Non-uniform temperature district heating system with decentralized heat storage units, a reliable solution for heat supply

Abstract

In this work, the novel concept of non-uniform temperature district heating system is proposed and analyzed. This system mainly works on a low-temperature supply mode for space heating, while it goes to high-temperature mode for domestic hot water supply only 4 h a day. The system employs decentralized heat storage units to be charged during the high-temperature mode. In this way, the system operates based on a minimum rate of heat loss and there is no legionella risk due to thermal disinfection. The system is designed for a town in Brazil and a detailed thermodynamic model of the system is presented. The performance of this system is compared with other popular district heating schemes. With a total annual heat loss of 64 MWh, the proposed system outperforms the third generation technology in which the loss is almost double. As such, although the heat loss of the ultralow-temperature system is 28% lower (i.e. around 50 MWh), the non-uniform temperature system is still preferred to this case as well. This is because not only the proposed case supplies both of the hot water and space heating demands of the buildings, but also it does not need any further actions for legionella prevention.