Holistic analysis on domestic hot water preparation concepts with decentral heat interface units
Domestic hot water (DHW) production remains a critical end-use in buildings, particularly for cleaning and hygiene. As advances in building-envelope insulation continue to lower space heating demand, especially in new construction and retrofits, the relative share of DHW in total heat demand is steadily rising, reaching up to 55% in highly efficient buildings. This growing proportion underscores the substantial potential of DHW systems for energy-saving measures and high-efficiency design, while still meeting stringent hygiene standards and occupant comfort requirements. This paper shows an experimental investigation on different hydraulics, regarding the DHW preparation and its influence on the efficiency of a heat pump heating system. Two decentralized concepts, one with a heat interface unit and one with an instantaneous water heater, are investigated. As a benchmark or state-of-the-art concept, a centralized DHW preparation with circulation line is examined. The three variants are evaluated in terms of energy efficiency by means of experimental system tests based on reference days on a test bench. The test cycles and load profiles used last several days. An economic and ecological evaluation is carried out for the concepts. Economic efficiency is assessed by using the annuity method of depreciation. Ecological efficiency is evaluated in terms of whole life carbon emissions. The energy savings, the CO2 savings potential and the whole life carbon emissions are compared and evaluated to the reference case. The study underscores the substantial potential of decentralized DHW concepts to enhance energy efficiency while delivering notable ecological and economic benefits.