Prediction of heat pump heat transfer rate and COP using a temperature–pressure based polynomial regression model
Global efforts to mitigate greenhouse gas emissions require the replacement of fossil-fuel-based heating systems, among which heat pumps can play a key role. In industrial applications, heat pumps are attractive for recovering and upgrading waste heat streams; however, their performance is highly sensitive to operating temperatures. In this study, an experimental investigation was conducted on a water-to-water heat pump using the low-GWP refrigerant R1234ze(E), focusing on the recovery and reuse of waste heat under industrial conditions. The influence of the condenser- and evaporator-side inlet water temperatures on system performance was systematically examined. The experimental results show that changes in the heat-source and heat-sink temperatures lead to systematic variations in compressor suction and discharge pressures, and that these pressure conditions strongly govern the condensation and evaporation heat transfer rates as well as the coefficient of performance (COP). Based on this insight, a temperature/pressure-based polynomial regression model was developed, in which the condenser- and evaporator-side inlet water temperatures together with the compressor suction and discharge pressures were used as independent variables to predict the condensation and evaporation heat transfer rates and COP. For the lab-scale water-to-water heat pump, the proposed correlations achieve coefficients of determination (R²) of 0.973, 0.954, and 0.989 for condensation heat transfer rate, evaporation heat transfer rate, and COP, respectively, demonstrating high predictive accuracy. When the same regression form is recalibrated using field data from an industrial waterto- water heat pump, the resulting correlations achieve R² values of 0.960, 0.917, and 0.965, confirming their applicability under real operating conditions. In addition, applying the same functional form to an air-to-air heat pump and re-estimating the coefficients yields an R² of 0.904 for the condensation heat transfer rate, indicating that the proposed approach can be extended to other types of heat pump systems.