A domestic solar/heat pump heating system incorporating latent and stratified thermal storage

Both solar and heat pump heating systems are innovative technologies for sustaining ecological heat generation. They are gaining more and more importance due to the accelerating pace of climate change and the rising cost of limited fossil resources. Against this background, a heating system combining solar thermal collectors, heat pump, stratified thermal storage and water/ice latent heat storage has been investigated. In order to investigate and optimise the heating system, a dynamic system simulation model was developed. On this basis, a fundamental control strategy was derived for the overall co-ordination of the heating system with particular regard to the performance of the two storage tanks. In a simulation study, a fundamental investigation of the heating system configuration was carried out and optimisation derived for the system control as well as the selection of components and their dimensioning. The influence of different parameters on the system performance was identified, where the collector area and the latent heat storage volume were found to be the predominant parameters for system dimensioning. For a modern one-family house, a solar collector area of 30m² and a latent heat store volume of 12.5m³ are proposed. In this configuration, the heating system reaches a seasonal performance factor of 4.6, meaning that 78% of the building’s and users’ heat demand are delivered by solar energy. The results show that the solar / heat pump heating system can give an acceptable performance using up-to-date components in a state-ofthe- art building. A novel but most significant component of the heating system is the latent heat store, working with water / ice as phase change material. For that reason, the store was developed in a systematic manner with special regard to the heat exchangers. Based on a detailed specification and a functional analysis, concept solutions were investigated and evaluated. A sheet matrix heat exchanger was eventually chosen as it fulfils the specialised requirements of the heating system. The heat exchanger’s behaviour and its performance during phase change were analysed in laboratory tests. In addition, a storage tank design was developed and a preliminary storage dimensioning carried out for the heating system as defined by the simulations, showing that five polymer tanks with 3.3m³ each and 14 sheet matrix heat exchangers in each tank are required.