Bachelor's thesis Fabian Wüllhorst


Implementation of a grey-box heat pump model in Modelica with focus on safety-related control strategies

Schematic illustration of the implemented heat pump system Copyright: EBC Schematic illustration of the implemented heat pump system

The AixLib provides dynamic simulation models for the evaluation of building energy systems. Existing heat pump models in the AixLib are dedicated to a specific research objective. Losses and inertias are not always reflected with sufficient accuracy. Therefore a generic grey-box heat pump model of an electric driven compression heat pump for dynamic building performance simulations is created and integrated into the AixLib. To reduce the computational time for annual simulations, the refrigeration circuit is modelled as a black-box. A modular approach of the black-box model allows multiple data sources. The simulation of both reversible heat pumps and chillers is possible. System inertia, heat losses and icing of the evaporator for air to water heat pumps are taken into account. The focus of the thesis is to model safety functions. The operational envelope, compliance to on/off and defrost cycles as well as frost and anti legionella protection are therefore taken into consideration. The aggregation of all submodels enables the simulation of the entire system including auxiliary heater and pumps or fans.

The plausibility of the implemented model is proved by carrying out a calibration based on testbench data. A computational time analysis is used to compare the new model with existing ones from the AixLib and several model configurations. The simulated seasonal coefficients of performance of the whole system are plausible, ranging from 1.88 to 2.44), compared to field tests for the given configuration.