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What’s The Context?

A significant, and growing, part of the debate about how best to deploy heat pumps at scale in the UK focuses on the refrigerants to use. It’s something we’ve discussed before, specifically about the use of CO2 as a refrigerant for heat pumps.

Many, if not most, heat pumps currently installed and in production use synthetic refrigerants.

But we believe that the future of heat pump production lies in natural refrigerants, and we’ll discuss why here.

What Are Natural Refrigerants?

Refrigerants or working fluids are broadly characterised by being either chemical or natural.  

Naturals – include CO2 and propane. Naturally occurring substances that are widely available, not subject to patents. These were the first working fluids to be used and now dominate the refrigeration market.  

Chemicals – including CFCs (banned), HFCs (being phased out) and HFOs (now the subject of litigation for environmental toxins). These are chemicals made specifically for refrigeration, many are patented and expensive. The global supply chain is largely in China and the US.  

Reason 1: Performance

Refrigerants are designed for refrigeration. They’re great at that job. Historically, as the refrigeration industry grew, natural refrigerants were displaced with synthetic alternatives. But in order for heat pumps to reach maximum efficiency heat pumps require different thermodynamics than refrigerators, so a new approach is required. Natural refrigerants are higher performance than synthetic refrigerants because:

-They’re more efficient. They achieve higher coefficient of performance (COP) than synthetics when used in a heat pump.

-Glide. Glide is a thermodynamic behaviour of some synthetic refrigerant (known as non-azeotripic or azeotropic). It can be useful in refrigeration but it’s a negative in heating applications.

-Wider delta temperatures. Delta temperature is the difference between the temperature the heat pump puts out and the temperature which returns to it from the heating system. Synthetic refrigerants in heat pump applications often require a small delta temperature of 5 or 10 deg C. This leads to large pipe diameters, excessive flow rates and pump costs and requires significant heating system upgrades. Natural refrigerants offer wider DTs which brings significant advantages to building efficiency.

-Higher temperatures. Low temperatures are one of the reasons people give for opposing wider roll out of heat pumps. This isn’t true for natural refrigerant heat pumps. Natural refrigerants can produce very high temperatures – CO2 has proven itself over 100 dec C.


Reason 2: GWP (Global Warming Potential)

The climate emergency should have a prominent place in all major social and business decision making processes now. If you’re not worried about the climate risk of decisions you make, you should be worried about future regulatory risk you could be exposed to as climate change forces legislation to change.

F-gas regulations have significantly reduced the GWP of available refrigerants using a combination of outright bans and price increases. This is set to continue under current regulation and, in all likelihood, regulations restricting the use of F-gas (of which synthetic refrigerants are a large part) are going to increase in severity as its use comes under increasing scrutiny.

There are three main aspects to consider here:

-F-gas – draw down continues but also as carbon footprints are reduced the proportion contributed by F-gas rises and will therefore be increasingly important.

-Toxicity – HFOs contain PFAS chemicals which are linked to environmental poisoning and high toxicity for the natural environment and are therefore likely to be subject to regulatory action.

-Availability now and in the future – a heat pump should have a 15 to 20 year life. Installing a high GWP refrigerant heat pump now carries a risk of becoming a stranded asset in the near future.

Reason 3: Cost

Cost, especially total cost of ownership, is a huge reason to choose natural refrigerants over synthetic refrigerants. Synthetic gasses are more expensive for three main reasons:

-They require more processing
-They are subject to the F-gas phase down
-The profit margins are higher for the producers

If you’re going to buy a synthetic refrigerant heat pump, the cost to buy will be higher, the cost to replace refrigerant losses over the plant’s lifetime will be higher, and the cost to dispose of the refrigerant at the end of life will be higher. Some synthetic options, particularly HFO, can’t be topped up after losses because they are a mix of gasses with a critical proportion of each constituent – so only a full replacement will do. Again, that costs more.

Leisure Centre

What Are The Challenges Around Natural Refrigerants?

Any refrigerant choice has challenges when compared to a gas boiler. Natural refrigerants are no different but with good engineering the advantages of naturals can be unlocked.

Flammability – hydrocarbon refrigerants are highly flammable. Gas risks are nothing new as most buildings have a gas connection. You can mitigate this by preventing leaks through pressure testing, good commissioning and servicing, fit detection and ventilation. You should also site units in clear open areas well away from inhabited areas. Using CO2 can overcome this too as CO2 is non-flammable.

Temperatures – CO2 requires a lower than normal return temperature. In a process engineering environment this is not an issue, but in building services it is seen by some as a hurdle. Proper design and specification, particularly in controls, followed by good installation and commissioning are key and should be expected on any project anyway.

Heating system modifications – it is possible to replicate 82/71 gas boiler performance but the resulting cascade system is not very efficient, typically less than half of what’s possible. All heat pumps require some amendment to heating systems if they are to be efficient and to have the lowest cost of ownership. Natural refrigerants often result in less amendments because of the higher temperatures and wider delta Ts.

Oak Heat Pump


Don’t use multiple small units. We’ve seen designs featuring 16 or more small heat pumps. When install cost is taken in to account these cost more than a single commercial heat pump and don’t feature the benefits of commercial specification (e.g. a full oil management system, efficient defrost with minimal impact on heat delivery). Resilience is often cited as a reason for this approach but this is a misunderstanding. Multiple unit systems still have single points of failure, for example the power supply or header. Turn down ratios of multi compressor commercial heat pumps are around 10% of total capacity, more than enough for building applications. Components are also better quality on commercial heat pumps because they are designed for a long service life, plus the units are almost infinitely serviceable.

1200kW v16


The challenges of natural refrigerants appear minor when compared to the performance advantages and the direction of travel for regulations and ESG, as well as cost and availability.

Natural refrigerants will dominate the future of both refrigeration and heating for many reasons but mainly because they are the best choice.

If you’d like to discuss a natural refrigerant heat pump for your project get in touch.


Speak with our team of experts and discuss your requirements. Complete this quick form and we will be in touch or contact us using:

0113 887 9604

Bristol & Bath Science Park
Dirac Crescent, Emersons Green
Bristol, BS16 7FR

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