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 pro- gram (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 pro- gram 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, con- tributed 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 ini- tiated major retrofit programs. In 1980, HUD

awarded $23 million to 47 PHAs for mod- ernizing 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 moderni- zation funds were used for energy conserva- tion.

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 Com- pany (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 con- sumption 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 rough- ly 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 ap- proaches for selection, marketing, and financ- ing 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. In- novative financial strategies are necessary in order to overcome existing institutional barriers and tight budgetary constraints. This study also adds to research on multi- family buildings. A significant fraction of the nation's public housing units are multi- family buildings. Until recently, the multi- family sector has received much less attention and study than have single-family residences.

RETROFIT AND BUILDING DESCRIPTION

Four of the five family housing projects in this s tudy 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 apart- ments are two-bedroom units; one- and three- bedroom units each account for approximate- ly 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 sug- gests that, in any energy conservation effort, additional funding for and at tention to basic maintenance must be considered in addition to weatherization measures.

Under the utility's conservation program, an interest-free loan of up to $1000/uni t 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 Authori ty staff inspected a repre- sentative sample of apartment types managed by the Authori ty to determine which conser- vation measures were suitable. Those housing projects with the highest estimated potential savings were chosen first. Typically these were townhouse apartments with accessible attics. Bid packages were prepared for each project and bids were then requested from weatherization contractors certified to partic- ipate in the zero-interest loan program (ZIP).

Attic insulation and exterior door weather stripping were installed at each project. Two sites with hot water heaters in individual dwelling units received insulating blankets (Table 1). Retrofi t costs ranged from $80 to $200 per unit, with an average of $150/ unit. In addition, inexpensive t ime clocks, costing approximately $85/boiler, were in- stalled on central boilers at three projects in October 1982; this measure was not part of the ZIP program. The t ime clocks regulate the space heat water circulation pump, so the pump would run for 14 hours rather than 24 hours a day. Housing Authori ty staff

TABLE 1

Building description and retrofit measures

Project name Alemany Potrero Terrace Sunnydale Alice Griffith Hayes Valleya

Total units 158 469 767 258 170 Occupied units b

Pre-retrofit 152 393 677 193 151 Post-retrofit 150 418 705 236 148

Avg. floor area (m 2) 81 77 81 78 72 Occupants/Unit c 4.0 3.3 3.7 4.8 2.6 Year built 1956 1942 1942 1962 1963 Heating system type d SH CB SH CB CB Retrofit measures e IA, CW, WH IA, CW, TC, SH IA, CW, WH IA, CW, TC IA, CW, TC

aHayes Valley is located at three separate sites. We have included results for only one site, Hayes B, which rep- resents 170 of 328 units. Hayes C (140 units) was excluded due to anomalous utility billing data. bAverages were computed over the number of billing periods used in regression analysis. cOccupant data are from 1982. dSH = room space heater; CB = central boilers that supply both space heat and domestic hot water. eIA = attic insulation, CW = caulking/weather stripping, TC = time clock on boiler, SH = low-flow shower-head, WH = water-heater jacket.

indicated that the timers would be discon- nected 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 com- puted heating degree-days to different refer- ence temperatures. Normal year heating degree-days were computed to different reference temperatures using the 30-year normal monthly outdoor average temper- ature 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 turn- over 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 con- sumption due to retrofitting would be masked by increases in the number of occupied dwel- lings (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-

91

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 indi- vidual 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 con- servation 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 (1940- 50s), have central heating plants, and are occupied by families. However, the Score- keeping results seem to be not reliable (e.g., large standard errors in the reference temper- atures; see Table 2). For these reasons, changes in energy consumption in the com- parison group and the corresponding adjust- ment in the treatment group's savings should be viewed cautiously.

RESULTS

Actual energy consumption Energy usage tracks seasonal weather

variations (as indicated by heating degree- days, 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 con- sumption 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 consump- tion. Average gas consumption/unit for cook- ing 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%

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400 400 -

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Fig. 1. Gas use/day, heating degree-days, and the number of occupied units for each "monthly" billing period at Sunnydale Project.

ZIP Retrofit 450 Boiler

\eTime Cloc i TOTAL GAS USE /r : HEATIN.-OHW

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

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.

Quality of the PRISM results 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 elim- inated from the final analysis because of anomalies in the pre-retrofit billing data and poor correlation between energy use and out- door temperature. The model was run iter- atively 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 com- parable 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 pre- and post-retrofit period. A substantial drop

TABLE 2

Scorekeeping results

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Project name Pre-retrofit (1/81 - 10/82) Post-retrofit (1/83 - 4/84)

eta ~b rc NAC d R 2 N e a ~ ~ NAC R 2 N

Hayes Valley B 2.50 176 11.7 83.8 0.83 10 2.32 88 18.3 88.1 0.90 10 (0.061) (66) (1.6) (1.4) (0.122) (22) (2.6) (1.3)

Alemany 2.19 308 14.8 91.4 0.98 11 1.75 220 16.9 81.4 0.95 14 (0.073) (22) (0.6) (1.2) (0.085) (22) (0.9) (1.2)

Sunnydale 2.60 330 13.5 98.3 0.97 10 2.16 308 14.7 89.1 0.86 14 (0.073) (44) (0.7) (1.3) (0.110) (66) (1.0) (2.2)

PotreroTerrace 3.65 374 14.8 142.1 0.94 11 2.77 264 17.3 120.0 0.92 15 (0.110) (66) (0.9) (2.0) (0.183) (44) (1.4) (2.0)

Alice Griffith 5.12 220 13.6 173.1 0.73 9 3.37 154 19.9 137.8 0.81 16 (0.098) (88) (1.6) (2.2) (0.647) (22) (5.2) (2.1)

Co mpariso n gro up Valencia 1.82 154 21.1 93.5 0.94 12 1.79 177 20.8 96.4 0.99 9

(4.65) (14) (12.8) (3.5) (0.46) (11) (3 .0 ) (o.5) North Beach 3.31 265 20.1 166.6 0.90 13 3.91 172 18.4 149.7 0.69 13

(0.41) (31) (14.0) (2.8) (0.54) (57) (6.3) (3.1)

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 in- terval. 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 cor- related 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 proj- ect's higher occupant density as well as improperly functioning heating system con- trols. We 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 disap- pointing 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

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TABLE 3

Summary of savings results for SFHA ZIP program

Project name NAC a

Before After Savings (GJth/unit-yr) (GJth/unit-yr) (GJth/unit-yr) (%)

Cost of retrofit (19835)

Simple b payback (years)

Hayes Valley 83.8 88.1 --4.3 --5 82 * Alemany 91.4 81.4 10.0 11 160 3.3 Sunnydale 98.3 89.1 9.2 9 203 4.5 Potrero Terrace 142.1 120.0 22.1 16 93 0.9 Alice Griffith 173.1 137.8 35.3 20 165 1.0

Aggregate results c 112.0 97.8 14.2 12.7 154 2.1

Co mpa riso n gro up Group A :

(Valencia, North Beach) 128.7 122.1 6.6 5.0

Net savings relative to 8.5 7.6 3.5 Group A d

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 expla- nation for this phenomenon: the absence of adequate heating system controls, such as outdoor resets or cutout controls.

When 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. NAC at the five projects (unadjusted for occupancy rates) decreased by an average of 8 GJth/unit, versus 14 GJth/unit (adjusted).

Base level and space hea 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 conserva- tion measures, a 20% decrease from the pre- retrofit level. The high a estimate in three of the projects (Fig. 4) suggests quite high appliance and domestic hot water consump- tion. 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 de- rived by PRISM, and provides additional evidence that temperature-independent demand declined after the retrofits. Central heating systems in San Francisco projects

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Fig. 3. P lo t o f t o ta l gas use versus heat ing degree- days, both normalized by 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<lays are calculated based on the pre-retrofit reference temperature (14.8 °C). Lines represent the best fit o f pre- and post-retrofi t consumption data to that HDD base.

4.0

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San Francisco Housing Authority Projects

Fig. 4. Pre- and post-retrofit estimates of the temper- ature-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 by multiplying the heating slope, ~, by heating degree-days in a " typ ica l" year, Ho(T ). Arrows indicate scaled-up summer consumption.

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are not shut off during the summer months, unlike those in many Northeast and Midwest public housing authorities. Thus, space heat- ing 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 (pre- sumably 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 signif- icantly, despite uncertainties in model esti- mates 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:

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 Cali- fornia 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 re- trofit 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 life- time of the retrofit). The Housing Authority's retrofit cost containment policy contributes to the economic attractiveness of the weather- ization 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 contrac- tors; by utility cost estimates that were mis- leading because they were based on experi- ence with individual homes rather than multi- family buildings; and apparent economies of scale from retrofitting large tracts of similar buildings.

TABLE 4 Economic analysis of ZIP program

Retrofit Savings group relative to aggregate comparison savings group a

Net present value ($) 806 000 399 000 NPV/unit ($) 445 220 Benefit/cost ratio 4.8 2.9

aNet energy savings are calculated relative to compari- son group.

DISCUSSION

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 conserva- tion measures are selected [12,1]. For the most part, it appears that local authorities use whatever programs or financial arrange- ment are readily available, without neces- sarily matching energy conservation efforts to the most cost-effective strategies. For example, under existing conservation pro- grams, the San Francisco Authority is unable to fund adequately several highly cost- effective 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 invest- ment tax credits.

The Authority faces the institutional bar- rier 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 operat- ing budgets, most local authorities have turned to HUD modernization funds to finance ener- gy-efficiency investments. Modernization funds are used mostly for equipment replace- ment rather than retrofit; conservation po- tential and reduced life-cycle operating costs are secondary criteria in the allocation of funds. We believe that it is short-sighted pub- lic policy to neglect the energy and dollar sav- ings potential of prudent maintenance and energy management practices while encourag- ing capital-intensive equipment replacement that improves energy efficiency only as a by- product (and, in some cases, replaces equip-

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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 pro- gram success include strong technical assis- tance (e.g., engineering expertise, detailed site-specific building audit), sensitivity to tenant comfort concerns and lifestyle pat- terns (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 con- sumption declined in four out of five family housing projects in San Francisco after the implementation of various conservation mea- sures. The energy savings were strongly cor- related with pre-retrofit period consumption levels: large energy users saved more. Reduc- tions 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 deter- mining 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 cli- mates. 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 moni- toring than is typically done by HUD and local authorities. For example, in San Francis- co, several central boilers should be instru- mented in order to collect submetered data on space heat and hot 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 ex- pensive 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 assis- tance 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. The work described in this report was funded by the Assistant Secretary for Conservation and Renewable Energy, Office of Building Energy Research and Develop- ment, 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 conser- vation 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 Proj- ects, 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,

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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 contr ibution 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.