Improving Diagnostics and Energy Analysis for Multifamily Buildings: A Case Study

Multifamily buildings are approximately one quarter of the US housing stock, consuming over two quads of energy per year, and represent a considerable potential for energy conservation. This report describes a case study in multifamily retrofit research performed by Lawrence Berkeley Laboratory (LBL) in collaboration with the city energy office in Minneapolis, MN. The basis for the case study is a one-week experiment in a seven-unit brick apartment building in Minneapolis. The experiment was to use diagnostics that are not conventionally performed in multifamily buildings to evaluate existing and potential retrofits. The project included a detailed energy balance on the building's brick set steam boiler and an examination of the air leakage paths throughout the building. The boiler diagnostics involved determination of jacket heat loss from surface temperature measurements, and determination of off-cycle stack loss from tracer gas and stack gas temperature measurements. The off-cycle stack loss measurements showed that a vent damper, a retrofit that restricts the flow through the boiler flue when the boiler is not operating, reduced the energy consumption of the boiler by approximately 10%. The air leakage diagnostics involved blower door tests to measure the total external leakage area, (using six blowers doors to pressurizemore » the entire building), and tests to distinguish the leakage areas of different flow paths, made by testing individual apartments with and without simultaneous pressurization of adjacent apartments. These tests show that only 40% of the leakage area of the apartments is in the exterior envelope. These leakage areas are used in conjunction with a multizone air infiltration model to determine the flows between apartments and to the outside.« less