a plain, exposed concrete soffit. The cooling output for these
and other floor options are summarised in Figure 6 on page 9.
Another active cooling option increasing in popularity is the use of water
rather than air to regulate slab temperature, made possible by embedding
plastic water pipes in the soffit. Heat flow between the water and the
concrete is by conduction, making it relatively rapid and enabling all the
available thermal mass in the slab to be exploited.
Regardless of whether a passive or active approach to cooling

is used, the thermal mass in precast or in-situ concrete floor
slabs with depths in excess of 100mm can be fully utilised to
maximise cooling output and provide enhanced performance.
The suggestion that 100mm of concrete provides sufficient
thermal mass is too simplistic and fails to take into account
how floors are used in practice and the range of conditions
under which they must perform.
A water cooled concrete soffit is used at the Manchester Metropolitan

Business School, see page 23.
Photo: courtesy of Feilden Clegg Bradley Architects.
Other design considerations

Embodied CO2 Adaptation to future climate
Detailed studies8,9 looking at the comparative embodied CO2 of concrete FES can help mitigate climate change through reduced operational CO2
frame and steel frame office buildings have been undertaken by the emissions, whilst also offering a degree of adaptation to the warming
trade bodies for these materials. Both studies concluded that generally climate. Central to this is the ability of concrete frame buildings to very
there is very little difference in the embodied CO2 of either option. So, effectively combine passive and active cooling measures, varying the
not withstanding the importance of designing and specifying steel and balance between the two as conditions dictate. This applies equally to both
concrete frames with a view to minimising their carbon footprint, the daily weather patterns and the much longer-term trends linked to climate
focus should be on the operational emissions, as this provides the greatest change. Concrete floor slabs also offer a means of designing out the risk of
opportunity to reduce the whole life CO2 emissions. climatic obsolescence in a number of other ways including:
¢¢ The ability to embed dormant water cooling pipes for future use.
Operational CO2 ¢¢ The relative ease in which chilled beams can be retrofitted with an
exposed soffit.
Figure 1 (page 3) compares the operational CO2 emissions of a typical and ¢¢ The ability to activate dormant thermal mass by removing false ceilings
good practice air-conditioned office with that of a high thermal mass office if fitted.
with passive and/or active cooling; the reduced CO2 emissions for the ¢¢ The ability to retrofit micro-bore cooling pipes to the soffit for increased
latter approach is quite apparent. There are obviously some environments performance.
that dictate the need for air conditioning, although emissions can still be ¢¢ Greater effectiveness of night cooling as an adaptation measure
significantly reduced through the use of the building fabric as described in compared to buildings with lighter weight floors (night cooling is likely
this guide. A further incentive for adopting a more passive approach where to be used as a future adaptation measure in many existing buildings).
possible, is the increasingly demanding emissions targets imposed by Part
L2 of the Building Regulations, along with challenging new seasonal energy
efficiency requirements for cooling plant, if used. BREEAM
There are three key BREEAM categories in which concrete floors have the
potential to influence the overall rating of a building. These are Health &
Wellbeing, Energy and Materials. A breakdown of these categories and
how they may relate to concrete floors is shown in Figure 4. For further
information on BREEAM, see The Concrete Centre guide, Concrete and
BREEAM, available from www.concretecentre.com/publications.
% contribution to overall BREEAM rating
No. of sub- 1. Visual comfort Scores up to 2.8% (daylight, glare, view etc)
BREEAM category Weighting categories 2. Safety & security
3. Thermal comfort Scores up to 1.9% (thermal modelling of design)
1. Health & wellbeing 15% 6 4. Water quality
5. Acoustics performance Scores up to 1.9% (meets acoustic standards)
2. Management 12% 5 6. Indoor air quality Scores up to 5.6% (0.95% for nat. vent. capability)
3. Transport 8% 5 1. Reduced CO2 emissions Scores up to 8.1%
2. Energy monitoring
4. Water 6% 4 3. Efficient external lighting
4. Low/zero carbon tech. Scores up to 2.7% (0.54% for night time cooling)
5. Energy 19% 9 5. Efficient cold storage
6. Efficient transport systems
6. Pollution 10% 5
7. Efficient laboratory systems
7. Waste 7.5% 4 8. Efficient equipment (process)
9. Drying space
8. Land use & ecology 10% 5
1. Life cycle impacts Scores up to 4.8% (based on Green Guide rating)
9. Materials 12.5% 5 2. Hard landscaping
3. Responsible sourcing Scores up to 2.9%
Total 100% 4. Insulation
5. Designing for robustness
Innovation 10% 0
Figure 4: Influence of concrete floors on a BREEAM rating for offices.

Visual in-situ soffits Acoustic considerations

Making in-situ concrete soffits “visual” gives rise to a number of specification Concrete soffits provide little acoustic absorbency, resulting in increased
questions. The finish required determines the formwork. If a particular sound reflection and longer reverberation times. However, there are a
finish, such as board marking, is required then clearly the appropriate range of options that can be used to address this whilst minimising or
formwork should be used. For a plain, flat finish, the design and formwork avoiding the need for sound-absorbing materials to be located on the
supplier should jointly determine the level of variations in tone and texture soffit. More information on acoustics can be found in a companion guide
that are acceptable. The National Building Specification and the National entitled Utilisation of Thermal mass in Non-Residential Buildings, which is
Structural Concrete Specification for Building Construction include standard available from The Concrete Centre website.
in-situ concrete finish specifications.
The concrete mix is usually specified by the structural engineer based on System control
strength and durability requirements. But for visual concrete the mix is
adjusted to aid placing, compaction and to achieve a consistent finish. In terms of control, the main objective is to take maximum advantage
The siting of the project is important because the constituents of concrete of night cooling whilst avoiding over-cooling, which can result in
are locally sourced and vary depending on the local geology. With all this uncomfortable conditions at the start of the day and may cause the
determined, a coordinated concrete specification should be prepared, heating to be activated. Experience gained in the operation of buildings
giving structural and architectural requirements. It is best practice at the with FES over the last few years has helped refine and standardise the
early stages to consider having test panels made. Consideration should also general approach used. More information on ventilation control can be
be given to panel layouts. Joints between formwork panels are often visible, found in a companion guide entitled Utilisation of Thermal mass in Non-
so the architect should detail how the panels are to be laid out. Choose Residential Buildings, which is available from The Concrete Centre website.
reinforcement spacers that minimise visual impact while the falsework
design should minimise potential deflection which could be particularly
noticeable in plain walls. While high quality finishes are achieved in
concrete, a completely uniform finish as struck is unrealistic as some
variation and blemishes are part of concrete’s visual character. If a blemish-
free surface is required, consider a plain concrete finish, allow for blowholes
to be filled and the surface made good with a finishing coat.
For detailed information see Visual Concrete, available from

www.concretecentre.com
Locating building services

A different approach to the design of overhead services is needed when
exposing the soffit. There are a number of standard solutions that can be
used including grouping systems such as lighting, fire alarms, and sensors
into modular services rafts. Floor voids, perimeter bulkheads and ceiling
voids in corridors can be used to locate ventilation ductwork. Other
options include using the cores in hollowcore slabs for pipes and cabling or
integrating services into the design of in-situ or precast slabs. Rebates can
be cast into the soffit for extract grilles, smoke alarms, lighting etc. Water-
based slab cooling and heating offers a very neat option for concealing
all the associated pipework and avoiding or minimising the need for heat
emitters such as radiators (see page 18). More information on locating
services can be found in a companion guide entitled Utilisation of Thermal
mass in Non-Residential Buildings13 which is available from The Concrete
Centre website.
To find more information on The Concrete Centre publications on

this page, visit the Publications Library at
www.concretecentre.com/publications.
PowerGen’s HQ optimises acoustic performance by focusing sound

reflected off the soffit onto the acoustically absorbent wings located
on the lighting rafts suspended beneath each coffer. See page 13 for
more information. Photo: courtesy of Peter Cook.
Passive and active floor options

All of the standard types of concrete floor slab can form the basis of a passive or active FES system.
The properties of these floors are summarised in Figure 5, including details A summary of the approximate cooling output that can be expected from
of the specific FES systems they are compatible with. A detailed overview the main FES/floor options is provided in Figure 6. It should be noted that
of these systems is provided in this section of the guide, starting with the in some buildings additional cooling of around 25 W/m2 may be provided
most basic, passive approach and ending with the more sophisticated by natural ventilation10 i.e. from openable windows, although this will
water-based systems. diminish during hot weather.
Flat slab
Exposed hollowcore slab with cores supplied by
mechanical ventilation plus water cooling
Construction: In-situ
Span: 5m to 12m, but most economic
up to 9m. Can be 6m to 13m with
post-tensioning. Exposed profiled slab with embedded cooling/
heating pipework
Compatible FES systems: All systems
except TermoDeck.
Comments: Quick, versatile and easy
to construct. Exposed flat slab with embedded cooling/
heating pipework
Profiled slab e.g. coffered

Exposed in-situ or lattice girder slab with
embedded, finned aluminium ducts, supplied
Construction: In-situ or precast by mechanical ventilation
Span: Up to 13m, but typically 10-11m.
Compatible FES systems: All systems
except TermoDeck and Concretcool. Exposed hollowcore slab with cores
Comments: Lighter weight enables supplied by mechanical ventilation
longer spans. Increased surface area
improves FES performance. Compared
to flat slabs, formwork costs are higher
and more time may be required for Exposed slab, underfloor
mechanical ventilation
construction. Can be post-tensioned.
Composite lattice girder soffit slab

Exposed slab, naturally ventilated building
Construction: Precast soffit slab with

in-situ concrete topping.
Exposed steel composite floor
Span: Up to 5m without void formers
or 12m with void formers.
Compatible FES systems:
Exposed steel composite
All systems except TermoDeck. floor with a permeable ceiling
Comments: High quality precast soffit.
Quick to construct.
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 90 100
Hollowcore slab Approximate cooling output W/m2
Construction: Precast with optional

Figure 6: Summary of cooling outputs from the main FES/slab options
in-situ concrete topping.
Span: Economic across a wide span
range, but the maximum economic
span is typically around 14-16m.
Compatible FES systems:
All systems except Concretcool.
Comments: Relatively low cost option.
Structurally efficient and suitable
for a wide range of building types.
The addition of a structural concrete
topping can be used to enhance
performance.
Figure 5: Main types of floor slab

System 1:
Exposed slab, naturally ventilated
Construction: maintain comfortable conditions in buildings with good solar shading and
Works with all slab types i.e. in-situ, precast and composite. relatively low internal heat gains.
Flat slabs provide the simplest and most cost-effective floor solution and
Description:
are economical for spans up to about 9m, or slightly more with post-
Flat or profiled slab cooled at night by natural ventilation from perimeter tensioning. Profiled slabs offer an alternative e.g. with a coffered, troughed
windows and assisted in some cases by an atrium with high level openings or wave-form soffit, which reduces the weight and helps optimise the span
providing stack ventilation. that can be achieved. These can be either precast or cast in situ with the
option of post-tensioning (see PowerGen case study on page 13).
Maximum slab cooling output (approximate):
15-20 W/m2 (flat slab) Another benefit of profiled slabs is the increased surface area of the soffit,
20-25 W/m2 (profiled slab) which enhances the convective heat flow with the space below, enabling
it to be doubled in some instances. However, radiant heat flow to and
Key benefits: from the soffit is largely unaffected by the extra surface area, so the overall
increase in cooling output is limited to around 25% or 5 W/m2 compared to
¢¢ Highly energy efficient if building is controlled well.
a flat slab. Other benefits of a profiled slab can include enhanced daylight
¢¢ Relatively simple to design and operate. penetration and acoustic control, along with generally pleasing aesthetic
¢¢ Little to no maintenance. qualities.
¢¢ Works with all concrete slab types.
¢¢ Applicable to new build and existing concrete buildings where the slab
can be exposed.
¢¢ Cooling output can be increased if required e.g. with the addition of
chilled beams or by embedding dormant pipework that can be used in
the future if required.
Key considerations:
¢¢ Use is limited to spaces with relatively low heat gains and occupant
density.
¢¢ Cooling performance is more weather dependent than other FES
options.
¢¢ External noise, pollution and/or security issues may preclude the use of
natural ventilation.
¢¢ Good occupant understanding and control needed to optimise year-
round performance.
Case studies:
¢¢ Headquarters of the Cambridge Federation of Women’s Institutes
(see opposite).
The most basic form of FES system uses an exposed concrete soffit with
night cooling via openable windows, to regulate slab temperature during
the day. Whilst the cooling output is modest, it is generally sufficient to
Headquarters of the Cambridge, Federation of

Women’s Institutes
Location: Cambridge The RIBA award winning headquarters of the Cambridge Federation
of Women’s Institutes is a good example of a simple, slow response,
Year: 2005
high thermal mass envelope, used to help regulate internal
Client: Cambridge Federation of Women’s Institutes conditions. The site originally comprised two large pig sheds
which were gifted to the Women’s Institute. One was demolished
Architect: EllisMiller
to create space for a car park, whilst the other was developed into
Structural engineer: Whitbybird their headquarters. To comply with environmental and structural
requirements, much of the original structure had to be rebuilt.
M&E engineer: Roger Parker and Associates
Main contractor: Britaniabuild Cross ventilation is achieved from a combination of perimeter

windows on the main facade and vents on the adjacent rear wall. The
FES system: Exposed, precast concrete slabs and natural ventilation. narrow floor plan makes the use of natural ventilation a particularly
effective means of cooling the building during the summer months.
External insulation was added to the walls, which were then clad in
timber. The roof was replaced by 1.2m wide precast concrete panels
also insulated externally and then covered with a profiled metal
sheet. The underside of the slab has no finish, leaving the concrete
soffit fully exposed. The panels slope from front to back of the
narrow floor plan, forming a shallow mono pitch roof. Internal walls
are mostly fair-faced brick and block with a painted finish. Heating
is provided by a gas boiler and radiators, whilst a modest amount
of PV (700W) reduces the electrical demand. The total contract
value for the project was a modest £307,000 and has been skilfully
executed by architect Jonathan Ellis-Miller, with an outcome that the
occupants are very pleased with11.
Photo: courtesy of Timothy Soar Louvre grilles in the back wall enable cross ventilation.
System 2:
Exposed slab, underfloor

Case studies:
¢¢ PowerGen Headquarters, Coventry (see opposite).
¢¢ Greenfields Community Housing head office, Essex.
¢¢ Toyota Headquarters, Surrey.
¢¢ Canon Headquarters, Reigate.
¢¢ RSPCA Headquarters, West Sussex.
¢¢ Inland Revenue Headquarters, Nottingham.
When considering mechanical ventilation as part of an FES design, the case

for using underfloor ventilation is quite compelling for office environments,
not least because exposed soffits reduce the options available for air
Construction: distribution and the routing of services. It also has the advantage of
enabling floor outlets to be easily relocated to accommodate future
Works with all slab types i.e. in-situ, precast and composite, although the
layout changes. In terms of FES performance, underfloor ventilation offers
composite option is not compatible with a profiled soffit (illustrated).
a number of benefits. Firstly, it enables direct contact between the air
and the top of the slab, helping unlock some of the thermal mass in the
Description:
upper part of the slab. In other words, underfloor ventilation combined
The addition of underfloor mechanical ventilation enables some convective with an exposed soffit enables thermal linking of the slab from both
heat transfer to and from the top surface of the slab, enhancing FES sides, increasing the depth of concrete that is utilised during the day and
performance. The overall control strategy is typically mixed-mode i.e. increasing the overall cooling output.
natural ventilation from windows is used when summertime conditions
permit, with the mechanical system operating only when needed. During Secondly, a further increase in cooling performance can be achieved if the
the heating season, the mechanical system enables the ventilation rate to air moving across the floor void is made turbulent12. Turbulence helps to
be closely controlled, helping minimise heat loss. break up the relatively static layer of air that otherwise clings to the surface
of the concrete, restricting heat flow. The optimal rate of heat transfer
Maximum slab cooling output (approximate): is dependent upon achieving a balance between the mean air velocity,
20-25 W/m2 (flat slab) time spent in the floor void and fan power. Standard techniques to help
25-35 W/m2 (profiled slab) achieve this can be applied to the design of underfloor systems13. Other
advantages offered by an underfloor supply over ceiling-based systems
Key benefits: include14:
¢¢ Additional heat flow via the upper slab surface increases cooling ¢¢ A reduction in the construction materials needed.
performance. ¢¢ The ability to provide a higher proportion of fresh air to the occupants.
¢¢ Cooling performance can be further enhanced by ensuring air ¢¢ Lower maintenance.
circulating in the floor void is turbulent. ¢¢ Lower energy consumption.
¢¢ Floor outlets offer good flexibility, enabling changes in building layout
to be easily accommodated. Several notable offices that feature exposed coffered slabs and mixed
mode, underfloor ventilation, have been built over the last twenty years,
¢¢ Night cooling is less reliant on there being adequate wind speed.
for example the UK Headquarters of PowerGen (page 13). These all share a
¢¢ If required, a cooling coil can be added to the air handling plant, similar layout, characterised by long narrow floor plates arranged over three
offering a degree of future adaptation to climate change or an increase storeys, with an open balcony arrangement onto a central atrium, which
in the cooling output. enhances both daylight penetration and natural ventilation.
Key considerations:
¢¢ Space requirements for air handling plant.
¢¢ Higher capital and operating costs than a naturally ventilated building
(energy and maintenance).
¢¢ Mixed-mode ventilation has the potential to achieve greater control
and better overall performance than provided by natural ventilation
alone, but must be appropriately designed, commissioned and
controlled13.
PowerGen Headquarters
Location: Coventry plaster to form the coffers. This was invaluable for confirming and
tuning the design of the coffer profile and light fittings, and for
Year: 1994
testing the acoustic performance and artificial lighting levels.
Client: PowerGen
When Laing Midlands were appointed as design and build
Architect: Bennetts Associates contractors, they adopted the approved scheme and worked closely
Structural engineer: Curtins Consulting Engineers with the design team. The on-site mock-ups played an important
role in incorporating key refinements such as the prefabrication
M&E engineer: Ernest Griffiths & Son of slab reinforcement into the final design solution. The choice of
FES system: Exposed, coffered slabs and mixed-mode ventilation. natural ventilation required the service engineers Ernest Griffiths &
Son to consider all aspects of the building design. The arrangement
In many respects the 13,000m2 PowerGen Headquarters, completed of relatively narrow open plan office areas on either side of the
in 1994, represents a landmark in high thermal mass, passive office three storey atrium provided the ideal layout for good natural
design and has provided a successful template for many subsequent ventilation. The building management system controls the top row
buildings. The design offers a good balance between daylighting, of windows, which are opened at night to allow cool air to flow over
natural ventilation, thermal mass and office layout which has proved the coffered concrete soffit. Computer simulations by environmental-
effective in providing a comfortable, low-energy environment. modelling specialist EDSL were used to accurately model the office
environment and predict peak internal temperatures, taking into
The layout consists of two parallel floor plates separated by a central consideration external effects, internal heat loads and the passive
atrium and lies on an east-west axis, providing good daylighting and cooling effects of the exposed concrete. The modelling also helped
air-flow. The structural frame is made from reinforced concrete with to develop the design strategy and establish the right mix of
exposed, in-situ coffered floors which are central to the building’s use thermal mass and natural ventilation. It also showed that night time
of thermal mass to provide a stable internal temperature. This proved ventilation was able to exploit the long-term thermal dynamics of the
to be very effective during the summer of 1995, one of the hottest on floor. The latter were provided by the careful use of exposed concrete
record, during which the building performed very well. The recorded with sufficient thickness to absorb heat gains over many days.
internal temperatures closely matched predictions from thermal
modelling undertaken at the design stage. Internal heat gains are minimised by placing areas that require
airconditioning, such as the computer suite and kitchens, at the east
Detailed analysis of PowerGen’s overall design intent established and west ends of the building. The larger, heat-generating office
that the office space requirements would be best met by a series of equipment, such as photocopiers, is grouped into segregated rooms,
narrow floor plates. This would allow connection across the office out of the open-plan space. Staff have considerable control of their
space and encourage personal communication between occupants. environment as the lower windows may be opened manually during
The size of the floor plates also needed to accommodate a variety of the day.
departmental offices and allow for future flexibility. Within the 10.8m
x 7.2m structural grid are three coffers, each 2.4m wide, which span
from atrium to external window. The coffers’ elliptical cross-section
is designed to improve the acoustic performance of the office space
by focusing unwanted noise onto the acoustically absorbent wings
of the interior lighting rafts suspended beneath each coffer. The
lighting rafts partially up-light the coffers to enhance their sculptural
form. They also incorporate smoke detectors and the PA system. In
long section, the coffers taper towards their ends to increase the
penetration of natural light into the office space from the external
windows and the atrium.
Partial post-tensioning was used to minimise early thermal shrinkage

effects and so ensure that there were no visible cracks in the exposed
concrete coffers. The maximum designed crack width was 0.1-0.2mm
so that standard emulsion paint could be applied to the soffit
without the cracks showing through. The floor plates are supported
by 400mm diameter circular columns. Whilst the design was being
developed, key aspects were tested by modelling and mock-ups. A
1:40 scale model of a typical cross-section through the building was
made to develop the atrium glazing, office glazing and concrete
profiles for maximum lighting performance. A full-size mock-up of
Coffered slabs with as struck finish prior to painting.
a 7.2m x 10.8m structural bay was also built using glass-reinforced
For an image of the completed project, see page 8.
Photo: courtesy of Peter Cook.
System 3:
Exposed hollowcore slab with cores

supplied by mechanical ventilation
Case studies:
¢¢ Innovate Green Office, Leeds (see opposite).
¢¢ Peel Park, Blackpool.
¢¢ The Ionica Building, Cambridge.
¢¢ The Elizabeth Fry building, University of East Anglia.
¢¢ Meteorological Office, Exeter.
¢¢ Jubilee Library, Brighton.
Hollowcore slabs are made from pre-tensioned, precast concrete with

continuous hollowcores to reduce self-weight and achieve structural
efficiency. This type of slab can be used very effectively as part of an active
Construction: cooling system, using mechanical ventilation to channel air through the
Hollowcore is a precast option only. An in-situ concrete topping of cores before entering the occupied space. Air passes through the cores at
around 50mm is typically placed on the slab to enhance the structural low velocities, allowing prolonged contact between the air and concrete
performance. for good heat transfer. The operating principal is straightforward; on
summer days, the soffit provides radiant cooling in the usual way, whilst the
Description: ventilation supply is cooled as it passes through the cores prior to entering
Precast, hollowcore slab with fresh air from a mechanical ventilation system the occupied space. At night, heat flow effectively reverses with cool
channelled through the cores, enabling good heat transfer between the air ambient air removing heat from the concrete as it circulates through the
and slab. Cooling/heating is provided by a combination of the ventilation slab and lowers its temperature ready for the next day. During the heating
supply and radiant output of the exposed soffit (which is more significant). season, air extracted from the building is used to pre-heat the fresh air
The system is typically referred to by the trade name of TermoDeck. supply before it is further warmed by the floor slab, which is able to absorb
and recycle some of the internal heat gains. If required, additional heat is
Maximum slab cooling output (approximate): supplied by a heating coil in the air handling plant. At night the external
air supply damper is shut and the system can be operated in recirculation
40 W/m2 (basic system)
mode so the floor can absorb internal gains ready for the next day.
50 W/m2 (with cooling)
60 W/m2 (with cooling and switch-flow system) The temperature difference between the slab and the air leaving the cores
is not more than 1–2 degrees. The slabs are usually 1200mm wide and
Key benefits: approximately 250–400mm deep (depending on span), incorporating up to
¢¢ Widely used and well proven system. five smooth-faced extruded holes along the length. Three of these are used
to form a three-pass heat exchanger in each slab, linked to a supply diffuser
¢¢ Provides radiant and convective cooling.
located on the soffit. Alternatively, displacement ventilation can be used
¢¢ Economic across a wide range of spans of up to 16m. by ducting the air into an underfloor ventilation system, which may be a
¢¢ Provides an alternative to water as a means of actively cooling preferred option in spaces with a high floor to ceiling distance. Air supply
concrete slabs. to the slabs is via a duct, typically located in an adjacent corridor above a
¢¢ Air is typically introduced to the space at ceiling level but can also be false ceiling.
introduced at low level if the floor to ceiling distance is high.
As with other FES systems, a large proportion of the cooling is radiant,
¢¢ Soffit finish is suitable for painting on site if required. provided by the exposed underside of the slab. Supply diffusers are
¢¢ Can be used as part of a mixed-mode ventilation strategy. located about 1–2m from windows to prevent potential down-draughts
and/or clashing with partitions. Pre-drilled and sealed openings can
Key considerations: be incorporated at mid-span, making it possible to relocate diffusers
¢¢ The slab cores may require periodic cleaning (access points in the future. This enables conference rooms or similar spaces to be
are provided). accommodated in the centre of the building if required. The TermoDeck
system can be configured to suit a variety of applications and cooling
¢¢ Soffit finish may be slightly more utilitarian than some of the
duties. In its basic form, loads of up to 40W/m2 can be handled; although
alternative options in this guide.
experience at the Meteorological Office in Exeter shows that higher loads
¢¢ Units typically limited to a maximum width of around 1200mm. of around 47W/m2 are possible15. The addition of mechanical cooling
¢¢ TermoDeck is a registered trade mark and the supplier’s expertise is can increase the cooling capacity of the basic system to around 50W/m2.
an important element in ensuring the installation works effectively. Performance can also be increased through indirect evaporative cooling,
They provide a service that covers design (including controls), thermal which cools the supply air without increasing its moisture content. The
modelling and expertise in the treatment of the slabs e.g. drilling, cooling provided by an evaporative system is dependent on ambient
capping and sealing etc. conditions, and the efficiency of the humidifier and heat exchanger, but
can lower the air temperature by several degrees under average conditions
(evaporative cooling is also applicable to other systems with mechanical
ventilation detailed in this guide). The highest cooling performance
is achieved by using the TermoDeck switch-flow system. This enables
the temperature to be adjusted in individual rooms and can be used
in conjunction with mechanical or evaporative cooling. The system is
regulated by a switch unit incorporating a changeover damper to re-route
the supply air; when a room needs extra cooling, the air-supply route
through the slabs is changed directly to the core that contains the ceiling
diffuser, rather than the normal route through all three cores. The shorter
distance helps to prevent the supply air taking heat from the slab.
Innovate Green Office: The concrete mix incorporates fly ash as a cement replacement to
reduce embodied CO2, and Lytag, which is a lightweight aggregate
speculative office also made from fly ash. The external concrete walls provide an
airtight, weatherproof envelope in a single component and have
been designed to ensure solar gains from window openings are
Location: Leeds minimised. The walls achieve a very good U-value of 0.15 W/m2K
and are externally insulated to allow the concrete to be exposed
Year: 2007
internally for its thermal mass.
Client: Innovate Property
With the high level of insulation and airtightness achieved, heat
Architect: Rio Architects loss is reduced to a point where internal gains from people and
computers etc. are almost sufficient to maintain comfortable
Structural engineer: Scott Wilson
conditions from autumn to spring. The mechanical ventilation
M&E engineer: King Shaw Associates system recovers these gains, which are stored in the floor slabs for
beneficial re-use. Summer cooling is provided by a combination
FES system: Exposed hollowcore slabs and mechanical ventilation
of passive night-cooling and active cooling from the chiller, using
(TermoDeck™).
the TermoDeck system as a thermal store in a strategy similar to ice
The Innovate Green Office, completed in 2007, is a speculative storage i.e. to attenuate the peak cooling load and cut the size of the
development that achieved an impressive BREEAM rating of 87.55%; cooling plant.
the highest score ever awarded. Designed for Innovate Property by
The office achieved an average daylight factor of 4.5% so artificial
Rio Architects and King Shaw Associates, at first glance the office
lighting is only required for about 20% of the working year. External
does not look particularly ‘green’. There are no wind turbines or
vertical shades and internal blinds control excess gains and glare.
solar panels, yet the building emits 80% less CO2 than a typical air-
Other sustainable elements of the scheme include a vacuum
conditioned office, producing around 22kg of CO2 per m2 per year.
drainage system that utilises harvested rainwater for flushing the
This equates to a saving of roughly 350 tonnes of CO2 every year. The
toilets. This virtually eliminates the need for treated mains water to
approach developed by the project team achieves these savings by
convey sewage. The overall volume of waste discharged from the
fully applying the principals of fabric energy efficiency, rather than
building is reduced by 75%. Permeable paving and a natural wetland
relying on the addition of renewable systems. An engineering led
area prevents storm water flooding.
exercise produced an environmentally and commercially sustainable
plan, with the sustainability credentials of each element being The success of this speculative office development can be attributed
considered in conjunction with the client’s need for flexible and to the integrated approach given to fabric energy efficiency and
economically viable office space. structural requirements, which have been met using readily available
construction materials and technologies.
Yorkshire Forward, the regional development agency, worked with
Innovate Property to fund a proportion of the cost of prototyping
sustainable construction methods. The building services are
designed to produce minimal emissions helped by low energy
lighting, heating and cooling. Electricity is provided by a 30kW
base load combined heat and power (CHP) system with a matched
absorption chiller taking advantage of the waste heat in the summer.
Alongside the efficient services, the passive design features

contribute significantly to the low annual emissions. The whole
building was designed as a thermal store; the structural frame
consists of load bearing precast concrete wall panels and hollowcore
floor and roof units, which use the TermoDeck system to fully utilise
the thermal mass in the units.
Photo: courtesy of Rio Architects

System 4:
Exposed in-situ or lattice girder slab

with embedded air ducts supplied by
This relatively new system has been used in a number of European
projects, with a total floor area of over 260,000m2 to date17. In the UK,
the first building to employ Concretcool was the 4 West Building at the
University of Bath, completed in 2010. In many ways it is similar to the
TermoDeck system, but differs in its ability to be used with in-situ concrete
floors (TermoDeck uses precast hollowcore slabs). It can also be used with
composite lattice girder slabs with the option of installing the ductwork at
the precast factory.
The aluminium ducts are cast into the slab to form a series of parallel U
shape runs, each of which is between 7-10m in length (see front cover
image). The ducts are linked at one end to a mechanical ventilation system,
Construction: whilst the other end feeds a supply diffuser that is typically located on the
soffit, but can be on a perimeter bulk head. If located in the floor it can
Applicable to in-situ and composite flat slabs.
provide displacement ventilation. The ductwork is made by an extrusion
process and is available in a diameter of either 60mm or 80mm, both
Description:
incorporate a number of corrugated internal fins, effectively tripling the
An in-situ or composite lattice girder slab, incorporating proprietary internal surface area. This enhances the heat transfer rate between air and
aluminium ventilation ducts16 (known as ConcretCool). The fresh air supply concrete, achieving an efficiency of up to 90%18. It also results in a pressure
is channelled through the ducts in a similar manner as the TermoDeck drop of around 7 Pa/m or 50-70 Pa for a typical duct run. However, the
system (see page 14), with cooling/heating provided by a combination of overall fan pressure for an installed system is not unduly high.
the ventilation supply and the radiant output of the soffit.
Plastic spacers are used to ensure the correct position of the ducts between
Maximum slab cooling output (approximate): the upper and lower reinforcement and this prevents the ducts floating up
65 W/m2 when concrete is poured. However, a small amount of upwards movement is
encouraged as this lifts the plastic spacers clear of the formwork, preventing
Key benefits: the ends from remaining visible when the formwork is struck. To stop
¢¢ High cooling output. the ingress of water/wet concrete, the ductwork elbows and other joints
incorporate a watertight seal. The addition of ductwork into the slab does not
¢¢ Provides radiant and convective cooling.
affect the structural performance as it is located in the neutral zone i.e. in the
¢¢ Widely used in mainland Europe.
central area where the slab experiences least tension/compression.
¢¢ Flexible system that can be configured to meet a range of
design requirements. The basic operating principle is very similar to that of the TermoDeck
system (see page 14); on summer nights the air handling plant channels
¢¢ Provides an alternative to water as a means of actively cooling
cool external air through the embedded aluminium ducts, removing heat
concrete slabs.
from the concrete ready for the following day, when the heat flow naturally
¢¢ C
orrugated fins inside the ducts (see image below) increase heat
reverses and the floor cools the fresh air supply, whilst the soffit provides
transfer between the air and the slab.
radiant cooling. During the heating season, the floor warms the air supply
to almost the same temperature as the soffit i.e. around 21°C, which can be
Key considerations:
achieved with minimal or no supplementary heating for much of the season.
¢¢ Soffit located supply diffusers cannot be easily reconfigured to
reflect changes to internal layout.
¢¢ Performance is partially dependent on ambient conditions.
¢¢ The internal fins enhance heat transfer, but also have modest impact on
fan power.
Case studies:
¢¢ 4 West Building, University of Bath (see opposite).
The ConcretCool aluminium ductwork and ancillary items are

manufactured by Kiefer; a German air conditioning company with a
UK distributor16.
Photo: courtesy of Rio Architects
4 West Building series of circular aluminium ducts embedded in the slab to create
U shape runs of up to 10m in overall length. Each duct is linked at
University of Bath one end to the mechanical ventilation system, whilst the other end
feeds a supply diffuser typically located on the soffit. The ducting is
available in diameters of 60mm and 80mm, with the latter used in
Location: Bath the 4 West Building. It is made using an extrusion process, enabling
corrugated internal fines to be formed, effectively tripling the internal
Year: 2010
surface area for maximum heat transfer.
Client: University of Bath
On summer days, the building’s fresh air supply is cooled by the floor
Architect: Stride Treglown Tektus slabs as it passes through the ducts prior to entering the occupied
space. At night, the heat flow reverses, and the cool fresh air supply
Structural engineer: Ramboll
removes the accumulated heat from the slab, so the cycle can be
M&E engineer: Roger Preston & Partners repeated the following day. During the heating season, the floor
warms the air supply to almost the same temperature as the soffit.
Main contractor: Cowlin Construction
Further heating is provided by TRV controlled radiators. Windows can
FES system: Exposed, in-situ slabs incorporating the be opened to supplement the mechanical ventilation and enhance
Concretcool™ system. the level of control occupants have over the internal environment.
The 4 West Building at the University of Bath accommodates Whilst the Concretcool system has been widely used in mainland
general teaching areas, student services and office space. It was Europe, the 4 West project is the first application of this technology
completed on time and within budget in April 2010 and achieved a in the UK. Cowlin Construction, the main contractor, worked closely
BREEAM rating of ‘Excellent’. Built over six floors, the concrete frame with LTi Advanced System Technology who are the UK distributor
construction has in-situ concrete floors incorporating the Kiefer for this system. Two months before work started on the concrete
Concretcool system, which uses mechanical ventilation to regulate frame, LTi gave a presentation to the construction team so they could
the temperature of the exposed soffits. understand the system and develop a plan to ensure it was fully
integrated into the works. The aluminium ducts were pre-cut at the
Prior to this systems development there were only two methods for German factory, so all the components arrived ready for installation.
using mechanical ventilation to directly cool the slab. Firstly, by using 31 days were allowed for the work, but ease of installation enabled
an underfloor ventilation supply, which typically offers a modest this to be reduced to 15 days. The project manager for Cowlin
increase in cooling output, or secondly by using the TermoDeck Construction commented that any initial uncertainty about working
system (see page 14) which performs well, but is limited to precast with the new product was soon dispelled as it proved to be very
hollowcore flooring. The German Kiefer system provides a third robust and user-friendly.
option and can be used with in-situ concrete floors. It comprises a
Photo: courtesy of Cowlin Construction Ltd Photo: courtesy of University of Bath

System 5:
Exposed slab with embedded

cooling/heating pipework
Alongside the proprietary water-based precast systems described in this guide
(see pages 20 and 22), there is also the option of embedding pipework in
in-situ concrete slabs or bespoke precast units. An example of the in-situ option
can be found at the CAFOD Headquarters in London (see opposite). Similarly,
IFDS House, (originally built for Barclays Bank and formally called the Basilica)
provides an example of the bespoke precast option13. Both options offer
good design flexibility, including the ability to specify a profiled slab which can
increase the cooling output; an option otherwise not available with the current
proprietary options (which are all based on a flat slab). However, this system
requires greater upfront design and there is an increased potential for on site
damage to the pipework when in-situ slabs are being constructed. Consultants
and suppliers20 offer expertise to help with the design and ensure the build
programme runs smoothly. If required, they can also provide a single package
for the installation and warranty of the system.
Construction:
The use of water rather than air to regulate the slab temperature will
In-situ or precast slab, with either a flat or profiled soffit.
generally provide a slightly higher cooling capacity. Water-based systems
also have the ability to continually regulate the soffit temperature to
Description:
maintain close control of internal conditions; it takes around 30 minutes
A flat or profiled slab with PEX or polybutylene plastic pipework for a change to the flow temperature to have a discernable effect on the
configured in a serpentine layout and embedded close to the soffit. This soffit temperature21. This relatively rapid response is made possible by the
is supplied with chilled water in summer and, if required, warm water low resistance to heat flow between the water and the concrete, which
during the heating season. The active cooling/heating system works with is around 100 times less than exists between air and concrete22. The large
thermal mass and the large area of the soffit to maintain a stable surface surface area of the soffit and stabilising effect of the thermal mass enables
temperature close to that of the air in the room. This enables the flow the system to operate with flow temperatures close to that of the occupied
temperature to be optimised for maximum energy efficiency i.e. relatively space, allowing the use of efficient sources of heating and cooling. The
high for cooling and low for heating. ability to spread loads over a 24 hour period also reduces plant size.
Maximum slab cooling output (approximate): Not withstanding any limitations on cooling output imposed by the system
65 W/m2 (flat slab) supplying the chilled water, the main restriction on performance is the risk
80 W/m2 (profiled slab)19 of condensation forming on the soffit if the surface temperature is allowed
to drop too low. The point at which this occurs is governed largely by the
Key benefits: relative humidity of the air in the room, and the lower limit for the surface
temperature is generally about 19-20°C, although it may be slightly lower
¢¢ High cooling output.
if mechanical ventilation is used with the ability to regulate humidity. In
¢¢ Ability to continually regulate the soffit temperature. summer, the flow temperature to the slab is typically between 14-20°C,
¢¢ Unobtrusive and silent. increasing to around 25-40°C during the heating season.
¢¢ Can be integrated with virtually any slab design.
Although water cooling may be the primary method for regulating
¢¢ Modest flow temperature permits use of energy efficient sources of temperature in summer, night time ventilation can also be used to remove
heating and cooling. accumulated heat from the slab, with the option of supplementary water
cooling used as necessary to achieve the required soffit temperature at the
Key considerations:
start of the next day. The CAFOD Headquarters combines both techniques
¢¢ Void formers can be incorporated into slab to optimise structural to optimise overall performance and energy efficiency.
efficiency i.e. weight/span.
¢¢ Good on site practice needed to ensure accidental damage to pipes The basic design sequence23 of a bespoke water-based system is as follows:
from drilling etc. is avoided. The in-situ option is potentially more ¢¢ Determine the zoning requirements of the building and associated
vulnerable to general on site damage before the concrete is placed. heating and cooling loads.
¢¢ Define the available areas for the coils, taking into account any
Case Studies: structural constraints.
¢¢ CAFOD Headquarters, London (see opposite). ¢¢ Calculate the cooling circuit requirements to match the zoning and
¢¢ IFDS House Barclays Bank/Basilica, Basildon. active soffit area.
¢¢ Incorporate the coil layout into the construction plans.
¢¢ Design the interconnecting pipework between the coils and the chilling
and heating plant.
CAFOD Headquarters Concrete forms an important part of the overall design strategy,
and the complex geometry on each floor resulted in the use of
(Romero House) an in-situ concrete slab, which was formed using simple plywood
shuttering. The concrete mix incorporates cement replacement in
the form of ground granulated blast furnace slag (GGBS), helping
Location: Southwark, London lower embodied CO2. With the exception of the stairwell, the
exposed concrete is painted white to improve reflectivity and help
Year: 2010
increase the daylighting toward the centre of the floor plan. The
Client: Catholic Agency for Overseas Development (CAFOD) exposed stair wall has a rough, needle-gunned finish providing a
powerful visual contrast to the painted concrete and galvanised
Architect: Black Architecture steel stair. The exposed concrete soffit on each floor incorporates
Structural engineer: WSP the Velta Thermally Active Building System (TABS) i.e. embedded
PEX cooling pipes, which off set some of the building’s heating and
M&E engineer: King Shaw Associates cooling load; the system is only designed to handle what can’t be
Main contractor: Volker Fitzpatrick achieved passively. The network of embedded pipes are linked to a
ground source heating and cooling system incorporating five closed
FES system: Exposed, in-situ slabs with embedded water cooling loop boreholes and a heat pump. Each borehole is 125m deep and
pipes and mixed-mode ventilation. produces water at around 12°C. Some additional heating is provided
by trench heaters on each floor. Roof mounted PV panels generate
CAFOD’s £8.6m Headquarters is situated on a former car park
around 3,500 kWh per year, whilst hot water is provided by a solar hot
adjoining St George’s Cathedral in Southwark. The five storey 3,000m2
water system.
building reflects the charity’s core values through its restrained
design and low environmental impact. The building makes use of A mixed-mode ventilation strategy allows occupants to open
a range of passive and low energy systems, including rainwater high-level windows (using winders) for natural ventilation during
harvesting, stack ventilation and a thermal mass system that the summer, with mechanical underfloor ventilation taking over
combines passive and active features. Overall, the office achieved a during periods of particularity high or low external temperatures
BREEAM rating of ‘Excellent’. when windows are best kept shut. Exhaust air is drawn passively
across the soffit by the stack effect created by warm air rising
Romero House is composed of three distinct elements. The triangular
through the atrium and exiting at roof level. Monitoring during
open plan office floors are separated from the ancillary spaces by
the summer of 2010 showed that the active thermal mass and
an atrium circulation spine. This arrangement encourages people
ventilation strategy achieved a very stable internal temperature that
to leave their floor to use the breakout spaces, toilets and meeting
only varied by around 2-3 degrees across each day24 and typically
rooms. A half level stepped section gives occupants the option
stayed around 22-23°C. During the hottest period when the external
to use facilities on upper and lower floors and so increases the
temperature reached 32°C, internal conditions did not exceed 26°C.
opportunities for communication and social interaction. Overall, the
This impressive performance should be further enhanced by minor
design helps promote a sense of community within the organisation
adjustments to the internal layout carried out to improve air flow; on
while fulfilling CAFOD’s spatial needs.
one floor storage units were too high, preventing air from circulating
properly25.
Photo: courtesy of Black Architecture

System 6:
Exposed hollowcore slab with

embedded cooling/heating pipework
Construction: For a general overview of water-based systems see: Exposed soffit with
Hollowcore slabs are a precast option only. An in-situ concrete topping embedded cooling/heating pipework on page 18.
of around 50mm is typically placed on the slab to enhance the overall
Hollowcore slabs are made from pre-tensioned, precast concrete with
structural performance.
continuous hollowcores to reduce self-weight and provide good structural
efficiency. Overall, the weight is around 32% less than for an equivalent
Description:
solid slab. In this water-based system, plastic pipework (PEX) is cast into
Precast, hollowcore slabs with PEX plastic pipework embedded near the the slab about 60mm above the soffit. Services such as cables and pipes
soffit for heating and cooling. In contrast to the TermoDeck system, the for sprinklers etc. can be routed through the cores. Alternatively, cables can
cores are not active i.e. do not form part of the ventilation supply. However, be placed in the in-situ concrete topping. The joint between slabs is visible
the two systems can be combined, increasing the overall cooling output, from below and can be plastered over or partially obscured by the lighting
see Figure 6 on page 9. raft, however it is not particularly conspicuous and is typically ignored.
Maximum slab cooling output (approximate): Hollowcore slabs are available with top strand reinforcing, which removes
65 W/m2 any camber that might otherwise be present ensuring a flat soffit.
Key benefits: Along with other water-based options in this guide, the cooling/heating
output is chiefly radiant as ventilation is handled separately. However,
since this system option uses hollowcore slabs, it offers the opportunity of
¢¢ Ability to continually regulate the soffit temperature. utilising the otherwise dormant cores to channel mechanical ventilation
¢¢ Provides the benefits of a precast solution. into the space and use some of the thermal mass to regulate the air
¢¢ Relatively low cost option. temperature. This provides greater convective cooling, which may increase
the overall cooling output to approximately 90 W/m2 26. This system is
¢¢ Economic across a wide range of spans of up to 15m.
commercially available by specifying a combination of Systems 3 and 5 in
¢¢ Modest flow temperature permits use of energy efficient sources this guide.
of heating and cooling.
¢¢ Soffit finish suitable for painting on site if required.
¢¢ Can be combined with the TermoDeck system to increase the
cooling capacity.
Key considerations:
¢¢ Soffit finish may be slightly more utilitarian than some of the
alternative floor options.
¢¢ Units typically limited to a maximum width of around 1200mm.
¢¢ Good on site practice needed to ensure accidental damage to
pipes is avoided.
¢¢ System limited to flat slabs.
Case studies:
¢¢ Vanguard House, Daresbury Science and Innovation Campus,
Warrington (see opposite).
Vanguard House The building uses a combination of passive design and geo-thermal
technology to provide heating and cooling. During the summer
months water extracted from a 120m borehole supplies the precast
Location: Daresbury Science & Innovation Campus, Cheshire hollowcore floor slabs with plastic pipework embedded close to
the soffit. These were manufactured by Creagh Concrete, under the
Year: 2011
product name Climaspan. Each precast unit spans up to 10m, and
Client: North West Development Agency is 1.2m wide x 0.3m deep. The cooling/heating pipework is located
at a depth of 60mm from the soffit and, to ensure it could not be
Architect: Fletcher Architects
accidentally damaged during construction, site operatives were issued
Structural engineer: Pick Everard with shanked drill bits with a limited drilling depth. The units make
use of top strand reinforcing which virtually eliminates the camber
M&E engineer: Atkins / Giffords
that can sometimes be visible with exposed hollowcore floors.
Main contractor: Cowlin Construction
The water cooling system, often referred to as a ‘Thermally Active
FES system: Exposed, hollowcore slabs with embedded cooling/ Building System’ or TABS, was designed by Velta and can provide up
heating pipework (e.g. Climaspan™). to 65 W/m2 of cooling. At Vanguard House it is used in conjunction
with night cooling to optimise summertime performance. During
Vanguard House provides three-storeys of office and laboratory the heating season, the temperature of the ground water is boosted
space, covering 3,600m². The client, North West Development using a heat pump before being supplied to the floor units. Tenants
Agency wanted a low carbon, BREEAM ‘Excellent’ facility (which have individual control of the system to regulate heating and cooling
was achieved) for its latest phase of development at the Daresbury in their space.
Science & Innovation Campus; a UK centre of excellence in
accelerometer research.
Photo: courtesy of Creagh Concrete Products Ltd

System 7:
Exposed composite lattice girder

soffit slab with embedded pipework
For a general overview of water-based systems, see: Exposed soffit with
embedded cooling/heating pipework on page 18.
The precast units are typically around 1.5-2.4m wide and include most, if
not all, of the bottom reinforcement. The top reinforcement is fixed on site
prior to placing the in-situ concrete topping. Void formers can be used to
reduce weight and increase the span up to a maximum of around 12m.
The surface finish of the soffit is typically very good, and the concrete
mix design can be tailored to achieve a specific visual appearance as
an alternative to painting. For example, at the Manchester Metropolitan
University Business School the concrete mix used a combination of white
Construction: cement and ordinary Portland cement.
Composite i.e. precast soffit with in-situ concrete topping. Void formers can
The PEX plastic pipes are located on top of the reinforcement, making
be used to optimise the structural efficiency and increase the span.
the reinforcement work more efficiently and provide some additional
Description: protection against accidental drilling of the pipework. During the
manufacturing process, the pipework is pressure tested with air before the
Factory produced, high quality precast soffit that acts as permanent
concrete is placed to ensure there are no leaks. Once installed on site, it is
formwork to an in-situ concrete topping. PEX plastic pipework for cooling/
kept pressurised with water so its integrity can be monitored during the
heating is embedded in the precast soffit.
construction process and enable any accidental damage to be more easily
found and rectified.
Maximum slab cooling output (approximate):
65 W/m2 (flat slab)
Key benefits:
¢¢ Ability to continually regulate the soffit temperature.
¢¢ Combines the benefits of a high quality precast finish with an in-situ
concrete slab.
¢¢ Soffit can be left unpainted if preferred.
¢¢ Quick to construct and provides a safe working platform that requires
little or no propping.
¢¢ Available in a broad range of widths.
¢¢ Modest flow temperature permits use of energy efficient sources of
heating and cooling.
Key considerations:
¢¢ Void formers can be incorporated to optimise weight and
structural efficiency.
¢¢ Good on site practice needed to ensure accidental damage to pipes
from drilling etc. is avoided.
¢¢ Early design consideration needed so holes for services can be
allowed for.
¢¢ System limited to flat slabs.
Case studies:
¢¢ Manchester Metropolitan University Business School (see opposite).
Photo: courtesy of Hanson UK
Manchester the contractor Sir Robert McAlpine enabled them to work with the
project team and embed the water pipes.
Metropolitan University The contractor hoped to install a fully precast system with embedded
27 water pipes, but following the tender process Hanson’s Coolslab
Business School system was selected as the best option. Coolslab is a development
of Hanson’s Omnicore product, a precast soffit panel which acts as
permanent formwork, to an in-situ concrete topping containing
Location: Manchester
polystyrene void formers. The pipework is cast into the panels at the
Year: 2011 precast factory and is pressure tested before being despatched. The
concrete specified for the panels uses a combination of 75% white
Client: Manchester Metropolitan University
cement and 25% ordinary Portland cement to create a light finish.
Architect: Feilden Clegg Bradley Studios Whilst this increased the cost of the mix, overall there was a saving as
it was cheaper than the alternative option of painting the soffit.
Structural engineer: WYG
M&E engineer: AECOM Hanson worked with cooling and heating systems developer
Velta, which has seen its products used widely across Europe. Velta
FES system: Exposed, lattice girder soffit slabs with embedded specialises in Thermo-Active Building Systems (TABS), which uses
water cooling pipes (Hanson Coolslab™). plastic water cooling/heating pipes embedded in the building
structure. For Manchester Metropolitan University, Sir Robert
McAlpine and Hanson developed a bespoke 1.5m wide slab with an
overall depth of 475mm spanning 12m. Once on site, the slabs were
craned into position and the joints propped underneath to achieve a
10mm positive camber, as engineers had calculated a maximum sag
of 20mm due to self weight.
The biggest operational issue was connecting the pipes to the

centralised chilled water flow and return pipework. So as not to
compromise floor space, a box housing the pipe terminations was
installed within the floor slab. Velta designed a steel box that is
flush with the top surface and able to withstand the floor loading.
Following the installation of the reinforcement, the concrete topping
was poured. To prevent accidental damage to the pipework from
contractors working on site, Hilti drill bits of the correct length
were issued. The pipework was kept under pressure during the
construction phase so its integrity could be monitored at all times.
Mechanical ventilation is provided to the majority of areas using the

raised access floor as a supply plenum. Return air passes into the
atriums via cross-talk attenuators, where it rises to the air handling
Photo: courtesy of Feilden Clegg Bradley Architects
plant at roof level. Cooling is provided by a combination of the
The new Business School at Manchester Metropolitan University is ventilation and Hanson Coolslab system. The air handling plant is
split into three interconnected structures of four, six and eight storeys supplied with chilled water at 6°C from heat pumps, which are in turn
containing lecture theatres, seminar rooms and working spaces. supplied indirectly with cool water from a bore hole. A plate heat
Linking the structures are atriums housing multi-use workspaces. exchanger ensures the two water circuits are kept separate. Ground
Design of the £65m project was driven by the University’s ambition water is extracted at around 12°C and leaves the heat exchanger
to create a low energy building utilising thermal mass, natural at approximately 14°C. The supply to the Coolslab system is served
daylight and controlled ventilation. The architects Feilden Clegg directly by the heat exchanger i.e. without the need for the heat
Bradley Studios developed it as a building comprising three pump to modify the flow temperature, which at 14°C is ideal for
elements: a base, a solid exposed concrete frame, and a glass veil. water cooled soffits operating under peak summertime conditions.
Not withstanding this, the heat pump can be used to regulate the
Visually the colour and finish of the concrete was of particular flow temperature if needed. Another energy saving feature of the
importance to the design, but the major technical challenge was installation is the ability of the system to use heat extracted from
to control the temperature of the exposed concrete to 20˚C. This IT rooms etc. to warm other areas of the building or pre-heat the
has the effect of regulating the room’s air temperature between domestic hot water supply.
21˚C and 26˚C, which makes significant energy savings. During the
feasibility stage, M&E consultant AECOM determined that it was
possible to adopt an ‘open-loop’ temperature regulation system
using groundwater boreholes near to the site. Early involvement of
System 8:
Chilled beams with an exposed or

partially exposed soffit
The combination of chilled beams with an exposed concrete soffit has
become a popular option in new and retrofit projects. In particular,
multiservice chilled beams have found favour with many architects and
clients for a combination of reasons including their energy efficiency,
simplicity, low maintenance and avoidance of suspended ceilings. They also
work well in conjunction with a concrete soffit, as cooling from the beams
is mostly convective and is therefore complimented by the radiant output
from the soffit.
A chilled beam is a simple, long rectangular unit enclosing a finned tube

through which chilled water is pumped. The beams are mounted at a
high level where surrounding air is cooled, causing it to lose buoyancy
and travel downwards into the occupied space below. As the cooling is
Construction: largely convective, good air flow around the beams is essential. The cooling
Works with all slab types i.e. flat, profiled, in-situ and precast. output varies with the type of beam used i.e. active or passive. Ventilation is
essentially a separate provision and can be natural or mechanical, which in
Description: some systems is ducted directly to the beam.
Flat or profiled concrete soffit with chilled beams suspended below. These
FES can be employed using the basic principals described in this guide,
may also incorporate other services including lighting, smoke detectors, PIR
with the chilled beams operating during the daytime to boost the overall
sensors, and sound absorbent acoustic panels etc.
cooling capacity as necessary. Depending on the energy efficiency of the
Maximum slab cooling output (approximate): system used to provide the chilled water, it may be advantageous to also
operate the beams at night to help cool the soffit, particularly when night
15-25 W/m2 (depending on FES technique used).
ventilation is insufficient or not a practical option.
100-160+ W/m2 from the chilled beams.
Chilled beams can be custom made to specific requirements, allowing
Key benefits: them to be sympathetic to the overall aesthetics of the interior. The lighting
¢¢ High cooling output and good system control. can be designed to provide a particular effect. For example, uplighters can
be incorporated to avoid a dark soffit and acoustic panels can be included
¢¢ Combines the benefit of radiant cooling from the soffit with convective
to minimise reflected sound from the concrete.
cooling from the chilled beams.
¢¢ All overhead services can be integrated within the chilled beam, Chilled beams also provide a convenient way of incorporating cooling
offering an efficient and easy to install prefabricated system. and other services into refurbished offices, particularly, where the slab to
¢¢ Shallow unit depth works well in refurbishment projects with a low slab slab height is limited, which is often the case with 1950s-1960s buildings.
to slab height. Introducing a raised floor into such buildings can be difficult, but is made
easier by removing the false ceiling and using chilled beams, which
¢¢ Modest flow temperature permits use of energy efficient sources of
typically have a minimum depth requirement of only 300mm. A good
cooling.
example of a refurbished 1960s property is the Empress State Building in
Key considerations: London, which is an ex-Ministry of Defence office. Chilled beams were
used as part of the conversion of the floors into modern office space. They
¢¢ For optimal energy efficiency, FES requirements must not be overlooked
incorporated cooling, lighting, PIR sensors, primary fresh air and speakers,
when designing the chilled beam installation and associated controls.
all in a depth of around 280mm, and were suspended directly from the slab
¢¢ Water flow temperatures must be carefully controlled to avoid risk of which was left fully exposed.
condensation.
¢¢ Where possible, beams should be positioned so that air flow across the
soffit is maximised.
¢¢ If used in conjunction with a permeable ceiling, the open area must be
optimised to promote air flow in the void.
Case studies:
¢¢ Conquest House, London (see opposite).
¢¢ Barclaycard Headquarters, Northampton.
¢¢ Empress State Building, London.
Conquest House:
refurbished office
Location: London The existing concrete soffits have been fully exposed in the office
areas and, where necessary, made good before being painted with
Year: 1950s, refurbished 2012
vinyl matt emulsion. Raised access floors are installed at 285mm
Client: GMS Estates above slab level, providing space for cable distribution and a
pressured supply plenum for the mechanical ventilation system.
Architect: Emrys Architects
This could have significantly impacted on the floor to ceiling height
Structural engineer: Elliot Wood Partnership if suspended ceilings were also installed, but the problem has been
avoided by using multi-service chilled beams suspended below soffit
M&E engineer: Arup
between existing downstand beams. This has ensured a minimum
FES system: Exposed concrete slab with multi-service chilled beams. distance of 2.7m is achieved on the lower ground floor, increasing
to an average of around 2.8m on the other floors. The mechanical
Conquest House is a 1950s office block in the heart of the plant has been located at roof level and in a lower ground floor
Bloomsbury conservation area. Like many buildings of its type, it plant room, both of which are linked by two vertical cores. The
had out-lived its useful life and required extensive redevelopment façade is effectively sealed during normal building operation, but
to provide high-quality, contemporary office space to live up to can be opened during any system failure or for smoke clearance. The
its prestigious location by Grays Inn Fields. This has now been internal temperature is controlled between 22°C and 26°C during
completed and the 22,500 sq ft, six floor building has been fully the summer and 20°C +/- 2°C in the winter. Heating is provided by
renovated and extended to a high standard of finish. A glazed atrium perimeter trench heaters and cooling by the chilled beams, with the
to the rear creates valuable breakout space and floods light into the concrete soffit providing a stabilising effect on internal conditions
building. A dramatic link bridge suspended within the atrium allows that helps aid summertime comfort.
access to the rear courtyard garden.
Photo: courtesy of Alan Williams

Further case studies

55 Gee Street, London
FES system: Exposed, coffered slab and mixed-mode ventilation.
Munkenbeck and Partners’ 55 Gee Street in Clerkenwell, London is an eight-storey mixed-use

building with six apartments perched on top. Fresh air is drawn from roof level via a vertical shaft
supplying an underfloor mechanical ventilation system. A second shaft forms part of the extract
system, carrying air back to roof level where dampers regulate the flow, enabling it to be either
exhausted to the outside or recirculated to save energy during the heating season (up to 90%
recirculation). During the summer, the system can be run at night to cool the building’s thermal
mass (provided by the exposed concrete soffits).
Watermead Business Park, Leicestershire

FES system: Exposed, hollowcore slabs and mechanical ventilation with a ground
cooled air supply.
In 2011, the UK’s first PassivHaus accredited office building was completed at Watermead
Business Park, Leicester. Mechanical ventilation is used in combination with an air source heat
pump, which preheats the air in winter. It is also warmed by heat recovered from the extract air
via a high efficiency plate exchanger. The fresh air supply comes from an array of plastic pipes
buried 1.5m below the car park.
Loughborough University East Park Design Centre, Leicestershire

FES system: Exposed, in-situ slabs and walls, with a natural ventilation system.
The brief for the East Park Design Centre called for state-of-the-art facilities that would allow a
broad spectrum of design disciplines to collaborate. The extensive natural ventilation control
and actuation system was designed to not only manage the CO2 levels, but also ensure the
temperature within the building is maintained within comfortable limits. This is achieved with
over 400 chain actuators which control the louvres and high level vertical vents.
Greenfields Community Housing head office, Essex

FES system: Exposed, in-situ slab and mixed-mode ventilation.
The brief from Greenfields Community Housing was for a flexible head office that demonstrated
and embodied the organisation’s commitment to the environment. The layout is deigned to
achieve good cross ventilation via high level windows, with perforated panelling above the
internal glazed partitions to ensure air flow is not impeded. In periods of hot weather, night time
ventilation is used to cool the building fabric. Mechanical ventilation is also available via a raised
floor, allowing a mixed-mode approach that takes full advantage of natural ventilation during
the summer months.
160 Tooley Street, London

FES system: Exposed, lattice girder soffit slabs with underfloor displacement
ventilation.
160 Tooley Street is a mixed-use development of nearly 20,000m2, constructed for Great
Portland Estates. Thermal mass provided by the exposed concrete helps optimise the building’s
passive cooling performance and provides radiant cooling that complements the convective
cooling from the displacement ventilation system.
Bermondsey Square, London

FES system: Exposed, hollowcore concrete slabs with underfloor ventilation and
evaporative cooling.
Bermondsey Square is a mixed-use development and cooling is provided by a combination

of mechanical ventilation from an underfloor system and radiant cooling from the concrete
soffit. Evaporative cooling is also used to help regulate summertime performance of the
ventilation system.
For these, and other case studies, visit www.concretecentre.com/casestudies

References
1. CoreNet Global, 2008
2. Hirigoyen, J. Sense and Sustainability, BSD, Issue 10, Nov, 2009.
3. Non-domestic Real Estate Climatic Change Model, Royal Institute of Chartered Surveyors, 2012.
4. The values plotted for the “typical” and “best practice” offices are based on those published in the 2012 edition of CIBSE Guide F (Energy efficiency in
Buildings) with a 25% +/- margin added. A value for passively cooled, high thermal mass offices is not published in guide F and the value used is
therefore based on an average of the following, with 25% +/- margin added:
1. Edinburgh Gate Building, Harlow
2. Innovate Building, Leeds
3. Elizabeth Fry Building, Norwich
4. Ionica Building, Cambridge
5. Canon Headquarters, Reigate
6. Inland Revenue building, Nottingham
7. BRE Building 16, Watford
8. National Trust HQ, Swindon
5. Chartered Institute of Building Services Engineers (CIBSE), Mixed Mode Ventilation, Applications Manual AM13, CIBSE, 2000
6. Incropera, F. DeWitt, D. Fundamentals of heat and mass transfer, 3rd edition, John Wiley & Sons, 1990.
7. De Saulles, T. Increased cooling potential with in-situ and precast flooring, CONCRETE, The Concrete Society, August 2012.
8. Eaton, K.J., Amato, A., Comparative Environmental Life Cycle Assessment of Modern Office Buildings, SCI Publication 182, Steel Construction Institute, 1998.
9. Kaethner, S. C., Burridge, J. A., Embodied CO2 of Structural Frames, The Structural Engineer, Vol 90, May 2012, pp 33-40.
10. BRE Digest 399, Natural Ventilation in Non-Domestic Buildings, BRE, 1994.
11. Avery. B., Building Study, Architects Journal, 21 July 2005.
12. Braham, D., Barnard, N., Jaunzens, D., Thermal Mass in Office Buildings: Design Criteria, BRE Digest 454, Part 2, BRE, 2001.
13. De Saulles, T. Utilisation of Thermal Mass in Non-Residential Buildings, CCIP-020, The Concrete Centre, 2006.
14. Arup Associates, Sustainable Buildings are Better Business: Can We Deliver Them Together?, British Council for Offices, 2002.
15. Kennett, S., Location location location?, Building Services Journal, June 2004.
16. The ductwork is made by Kiefer in Germany. The UK distributor is LTi Advanced System Technology (www.lti-ast.co.uk)
which also provides system design expertise for the Concretcool system.
17. Concrete Core Cooling with air – Concretcool. PDF document from Kiefer website (www.kieferlkima.de), 2011
18. Kiefer C., Concrete Core Cooling with Supply Air, Kiefer Special Print Edition of TAB 6/2002.
19. Buro Happold, Thermal Performance of the Thermocast System, Research Report 008939 for Tarmac plc, 2004.
20. For example, Velta and Warmafloor.
21. Arnold, D., Othen, P., What a Mass, HAC, 2002.
22. Arnold. D., Building Mass Cooling: Case Study of Alternative Slab Cooling Strategies, CIBSE National Conference, Harrogate, Oct 1999.
23. Based on guidance provided by LTI Advanced System Technology (www.lti-ast.co.uk)
24. Velta Sustainable Design and Construction Forum held at Lords Cricket Ground on the 24th March 2011.
25. FM World, Simply Cafod, December 2010 (www.fm-world.co.uk/features)
26. Based on an approximate calculation of the cooling performance undertaken by The Concrete Centre.
27. Case study is based on three sources: 1) An article by Declan Lynch in the New Civil Engineer (Cool concrete for clever brains, Nov 2010). 2)
Notes taken at the Velta Sustainable Design and Construction Forum on 24th March 2011. 3) Case study information from Velta’s website (www.velta-uk.com).
The Concrete Centre’s vision is to make The Concrete Centre provides design
concrete the material of choice. We provide guidance, seminars, courses, online
material, design and construction guidance. resources and industry research to the
Our aim is to enable all those involved in the design community.
design, use and performance of concrete to
realise the potential of the material. For more information and downloads, visit:
www.concretecentre.com/publications
The Concrete Centre is part of the www.concretecentre.com/events
Mineral Products Association, the www.concretecentre.com/cq
trade association for the aggregates,
asphalt, cement, concrete, dimension stone, Subscribe to our email updates:
lime, mortar and silica sand industries. www.concretecentre.com/register
www.mineralproducts.org
Follow us on Twitter:
@concretecentre
@thisisconcrete
www.concretecentre.com
The Concrete Centre, Gillingham House, 38-44 Gillingham Street, London SW1V 1HU
Ref. TCC/05/26
ISBN 978-1-908257-09-03
First published 2012 – updated January 2017
© MPA The Concrete Centre 2017
All advice or information from MPA The Concrete Centre is intended only for use in the UK by those who will evaluate
the significance and limitations of its contents and take responsibility for its use and application. No liability (including
that for negligence) for any loss resulting from such advice or information is accepted by the Mineral Products
Association or its subcontractors, suppliers or advisors. Readers should note that the publications from MPA The
Concrete Centre are subject to revision from time to time and should therefore ensure that they are in possession of
the latest version.
Printed onto 9Lives silk comprising 55% recycled fibre with 45% ECF virgin fibre.
Certified by the Forest Stewardship Council.

MB Passive Active Floors Jan17

Uploaded by

Copyright:

Available Formats

MB Passive Active Floors Jan17

Uploaded by

Document Information

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

MB Passive Active Floors Jan17

Uploaded by

Copyright:

Available Formats

Concrete floor solutions for

passive and active cooling

Design options for low energy buildings

Fabric Energy Storage (FES) and thermal mass. . . . . . . . . . . . . . . . 4

How much thermal mass do you need? . . . . . . . . . . . . . . . . . . . . . . . . . 5

Other design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Exposed slab, naturally ventilated building.

Exposed in-situ or lattice girder slab with embedded

Exposed slab with embedded cooling/heating pipework.

Exposed hollowcore slab with embedded heating/

Exposed composite lattice girder soffit slab with

Chilled beams with an exposed

CAFOD Headquarters (Romero House), London, features exposed, in-situ

Top insert: A coffered slab with underfloor ventilation

Introduction About this publication

The use of thermal mass to optimise fabric performance centres on the

0 25 50 75 100 125 150 175 200

Fabric Energy Storage (FES)

In addition to stabilising the internal temperature an exposed concrete

Day Night Day

Figure 2: Stabilising effect of thermal mass on the internal temperature

How much thermal mass

buildings of hot weather, during which it continues to provide a useful amount of

24 Exposed 100mm lightweight floor

(steel decking with concrete topping)

21 The 300mm floor stays around two

Figure 3: Change in soffit temperature in response to a period of hot weather

Thermal mass in air-conditioned Surface emissivity –

Regardless of whether a passive or active approach to cooling

A water cooled concrete soffit is used at the Manchester Metropolitan

Other design considerations

% contribution to overall BREEAM rating

Figure 4: Influence of concrete floors on a BREEAM rating for offices.

Visual in-situ soffits Acoustic considerations

For detailed information see Visual Concrete, available from

Locating building services

To find more information on The Concrete Centre publications on

PowerGen’s HQ optimises acoustic performance by focusing sound

Passive and active floor options

Profiled slab e.g. coffered

Composite lattice girder soffit slab

Construction: Precast soffit slab with

Construction: Precast with optional

Figure 5: Main types of floor slab

Exposed slab, naturally ventilated

Headquarters of the Cambridge, Federation of

Main contractor: Britaniabuild Cross ventilation is achieved from a combination of perimeter

Exposed slab, underfloor

When considering mechanical ventilation as part of an FES design, the case

Partial post-tensioning was used to minimise early thermal shrinkage

Exposed hollowcore slab with cores

Hollowcore slabs are made from pre-tensioned, precast concrete with

Alongside the efficient services, the passive design features

Photo: courtesy of Rio Architects

Exposed in-situ or lattice girder slab

The ConcretCool aluminium ductwork and ancillary items are

Photo: courtesy of Cowlin Construction Ltd Photo: courtesy of University of Bath

Exposed slab with embedded

Photo: courtesy of Black Architecture

Exposed hollowcore slab with embedded heating/

Exposed composite lattice girder soffit slab with

Chilled beams with an exposed