Post-Retrofit Performance Evaluation of Heat Pump Systems Using Regression-Based Benchmarking

The retrofit of existing HVAC systems with high-efficiency heat pumps is increasingly recognized as an effective strategy for reducing energy use and operational costs. Yet few empirical studies have verified whether retrofitted systems actually operate in line with design capacities and intended schedules. This study reports on a field-based evaluation of a hospital in Seoul, South Korea, where two air-source heat pump chillers replaced an aging chiller. The aim of this study is to determine whether the system achieved the expected cooling performance and adhered to the planned nighttime operation for chilled water storage. This study introduces a workflow for post-retrofit performance evaluation using systematic monitoring, key parameter identification, and regression-based benchmarking. This approach provides a practical methodology for avoiding oversizing and improving retrofit decision-making. Hourly operational data were collected from July 7 to August 6. Cooling capacity was calculated from water temperature differentials, while power consumption was calculated from measured current and rated voltage. The cooling coefficient of performance (COP) was adopted as the primary evaluation indicator. A two-variable quadratic regression model was developed from manufacturer tables, and measured COP values were compared with this reference. Results indicated that both heat pumps predominantly operated under part-load conditions. Average COPs of 5.13 for Unit A and 5.11 for Unit B were within 5% of the rated part-load efficiency of 5.3, confirming close agreement with design expectations. However, schedule analysis revealed frequent daytime operation during extreme summer conditions above 30 °C. Quantitative analysis indicated that the current thermal storage capacity must be increased by approximately 134% to fully cover daytime loads solely through nighttime charging. These findings highlight the engineering importance of properly sizing thermal storage in retrofit projects and demonstrate a transferable approach for validating post-retrofit performance with relevance for engineers and policymakers.