18 May 2017
This paper presents a study on the effect of the modulation capacity of three different kinds of air-to-water heat pumps (i.e.
single stage, multi-stage and inverter-driven heat pumps) on the seasonal energy performance of the heating system coupled
to a typical single-family house located in Bolzano (Italy). The specific dynamic model of each heat pump and its control
logic has been developed by using TRNSYS 17. These models are able to take into account the energy penalty linked to the
on-off cycles by using experimental data obtained by the manufacturer of the selected heat pump units. A comparison of the
energy performance of the HVAC system as a function of the heat pump typology is presented. Results highlight the strong
influence of the control algorithm on the performance of the heat pump: it is shown that the multi-stage unit is unable to fully
exploit its energy saving potential since its typical control logic is not able to reduce the number of start-ups during the
warmer period of the heating season, when only one compressor is switched on. It has been demonstrated that dynamic
simulation can be a valid tool for the optimization of the control logic of the multi-stage and inverter-driven heat pumps, in
order to maximize the seasonal performance of the system and to minimize the number of on-off cycles.