Decarbonizing Campus Heating: Preliminary field Performance data of a Subcritical R744 Heat Pump for Ambient District Energy System
This applied research paper presents the first field-performance evaluation of a 1.5 MW reversible R744 (CO2) air-source heat pump (ASHP) installed at the University of British Columbia Okanagan (UBCO)—the largest known CO2 ASHP deployed for a district energy application in North America. The system is integrated into UBCO’s ambient low-temperature district energy system (LDES), a bidirectional thermal network operating between 8 °C and 25 °C that supports energy sharing, high-efficiency nodal heat pumps, and campus-wide decarbonization. Building on earlier theoretical studies, this work analyzes preliminary operating data collected during a oneweek period in November shortly after system commissioning. The analysis evaluates subcritical heating performance, part-load behavior, and the control strategies used to optimize compressor staging, fan modulation, and pump operation. Measured COP values ranged from 3.7 to 4.3 under mild winter conditions, consistent with prior modeling and supporting an expected seasonal COP of approximately 3.5. Over the oneweek period, the ASHP delivered more than 55,000 kWh of heat to the LDES, corresponding to approximately 25 t of CO2 emissions avoided and nearly 6,000 m³ of natural gas savings relative to boiler-based operation. Commissioning improvements—including optimized fan and pump modulation, refined staging logic, and stable defrost management—significantly enhanced part-load efficiency and operational stability. These early results demonstrate the practical viability of large-scale CO2 ASHPs for ambient district energy networks and highlight their potential as scalable, low-carbon solutions for cold-climate district heating decarbonization.