Heat loss reduction and tap temperature equalization of a centralized domestic hot water system in a modernized pre-WWI residential building

Abstract

Savings potentials in Domestic Hot Water (DHW) systems are very often overlooked, as these systems are designed to require as little maintenance as possible. The present work therefore focuses on the optimization of a DHW circulation system in a modernized pre-WWI multistory residential building in Vienna, Austria. To minimize the heat losses of the system and reduce the natural gas consumption for DHW production, a simple approach was chosen and implemented by installing and adjusting (i) a plug-in type timer switch and (ii) a plug-in type temperature switch to control the operation of the DHW circulation pump. In terms of piping and insulation, the DHW system was not modified whatsoever. Measurements were carried out to test the suitability and effectiveness of the selected concepts. The data obtained were evaluated in terms of reproducibility, DHW system heat losses and primary energy savings, as well as user comfort (tap temperature progression) and health and safety aspects. The results show that the implementation of a widely available and inexpensive temperature switch for controlling the DHW circulation pump led to remarkable DHW system heat loss reductions in the range of 20–30%, which corresponds to primary energy savings of 15–20%, with no negative impact on user comfort and DHW safety compliance. The share of electrical energy savings due to the reduction of the operating time of the circulation pump is negligible, as are the costs of the installed equipment of the presented energy efficiency measure.