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OCR for page 516
APPENDIX B
ESTIMATING THE I~=T OF "SID~IAL
ENI3~;Y~CONSERVATI~ ITS ON
AIR QuArrlqr: A lIYPaDIErICAL CASE
BYP=~IC" CASE ST=Y
Two of the simplest and most cost-effective methods of reducing the
energy consumption of a residence are to increase the insulation and to
decrease air inf filtration. However, infiltration is she primary source
of ventilation for residences, and reducing it may adversely affect air
quality. Therefore, although caulking and weatherstripping ~ home may
reduce energy consumption, they may also adversely affect the health
and reduce the comfort of the occupants, unless alternative methods of
controlling air quality are applied.
Attempts to estimate the impact of residential energy-oonservation
measures on air quality in the home and, consequently, on Me health
and comfort of the residents are fraught with difficulty. Host
troublesome in the issue of incommensurability: one cannot confidently
compare the dollar costs of insulating a house and the associated
reductions in fue' bills with the essentially nonquantifiable potential
adverse effects ^ sir quality, health, and comfort. Furthermore,
numerous assumpt; ns must be ~de. Some of the assumptions are
relatively reliable; for example, demographic studies can provide
evidence on average family size, lifestyle characteristics (such as
smoking habits), and proportion of homes with ~ particular applim-.~e
(such as a gas oven}. Other a~ssu~tions may be based on evidence and
experience from the building trades--for example, the effectiveness of
caulking the windows o~ a home. (engineering analyses of related
interactions have bee;- performed. ~ Assumptions concerning the air
quality in homes before and after the institution of energy-
conservation measures can be based on evidence now being accumulated or
on data already in hand.
The following case study is an Invalidated example of the type of
analysis that might be considered to assist in Eking decisions
concerning energy conservation versus indoor air quality. It i8
proposed not as ~ solution to the analytic problem, but as an approach
Subject to further study and refinement. As ~ discussion piece, it may
assist in identifying the types of data needed for analysis, the Host
appropriate mathematical models, and, most important. the assumptions
S16
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517
that may be validly applied. The reader Ant be aware that the models
presented here have not been validated or tested in practical cases to
determine their effectiveness in predicting results. This presentation
i s for the purpose of illustration and discussion of a possible
approach.
EXISTING CONDITIONS
To evaluate the possible impact of energy-conservation measures on
ingle-family residences, conditions in a hypothetical home in central
Iowa are simulated. It is a 15-yr-old, split-level house with a
basement and an attached two-car garage. The total heated floor apace
is 2,100 ft2, of which 700 ft2 is below grade. The house is of
wood frame construction on a concrete-block foundation. It has
insulation values of R7 in the walls and R11 in the ceilings,
double-pane windows, and an infiltration rate of 0.8 air change per
hour (ach) with windows and doors closed. The house is heated with a
natural-gas, forced-air furnace and cooled with an electric central
air-conditioning system. The house is occupied by a family of five: a
father, who smokes cigarettes; his wife; her mother; and two children,
2 and 10 yr old. Appliances include a natural-gas stove, a gas
clothes-dryer, an electric washing machine, an electric dishwasher, and
a gas water-heater.
All this is assumed to be fairly typical of a middle-class family
in central Iowa. These conditions were used as the basis of an energy
and Virtuality analysis of the home. The home was then reanalyzed for
two mutually exclusive conservation measures, to determine the changes
in energy consumption and air quality. The first measure was to
reinsulate the walls to a value of Rll (1 additional inch of cellulose
insulation) and the ceiling to Rl9 (2 additional inches of cellulose
insulation); this measure was assumed to be accompanied by a reduction
in the infiltration rate to 0.5 ach. The second measure was a higher
insulation alternative in which the walls were increased to Rll and the
ceiling to R30; the infiltration rate was assumed to decrease to 0.3
ach. Two other independent measures were analyzed for air~quality
impact: the installation of an electronic air-cleaner and the
cessation of cigarette-smoking. A summary of these alternatives is
shown in Table B-1. The results of the energy-consumption and
air-quality analyses for these alternatives were either directly or
indirectly used in an economic model to determine the rate of return
available to the homeowners for the various alteratives.
CASE ANALYSIS
Energy Consumption
The annual heat loss and heat gain for the building were calculated
from a simple steady-state model, with an overall heat-transfer
coef f icient and annual degree-days for heating and cooling. The model
was exercised for each of the three cases listed in Table B-2. Values
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TABLE B-1
Summary of Scenario Analyzed tn Hypothetical Example
Insulation Infiltration Air
.
Condition Case Wall Ceiling (ach) Cleaner Smoker
. . ,
Existing P R-7 R-11 0.8 No Yes
Alterna- A-1 R-ll R-19 0.5 No Yes
tive A-2 R-11 R-19 0. 5 Yes Yes
B-1 R-ll R-30 0.3 No Yes
B-2 R-ll R-30 0. 3 Yes Yes
B-3 R-ll R-30 0.3 No No
TABLE B~2
Insulation Alternatlves
R Value (h · ft2, °F/Btu)
C_ Description ~ Cats Infiltration
P Existing condition 7 11 O. ~
A Low insulation 11 19 0.5
B High insulation 11 30 O. 3
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519
for the overall heat-transfer coef f icient (UA) were calculated in
accordance with the method used by ASHAAE; 2 the results are listed in
Table B-3.
The annual degree-days~i are based on 30-yr averages for Des
Moines, Iowa, and are based on 65°F. The values used for heating and
cooling were 6, 710 and 928 degree~days/yr, respectively. These values
for the overall heat-transfer coefficient and degree-days were used in
the following equation to calculate the annual heat loss and heat
gain: Q ~ 24 (UA) (DD), where Q ~ annual heat loss or heat gain {Btu),
UA - overall heat-transfer coefficient (Btu/h - F), and DD - annual
heating (cooling) degree-days. The results of these calculations are
also listed in Table B-3.
To estimate more accurately the energy consumed for heating. a
seasonal furnace efficiency had to be determined. This efficiency
depends on the steady-state efficiency of the furnace and the amount by
which it is oversized. As the beating load is reduced, owing to the
conservation measures, the seasonal furnace efficiency is also
reduced--by approximately 2% for each 10% oversize increment (John E.
Janssen, personal communication). The seasonal furnace efficiencies
used for each of the cases are shown in Table B-4. By dividing these
efficiencies into the heating loads, the energy input to the house can
be calculated; by applying the energy conversion factor for natural gas
{100,000 Btu/ccf}, the annual fuel consumption can be determined.
These results are shown in Table B-4.
The annual electric consumption for cooling is calculated from the
following equation: Qelec ~ 1.3Q/(COP)~3,412), where Qelec
electric-energy consumption (kWh), Q ~ sensible heat gain (Btu), 1.3
adjustment for latent load (assumed to be 30t of sensible load), COP
seasonal chef f icient of performance (assumed to be 2 . 5 ), and 3 , 412 -
conversion factor (Btu/kWh). The result" of these calculations are
listed in Table B-5.
Air Quality
The air quality in the conditioned space was evaluated for the
three cases and for the two independent measures (installation of an
air-cleaner and cessation of cigarette-~moking). The contaminants
evaluated were carbon monoxide, nitrogen dioxide, formaldehyde, radon,
and Despicable suspended particles (RSP), which include dust and
cigarette smoke. The models used in these evaluations are simple ones
that have not been experimentally validated. There is ~ need to
validate these findings not only experimentally, but also in practical
test cases. The objective of there analyses was to determine the
sensitivity of various parameters to the contaminant concentrations,
and absolute values may only be assumed an approximate.
General Models. The general model used to calculate the
contaminant concentration profiles (except that for radons ts anon
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520
TABLE B-3
Overall Heat-Transfer Coeff icients
Heat Lose, Heat Gain,
Case Description UA (Btu/h · OF) 10° Btu/yr 10° Btu/yr
P Existing condition 737 il9 16
A Low insulation 582 94 13
B High insulation 502 81 11
TABLE B-4
Annual Natural-Gas Consumption for Heating
Seasonal
Heat Los s, Furnace Natural-Gas Consumption
C_ 10 Btu/yr Ef ficiency ~7
P 119 0.60 198 1,980
A 94 0.56 168 1,680
B 81 0. 53 153 1, 530
TABLE B-5
Annual Electricity Consumption for Cooling
Hew Gain, Electric Consump-
Case 10 Btu/yr tion, kWh
P -16 2,400
A 13 2, 000
B 11 1, 700
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521
Chemically in Figure B-1. The 888umption8 and nomenclature us" are
as follows:
· Equal inf titration and exf iltration rates (Vi ~ .
· Uniform contaminant concentration (C) in the occupied volume
.
· Constant outdoor contaminant concentration (CO).
· An electronic air-cleaner with an RSP-remova1 efficiency.of
c, operating continuously with a constant-supply airflow rate (~ ~ .
· A net contaminant generation rate {N)-~decay rates are
neglected. A mass balance equation that describes the sir quality of
the house is given as follows:
· · ~
Vi (CO - C) + Vs (Cs - C) + N 2 V6C
and
CS ~ (1 - c)C.
This set of equations can be combined and rearranged to give the
following differential equation for the indoor concentration (C):
VdC + (Vi + £V5 ~ C ~ N +
at
rate of dilution
change and
in air removal
quality ef feats
The solution of this equation in:
V:CO
generation
and
inf titration
effects
(1)
(2)
C = Aft _ ( i 0 )] exp ~—( V ) 41 + (I) ' (3)
where C i is the initial condition for the concentratio.n . This
equation is valid only for constant values of N. vi ~ hi, c, and
CO. For this analysis, the generation rate is assumed to vary by
steps. Therefore, Equation 3 can be applied to each step separately,
with the initial condition for a given step being the final
concentration of the previous step.
A slightly different model is used for radon, because of the
assumption of different concentrations above and below grade. The
Mel is shown schematically in Figure B-2 and includes an air exchange
(dab} between the above- and below-grade spaces and no generation in
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522
f
~ air cleaner, ~
C
8 S
V8, C
C, V
~1
1 ~
V1, Co
FIGURE B-1 General air~quality model for hypothetical single-family
residence.
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523
above grade
ca ~ ma
Gibe CO I
I_
Gabs Ca
] L
Via, CO Cb' Vb ~ N
1
Vab. Cat
FIGURE B-2 Radon model.
Vib, Ca
1
—Via Cb
$
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524
the above-grade space . All concentrations, air-exchange rates, and the
generation rate are assumed to be constant, to give the following aces
balances:
· · ~
below: Vib{Cb - CO) + Vab (Cb ~ Cal A' and
above: Via (Ca - CO) ~ tab (Ca ~ 4) O.
These equations can be solved ~ ieoltaneoualy for the above- and
below~grade radon concentrations (Ca' Cb):
C, = (V V V V V V ) N + CO ,
(5a)
b (ViaVjb ~ Vj,Vab ~ VjbV,b) ° (5b)
Generation Rates. The contaminants are generated front several
sources, including cooking {carbon monoxide, nitrogen dioxide, and
formaldehyde), Smoking (carbon monoxide, nitrogen dioxide,
f ormaldehyde , and RSP I, mater ial outgassing ~ formaldehyde and radon),
and indoor dust generation (RSP). The assumed daily generation
prof iles of these sources are shown in Figure B-3. The generation
rate for cooking is assumed to be constant and occurs at 7 a.~., 12
noon, and 5 p.m. for 15, 30, and 60 min. respectively. Smoking occurs
at 7 s.m. and 7:30 a.m. and every half-hour from 5:30 pa.. to lie 30
pa.., inclusive. The duration of each occurrence of smoking is 10
min. ~ Material outgassing is assumed to be constant throughout the
day. Indoor dust is generated from 7 a.m. to 11 pa.., prisurily acing
to resuspension of particles from carpeting. The generation rates for
all these sources are listed in Table B-6, with the outdoor
concentrations .
Concentration Profiles. To determine the daily indoor~ont~inant
-
concentration profiles' a daily generation prof ile for each
contaminant (carbon monoxide, nitrogen dioxide, formaldehyde, and ESPY
was determined by supine the generation rates of the appropriate
sources. This provides an overall generation profile consisting of
step changes to which Equation 3 can be applied, as discuss
previously. The solution is started by choosing an initial condition
(usually Ci ~ CO) at the beginning of a period (usually 7 ape.)
and applying 13qustion 3 to each interval of constant generation rate.
The solution proceeds throughout the day and is repeated until no
changes occur in the initial conditions from one day to the next.
The concentration profiles for carbon Monoxide, nitrogen dioxide,
and formaldehyde are shown in Figures B-4 through B-6 for cases 8, A,
and B (0.8, O.S, and 0.3 ach). Figure B-7 shows the Patina
concentration profiles for RAP for each of the infiltration rates and
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525
sutcria1 a:tgass~g-.
indoor dust
Ga~erat ion
Rates
N
-
coo~tclug
|~3k$~g ~ woke,
l
0 6 12 18 24
Time, has
FIGURE B-3 Generation profiles of indoor pollutants for hypothetical
single-family residence.
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S26
TABLE B-6
A88~P~ Contamtnant Source S~mrA-y
Outdoor Indoor Totd1
ConcentratiQn Generation Productlon,
Contaminant (CO),a ug/m~ Indoor Source Rate (~), ug/h ~e/d
Carbon 1,500 Cigarettesb 31,000 70
monoxide CookingC 1~000~000 1~750
Nitrogen 50 Clgarettesb 474 1
dioxide CookingC 57,000 100
Formaltehyde 5 -Cigarettesb ~ 684 2
CookingC 10~000 18
Materi~ sd 11~000 264
Respirable 2oe Cigarettesb 192,000 450
particles Indoor activitye 8,600 140
Radone O Above grade O O
Below grade 256,000f 6,140g
aSee Hollowell et al.4
bsee Woods.l2
CCalcula ted from data in Hollowell et al.;6 oven at 350 °F (177.C).
dCalculated from data in Hollowe11 et al.
eAssumed values
fpCi/h.
gnCi/d.
.
OCR for page 528
528
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OCR for page 532
532
a fourth profile for the effect of the electronic air cleaner ( e
O. 93, Vs ~ 1,000 cfm) .* The infiltration rate has a negligible
effect on the concentration profile after inclusion of the
air-cleaner; therefore, only one profile for all infiltration rates is
s hown .
The cessation of cigarette-amoking has no significant effect on
the carbon monoxide, nitrogen dioxide, or formaldehyde concentration
profiles. However, it does have a significant effect on RSP
concentrations, as shown in Figure B-8 for an infiltration rate of Oe3
ach.
Radon, an inert gas, is generated from the decay of radium in the
below-grade building materials {i.e., concrete).' The hazardous
radiation effects of radon are due primarily to its progeny {R~A, RaB,
and RaC). The combined radiation effect of these progeny is taken
into account with the working level (WL) defined as:' AL ~ 0.00103
RaA + 0.00507 RaB + 0.00373 RaC, where RaA, RaB, and RaC are
concentration in picocuries per liter. The decay rate of radon is
0.0075/h, which is negligible, compared with the assumed infiltration
rates of 0.8, 0.5, and 0.3 ach. Therefore, infiltration was assumed
to be the only method of radon removal in the model.
To calculate the radon concentration profiles, radiation of 0.5
and 1.0 pCi/L we" assumed for the above- and below-grade spaces at the
present condition (P). When these values are substituted for Cal and
Cb in Equations 5 and it is assumed that the outdoor radon
concentration is negligible, compared with,the indoor concentration
(CO ~ 0), values of vab ~ 8,960 ft3/h and N ~ 256,000 pCi/h are
obtained. The values for the air-exchange rate between the above- and
below-grade spaces and the radon generation rate are assumed to remain
unchanged for cases A and B. If these values are substituted in
Equations 5 with the appropriate infiltration rates, the abo~re~grad e
radon concentrations can be calculated for cares A and B; they are
listed in Table B-7.
Then, from the radon concentration, the corresponding working
levels were calculated from WL ~ 1~/100, where Rn is the radon
concentration in picocuries per liter and ~ is the Equilibria
factor, which is ~ function of the progeny concentrations., Per
test cases £, A, and B. a value of ~ ~ 0.84 was used to take into
account plateout of the progeny to the walls, and F - 0.32 was used to
take into account progeny remover with the electronic air-cleaner.
These values for F are approximate comparisons with experimental data
from Jonassen. ~ The resulting working levels are shown in Table B-7.
A major assumption is made in the remainder of this section: the
predicted values are treated as zeal pollutant concentrations. The
reader is reminded that the models used to estimate pollutant
concentrations have not been validated against measured
concentrations. All subsequent comparisons, therefore, are
constrained by this lack of model validation.
Air~quality health standards for each of We contaminants
considered in thin section are listed in Table B-8. These minimal
*From manufacturer's data for a Lennox BAC 7-20 electronic air-cleaner.
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TABLE B~7
Radon Concentrations and Working Levels
.
Above Grade Below Grade
_
Radon Radon
Eq uilibrium Concentra- Concentra-
Case Factor (F) tion, pCi/L WL tion' pCifI~ WL
P 0.84 0.50 0.004 1.00 0.008
A 0.84 0.88 0.007 1.43 0.012
B 0.84 1.58 0.013 2.17 0.018
A filtered . 0.32 0.88 0.003 1.43 0.005
B f iltered 0. 32 ~ .58 0.005 2. 17 0.007
TABLE B-8
At r~Quali ty S tandardsa
Coneaminant Concentration Time Stantard
Carbon monoxide 40 118/m3 1 h NN~QS
Nitrogen tioxide 100 ug/m3 1 yr NMQS
Total suspended particles 75 l~8/m3 14yrh NN - QQS
Forn~aldehvde 120 ug/m3 Continuous West Ger~an
Radon 0.01 WL Continuous 37 FR 25918
aDeri~red from ANSI and ASHRAE.1
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534
acceptable values are also plotted in Figures 8-5, B-6, and B-7 for
nitrogen dioxide, formaldehyde, and REP, respectively, for comparison
with the predicted indoor contaminant concentrations. The carbon
monoxide health standard greatly exceeds the predicted values in
Figure B-4 and thus are not shown there. Figure B-S shows that the
long-term standard (1 ye) for nitrogen dioxide concentration would be
exceeded for approximately ~ hid for the present condition (P),
whereas cases A and B would exceed the standard for 2 and ~ in/d,
respectively. The formaldehyde concentration in Figure B-6 would
reach 411 of the short-term standard {continuous) for the present
condition {P), 588 for case A, and 86% for case B. Figure B-7 shows
that the RSP concentrations would exceed the short-term standard (24
hi for case A during 3.5 hid and case B during 6 in/d, whereas the
present condition never exceeds this standard. The lonq-term standard
(1 yr) would be exceeded by cases P and A for 11 and 17 in/d,
respectively, and cane B would constantly exceed the short-term
standard. The inclusion of the electronic air-cleaner would reduce
the RSP concentration to a point below the long-term standard for all
cases. The cessation of cigarette-smoking without the air-cleaner
would also reduce RSP concentrations below this standard for cases P
and A. However, case B would exceed ache standard slightly for 13 h,
owing to indoor dust generation, as shown in Figure B-8 . Table B-7
shows that the abort-term standard (continuous) of 0.01 WL for radon
would be exceeded below grade for care A and above and below grade for
cane B. unless the electronic air~cleaner were used.
Economics
To perform the economic analyst`;, estimates for the installation
costs and energy-cost savings were needed for each of the conservation
measures considered. ' ' I' Present annual energy costs for natural
gas and electricity were calculated by multiplying the annual energy
requirements (Tables B-3 and B-4) by the present fuel costs in Ames,
Iowa (0.28 $/caf for natural gas and 0.057 S/kWh for electricity) for
each of the three cases (P. A, and B). Energy~cost savings for each
of the insulation alternatives (A and B) over the present condition
{P) were then calculated. The results are listed in Table B-9.
The assumed method of insulating for each of the alternatives was
to add sufficient cellulose insulation to the walls and ceiling to
obtain the desired R value. Installation and material cost e~tinutes
from ~ local insulation contractor in Antes, Iowa, were 0.20 S/ft2 Of
ceiling area to upgrade from Rll to Rl9 (case A), 0.31 S/ft2 °f2
ceiling area to upgrade from Rll to R30 (case B), and 0.50 S/ft of
gross exterior wall area to upgrade from R] to Rll (cases A and B).
With an insulated ceiling area of 1,400 It and a gross exterior
wall area of 1,576 ftZ, total installed insulation costs of S1.218
and 31.378 were obtained for cases A and B. respectively. These cost"
include S150 for caulking and weatherstripping. The only other first
cost needed in the economic analysis was S726 for the installed cost
of the electronic air-cleaner.
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535
Salvage values at the end of the economic life for the various
alternatives were also needed. The economic life used was the length
of time that the present owner would continue to own the house. At
the end of this life (assumed deco be 7 ye}, it was sssumed that the
salvage value of the insulation in terms of today's dollars would be
the same as its first cost, owing to the increase in resale value of
the house. The salvage value of the electronic sir~cleaner was
assumed to be 6250.
Rates for electricity and natural gas were assumed to increase by
18 and 22%/y:, respectively, and the Farce of general inflation was
assumed to be I0%/yr.
The economic analysis was performed for three distinct situations,
each containing two mutually exclusive alternatives, as shown in Table
B—10.
The inflation-adjusted rates of return, shown in Table 8-10, were
calculated for each alterne~i~re over present condition, as well as the
inflatzon-adjusted rate of return on the incremental costs for each
pair of alternatives.
If the homeowner's marginally acceptable rate of return {HARR)
were 10%, he should choose alternative B for situation I, alternative
A for situation II, and alternative B for situation III.
SUMMARY
Care must be exercised when considering estimates based on models
that have not been validated against measurements. In such cases, the
magnitude of the estimated values may not be equivalent to that of ache
observed values. Model estimates can be used, however, for
comparative studies to illustrate cause-effect relationships among
various parameters. From this perspective, the scenarios described in
this appendix show that energy-conservation measures may adversely
affect the indoor air quality of single-family residences. The
inclusion of the cost of sir~quality control may reduce the economic
attractiveness of some energy-conservation measures. Although these
simulations have been based on several assumptions. they demonstrate
the inter- relationships between energy conservation and indoor air
quality. In addition, the simulations of this hypothetical residence
focus attention on the factors that must be considered in the
regulation of indoor environments.
R}3CO~=ATIOttS
Some parts of the models presented here have not ban validated in
practical cases that show their utility. Further research is needed
to develop models and to test and validate their usefulness in
assessing the relationships between air quality and energy
conservation in residential and commercial buildings. A large program
should be established to develop this research tool further and to
demonstrate the usefulness of models in evaluating indoor
OCR for page 536
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TABLE B-9
Present Annual Energy Costs
C08t, $
Case Natural Gas Electricity Total
p 550 140 690
A 470 110 580
B 430 100 S30
P - A 80 30 110
P - B 12 0 40 160
e
TABLE B-10
Inflation-Ad Justed Rates of Return for Hypothetical Examples
ROR over ROR on Incremental
P coed, % Investment over A' %
Situation Alternative
1 A-1 18.3
B-1 23.0 55.1
II A-1 18.3
B-2 13.8 6.2
III A-2 9.5 --
B-2 13.8 55.1
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environmental conditions. Models may be used in the design of future
structures to ensure the health and comfort of the public and
conservation of natural resources.
REFERENCES
1. American National Standards Institute, and American Society of
Heating, Refrigerating and Air - Conditioning Engineers. ANSI/ASHRAE
Standard 62-1981. Ventilation for Acceptable Indoor Air Quality.
New York: American Society of Beating, Refrigerating and Air
Conditioning Engineers, Inc., 1980. 48 pp.
American Society of Beating, Refrigerating, and Air Conditioning
Engineers. ASERAE Handbook and Product Directory. 1977
Fundamentals, Chapter 22. New York: American Society of Beating,
Refrigerating, and Air Conditioning Engineers, Inc., 1977.
3. Engineering Research Institute. Manual of Procedures for
Authorized Claus A Energy Auditors in Iowa. Ames, Iowa: Iowa State
University Press, 1979.
4. Mollowell, C. D., J. V. Berk, M. L. 8Oegel, R. R. Mike, W. W.
Nazaroff, and G. W. Traynor. Indoor air quality In residential
buildings. In F. E. de Oliveira, J. E. Woods, and A. Faist, Eds.
Building Energy Management--Conventiona1 and Solar Approaches.
Proceedings of the International Congress, May 12-16, 1980, Povoa
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OCR for page 538
Representative terms from entire chapter:
indoor air
