Building energy assessments of cold climate heat pumps using two-capacity and three-capacity compressors

This study explores two innovative cold-climate heat pump (CCHP) prototypes—one featuring a tandem arrangement of two parallel compressors and the other using a single three-capacity compressor—designed to address heating and cooling challenges in colder regions. The prototypes aim to improveaims to energy efficiency, reduce peak power, and enhance energy-saving potential, and were assessed against a baseline single-speed heat pump through laboratory experiments and EnergyPlus building energy simulations. The tandem system uses two parallel single-speed compressors to modulate capacity and improve heating and cooling performance, while the three-capacity compressor provides output levels of 45%, 67%, and 100%. Laboratory results and calibrated EnergyPlus simulations demonstrated substantial performance improvements. Simulations were conducted for multiple residential building types meeting IECC 2006, 2009, 2012 standards across seven U.S. cold-climate cities. Compared with the baseline, the CCHPs achieved peak power reductions of 10–20% and annual energy savings of 17–26 %, with colder climates yielding greater absolute savings due to higher heating demand. In newer, well-insulated homes, balanced heating and cooling loads produced similar annual energy consumption for both prototypes, underscoring the importance of cooling efficiency. In older, less efficient buildings, energy savings were greater, resulting in higher overall energy-saving potential. The tandem system generally delivered higher total energy savings due to superior heating performance, though its cooling efficiency was slightly lower than the three-capacity system. This research demonstrates the potential of advanced heat pump technologies to address heating-dominated energy needs in cold climates while ensuring cost-effectiveness, efficiency, and reliability.