Solplan Review No 114

7.1 MB·English

by  Richard Kadulski

/oiplan review
the independent ■ journal of energy conservation, building science & construction practice
Inside
From the Editor................................. 2 Technical Research Committee News.................... 12
Roof and Attic Ventilation............... 3 Arc Fault Circuit Interrupters
Guidelines for Seismic Evaluation of Building Science Spring Training Camp................. 12
One & Two Family Dwellings 7 IRC Studies on the Control of Rain
Thermal Comfort............................... 8 Penetration in Exterior Wood-frame Walls 14
Continuous Ventilation: Energy Answers.......................................................... 16
The Heart of a Healthy House 10 Canadian Residential Fuel Cell Demonstration...... 17
Smart Vapour Barrier................................................ 18
Roof and Attic Ventilation
2 SOLPLAN REVIEW January 2004 SOLPLAN REVIEW January 2004 3
From the Editor
Roof and Attic Ventilation
I was astounded recently by a call I received from a person rather than in the inherent products. In the late 1970s, the US
in Washington state. The caller asked what sort of incentives introduced tax credits for solar water systems to help develop
Buildings must be durable and able to airports. In suburban and rural areas subject to
the Canadian government was offering homebuyers to build the solar industry. However, when the tax credits expired, the
withstand the elements acting on them. The forest fires, roof vents may provide an entry path
energy efficient homes. I pointed out that there were no direct industry collapsed. It was then realized that the marketers
intent of specific code requirements is based on for sparks into the roof cavity and a fire may
incentives, other than some modest ones to encourage owners were really selling tax credits, rather than environmentally
sound building science principles. How these spread more rapidly due to the draft in the
to improve the energy efficiency of existing homes. Rather benign solar technology. It did not help that the incentives to
are applied must also take local climatic condi­ ventilated space.
than direct cash incentives, the Canadian government was the oil and gas industry continued, helping to keep the price of
tions into account. Over time construction A fire in the building housing CHBA-BC
providing support for research, education and training of the non-renewable fossil fuels low, further distorting the market.
practices and materials may change, but codes offices in Burnaby pointed this out. The fire
industry that will benefit everyone. Noises are now being made by some within our industry -
and standards may not adapt quickly enough to entered the vaulted ceiling structure through the
The caller sounded genuinely surprised that there are no and heard by Conservative politicians - to introduce mortgage
keep pace with the changes. This could be the soffit vents. Its spread was only held in check by
grants. He could not understand that the benefit of the better interest tax deductions in Canada, copying an American
case with code requirements for roof and attic a ridge beam that compartmentalized the
quality, more comfortable home with lower operating costs policy. Tax deductibility of mortgage interest does not
venting details. cathedral roof vent cavity.
should be an incentive in its own right. He did not sound necessarily make the homes more affordable or accessible, as
Building codes typically require attic ventila­ It is worth considering how construction
pleased when I asked Why should I (through my taxes) pay him most of those likely to take advantage of the deductions are
tion. The intent is to manage moisture in the practices and designs have changed over the
to get a better house? those for whom affordability is not as big an issue. Cost and
roof by avoiding condensation on the framing years, as this can also have an impact on a
I do not mean we should avoid any initiatives that will affordability are too often confused with expectations for
and underside of the roof sheathing. Summer building’s performance. Older houses typically
improve the energy efficiency of homes. Setting high-energy features and appointments in the home.
cooling of attic air, minimizing ice dams, and were built with large attic spaces, low insulation
efficiency standards and encouraging lower resource consump­ If anything, mortgage interest deductibility encourages
extending the service life of the roof materials levels, and were not airtight. Large volumes of
tion is something that we as a society must do. It is the only owners to maintain higher mortgages. The home becomes
are often cited as additional benefits of attic air change and considerable heat loss from the
responsible thing to do if we are serious about leaving a better another disposable commodity to trade rather than to pay
ventilation. Lack of attic ventilation is routinely house meant low relative humidity levels in the
world for future generations. To take no action is simply down, because the cost of financing is that much lower. In
blamed for a variety of problems and failures. house during winter and low moisture content in
irresponsible. The question is what is an equitable way to do it the short term, it may have an impact on the housing market,
Venting rules for attics have been extended to the construction assemblies. Cold outside air
to get meaningful results. but in the longer term it will likely do little to it. At the same
apply to cathedral ceilings, but few studies have coming into the attic was heated by the heat loss
We need to question our expectations as consumers and time, the lost tax revenues simply have to be replaced by
been made to confirm the validity of extending through poorly insulated ceilings, thus increas­
what weight we place on the inherent value of the products we some other form of tax to provide the public services the
them. However, papers presented at various ing the drying potential.
make and use. We know that it is possible to build energy- taxes are financing.
conferences in recent years and summarized in Today homes are well insulated and more
efficient homes that can meet at least the R-2000 standard In any event, we presently have a critical shortage of
an article in the October 2002 ASHRAE Journal attention is given to air sealing to reduce
without significant incremental costs. It may mean some skilled trades, so there is little benefit in stimulating the
have raised questions about the importance we uncontrolled air leakage. However, the glass
adjustments to expectations about the kinds of features that are market further. I suspect that the main beneficiaries for tax
place on attic ventilation. fibre insulation commonly used is porous to air
included, but it is doable. We just have to act rather than pay deductibility would be mortgage lenders, as there would be
Unvented attic construction is indirectly leakage. We also use more sophisticated me-
lip service to the idea. less incentive for homeowners to pay down their loans.
recognized by the Building Code as an accept­
Given the many hidden subsidies the energy industry
able construction detail. Section 9.19 of the
receives, perhaps the caller was not off the mark in looking for
NBC recognizes that roof venting can be omitted An Ontario Ministry of Municipal Affairs and Housing opinion
handouts. The downside of an economy where marketing is
done with handouts or rebates is that it leads to a false economy Richard Kadulski, if it can be shown that it is not needed. The about the ventilation requirements for roof spaces (Ontario Building
where much trade becomes trade in incentives and rebates. Editor provision for unvented attics was drafted largely Code [OBC] Subsection 9.19, which is the same in the National
to deal with manufactured homes, which can Building Code) made in May, 1997, stated:
achieve a better level ceiling airtightness than is
/olplan review Publications Mail Agreement No. 40013363 CHANGE OF ADDRESS: include a mailing label normally the case in site built construction. According to Subsection 9.19. of the OBC, ventilation must be pro­
Postage paid in Vancouver. BC. orcopy all in formation off label for faster, accu rate
However, with new construction practices, it is vided to all roof or attic spaces. This requirement is intended to provide
Return undeliverable Canadian addresses to processing.
PO Box 86627. North Vancouver. BC V7L 4L2 CONTRIBUTIONS: Unsolicited contributions and possible to achieve airtight ceiling assemblies adequate air circulation in order to avoid air being trapped and con­
Editor-Publisher: Richard Kadulski COPYRIGHT 2004 by The Drawing-Room Graphic manuscriptswelcome. Include self-addressed pre­ with site-built construction. Although it is still densed. However, it is the opinion of the Housing Development &
Illustrations: Terry Lyster Services Ltd. All rights reserved. stamped mailer if return requested. Publisher not prudent to design for vented attics, unvented Buildings Branch that, where a roof assembly is filled with rigid insula­
Contributors: David Hill. Ken Farrish. Michael A. Reproduction without written permission of the responsible for loss or damage of same.
Lacasse, Tex McLeod. Rob Dumont. Jim Stewart publisher is strictly fprbidden. Transgressors who While every effort is made to provide accurate and ceiling assemblies can provide satisfactory tion (no gaps or empty space in between), Subsection 9.19. of the OBC
ISSN: 0828-6574 don’t take heed note: you'll get an offer you can't complete information, we do not warrant or solutions in some cases, especially for cathedral need not apply and may be considered to be acceptable under sufficiency
Date of Issue: February 2004 turn down but will wish you had. guarantee the accuracy and completeness of such ceilings and smaller roof decks over living of compliance in Section 2.7 of the OBC. This opinion is based on the fact
SOLPLAN REVIEW is published 6 times per year by: A license for photocopying or other reprographic information.
the drawing-room graphic services ltd. copying can be also be obtained from Access ADVERTISING POLICY: Publisher's discretion spaces. that, if a roof assembly does not contain any air space or air pockets in
PO Box 86627. North Vancouver. BC V7L 4L2 Copyright (Canadian Copyright Licensing Agency, in the acceptance of any advertisement. No Sometimes attic vents can be either impracti­ between, air will not turn into vapour and condense within such an
Tel: [phone] Fax:[phone] #1900-1 Yonge St. Toronto ON M5E 1E5). endorsement is stated orimplied by the publisher. cal or undesirable. Closing attic vents may be assembly even under extreme weather conditions.
e-mail: [email protected] SUBSCRIPTIONS: In Canada 1 year $50.29 (incl PRINTED IN CANADA
Street address: GST) (NB. NS, NF $54.05 includes HST); 2 years GST Registration: R105208805 desirable for sound mitigation, especially near
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SOLPLAN REVIEW January 2004 5
4 SOLPLAN REVIEW January 2004
the pressure indoors. In other words, the attic because it can fill all voids not otherwise
as it is impacted by occupant behaviour. The
should be pressurized or the house placed under accessible. Because air movement is blocked
The theory behind attic ventilation is that air movement through other two measures are outside occupants’
a negative pressure. A house completely under through the material itself, moisture cannot get
the attic will be a drying mechanism for any moisture that control.
negative pressure could lead to other problems into the roof structure, so the structure will be
accumulates oris trapped in the attic. However, attic ventilation The earliest testing of the effectiveness of attic
especially if there are spillage-susceptible free of moisture problems.
requires heat loss to remove moisture, since cold air cannot hold ventilation was done in the 1930s on model
combustion appliances or soil gases that could Functionally, spraying foam directly against
much moisture. houses indoors in a laboratory, not full-size
be drawn into the house. the interior side of the roof sheathing is the same
Winter air has little capacity to absorb more moisture as it is buildings exposed to actual weather. The results
Achieving good airtightness can be a chal­ as structurally insulated (or stressed skin) panels
usually at a high relative humidity and the absolute amount of showed that attic ventilation could reduce conden­
lenge due to the many appliances and light which have been used successfully in thousands
moisture that air at 0°C or colder can hold is very small. Air sation on roof sheatiling during cold weather.
fixtures used today. A major problem is the of buildings throughout North America.
movement will help remove moisture, but it will not be quick and Attic moisture readings taken in the 1940s in
popularity of recessed ceiling lights. As typi­ Attic ventilation in a very cold climate helps
may not prevent significant condensation in the attic, especially if Wisconsin found that condensation in the attic
there is considerable air leakage through the ceiling. occurred only in those houses that had high cally installed, each pot light is a significant makes a cavity roof more moisture-tolerant and
source of air leakage. Proper air sealing at pot should be used as an additional safeguard.
According to the psychometric chart, which plots the humidity levels indoors. In all houses, higher
lights requires special care and attention that is However, alternative strategies also are accept­
relationship between temperatures, relative humidity and moisture conditions in the attic corresponded
seldom achieved in practice unless the builder is able, especially in the case of older buildings and
moisture capacity, 100 m3 of air at 0°C is only able to hold about with higher humidity conditions in the living
0.4 litres of water. At -10° C the same volume of air can only hold space.The code ventilation requirement was setting out to meet a stringent air test such as homes that have shown satisfactory performance
0.2 litres. However, at 21°C, a typical indoor temperature, the established by trial and error after the early tests the test for R-2000 certification. Other or in new buildings where carefully sealed foam
same volume of air can absorb almost 1.5 litres of water. and monitoring studies. With a 1:300 ratio, the penetrations through the ceiling can include insulation is directly applied to the roof sheathing.
If the indoor air that is at 21° C and 40% RH leaks out to an attics seemed to be reasonably dry. Studies on wiring and mechanical services running through In cold climates, cathedral ceiling construc­
attic space which is at -10°C, every 100 m3 of air will deposit attic moisture generally concluded that indoor the attic. Even ceiling mounted fire sprinklers tion is inherently more prone to moisture
about 0.6 litres of water. (100m3 is approximately the volume of a humidity control is important in reducing can be a major source of air leakage. damage than attic construction because each
20 ft by 20 ft room with an 8-ft ceiling). condensation in the roof and walls. Ceiling Increasingly, new approaches to construction rafter space creates its own cavity. That is why
vapour retarders were identified as being are being used for houses or for portions of code language requires cross strapping in an
effective in lowering attic moisture levels. Some them. These include structural insulated panels effort to link all cavities.
and roof systems with foam insulation applied The more frequent use of designs with
chanical systems indoors, which often include studies suggested that the attic vent area could
directly to the underside of the roof sheathing. cathedral ceilings and roof decks over living
humidifiers. Houses in the past may have had a be lowered to 1:600 if a ceiling vapour retarder
Spray-in-place polyurethane insulation can be space are details that were not commonly
relative humidity of 10-15% on a winter day, were present.
both an air barrier and insulation. Lower considered when the codes were drafted years
while today it may be 30-40%. Even a modest By the 1960s, with a better understanding of
density spray foam like Icynene and Demilec are ago. Cathedral ceilings, with narrow vent
amount of air leakage from the house can move the performance of residential buildings, it was
good air barriers but are vapour permeable, so cavities and flat roof and decks over living
significant quantities of moisture into the attic. recognized that a vapour retarder was not a
will still require a vapour diffusion retarder. spaces are not likely to experience the air flows
It is important to remember that air flows and dependable means of attic moisture control. It is
However, a polyethylene vapour barrier in such required to create the nominal drying that is
moisture movement are influenced by climatic air movement by air leakage through the ceiling
applications is actually too effective a vapour acliievable in a vented space.
conditions. If you plan to build in the southeast­ into the attic that is the major source of attic
barrier and can impede the ability of any Wind washing of the insulation, when cold
ern United States, southern Japan or in a moisture. Thus, an air barrier in the ceiling is
residual construction moisture to dry out, so a air penetrates the ceiling insulation, is another
tropical or semitropical climate, building more important than a vapour retarder.
more permeable vapour barrier like paint is common problem with ventilated attics and
practices and details will be different from those It is now recognized that attic ventilation above
preferable to permit the moisture to dry into the cathedral ceilings, especially near the soffit
that are appropriate in Canada. Even in the insulation in a leaky ceiling assembly can
interior space. vents. In an unvented cathedral ceiling, the air
Canada, although all areas are cold heating- draw warm moist air from the interior through air
When foam insulation is used in walls and space required for venting can be filled with
dominated climates, there are differences in the leakage in the building envelope, thus contribut­
low-slope roof systems, it generally provides additional insulation. This benefit should be
severity of the climate. Climate conditions in ing to moisture problems. That is why the
good moisture control. If the spray foam is weighed against factors that would reduce ventila­
southwestern BC and possibly portions of Nova ASHRAE Handbook of Fundamentals now
applied directly to the underside of the roof tion effectiveness, the feasibility of foam-based
Scotia and southern Ontario are milder than the stresses the importance of controlling airflow.
sheathing, there is no moisture performance and other unvented assemblies, and the possible
extreme cold of the Prairies or far north, so Proposed changes to the “International"
advantage to venting such roof systems. The detrimental or undesirable effects of ventilation.
specific construction details may be different. Energy Conservation Code, which is one of the
spray-in-place foam insulation provides the In milder cool and wet coastal climates,
In cold climates the three most effective major building codes in the US, will permit
required insulation as well as performing an air moisture contained in the outside air is carried
measures to lower attic moisture conditions are unvented attics if the insulation is air imperme­
barrier function, thus also controlling moisture into the attic by ventilation and can become a
indoor humidity control, airtight ceilings able and the ceiling does not include poly
migration into a space where it could be harm­ source of moisture.
preferably combined with positive active pres­ vapour barrier.
ful. The expanding foam insulation ensures a CMHC studies on the West Coast found that
sures, and attic ventilation. Indoor humidity To ensure there is no indoor air movement
better, more even and inherently airtight assem­ high attic ventilation rates led to higher mois­
control can be built-in only to a certain degree, into the attic, the ceiling has to be airtight and
bly than conventional batt insulation materials ture content in the roof sheathing. The higher
the pressure of the attic should be higher than
6 SOLPLAN REVIEW January 2004 SOLPLAN REVIEW January 2004 7
Guidelines for Seismic Evaluation of
ventilation rates meant colder attics without without ice dams. Houses with ice dams also
lowering attic water vapour pressures, resulting tended to have less insulation in the ceiling and One & Two Family Dwellings
in high attic relative humidities and moisture less eaves ventilation, either due to fewer soffit
Many parts of Canada are in zones of high The City of Vancouver has recently stepped
content in the sheathing. The studies suggested vents or fewer insulation baffles at the eaves.
earthquake potential. Although these areas may up enforcement of seismic design. They have
that unvented attics perform better in wet, cool Ice dams can be avoided in vented attics if the
not be as seismically active as California, Japan issued a bulletin with guidelines that are based
coastal climates as long as indoor humidity is attic temperature can be kept below freezing
or the Middle East, the potential is still there. In on the Canadian Wood Council’s (CWC)
controlled by ventilation or dehumidification, when the outside temperature is -5.5°C (22°F)
recent years, more attention has been given to Engineering Guide for Wood Frame Construc­
and the ceiling assembly is built airtight. so that heat from below does not melt the snow
the subject, especially in southwestern BC where tion. The intent of the guidelines is to provide a
In hot humid climates attic venting tends to on the roof. That is why higher ceiling insula­
geologists suggest the area is overdue for a tool to assist designers in identifying conditions
increase rather than reduce moisture levels in tion levels are always beneficial.
major tremor. and building designs that may require special
the attic. When the ceiling is not airtight, attic The need for attic venting to avoid icing
Engineers study the performance of buildings attention.
ventilation may also increase the cooling load in depends on the climate, the amount of insulation
after each major earthquake anywhere in the This Guide uses the idea of “braced wall
the building. in the ceiling, the design of the roof, and solar
world. A review of the survivors as well as panels” arid “braced wall lines” to determine
exposure. To minimize the danger of ice dam
damaged structures adds to the understanding of how much structural redundancy a building has.
Ice Dams formation, heat sources in the attic such as
structural performance in an earthquake. As a Although not referenced in the National Build­
Attic ventilation is generally credited for warm chimneys and poorly insulated heating
result, structural design for seismic loading has ing Code of Canada, the
minimizing ice dams. However, it is the heat and ventilation ducts as well as warm air
improved significantly in recent years. New CWC Guide is now Braced Wall Panels - sections of walls
loss through the ceiling that is a major contribu­ leakage into the attic from below must be
buildings built according to the latest practices considered as a national built in a way to provide some resistance to
tor to ice damming. An Ottawa study found that avoided.
are far better able to withstand major earth­ standard for small wood lateral loads
all monitored houses with ice dams had interior
quakes. frame buildings, particu­ Braced Wall Lines - a number of braced
chimneys that warmed the attics which were Durability of Shingles and Roof
The Building Code requires that buildings larly with regard to wall panels used in combination within the
about 4°C (7°F) warmer than attics of houses Ventilation
must be adequately designed for the loads they determining when addi­ limits identified in the CWC Guide.
Many asphalt shingle manufacturers require
may experience. In areas of high seismic tional design is required.
“code-level” ventilation for their warranties to
activity or high wind loads, the structures must
be effective. The rationale is that venting cools
Do Attics Need Ventilation? be designed to properly withstand the forces that
shingles and thus affects their durability. Spacing between braced Spacing between braced
On balance, venting is recommended for cold climates. While attic However, ventilation is a minor factor in may impact the building. The City of Vancou­ wal lines-transverse wal lines - transverse
ver Building Bylaw (which is essentially the
ventilation can be beneficial, it should not be viewed as the principal determining shingle temperature.
same as the National Building Code) exempts
strategy to eliminate moisture and other problems in the attic and roof Shingle temperature is more strongly influ­
one and two family dwellings from the engineer­
in all climates. Attic ventilation needs to be part of broader range of enced by the geographic location and the
ing design provisions of Part 4 when these are
moisture control strategies. direction a roof faces, rather than ventilation.
built in accordance with the prescriptive require­
^Indoor humidity control should be the primaiy means of limiting Venting can cool shingles, but the cooling effect
ments of Part 9. This does not mean that Part 9
moisture accumulation in attics in cold and mixed climates. is not strong. US studies have shown that attic Spacing
buildings are exempt from compliance with the
^Unvented roofs can perform well in cold and mixed climates if ventilation in a black shingle, truss-framed roof between
proper structural design requirements to accept braced wall
measures are taken to control indoor humidity, to minimize heat assembly has a 2 to 3% cooling effect on wind and earthquake loads. Rather, this exemp­ lines-
sources in the attic, and to minimize air leakage into the attic shingles, but the effect of colour is 20 to 30%. longitudinal
tion recognizes that traditional residential
from below. White roofs have been found to be up to 20°C
building designs have a lot of load sharing
^Ventilation should be treated as a design option in cold, wet coastal (36°F) cooler than grey roofs, and up to 30°C Centre to centre
between many non-structural elements which
climates and hot climates. Current technical information does not (54°F) cooler than brown roofs. spacing of
help the building stand up to wind and earth­ braced wall panels
support a universal requirement for the ventilation of attics or Building Science Corporation in their Build quake loads. 7.6 m maximum
cathedral ceilings in these climates. America projects in Nevada and Texas have
What has not been recognized, however, is
calculated that the life span of shingles in an
that current house designs, which have moved
unvented roof may be reduced by 3 to 5%.0
away from traditional design forms, are moving Spacing
away from the assumptions behind the building between
braced wall
code requirements. Today’s homes feature the lines -
use of large span framing systems, large glass longitudinal
areas, and open floor areas with fewer interior ^ Max. 2.4 m
partitions, including double or triple garages
with living spaces over, so that many of the
h----H
assumptions on which Part 9 is based are no
Length of braced wal Distance from comer
longer valid.
panel max. 2.4 m
8 SOLPLAN REVIEW January 2004 SOLPLAN REVIEW January 2004 9
The basic design principle is that when this requirement, the following conditions designed systems the difference can be as much controllable. The thermal flywheel of building
braced wall panels have adequate strength and should be met: as 7°C between floor and ceiling. materials can cause discomfort during periods of
spacing for the load conditions, there is enough ♦ the perpendicular distance betw een braced wall It is tlie temperature difference in the zone high solar gains or sudden changes in internal
redundancy built into the system and the lateral lines must not be more than 25 ft. (7.6m). between the ankles and the head level that gains, so the building and building envelope
design requirements will be satisfied. Roof and ♦ the offset of any braced wall panel within affects the perceived thermal comfort. Radiant have to be designed carefully.
floor elements must be sheathed with enough the braced wall line must not be more than 4 heat transfer which has relatively cool air Higher building insulation levels, lower
strength and rigidity to act as diaphragms. This ft. (1.2 m). temperature but warm surrounding surfaces infiltration losses and solar gains can increase
requires panel-type sheathing or continuous ♦any braced wall panel must not be more than better satisfies the comfort needs of human the risk of overheating during the summer.
lumber sheathing applied diagonally. 8 ft. (2.4 m) from the comer of the building. beings because it is more “natural” - like solar Proper building design is needed to avoid
The CWC Guide shows the maximum ♦ the spacing of braced wall panels along the radiation on the skin. overheating problems. Heavy masonry materi­
spacing between braced wall lines for specific braced wall line must not be more than 25 A heated floor makes it more comfortable als, such as brick feature walls and concrete
lateral loads. One and two family dwellings are ft. (7.6 m). when people walk barefoot. Optimal floor floor slabs with tile or stone finishes are very
assumed to meet the seismic design require­ ♦ the minimum length of any braced wall temperatures range from 20-28°C if people walk effective at soaking up excessive heat gains and
ments if: panel is 4 ft (1.2 m). with shoes and 23-30°C with bare feet depend­ acting as a heat storage medium. This is an
♦ the building area does not exceed 600 m2. ♦ all exterior and interior braced walls must ing on the floor material. important principle of passive solar design.
♦ the building height does not exceed three be supported on continuous foundations. The IEA studies were done in Europe, where
stories. ♦ the maximum height of any knee wall most heating is done by baseboards or floor Windows
♦ the maximum spacing for wood studs and (cripple wall) is 4 ft. (1.2 m). radiant heating. The forced warm air heating Cold window surfaces can make rooms
joists is 600 mm o/c commonly found in North American homes uncomfortable because of the radiant heat losses
♦ the clear span of framing members is not If the design meets all of these requirements, helps reduce temperature stratification by to them as our bodies become the heat source to
more than 40 feet (12.2 m) it is assumed to meet lateral wind and seismic forcing air movement which tends to mix the air the colder surface of the window. As well, drafts
♦ the design load of floors is not more than 50 loading. If the design does not meet all of these in tlie house. Good performance is achieved can be caused by larger window surfaces when
psf (2.4 kPa). requirements, then a design review must be when the furnace blower is run continuously at the boundaiy air layer at the glass cools and
done, and some additional detailing may be low speed. flows downwards. The traditional way to
There must be enough built-in redundancy required. O Conventional forced warm air or high compensate for the cold surfaces is to place
in the structure. In order for the plan to meet temperature baseboard heating systems have a heating registers or radiators close to or under
shorter heating-pickup period after cooling the window. This discomfort can also be
down with a setback thermostat because of these reduced by limiting window dimensions to a
Thermal Comfort
systems’ low thermal capacity. They will raise reasonable size. Use of high performance
the air temperature up to the set-point fairly windows also helps improve comfort.
We normally look to the air temperature, find interiors to have a better air quality and not
quickly, but this may still not be enough to In tlie case of radiant heating systems, low R-
which is measured by a standard thermostat, as to be as stuffy when air temperatures are lower.
provide comfort because of the thermal lag of value (high -U value) windows, because of their
the indicator of comfort conditions. However, Mucous irritation complaints increase signifi­
the cold building materials. For comfort greater heat loss and colder surface tempera­
comfort conditions are much more complex. cantly when air temperatures go over 22-24°C.
conditions, the mean radiant temperature is very tures, require more care when the system is
Comfort depends on a combination of air The annoyance from all kinds of volatile
important, and the time to warm cool building being laid out. Very large window areas may
movement, humidity, the temperature of the chemical emissions (VOCs, etc.) has been
materials means it takes longer for the mean have to be reduced when radiant heating is used,
surfaces surrounding us (referred to as the mean correlated to the air temperature. A relation­
radiant temperature to rise. although extra heating pipes can be placed close
radiant temperature) as well as the temperature ship has also been found between Sick Building
Large temperature fluctuations, like large to the outer loops of a floor heating system to
of the air. Syndrome and the air temperature.
temperature gradients between floor and ceiling, compensate for the greater heat loss to ensure
All heating systems rely on the three heat Computer simulations and laboratory and field
are annoying for people. It is one of the reasons that discomfort does not occur.
transfer mechanisms - convection, conduction experiments done for the International Energy
why poorly sized forced warm air heating
and radiation. The degree to which each is Agency (IEA) found that there is a difference in
systems often generate complaints, because the Indoor Air Quality
important in a given type of heating system the temperature gradients between the floor and
furnace may cycle infrequently. Low tempera­ Inhaling dust can cause allergic reactions.
differs. The radiant heat component is more ceiling in rooms heated by floor radiant heating
ture radiant heating systems have less fluctua­ Human sensitivity to inhaled particles is more
important in low temperature heating systems systems compared to high temperature baseboard
tion because heat is stored in the building dependent on the quality of the particles than on
than it is in other systems. Because the heat radiators. Rooms in well-insulated buildings with
materials, especially in the thermal mass floor the quantity. At temperatures exceeding 55°C,
transfer accounted for by convection is lower, floor radiant heating have very even temperature
toppings, leading to more even temperatures. the process of dust singe starts. The particles get
tlie air temperatures can be 1-2°C lower to distribution. On the other hand, temperature
Generally, radiant systems operate at small more reactive and irritating from tlie higher
provide the same comfort level. distribution in rooms with high temperature
temperature differences, so any change in the temperatures that occur at high temperature
Some radiator systems is very dependent on the system
indoor temperature will quickly shut off the heat heating elements such as electric or hot water
studies show design. Normally, gradients range from 2-3°C
Thermal Comfort Formula supply, but other heat gains may not be as baseboards.
that people between floor and ceiling, while in poorly
Air temperature (°F) + Mean Radiant Temperature (°F) = 140°F
10 SOLPLAN REVIEW January 2004 SOLPLAN REVIEW January 2004 11
Low temperature heating systems not only lower quantity of suspended particles in build­ emergency trip to the hospital per season was could have contributed to their improved state of
emit less suspending particles into the air but ings. On the downside, radiant systems do not required. health after installing the HRV. This family’s
also the particle spread is less aggressive due to have the air circulation systems that make it The 8-year-old daughter’s allergies were experience showed that the quality of indoor air
absence of dust singe. A study in Finland found easier to add filters to clean the air. expressed in the form of eczema on her hands improved by the continuous exchange had a
that visible dust on floors correlated with Many studies have found that floor radiant and both upper and lower legs. The mother also significant effect on family members’ health,
complaints such as chronic headaches, fatigue, heating is beneficial in reducing dust mite was bothered by eczema, often having raw and each in different ways.
For information on the and problems with concentration. Low tempera­ concentrations in homes. This is mainly because bleeding hands. The father was almost always After four years in that house, last year the
R-2000 Program, ture radiant heating systems were found to of the lower relative humidity (RH) in the congested but not nearly as affected as his son. family moved to a new (but not a brand new)
contact your local reduce eye-irritation and throat and other boundary layers above the floor and within the In September of 1999 the family had an home. Their new house did not have a central
program office, or call mucous diseases. floor covering. To survive, mites need an Eneready 2000 HRV installed in their home. It ventilation system, and all their chronic health
1-800-387-2000 A relationship was also found between the average relative humidity of 45% or more over was ducted to exhaust the kitchen and two symptoms returned. After a few months, they
www. R-2000. ca temperature of the heating surface and particle the long term. Calculations have shown that bathrooms and to directly supply fresh, pre­ installed an HRV, again set to operate continu­
deposition, such as is often seen above high floor heating reduces the RH in the boundary warmed air overhead to the bedrooms and the ously. Within a few days, they noted a signifi­
temperature hot water or electric baseboard layer by about 10%, which can be enough to living, dining and recreation room. cant improvement to their home and to their
heaters. It is thought that the lower air tempera­ bring the RH below the threshold value. O During the first three weeks after the HRV family’s health.
ture fluctuations from radiant systems result in a was installed, more than 4 gallons of water was This is what generated the note the HRV
removed as it helped dry out the house. The supplier received just before Christmas. O
relative humidity in the house dropped by about
Continuous Ventilation: The Heart of 10% to a range of 45-54%. This solved the
window condensation problem and improved the
Today we are very concerned about the food we eat. We eat
a Healthy House indoor air quality.
about 1 lb. (dry weight) of food each day.
The family discovered they had more energy,
For the past few years, we have been concerned about the
while the boy could reduce the amount of
water we drink. We drink about 5 lb. of water each day.
of the home without continuous ventilation. medication he took - only occasionally using his
Each day, the average adult inhales 54 lbs. of air every day.
"I have to admit that when all our ailments and allergies The home was a typical Abbotsford, BC home puffer. The daughter had a marked decrease in
We are not fully aware of this (maybe because unlike for food and
cleared up after the HRV was installed at our old house, I was built in the mid 1980s. The house had 1,200 sq. her eczema and the mother’s eczema disap­
water, we don’t yet directly exchange money for this).
sceptical. ft. on the main living level over a 1,000 sq. ft. peared. All felt that their home was fresher.
Perhaps the quality of the air is equally as important as the
Well, 1 truly eat humble pie now and I apologize 1 ever walkout basement and a 200 sq. ft garage on a Even guests noticed the difference.
quality of the food and water we consume.
doubted you! The HRV has been hooked up five days now and sloping lot. The home was heated by a gas The family noted that they had made no
the eczema (which reappeared upon moving), is almost gone; forced air furnace located centrally in tire change to their diet, routine, or medications that
basement. The house was not airtight, and had
Andrew’s stopped snoring; Emily has stopped waking up
high relative humidity even after the perimeter
stuffed up, and Ben stopped wheezing! Plus my arthritis has
drainage was dug up and relaid. Winter relative BCBuilding.info
gone.
humidity was observed to range from 54 to 74%.
Wow! BCBuilding.info is a free, e-mail newsletter A unique feature of the electronic newsletter is
The windows on the lower level had a lot of
issued every three weeks, serving the residential that it does not present articles as such, but rather
Thanks for the wonderful Christmas present!"
condensation, and the sashes remained wet and
construction industry of British Columbia. Al­ a one or two sentence summary of a topic with a
were mouldy.
though its focus is on BC, the newsletter may also number of links to other Web sites where more
In that house, the family of four had all
be of interest to builders in other parts of the detailed and topical information can be accessed.
Testimonial letters from past customers are experienced a degree of low-level chronic health
country. In this respect, it is very much like an annotated
the most valuable marketing tools anyone problems. The 10-year-old son was the major
Each issue contains a focus on a specific topic as bibliography, saving readers a considerable amount
selling a service can have. They are especially exception as he is an asthmatic and had frequent
well as short articles written for builders and of time when searching for information.
valuable when they arrive unsolicited. This is a attacks in the winter. He had suffered from
renovators with links for more detailed informa­ Ken Farrish, a building industry veteran and
tale of a testimonial that a Vancouver ventila­ asthma for many years. His triggers were grass,
tion. Past issues are archived on the BC Building past president of the Greater Vancouver Home
tion equipment distributor received. While it is pollen, dust and mould. His prescribed medica­
Web site. Some of the topics covered in past issues Builders Association, is the person behind
anecdotal, it confirms the observations that R- tion included inhaling two Salbutamol puffers in
include: Flooring; Insulation; Green Building; BCBuilding.info. He set out to provide BC build­
2000 builders make, and emphasizes that a well- the average 100-day winter period. This repre­
Doors & Hardware; Building Science; Exterior ers and renovators with resources to help them
built home can be a healthier home. sented two doses/day increasing to five doses/
Finishing; Roofing Systems; Energy Efficiency; build the best quality buildings possible.
In this case, the homeowners had installed a day during a crisis. A corticosteroid puffer
Ventilation & Indoor Air Quality; Foundations &
heat recovery ventilator in an older house. They would often follow at two doses per day for three
Basements; Heating Systems; Advanced Framing Information: www. bcbuilding. info
had lived in their home for some time before to four weeks after a crisis. Sometimes home
& Wall Systems; Windows; Building Envelope
installing the HRV, so they had the experience treatments were not enough. At least one
Resources.
12 SOLPLAN REVIEW January 2004 SOLPLAN REVIEW January 2004 13
Technical Research Committee News
Spring Camp 2004 once again will bring day and Tuesday, accommodation and all the
tit Arc Fault Circuit Interrupters these resulting from arc faults, sometimes causing together some of North America’s leading hospitality and great meals. Send in your
injury and death. building scientists and educators along with application today! Just like real spring training
The Canadian Electrical Code now requires the Arc faults escape detection by traditional circuit some of Canada’s most dynamic innovative camp, you have to be invited. We’ve only got
installation of an arc fault circuit interrupter (AFCI) breakers because the arc fault current may not be builders. The event starts with a “get to know space for about 70 and we need to ensure a good
on all bedroom electrical circuits. This has created consistent enough or high enough to trip a conven­ you” opening reception on Sunday evening mix - the right amount of salt & pepper, scotch
a lot of concern about extra cost as well as doubts tional breaker. Typical household fuses and circuit April 18, with two full days of sessions Monday and chocolate. Let us know something about
Canadian about how effective arc fault circuit interrupters breakers do not respond to early arcing and spark­ and Tuesday. Topics that will be discussed in yourself and why you want to attend. Bribery or
maybe. ing conditions in home wiring. By the time a fuse some depth with leading experts will probably other payments above (or under) the table will
Home Builders'
or circuit breaker opens a circuit to defuse these include mould and healthy housing, effective not be considered.
Association
What Is An Arc Fault And Why Is It A conditions, a fire may already have begun. mechanical systems, and combustion safety in Spring Training Camp is organized by
Concern? home appliances. Specifics will depend on Enerquality Corporation and Mcleod Associates
An arc fault is an unintended arc flowing through What Do AFCIs Do? where the experts leading the discussions and in association with the Ontario Home Builders
an unintentional path. Common causes of arc Arc fault circuit interrupters are able to detect the participants take the topics. We will also Association, Solplan Review, and the University
faults in a home include: certain types of dangerous arcing conditions. They visit some world-class research facilities in of Waterloo. Sponsors include the EnerQuality
* Loose or improper connections, such as elec­ look and work just like conventional circuit break­ Ottawa that have been so instrumental in the Corporation and the McLeod Associates in
trical wires to outlets or switches ers and fit into electrical panels in the same way. development of Canadian building science association with OHB A, University of Waterloo,
* Frayed or ruptured appliance or extension They protect against overloads and short circuits research. At press time all details have not Solplan Review, NRCan, CMHC, and NRC.
cords and also electronically sense arcing. AFCIs were completed, so we can’t give you names of the
* Pinched or pierced wire insulation, such as a first developed by electric utilities to deal with speakers. For more information, and to register,
wire inside a wall nipped by a nail or screw or a downed power lines. We are putting finishing touches on an all- contact Susan Woolsey at the OHBA, 20 Upjohn
chair leg sitting on an extension cord Arc fault circuit interrupters are now required in inclusive package that includes an opening Rd, Toronto, ONM3B 2V9; fax [phone];
* Cracked wire insulation stemming from age, the Canadian Electrical Code for installation on all reception on Sunday night, the seminars Mon­ e-mail: swoolsey@ohba. ca
heat, corrosion, or bending stress bedroom circuits. State Farm Insurance suggests
* Overheated wires or cords that AFCIs be used in older homes that may have Home Construction Manager Wanted
* Damaged electrical appliances aged or damaged electrical wire insulation. Others WISA Healthy Homes is a small-volume custom home be familiar with computers and job costing, scheduling and
* Wires or cords touching vibrating metal have suggested that AFCI may be a good safety design-build contractor. We provide complete“One-Stop-Shop'’ estimating software
The Technical Research * Electrical wire insulation chewed by rodents feature for use in homes that have aluminum wiring. services to deliver R2000 energy efficient, durable, healthy and «■ have a good understanding of contracts, plans, and specifica­
Committee (TRC) is the competitively priced tailor-made homes, giving clients a real- tions, and be knowledgeable about construction methods, materials,
industry's forum for the and regulations, and identify any discrepancies in construction docu­
Arcing generates high intensity heat, which can Arc Fault Circuit Interrupters vs. Ground home building choice in the easiest, most hassle-free, and
exchange of information ments
on research and easily ignite combustible materials. Arcs can Fault Circuit Interrupters rewarding way possible. Because we project a sustained have a Bachelor’s degree in building science, construction
development in the happen anywhere in the electrical system - in the AFCIs are not to be confused with ground fault increase in the demand for our services, we are seeking an management or civil engineering, and related experience in the industry
housing sector. fixed wiring behind the walls, in extension cords, circuit interrupters or GFCIs. Both are safety exceptional individual to be our Home Construction Manager. fF’ be flexible and able to work and lead effectively in a fast-paced
Canadian Home This individual must be exceptionally well-experienced, environment
Builders’Association, within receptacle boxes, or in the end appliance. devices but each has a different function. GFCIs proactive, resourceful and focused; an exceptional problem «■ be prepared to be “on call" to deal with delays, bad weather or
Suite 500,150 Laurier When wire insulation breaks down, the arcing provide protection from the serious consequences solver, leader and team player who will bring goodwill to each emergencies at job sites
Ave. West, Ottawa, Ont. circuit becomes so hot that parts of the wire can of electric shock. AFCIs are intended to address working day. We at WISA will offer exceptional opportunities in «■ be decisive and able to work well under pressure, particularly
K1P5J4 soften and sputter by the force of the arc, which can fire hazards. return. when faced with unexpected demands, occurrences or delays
Tel: [phone] «■ work well with colleagues, workers, trades, suppliers, consult­
Fax: [phone] then ignite nearby combustible materials. AFCIs can be installed in any 15- or 20-ainpere The successful candidate will: ants, architects, engineers, inspectors and clients
e-mail: [email protected] It is estimated that on a typical day in Canada branch circuit and are available as circuit breakers evaluate construction methods and ensure that all work is completed be able to co-ordinate several major activities and meet multiple
www.chba.ca there are 40 fires of electrical origin, one third of with built-in AFCI features. O on schedule, in a cost-effective and environmentally responsible manner objectives (including green building practices) at once
schedule construction site activities into logical, specific steps and be able to analyze and resolve problems, prevent problems from
budget the time required to meet established deadlines escalating, acknowledge mistakes, fix them and share the experience
Building Science Spring Training Camp selects co-ordinate trade contractors and oversee their performance be able to seize opportunities to improve the quality of WISA work
determine labour requirements and, in some cases, supervise or and sen/ices
April 18-20, 2004 monitor worker hiring and dismissal
oversee the delivery, use, salvage, and recycling of materials, tools Please forward your resume with a covering letter stating
Shake off the cobwebs after winter hibernation was overwhelmingly positive. Planning is well and equipment; construction quality, worker productivity, safety and pollu­ expected remuneration to:
tion control
underway for this year’s spring camp which is to
Last year Tex McLeod, an Ontario housing review engineering and architectural drawings and specifications to Wilma Leung
consultant and R-2000 trainer, had the idea for a be held in Ottawa, where we can take advantage ensure compliance with plans and schedules WISA Healthy Homes
of the technical resources available there. A «■ check compliance with building codes, safety and other regulations, #80-1089 West Broadway,
building science spring camp. The event was a
post conference day (April 21) will offer an and with environmental best practices and guidelines Vancouver, B.C., Canada V6H 1E5
sellout, despite a late burst of winter that made
optional program of building science activities track and control construction costs against the project budget to E-mail: [email protected]
access over icy roads hazardous. Feedback from avoid cost overruns
Fax: [phone]
in the Ottawa area.
participants who came from all parts of Canada
WISA Healthy Homes: Where R2000 is the Minimum Standard
14 SOLPLAN REVIEW January 2004 SOLPLAN REVIEW January 2004 15
NIC CMC
IRC Studies on the Control of Rain Penetration
Benefits of a Drained Air Space Behind the component of the
in Exterior Wood-frame Walls the Cladding assembly acting as
One aspect of the laboratory investigation second line of defence, be
A key requirement for exterior walls is the force to drive it inwards and an opening provid­
examined the benefits of a drained clear cavity it a water-resistive
control of rain penetration. Lack of attention to ing a path for water to flow. The forces acting
behind the cladding. Results showed that a clear membrane or a board
design principles or failure to implement them on the facade to cause water penetration are:
drained air space behind the cladding consider­ stock material, be
By Michael A. Lacasse
in the detailing of the wall assembly may lead to gravity, capillary action, air pressure difference,
ably reduced the water load into the stud cavity attached in a water-
premature deterioration of wall elements. Over surface tension, and kinetic energy of the
This article is an extract of the wall. Figure 3 shows a sectional view at a resistant manner to
from a paper and talk the past four years, NRC’s Institute for Research raindrops. Two key climatic factors to include in ventilation duct penetration of a wall test penetrating elements
authored by Dr. Michael in Construction carried out experimental work a laboratory testing program are wind speed and
specimen having two different cladding configu­ such as ventilation ducts,
Lacasse, presented at IRC's on the watertightness of 17 wall assemblies to rainfall intensity. Higher wind speeds cause a
rations: one with a clear air space (use of electrical outlets and
Building Science Insight determine how deficiencies in the wall systems greater air pressure differential across the wall
vertical furring strips) and one without it. Water windows, to ensure the
2003 seminar series held might affect the water deposition rate into the and cladding elements, which will cause the
infiltration into the stud cavity was permitted by continuity of this second
across Canada from
stud cavity. This research was part of the water present at deficiencies in the cladding
October 2003 to January leaving out sections of sealant at the junction line.
Moisture Management for Exterior Wall assembly (e.g., missing length of sealant) to
2004. Dr. Lacasse is a between the wall and the ventilation duct,
Systems (MEWS) project (Solplan Review, No. infiltrate the layers of the wall. Deficiencies are
senior research officer in providing a path for water to get in. A large Conclusion
113, November 2003). often found at the interface between the wall and
the Building Envelope and portion of the infiltrating water was drained into Including an air space
Figure 2. IRC researchers use the Dynamic
Structure program of the The wall specimens combined different types openings for windows, ventilation ducts and the clear air space behind the cladding, where it behind the cladding and
Wind and Wall Testing Facility to expose wall
National Research of cladding, sheathing membranes and boards, electrical outlets and thereby potentially offer a
could be evacuated outside through the use of ensuring the continuity of
specimens to wind-driven rain loads and
Council's Institute for and insulation of typical use in North American direct path for water entry.
proper flashing techniques. The water load into the water-resistive layer
Research in Construction. construction. Cladding types included stucco, investigate where (and how much) water gets
the stud cavity was about 10 times less for the on the outside of the stud
deposited into the layers of the wall assembly.
brick veneer, hardboard and vinyl siding, and Simulating Wind-driven Rain in a
specimen containing a drained cavity (Wall B) cavity are two design
The facility comprises a water spray system that
exterior insulation and finish systems (EIFS). Laboratory Setting
as compared to the one without it (Wall A). strategies that promote
simulates the action of rain; a blower to
Certain cladding systems included a clear Watertightness performance testing should be
In Canada, the installation of a clear drained the long-term service life
simulate wind effects; and a piston that,
continuous air space. Sheathing boards included based on climatic design criteria such as those
cavity behind cladding systems has been consid­ of the structural elements
through its cyclic action, varies air pressure to
glass mat gypsum board, oriented strand board given by ASTM and the rainfall intensities and
ered a best practice in the application of the of wall assemblies. O
simulate wind gusts.
(OSB), fibreboard and XPS (extruded polysty­ wind speeds expected in a given location. In
rainscreen principle that was formulated more
rene) foam sheathings (Figure 1). Deficiencies IRC’s test facility (Figure 2), a continuous spray
than forty years ago. It provides a level of
included discontinuities of rain penetration of water is applied on a wall specimen while
redundancy in the wall assembly for rain
control elements at junctions with windows, subjecting it to a specified air pressure differen­
penetration control because of its capability to
ventilation ducts and electrical outlets, such as a tial. This test is useful for determining loads at
provide three key control mechanisms: drainage
missing length of sealant or construction tape. which failure may be observed, the nature and
of incidental water entry, a capillary break to
Researchers subjected each wall specimen to location of the failure, and insights into the
trapped water, and its potential for reducing
simulated wind-driven vulnerability of different wall components to
pressure differentials across the cladding.
rain of various water entry.
Interestingly, the IRC test results also indi­
intensities in ERC’s For the MEWS project, the watertightness
cated that even with the presence of this clear,
unique Dynamic Wind performance test used a series of different spray
drained cavity behind the cladding, a small
and Wall Testing rates and air pressure differentials to simulate
quantity of water could still find its way into the
Facility (DWTF) and extreme wind-driven rain intensities. These
stud cavity. The path for water leakage was
investigated how much included spray levels typically used in industry
provided by the presence of discontinuities at the
water got deposited in performance tests and a range of pressure
junction between the ventilation duct and the
the stud cavity under a differentials representing expected occurrences
water-resistive membrane acting as the second
variety of climate loads of elevated wind speeds across Canada and the
line of defence against rain penetration. Even
(Figure 2). United States. In a typical test, deficiencies, such Figure 3. Cross-sectional view of two siding-clad wall sections at the
when an air space was present behind the
as missing sealant at interfaces with windows, ventilation duct penetration. Wall A did not have a clear continuous air space
cladding system, it was beneficial to ensure that
Conditions for Rain ventilation ducts and electrical outlets, were over the height of the wall, whereas Wall B included a clear 19-mm air space
Penetration incorporated in a test specimen and water was
For water to enter sprayed on the wall. The water entering through Further reading
into the wall assembly, the gaps was collected in troughs located in the Exterior wall design using the rainscreen principle has been documented in several IRC Construc­
Figure 1. Full-scale 2400-mm by 2400-mm test three conditions must stud cavity directly below the penetrating tion Technology Updates, such as nos. 9, 17, 23 and 34. These can be downloaded from the IRC
specimens shown at different stages of be met: the presence of component. Web site: http://irc.nrc-cnrc.gc.ca/catalogue/ctu.html
fabrication. Four of the 17 wall specimens water on the facade, a MEWS project reports and related articles can be found on the IRC Web site at
included brick veneer. http://ire. nrc-cnrc.gc. ca/bes/mews/index. html
Itl National Research Conseil national
Council Canada de recherches Canada
16 SOLPLAN REVIEW January 2004 SOLPLAN REVIEW January 2004 17
Energy Answers
I want to heat domestic hot water using a nominal (5/8-inch outside diameter) pipes, with
flow rate per pipe is cut in half. If we use two
copper coil passing through a large water tank each pipe 75 feet long.
75-foot lengths in parallel, the NTU value is
filled with solar heated water. How big a copper A Canadian solar installer that I spoke with
1.85 and the effectiveness is about 82%. In order
coil should I use? said that he installs a 60-foot long 3/4-inch
to get 90% effectiveness, the length of the pipes
nominal pipe.
would have to be increased to 93 feet each, or
The diagram in figure 1 shows the applica­ Three answers to the same question.
186 feet in total.
tion. On my own house, I have such a solar tank I went back to the theory to see if some
In order to get the effectiveness up to 99%,
with a copper heat exchanger to extract heat for answers could be garnered.
the domestic hot water. The heat exchanger is Ideally, you would want the water exiting the Figure 2 Heat Exchanger Effectiveness vs- NTU you would have to double the length of pipe
compared with the 90% effectiveness. Diminish­
shown on the right-hand side of the large pipe equal in temperature to the tank tempera­
ing returns definitely comes into play with heat
storage tank. With this type of heat exchanger, ture. Unfortunately, you would need a very long BTU units, according to my old university heat
exchangers.
there is only one pass of the cold water through pipe to achieve this. The attached graph shows transfer textbook. Note that this is a very small
I would argue that it is worth going for the
the coil. Many other types of heat exchange the effectiveness of a cross-flow heat exchanger resistance compared to an inch of glass fibre
90% effectiveness heat exchanger. Collected
Rob Dumont systems recirculate the fluids (as is shown on the with one fluid mixed as a function of a param­ insulation, which has an insulating value of
solar energy is a precious commodity, and
glycol-to-water heat exchanger on the left-hand eter called the Number of Transfer Units (NTU). about R3.5. Water is a much better conductor of
extracting as much energy as possible is desirable
side of the large tank.) For this type of heat exchanger, you want to get heat than air, thus the low thermal resistance.
to minimize the auxiliary heat that has to be
One of the interesting tilings about this an effectiveness value close to 100%. In general, However, the low resistance of the copper coil/
supplied by conventional sources. Designing for
question is that there is no one right answer. It a higher NTU value will give you a higher water combination is not zero.
90% effectiveness at the highest flow rate ensures
is akin to the question of how much life insur­ effectiveness value. Note that there are dimin­ If we assume a 3/4-inch copper pipe, 100 feet
a higher effectiveness at lower flow rates.
ance one should have, or how much insulation ishing returns, however. Doubling the NTU long, with a water flow of 3.3 imperial gallons per
I checked with a pipe supplier, and a 3/4-inch
one should have in the attic. value does not double the effectiveness. minute (1980 lb/hr), with a thermal resistance as
soft copper pipe 150 feet long costs about $200.
I checked with a number of sources to see The NTU is defined as follows quoted above, the NTU value is equal to 1.5.
Although not cheap, this pipe cost is rela­
their recommendations. Here they are: With that NTU value, the effectiveness is
In The Solar Water Heater Book, Bryenton, NTU = A equal to about 78%. In order to get an effective­ tively small compared to the cost of a good solar
system (approximately $4000 to $5000) and will
Cooper, Mattock and Lyster recommend a 3/4- (R*M*C) ness of about 90%, the pipe would have to be
inch nominal (7/8-inch outside diameter) soft Where lengthened to about 150 feet. ensure that a high proportion of the solar heat is
well used. O
copper pipe 100 ft long. A = surface area of the heat exchanger An alternative approach is to use two '/$-inch
In the Davis Energy Group design manual for (square feet or square metres) copper pipes in parallel. With this approach, the
large (500 gallon plus) membrane-lined solar R= thermal resistance between the two
storage tanks, they recommend 2 parallel '/ -inch fluids (hr-ft2 F/Btu or m2 K/watt)
2
First Canadian Residential Fuel Cell
M= mass flow rate (lbs water per hour or
kg/second)
Demonstration
C = specific heat of water (1.0 Btu/lb-F or A 5-kilowatt fuel cell manufactured by Fuel Cell
Ssoellaerc tpivane eslusr (f1a5c.e6 amc*ti)ve Electric water heater 4180 Joules/kg C) Technologies Ltd. will be installed at the Canadian
(back-up) 182 litres with Centre for Housing Technology (CCHT) at the furnaces, it converts hydrocarbon fuels directly
R-28 (RSI 4.6)
insulation To get a high NTU value in this type of National Research Council campus in Ottawa. It into electrical energy and heat but without using a
demand heat exchanger, you must use a large has the capacity to generate 5 kW of electricity and combustion process. As a result, the fuel cell is
surface area A or a low flow rate M. 6 kW of heat on-site for home use. Natural more fuel-efficient and has lower emissions than
In a typical house, the maximum mass flow Resources Canada is contributing funding to the conventional power sources such as internal com­
rate of hot water is about 15 litres/minute (3.3 project to demonstrate the first installation of a bustion engines, gas turbines, and steam turbines.
imperial gallons per minute) from a single tap. I residential fuel cell in a house in Canada. For every 100 units of energy that enter the fuel cell
checked this recently using the second hand on The solid oxide fuel cell unit can use a variety of system, the appliance produces 50 units of electri­
my watch and a milk container on the hot water fuels such as natural gas, methanol, hydrogen, cal power and 50 units of energy liberated as heat.
tap in our bathtub at home. The kitchen sink propane, and heavier hydrocarbons to generate Some of this heat is required to keep the fuel cell at
hot water flow was 4 litres/minute. The hot electricity and heat without combustion. This operating temperature and the remaining heat can
water draws from a laundry machine or a co-generation capability creates an overall energy be used to heat water and/or air.
dishwasher are also about 4 litres/minute, efficiency of about 90%, when all energy losses The CCHT house is a technically sophisticated
according to a recent publication. throughout the system are considered. This com­ facility that can simulate occupancy. A virtual
water storage tank
6,000 litres with R-20 The thermal resistance for the heat transfer pares to an operating efficiency of about 35% for family makes demands on the house as its members
(RSI 3.5) Insulation
from the water in the large tank into the water conventional power and heating systems. carry on normal household activities. This means
Figure 1. Solar System with large water storage tank and copper heat in the copper pipe is around 0.0066 hr-ft2-F/ The solid oxide fuel cell system operates at that the fuel cell will have to respond automatically
700°C to 1000°C. Similar to existing oil and gas to the demands of a typical household during each
transfer coils
18 SOLPLAN REVIEW January 2004 SOLPLAN REVIEW January 2004 19
of the winter, summer, and shoulder seasons. readily available fuels to provide electricity and Maintenance and Replacement Parts
Over the term of the demonstration, the exper­ heat for stationary applications such as houses, for Saskatoon-built vanEE®,
tise of CCHT’s personnel and the monitoring small commercial enterprises, industrial applica­ ENEREADY™ vanEE® and ENEREADY™
capabilities of the CCHT facility should provide tions, and remote sites. ______Heat Recovery Ventilators
feedback on the operation of the residential fuel For a homeowner, the expected payback period
cell. on a commercial system is estimated to be four
The fuel cell unit is a solid oxide fuel cell power years. The size of the 5 kW commercial system will
system manufactured by Fuel Cell Technologies be similar to that of a home furnace. Units will
Ltd. of Kingston ON. FCT is a leading developer initially be available in low volume production.
For further information
of small-scale power systems (1 kW to 50 kW) that The price is expected to approach $1,000 per kW
contact: I I
provide on-site generation of electricity. Their when high volume production and full coinmer-
www.fct.ca > Electrical Parts
power units can operate on any one of several calEatxn aoeundaw^. 0
> Summer By-pass Cores
> Defrost Damper Motors
> Motors, Wheels, Housings
MemBrain™, The Smart Vapor Retarder
' > Sponge Airseal Rings for Grills ■
MemBrain™ is a unique vapor retarder made This product can be used in place of tradi­ > Standard & Mid-Efficient Filters
from a polyamide (nylon-6) film that changes tional vapour retarders with unfaced fibre glass
permeability according to relative humidity. It insulation to provide an insulation system that is
varies from less than one perm (57ng/Pa-s-m2) ideal in some of the more severe climate condi­
at 20% relative humidity (RH), as would be tion areas in terms of both temperature and
found during winter months in a cold climate, to humidity. It protects against condensation in the ENEREADY
more than 10 perms (l,144ng/Pa-s-m2) at 70% winter, while allowing for the drying of the
ENEREADY PRODUCTS LTD. PHONE [phone] FAX [phone]
RH and over 20 perms at 95% RH. This process building envelope in the summer, when humid­
#4 - 6420 Beresford Street, Burnaby, British Columbia CANADA V5E 1B6
allows closed building envelope systems to ity levels are typically much higher. The 2-mil- I
increase their drying potential with seasonal thick, high-tensile-strength sheet is stronger and
climatic changes. MemBrain reacts to relative more durable than standard 6-mil polyethylene.
humidity by altering its pore size, allowing This product is not for use with specialty-
Solplan Review Back issues
water vapour to pass through it. When condi­ conditioned spaces where relative humidities are
tions change and relative humidity increases intentionally kept at more than 50% or spaces
A limited number of back issues are available,
above 60%, the pores in the material expand and such as indoor spas or swimming pools. Its at a special price of $5.50 each (plus 7% GST).
its permeability increases. This transformation performance in rooms with short peaks of high Bundle special: a random selection of back
permits drying to occur in either direction, humidity, such as bathrooms and kitchens, will issues (minimum 22 copies) are available for
through vapour diffusion. Thus, its lowered not be affected because of the buffering action of only $60.00 (plus 7% GST)
Solplan Review
resistance value supports the drying process, interior finishes.
Box 86627 ( ^
decreasing moisture accumulation within the Interior finish materials and cavity-fill North Vancouver, BC V7L 4L2 K. W. DOORS & WINDOWS
construction and potential moisture damage. insulation must also be highly permeable (for
e-mail: [email protected]
example, unfaced fiberglass and vapor-perme­
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able paints). The diying benefits of MemBrain ♦ Eclipse Folding Door Systems
energy efficient, sustainable, and healthy buildings
will diminish with the use of low permeance
design & consulting services ♦ Douglas Fir Doors <& Windows
finishes so it should not be used where low
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SuperE™ House Program Design Professional wallpaper or vapour retarder paints are used. □ Full Spectrum solar simulator
This is the smart vapour barrier we featured
Richard Kadulski Architect □ -20° C to 50° C with full sun Phone/fax: [phone]
in Solplan Review (No. 108, January 2003), and
□ RH, Wind, Solar & Air temp,
is now being manufactured and marketed in 1-800-477-1577
#204 - 1037 West Broadway control
North America by CertainTeed Corporation ISO/IEC 17025
Vancouver, B.C. V6H 1E3 Accredited Testing □ Solar Equipmen^Building Visit us at
Tel: [phone] iMlwratory Products/Automotive/
Information: www. kwc/oorsandwindows. com
Fax: [phone] MIL-STD-810
Phone: [phone], [email protected]______________ l-866-BODYCOT(BJ
e-mail: [email protected]
Toll-free: 800-233-8990 Drive-in solar environmental chamber \______________________________________________________y
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