Abstract
Low temperature is the most significant feature of the future district heating (DH) - the 4th generation district heating (4GDH). The revolutionary temperature level (50–55/25°C) will improve the efficiency of heat sources, thermal storages, and distribution systems, meanwhile, bring huge potentials to renewable energies. One challenge of transition to the future DH is the compatibility of current customer installations and the future temperature level. The aim of this study was to find the temperature potential of Norwegian residential buildings for the future DH system. A reference apartment was created, and typical space heating (SH) system was designed. A detailed building and SH system model were built in Modelica® language, and simulation was conducted via Dymola environment. Different operation strategies: PI control of the supply temperature, weather compensated control of the supply temperature, and PI control of the return temperature were tested. The results of the study showed the average supply temperature could be as low as 56~58°C, and only limited time the temperature was above 60 °C, when the controlled supply temperature strategies were applied. For the case with controlled return temperature strategies, the average return temperature were 30 and 37°C, while the average required supply temperature could be 72 and 94°C. The conclusion was that the low supply temperature could be achieved through optimized operation strategies. Whereas, the low return temperature was not able to be achieved only by improving the operation strategy.
Highlights
District heating (DH) is an energy service, which moves the heat from available heat sources to customers
The reason was that the weather compensation (WC) control is an open loop control strategy and the supply temperature is only decided by the outdoor air temperature, ignoring any other impact factors, such as heat gain from solar radiation, occupant, and other devices
The proportional integral (PI) controller is a feedback control strategy and any overheating caused by extra heat gain will be compensated by the change in the supply temperature
Summary
District heating (DH) is an energy service, which moves the heat from available heat sources to customers. The fundamental idea of DH is to use local fuel or heat resources, which would otherwise be wasted, to satisfy local customer heat demands, by using heat distribution networks [1]. The 1st generation DH system uses steam as heat carrier. The 2nd generation DH system uses pressurized hot water as the heat carrier, with supply temperature mostly higher than 100°C. These systems emerge in the 1930s and dominate all new systems until the 1970s. The 3rd generation DH system still uses pressurized water as the heat carrier, but the supply temperatures are often below 100°C. The system is introduced in the 1970s and take a major share of all extensions in the 1980s and beyond [2]
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