Dynamic Heat Process in a Climate Chamber

Abstract

Heat pumping technology is commonly used for heating and cooling purposes within building services nowadays. It has quick response for improving the indoor climate with high heat to power ratio. SP* was the first accredited European institute for heat pump performace testing with a focus on measuring the Coefficient of Performance (COP). The testing is commonly performed by installing the heat pump in a climate chamber which can provide standard testing conditions. In the energy technology department of SP there is a new climate chamber that has recently been used in a research project to evaluate the performance of two air-to-air heat pumps. The performance of the climate chamber is critical to the accuracy of the testing results. The objective of this study is to determine the thermal property of the climate chamber, develop a numerical model to describe the dynamic thermal process of the chamber and evaluate the testing results by simulating the heating process. By transforming the chamber thermal model to an equivalent analog electrical circuit and solving this first order system, an equation set was derived to describe the chamber thermal process. Several measurements and computer calculations were performed to determine the optimal parameters for the model. Finally the model was integrated with Matlab GUI and developed as a programme with user interface. Several heat pump testing cases were investigated with this model. The results show that for measurements without large power variation and defrosting cycles the COP values from the Calorimeter test method and the simulations are very close. However, for measurements with large power variation or defrosting cycles there is a difference between these two results. This is mainly derives from the dynamic heat process where heat storage and heat loss influence the heat balance calculation. For defrosting process, the model can recreate the heating capacities reflecting real heat pump running condition. Another utilization of the model is to analyze upgrade scenarios of the climate chamber. The chamber size is the most critical factor and should be kept small besides the necessary operation space. An increase of the thickness of the insulation layer can also improve the testing quality. Further effort is suggested to expand the model to other climate chambers and real buildings. By combining the model with climate control systems, it could also improve the control quality of the climate chamber.