A detailed methodology is proposed to design and optimise the operation of a ground-source heat pump
(GSHP) coupled to a phase-change material (PCM) thermal battery. The objective is to minimise the cost of
supplying space heating and hot water to a medium-demand house in the UK during a typical winter day with
fluctuating electricity prices. A bespoke 8-kW GSHP is designed and used to optimise the charging schedule
of the thermal battery to minimise daily operational costs while meeting the heat demand. If no limit is imposed
on the size of the thermal battery, in the best scenario, a 41-kWh thermal battery is required to achieve costs
as low as 1.85 £/day. However, large PCM batteries mean high upfront costs and little space restrictions.
Therefore, a constraint is imposed on the thermal store capacity to identify the optimal trade-off that can be
achieved between PCM battery size and daily power consumption costs. Operational costs strongly depend on
the battery size, increasing from 1.85 £/day for a 41-kWh thermal battery to 3.50 £/day for a 6.3-kWh store.