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Fenestration devices for energy conservation-IV. Field study
Enqy Vol 6. No. 9. pp. 883-894. 1981 Printed m Great Bntam
03~5442/8l/OWBR3-12102.00/(1 Pergamon Press Ltd
FENESTRATION DEVICES FOR ENERGY CONSERVATION-IV. FIELD STUDYt
M. R. Energy
Center
BRAMBLEYS,
and Department
E. M. KENNEDY, and S. S.
of Applied Mechanics and Engineering Sciences, San Diego, La Jolla,CA92093, U.S.A.
(Receioed 12 March
PENNER UniverGty
of California,
1981)
Abstract-We present the results of field studies concerning the performance of sunscreens for reducing air-conditioning loads in single-family residences. We used data on houses (725) in the San Diego transition climatic region which had sunscreens installed during 1978 or 1979. The sample size was reduced by the following factors: failure by homeowners to respond to the questionnaire, houses which were not air-conditioned, failure to satisfy characteristics important for matching of houses, and criteria related to changes in occupancy. As the result, our control and test groups were reduced to 34 and 32 for the 1978 study and to 36 and 31 households for the 1979 study, respectively. For these small remaining sample sizes, the predicted small effects of sunscreens on total electricity consumption were obscured by variances in the field results. The observed large variances in the field results were produced, in large measure. by deliberate changes in thermostat settings as a response by homeowners to rapidly escalating electricity costs.
NOTATION differences
in electricity
consumption
between
the summers
before
and after
sunscreens
were installed
electricity consumption during the first summer (before installation of sunscreens) of the study electricity consumption during the final summer (after installation of sunscreens) of the study electricity consumption for air conditioning electricity consumption for uses other than air conditioning expected value of a variable; thus, E(S) is the expected value of the energy savings mean value of At/c, for the control group mean value of 11c/c, for the test group number of households in the control group number of households in the test group seasonal solar heat gain per unit area of windows seasonal heat gain per unit area of windows becausr of temperature differences between the insides outsides of buildings total seasonal heat gain per unit area of windows total seasonal heat gain per unit area of l/8% thick, double-strength single glass random variable representing the fractional change in electricity consumption random variable representing the change in electricity consumption unbiased estimator of the population v )riance for the control group unbiased estimator of the population variance for the test group total number of residences in the control group population total number of residences in the test group population true mean value of S sample mean value of S standard deviation of G,S unbiased estimate of the variance of the mean value of At/c, for the control group unbiased estimate of the variance of the mean value of At/t, for the test group unbiased estimate of the variance of 6,s
=
and
Subscripts control group test group (except where otherwise noted) summer before sunscreens were installed summer after sunscreens were installed
I. INTRODUCTION
Externally-fixed fenestration devices and insulating window films applied to the inside surfaces of glass mayIF save as much as 35-40% of the energy required for cooling in houses located in the transition climatic region of San Diego County, when they are installed in windows without tSupported by the San Diego Gas and Electric Company SPresent address: Department of Technology and Human
under a grant to the UCSD Energy Center. Affairs, Washington University, St. Louis, MO 63130. U.S.A. 883
884
M. R. BRAMBLEY et al
other coverings or shade trees and exposed to clear-sky radiation. In windows with other coverings, the energy savings will be greatly reduced. Field studies are required to determine the conditions under which fenestration devices are actually being used and the fractional reduction of the cooling load achieved in residences where these devices were installed. During 1978 and 1979, approx. 725 residential buildings in the transition climatic region of San Diego County had sunscreenst installed through a program managed by the San Diego Gas and Electric Company (SDG&E). We have studied residences selected from this group to estimate the effectiveness of sunscreens for reducing air-conditioning loads. 2. STATISTICAL
STUDY
Electricity savings were estimated by comparing the differences in electricity consumption for cooling seasons before and after sunscreens were installed in groups of test and control houses. Sunscreens were installed in the test houses and were not installed in the control houses, Comparisons of carefully matched test and control groups should hopefully eliminate statistically those factors not relating to window coverings that may affect electricity consumption (e.g. weather, escalating fuel costs, responses to governmental directives concerning energy conservation) or are peculiar to individual households (e.g. the orientations of the houses). The only differences between the two groups should be the effects of sunscreens on electricity consumption. Sebald and Langenbacher3 have previously developed an analogous methodology for the study of energy savings during the heating season attributable to the use of ceiling insulation in San Diego County. The names, addresses, and installation dates for sunscreens corresponding to all (about 725) householders located in the transition climatic region of San Diego County, who purchased sunscreens through SDG&E during 1978 and 1979, were obtained from SDG&E files. These householders were surveyed by mail to determine characteristics required for classifying and matching of data for statistical purposes (e.g. information concerning the size and type of residence, the time of occupancy, changes in appliance inventories, the number of occupants, the type of air-conditioning system present and when it was used, the types of fuel used for cooking and water heating, and information concerning other energy conservation measures). The survey was designed to maximize the rate of response and to avoid introducing bias. Criteria of importance for designing surveys are discussed in Refs. 4-l 1. Approximately 60% of the delivered surveys were returned in usable form. The households were sorted to eliminate all residences not meeting the following criteria: (1) single-family residence; (2) owner-occupied; (3) principal residence; (4) no change in the number of occupants during the past three years; (5) no living space added during the past three years; (6) residences that had sunscreens installed during 1978 and 1979 and have been occupied for two or more years and three or more years, respectively; (7) located within the El Cajon or Escondido climatic subzones (see Fig. 1); (8) residences that did not install ceiling insulation during the period of the study. The remaining households (155) were classified as air-conditioned or not. The 92 air-conditioned residences formed two test groups corresponding to the year during which sunscreens were installed (1978 or 1979). Approximately 24% of these residences were not qualified because of anomalies in electricity billing data. The final two test groups contained 34 and 36 residences, respectively. Five hundred candidates for a control group were selected from SIX&E billing records and were surveyed. Approximately 49% of the questionnaries were completed and returned. A control group was formed consisting of residences that satisfy the same criteria as the test group, except that sunscreens were not installed. The remaining households were used to form two control groups of 32 and 31 residences, respectively, for comparison with households in the test groups in which sunscreens had been installed during 1978 and 1979. The appropriate electricity-consumption data, for the summers of 1977-80 for residences in the test and control groups, were obtained from SDG6E billing files. Besides sorting according to the specified criteria, the following distributions were compared and found to be in reasonable agreement (although not identical) for the test and control groups (see Figs. 24 and Table 1): fractions of the residences in each group with a specified number of tPhifergIass sunscreens than ordinary fly screens.
are woven fiberglass screens characterized
by smaller open to closed area ratios (0.300.35)
88s
Fenestration devices for energy conservation-IV _,
CTIW
CLIMATIC
ESCONDIDO
ZONE
,
SUEZONE
EL CAlON
SU0ZONE
!
MEXICO Fig. 1. The Escondido and El Cajon climatic subzones of the transition climatic region of San Diego County; based on maps from Climates of San Diego County, University of California, Agricultural Extension Service. 1970;see also Ref. 1.
1978 2
g I? Z g ._ t Z 0.0
13
5 6 7 number of rooms
4
0
9
0.4 0.3 0.2 0.1 0.0
s3
4
5
6
number
of
7
8
rooms
Fig. 2. Fractions of the sampled houses are shown plotted against the number of rooms per house for the test groups (open bars) and control groups (shaded bars) for the 1978and 1979studies. I979
L 2
3
numberof opphanca chongar
number
of
opphance changes
Fig. 3. Fractions of the sampled houses are shown plotted against the number of major appliances acquired during the study period, which were not replacements for old units. Results are shown for the test groups (open bars) and control groups (shaded bars) for the 1978and 1979studies.
O.”
0.0 0
I number
2 of energy
3
4
wn~rvahon
5 mwsurn
6
I number
of energy
conservatmn
measuras
Fig. 4. Fractions of the sampled houses are shown plotted against the number of energy-conservation measures (other than the installation of sunscreens or ceiling insulation) that were implemented during the study periods. Results are shown for the test (open bars) and control (shaded bars) groups used for the 1978and 1979studies.
M. R. BRAMBLEY et al.
886
Table I. The fractions of each sample using electricity for cooking, water heating, and both cooking and water heating are shown. Prrcentnye
1978
studv
of /
sample 1979
studv
+ 59 6 6
rooms in the houses (indicating similar distributions of house sizes); fractions of the samples with the same number of major appliances acquired during the period of the study which were not replacements for old units; fractions using electricity for cooking, water heating, and both cooking and water heating; fractions with the same number of energy-conservation measures employed during the study period (other than the installation of sunscreens). Since the distributions of the number of energy-conservation measures were similar for the test and control groups, it is not unreasonable to assume that the people in the test and control groups had similar attitudes toward energy conservation. 3. STUDIES OF FRACTIONAL
CHANGES IN ELECTRICITY
CONSUMPTION
We define a random variable S that represents fractional electricity savings (savings take negative values) by the relation
where AC= ej - ci, ei and ef represent, respectively, the seasonal total electricity consumption of a residence for the cooling seasons before and after sunscreens were installed in the test group residences, and the subscripts T and C designate test and control groups, respectively. The members of the the test group are air-conditioned residences that had sunscreens installed between cooling seasons i and f, while the control group consists of randomly-chosen, air-conditioned residences that did not have sunscreens (or other window devices) installed. The expected value (indicated by E) of the random variable S (which represents the fractional change in electricity consumption) may be expressed by the relation
I C’
where the subscripts AC and OU identify electricity consumption for air conditioning and all other uses, respectively. For matched, randomly-chosen test and control groups,
(1) 3 C
and, therefore,
(2) Furthermore, for large and matched samples, E[(EAc
+
EOU)iIT
=
E[(cAc
-t
Eou)iIc 3 E[(~Ac
•t
EOU)iIr
E[(EAdilT = E[(~AdiIC,E[(Qu)iIT= E[(EOU)iIC,
(3)
devices for energy conservation--IV
Fenestration
887
because both groups are initially air-conditioned residences without sunscreens. Therefore, (4) According to Eq. (4), E(S) provides an immediate estimate of the average electricity savings attributable to the use of sunscreens in the test residences. The unbiased estimate of the expected value of S (fis) represents the average fractional electricity savings. Unbiased estimates of the variance of fis (i.e., ati,) and probabilistic confidence intervals are determined by using standard statistical procedures for finite samples (see, for example, Ref. 12).1 The results for two statistical experiments corresponding to test groups that had sunscreens installed during 1978 and 1979 are shown in Table 2. For the 1978 study, electricity consumptions for the summersS of 1977 and 1979 were compared; for the 1979 study, the summers of 1978 and 1980 were compared. 4. STUDIES
OF THE MAGNITUDES
OF CHANGES
IN ELECTRICITY
CONSUMPTION
We define the random variable S’ that represents the electricity savings (savings are negative) by the relation S’ = (Ef- Ei)T- (Ef- E;)C. Table 2. The results of statistical studies of fractional changes in electricity consumption are shown for test groups that installed sunscreens during 1978 and 1979. Savings are indicated as negative quantities. Years of installation screens III the test
Statistical parameter
est.
1978
1979
0.092
-0.004
0.146
-0.020
1 1
E [(AE/E~)~]
(= unbiased estimate of the fractional changes in electrlcity consumption for the test group) est.
of ciunresideaces
E [(AE/E~)~]
(= unbiased
estimate of the fractional changes 1x1 electrlclty consumption for the control group)
k
(= unbiased estimate of the fractIona energy savings)
o:z Irs e~;l~~~~a~~dthe variance of Ci,) NT
(= number of resider.ccs in test group)
95% confidence Probability
the
interval [c,
b 01
-0.054
2.55
x 10
0.016
-3
9.24
x 1o-4
34
36
32
31
[-0.153,0.045] 0.66
[-0.044,0.076] 0.30
I
tMore detailed relations are given in the Ph.D. thesis (1981) of M. R. Brambley (University of California, San Diego, La Jolla, CA 92093); this thesis will be referred to as Ref. B. fThe utility billings for periods beginning in June, July, and August were used. Since all bills are not sent out simultaneously, the electricity consumption data may correspond to any 3 months of billings from June I through September 30.
M. R. BRAMBLEY et al.
888
For matched groups,
the expected value of S’ is given by the relation E(S’) = E{h&
-
(eAC)i]T - [(CA& - (EAC)iIC)*
If the test and control groups are matched so that the only difference between the groups is the installation of suncreeens in the test houses, then E(S) represents the savings in electricity consumption attributable to the use of sunscreens. The results of this analysis are shown in Table 3 for studies involving test residences that had sunscreens installed during 1978 and 1979. 5. CALCULATED ESTIMATES OF ENERGY SAVINGS In earlier papers,‘v2we have estimated upper limits for the energy and monetary savings that are possible by the installation of sunscreens. Results of our survey indicate that draperies or roller shades are used in essentially 100% of the test and control houses. In this section, we estimate energy savings for a canonical house in the transition climatic region of San Diego County that has draperies closed during periods of sunlight. We have estimated the solar heat gain (Qs), heat gain caused by temperature differences between the insides and outsides of buildings (Qhr), the total heat gain through windows (QT), Table 3. The results of statistical studies of changes in electricity consumption are shown for studies involving test groups that installed sunscreens during 1978and 1979.Savings are indicated by negative quantities. Year of screens
Statistical parameter
est.
of sunresidences
1976
1979
89
-83
153
-95
E [(AC),,.]
(= unbiased estimate of the changes in electricity consumption for the test group) est.
E [(Ac)C]
(= unbiased estimate of the changes in electricity consumption for the control group) . %’
installation in the test
(= unbiased estimate of energy savings)
oG2 ‘S’
(= unbiased estimate of variance of
the CS,)
NC r~~ind~~bc~~ 7: the control group) 95% confidence Probability
interval [US,
6 0]
-64
kwh
12 kwh
6562
3666
34
36
32
31
[-223,951 79%
[-107,131] 42%
rproperties $Sunscreen
-
3.48
0.191
__.~_
7.21
0.397
SC
-_
97.6
East
incident
36.1
North
85.2 115
South
203
75.0
239
177
m2-yr)
West
East
North
West
South
Orientation
correspond to a light translucent shade in Ref. 13. properties are for a Phiferglass Sunscreen for normally
Single glass with an unsc,aled drape or roller shade
Fenestration
QS (kwhth/
direct
! i
! I
'
I
glass-QT
I4 and B)
562
435
330
136
385
290
(kwhth/m2-yr)
Q T,l/S"DSS
(see Refs.
165
135
306
178
342
280
m2-yr)
QT (kwhth/
solar radiation
49.5
49.5
49.5
49.5
103
103
103
103
m2-yr)
QAT (kwht,,/
0.77
0.73
0.77
0.76
0.52
0.43
0.53
0.51
(kwhth/m 2-yr)
-
glass-QT
QT,l/8"DSS glass
QT,lWDSS
Table 4. Fenestration performance characteristics during the cooling season in the transition climatic region of San Diego County assuming that the cooling season lasts from May through October with solar insolation values corresponding to a clear day on the 21st of each month. an indoor temperature of 65°F. and outdoor daily temperature profiles for each month based on monthly mean daily maximum and minimum temperatures. The solar optical properties for the draper (subscript D) and sunscreenS (sunscript SD) are 7~ = 0.25. pn = 0.60, (III = 0. IS. rsn = 0.20, pm, = 0.10, and ~lsn = 0.70. The shading coefficients are determined by using the relations given in Ref. I and in Chap. 111 of Ref. 14(B).
M. R. BRAMBLEY et al.
890
and energy savings compared to l/8-in. DSS glass (QT l/sin.nssglars- QT) by using the methodology described in Ref. 1.t The results are listed in Table 4 for a draped window and for a window with an externally-mounted sunscreen and an internal drapery. The incremental energy savings obtained when sunscreens are installed on windows that already have drapes are shown in Table 5. For a canonical house in the transition climatic region of San Diego County with 15OOft’ floor area and 300ft2 of total window area, with equal window areas facing each of the four cardinal directions, adding sunscreens to windows that have drapes will reduce the cooling load by approximately 23%. Comparisons of electricity consumptions for the test and control groups during March and April with July and August show that air-conditioning represents approx. l/3 of the total electricity consumption. Adding sunscreens to draped windows will, therefore, save about 7.7% of the total electricity bill. The average electricity use for all houses in the two test groups for the year preceding the installation of sunscreens was about 2300 kWh for June, July, and August. If twice this amount is used during the entire cooling season, sunscreens will save an average of 354 kWh (for six months of cooling) with a monetary value of $24.80 (for electricity priced at 7.0g/kWh). Monetary savings of this magnitude are roughly equal to the price of a sunscreen for a single window. 6. DISCUSSION
OF RESULTS
The electricity savings shown in Tables 2 and 3 are small percentages of total electricity bills. Actual values of the savings are obscured by the large variances in the results. For the calculated upper limit on the savings in cooling load (for houses initially without drapes, shading plants, etc.) of 35-40%,‘.2s’4savings of only about 13% of the total electricity bill are expected. Calculated estimates show that when sunscreens are retrofitted in houses with drapes, less than 7.7% of the total electricity bill will be saved under clear-sky climatic conditions. The statistical results are not inconsistent with the calculated savings for windows with drapes. The results shown in Tables 2 and 3 are inconclusive without detailed study of behavioral changes and comfort levels in the test and control residences. Several scenarios are consistent with the observed results. For example, the test houses may have been maintained at the same comfort levels after sunscreens were installed as before, thereby reducing electricity consumption compared to the values that would have occurred without sunscreens. At the same time, the control houses may have had increased thermostat settings and were less comfortable, thereby leading to reduced electricity consumption by the same average amount as in the test houses. For this scenario, no savings would be observed in the test group compared to the control group. Calculations show that, for a canonical house in the transition region of San Diego County, about 28% of the cooling load may be eliminated by raising the thermostat setting from 65 to 75°F during the cooling season. These savings are 124% of the values estimated for sunscreens installed on houses that have drapes present. Table 5. Estimates of incremental energy savings obtained by installing sunscreens on draped windows are shown for the four cardinal directions.
I Orientation
Incremental
energy
a drapery 2 (kwhth/m -yr)
South
145
West
177
North East
savings,
Q T single glass with -9 T single glass
I
with a drapery and sunscreen
92.0 159
tDetaiIed relations for evaluating heat gain through windows with draperies and sunscreens are given in the Addendum to Chap. 3 in Ref. B.
Fenestration 7. A FIELD
STUDY
TO ASSESS
devices for energy conservation-IV
THE
EFFECTS
OF BEHAVIORAL
ELECTRICITY
891 RESPONSES
TO RISING
PRICES
A second survey of all residences in the test and control groups was used to identify changes in the control of air-conditioning. We obtained an 81% rate of response for this survey.
c
(0) 1978 Test Group
7
r
6-
f”P 8433%
33%
d E3c’
2-
l--u 14%
I
IO%
5%
5% <5
0
increase
(b) 1979
Test
in thermostat
settmg
%
used
Group
25%
1 13%
IO
0 increase
(c)Control
Grcups
for 1978
in thermostat
15
%
settmg
used
1
and 1979
7-
6-
f
5-
co a
4-
% E 2
3
4 I% _
-
2-
-
18%
18%
I -
12%
0
<5
5 increase
IO in thermostot
I5 setting
> I5
fS used
Fig. 5. Numbers of residences are shown plotted against increases in the thermostat settings for air conditioning during the study periods. Results are shown for the test and control groups used in the 1978 and 1979 studies. EGY
Vol.
6. No.
g-B
M. R.
892
BRAMBLEY et al.
The results are summarized in Figs. 5 and 6. Residents of centrally air-conditioned houses changed thermostat settings and associated overall use of air conditioning during the cooling season substantially. In Section 6, we noted that 28% of the cooling load may be eliminated by raising the thermostat setting by 10°F. These savings are equivalent to 124% of the savings expected for houses with draperies that were retrofitted with sunscreens. Responses to the survey show that from 30 to 52% of the residents in houses with central air conditioning increased their thermostat settings by at least 10°F during the cooling season (this estimate
5
rl 12%
0
25
50 %rrduction
75 in AC. uss
ki:, used
(b) 1979 Test Group
25
75
50 SC reduction in A.C. uss
(c) 1978 Control Group
75
50
25 %rrductnn
Fig. 6.
in A.C. us@
?5. und
Fenestration devices for energy conservation-IV (
893
(d) 1979 Control Group
r 0
25
50 Xrrduction
75 in A.C. use
Fig. 6. Numbers of residences are shown plotted against estimates of the percentage reductions in air-conditioning use. Results are shown for the test and control groups used in the 1978and 1979studies.
includes homeowners who discontinued using air-conditioning systems, which ranged from 13 to 33% of the homes with central air conditioning). The same pattern of results was found for homes with room air conditioners. From 70 to 88% of residents with room air conditioners reduced air-conditioning use by at least 50%; 40-50% of residents with room air conditioners did not use these units at all. Billing records indicate that the average price of electricity, for residences that were studied, increased by 1.3 g/kWh (-31%) from 1977 to 1979. Between 1978 and 1980, the average price of electricity was increased by 4.4g/kWh (90%). The results shown in Tables 1 and 3 show that electricity consumption increased in the test and control residences between 1977 and 1979 but decreased between 1978 and 1980. These differences in growth rates in electricity consumption are evidently attributable to behavioral changes of consumers, stimulated by substantial increases in price escalation rates for electricity (from about 14 to 38%/yr). Regression analyses were performed to obtain a relation between electricity consumption, fuel price changes, and the number of cooling degree days. Cooling degree days were used as explanatory variables because the effects of the sunscreens on electricity use for air conditioning should be directly related to the number of cooling degree days. We were unable to obtain meaningful regression results. Thus, we must conclude that the data obtained for energy consumption were too strongly affected by changes in thermostat settings and air conditioning use to allow meaningful identification of an appropriate relation between energy consumption and sunscreen installation. 8. CONCLUSIONS
Our data are consistent with the conclusion that, for the particular years studied, the residences with installed sunscreens did not, on the average, reduce electricity consumption significantly compared to similar households without sunscreens. Sunscreens may improve comfort levels to the point where homeowners may choose to install fenestration devices instead of purchasing air-conditioning systems. Experimental studies are required to determine the benefit in comfort attributable to the use of sunscreens. A previous analysis’ has shown that undamaged fly screens should not be replaced by sunscreens. Sunscreens may provide an alternative to conventional fly screens in new installations and for replacements (of damaged screens) if the costs are comparable. Externally-mounted fenestration devices (such as sunscreens) will perform best on houses that have little external shading (e.g. by other buildings, trees and shrubs), have large east- and west-facing window areas (they should be installed selectively on building windows facing in these general directions), are characterized by large electricity bills, and by high percentages of these bills attributable to air conditioning. High-rise buildings with large glass areas and internal heat sources will benefit most from installing sunscreens. Even for buildings for which
894
M. R. BRAMLILEY et al.
sunscreens are economically attractive, the decision whether to install window devices may ultimately be determined by esthetic considerations. The results of this field study emphasize the importance of experimental verification of the effectiveness of energy-conservation measures and illustrate the difficulties that are encountered in verifying the performance of marginally effective energy-conservation devices. It is clearly undesirable to mandate the implementation of energy-conservation programs until field measurements have been made on the actual performance of energy-conservation devices and strategies. Even when devices are proven to save energy, installations should be carefully monitored to ensure that the devices are used in the prescribed manner.
REFERENCES 1. M. R. Brambley and S. S. Penner, Energy 4,
I (1979).
2. M. R. Brambley and S. S. Penner, Energy 6.61 (1981). 3. A. V. Sebald and F. Langenbacher, Energy 5,87 (1980). 4. J. R. Hochstim, J. Am. Statist. Assoc. 62, 976 (1967). 5. W. H. Jones and G. Linda, .I. Market. Res. 15, 280 (1978). 6. C. S. Craig and J. M. McCann, .I Market. Res. 15, 285 (1978). I. J. R. Harris and H. J. Guffey, Jr., J. Market. Res. 15, 290 (1978). 8. L. Mandell and L. L. Lundsten, .I Market. Res. 15, 294 (1978). 9. M. J. Houston and N. M. Ford, J. Market Res. 13, 397 (1976). 10. W. Locander, S. Sudman and N. Bradburn, J. Am. Statistic. Assoc. 71, 269 (1976). 11. P. R. Stopher and A. H. Meyburg, Suroey Sampling and Multivariate Analysis for Social Scientists and Engineers, pp. 9-44 and 101-120.Lexington Books, Lexington, Mass. (1979). 12. W. L. Hays and R. L. Winkler, Statistics: Probability Inference and Decision, Vol. 1. Holt, Rinehart and Winston, New York (1970). 13. ASHRAE Handbook and Product Directory-1977 Fundamentals, p. 26-31. American Society of Heating, Refrigerating, and Air-Conditioning Engineers, New York (1977). 14. M. R. Brambley and S. S. Penner, “Fenestration Devices for Energy Conservation-III. Experimental Results for Selected Fenestrations”. Energy Center, University of California, San Diego, La Jolla, CA 92093(March 1980);(B) M. R. Brambley, Ph.D. Thesis, University of California, San Diego, La Jolla, CA 92093, 1981.
03~5442/8l/OWBR3-12102.00/(1 Pergamon Press Ltd
FENESTRATION DEVICES FOR ENERGY CONSERVATION-IV. FIELD STUDYt
M. R. Energy
Center
BRAMBLEYS,
and Department
E. M. KENNEDY, and S. S.
of Applied Mechanics and Engineering Sciences, San Diego, La Jolla,CA92093, U.S.A.
(Receioed 12 March
PENNER UniverGty
of California,
1981)
Abstract-We present the results of field studies concerning the performance of sunscreens for reducing air-conditioning loads in single-family residences. We used data on houses (725) in the San Diego transition climatic region which had sunscreens installed during 1978 or 1979. The sample size was reduced by the following factors: failure by homeowners to respond to the questionnaire, houses which were not air-conditioned, failure to satisfy characteristics important for matching of houses, and criteria related to changes in occupancy. As the result, our control and test groups were reduced to 34 and 32 for the 1978 study and to 36 and 31 households for the 1979 study, respectively. For these small remaining sample sizes, the predicted small effects of sunscreens on total electricity consumption were obscured by variances in the field results. The observed large variances in the field results were produced, in large measure. by deliberate changes in thermostat settings as a response by homeowners to rapidly escalating electricity costs.
NOTATION differences
in electricity
consumption
between
the summers
before
and after
sunscreens
were installed
electricity consumption during the first summer (before installation of sunscreens) of the study electricity consumption during the final summer (after installation of sunscreens) of the study electricity consumption for air conditioning electricity consumption for uses other than air conditioning expected value of a variable; thus, E(S) is the expected value of the energy savings mean value of At/c, for the control group mean value of 11c/c, for the test group number of households in the control group number of households in the test group seasonal solar heat gain per unit area of windows seasonal heat gain per unit area of windows becausr of temperature differences between the insides outsides of buildings total seasonal heat gain per unit area of windows total seasonal heat gain per unit area of l/8% thick, double-strength single glass random variable representing the fractional change in electricity consumption random variable representing the change in electricity consumption unbiased estimator of the population v )riance for the control group unbiased estimator of the population variance for the test group total number of residences in the control group population total number of residences in the test group population true mean value of S sample mean value of S standard deviation of G,S unbiased estimate of the variance of the mean value of At/c, for the control group unbiased estimate of the variance of the mean value of At/t, for the test group unbiased estimate of the variance of 6,s
=
and
Subscripts control group test group (except where otherwise noted) summer before sunscreens were installed summer after sunscreens were installed
I. INTRODUCTION
Externally-fixed fenestration devices and insulating window films applied to the inside surfaces of glass mayIF save as much as 35-40% of the energy required for cooling in houses located in the transition climatic region of San Diego County, when they are installed in windows without tSupported by the San Diego Gas and Electric Company SPresent address: Department of Technology and Human
under a grant to the UCSD Energy Center. Affairs, Washington University, St. Louis, MO 63130. U.S.A. 883
884
M. R. BRAMBLEY et al
other coverings or shade trees and exposed to clear-sky radiation. In windows with other coverings, the energy savings will be greatly reduced. Field studies are required to determine the conditions under which fenestration devices are actually being used and the fractional reduction of the cooling load achieved in residences where these devices were installed. During 1978 and 1979, approx. 725 residential buildings in the transition climatic region of San Diego County had sunscreenst installed through a program managed by the San Diego Gas and Electric Company (SDG&E). We have studied residences selected from this group to estimate the effectiveness of sunscreens for reducing air-conditioning loads. 2. STATISTICAL
STUDY
Electricity savings were estimated by comparing the differences in electricity consumption for cooling seasons before and after sunscreens were installed in groups of test and control houses. Sunscreens were installed in the test houses and were not installed in the control houses, Comparisons of carefully matched test and control groups should hopefully eliminate statistically those factors not relating to window coverings that may affect electricity consumption (e.g. weather, escalating fuel costs, responses to governmental directives concerning energy conservation) or are peculiar to individual households (e.g. the orientations of the houses). The only differences between the two groups should be the effects of sunscreens on electricity consumption. Sebald and Langenbacher3 have previously developed an analogous methodology for the study of energy savings during the heating season attributable to the use of ceiling insulation in San Diego County. The names, addresses, and installation dates for sunscreens corresponding to all (about 725) householders located in the transition climatic region of San Diego County, who purchased sunscreens through SDG&E during 1978 and 1979, were obtained from SDG&E files. These householders were surveyed by mail to determine characteristics required for classifying and matching of data for statistical purposes (e.g. information concerning the size and type of residence, the time of occupancy, changes in appliance inventories, the number of occupants, the type of air-conditioning system present and when it was used, the types of fuel used for cooking and water heating, and information concerning other energy conservation measures). The survey was designed to maximize the rate of response and to avoid introducing bias. Criteria of importance for designing surveys are discussed in Refs. 4-l 1. Approximately 60% of the delivered surveys were returned in usable form. The households were sorted to eliminate all residences not meeting the following criteria: (1) single-family residence; (2) owner-occupied; (3) principal residence; (4) no change in the number of occupants during the past three years; (5) no living space added during the past three years; (6) residences that had sunscreens installed during 1978 and 1979 and have been occupied for two or more years and three or more years, respectively; (7) located within the El Cajon or Escondido climatic subzones (see Fig. 1); (8) residences that did not install ceiling insulation during the period of the study. The remaining households (155) were classified as air-conditioned or not. The 92 air-conditioned residences formed two test groups corresponding to the year during which sunscreens were installed (1978 or 1979). Approximately 24% of these residences were not qualified because of anomalies in electricity billing data. The final two test groups contained 34 and 36 residences, respectively. Five hundred candidates for a control group were selected from SIX&E billing records and were surveyed. Approximately 49% of the questionnaries were completed and returned. A control group was formed consisting of residences that satisfy the same criteria as the test group, except that sunscreens were not installed. The remaining households were used to form two control groups of 32 and 31 residences, respectively, for comparison with households in the test groups in which sunscreens had been installed during 1978 and 1979. The appropriate electricity-consumption data, for the summers of 1977-80 for residences in the test and control groups, were obtained from SDG6E billing files. Besides sorting according to the specified criteria, the following distributions were compared and found to be in reasonable agreement (although not identical) for the test and control groups (see Figs. 24 and Table 1): fractions of the residences in each group with a specified number of tPhifergIass sunscreens than ordinary fly screens.
are woven fiberglass screens characterized
by smaller open to closed area ratios (0.300.35)
88s
Fenestration devices for energy conservation-IV _,
CTIW
CLIMATIC
ESCONDIDO
ZONE
,
SUEZONE
EL CAlON
SU0ZONE
!
MEXICO Fig. 1. The Escondido and El Cajon climatic subzones of the transition climatic region of San Diego County; based on maps from Climates of San Diego County, University of California, Agricultural Extension Service. 1970;see also Ref. 1.
1978 2
g I? Z g ._ t Z 0.0
13
5 6 7 number of rooms
4
0
9
0.4 0.3 0.2 0.1 0.0
s3
4
5
6
number
of
7
8
rooms
Fig. 2. Fractions of the sampled houses are shown plotted against the number of rooms per house for the test groups (open bars) and control groups (shaded bars) for the 1978and 1979studies. I979
L 2
3
numberof opphanca chongar
number
of
opphance changes
Fig. 3. Fractions of the sampled houses are shown plotted against the number of major appliances acquired during the study period, which were not replacements for old units. Results are shown for the test groups (open bars) and control groups (shaded bars) for the 1978and 1979studies.
O.”
0.0 0
I number
2 of energy
3
4
wn~rvahon
5 mwsurn
6
I number
of energy
conservatmn
measuras
Fig. 4. Fractions of the sampled houses are shown plotted against the number of energy-conservation measures (other than the installation of sunscreens or ceiling insulation) that were implemented during the study periods. Results are shown for the test (open bars) and control (shaded bars) groups used for the 1978and 1979studies.
M. R. BRAMBLEY et al.
886
Table I. The fractions of each sample using electricity for cooking, water heating, and both cooking and water heating are shown. Prrcentnye
1978
studv
of /
sample 1979
studv
+ 59 6 6
rooms in the houses (indicating similar distributions of house sizes); fractions of the samples with the same number of major appliances acquired during the period of the study which were not replacements for old units; fractions using electricity for cooking, water heating, and both cooking and water heating; fractions with the same number of energy-conservation measures employed during the study period (other than the installation of sunscreens). Since the distributions of the number of energy-conservation measures were similar for the test and control groups, it is not unreasonable to assume that the people in the test and control groups had similar attitudes toward energy conservation. 3. STUDIES OF FRACTIONAL
CHANGES IN ELECTRICITY
CONSUMPTION
We define a random variable S that represents fractional electricity savings (savings take negative values) by the relation
where AC= ej - ci, ei and ef represent, respectively, the seasonal total electricity consumption of a residence for the cooling seasons before and after sunscreens were installed in the test group residences, and the subscripts T and C designate test and control groups, respectively. The members of the the test group are air-conditioned residences that had sunscreens installed between cooling seasons i and f, while the control group consists of randomly-chosen, air-conditioned residences that did not have sunscreens (or other window devices) installed. The expected value (indicated by E) of the random variable S (which represents the fractional change in electricity consumption) may be expressed by the relation
I C’
where the subscripts AC and OU identify electricity consumption for air conditioning and all other uses, respectively. For matched, randomly-chosen test and control groups,
(1) 3 C
and, therefore,
(2) Furthermore, for large and matched samples, E[(EAc
+
EOU)iIT
=
E[(cAc
-t
Eou)iIc 3 E[(~Ac
•t
EOU)iIr
E[(EAdilT = E[(~AdiIC,E[(Qu)iIT= E[(EOU)iIC,
(3)
devices for energy conservation--IV
Fenestration
887
because both groups are initially air-conditioned residences without sunscreens. Therefore, (4) According to Eq. (4), E(S) provides an immediate estimate of the average electricity savings attributable to the use of sunscreens in the test residences. The unbiased estimate of the expected value of S (fis) represents the average fractional electricity savings. Unbiased estimates of the variance of fis (i.e., ati,) and probabilistic confidence intervals are determined by using standard statistical procedures for finite samples (see, for example, Ref. 12).1 The results for two statistical experiments corresponding to test groups that had sunscreens installed during 1978 and 1979 are shown in Table 2. For the 1978 study, electricity consumptions for the summersS of 1977 and 1979 were compared; for the 1979 study, the summers of 1978 and 1980 were compared. 4. STUDIES
OF THE MAGNITUDES
OF CHANGES
IN ELECTRICITY
CONSUMPTION
We define the random variable S’ that represents the electricity savings (savings are negative) by the relation S’ = (Ef- Ei)T- (Ef- E;)C. Table 2. The results of statistical studies of fractional changes in electricity consumption are shown for test groups that installed sunscreens during 1978 and 1979. Savings are indicated as negative quantities. Years of installation screens III the test
Statistical parameter
est.
1978
1979
0.092
-0.004
0.146
-0.020
1 1
E [(AE/E~)~]
(= unbiased estimate of the fractional changes in electrlcity consumption for the test group) est.
of ciunresideaces
E [(AE/E~)~]
(= unbiased
estimate of the fractional changes 1x1 electrlclty consumption for the control group)
k
(= unbiased estimate of the fractIona energy savings)
o:z Irs e~;l~~~~a~~dthe variance of Ci,) NT
(= number of resider.ccs in test group)
95% confidence Probability
the
interval [c,
b 01
-0.054
2.55
x 10
0.016
-3
9.24
x 1o-4
34
36
32
31
[-0.153,0.045] 0.66
[-0.044,0.076] 0.30
I
tMore detailed relations are given in the Ph.D. thesis (1981) of M. R. Brambley (University of California, San Diego, La Jolla, CA 92093); this thesis will be referred to as Ref. B. fThe utility billings for periods beginning in June, July, and August were used. Since all bills are not sent out simultaneously, the electricity consumption data may correspond to any 3 months of billings from June I through September 30.
M. R. BRAMBLEY et al.
888
For matched groups,
the expected value of S’ is given by the relation E(S’) = E{h&
-
(eAC)i]T - [(CA& - (EAC)iIC)*
If the test and control groups are matched so that the only difference between the groups is the installation of suncreeens in the test houses, then E(S) represents the savings in electricity consumption attributable to the use of sunscreens. The results of this analysis are shown in Table 3 for studies involving test residences that had sunscreens installed during 1978 and 1979. 5. CALCULATED ESTIMATES OF ENERGY SAVINGS In earlier papers,‘v2we have estimated upper limits for the energy and monetary savings that are possible by the installation of sunscreens. Results of our survey indicate that draperies or roller shades are used in essentially 100% of the test and control houses. In this section, we estimate energy savings for a canonical house in the transition climatic region of San Diego County that has draperies closed during periods of sunlight. We have estimated the solar heat gain (Qs), heat gain caused by temperature differences between the insides and outsides of buildings (Qhr), the total heat gain through windows (QT), Table 3. The results of statistical studies of changes in electricity consumption are shown for studies involving test groups that installed sunscreens during 1978and 1979.Savings are indicated by negative quantities. Year of screens
Statistical parameter
est.
of sunresidences
1976
1979
89
-83
153
-95
E [(AC),,.]
(= unbiased estimate of the changes in electricity consumption for the test group) est.
E [(Ac)C]
(= unbiased estimate of the changes in electricity consumption for the control group) . %’
installation in the test
(= unbiased estimate of energy savings)
oG2 ‘S’
(= unbiased estimate of variance of
the CS,)
NC r~~ind~~bc~~ 7: the control group) 95% confidence Probability
interval [US,
6 0]
-64
kwh
12 kwh
6562
3666
34
36
32
31
[-223,951 79%
[-107,131] 42%
rproperties $Sunscreen
-
3.48
0.191
__.~_
7.21
0.397
SC
-_
97.6
East
incident
36.1
North
85.2 115
South
203
75.0
239
177
m2-yr)
West
East
North
West
South
Orientation
correspond to a light translucent shade in Ref. 13. properties are for a Phiferglass Sunscreen for normally
Single glass with an unsc,aled drape or roller shade
Fenestration
QS (kwhth/
direct
! i
! I
'
I
glass-QT
I4 and B)
562
435
330
136
385
290
(kwhth/m2-yr)
Q T,l/S"DSS
(see Refs.
165
135
306
178
342
280
m2-yr)
QT (kwhth/
solar radiation
49.5
49.5
49.5
49.5
103
103
103
103
m2-yr)
QAT (kwht,,/
0.77
0.73
0.77
0.76
0.52
0.43
0.53
0.51
(kwhth/m 2-yr)
-
glass-QT
QT,l/8"DSS glass
QT,lWDSS
Table 4. Fenestration performance characteristics during the cooling season in the transition climatic region of San Diego County assuming that the cooling season lasts from May through October with solar insolation values corresponding to a clear day on the 21st of each month. an indoor temperature of 65°F. and outdoor daily temperature profiles for each month based on monthly mean daily maximum and minimum temperatures. The solar optical properties for the draper (subscript D) and sunscreenS (sunscript SD) are 7~ = 0.25. pn = 0.60, (III = 0. IS. rsn = 0.20, pm, = 0.10, and ~lsn = 0.70. The shading coefficients are determined by using the relations given in Ref. I and in Chap. 111 of Ref. 14(B).
M. R. BRAMBLEY et al.
890
and energy savings compared to l/8-in. DSS glass (QT l/sin.nssglars- QT) by using the methodology described in Ref. 1.t The results are listed in Table 4 for a draped window and for a window with an externally-mounted sunscreen and an internal drapery. The incremental energy savings obtained when sunscreens are installed on windows that already have drapes are shown in Table 5. For a canonical house in the transition climatic region of San Diego County with 15OOft’ floor area and 300ft2 of total window area, with equal window areas facing each of the four cardinal directions, adding sunscreens to windows that have drapes will reduce the cooling load by approximately 23%. Comparisons of electricity consumptions for the test and control groups during March and April with July and August show that air-conditioning represents approx. l/3 of the total electricity consumption. Adding sunscreens to draped windows will, therefore, save about 7.7% of the total electricity bill. The average electricity use for all houses in the two test groups for the year preceding the installation of sunscreens was about 2300 kWh for June, July, and August. If twice this amount is used during the entire cooling season, sunscreens will save an average of 354 kWh (for six months of cooling) with a monetary value of $24.80 (for electricity priced at 7.0g/kWh). Monetary savings of this magnitude are roughly equal to the price of a sunscreen for a single window. 6. DISCUSSION
OF RESULTS
The electricity savings shown in Tables 2 and 3 are small percentages of total electricity bills. Actual values of the savings are obscured by the large variances in the results. For the calculated upper limit on the savings in cooling load (for houses initially without drapes, shading plants, etc.) of 35-40%,‘.2s’4savings of only about 13% of the total electricity bill are expected. Calculated estimates show that when sunscreens are retrofitted in houses with drapes, less than 7.7% of the total electricity bill will be saved under clear-sky climatic conditions. The statistical results are not inconsistent with the calculated savings for windows with drapes. The results shown in Tables 2 and 3 are inconclusive without detailed study of behavioral changes and comfort levels in the test and control residences. Several scenarios are consistent with the observed results. For example, the test houses may have been maintained at the same comfort levels after sunscreens were installed as before, thereby reducing electricity consumption compared to the values that would have occurred without sunscreens. At the same time, the control houses may have had increased thermostat settings and were less comfortable, thereby leading to reduced electricity consumption by the same average amount as in the test houses. For this scenario, no savings would be observed in the test group compared to the control group. Calculations show that, for a canonical house in the transition region of San Diego County, about 28% of the cooling load may be eliminated by raising the thermostat setting from 65 to 75°F during the cooling season. These savings are 124% of the values estimated for sunscreens installed on houses that have drapes present. Table 5. Estimates of incremental energy savings obtained by installing sunscreens on draped windows are shown for the four cardinal directions.
I Orientation
Incremental
energy
a drapery 2 (kwhth/m -yr)
South
145
West
177
North East
savings,
Q T single glass with -9 T single glass
I
with a drapery and sunscreen
92.0 159
tDetaiIed relations for evaluating heat gain through windows with draperies and sunscreens are given in the Addendum to Chap. 3 in Ref. B.
Fenestration 7. A FIELD
STUDY
TO ASSESS
devices for energy conservation-IV
THE
EFFECTS
OF BEHAVIORAL
ELECTRICITY
891 RESPONSES
TO RISING
PRICES
A second survey of all residences in the test and control groups was used to identify changes in the control of air-conditioning. We obtained an 81% rate of response for this survey.
c
(0) 1978 Test Group
7
r
6-
f”P 8433%
33%
d E3c’
2-
l--u 14%
I
IO%
5%
5% <5
0
increase
(b) 1979
Test
in thermostat
settmg
%
used
Group
25%
1 13%
IO
0 increase
(c)Control
Grcups
for 1978
in thermostat
15
%
settmg
used
1
and 1979
7-
6-
f
5-
co a
4-
% E 2
3
4 I% _
-
2-
-
18%
18%
I -
12%
0
<5
5 increase
IO in thermostot
I5 setting
> I5
fS used
Fig. 5. Numbers of residences are shown plotted against increases in the thermostat settings for air conditioning during the study periods. Results are shown for the test and control groups used in the 1978 and 1979 studies. EGY
Vol.
6. No.
g-B
M. R.
892
BRAMBLEY et al.
The results are summarized in Figs. 5 and 6. Residents of centrally air-conditioned houses changed thermostat settings and associated overall use of air conditioning during the cooling season substantially. In Section 6, we noted that 28% of the cooling load may be eliminated by raising the thermostat setting by 10°F. These savings are equivalent to 124% of the savings expected for houses with draperies that were retrofitted with sunscreens. Responses to the survey show that from 30 to 52% of the residents in houses with central air conditioning increased their thermostat settings by at least 10°F during the cooling season (this estimate
5
rl 12%
0
25
50 %rrduction
75 in AC. uss
ki:, used
(b) 1979 Test Group
25
75
50 SC reduction in A.C. uss
(c) 1978 Control Group
75
50
25 %rrductnn
Fig. 6.
in A.C. us@
?5. und
Fenestration devices for energy conservation-IV (
893
(d) 1979 Control Group
r 0
25
50 Xrrduction
75 in A.C. use
Fig. 6. Numbers of residences are shown plotted against estimates of the percentage reductions in air-conditioning use. Results are shown for the test and control groups used in the 1978and 1979studies.
includes homeowners who discontinued using air-conditioning systems, which ranged from 13 to 33% of the homes with central air conditioning). The same pattern of results was found for homes with room air conditioners. From 70 to 88% of residents with room air conditioners reduced air-conditioning use by at least 50%; 40-50% of residents with room air conditioners did not use these units at all. Billing records indicate that the average price of electricity, for residences that were studied, increased by 1.3 g/kWh (-31%) from 1977 to 1979. Between 1978 and 1980, the average price of electricity was increased by 4.4g/kWh (90%). The results shown in Tables 1 and 3 show that electricity consumption increased in the test and control residences between 1977 and 1979 but decreased between 1978 and 1980. These differences in growth rates in electricity consumption are evidently attributable to behavioral changes of consumers, stimulated by substantial increases in price escalation rates for electricity (from about 14 to 38%/yr). Regression analyses were performed to obtain a relation between electricity consumption, fuel price changes, and the number of cooling degree days. Cooling degree days were used as explanatory variables because the effects of the sunscreens on electricity use for air conditioning should be directly related to the number of cooling degree days. We were unable to obtain meaningful regression results. Thus, we must conclude that the data obtained for energy consumption were too strongly affected by changes in thermostat settings and air conditioning use to allow meaningful identification of an appropriate relation between energy consumption and sunscreen installation. 8. CONCLUSIONS
Our data are consistent with the conclusion that, for the particular years studied, the residences with installed sunscreens did not, on the average, reduce electricity consumption significantly compared to similar households without sunscreens. Sunscreens may improve comfort levels to the point where homeowners may choose to install fenestration devices instead of purchasing air-conditioning systems. Experimental studies are required to determine the benefit in comfort attributable to the use of sunscreens. A previous analysis’ has shown that undamaged fly screens should not be replaced by sunscreens. Sunscreens may provide an alternative to conventional fly screens in new installations and for replacements (of damaged screens) if the costs are comparable. Externally-mounted fenestration devices (such as sunscreens) will perform best on houses that have little external shading (e.g. by other buildings, trees and shrubs), have large east- and west-facing window areas (they should be installed selectively on building windows facing in these general directions), are characterized by large electricity bills, and by high percentages of these bills attributable to air conditioning. High-rise buildings with large glass areas and internal heat sources will benefit most from installing sunscreens. Even for buildings for which
894
M. R. BRAMLILEY et al.
sunscreens are economically attractive, the decision whether to install window devices may ultimately be determined by esthetic considerations. The results of this field study emphasize the importance of experimental verification of the effectiveness of energy-conservation measures and illustrate the difficulties that are encountered in verifying the performance of marginally effective energy-conservation devices. It is clearly undesirable to mandate the implementation of energy-conservation programs until field measurements have been made on the actual performance of energy-conservation devices and strategies. Even when devices are proven to save energy, installations should be carefully monitored to ensure that the devices are used in the prescribed manner.
REFERENCES 1. M. R. Brambley and S. S. Penner, Energy 4,
I (1979).
2. M. R. Brambley and S. S. Penner, Energy 6.61 (1981). 3. A. V. Sebald and F. Langenbacher, Energy 5,87 (1980). 4. J. R. Hochstim, J. Am. Statist. Assoc. 62, 976 (1967). 5. W. H. Jones and G. Linda, .I. Market. Res. 15, 280 (1978). 6. C. S. Craig and J. M. McCann, .I Market. Res. 15, 285 (1978). I. J. R. Harris and H. J. Guffey, Jr., J. Market. Res. 15, 290 (1978). 8. L. Mandell and L. L. Lundsten, .I Market. Res. 15, 294 (1978). 9. M. J. Houston and N. M. Ford, J. Market Res. 13, 397 (1976). 10. W. Locander, S. Sudman and N. Bradburn, J. Am. Statistic. Assoc. 71, 269 (1976). 11. P. R. Stopher and A. H. Meyburg, Suroey Sampling and Multivariate Analysis for Social Scientists and Engineers, pp. 9-44 and 101-120.Lexington Books, Lexington, Mass. (1979). 12. W. L. Hays and R. L. Winkler, Statistics: Probability Inference and Decision, Vol. 1. Holt, Rinehart and Winston, New York (1970). 13. ASHRAE Handbook and Product Directory-1977 Fundamentals, p. 26-31. American Society of Heating, Refrigerating, and Air-Conditioning Engineers, New York (1977). 14. M. R. Brambley and S. S. Penner, “Fenestration Devices for Energy Conservation-III. Experimental Results for Selected Fenestrations”. Energy Center, University of California, San Diego, La Jolla, CA 92093(March 1980);(B) M. R. Brambley, Ph.D. Thesis, University of California, San Diego, La Jolla, CA 92093, 1981.