Darren Johnson, IBD’s Technical Director reports:


The UK’s housing stock is made up of predominantly older and less energy efficient buildings. Although significantly improving building fabric is the obvious first option for any property, renovation it is not always possible to achieve the levels of insulation required by lower flow temperature (35-50⁰C) air to water heat pump systems. Also, it is not everyone’s preferred option given the upheaval involved when occupying the property at the time the work is in progress. So what are the options for replacing an end of life fossil fuel boiler with a heat pump only solution?

Recently the government has allowed the inclusion of what are being termed, “Very High Temperature Heat Pumps” or VHTHP’s into the Microgeneration Certification Scheme (MCS). Installers of renewable energy products now have this additional option to offer their customers so that they still qualify for payments under the Renewable Heat Incentive (RHI) Scheme. Although the MCS Heat Pump Standard (MIS 3005 rev 4.3) cautions the installer to use this option as a last resort and to advise their customer of the implications in contrast to improving building fabrics, the practicalities of the option are attractive. Provided the homeowner has a minimum depth of loft insulation of 250mm (or equivalent) and cavity wall insulation* if not of solid wall construction, they are able to apply for the RHI payment for a VHTHP.

System design and best practice is most important as the major benefit of this type of system is the ability to use the existing radiators. Care should still be taken to ensure that the radiators installed are actually capable of meeting the room heat loss. It should be noted that despite the inclusion of VHTHP products under the RHI scheme, there is still a limiting design factor that they must not operate over 65⁰C flow temperatures. Although this is an improvement on the previous limit of 50⁰C with non VHTHP’s, this can still affect system performance when using existing older radiators designed to operate in excess of 65⁰C. Furthermore, older radiators lose efficiency with age and need to be thoroughly cleaned and flushed through before the new heating equipment is fully commissioned.
The inclusion of VHTHP products into the MCS is a welcome one given that this is a viable option for the replacement Oil and LPG boiler market. This gives renewable energy installers a broader platform to conduct their business and consumers more choice.

* Exemption’s can apply if building is not suitable for cavity wall insulation. A letter from a RIBA surveyor will be required by Ofgem with the RHI application. choice.