Residential buildings in the US, both single and multi-family, consumed 20.99 quadrillion Btu (quads) of primary energy in 2009, which is 54% of total building consumption. Much of this energy, about 49%, is lost during transmission and distribution [1]. Even though around 30% of the American population lives in multifamily dwellings, which accounts for around 25% of households, multifamily buildings have not received significant attention for energy conserving technology. Moreover, multifamily housing is usually older than single family housing. More than 70% of existing multifamily buildings were built before 1978, and during that time, there were no energy codes
