MODELING AND PERFORMANCE EVALUATION OF COLD CLIMATE HEAT PUMP SYSTEMS IN COMMERCIAL AND RESIDENTIAL BUILDINGS

Abstract

Heat pumps are increasingly recognized as a critical technology for building decarbonization due to their ability to provide space heating and cooling with efficiencies well above those of conventional fossil-fuel systems. However, their adoption for electrified heating in cold climates remains limited in both residential and commercial applications, owing to capacity degradation and efficiency losses at low ambient temperatures. While substantial research exists on the component-level performance of cold climate heat pumps (CCHPs), there is a lack of building-level analysis evaluating their operation under real-world cold climate conditions. Additionally, few studies have incorporated the performance of low-GWP (Global Warming Potential) refrigerant alternatives directly into whole-building energy models or examined the feasibility of integrated cascaded heat pump systems for simultaneous space heating and domestic hot water production. This thesis addresses these gaps through two complementary studies. The first evaluates the quasi-steady-state heating performance of a commercially available air-source rooftop heat pump in a modeled outpatient healthcare facility located in ASHRAE Climate Zone 5B, using EnergyPlus™ as the simulation engine. R-410A serves as the baseline refrigerant, with R-454B, R-32, R-290, and R-1234yf assessed as low-GWP alternatives, using literature-based performance-scaling ratios applied under consistent system boundary conditions. R-32 emerges as the most promising alternative, offering improved SCOP over R-410A with comparable capacity and near-term market feasibility as an A2L refrigerant, with annual operating cost savings of approximately 6% compared to R-410A. Although R-290 achieved the highest SCOP and a slightly larger cost savings at approximately 7%, its capacity loss at low ambient temperatures and charge limitations reduce its suitability for large-scale commercial adoption. R-454B performed comparably to R-410A with minimal efficiency penalty, making it a viable near-term drop-in replacement. R-1234yf resulted in the lowest summer-season electricity costs but had the highest winter-season costs. A Life Cycle Climate Performance (LCCP) analysis confirmed that indirect emissions from energy use dominate total climate impact, making system efficiency a more critical factor than refrigerant GWP alone. The second study develops and validates a field-calibrated BEopt / EnergyPlus™ model for a 382.4 m2 (4,116 ft²) single-family residence in Ellicott City, MD (ASHRAE Climate Zone 4A), and uses it to evaluate the energy, economic, and environmental performance of a gas-to-electric retrofit. The retrofit replaces a natural gas furnace and gas-powered water heater with a cascaded R-32 variable refrigerant flow (VRF) system and R-134a heat pump water heater (HPWH). The model was validated against field measurements collected during the 2024–2025 heating season, with simulation errors within the ±15% tolerance specified by ASHRAE Guideline 14. Field data were used to calculate the COP of the cascaded system across three water heater setpoint temperatures, with the system COP ranging from 3.13 at 55°C to 2.22 at 65°C, confirming that setpoint temperature is a meaningful driver of water heating efficiency. Utility bill analysis showed source energy savings of up to 50% in the peak winter months, though overall utility costs increased due to the higher per-unit electricity costs in the Maryland market. Performance projections across five U.S. climate regions showed annual source energy savings of 11.1% to 37.0% and CO2 emissions reductions of 26% to 64%, with the strongest results in colder climates. Life-cycle cost analysis over a 30-year horizon indicates that the retrofit carries a modest cost premium, the smallest in high-HDD climates where energy savings are greatest. Together, these results demonstrate that both low-GWP refrigerant substitution and cascaded heat pump retrofits represent technically viable, energy-efficient pathways toward building decarbonization, and highlight the importance of building-level analysis over component-level evaluation alone.