Refrigerants

Key Takeaways

The refrigerant is the hero of the heat pump
People should choose heat pump hot water units that use carbon dioxide or propane
The only case I see for a heat pump hot water unit with R-134a is if someone needs a heat pump hot water unit now and has a very tight budget

The refrigerant is often described as the ‘hero’ in a heat pump hot water unit. It continuously changes from liquid to gas, absorbing heat, being compressed, heating up further and then releasing heat into the water. To learn how the refrigerant works in a unit, please see my article “How does heat pump hot water work.”

I wouldn’t select a unit purely based on its refrigerant. As I outline in "How to Choose a Heat Pump Hot Water Unit", there are three key factors to take into account. Refrigerant is one factor, but cost and reliability are also important.

Refrigerants are important because if they leak into the atmosphere, they contribute to our greenhouse gas emissions. Each refrigerant has a Global Warming Potential (GWP) - the measure of heat absorbed by one tonne of a gas relative to heat absorbed by one tonne of carbon dioxide. The higher the GWP, the more heat absorbed, the worse it is for the environment.

There are three refrigerants used in heat pump hot water units in the Australian market.

Carbon Dioxide (R-744)

Ironically, the gold standard in refrigeration is Carbon Dioxide (CO2). CO2 has a very low GWP of 1 and is found in premium heat pump hot water units. CO2 only works as a refrigerant under high pressure. Premium equipment is required to handle the high pressure. CO2 also has a low boiling point of -76C (the temperature at which it changes from liquid to gas), so it works well as a refrigerant in cold climates (in Australia, this is only really an issue in Canberra and Hobart).

Propane (R-290)

Propane is another common refrigerant and is found in mid-market heat pump hot water units.

Propane has a GWP somewhere between 0.02 and 3. I’ve seen various reports, but either way the number is very low, effectively the same as Carbon Dioxide. I have heard Chris Taylor, Managing Director of Reclaim (which uses CO2), say there is very little difference between propane and carbon dioxide.

Some more climate-friendly refrigerants like propane are highly flammable, so extra care is required. This is less of an issue for the homeowner, but more of a logistics issue for manufacturers and installers eg: moving units around on a forklift in a warehouse.

R-134a

R-134a or Tetrafluoroethane is a hydroflurocarbon (HFC) with a global warming potential of 1,430. Yes you read that right - 1,400 times more heat trapped than the same amount of Carbon Dioxide! R-134a is commonly used in heat pump hot water units, particularly the cheaper end of the market. However, with such a high GWP, the days are numbered for R-134a in heat pump hot water units (see more below).

Due to regulatory phasing out of R-134a, many heat pump hot water manufacturers are introducing a new unit that uses propane. I wouldn’t want to be the first customer that uses these new units - I’d be very happy to let others be the guinea pigs.

Source: https://www.dcceew.gov.au/environment/protection/ozone/rac/global-warming-potential-values-hfc-refrigerants

Which should you choose?

One of the more contentious questions on heat pump hot water units is whether it’s ok to select a unit that uses a refrigerant with a high GWP.

Here are some thoughts both for and against.

For	Against
Heat pump hot water is such an efficiency improvement, leading to significant carbon savings that the choice of the refrigerant isn’t significant.	Why do we need to sacrifice? Why not choose a good quality, affordable unit that uses a good refrigerant. This is the position I take, more below.
There are clear incentives for people to recover refrigerants at the end of the unit’s life and they will therefore not be leaked into the atmosphere.	While some may argue refrigerants will be recovered, things go wrong. Parts will break, people won’t do the right thing at the end of the unit’s life - there will be leaks (ozone layer anyone?)
The amount of refrigerant is so small (<1kg) that even if it does leak, the effect will be minimal.	There must be a clear reason behind the legislative direction of phasing out refrigerants with high GWPs.

What does Tim think?

I have two clear opinions on this.

First, the market is in a state of change. From 1 July 2024, discounts available under the Victorian Energy Upgrades program and the Solar Victoria $1,000 rebate will not be available to heat pump hot water units that use a refrigerant that has a global warming potential of more than 700. The Federal government is also in the process of phasing out HFCs, meaning the days are numbered for R-134a.

Second, for those looking to make a decision right now, it is my view that you don’t need to sacrifice refrigerant for quality or budget. There are some good quality units on the market like Aquatech, Haier, Emerald which use propane and don’t require the high upfront cost of some of the CO2 refrigerant units.

Still, even those units above generally require an investment of a few thousand dollars, and not everyone has that budget available. There will be many people that need a new hot water service now, and don’t have time to wait for more affordable units that use propane. They need something affordable now. They and the environment would be much better served by choosing a heat pump hot water unit with R-134a, rather than signing up to a new gas hot water service for another 15 years or so.