Implementation of PV/T collectors, controllable crystallisation PCM storage and a second latent heat storage unit on a solar-assisted heat pump to provide heating demand for a dwelling

Supercooled phase change materials (PCM) are promising in the use of space heating applications as their latent heat is only released when triggered to induce crystallisation, even when stored at ambient temperature. With this feature, utilisation of solar energy can be maximised and carbon release to the environment can be reduced considerably. However, the phase change temperature of commonly used PCM sodium acetate trihydrate (SAT) is around 56-58°C and the system requires booster heating, especially during cold seasons. In this paper, evacuated PV/T collectors were used for both thermal heat collection for a solar-assisted heat pump and electricity generation for heating resistances. Electric heaters were used for charging the secondary latent heat storage which was filled with erythritol. Since the erythritol had a melting point of 121°C, electric heaters fed by PVs could charge it and be used as a booster heater in the system. Although the SAT storage could be used for a weekly period, erythritol could be used for a daily period but still make an impact on the reduction of storage size and provide heating for peak hours. A comprehensive model was built including PV/T collectors, buffer tank, main heat storage unit with SAT tubes, secondary storage unit and building heating demand model. Real weather data was used for the calculation of heating demand, collector performance and overall system performance. Using 40m2 PV/T collectors, 750 litre buffer tank, maximum 6kW heating output heat pump, 252 kg SAT and 31 kg erythritol, the tank was charged and discharged to test its heating potential considering heating demand. Using an additional latent heat storage unit resulted in higher supply water temperature which increased from 30°C to 42°C at night.