This article was originally published in the September/October 1995 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online September/October 1995
Profiles of Multifamily
Crown Heights Jewish Community Center, 1082-1096 President Street, Brooklyn, NY
This Brooklyn block is like hundreds of others in the borough that were built in the first half of the twentieth century: four-story, heavy brick construction apartment buildings in the middle of the block, with taller apartment buildings on each corner flanking the row.
Two pairs of individual apartment buildings (each a 20-unit walk-up) were the subject of weatherization measures. Each set of two buildings encloses a central courtyard, creating a rectangular donut-shaped building plan. The average apartment size is 518 ft2 with 9-ft ceilings. Most apartments have windows on one side only, and these are the original wood double-hung units with no storm windows.
Like all multifamily building audits in New York City, this one was conducted with the aid of recent billing records and EA-QUIP, a computer-based analytical package (see Confessions of an `Addicted' Auditor, HE May/June '94, p. 29).
The weatherization agency upgraded the heating systems and switched to a lower cost fuel as part of a daring heating system retrofit. Originally, each of the four buildings had heat and domestic hot water (DHW) supplied by its own 1.2 MMBtu/h output natural gas-fired, atmospheric one-pipe steam boiler. The heating-system retrofit consisted of replacing all four units with one forced-air, steel-tube steam boiler with a 4.2 MMBtu/h output. It provides heat and DHW for all four buildings.
The new unit burns #6 fuel oil, which costs 42% less than natural gas in New York. The new control system includes a standard heat timer; however, a hot water mixing device was also installed. The mixer continually senses return water temperature from each building and automatically mixes the required cold water to maintain each building's minimum heat requirement while providing on-demand DHW.
The boiler replacement included interconnection of the basement area supply and return lines as well as extensive pipe insulation, sealing of miscellaneous pipe openings and window openings, and whitewashing walls and ceilings.
Reduction of heat loss due to the stack effect was addressed by controlling the access door opening at the top and bottom of the central stairwell and by weatherstripping apartment entry doors. The building's lower entrance doors are typically kept closed and locked for security reasons. However, before weatherization, the roof door did not lock and was very often left open. The roof door is now weatherstripped and closed. A burglar alarm system deters unauthorized access.
Energy-efficient fluorescent lighting was installed in the hallways and in the kitchens and bathrooms of each apartment.
Weatherization work was augmented by client education. The auditors informed the building residents of the nature of the work and of the importance of keeping doors closed. Education was also provided to the building superintendent, making sure he understood the new heating system and could manage it correctly.
The combined consumption rate in the four buildings was 30 Btu/ft2/HDD for a total normalized annual consumption (TNAC) prior to weatherization of 8,400 MMBtu. The postweatherization consumption rate was 26 Btu/ft2/HDD, a reduction of 16% in heating-only normalized annual consumption (HNAC).
These numbers are more impressive when the reduction in cost of fuel is considered. Natural gas from the local utility costs approximately $7.20 per MMBtu, while #6 fuel oil costs $4.20 per MMBtu. The calculated annual savings is $32,500. The total cost of the retrofits was $99,500, and the benefit-to-cost ratio, based on a 20 year life and 4.7% real discount rate, is 4.5.
The multifamily housing stock that was the subject of the Massachusetts case study is composed primarily of wood-framed, brick veneer buildings with flat roofs. These structures are built in a variety of early twentieth-century architectural styles and have interior light and ventilation shafts or building configurations that include courtyards. The attics are typically below a low-pitched flat roof and are accessible only through an interior trap door, which is usually installed during weatherization.
47-49 Vernon Street,
This three-story, wood-framed brick veneer building was built early this century by a local manufacturer to house employees. It contains nine apartments (475 ft2 each) and one commercial unit (which is not in use). Individual heating and domestic water heating, both gas fired, are located in each apartment. The heating units are combined with the cookstove. The heating portion of the unit is controlled by a thermostat and is vented; however, the cooktop is not vented. The windows are double-hung wood with vinyl storm windows.
The weatherization crew from the Hampden Hampshire Housing Partnership paid close attention to the safety of the mechanical and electrical systems. They inspected the knob-and-tube wiring throughout the building, paying special attention to areas that were to be insulated, and made electric wiring and panel box repairs before starting other work. They inspected the combination heater-cookstoves in each apartment and cleaned and tuned several that were burning inefficiently. Pre- and postweatherization tests for carbon monoxide are routinely done on all weatherization jobs in Massachusetts (see Carbon Monoxide from Ovens, p. 18). Gaps around the vent stacks of domestic water heaters, which are also located within the living space, were repaired.
The crew did blower door testing in conjunction with insulation and air sealing work. They tested one apartment on each floor of the building before and after weatherization measures were installed, and measured individual apartment air leakage reductions ranging between 300 and 1,000 cubic feet per minute at 50 pascals of pressure (cfm50). (A 1,000 cfm50 reduction would likely reduce annual fuel bills by about $50/unit.)
The crew made it a priority to control heat loss at the bottom of the building envelope in the basement area. They used spray foam to seal the basement sill, basement windows, and mechanical penetrations, and blocked bypasses with blue foam board. They doubly secured batt insulation at the basement ceiling with both staples and wire supports.
The most expensive item was storm windows, which accounted for 37% of the total cost.
The weatherization achieved 28% savings in natural gas, which amounted to $1,200. It cost $9,200 for this nine-unit building (a benefit-to-cost ratio of 1.6).
In Chicago, Illinois, the weatherization program is run by the city Department of Housing. The Department has traditionally increased the impact of the DOE weatherization investment by leveraging additional funds from building owners. Although the Department pays the full cost of, say, storm windows or a boiler tune-up, they require a 50% landlord contribution for especially expensive retrofits such as new primary windows or heating plant replacement.
5220 South Drexel Avenue,
For years, most of the larger retrofit projects involved city- or HUD-owned structures. The 5220 South Drexel Avenue site was the first large privately owned building weatherized by the city.
Built in 1926, this four-story, 72-unit building embraces nearly 56,000 ft2 of living space (about 778 ft2 per apartment). Originally the Drexel Residence Hotel in the fashionable Hyde Park area of Chicago, the building is solid brick with 18-in-thick fire walls between apartments.
The building is very well maintained, and the owners are both informed about and concerned with energy efficiency and other critical residential issues (such as lead paint). At present, over 40% of the tenants in this building are disabled, and the owners intend to convert unused ground floor space into additional apartments in order to make effective use of the handicapped access to that area.
In this 6,625 HDD climate, the heat and hot water are supplied by a large 2 million Btu/h input, gas-fired Kewanee steel fire tube boiler with a gas power burner.
The owner paid 50% of window replacement for 55 apartments and 100% for an additional 5 apartments. The installed windows are high-quality, double-glazed, vinyl-framed units. Work was completed by May of 1993, with $29,000 contributed by DOE.
At the same time, the owners installed new doors for each apartment and new steel fire doors in the stairways.
Heating-energy usage was cut 27% for a savings of nearly 10,500 therms of natural gas per year. The bill analysis also showed an unexplained 10% reduction in anual baseload energy use for a total annual savings of nearly 12,500 therms.
Such impressive fuel savings and payback from what was principally a window replacement may seem surprising given the Brooklyn results. However, in combination with the window replacements, the new doors contributed significantly to reducing stack effect and air leakage, thus allowing better control over the building temperatures and heating system operation. In addition, the building is now less drafty, maintenance costs are lower, the appearance is improved, and a major source of lead dust has been eliminated.
If this building were being retrofitted under the guidelines in place now for the City of Chicago, major retrofitting of the heating plant would be considered. The present boiler is getting thin on the bottom and demands $1,500-$2,000 per year in maintenance. Since all domestic hot water is supplied by this boiler, there are also extreme inefficiencies during summer operation. However, this project demonstrates that it is possible to get cost-effective savings in large multifamily buildings through architectural measures, when such retrofits are paired with careful operation and maintenance.
In the greater St. Paul, Minnesota, area, weatherization is carried out by the Ramsey Action Program (RAP). Making extensive use of many technical advancements of its own and other local research groups and individuals, RAP also uses a state-sponsored, comprehensive multifamily audit workbook and training program.
Pullman Avenue Buildings,
These two buildings are outwardly identical, three-story wood-framed structures, owned by the Housing Resource Authority (HRA). They have brick front facades and stucco side and rear walls. Each building has six apartments and a total of 8,950 ft2 of living space (about 1490 ft2 per unit). Prior to weatherization, each had fiberglass in the walls and 6 in of insulation in the attic. All have through-the-wall air conditioners and aluminum slider windows with aluminum storms.
Although both buildings were built in the mid-1970s by the same contractor, 316 has individually metered electric baseboards in each apartment, while 332 has central gas multizone hydronic heat.
Envelope measures in both buildings included
- Sealing bypasses in the attic.
- Increasing attic insulation from R-22 to R-44.
- Insulating a small crawlspace under the front entrance.
- Installing covers over through-the-wall air conditioners.
In the centrally heated building, the weatherization program also installed new outdoor reset and cutout controls on the boiler and added pipe insulation to all exposed distribution lines.
The electrically heated building, which received only envelope measures, cost $1,200, while the centrally heated building received about $1,900 of work.
These retrofits were particularly interesting because we could compare two otherwise identical buildings that had different heating systems, and to which different sets of measures were applied. The apartments in the electrically heated building (316 Pullman) are individually metered, which also facilitated an apartment-by-apartment comparison of pre- and postretrofit fuel use patterns.
In 332 Pullman, where both envelope and heating system retrofits were applied, the overall energy savings were significantly greater than in the electrically heated building (95 MMBtu versus 15 MMBtu). However, higher installation costs in 332 and significantly lower fuel prices result in a lower benefit-to-cost ratio (2.59 versus 3.92).
Although 316 Pullman showed moderate overall savings from the envelope improvements, there was wide variation among individual units. Results for individual apartments can be misleading because there is inevitable heat transfer among units and occupancy can change. Nonetheless, the individual apartment consumption data show some important patterns.
Apartments on the lower floors had lower preretrofit consumption than those on the top floor. This can be explained by the fact that only the top floor apartments were exposed to cold ceiling temperatures from the poorly insulated attic.
After retrofit, the third-floor apartments had not only the greatest savings but also the lowest postweatherization energy bills. However, energy use in the first-floor apartments actually increased. How can this be explained? The attic insulation not only reduces energy use for the upper apartments but may, in fact, cause these units to overheat as warm air rises from the lower units. If the overheating is great, the occupants are likely to open windows to alleviate the situation. This increases the impact of the stack effect and more heat is drawn from the lower apartments, thus increasing their energy use.
In extreme cases, such dynamics could actually lead to a condition where the addition of attic insulation in a multistory building will increase overall building energy use. In support of this theory, it should be noted that on the morning we visited these buildings the outside air temperature was 42deg.F, but the previous day had been unseasonably warm. We noted during our visit that all of the third floor apartments in all three buildings had at least one open window.
727 Front Street,
The 727 Front Street building is a 20-story high rise with 151 units, owned by the St. Paul Public Housing Agency. Heat is produced by two 5 million Btu/h dual-fuel Kewanee boilers, which use oil and gas. These provide multizone, two-pipe steam heat and hot water. Built in 1970, the building has 112,000 ft2 of conditioned space with a pre-retrofit calculated energy index of 12 Btu/ft2/HDD.
RAP determined that the most cost-effective energy savings would come from non-heating season hot water loads and common-space lighting. All of the weatherization work (completed in April 1991) focused on the mechanical systems and lighting except for the installation of room air conditioner covers.
Before this retrofit, boiler condensate, returning at 180deg.F, used to freeze as it passed the large combustion air intakes for the boiler. RAP insulated all exposed DHW pipes as well as the condensate return line from the boiler. The freezing problem was further mitigated through repair of combustion air dampers, which had been damaged.
RAP installed two Triad front-end modular boilers (240,000 Btu/h output each) for summer domestic hot water and recommended that the two larger boilers be run only in winter as staged units. Although the boilers were subsequently shut down in the summer as planned, during the heating season the building operator chose to run the two units in parallel, rather than in a staged sequence as recommended.
RAP replaced incandescent fixtures with fluorescents in exit signs and stairwells. Existing fluorescent fixtures in the common areas were retrofitted with new reflectors and high-frequency electronic ballasts (see Bright Prospects for Lighting Retrofits, p. 41).
The total installed cost of $39,000 included $22,400 for lighting retrofits. Proper disposal of old lighting ballasts, which may have contained PCBs, was funded with a grant from Northern States Power. The two front-end Triad boilers cost $10,000, and the cost of the pipe insulation was approximately $900.
The summer baseload consumption was reduced by 27% for a savings of 245 MMBtu. A lifetime savings of $10,500 and a benefit-to-cost ratio of 1.04 demonstrates that the retrofit was barely cost-effective, partly because the building operators failed to utilize the winter savings potential of staged boiler operation.
The lighting retrofits saved 170,000 kWh per year, approximately 20% of the electrical consumption for the building. The benefit-to-cost ratio is 4.0, which illustrates how cost-effective a thoughtfully designed lighting retrofit can be, especially since lights in common areas are typically illuminated 12 to 24 hours per day.
Most of the 91,000 apartments in Seattle are in two- to three-story low-rise buildings of 15 to 30 units. A high percentage of the older housing stock has electric baseboard heaters and electric water heaters, although natural gas is used for heating and water heating in newer units, a trend that is supported by Seattle City Light even though the utility does not sell natural gas.
Summers are mild in the Seattle area, so air conditioning is rare. However, winters are chilly; Seattle experiences 5121 heating degree days, slightly more than either New York City or Philadelphia. Nonetheless, wall insulation in multifamily housing stock is the exception and ceiling insulation tends to be either absent or minimal. On the other hand, many buildings are fairly airtight due to local construction techniques and the lack of flues and chimneys. This, in combination with Seattle's humid climate, sometimes results in moisture problems.
Crescent Arms Apartments,
This is architecturally the most unusual multifamily building encountered in this series of case studies. The Crescent Arms is built in the form of a fortified annulus, forming five-eighths of a circle, an architectural feature that allows each of the 37 apartments in the three-story structure to have light from two sides and cross ventilation. Each apartment is about 480 ft2.
Like most multifamily buildings in Seattle, the Crescent Arms is a wood frame structure with a masonry facade. It has poured-concrete partitions and a flat roof. It appears to be quite tight; before weatherization, conductive losses from uninsulated walls and single-glazed windows were the largest paths for heat loss.
Weatherization consisted principally of installing insulation and new windows. The wall insulation covered 4,200 ft2 at a cost of 70¢ per ft2. The space between the ceiling and the flat roof could not be accessed, but it is believed to be insulated. On the other hand, the floor above the crawlspace could be insulated, so 5,550 ft2 of 9-in unfaced batts were installed, using nails and nylon twine to hold the insulation in place. Material and labor for this measure cost 72¢ per ft2. To protect water pipes from freezing, 1,215 feet of pipe insulation was added at a cost of 67¢ per ft.
A total of 239 double-glazed vinyl windows were also installed at the Crescent Arms at a cost of $57,000, 73% of the total job cost. Finally, 78 energy-efficient lighting fixtures replaced incandescents (including 13 100W high-pressure sodium exterior lights to provide security) at a total cost of $6,000. Adding several air sealing measures and two power vents brought the cost of the entire job to $77,000, approximately four times the total annual energy cost for the building.
This weatherization job resulted in a 26% savings in heating energy, and a fuel cost savings of $3,300.
Larry Kinney is president of the Synertech Systems Corporation in Syracuse, New York and Tom Wilson is a building scientist with Synertech. Michael MacDonald is a program manager in Commercial and Multifamily Building Research with the Energy Division of the Oak Ridge National Laboratory.
Gerety, F. How to Get the Best from One-Pipe Steam, New York: City Books (1987), 1 Centre Street, Rm 2223, New York, NY 10007.
Goldman, C. A., Greely, K. M., and Harris, J. P. Retrofit Experience in U.S. Multifamily Buildings: Energy Savings, Costs, and Economics, LBL-25248. Berkeley, CA: Lawrence Berkeley Laboratory, 1988.
Goldner, F., and Judd, P. Building Energy Use Tracking System. Final Project Report prepared by the Energy Conservation Division of the New York City Department of Housing Preservation and Development for the New York State Energy Research and Development Authority, 1989.
Judd, P. The Overheated City: The Prospects for Improved Fuel Economy in the Multi-family Residential Buildings of New York City. New York: by the author, 285 Riverside Drive, 3D, New York, NY 10025, 1990.
Judd, P. How Much is Enough: Controlling Water Demand in Apartment Buildings: American Water Works Association (1993), 6666 West Quincy Ave., Denver, CO 80235.
MacDonald, J. Description of the Weatherization Assistance Program in Larger Multifamily Buildings for Program Year 1989, ORNL/CON-329. Oak Ridge, TN: Oak Ridge National Laboratory, 1993.
Rodberg, L., Cherry, R., Cohen, G. Computerization of the New York State Weatherization Assistance Program, Energy Authority Report 91-13. Final Project Report prepared by the New York Urban Coalition Housing Group Inc. for the New York State Energy Research and Development Authority, 1991.
|The publication of this article in Home Energy was underwritten in part by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy.|
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