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Thermal Response Testing: Reducing uncertainty in ground source heat pumps

Friday, July 26th, 2013

Homeowners and landlords deciding to invest in ground source heat pump systems, to take advantage of payments under the domestic Renewable Heat Incentive announced in July, should consider Thermal Response Testing (TRT) to finalise system design, according to geotechnical specialist Lankelma.

Homeowners, private and social landlords and third party owners of heating systems installing ground source heat pumps will receive some of the highest payments under the domestic RHI, with tariff levels set at 18.8p/kWh.

TRT is used to derive the thermal conductivity of the ground, the essential factor in the efficient design of ground source heat pump systems. The results are used in the final design of a vertical ground energy system, including the optimum depths of boreholes, their spacing and heat yield estimates, to ensure the required levels of heat energy will be produced.

TRT is carried out after ground investigations and once the outline design of the ground source energy system has been undertaken. A borehole heat exchanger (as proposed in the final system) is installed and heated water is circulated at a constant rate and temperature for up to 50 hours, with the drop in temperature of the water measured as it comes out of the borehole. Results are used to determine thermal conductivity.

Eric Zon, Managing Director of Lankelma, said: “By using TRT, homeowners and landlords considering investing in ground source energy can be confident of how much heat the ground will deliver and how many borehole heat exchangers are needed to deliver the required levels of heat energy.

“If thermal conductivity is higher than anticipated, fewer borehole heat exchangers will be needed, conversely if it is lower, more heat exchangers can be installed to guarantee system performance. And because the test borehole can be used in the final system, carrying out TRT does not significantly increase overall costs.”

The new domestic RHI, due to open for applications in Spring 2014, aims to drive uptake of renewable heat technologies in homes across Great Britain to cut carbon, help meet renewables targets and save money on bills.

Applicants will need to complete a Green Deal Assessment before submitting their application and must ensure they have met minimum loft (250mm) and cavity wall insulation requirements, where appropriate. All installations and installers must be MCS certified (or certified by an equivalent scheme). Other requirements, such as ensuring that the system is meter ready, will also apply. Domestic MCS accredited installations of ground source heat pumps since 15th July 2009 will be eligible.

Tariffs have been set to reflect the expected cost of renewable heat generation over 20 years. In most cases, payments will be made based on estimated heat demand of the property combined with the estimated system performance, and will be made on the portion of renewable energy generated. DECC will offer an extra set payment of £230 per year where consumers take out metering and monitoring support packages for heat pumps.

Separately, DECC is finalising the details of the expansion of the non-domestic RHI scheme and will confirm the way forward in the autumn, alongside the outcome of the tariff review.