Seasonal thermal energy storage with heat pumps and low temperatures in building projects—A comparative review

Application of seasonal thermal energy storage with heat pumps for heating and cooling buildings has received much consideration in recent decades, as it can help to cover gaps between energy availability and demand, e.g. from summer to winter. This has the potential to reduce the large proportion of energy consumed by buildings, especially in colder climate countries. The problem with seasonal storage, however, is heat loss. This can be reduced by low-temperature storage but a heat pump is then recommended to adjust temperatures as needed by buildings in use. The aim of this paper was to compare different seasonal thermal energy storage methods using a heat pump in terms of coefficient of performance (COP) of heat pump and solar fraction, and further, to investigate the relationship between those factors and the size of the system, i.e. collector area and storage volume based on past building projects including residences, offices and schools.