Shur Cliff 1986
Shur Cliff 1986
Shur Cliff 1986
REVIEWS
Further
SUPERINSULATED HOUSES
William A. Shurcliff
SHURCLIFF
SUPERINSULATED HOUSES
the field. Others struggled along, losing money year after year. Few made
satisfactory profits. Although several companies have found how to make
high-performance durable systems that are cost-effective in certain appli
cations [Rabl (5)], the enthusiasm of architects and builders for active solar
heating has diminished. For a while the preferred solar heating design has
been the passive type.
SHURCLIFF
SUPERINSULATED HOUSES
"ceiling" on room temperature, this house provides both floor and ceiling ;
room temperature is "clamped" within the desired range (about 69-72F
in winter, about 70-79F in summer). The house contains so many unusual,
simple, and nicely balanced features that a complete account necessarily
constitutes a full-length book [Shurcliff (12)] .
But even hybrid solar houses have limitations. Performance suffers if
the house orientation is far off-south or if nearby buildings or trees block
the sun's rays. To optimize the storage and distr ibution of solar heat the
designer may feel obliged to select certain orientations and sizes of rooms
and to limit the number of interior doors (closed doors may greatly reduce
the flow of warm air from south rooms to north rooms). He may feel
obliged to specify floors of concrete and may instruct the occupants not
to cover the floors with carpets. Keeping the rooms cool on sunny summer
days may be difficult unless air conditioners are used.
SUPERINSULATED HOUSES: INTRODUCTION
AND DEFINITION
In about 1980 a whole new approach to fuel saving came to the attention
of United States and Canadian architects. Called superinsulation, this
approach provided a high degree of comfort in winter and summer,
reduced fuel consumption by 75-95% relative to conventional houses,
allowed the architect great flexibility of house design, and increased con
struction costs by only a few percent.
The method was announced and explained in talks at building-con
struction conferences and, in 1980, in one full-length book [Shurcliff ( lO)].
Enthusiasm spread rapidly, and by 1986 several tens of thousands of
superinsulated houses were in routine use. The number of such houses has
more than doubled each year. In some colder regions of the contiguous
United States and in the colder provinces of Canada the new method now
completely dominates house construction practice.
Definition
Although there is no universally accepted definition of a superinsulated
house, the following definition is representative. A superinsulated house
is one that (a) receives only a modest amount of solar energy (for example,
has a south-facing window area not exceeding 8% of the floor area), and
(b) is so well-insulated and so airtight that, throughout most of the winter,
it is kept warm solely by the modest amount of solar energy received
through the windows and by intrinsic heat, that is, heat from miscellaneous
sources within the house. Little auxiliary heat is needed: less than 1 5 % as
much as is required in typical houses of comparable size built before 1974.
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SUPERINSULATED HOUSES
SHURCLIFF
In the last five years much progress has been made in superinsulated house
design . Some improvements provide better performance ; others simplify
construction and reduce costs.
Many different wall-frame designs have been tried out, many different
types of insulation have been used, and many approaches to securing
airtightness have been explored . Although all of the variants appear to
have been successful in providing good performance, opinions differ widely
as to which schemes are simplest and least costly . A likely conclusion is
that different methods suit different climates, different availabilities of
skilled labor, and different local costs o f lumber. Also, builders who rely
almost 100% on on-site construction have different preferences from those
who use factory-built subassemblies.
The commonest type of design employed in the United States and
Canada in the early 1980s was the type promoted by Harold Orr and
others at the Division of Building Research of the Canadian National
Research Council, assisted by faculty members of the D epartment of
Mechanical Engineering at the University of Saskatchewan .
I n 1984 a different approach, offering several possible advantages, was
widely promoted by J. W. Lstiburek and J. K. Lischkoff of Building Energy
Design Corporation, Toronto, Canada (3).
Clearly, further improvements are in prospect and will make an already
highly successful technology even more successful .
PERFORMANCE
SUPERINSULA TED
HOUSES
fuel and the reduction in furnace smoke. Governments endorse it for these
same reasons and also because (a) the amount of oil imported from foreign
lands is reduced (the balance of payments is improved), (b) persons who
cannot quite afford to buy and heat a house of conventional type can
afford to buy and heat a superinsulated house, and (c) the building industry
is stimulated.
An important-and often overlooked-advantage of superinsulation is
that house orientation is not critical. There is no need for the house to
face south or within 25 degrees of south. Almost any facing direction is
acceptable-an important advantage where street orientation is peculiar
or where the main view at a given house site is in some far-from-south
direction. Also the presence of nearby tall trees or houses does not greatly
hurt the performance of a superinsulated house (but can seriously hurt the
performance of a passively solar-heated house).
In summer a superinsulated house is easily kept cool, as explained in a
later section. Often no air-conditioning is needed. If it is needed, a single
moderate-size conditioner may suffice to keep the entire house cool.
What is the additional cost of making a house superinsulated? Estimates
range from 10% to 0%. Builders experienced in the new techniques find
the additional cost to be negligible, or nearly so . The cost of the extra
insulation and the vapor barrier is nearly offset by the omission. of a
furnace, chimney, oil tank, and heat distribution system.
The financial benefits include, besides the low annual heating bill, (a)
the great attraction of the house (because of added comfort and low
heating bills) to possible renters, and (b) the attraction to possible buyers.
Agencies that lend money for house mortgages look with favor on such
houses because, thanks to the low annual heating cost, the owner is
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PROMOTION
SUPERINSULATED HOUSES
11
4 . allow visitors to i nspect the house during certain hours each week, for
one month.
Prospective house buyers benefited from having an authoritative certi
fication that the house was well-insulated and tightly built and that the
annual heating bills would be very low.
Builders benefited from receiving free instruction and advice and from
receiving a certificate that had great appeal to buyers.
The R-2000 program enjoyed broad assistance from industry, from
private institutions such as the Heating, Refrigerating, and Air Con
ditioning Institute of Canada, and also from various home builders'
associations.
DESIGN
Insulation
The entire shell of a superinsulated house is well-insulated. The insulation
on the attic floor is made especially thick, partly because of the familiar
rule that heated air rises but mainly because the attic floor is large and
unobstructed and accordingly installing the i nsulation here is simplicitly
itself: just lay it on the floor, or spray it on the floor. In cold climates such
a floor may be covered with 6- 12 i nches of fiberglass or with equivalent
amounts of blown-in wood-fiber. [Fiberglass batts provide a thermal resis
tance of about 3.0 (ft2 OF hr/Btu), called R-3, per inch of thickness. This
means that a one-inch-thick layer of such material will transmit 1/3 Btu
per square foot of area per hour if one face of the material is hotter than
the other face by one Fahrenheit degree.] Thus a 12-inch-thick layer on
the attic floor provides about R-36; the flooring and roof add to this, so
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SHURCLIFF
that the overall insulation above the main rooms may be about R-40 or
R-45.
The R-values ascribed to insulation are often approximate only. The
true R-value of fiberglass depends on the extent to which the material is
compressed or expanded. It depends also on temperature, being greater
the lower the temperature. The same remarks apply to blown chopped
fiberglass and to blown wood fiber. Plates of extruded polystyrene
(StyrofoamTM, for example) have greater R-value when the temperature is
reduced, but may have lower R-value some years after manufacture
because the "blowing gas," freon, gradually leaks away and is replaced by
air, and air is a more efficient transporter of heat than freon is. The
same applies to urethane foam and isocyanurate foam (Thermax for
example): the R-value increases when the material is cooled and tends to
decrease with time. The R-v alues of such high-quality foam plates range
from 5 to 8 (ft2 OF hrjBtu) per inch of thickness.
Exterior walls also are heavily insulated, usually with fiberglass batts,
foam plates, or blown wood-fiber. Because the walls are obstructed by
windows and doors, installing insulation is a little complicated, and com
monly the R-value chosen is less than that of the attic insulation . In cold
climates, walls are extra-thick and R-values of 25--45 are common.
Basement walls are usually insulated with two to four inches of extruded
polystyrene (example: Styrofoam), which is practically water-and-mois
ture-proof and lasts almost indefinitely . Usually it is placed on the exterior
face of the concrete basement wall; it may extend all the way to the bottom
of the w all, or (with some s aving of material and money) it may extend
only about two feet downward with a terminal outward flare; the flare
effectively adds many tons of earth to the insulated region and thus adds
to the thermal mass of the house.
Initially, fears were expressed that the use of such insulation would
permit the earth immediately adjacent to the foundations to freeze, and
that when it froze it would expand, press strongly against the basement
wall, and perhaps crack it. Experience has shown that usually no trouble
anses.
Sometimes the builder installs the insulatio n on the basement-wall inner
face. The insulation is then protected from outside threats such as bur
rowing rodents, insects, tree roots, and frost-heave. But the concrete itself
may become so cold that when any moist basement air reaches it, moisture
will condense on it and will eventually form puddles. Another disadvantage
of applying insulation to the basement-wall inner face is that the walls
then do not contribute to thermal mass.
Sometimes a two-inch-thick plate of insulating foam is installed beneath
'
the basement floor. What about houses that have concrete floor slabs and
SUPERINSULATED HOUSES
13
no basement? Some builders install foam plates beneath the entire slab;
others install such plates along the slab periphery only. Many houses have
crawl spaces and outdoor air is allowed to circulate through them; thick
insulation, such as six inches of fiberglass or four inches of foam plates, is
installed beneath the floors of the living rooms.
Many manufacturers of exterior doors sell doors that are well-insulated,
having R-values of 10-15. Such doors are highly cost-effective. Typical
doors of a decade ago had R-values of only 1-3 and allowed much heat
to escape .
What are the best-compromise R-values of walls, ceilings, etc? There is
no one best set. Different values are appropriate to different conditions of
coldness, cloudiness, wind, size of house, ventilation rate, thermal mass,
materials cost, labor cost, and auxiliary heat cost.
A set ofrepresentative ranges of R-values has been arrived at by Howard
Faulkner, architect and superinsulation expert at the University of
Southern Maine. The recommended values, applicable to cold regions
in the northern contiguous United States, are as follows: exterior wall,
R-35 to R-45; attic and/or ceiling, R-55 to R-70; floor over crawl space,
R-25 to R-35; foundation wall, R-lO to R-30; floor slab, R-5 to R-20;
exterior door, R- lO to R- 15.
How does the designer arrange for the walls to be thick enough to
accommodate very thick insulation? In past years the use of studs 3! in.
wide has been standard practice ; and accordingly the space available for
insulation was only 3! in. thick. One obvious solution is to use wider
studs, such as 2 x 6 inch studs. Another solution is to use two sets of 2 x 4
studs offset so as to provide a space two or three times the usual width. A
third solution is to use a single set of 2 x 4 studs, fill the 3!-inch space
with fiberglass, then apply a 2-inch layer of high-R-per-inch rigid foam;
apply it either on the outside, to serve as insulating sheathing, or to the
inside, supported by 2-inch furring strips. Very recently, several other
strategies have been developed: prefabricated 4- or 5-inch-thick assemblies
of plywood-foam-plywood are used; the assemblies are joined easily and
snugly by means of bolts or splines; studs and applied insulation are not
needed.
The overall R-value of a wall or floor etc is reduced by the presence of
wooden timbers (such as studs, joists, or window-frame members) or any
other thermally conducting member situated where it can form a "thermal
bridge" that, to some extent, short-circuits the insulation . If there are any
accidental gaps in the insulation, the overall R-value is reduced further. It
is a waste of time and money to install very thick insulation and then
degrade the overall performance by installing thermal bridges or leaving
gaps in the insulation.
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SHURCLIFF
SUPERINSULATED HOUSES
15
not yet fully developed and still expensive, have great promise; they may
greatly ease the restriction on maximum amount of window areas per
missible in superinsulated houses in cold locations.
An alternative to the use of high-R windows is the use, at night, ofhigh-R
window coverings: thermal shades or shutters. An enormous variety of
such devices is now available, with R-values ranging from 2 to 12 (Shurcliff
(9)]. However, the better ones are expensive ($6-$15 per square foot,
installed), may be cumbersome in appearance, and require occupant atten
tion twice a day.
Annu. Rev. Energy. 1986.11:1-24. Downloaded from www.annualreviews.org
Access provided by University of Otago on 10/25/15. For personal use only.
Airtight Construction
Builders of superinsulated houses take pains to build houses that are nearly
airtight. Decades ago little attention was given to air in-leak or out-leak
(together called infiltration), and, typically, one third to one half of the
wintertime heat loss from the house was the result of infiltration. The air
leakage rates were high enough, typically, to produce one complete change
of house air every hour or half-hour-or, on windy days, every quarter
hour. Such rates of fresh air input are three to ten times the rate needed
to ensure indoor comfort and health.
Today's builders use refined techniques to reduce infiltration rates
almost to zero . Rates as low as one complete air change per two hours or
even per ten hours are common; they are so low that special equipment is
required to provide the amount of fresh air needed, as explained in a later
section. Much use is made of caulking materials to fill cracks around sills,
window frames, etc. All wall penetrations for pipes and electric cables
are made very tight. Even basements and attics are tightly built (unless
deliberately vented to allow moisture to escape).
The task of ensuring tightness is made easier by the availability of
equipment that can evaluate the tightness quickly and accurately. Called
blower doors, these devices permit the construction workers to find out
just how tight the house is; and, when additional caulking has been
completed, they can measure the improvement accurately. By use of smoke
candles or other means they can pinpoint the locations of air leaks . Some
contractors encourage healthy competitions among thcir construction
crews, to see which crew can build the tightest house. Today, experienced
crews find it easy to make houses that are almost tighter than need be.
16
SHURCLIFF
into room air per 24-hour day. In the houses of 20 or 30 years ago, no
significant build-up of moisture occurred; the rate of air-change was so
great that the moisture was promptly dissipated to the outdoors. In today's
tight houses, though, build-up of moisture in room air is a serious threat
in winter. (A later section explains how excess moisture can be eliminated
by air-to-air heat-exchangers.)
The threat is very real even with room air at moderate relative humidity
( RR), such as 40%. If such air finds its way deep into a tight, well-insulated
exterior wall, it will reach wall components that are cold enough to cause
some of the moisture in the air to condense. For example, condensation
will occur in 70F, 40%-RR air that encounters a surface colder than
44F. Surfaces that are even colder may cause frost to form-frost that
will eventually melt and form puddles. Two harmful consequences of
condensation are 1. wooden components of the wall (studs, sheathing, etc)
may remain wet for many months each winter and may rot, and 2. the
R-value of the insulation is reduced.
Migration of moisture into walls, ceilings, etc, is avoided by the use of
a vapor barrier, usually a 0.006-inch-thick sheet of polyethylene. Such
sheets are applied to all of the boundary surfaces of the living region of
the house: exterior walls, ceilings, etc . They are applied also to the walls
and floor of the heated basement, if any. Usually the sheet applied to a
wall is applied within the wall, so as to be protected from daylight and
from mechanical impact. Often it is situated a half-inch from the indoor
exposed surface of the wall, i.e. directly behind a half-inch-thick sheet of
gypsum board. Sometimes it is situated three or four inches from the
exposed surface, to allow room for within-wall pipes, electrical wires, etc.
Always the situation is such that at least two thirds of the insulation is
outside the sheet ; this ensures that the sheet itself will never become very
cold and no moisture will condense on it.
Construction supervisors have devised detailed techniques for ensuring
the complete integrity of the set of vapor-barrier sheets. There must be no
gaps between sheet edges, no gaps at window or door frames, no gaps at
sills, headers, or ceiling-or-wall penetrations for wires, water pipes, or
vent pipes. The techniques, worked out after painful experiences in first
attempts at superinsulation, involve much use of sheet overlap and also
caulking with sealants that retain their elasticity indefinitely. No aspect of
.superinsulated house construction has been the subject of so much thought
and discussion as the proper installation of vapor barriers. There is always
the worry that if a gap occurs in the vapor barrier, and gypsum board is
installed and hides the gap, the architect and house owner may remain
entirely unaware of the defect until, a few years later, rotting of timbers is
well under way.
Some builders use vapor barriers consisting of the aluminum-foil cover-
SUPERINSULATED HOUSES
17
Window Area
Although the window area of a superinsulated house is not large, it is large
enough to provide, in winter, a considerable fraction (40-80%, say) of the
heat needed. Thus in a sense a superinsulated house is a special type of
direct-gain passive solar house. Typically, the total area of the south-facing
windows is 5-8% of the floor area. Windows on the other three sides of
the house comprise, collectively, another 5-8%. The area of the west
windows is kept small for two reasons : 1. such windows receive intense
solar radiation late in the day when the rooms are already warm enough,
and 2. the radiation received here is so nearly horizontal that eaves, even
if wide, provide little or no shading.
Usually the sills of the south-facing windows are kept fairly high so that,
in summer, even the lowest portions of the windows will be shaded by the
wide eaves.
If the windows h ave especially high thermal resistance-for example,
if they are triple- or quadruple-glazed or employ far-infrared-reflecting
coatings-nighttime heat loss here is so small that use of a somewhat
larger window area is permissible. Alternatively, the provision of nighttime
thermal shades makes it permissible to have a larger window area.
Should the floors or walls that directly receive solar radiation via the
south windows be very massive-of concrete, for example-in order to
provide especially large thermal mass and reduce the diurnal fluctuations
in room-air temperature? No. Because the window area is modest (and
the solar energy intake likewise) the building's intrinsic mass (mass of
floors, gypsum-board wall covering, etc, amounting to 20-40 tons) is great
enough so that additional thermal mass is not needed.
The main difference between superinsulated houses and passive solar
houses is in the choice of area and slope of the south windows. In a passive
solar house the area is very large ; in extreme cases the entire south face
of the house is glazed. The amount of solar energy received is enormous,
which is very pleasing until the rooms begin to overheat. Often the windows
18
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extend from floor to ceiling, which renders eaves ineffective and may
require, on warm days, the deployment of reflective shades. In some houses
a large fraction of the south-facing glass is sloped, to increase the solar
energy intake; this can lead to acute overheating. On cold nights, large
window areas lose much heat and the rooms may become too cold. To
counter these tendencies the architect may provide large-area thermal
shades to be used at night and may employ walls and floors of concrete
or other massive material. In summer, overheating is a frequent threat;
much venting of hot air is required. The designer must provide one or
more large (20-40 square feet) vents situated high up, for hot-air outflow,
and one or more vents situated low down, for cooler-air inflow. Fly screens
may be needed, and perhaps protection from driving rain. The house
occupants must learn when to open the vents, and when to close them.
Obviously, venting is of little use if the outdoor air itself is excessively hot.
THE FRESH AIR PROBLEM
The Achilles heel of superinsulation is the threat that indoor air may
become polluted . If a superinsulated house has been built so tightly that
the natural rate of air change is only once per several -hours, it is likely
that the relative humidity (RH) will increase to unacceptable levels and
the same may be true of various bad-smelling gases and also radon, which
is odorless. The indoor atmosphere may be not only unpleasant but also
a threat to health.
Humidity
If the house occupants take many baths or long showers, or do much
cooking that involves the boiling of water, the relative humidity of room
air may increase greatly. For maximum comfort, wintertime indoor-air
RH should be in the neighborhood of 35-60%. In extremely cold weather
the RH should not greatly exceed 40%, otherwise condensation on double
glazed windows may occur. The obvious way to keep the RH below such
levels is to continuously expel humid indoor air and replace it with outdoor
air, which in winter contains very little moisture-only about 1/10 or 1/5
as much as 70F air at 50% RH contains. An alternative would be to
employ a dehumidifier; but such devices are powered by electricity and
thus are expensive to operate, and in addition they are ineffective with
respect to radon and other noxious gases.
Radon
In the last few years public health experts have found that some tightly
built houses have significant concentrations of the rare gas radon, a decay
SUPERINSULATED HOUSES
19
Other Pollutants
Other pollutants commonly present in houses are
1.
2.
3.
4.
5.
6.
Air-to-Air Heat-Exchangers
The ideal way to ensure a fixed and known rate of ventilation is to employ
an air-to-air heat-exchanger, a device that contains one or more fans or
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blowers, brings in fresh air at a constant rate, expels stale air at the same
constant rate, and recovers most of the heat from the outgoing air. In such
a device the two airflo ws are in opposite directions, and accordingly the
available heat in the outgoing air is transferred to the incoming air with
high efficiency. Although such devices have been in use in industry for a
century, small devices designed for use in houses are relatively new.
There are two main types of air-to-air heat-exchangers : fixed-plate type
and rotary type. The former employs 20-50 fixed, parallel, thin plates,
usually of aluminum, separated by small airspaces ; warm stale air passes
from the house via airspaces 1, 3, 5, etc, while cold fresh air enters (in the
opposite direction) via airspaces 2, 4, 6, etc. In principle, the upper limit
on efficiency of heat transfer is 100% ; but in practice the efficiency is about
50-80%.
The rotary type employs a rotor, or wheel, that may be 16 inches in
diameter and consists of hundreds of turns of thin aluminum or plastic
ribbon, the successive turns being separated by airspaces about 0 .020 . 1 inch thick. The rotor is rotated at the rate of about 10 or 20 revolutions
per minute, with the result that any given sector of the rotor passes
successively in front of the stale air duct and the (counter-directed) fresh
air duct ; thus the sector successively takes up heat from one airstream
and, seconds later, delivers it to the other. Note that in such an exchanger
there is no need for heat to flow through anything ; also, if some of the air
passages become clogged, both airstreams are reduced equally; they
remain in balance and accordingly no pressurization or depressurization
of the house occurs. Again the heat transfer efficiency is about 50-80%.
Exchangers of small size (about the size of a small air conditioner) are
usually mounted in the wall of the living room and supply it with up to
100 cubic feet per minute (cfm) of fresh air, some of which finds its way,
through open doorways, to the kitchen, bathroom, and bedrooms.
Larger exchangers are mounted in a utility room, basement, or attic.
They receive fresh air via a duct 4--6 inches in diameter and deliver the
warmed fresh air, via similar ducts, to the living room and perhaps other
locations also. The stale air is collected from the kitchen and bathrooms,
is ducted to the exchanger, and thence is ducted to the outdoors. Of
course, the intake and outlet ports are kept well separated so that no cross
contamination will occur. The larger exchangers supply 100-250 cfm.
Such a device can be operated continuously throughout the winter, or
can be controlled by a timer so as to provide fresh air only at the times of
day when most needed, or can be controlled by a dehumidistat that turns
the equipment on (or turns it to higher-speed operation) whenever room
air humidity rises above a preselected value, such as 60% in mild weather
SUPERINSULATED HOUSES
21
and 40% i n very cold weather. Typically any such control scheme ensures
a ventilation rate equivalent to about one half of a complete air change
per hour-a rate low enough to avoid large loss of heat yet high enough
to ensure good quality of indoor air.
A few types of rotary exchangers employ rotors that have been coated
with a desiccant. Such an exchanger recovers not only sensible heat but
also moisture ; that is, it recovers sensible heat and latent heat, together
called enthalpy. In houses that tend, even in winter, to be too dry, the
recovery of moisture from the outgoing stale air is highly desirable. A
special virtue of exchangers that employ desiccants is that the outgoing air
contains relatively little water and therefore the threat of frost formation
in the exchanger passages is greatly reduced.
Such devices have some drawbacks. The cost may be $500-$800, or
possibly twice this amount if an extensive set of ducts is needed. Operating
costs-about $40-$ 100 per winter-are appreciable. In very cold weather
some of the moisture in the outgoing stale air will become cold enough
(inside the exchanger) so that some moisture will condense, forming water
droplets and perhaps forming frost. The frost will cause partial blockage
of airflow unless a special defrost cycle is employed several times a day.
The exchangers contain air filters which may need to be cleaned or replaced
once or more a winter. If the two airstreams are not equalized, the house
will be under slight positive or negative pressure, which may interfere with
fireplace or gas stove drafts. The blowers produce some noise.
Nevertheless the exchangers normally perform well, ridding the house
of excessive levels of any and all pollutants. The defects present in early
model exchangers have now largely been eliminated, and more than a
dozen manufacturers are now selling thousands of high-performance
devices per year [Shurcliff ( 11)].
AUXILIARY HEATING SYSTEMS
22
SHURCLIFF
cool down so slowly that their electrical heating needs could be satisfied
at delayed, off-peak hours. Of course, electric heat is expensive and may
soon become much more so.
Gas heat is cheap, and new small heaters that need no chimney-only
a small vent in a wall-have been developed. But gas heaters, if operated
incorrectly, may produce large quantities of pollutants ; superinsulated
houses are so tightly built that, whenever the windows remain shut and
there is no forced ventilation, concentrations of pollutants could become
dangerously high. Also, the discharge of combustion gases to the outdoors
can produce a small negative pressure in the room air, unless air is specially
ducted to the gas heater .
Oil furnaces can, of course, be used. But nearly all of the available
furnace models are much too large and thus would run only occasionally
and briefly, which makes for low efficiency. Again, special ducting of
outside air to the furnace may be necessary . Wood stoves have the obvious
drawbacks of creating the threat of indoor-air pollution and requiring the
ducting of outdoor air .
Heat pumps that draw their heat from outdoor air have the great
drawback that in very cold weather their efficiency is very low and electric
back-up heat is needed. However, heat pumps that draw their heat from
the ground or from deep wells have much promise ; they perform efficiently
and reliably regardless of outdoor temperature. Also, they can provide
cooling of room air in summer and supply heat to the domestic hot water
system. When and if the costs of such equipment are reduced, this approach
may be preferred .
At present all of the above-mentioned approaches are used. Perhaps in
the next few years a clear-cut winner will emerge.
SUMMERTIME COOLING
SUPERINSULATED HOUSES
23
Canada and the United States are not the only countries that are rapidly
exploiting superinsulation. Sweden, which must import nearly all of the
fossil fuel it consumes, has pushed hard to persuade, or even compel,
the building industry and the public to adopt superinsulation. Rigorous
standards on insulation and airtightness have been adopted and very-Iow
interest loans are offered to assist the construction of houses meeting the
standards. Because the country is small and embraces only a narrow range
of climates, it has been possible to concentrate h ouse construction in a few
centrally located, large, highly mechanized factories. Modular houses,
covering a wide range of styles and room layouts, are built to order,
shipped in trucks, and then assembled on-site very quickly-in a few weeks
or, in some cases, a few days. Because the houses are of especially high
quality and have a variety of luxury features, and because the government
loans have such a low rate of interest, the public has eagerly bought such
houses. The low annual heating bills and high degree of thermal comfort
the year around are added inducements. By early 1986 efforts to sell
Swedish-built superinsulated houses in the United States were well under
way.
Japanese efforts to produce superinsulated houses are progressing and
Japan also may soon be marketing its houses in the United States.
The United States has such a great variety of climates, great range of
building-material availability, and great variety of labor practices that
there is no dominating centralization of house construction, no ' highly
automated facility for producing full-size houses.
In conclusion, superinsulation appears to be an outstandingly successful
strategy for building high-comfort, low-cost houses that require little heat
in winter and little cooling in summer. Passive solar heating may be
preferred by persons with special requirements, such as greenhouses, sun
spaces, or enormous window areas for view. In some circumstances active
solar heating may be the appropriate choice . But for persons whose main
goals are high comfort, low initial cost, and low operating cost, super
insulation appears to be the logical choice.
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24
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