Evaluation and Modelling of a Water-to-Water Heat Pump System

Abstract

In the present work, a water-to-water heat pump system has been assembled, with sensors mounted at appropriate places around the system to measure such quantities as temperature, pressure, and flow rate. The necessary electronic instrumentation for each transducer was developed, and the transducer-instrument combinations tested, calibrated, and interfaced to a microcomputer. The performance of the heat pump for water heating in an ordinary domestic hot water tank was analysed in three different modes: With thermal stratification; condenser water flow rate controlled by water regulator. With thermal stratification; water regulator bypassed, i.e., flow uncontrolled. Without stratification; deliberate water mixing, water regulator in circuit. The analysis shows that the best C.O.P. is given by mode 1. This shows that, for water heating purposes, a suitable hot water tank design is required to match the heat pump system. Analysis of heat being extracted from a storage tank was also carried out by recycling the water through the evaporator. The performance of the system during heat extraction as a function of reducing evaporating temperature was observed. The analysis enables one to predict the performance of the system during heat extraction from a heat store. It shows that the C.O.P. of the heat pump system is higher the hotter the water, and the higher the flow rate passing through the evaporator. The performance of each component of the heat pump system was also analysed in a quantitative manner. In order to analyse and calculate the heating load for the system, empirical mathematical relations based on experimental data were developed. A computer model for the system was developed based on these empirical equations. The model includes details of the heat source and sink system. The effects on performance of various evaporator water flow rates and various condensing pressures could be observed.