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Hybrid heat pumps - our heating future?

21/11/2020

 

What is a hybrid heat pump?

A hybrid heat pump is a heating system that combines an air source heat pump with a gas or oil boiler. The oil or gas boiler is used to 'top-up' a low temperature heat pump to meet the heating demands of the property where the heat pump cannot do it alone. Purpose designed hybrid systems can be set to control which heat source comes on when, depending on efficiency or energy cost targets.

How does it work?

Most air source heat pumps work at lower temperatures than our gas or oil fired heating systems; commonly 40-45 degrees C compared with 65-75 degrees C from fossil fuel systems.

Without insulating our homes or upsizing our radiators to run a lower temperatures, low temperature air source heat pumps are unsuitable for existing properties. Some manufacturers have produced heat pumps that can run at higher temperatures of 65 degrees C, but the efficiencies drop. There are many horror stories of heat pumps being wrongly fitted into older homes and failing to heat the home and/or massively increasing electricity bills. .

Hybrid heat pumps let the heat pump run at its happy and efficient temperature of 40 degrees C, which will provide sufficient heat for a large part of the year. As outside temperatures drop, and when hot water is used, the gas or oil boiler can step in to raise the temperate of the water.

A number of hybrid heat pump trials have been undertaken in existing homes to better understand the contribution a heat pump can make to a heating system. The results varied widely, which heat pumps providing between 50% and 80% of heating and hot water supplies in a sample of house types*.

Hybrid v bivalent systems

A hybrid system is a purpose built combined heat pump with oil or gas boiler from the same manufacturer. In this set up, the heat pump can run all or most of the time and the gas or oil boiler tops it up.

A bivalent system is when any heat pump is paired with any gas or oil boiler and combined via a buffer tank. This means you can potentially work with your existing gas or oil boiler if it still in good order. In this set up, the heat pump will run as much as possible when it can meet your demand. When the outside temperature drops below a certain point the heat pump will switch off and the oil boiler will fire. I.e. they do not run at the same time.

Why do we need hybrid heat pumps?

The UK has a legal obligation to be net zero by 2050. As homes account for 20% of greenhouse gases it is important to find ways of reducing our reliance on fossil fuels. Home insulation will form the majority of the works needed to achieve this and in reducing our heat requirement we prepare homes for low temperature air source heat pumps.

However for poorly insulated homes and larger homes, fossil fuels may still have a role to pay in the medium term to provide the higher temperatures needed for conventional radiator systems.

In 2019 the Committee for Climate Change (CCC) identified hybrid heat pumps as vital and fast track way to reduce our consumption of fossil fuels and begin decarbonising UK homes. They urged for the immediate deployment of hybrid heat pumps in large volumes with a target of fitting 10 million by 2035. The CCC continue to emphasise their importance in their recently published Sixth Carbon Budget.

What are the benefits for UK households?

For UK households, hybrid systems offer an opportunity to reduce our gas or oil consumption without waiting for our homes to be insulated or replacing all our radiators. For off-grid homes they can also reduce your running costs. For those on mains gas, providing the heat pump is set to run efficiently, the running costs will be similar to mains gas (depending on the cost of electricity).

Hybrid heat pump manufacturers

There are a few options for homeowners to combine a heat pump with a fossil fuel boiler and in some cases they can keep their existing boiler in place. Alternatively, any heat pump and gas or oil boiler can be combined via a buffer tank.

Daikin Vaillant Grant Firebird
5kW or 8kW Altherma heat pump VRC control with aroTHERM heat pump 5, 8, 11 and 15kW 17kW Aerona R32 heat pump 7.5-16kW Enviroair heat pump
33kW gas boiler or can use a third party gas boiler Vaillant gas boiler or existing third party gas or oil ; boiler VortexAir Blue Flame oil boiler Envirogreen oil boiler

Financial support

Hybrid heat pumps are eligible for the Renewable Heat Incentive payback scheme, however the installation will need to be metered so that you are paid for the renewable energy you generate. For more see our Guide to the domestic RHI.

Need more help?

If you are considering a renewable technology for your home we can help. We provide impartial, expert advice for small and large projects. We will get you the right heating system and consider a full range of heat sources. Find out more about our ground-breaking services for consumers, contact us.

 

Jo & Caroline - Heating Heroes

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*https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/700572/Hybrid_heat_pumps_Final_report-.pdf

 

Jo Alsop

Heating Hero

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