heat pump, domestic hot water, simulation, measurement
In multiple family dwellings of central Europe heat pumps are not only used for space heating but also increasingly for domestic hot water (dhw) supply. The water is often heated in a centralized or decentralized installation with a large distribution network. This leads to the combination of heat pumps with various trace heating systems to ensure both comfort and protection from legionella disease. The COP of the heat pump can be greatly affected by the choice of the heat tracing system which influences the overall efficiency (OE) of the domestic hot water supply system significantly. In this study several heat storage and heat tracing methods were coupled with heat pumps as the main heat source. The investigated installations feature either a recirculation loop or some kind of electrical trace heating. Focused on multiple family dwellings the energy consumption of the overall system including hot water supply system and water heating system is analyzed. A physics based model for four different systems was built and applied to several virtual building complexes sized from 8 to 192 apartments. After the validation of the model (using data from three different field measurements) each system was simulated for a week of domestic hot water consumption. In order to compare the systems the overall efficiency was evaluated using the amount of energy provided by hot water at the distributed tap devices in relation to the electrical power consumption of the complete installation. In general dhw supply systems using heat pumps can reach good performances especially when the dhw storage tank is kept unmixed. Installations featuring an externally reheated recirculation loop (using a dedicated heat pump) therefore show the best performances. Without this external reheating the overall efficiency is reduced by about 5% in the best case. Installations using electric heating cables are showing a performance reduction of about 10% compared to the optimized system. Installations using a central heat pump to increase the temperature of the overall heating system, which in turn is used to load decentral dhw-storage tanks, are consuming at least twice the amount of electrical energy compared to the other investigated systems.