Enhancing heat pump performance for domestic hot water preparation: A comparative analysis in existing multi-family houses

The building sector is accountable for roughly one third of global energy- and process-related greenhouse gas emissions. Besides space heating, domestic hot water (DHW) heating contributes substantially to energy consumption and related greenhouse gas emissions in the building sector. Depending on the DHW system design and its required supply temperature, heat losses make up around 30…60 % of the energy required for DHW heating. To decrease energy consumption and reduce associated greenhouse gas emissions, it is essential to minimize heat losses and implement efficient DHW concepts. Heat pumps can potentially reduce energy consumption, but their efficiency strongly depends on the DHW system design and its required supply temperature. These aspects are evaluated by performing a comprehensive analysis of different DHW concepts utilizing heat pumps. Based on annual heat demands extracted from one year measurement data of a typical multi-family house in Germany, simulations of six different DHW concepts are performed. Our findings reveal that decentralized DHW systems or low system temperatures (48 °C), e.g. in combination with ultrafiltration for legionella treatment in centralized DHW systems, can lead to a substantial reduction in heat losses for DHW preparation of around 25 % and in final energy of 20 % compared to the reference case. In large systems the share of losses should be kept below 30 % by reducing pipe lengths and equipping the most distant tapping points with direct electric water heaters.