The Impact of Controller Settings in Heat Pumps: Numerical Findings and Experimental Verification

Abstract

In residential buildings, the efficiency of heat pump systems (HPS) significantly depends on the HPS design and operation. In particular, HPS controllers often use ambient temperature-dependent heating curves for operation. The resulting supply temperature serves as the reference variable for the internal controller, which is used to manipulate the compressor speed. Typically, the internal controller has constant parameters for the PI controller, hysteresis, and operational time. While buildings have a highly dynamic, time-variant demand, these dynamics are rarely considered in controller development. This work investigates internal control parameters' sensitivity to the overall HPS efficiency in annual, dynamic simulations and experiments. To consider different supply temperatures, two buildings with underfloor heating and radiators serve as case studies. Based on a validated simulation model, the one-factor-at-a-time sensitivity analysis method determines the controller's influence on the seasonal coefficient of performance (SCOP). Hardware-in-the-loop experiments are conducted for representative periods extracted from annual simulation results for experimental verification. The results for the building with underfloor heating and radiators prove that the control parameter influences the SCOP up to 18.5 % and 4.2 %, respectively. In particular, different control parameters for the optimal operation were determined for both case studies, challenging the constant settings used in the state-of-theart. In addition, we observe a significant increase of 300 % in the avoidable compressor starts in experiments due to poor parameter settings. To ensure maximum efficiency of HPS and significantly reduce the number of compressor starts in any residential building, we recommend integrating adaptive setting of control parameters into the HPS controller.