One of the favourite critiques of heat pumps, especially in the UK press, is around the temperature they generate.
It is claimed, for example in this Daily Mail article, that individual homes would have to turn down their radiators by 10 degrees because heat pumps can’t generate water temperatures as high as those generated by gas boilers.
This is wrong on two fronts: the premise, and the facts.
Firstly – the premise. The idea that a heat pump needs to generate the same temperatures as a gas boiler is wrong-headed. With modern building standards, lower temperatures can perfectly well keep a home warm all year round and at far lower energy consumption. We’re used to the idea that our heating systems need to instantly heat water to very high temperatures on demand to ensure our home stays cosy. But this is based on the easy but wasteful combustion of gas and has led to inefficient systems which are poorly controlled. A heat pump can be set, or learn, to generate heat for when you need it without you ever having to think about ‘turning the heating up’. CO2 heat pumps are efficient at 70 degC flow and 30 deg return, and at this level make for a much better solution than a gas boiler.
Secondly – the facts. Natural gas boilers create a flow temperature of up to 85 degrees. CO2 heat pumps can also hit exactly the same temperature, and they can do it three times as efficiently as gas boilers. However, in most cases you won’t need to hit these kinds of temperatures if the heat pump is calibrated correctly.
What are High Temperature Heat Pumps?
Perhaps in response to the kind of press coverage above, there has been increasing discussion about the viability of high temperature heat pumps.
Low temperature heat pumps can perfectly well keep a home or commercial building warm when controlled correctly for the type and construction of the building. They are available with capacities of 3- kW to multi-megawatt.
However, high temperature heat pumps are now available which can be appropriate in some circumstances, especially when replacing gas boilers, and can heat water to the same temperature as gas boilers. The main cases where you might want a high temperature heat pump instead of a low temperature heat pump are:
1) Process heating where specific temperatures are required for manufacturing, cleaning or process industry. Examples include food production, wash down facilities and chemical production.
2) Where large volumes of domestic hot water are required. Often this is in healthcare, leisure or food preparation where there are increased controls for risks such as legionella. Instantaneous hot water production is best but can lead to over sized generation plant and so stored hot water is very common. Storing at high temperature reduces risk and the volume required.
Very large heating systems such as district heating, shopping centres and industrial complexes require higher temperatures because the distribution is more efficient. Higher temperatures of 70 to 80DegC reduces the distribution pipe sizes and pumping energy required, as well as enabling the provision of heat via a variety of heat emitters. Additionally higher temperatures are better when thermal storage plays a role in separating generation from use for grid flexibility. A well designed system that returns at 30 to 35degC can achieve COPS of 4 with an air source heat pump working on CO2.
If you’re interested in learning what sort of system would suit you, take our quick questionnaire or get in touch.