Impact of Domestic Hot Water Systems on District Heating Temperatures

Abstract

When buildings become more energy effective, the temperature levels of district heating systems need to be lower to decrease the losses from the distribution system and to keep district heating a competitive alternative on the heating market. For this reason, buildings that are refurbished need to be adapted to suit low-temperature district heating. The aim of this paper is to examine whether four different energy refurbishment packages (ERPs) can be used for lowering the temperature need of a multi-family buildings space heating and domestic hot water (DHW) system as well as to analyse the impact of the DHW circulation system on the return temperature. The results show that for all ERPs examined in this study, the space heating supply temperature agreed well with the temperature levels of a low-temperature district heating system. The results show that the temperature need of the DHW system will determine the supply temperature of the district heating system. In addition, the amount of days with heating demand decreases for all ERPs, which further increases the influence of the DHW system on the district heating system. In conclusion, the DHW system needs to be improved to enable the temperature levels of a low-temperature district heating system.

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“…Both this study and other recent studies therefore indicate, that there is a need for further research in this field, if the return temperatures from existing domestic hot water installations in apartment buildings are to be lowered further than the 35-40 °C that have been identified for older buildings in this study, and that has also been estimated in another recent study [41]. Possible solutions that are currently investigated include the installation of small heat pumps for domestic hot water circulation heat losses or improved charging schedules for domestic hot water tanks [29,43,44].…”

“…It should be noted however, that the domestic hot water circulation temperatures have not been investigated in detail, and therefore it has not been verified whether the installations are operated with temperatures that meet the requirements for limitation of Legionella bacteria growth, which was seen to be an issue in another recent study. The return temperature from domestic hot water systems may be increasingly important for the district heating system in the future, as there may be a tendency for energy renovations to lower the space heating demands and required space heating temperatures, which causes heat demands for domestic hot water to make up a larger share of the total heating consumption, and therefore causes return temperatures from domestic hot water installations to be equally more dominating [40][41][42]. While new buildings can be designed with apartment substations as suggested in [22], it may be necessary to accept that existing apartment buildings, are operated with the existing installations for several decades.…”

Overview of Solutions for the Low-Temperature Operation of Domestic Hot-Water Systems with a Circulation Loop

“…According to the regulations for hygiene and comfort, the operation and design of current DHW systems are an obstacle to reducing the operating temperatures to be suitable for LTDH systems [22][23][24].…”