Impact of Legionella regulation on a 4th generation district heating substation energy use and cost: the case of a Swiss single-family household

Highlights: • Impact of DHW regulations on a 4GDH substation energy and economic performance. • DHW regulations in Europe with different temperatures or specific exceptions. • Swiss DHW standard compared with Danish and German regulations. • Danish standard reduced the annualized system cost and the annual running cost. • German 3-litre rule with lowest investment cost but highest annual cost. 4^th Generation District Heating (4GDH) systems can have a supply temperature lower than 50 °C to decrease losses and to favour the integration of renewable and waste heat. As the temperature requirement for space heating in new and retrofitted buildings is around 35 °C or lower, they would be suitable for 4GDH. However, Domestic Hot Water (DHW) is a significant barrier in district heating, because the temperature needs to be maintained above the standard Legionella growing range (25 °C–55 °C), even if 45 °C would be sufficient for comfort. Nonetheless, current regulations vary widely across countries in Europe, especially for small buildings. This paper aims to study the effect of different Legionella regulations on the DHW energy use, and on the substation cost of a Swiss single-family household connected to a 4GDH network. The Swiss standard is confronted with the requirements of the Danish regulation and the German "3-litre rule". Results demonstrated that a relaxation of the current Swiss regulation could present energy and economic savings. The "3-litre rule" resulted in an annual heat consumption reduction of 13% while the Danish standard achieved the lowest annual running cost and annualized total cost.