Classification of hydraulic designs and hardware-in-the-loop-tests of solar assisted heating systems for multi-family houses

Abstract

In the “Solar-supported heat stations” joint project funded by BMWi (venture partner: Institut für Solarenergieforschung Hamelin), hydraulic concepts for solar heat stations to support heating and DHW in multi-family housing are being investigated and compared with the help of simulations and hardware-in-the-loop tests. The aim is the definition of best-practice solutions. It is not only the system with the highest energy savings which will be considered to be “optimum” but that which offers the best compromise between lower overall costs and high energy savings (in addition to low equipment complexity and error susceptibility. The concepts being analysed are divided into central and decentral concepts. Nowadays the standard for new construction of multi-family housing is a central buffer storage system with freshwater station. Hot water storage systems are also being used. In particular, they are combined with solar heat storage systems when built in existing housing stock. Tank-in-tank storage systems only enable smaller hot water capacities and are rarely used in multi-family housing. In the future it is probable that more systems will be built with home stations in which hot water is provided decentrally. The concept of a heat station with a buffer storage system and a freshwater station was measured in the laboratory on a hardware-in-the-loop test bench. The system consists of a gas-fired boiler, a 1500 litre buffer storage system with freshwater station and a solar station with stratified solar charging. The simulation models were successfully validated using the measurements. The measurements show that the system works well with regard to comfort requirements but was not perfectly suitable for use in multi-family housing which is fitted with a continuously-operated circulation system. The heating of the lower storage layers due to the circulation had a disadvantageous effect on the solar energy input. Corresponding solution approaches were further investigated (in the laboratory and using the validated models in a simulation). For the estimation of the solar combi systems' performance a benchmark has been developed comparing the end energy savings of a system to a fictional maximum potential.