The heating system investigated in this work was designed as a simple yet competitive solar combisystem. The scope was to generate a system concept that can be easily integrated into the heating system of an existing house with water-based central heating and which, involving some further steps, is suitable for thorough cost reduction while maintaining a good thermal energetic performance. As such, drainback technology in combination with a pressure-less storage tank is foreseen, whereby the latter would possibly be made of plastics instead of steel, leading to a reduction of both material and production costs. The solar collectors are driven with water taken directly from the tank that also serves as a drainback vessel (see Fig. 1). The various peripheral components are connected to the storage tank by independent hydraulic circuits without any heat exchangers built into the store. The auxiliary heater loop is connected directly to the tank. All components included in this theoretical approach are readily available on the market, however none of the existing system concepts includes all of the features mentioned. A further conceptual modification has been developed regarding the

flat-plate collector circuit with stratifier, DHW plate

space heating system. Here a thermostatic heat exchanger, flow rate controlled heating loop

mixing valve is applied with a fixed set with stratifier.

temperature (50°C) such that a variation of the

volume flow rate (through the radiators or the heating floor) modulates the space heating power instead of the more commonly used flow temperature modulation with a mixing valve and a variable temperature set according to a heating curve. A comprehensive description of the system concept and the advantages of the improvements can be found in [1].