Load management of heat pumps using phase change heat storage

In the UK, heat pumps are often promoted as the means to provide low-carbon space heating and hot water for future dwellings as the electricity supply decarbonises. However, a major issue with growing heat pump use would be the additional load that this could place on the electrical network at times of peak heat and power demand. A means to alleviate potential demand problems is to stagger the operating times of heat pumps by integrating them with thermal buffering. However, focusing on the domestic sector, substantial volumes of thermal storage would be required to achieve the necessary level of operational flexibility in heat pumps and this poses a particular problem in the UK where the floor areas of urban dwellings are small. Thermal storage featuring phase change material (PCM) offers the potential of more volumetrically efficient heat buffering, which may be more suitable for integration into domestic heating systems. In this paper, the potential to shift the operating time of heat pumps integrated with phasechange- material-enhanced thermal storage is assessed and compared to conventional hot water storage, where the limits of flexible operation are determined by the comfort and hot water needs of the end-user. The results indicate that the use of PCM-enhanced thermal storage can reduce the volume of the buffering required for load shifting by up to 3 times. However, thermal buffering with load shifting can increase heat pump energy demand and (at present) in the UK results in increased emissions and cost penalties for the end user