Existing multi-unit residential buildings (MURBs) are important assets for urban regions such as Toronto, Canada. These buildings provide high-density housing and allow for the efficient provision of public services and utilities. However, MURB energy-use imposes a significant environmental burden. A preliminary part of the study presented here found that the median energy intensity of MURBs in Toronto is 300ekWh/m² and that this energy-use accounts for 17% of residential greenhouse gas (GHG) emissions in the City.

To reduce this environmental burden, this work explores a novel energy retrofit strategy involving a suite-based air-source heat pump (ASHP) operating in an enclosed balcony space which serves as a thermal buffer zone (TBZ) to improve the cold-weather ASHP performance in a heating-dominated climate. More broadly, a methodology for assessing the impact of an energy retrofit measure is developed.

First, energy-use and interior condition data were collected from a 1960s MURB over the course of one year. The subject building was found to have a higher-than-average energy intensity of 374ekWh/m² and other operational issues including overheating of suites. These data were then used to calibrate an energy model so that the proposed retrofit strategy could be modeled.

Next, the proposed retrofit strategy was tested in a mock apartment unit constructed in a climatecontrolled chamber. The testing showed that the coefficient of performance of the ASHP could be improved by operating it in a TBZ with access to heat from solar gains. This finding was used to modify the subject building energy model which showed that applying the proposed retrofit could reduce the annual energy intensity and GHG emissions of the building by 39% and 45%, respectively. An estimate of the impact of applying this retrofit strategy to Toronto MURBs with energy intensities greater than the median results in a median sector energy intensity of 236ekWh/m².