Multifamily building energy retrofit comparison between the United States and Finland

Due to the high heating demand, energy savings in residential buildings in cold climates has played an important role in reducing carbon emissions. This study aims to investigate differences between the United States and Finland regarding characteristics and energy retrofit practices of current multifamily buildings (MFBs). The study focuses on net zero energy or nearly zero energy performance in cold and very cold climatic conditions. First an overview is presented of the status of multifamily housing stocks in the two countries, followed by an explanation of energy use patterns of residential buildings in both countries. Then, building codes related to energy efficiency in Finland and the United States are examined as well as major differences between the codes. Lastly, to further understand the different strategies and techniques used in energy retrofit projects, a dataset of 57 MFBs from both countries, both net zero energy buildings (ZEB) and nearly zero energy buildings (nZEB), were collected and analyzed. The preliminary results indicate three differences: (1) For the existing national MFB stock, the United States has a higher average energy use (EUI), at 266 kWh/m² per year (cold and very cold regions), compared to that of Finland, at 235 kWh/m² per year, (2) Finland has more stringent energy code requirements that contribute to lower energy use in studied case projects with a mean EUI of 80 kWh/m² per year compared to 148 kWh/m² per year in the U.S. sample,(3) In the Finnish studied cases, the heating and ventilation systems play a more critical role in explaining the building energy use differences in the sample, while in the U.S. cases, building envelope thermal properties explained the energy use intensity variations in the sample. Overall, the comparison of the Finnish and American cases showed that good technical practices from Finland can be learned to reduce the heating demand in cold and very cold climate regions of the United States.