Energy conservation in public housing: A case study of the San Francisco housing authority

Energy and Buildings, 9 (1986) 89 - 98

89

Energy Conservation in Public Housing: A Case Study of the San Francisco Housing Authority CHARLES A. GOLDMAN and RONALD L. RITSCHARD

Applied Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720 (U.S.A.)

(Received November 1984; accepted February 1985;revised April 1985)

SUMMARY

In 1982, the San Francisco Housing Authority began trying to reduce rapidly increasing energy expenses by installing attic insulation, exterior door weather stripping, low-flow shower-heads, and water-heater blankets in the buildings that it manages. The conservation measures were financed by the local utility's zero-interest loan program (ZIP). We analyze utility billing data for three years, including one post-retrofit year, at five multifamily housing projects (totalling 1822 units). Weather-normalized annual natural gas consumption declined by 13% after the retrofit at the five projects; net savings relative to a comparison group were 8%. We determined that most o f the energy savings resulted from reduced base level usage. We found that the retrofit program was cost-effective, with a net present value o f $399 000 or $220/unit. The Housing Authority's careful efforts to control retrofit costs, which averaged only $150/unit, contributed to the program's success.

INTRODUCTION

In the next decade, public housing officials will have to pay increasing attention to improving the energy efficiency of buildings as rising energy costs create an ever-widening gap between expenses and rental income. A recent review of the topic concludes that great potential exists for energy and cost savings in public housing [1]. During the last ten years, the U.S. Department of Housing and Urban Development (HUD) and local public housing authorities (PHAs) have initiated major retrofit programs. In 1980, HUD

awarded $23 million to 47 PHAs for modernizing oil heating systems and another $5 million to 61 PHAs to install and test innovative energy conservation and solar measures. In addition, between 1975 and 1979, approximately 25% of HUD modernization funds were used for energy conservation. Savings estimates for these programs have been based almost exclusively on engineering calculations; only a few evaluations of public housing retrofit efforts have used metered data [ 2 - 5 ] . Actual measured data give credibility to predictions, help guide retrofit investment decisions, and help identify issues that deserve further analysis. This report focuses on the San Francisco Housing Authority, which cooperated with the local utility, Pacific Gas & Electric Company (PG&E), to finance energy conservation measures. The Housing Authority was deeply concerned with energy expenses, which had increased from $1.7 million in 1977 to $4.3 million in 1983, although energy consumption actually decreased slightly during this period. We analyze utility bills over a three-year period at five housing projects, including one year of post-retrofit data, in order to estimate energy savings attributable to the Housing Authority 's weatherization program. These five projects represent roughly 25% of the dwelling units managed by the Authority. The projects are occupied by families and are master-metered; thus tenants do not pay utility costs directly. In this study, we discuss optimal approaches for selection, marketing, and financing of energy conservation retrofits in public housing. Very little research has been done in this area and San Francisco is one of the first public housing authorities to fund Elsevier Sequoia/Printed in The Netherlands

90

energy-efficiency improvements using a utility-sponsored conservation program. Innovative financial strategies are necessary in order to overcome existing institutional barriers and tight budgetary constraints. This study also adds to research on multifamily buildings. A significant fraction of the nation's public housing units are multifamily buildings. Until recently, the multifamily sector has received m u c h less attention and study than have single-family residences.

R E T R O F I T AND BUILDING DESCRIPTION

F o u r of the five family housing projects in this study are located on the east side of San Francisco. Each site has many low-rise buildings ( 2 - 3 story) with 8 - 20 apartment units per building. Average floor area per unit ranges from approximately 70 m 2 to 80 m 2 with an average of 3.6 occupants per unit (see Table 1). Roughly 65% of the apartments are t w o - b e d r o o m units; one- and threeb e d r o o m units each account for approximately 15% of the total. During post-retrofit site visits, we observed many apartments with broken or boarded windows (perhaps 2% 4% of all windows). This observation suggests that, in any energy conservation effort, additional funding for and attention to basic maintenance must be considered in addition to weatherization measures.

TABLE

Under the utility's conservation program, an interest-free loan of up to $1000/unit is available for the following conservation measures: attic and duct insulation, low-flow shower-heads, water-heater blankets, caulking, and weather stripping. Loans may be used for both material and labor costs and are repayable over an eight-year period. Initially, PG&E and Authority staff inspected a representative sample of apartment types managed b y the Authority to determine which conservation measures were suitable. Those housing projects with the highest estimated potential savings were chosen first. Typically these were t o w n h o u s e apartments with accessible attics. Bid packages were prepared for each project and bids were then requested from weatherization contractors certified to participate in the zero-interest loan program (ZIP). Attic insulation and exterior door weather stripping were installed at each project. Two sites with h o t water heaters in individual dwelling units received insulating blankets (Table 1). Retrofit costs ranged from $80 to $200 per unit, with an average of $150/ unit. In addition, inexpensive time clocks, costing approximately $85/boiler, were installed on central boilers at three projects in October 1982; this measure was not part of the ZIP program. The time clocks regulate the space heat water circulation pump, so the p u m p would run for 14 hours rather than 24 hours a day. Housing Authority staff

1

Building description and retrofit measures Project name

Alemany

Potrero Terrace

Sunnydale

Alice Griffith

Hayes Valleya

Total units Occupied units b Pre-retrofit Post-retrofit Avg. floor area (m 2) Occupants/Unit c Year built Heating system type d Retrofit measures e

158

469

767

258

170

152 150 81 4.0 1956 SH IA, CW, W H

393 418 77 3.3 1942 CB IA, CW, TC, S H

677 705 81 3.7 1942 SH IA, CW, W H

193 236 78 4.8 1962 CB IA, CW, T C

151 148 72 2.6 1963 CB IA, CW, T C

aHayes Valley is located at three separate sites. W e have included results for only one site, Hayes B, which represents 170 of 328 units. Hayes C (140 units) was excluded due to anomalous utilitybillingdata. bAverages were computed over the number of billing periods used in regression analysis. cOccupant data are from 1982. d S H = r o o m space heater; C B = central boilers that supply both space heat and domestic hot water. eIA = attic insulation, C W = caulking/weather stripping, T C = time clock on boiler, S H = low-flow shower-head, W H = water-heater jacket.

91 indicated that the timers would be disconnected if tenants at a project complained about insufficient heat. The time clocks were not in use on some boilers during our site visits. The systems either had manual override switches in effect or the on-and-off tripper switches were missing from timer dials. We have been unable to determine how long the timers were in operation before they were disconnected.

ANALYSIS

We use the Princeton Scorekeeping Method (PRISM) to adjust for weather differences during the pre- and post-retrofit periods (described in the introductory paper to this issue). The Housing Authority provided us with monthly utility bills from January 1981 to April 1984. Daily average temperatures were obtained from the San Francisco Airport NOAA weather station, from which we computed heating degree-days to different reference temperatures. Normal year heating degree-days were computed to different reference temperatures using the 30-year normal monthly outdoor average temperature and its standard deviation [6]. In this paper we also explore ways to adjust for changing occupancy rates. Evaluations of retrofit programs directed at single-family homes generally exclude homes in which occupancy has changed [7]. However, this approach is not feasible in master-metered, multifamily buildings. This is particularly true in family housing projects where turnover is often high and occupancy rates vary greatly over time. To adjust for occupancy effects, we used monthly data on the number of occupied units in each project as a rough indicator of the number of units being heated. It is worth noting that many more units were occupied at Sunnydale, Potrero Terrace, and Alice Griffith Projects after the retrofit than in the pre-retrofit period [see Table 1]. We were concerned that decreases in gas consumption due to retrofitting would be masked by increases in the number of occupied dwellings (and presumably the heating load). To account for this effect, we divided gas use during each billing period by the number of occupied units in that period. We recognize the limitations of this approach, which as-

sumes that no energy is being consumed in vacant units. This assumption is probably reasonable for appliance and hot water use, particularly for the two projects with individual unit hot water heaters. However, in the three projects with central heating plants, unoccupied units were probably receiving some direct heat (we found some vacant units with manual radiator controller valves stuck in the "open" position). We used a comparison group to obtain a rough estimate of the net impact of the conservation measures on energy consumption in the five projects. The comparison group, Group A, consists of two non-retrofitted projects with characteristics similar to those of the study group. These projects were constructed during the same period (194050s), have central heating plants, and are occupied by families. However, the Scorekeeping results seem to be not reliable (e.g., large standard errors in the reference temperatures; see Table 2). For these reasons, changes in energy consumption in the comparison group and the corresponding adjustment in the treatment group's savings should be viewed cautiously.

RESULTS Actual energy consumption Energy usage tracks seasonal weather variations (as indicated by heating degreedays, HDD) fairly closely at the Sunnydale Project (Fig. 1). Milder weather conditions prevailed in the post-retrofit period than during either of the pre-retrofit periods: 1402 HDD (base 18.3 °C) in the post-retrofit period versus 1776 and 1737 HDD during the 1981 - 82 and 1982- 83 pre-retrofit periods respectively. In addition to weather, another factor that could affect energy consumption is occupancy, which increased by an average of 4% after the conservation measures were installed. Cooking energy use is metered separately at two projects, Hayes Valley and Potrero Terrace, and accounts for a surprisingly large fraction (19%- 29%) of total gas consumption. Average gas consumption/unit for cooking is much higher at Potrero Terrace than at Hayes Valley (1.2 vs. 0.5 kWth/unit). In addition, cooking energy use is 30% - 50%

92 400 400

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gas ranges for heat, particularly in projects like Potrero Terrace, where there are many 2- 3 bedroom units with only one radiator per apartment. In some instances, the time-trend plots revealed questionable or anomalous data. For example, energy usage was extremely low at the Sunnydale Project in May 1982 (see Fig. 1). Some investigation revealed that the project gas meter had been vandalized and was operable during only part of May 1982; data from this billing period were excluded from the regression analysis.

0

1083

Fig. 2. Cooking, space heating/domestic hot water, and total gas use for each "monthly" billing period

at Potrero Terrace Project. higher in winter months compared to summer averages at the two projects (Fig. 2). Residents probably cook at home more during the winter and holiday season. Local housing authority staff also believe that tenants use

The Normalized Annual Consumption (NAC) and parameter estimates for each project are summarized in Table 2. One of the Hayes Valley sites (Hayes C) was eliminated from the final analysis because of anomalies in the pre-retrofit billing data and poor correlation between energy use and outdoor temperature. The model was run iteratively to include various time spans in the pre- and post-retrofit periods in order to optimize results (i.e., highest coefficient of determination (R 2) and minimum standard errors in reference temperature). Typically, 10- 15 billing months are included in the final analysis. It is worth noting that higher quality results were obtained at the two projects with individual-unit space heaters than the three centrally heated projects. Occasionally, exclusion of a segment of the billing history significantly reduced the standard errors of the estimates, yet resulted in only small changes (1%- 2%) in NAC. The NAC indicator has a standard error of 1%- 2%. Not unexpectedly, this is much smaller than the errors in the individual parameters: base level, ~ (5%-10%), and heating slope,/~ (10% - 30%). R 2 values were greater than 0.83 at four projects, with typical values above 0.9, except for Alice Griffith Project. These values are much lower than values reported elsewhere in this issue for single-family houses in New Jersey (median R 2 above 0.95), yet are comparable to values (mean of 0.79) reported in 400 single-family, electric-heat homes located in the Pacific Northwest [8 - 10]. The reference temperature increased (by 1 - 6 °C) at all five projects between the preand post-retrofit period. A substantial drop

93

TABLE 2 Scorekeeping results

Project name

Pre-retrofit (1/81 - 10/82) eta

~b

Post-retrofit (1/83 - 4/84)

rc

NAC d

R 2

Ne

a

~

~

NAC

R 2

N

Hayes Valley B

2.50 176 (0.061) (66)

11.7 (1.6)

83.8 (1.4)

0.83 10

2.32 88 (0.122) (22)

18.3 (2.6)

88.1 (1.3)

0.90 10

Alemany

2.19 308 (0.073) (22)

14.8 (0.6)

91.4 (1.2)

0.98 11

1.75 220 (0.085) (22)

16.9 (0.9)

81.4 (1.2)

0.95 14

Sunnydale

2.60 330 (0.073) (44)

13.5 (0.7)

98.3 (1.3)

0.97 10

2.16 308 (0.110) (66)

14.7 (1.0)

89.1 (2.2)

0.86 14

PotreroTerrace

3.65 374 (0.110) (66)

14.8 (0.9)

142.1 (2.0)

0.94 11

2.77 264 (0.183) (44)

17.3 (1.4)

120.0 0.92 15 (2.0)

Alice Griffith

5.12 220 (0.098) (88)

13.6 (1.6)

173.1 (2.2)

0.73

3.37 154 (0.647) (22)

19.9 (5.2)

137.8 0.81 16 (2.1)

21.1

93.5

0.94 12

9

Co mpariso n gro u p

Valencia North Beach

1.82

154

(4.65) (14)

(12.8) (3.5)

3.31 (0.41)

20.1 (14.0)

265 (31)

166.6 (2.8)

0.90 13

1.79

20.8

96.4

(0.46) (11)

177

(3.0)

(o.5)

3.91 (0.54)

18.4 (6.3)

149.7 0.69 13 (3.1)

172 (57)

0.99

9

Results are from billing data adjusted for occupancy rates. Numbers in parentheses indicate the standard errors of the estimate. Multiplication of the standard error by 2.5 approximates the half-width of the 95% confidence interval. a~ is the temperature-independent or base level usage (kWth/unit). b~ is the heating slope (Wth/unit °C). cT is the reference temperature (°C). dNAC is Normalized Annual Consumption (GJth/year). eN is number of billing months included in regression analysis.

in base level, ~, accompanied this increase in reference temperature, T, in each of these cases. This drop in base level, if due to a real physical effect, could reasonably lead to a rise in reference temperature because of the concomitant drop in free heat. However, it is difficult to separate real physical effects from statistical effects when evaluating changes over time in individual parameter estimates.

Energy savings Gas savings are calculated in two ways -changes in the NAC between the pre- and post-retrofit periods, and changes relative to a comparison group (i.e., net savings). Table 3 summarizes individual project and aggregate results. NAC at the five projects decreased by an average of 14 GJth/unit after retrofit. The weatherization program achieved net energy savings of 8.5 GJth/unit, an 8% reduction, if we consider changes in consumption that occurred in the comparison

group. Energy savings varied widely, ranging from 9 % of pre-retrofit consumption at Alemany to 20% at the Alice Griffith site. The level of savings was more strongly correlated with pre-retrofit usage levels than with amount invested in retrofits. Those projects with the largest savings, in relative and absolute terms, also had the highest energy usage per unit before implementation of the program. The high consumption levels at Alice Griffith are due in part to the project's higher occupant density as well as improperly functioning heating system controls. W e observed room radiators with manual controller valves stuck in the "open" position and time clocks that were inoperable on several boilers. Energy use increased slightly at the Hayes Valley project after the retrofit.These disappointing results are difficult to explain. However, this project had the lowest initial gas consumption and therefore the smallest potential energy savings from the installed retrofit measures. At three-story Hayes

94 TABLE 3 Summary of savings results for SFHA ZIP program Project name

NAC a Before (GJth/unit-yr)

After (GJth/unit-yr)

Savings (GJth/unit-yr)

(%)

Hayes Valley Alemany Sunnydale Potrero Terrace Alice Griffith

83.8 91.4 98.3 142.1 173.1

88.1 81.4 89.1 120.0 137.8

--4.3 10.0 9.2 22.1 35.3

--5 11 9 16 20

Aggregate results c

112.0

97.8

14.2

12.7

Group A : 128.7 (Valencia, North Beach)

122.1

6.6

5.0

8.5

7.6

Cost of retrofit (19835)

Simple b payback (years)

82 160 203 93 165

* 3.3 4.5 0.9 1.0

154

2.1

Co m p a riso n gro u p

Net savings relative to Group A d

3.5

aComputed for data adjusted for occupancy rates. bSimple payback period is computed as cost divided by first year savings (gas savings multiplied by $5.10/MBtu). CAggregate results are obtained by weighting gas usage/unit before and after by the total number of units in each project. dNet savings (S) are calculated as follows: S = NACpre*(NACcpost/NACcpre ) -- NACpost. *Economic indicator cannot be calculated when there are negative savings.

Valley, only one-third of the units have direct contact with an insulated attic. This contrasts with the two-story townhouses at Alemany, Sunnydale, and Alice Griffith, where every apartment has an attic exposure. In addition, energy consumption at Hayes Valley was relatively insensitive to outdoor temperature as indicated by the large uncertainties in T (2.6 °C), and the relatively low heating slope, ~. Our site visits revealed one probable explanation for this phenomenon: the absence of adequate heating system controls, such as outdoor resets or cutout controls. W h e n we do not adjust for occupancy rates, we see a significant change in measured energy savings at the three projects with large changes in the number of occupied units between the pre- and post-retrofit period (see Table 1). For example, at the Alice Griffith project, the most extreme case, energy consumption decreased by 7.5 GJth/ unit after retrofit if we make no adjustment for occupancy, versus 35 GJth/unit when changes in the number of occupied units are explicitly considered. N A C at the five projects (unadjusted for occupancy rates) decreased by an average of 8 GJth/unit, versus 14 GJth/unit (adjusted).

Base level a n d space h e a t use

PRISM also allows us to estimate annual heating and base level consumption (although these parameters are less well determined than NAC) and thus to identify end uses with a large conservation potential. After retrofit, energy use declined markedly during the summer months at all projects except Hayes Valley. This trend is clear at the Alemany project when pre- and post-retrofit energy use are compared at zero heating degree-days (Fig. 3). Base level use, c~, is estimated at 1.75 kWth/unit after installation of conservation measures, a 20% decrease from the preretrofit level. The high a estimate in three of the projects (Fig. 4) suggests quite high appliance and domestic hot water consumption. We alternatively estimated base level gas use by taking utility bills from the summer months (July - September) and scaling consumption per day to a full year (indicated by arrows in Fig. 4). This technique yields base-level estimates that agree closely (within 2 - 3%) with those derived by PRISM, and provides additional evidence that temperature-independent demand declined after the retrofits. Central heating systems in San Francisco projects

95 4.0

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days, b o t h normalized b y the number of days in each billing period, at Alemany Project. NAC is expressed in GJth/year; units for (~ are kWth/unit; and ~, the heating slope, is expressed in Wth/unit °C. Heating degree
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Potrero Sunnydale Terrace San Francisco Housing Authority Projects

Fig. 4. Pre- and post-retrofit estimates of the temperature-dependent (dominated by space heating) and temperature-independent (base level) components of total gas consumption at three projects. Base level consumption is given by 365 × ~ and space heat use is calculated b y multiplying the heating slope, ~, b y heating degree-days in a " t y p i c a l " year, Ho(T ). Arrows indicate scaled-up summer consumption.

are not shut off during the summer months, unlike those in many Northeast and Midwest public housing authorities. Thus, space heating probably accounts for a small fraction of summer gas use, particularly in view of San Francisco's typical summer weather (e.g., mild temperature and coastal fog). Temperature-dependent consumption (presumably dominated by space heating), as estimated by PRISM, is a relatively small fraction (20%-25%) of total gas use. It increased slightly after retrofit, in contrast to what we expected, although ~, the heating slope, decreased at each project. Possible decreases in space heat use are masked by interactive effects among individual model parameters, especially in view of the large increase in r seen in four of the projects. Fels et al. performed parametric tests on the sensitivity of individual parameters and NAC to changes in reference temperature on single-family homes. They demonstrated that, as the reference temperature, T, increases, decreases and the space heat term increases, leaving the much more stable NAC indicator relatively unchanged [10]. This effect alone can produce an increase in the estimated space heat use, irrespective of the impact of conservation measures. Note that the change in base level is much larger than its standard error, while the change in heating use estimate is not (Fig. 4). Two major conclusions emerge from this analysis of individual parameter estimates: (1) annual base-level usage decreased significantly, despite uncertainties in model estimates and interactive effects, and (2) more detailed monitoring (e.g., indoor temperature measurements and submetered end-use data) is necessary before we can establish a causal link between changes in individual parameter estimates and associated conservation actions. Economic analysis We use two indicators of cost-effectiveness in the economic analysis: simple payback period and net present value (NPV). Simple payback period is the time required for the undiscounted value of the energy savings, at today's energy prices, to equal the original investment. The net present value of an investment is the difference between the present value of benefits and costs. A worth-

96

while investment has a NPV greater than zero. The NPV is determined as follows:

DISCUSSION

Bj--C

NPV j.0

where n is 10 years, the expected lifetime of the measures, when we estimate benefits, and eight years, the loan repayment period, in calculating costs; Bj is the annual (for year j) economic benefit {19835), Cj is the annual cost {19835) of the measures, and d is the discount rate. In calculating net present value, we assume that the real discount rate is 7%, that incremental maintenance costs are negligible, and that gas prices would increase at a real rate of 1.8% (based on California Energy Commission forecasts) [11]. The aggregate simple payback period is between 2 and 3.5 years, depending on whether we use gross or net energy savings, respectively {Table 3). In either case, the retrofit measures are worthwhile investments according to this criteria. The aggregate NPV results suggest that the ZIP program produces a gross benefit of $445/unit, and a net benefit of $220/unit at the five projects (see Table 4). The net benefit/cost ratio is 2.9 (assuming energy savings persist over the expected lifetime of the retrofit). The Housing Authority's retrofit cost containment policy contributes to the economic attractiveness of the weatherization effort. Retrofit costs, which averaged $150/unit, were only one-fifth of original utility estimates [12]. This low cost can be explained, in part, by competition that the bid process generated among private contractors; by utility cost estimates that were misleading because they were based on experience with individual homes rather than multifamily buildings; and apparent economies of scale from retrofitting large tracts of similar buildings. TABLE 4 Economic analysis of ZIP program

Net present value ($)

NPV/unit ($) Benefit/cost ratio

Retrofit

Savings

group aggregate savings

relative to group a

806 000 445 4.8

399 000 220 2.9

comparison

aNet energy savings are calculated relative t o comparison group.

Through our work with the San Francisco Housing Authority and survey of other local authorities, we have gained some insight into the process by which specific conservation measures are selected [12,1]. For the most part, it appears that local authorities use whatever programs or financial arrangement are readily available, without necessarily matching energy conservation efforts to the most cost-effective strategies. For example, under existing conservation programs, the San Francisco Authority is unable to fund adequately several highly costeffective retrofit options, including lighting conversions (incandescent to fluorescent) and improved operations and maintenance practices. Yet, the Authority had recently allowed an energy management firm to install a less predictably cost-effective measure, a solar hot water heating system at each of seven senior projects, in a "shared savings" venture. This retrofit has an estimated payback time greater than 10 years and its economic viability is dependent largely on utility rebates and existing energy and investment tax credits. The Authority faces the institutional barrier of reduced maintenance budgets, at the same time that it is attempting to improve routine building maintenance practices. There are several low-cost procedures that are likely to yield highly cost-effective energy savings. These practices include periodic checking and adjustment of heating system controls, repair of inoperable controller valves on apartment unit radiators, and repair of broken windows and boiler leaks. Faced with reduced operating budgets, most local authorities have turned to HUD modernization funds to finance energy-efficiency investments. Modernization funds are used mostly for equipment replacement rather than retrofit; conservation potential and reduced life-cycle operating costs are secondary criteria in the allocation of funds. We believe that it is short-sighted public policy to neglect the energy and dollar savings potential of prudent maintenance and energy management practices while encouraging capital-intensive equipment replacement that improves energy efficiency only as a byproduct (and, in some cases, replaces equip-

97

ment whose main problem is inadequate maintenance). Given the limitations of existing programs, optimal results in retrofitting low-income, multifamily buildings can only be achieved through conservation programs specifically aimed at that sector. Key elements for program success include strong technical assistance (e.g., engineering expertise, detailed site-specific building audit), sensitivity to tenant comfort concerns and lifestyle patterns (e.g., to avoid problems like vandalism), and program design that recognizes the severe financial constraints faced by most building owners, public or private.

CONCLUSION

Weather-normalized annual energy consumption declined in four out of five family housing projects in San Francisco after the implementation of various conservation measures. The energy savings were strongly correlated with pre-retrofit period consumption levels: large energy users saved more. Reductions in base-level consumption account for most of the savings. Our analysis indicates that the Housing Authority's retrofit efforts were cost-effective, with an average simple payback time of 3.5 years when adjusted for a comparison group, and a net benefit of $400 000 over the estimated lifetime of the retrofits. We found PRISM a useful tool for determining energy savings due to conservation measures in multifamily buildings. We believe that it is important also to account explicitly for changes in vacancy rates when analyzing changes in consumption patterns. Our results suggest that there are large uncertainties in the estimate of base level and space heat portions of total gas usage for muitifamily buildings that are located in very mild climates. Yet, accurate end-use estimates are an important first step in defining appropriate retrofit strategies. We believe that end-use estimates derived from model parameters need to be validated by more detailed monitoring than is typically done by HUD and local authorities. For example, in San Francisco, several central boilers should be instrumented in order to collect submetered data on space heat and h o t water use. This small-

scale research monitoring effort, along with technical audits that focus on heating system retrofits, would be useful initial steps for the Authority to take before embarking on expensive heating system capital improvements. The San Francisco Housing Authority has adopted an innovative approach in attempting simultaneously to maintain its housing stock, reduce energy consumption, and improve tenant comfort levels. The first generation of retrofits (mostly building shell improvements and low~ost hot water measures) has been completed at most projects and the Authority is currently investigating new opportunities (e.g., cogeneration, additional solar hot water systems, and heating system retrofits). The lessons learned here can help other public housing authorities across the country that face similar dilemmas: how to regain control over spiraling operating expenses yet still provide tenants with reasonable comfort and amenities in a period of tight budgets.

ACKNOWLEDGEMENTS The authors gratefully acknowledge assistance from Ronald Atkielski at the San Francisco Housing Authority. We thank Richard Diamond, Ed Vine, and Margaret Fels for their helpful comments on a draft of this report. T h e work described in this report was funded by the Assistant Secretary for Conservation and Renewable Energy, Office of Building Energy Research and Development, Buildings Systems Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

REFERENCES 1 R. L. Ritschard and D. Dickey, Energy conservation in public housing: it can work, Energy Systems and Policy, 8(3) (1984) 269 - 291. 2 C. Gold, The Page Homes Demonstration Project

for the Application of Computers to Energy Conservation in Public Housing Authority Projects, Bumblebee Energy Systems Inc., Trenton, NJ, February 1982. 3 C. Patten, M. Sherman and B. Shapiro, Case Studies of Successful Energy Conservation Programs in PHA's: St. Paul, Minnesota, Council

of Large Public Housing Authorities, Boston, MA, December 1982. 4 J. DeCicco, G. Dutt, D. Harrje and R. Socolow,

98 PRISM applied to a multifamily building: the Lumley Homes case study, Energy Build., this issue, pp. 77 - 88.

5 Greeneville Passive Solar Retrofit Demonstration, TVA/OP/ECR-84/62, Solar Applications Branch, Tennessee Valley Authority, Knoxville TN, 1984. 6 D. Erbs, S. Klein and W. Beckman, Estimation of degree-days and ambient temperature bin data from monthly-average temperatures, ASHRAE J., 25 (6) (1983) 60- 65. 7 R. C. Sonderegger, Movers and stayers: the resident's contribution to variation across houses in energy consumption for space heating, Energy Build., 1 (1978) 313 - 324. 8 D. Stram and M. Fels, The applicability of PRISM

8 to electric heating and cooling, Energy Build., this issue, pp. 101 - 110. 9 E. Hirst, Electricity savings one, two and three years after participation in the BPA Residential Weatherization Pilot Program, Energy Build., this issue, pp. 45 - 53. 10 M. Fels, M. Goldberg and M. Lavine, Exploratory scorekeeping for oil-heated houses, Energy Build., this issue, pp. 127 - 136. 11 Securing California's Energy Future: 1983 Biennial Report, California Energy Commission, Sacramento, CA, 1983. 12 Weatherization Program Report, San Francisco Housing Authority, San Francisco, CA, memo dated October 1, 1983.