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Air Source Heat Pump metering requirements for Domestic RHI Scheme
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Air Source Heat Pump metering requirements for Domestic RHI Scheme
Engineers who install air source heat pumps should make themselves familiar with metering requirements for these appliances.

Earlier this year, changes were introduced by Ofgem relating to the metering requirements for the Domestic Renewable Heat Incentive (RHI) Scheme. Homeowners and installers need to be familiar with the criteria when completing air source heat pump installations.

Applicants who join the Government’s Domestic RHI must meet and adhere to the Scheme’s requirements in order to receive the quarterly payments for their home’s renewable heating. One of the conditions relates to metering. To meet the current Ofgem requirements, there are two elements to the metering of ASHPs that must be considered: metering for payment and metering for performance.

Metering for payment (heat meter)
Many domestic ASHP installations will not need to be metered for payment. Under these circumstances, the RHI payment will simply be based on the EPC annual heat demand for the property concerned or the heat demand limit. Effective from 20th September 2017, heat demand limits were introduced with the annual heat demand for ASHP installations limited to a maximum of 20,000kWh. In brief, RHI payments will either be based on the annual heat demand limit of 20,000 kWh per year or the EPC annual heat demand figure, whichever is the lesser value.

Even if an ASHP installation is not metered for payment, it must be ‘meter ready’. In other words, the installing engineer must leave sufficient accessible pipework for the installation of a heat meter in accordance with the requirements set out in the MCS Domestic RHI Metering Guidance document.

However, some domestic installations must be metered for payment, whereby a heat meter is fitted to record the heat produced by the ASHP. Heat meters are required if:

  • There is a ‘back-up’ heating system installed (for example, a fossil fuel appliance is used alongside the ASHP such as with a hybrid system)
  • The home is occupied for less than 183 days per year (i.e. a second or holiday home).

It is important to understand that in the case of ‘self-build’ or ‘custom build’ homes, if the homeowners move into the property before the system is commissioned and have not lived in the property for a minimum of 183 days, the installation will either have to be metered for payment or they must wait at least 183 days before applying for the RHI.

Metering for performance (electricity meter)
New regulations came into force on the 22nd May 2018 which now require that all ASHP installations are metered for performance to meet Ofgem requirements for the Domestic RHI. This stipulates that all ASHPs must be fitted with one (or more) electricity meters to record and display the electricity used by:

  • The ASHP
  • Any supplementary heater for space heating controlled by the same control system as the ASHP (for example, an immersion heater in a buffer tank)
  • Any immersion heater used to heat domestic hot water controlled by the same control system as the ASHP (for example, using a Grant Automatic DHW boost kit).

It must be understood that this metering is NOT used to determine the Domestic RHI payment. It is only to record the amount of electricity being used by the ASHP installation to allow users to monitor the energy consumption and performance of their system. Domestic RHI payments will continue to be based on either the annual heat demand or a heat meter reading, as previously mentioned.

The electricity meter(s) used may be installed as either a separate ‘stand-alone’ meter for each device used (this may require up to three meters being used on a single installation) or a single ‘stand-alone’ meter for all devices used. Where a single meter is used for more than one device, a separate sub-consumer unit will also be required to provide separate protection and isolation for each device concerned.

The electricity meters used must be MID compliant and Class A or better, remembering that classes B and C are better than A!

Hybrid Systems
As mentioned above, a hybrid system must be metered for payment. To meet this requirement, the Grant VortexAir Hybrid (which combines a 16kW Grant Aerona³ ASHP with an oil-fired boiler backup) is supplied ‘meter ready’ from the factory and an optional heat meter and electricity meter are available to be used when necessary for installations applying for the Domestic RHI. Whilst both are required to meet the Ofgem requirements for payment, the electricity meter will also allow users to monitor the energy consumption and performance of the ASHP.

However, to comply with the ‘metering for performance’ regulations, a further electricity meter will be required if an immersion heater (used to assist the ASHP with the heating of the domestic hot water) is controlled by the same control system as the ASHP. This ‘stand-alone’ meter will record the electricity consumption of the immersion heater only and this can be combined with the ASHP meter readings to monitor the electrical consumption of the hybrid system.

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