What is Ground Sourced Heat Energy?
A ground source heat pump (GSHP) extracts low temperature geothermal heat energy from the ground (soil, rock and groundwater) – whose temperature will be warmer than ambient air in Winter (and cooler than the air in Summer). For this reason, GSHPs are more efficient than air source heat pumps, especially in the coldest weather when they are most in demand. A heat pump concentrates low grade heat into higher grade heat that can be used for space heating and domestic hot water.
The most practical way of extracting this energy is through water circulating through pipes in the ground (i.e. ‘closed loop’ systems), but pumping of abstracted groundwater from water wells (i.e. ‘open loop’ systems) is the most energy efficient and requires minimal space compared to closed loop systems, so are particularly good for dense development sites in urban areas.
At a depth below 2m, UK ground temperature remains constant at around 10-11°C throughout all seasons and does not vary much compared to air temperatures. However, this temperature will drop quickly where a heat pump is extracting excessive heat from the ground unless heat is being replenished in the summer by reversing the heat pumps to provide building cooling. It is therefore very important that the size of the ground loop matches the heating load of the building. The key to achieving this balance is a full thermal modelling exercise.
At Patrick Parsons, we have been working on geothermal energy projects in commercial and residential buildings for over 10 years, delivering integrated projects with ground source heat pump (GSHP) systems ranging from 6.5kWth to 6MWth. Geothermal energy systems can provide heating and hot water requirements for residential developments.
Ticking the Sustainability Box
In planning policy, the 2003 ‘Merton Rule’, pioneered by the London Borough of Merton requires new developments to generate at least 10% of their energy needs from on-site renewable sources to reduce CO2 emissions in the built environment. Many local authorities in England request the minimum Merton’s rule performance target in planning permissions for all new major developments.
Where heating and hot water demand is met via GCHPs, your scheme will benefit from:
- 10% of on-site renewable energy generation
- up to 75% carbon savings compared to fossil fuel gas-fired systems
- lower cost energy for future property owners
- long-term energy security for future property owners
- enhanced sustainability throughout building life cycle
The mechanical principles of GSHPs are as simple as a domestic refrigerator and are extremely reliable, so there is no need for back-up boilers, provided the selection of GSHPs and associated heat distribution infrastructure is selected and then subject to routine system maintenance and servicing. GSHPs generate very little noise and should last for many years with minimal servicing. They offer incredible energy efficiency, providing Coefficient of Performance (CoP) of over 400%, compared to 85% for modern efficient gas-fired boilers, meaning they return 4kW of heat energy for an input of 1kW of electrical energy.
Government has incentivised the use of renewable heat recovery systems via the Renewable Heat Incentive (RHI) scheme, which currently pays out 20.89p/kWh for domestic applications for ground sourced heat generation, compared to the current average UK electrical power unit cost of 12.5p/kWh.
At feasibility stage, we assess GSHP scheme viability and optimum technology selection and configuration options in addition to budget capital costs, feed-in tariff income and payback time to allow clients and investors to make informed purchasing decisions.