Design of a Simple Control Strategy for a Community-size Solar Heating System with a Seasonal Storage

The presented paper focuses on the design of different control strategies of a cold climate community-size solar thermal system located in Finland. The system was designed on TRNSYS software in order to perform dynamic simulation. A solar thermal system operating with various control strategies has been designed with an integrated ground source heat pump and a seasonal borehole storage to provide domestic hot water (DHW) and space heating (SH) for community-size demand. The system has two short term storage tanks, a hot tank and a warm tank. The impact of the considered system solutions on electricity consumption has been evaluated and compared as a function of the different collector control modes and different tank configurations (short term tanks sizes). Results have shown that the proposed system was able to provide a 78-83% renewable energy fraction. Total electricity consumption of the heating system varied by 20% between the best and the worst cases. Furthermore, system performance was better when solar energy was mainly stored in the warm tank. During a 5-year simulation, the annual seasonal storage efficiency improved from 0.23 to 0.31, whereas the heat pump electricity consumption reduced from 57.17 MWh to 45.93 MWh. The demand in winter was met mainly through ground heat and the rest was provided by the heat pump compressor. However, the demand in summer was met almost completely by solar energy.