Hybrid Systems

The most typical configuration of a hybrid heat pump will likely be a combination of a gas boiler and heat pump.

On average a hybrid system can take 2 to 5 days to install, depending on the complexity of the system and what the technology configuration is. To compare that to a sole heat pump installation it is significantly reduced.

There are quite a few different controls, from a quite basic control that simply allows the heat pump to heat the system whilst the external air temperature is higher than 7ºC, to a control that takes into consideration the cost of the fuels, the amount of over or under generation of grid electricity and numerous other factors.

A typical system will have either

1. An internal room temperature controller and an external weather sensor
2. Or an internal room temperature controller that accesses the external temperature via the internet.

We would recommend you book onto our heat pump and hybrid training course in the first instance.

For more information learn more here.

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Most existing heating systems which are heated by a gas or oil-fired boiler, (circa 24m), have radiators installed that were sized on the basis that the water temperature within was around 75ºC and an external air temperature of -3ºC. They were also sized on the basis that the boiler would be operated intermittently, perhaps for one or two hours in the morning and 4 or 5 hours at night. Outside of these times, the heating system would be switched off with a small number of systems having controls that allowed the air temperature in the house to drop to a set-back temperature 4 or 5ºC lower than the comfort temperature (which is typically 21-22ºC). If the setback temperature is reached then the boiler will fire and keep the house at this set-back temperature until the next demand for the higher comfort temperature.

Consequently, there are many occasions where only putting air-source heat pump water temperatures, (40-45ºC) into radiators sized for temperatures more like 75ºC will result in lower room air temperatures being experienced and discomfort and perhaps secondary heating devices needing to be used with more carbon being emitted.

Conversely, there will be moments in the year when the outside air temperature is higher than the design temperature basis and the required room temperatures will be achieved by the lower fl ow temperatures of a heat pump, with no noticeable drop in heat pump efficiency. Typically with anything over around 7ºC external air temperatures, it is likely that the heat pump will be suitable for the existing radiators to achieve the desired room temperatures and therefore with the lowering carbon intensity of electricity generation, a worthy consideration for carbon reduction measures.

A major advantage of a hybrid system is the reduced alterations needed to an existing heating and hot water system and the property itself. To substitute a gas or oil-fi red boiler totally with a heat pump is likely to require improvements to the fabric of the house to reduce the heat loss and also make the existing radiators and pipework suitably sized for the lower water temperatures. Also and perhaps more significantly there are around 17 million homes with combi or combination boilers installed and therefore no hot water storage cylinder. To remove a combi and replace it with a heat pump would require a hot water storage cylinder to be installed and a location for it found, and in most cases this will mean taking a portion of the landing or one of the bedrooms and constructional work to facilitate this. As you can imagine there will be very few people happy to accept this requirement.

Using a hybrid heat pump system would allow the heat pump to be sited externally and no or very few remedial changes are required to the heating and hot water system or the property. The boiler would heat the house during the colder periods and, when the weather isn’t quite so cold, yet heating is still required, a combi can provide hot water whilst the heat pump warms the property.

The cost of a hybrid heat pump installation will vary significantly on a number of factors;

• Is the installation both a new boiler and a new heat pump?
• If the existing boiler is retained and it’s just a heat pump that is the new addition
• The proximity between the heat pump and the boiler
• Is the hybrid system going to be with a Regular boiler system or a combi boiler system
• Is the heat pump a split or monoblock  

Generally, a heat pump of around 6kW output is the size of the majority of hybrid installations and can therefore provide the heating requirements for around 70% of the time. The heat pump, excluding installation cost, would be around £4k and a boiler, such as a 30kW gas-fi red combi, would be around £1k. The controls and installation will again vary from site to site but the installation of the component parts onto an existing system, with labour and other materials, could be anything up to and around £8k-£10k.