Heat pump simulation model and optimal variable-speed control for a wide range of cooling conditions

Abstract

The steady-state air-to-air heat pump model presented in this thesis was developed from the first principles. The main objective was to develop a heat pump model that can be used as a part of larger simulation models, and that will make a connection between simple models that do not describe equipment behavior accurately enough and complicated models that are computationally very expensive. The model consists of the evaporator, compressor and condenser sub-model, each modeling the steady-state behavior of a particular component. To confirm the model accuracy, simulation results are compared with the experimental data from the Mitsubishi "Mr. Slim"® heat pump. The reported COP prediction errors are up to 20% under-prediction when the evaporating temperature is more than 2 K under-predicted, and 10% when the evaporating temperatures are more accurately predicted (less then 2K underpredicted). The model is strongly sensitive on the evaporator temperature prediction errors, since they influence the compressor inlet density. A grid search optimization algorithm is used to find the heat pump optimal performance map. The map defines the optimal evaporator fan speed, condenser fan speed and compressor speed needed to achieve the lowest total power consumption for the given cooling rate, ambient and zone temperature.