Evaluating thermal dynamics of air to water heat pump due to stratification: Experiment and modelling

Abstract

The employment of 1D model of the thermal stratification in the tank of an air to water heat pump (AWHP) may accurately predict the evolution of the temperatures at the different layers. The study predicted the water temperatures at different levels in a 150 L tank coupled with 1.2 kW heat pump unit. A data acquisition system was designed and built to monitor the input and output parameters used in the model to evaluate the evolution of the water layers’ temperatures. The results depicted that the 1D linear model accurately predicted the evolution of the water temperatures at each layer due to thermal stratification with a determination coefficient (R2) and root mean square error (RMSE) of 0.9932 and 0.9253. The modelled validation showed a very good R2 and RMSE of 0.9940 and 0.8595. The average thermal energy gained and the average COP due to the first hour heating rating (the withdrawal of 150 L of the hot water) was 5.67% lowered under the stratification condition when compared to the scenario without stratification. The p-values show no significant differences among the water temperatures at the different layers due to first hour heating rating. The study will encourage researchers and energy service companies to highlight the impact of thermal stratification regarding to the dynamics of an AWHP.