Measured vs. Rated COP and Carbon Emissions of an Air-Source Heat Pump

This study evaluates the operational performance and carbon emissions of an air-source heat pump (ASHP) system based on a one-year field monitoring campaign conducted at a single-family detached house in Gongju, South Korea. The system, equipped with a 9 kW air-to-water ASHP, supplied both space heating (SH) and domestic hot water (DHW), achieving average coefficients of performance (COPs) of 2.27 for SH and 2.06 for DHW. To estimate nominal COPs, a bi-quadratic regression model was developed using manufacturer catalog data and compared against field measurements. The analysis revealed a significant performance decline during winter: a paired t-test using 7119 samples confirmed a statistically significant discrepancy under low-temperature conditions. Annual CO2-equivalent (CO2eq) emissions were also evaluated. Under current grid emission factors, the ASHP system emitted 1532 kgCO2eq—approximately 8.6% more than a condensing gas boiler (1411 kgCO2eq), primarily due to winter performance degradation and the relatively high carbon intensity of electricity. These findings underscore the importance of incorporating actual operating conditions, seasonal variability, and the national electricity emission factor when assessing ASHP performance and life cycle climate performance (LCCP).