|Welcome To Home Energy Magazine Online|
|Welcome To Home Energy Magazine Online
by Kathy Robinson, Mike Myers, and Bert Brown
Multifamily buildings in warm climates often use a lot of electricity for air conditioning, presenting excellent opportunities for energy savings. The City of Austin has found that fixing leaky ducts and installing higher-efficiency air conditioners and heat pumps in these buildings can provide significant demand reductions.
The multifamily program began by providing HVAC tune-ups and audits to about 28,000 units in 1990. The program saved approximately 27 MW through 1993 and provided services to about 73,000 units. The city now offers rebates and technical assistance for building rehabilitation and new construction. For existing buildings, Austin has rebates and free energy audits on building envelope measures, such as ceiling insulation; solar water heaters; window treatments; duct system testing and repair; lighting systems; and high efficiency HVAC systems.
The audit for existing buildings consists of a quick walk-through survey of the property with the building management staff. The city then sends a letter to the property owner and manager describing in detail energy efficiency options that they should consider. Several factors have made the program successful: continual education of property managers and their staff; local contractor training; and direct communication with property owners, builders, and architects.
Duct Sealing Is Cost-Effective
Many multifamily buildings in Austin have individual central air conditioning with ducted distribution to the units. (They are usually heated by central gas furnaces, central electric resistance, or, in the newer buildings, heat pumps.) The average apartment complex has 150 units, with 8 to 15 units per building.
In late 1993 and 1994, the city conducted a pilot study of 100 existing apartments to ascertain the energy savings, if any, associated with duct system repairs. Using the MADAIR methodology from John Tooley at Natural Florida Retrofit, we tested units in 10 different complexes of varying ages, construction, and locations. Two of the buildings used natural gas for heating. The rest were all-electric, which is common for this area.
The city hired a local HVAC contractor to test the duct leakage, seal the ducts, and then retest to determine the improvement. The contractor also collected information (the capacity and efficiency of the air conditioner) to estimate cooling load. Blower doors were used to test for infiltration. From this information, we estimated an average demand savings of 0.29 kW per apartment, making duct sealing a cost-effective retrofit.
The Hills of
Chevy Chase Apartments
The Hills of Chevy Chase apartments are an example of the high savings that can be achieved with cooling system retrofits. This complex consists of 20 brick veneer, two-story buildings, which each have nine 780-ft2 units. Each unit had a packaged air conditioner and electric furnace installed on the roof. The ducts were leaky, and first- and second-floor units shared a common return air cavity. The existing air conditioners had been installed in 1968 and had an Energy Efficiency Ratio (EER) of 6.0. Some residents complained of bills as high as $200 per month during the summer, and many in the lower apartments (furthest from the rooftop cooling systems) could never sufficiently cool their units. The owner spent $20,000-$30,000 each year on air conditioner maintenance, and the complex had a high tenant turnover rate.
The contractors air-sealed between floors and installed new split system air conditioners with a Seasonal Energy Efficiency Ratio (SEER) of 12.7. The evaporator coils were installed with new electric furnaces in the linen closet of each apartment. They sealed existing ductwork within each apartment and installed new returns and ducts at each unit.
The retrofit cost about $2,100 per apartment. The occupants saved approximately $1,200 per apartment each year on utility bills; during the summer, they saved as much as $160 a month. And the City of Austin reduced its source peak demand by 307 kW.
Kathy Robinson is the multifamily program coordinator for the City of Austin. Bert Brown was the city's multifamily program manager from 1992 to 1994. Mike Myers is currently with the U.S. Department of Energy; he was previously the manager of energy services for the City of Austin.