The novel aspect of this system is that the thermal store is underneath the house in the form of shallow boreholes in the soil. This makes the system cheaper than a conventional ground source heat pump since it can be built using tools available to most builders, even though the system is best suited to new-built homes.
“The team at DMU is investigating ways to reduce the system cost as well as exploring its suitability as a retrofit heating solution” says Greenough, explaining that their research system is installed in a small terraced house built in the 1800s, but currently unoccupied, while the thermal store (called an ‘earth energy bank’) is in a grass verge between the house and the university. The team is monitoring the electrical and thermal performance of the solar panels, the thermal performance of the system and the behaviour of the thermal store as heat is added and removed. Data are collected and used to validate system models that the team will use to explore modifications to the basic system design.
Seasonal heat storage allows the system to make use of the surplus heat available in the summer to heat the home in winter, but there are many days in which heat is added (typically around noon) and removed during the same day. This means that the heat does not get time to soak into the soil and the properties of the thermal grout around the boreholes improves system performance. In theory, cooling solar PV should increase the electrical energy capture, and coupling the heat pump with a warm thermal store should increase its Coefficient of Performance (CoP). In practice, the seasonal and diurnal heat flows are complex and there are questions around the optimal size and configuration of thermal store, the control system logic the impact on CoP and the overall lifecycle cost.
The system has potential for exploitation in industry, according to Greenough, in particular in sectors where there is waste heat available and a heat requirement later in the day or year. Other applications include the possibility of heating other buildings in a city using waste industrial heat without the expense of district heating systems.
17 June 2016