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Focus on high temperature heat pumps - updated Oct 2023

22/11/2020

Jo Alsop

Heating Hero

The Heating Hub

Jo explores why high temperature heat pumps might have an important role to play in decarbonising some properties.

 

Is a high temperature heat pump the right renewable for you?

Heat pumps have been identified as having a major part to play in decarbonising our homes. It is expected that 80% of homes will move to a heat pump. The remaining 20% of homes will be connected to heat networks using a large heat pump or other sources of clean energy. These will be communal systems that heat whole blocks of flats, villages and even towns.

Low temperature heat pumps can comfortably heat most homes, however in order to achieve conventionally low temperatures (45degC or less) they will require us to fit larger radiators and/or insulate further. High temperature heat pumps on the other hand can match gas and oil boiler temperatures and work without any changes to the home.

The Committee for Climate Change has identified high temperature (HT) heat pumps as a viable option for many households where low temperature heat pumps are not practical. HT heat pumps can run our existing radiators with little or no adjustment. We explore the benefits of and developments in this renewable technology.

Our existing housing stock

The vast majority of UK homes are set up to run with a gas or oil boiler and high temperature radiators. For the old-style non-condensing boilers, temperatures from the boiler to the radiators are 70-80degC.

For modern condensing boilers, heating temperatures should be lower in order for the boiler to run at its higher efficiency, although this rarely happens in practice. But certainly 60degC temperatures from the boiler can keep most homes warm in the coldest weathers and much lower temperatures are needed the rest of the year.

Perceived barriers to low temperature heat pumps

All air source heat pumps are viable alternatives to our gas and oil boilers. With capacities between 3-16kW as standard, they have the potential to heat most UK homes; the average heat requirement being just 6-8kW on a very cold day.

Older low temperature heat pump models are at their most efficient when the heating system temperatures run at 35-45degC. Older homes can still be heated using this lower temperature, but radiators will need to be much bigger in order to give off more heat. A new low temperature heat pump will therefore also mean new radiators throughout, unless we have drastically improved our insulation levels.

However, times have moved on since 2020 when this blog was written and high temperature heat pumps offering 70degC flow temperatures are available as standard from most of the mainstream heat pump manufacturers and tests have found them to produce decent efficiencies.

High temperature heat pumps

HT heat pumps have been designed to operate at 70-80degCs and so can heat standard radiators. In theory high temperature heat pumps are less efficient than low temperature models on that basis that the higher the operating temperature, the lower its efficiency.

In practice however, higher temperature heat pumps have been found to run as efficiently has low temperature models. This is because our homes are better suited than we think to lower temperatures, so whilst high temperature models were fitted in the trials, the weather compensation controls (an absolute must for all heat pumps) only called for lower temperatures in practice. In other words, just because a high temperature heat pump is fitted, it does not mean it has to operate at a high temperature.

Technology improvements

Older style high temperature heat pumps had two compressors to raise the temperature twice, hence using more electricity to achieve a higher temperature. Modern high temperature heat pumps use a R290 refrigerant (the chemical used to increase the temperature of the water in your radiators) which can achieve similarly high temperature with a single compressor. NB some heat pumps still have a larger compressor but that is to increase the kW output of the unit for larger homes.

HT efficiencies

Whilst high temperature heat pumps are now widely available, not all manufacturers provide an 'lab-tested' efficiency figure when operating at their top temperatures. The efficiencies shown in the table below are all tested at 55degC flow temperatures, with the exception of Samsung who have tested to 65degC. Even at that high temperature, which field tests have shown is rarely needed, the heat pump achieves an efficiency of 3.03 SCOP (Seasonable Co-efficient of Performance).

SCOP gives an estimate of efficiency over the year. Efficiency will be lower in winter when the heat pump will be providing higher temperatures to the home and more efficient during spring and autumn months when it can run at lower temperatures. However the period when the heat pump needs to run at a high temperatures is small, even in less well insulated properties, which means over the year the SCOP is decent.

High temperature heat pump options

Manufacturer Name Operating temperature Size kW SCOP
Daikin Altherma HT 70degC 10-12kW 3.58 @ 55degC
Vaillant arotherm plus 70degC 3.1kW 3.39 @ 55degC
Vaillant arotherm plus 70degC 5kW 3.39 @ 55degC
Vaillant arotherm plus 70degC 7kW 3.39 @ 55degC
Vaillant arotherm plus 70degC 10kW 3.58 @ 55degC
Vaillant arotherm plus 70degC 12kW 3.63 @ 55degC
Samsung HTQ 70degC 8-14kW 3.61 @ 55degC
Samsung HTQ 70degC 8-15kW 3.03 @ 65degC
Viessmann Vitocal 70degC 10kW 3.70 @ 55degC
Viessmann Vitocal 70degC 13-16kW 3.60 @ 55degC

When is a high temperature heat pump right for me?

Without doubt the next decade will be a drive towards insulating our homes so that we can fit low carbon technologies and heat pumps in particular, but home insulation is a slow process and we need to decarbonise quicker. Higher temperature heat pumps provide all households with the opportunity to move to a renewable heat source quickly. This is not to say insulation is not important and low cost measures should be fitted as a priority, cavity wall insulation and loft insulation in particular. Both will reduce the home's heat loss, cut energy demand and improve a heat pump's efficiency.

There will be some properties for which significant levels of insulation is not possible however and increasing radiator sizes impractical, for example listed and older properties. Where there seems little prospect of your heating system ever running at 45-55degC, then a high temperature heat pump is a great option that can be fitted now and you can decarbonise your home immediately. As electricity prices come down, the cost of running a less efficient heat pump will still be low.

How do I find an installer?

There are lots of heat pump installers across the UK. In all cases they must be MCS registered. The standard of installation is patchy as we are still getting to grips with the technology and demand is rising. We have some of the best heating engineers in the UK on our Elite Installer network. You can contact us if you would like to explore a heat pump for your home.

 

Jo & Caroline - Heating Heroes

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