Modelling of solar assisted district heating system with seasonal storage tank by two mathematical methods and with two climatic data as input

The goal of the study is to present two independent solutions capable of modelling the thermal behaviour of the solar assisted district heating systems with seasonal thermal storage. The study uses a new approach in modelling the thermal behaviour of the solar assisted district heating systems, by using two calculation methods: the analytical method and TRNSYS to perform the simulations, and by using two climatic data as input: EnergyPlus and Meteonorm. The heat demand of the buildings, the shares of energy produced by the solar thermal system, and by the gas boiler used as backup, and a very large number of the system parameters: temperature variation in each layer of the seasonal heat storage tank, temperatures, and flow rates on all the circuits, etc. were calculated. The results were compared using three parameters: Mean Deviation, Mean Bias Error and Root Mean Square Error. All the results calculated with the two methods were found to be very close. The annual solar fraction was found to be in the range of (34.9-50.2) %, depending on the type of the considered solar thermal collector, the combination of calculation method and climatic data as input. The study proves that both analytical method and TRNSYS can be used successfully to simulate the thermal behaviour of solar assisted district heating systems with seasonal heat storage.