Global Warming Potentials, actually.

In this explainer post, we’re going to look at:

• What is a refrigerants' GWP?
• What are the issues with simple GWP numbers for refrigerants?
• What you should be looking at other than a single number.

Our understanding of the world, climate, science changes and is revised over time, and selecting refrigerants and refrigeration systems is an multifactorial problem.

What is GWP?

Global Warming Potential or GWP is the ratio of the radiative forcing from the instantaneous release of 1 kg a substance relative to 1 kg of CO2 over a hundred-year duration (or time horizon).

GWP values used in legislation are drawn from the Intergovernmental Panel on Climate Change (IPCC) Assessment Reports. For UK and EU current legislation, GWPs are drawn from the Fourth Assessment Report (AR4).

What does this mean? To use a decades old example, the effect of an instantaneous release of 1 kg of refrigerant, it means that a leakage is the equivalent to the below

Now the chances are, you already know this. ?So what are the issues with GWP values? Well, some of my issues are in those first 3 sentences.

What issues are there with GWP figures?

It’s 'just' a ratio of Radiative Forcing

GWP is a single measure of what happens when refrigerant as a final product is released. It does not account for the embodied carbon of the refrigerant (from the extraction of raw materials, transport, manufacture, and onwards transport), the emissions of Ozone Depletion (Montreal regulated) and Global Warming (Kyoto regulated) substances that are inadvertently released, of the associated fugitive emissions.

In other words, it’s Scope 1 emission types.

Accordingly, it might not reflect the related input differences between refrigerants. For example, natural refrigerants have very low levels of embodied carbon. Carbon Dioxide is generally a repurposed waste product from Fertiliser Production. Bar the removal of water – the energy and resource input is minimal <1 kgCO2e per kg of CO2 recovered.

Ammonia is more energy intensive, but as a simple molecule, and frankly a huge demand for fertiliser (Of which ~80% of worldwide production is for), its embodied carbon per kg is quite small, 1-2 kg of CO2e per kg of Ammonia produced.

Propane and other hydrocarbons are in a similar situation, depending on how it is refined.

And what so we compare that to? Synthetic refrigerants require specific raw materials to be extracted, such as fluorite. Synthetic refrigerant production might require the production of feedstock such as Carbon tetrachloride (CTC), or chlorodifluoromethane (R22) ozone depleting substances with high GWP, and might result in the by products of chlorodifluoromethane (R23), a molecule with a very high GWP.

Unfortunately, Scope 3 emissions of synthetic refrigerant production (i.e. the production and disposal of a product) are quite hard to come by.

What I would recommend is that users, designers, and manufacturers at least consider how refrigerants are produced, and weight their refrigerant selections accordingly, especially if a refrigerant system is more likely to leak, than not.

GWP does not account for wider adverse environmental impacts or risks of such.

GWP values are based on a 100-year time horizon

The IPCC gives GWP valves based a 20-year, 100-year, and 500-year time horizons. Since 2007 and the fourth assessment report, F-Gas regulations have been based on a 100-year horizon. Looking at typical refrigerants over the other time horizons.

And we can see that modern refrigerants GWP decreases as the time horizon extends, but over the short term, the radiative forcing effect is much higher. ?For R404A, the GWP increases by more than 50%. For R407F, the GWP increases by over 125%. Whilst in this selection we see GWP decrease with time, and it is true for most molecules which will break down, notable CFCs (R13) & HFCs (R23), and all PFCs (including Sulphur hexafluoride (the "deep voice gas" used in electrical switchgear) have their greatest warming effects over the 100-to-500-year time horizons.

What’s the issue with a 100-year time horizon, you may ask? As climate change is further understood, new terms enter the vernacular – in this case the “Climate Tipping point”.

To quote Professor Mark Maklin at University College London “Climate tipping points are thresholds that, once crossed, result in dramatic climate change to a new stable climate.” Such tipping points may have drastic effects on global populations already at risk of the impacts of climate change.

With such potential impacts and tipping points being foreseen at likely 1°C and very liked 2°C warming increases over pre-industrial times, and such warming either has been achieved or will be achieved in the next two decades - is a 100-year horizon appropriate?

Since R32 is a critical building block for many new refrigerant blends (to add capacity to the refrigerant). We can see the effect of considering the 20-year horizon on new refrigerant blends.

Effectively due to R32’s high GWP at the 20-year time horizon, we see most modern synthetic blends will have a much higher 20 year radiative forcing effect.

GWP 100-year Time horizon values do not give a full picture of the warming effect of substances, at a time when we should be focusing heavily on the near to medium term warming effects.

GWP Values in legislation are already outdated.

The Fourth Assessment Report (AR4) came out in 2007, the Fifth Assessment Report (AR5) in 2014, and the Sixth Assessment Report (AR6) was released in 2023. And in legislation (drawn from Regulation (EU) No 517/2014), GWP values are based on AR4 (where possible), so frankly such values might be some 20 years old.

The table above shows the changes from AR4 to AR6, have resulted in increases across the board for GWP. Resulting, this would increase the latest 100-year GWP valves accordingly, as well as the 20-year time horizons.

What are the potential ramifications? Should F-Gas regulations be updated to account for the latest data on GWP, it might mean.

• Fundamentally it means that most synthetic refrigerants have a higher GWP than first thought, and currently sold as.
• R32 could be prohibited from single AC splits if it has a charge size lower than 3 kg, as it has a an actual GWP higher than 750. (Point 15 of Annex III of EU Regulation 517/2014)
• Sub 150 GWP synthetic refrigerant blends which have a proportion of R32 in it (pretty much all of them) for food retail refrigeration, would now be subject to the 40 kW duty system limit, as they have an actual GWP higher than 150 (Point 13 of Annex III of EU Regulation 517/2014)

GWP Values for most refrigerants and their related blends require revision.

Conclusion

What does this mean for users, designers, manufacturers, service and maintenance providers?

1. Refrigerant GWP values do not account for the embodied carbon of the refrigerant nor does it account for any wider adverse environmental effects of the refrigerant and it's production. It is prudent to assess this when choosing a refrigerant.
2. The majority of synthetic refrigerants demonstrate an increased warming effect at the 20-year horizon (somewhat disproportionately), which is where a climate tipping point might be encountered, and where our 2050 emissions target is. I recommend that the we need to favour the 20-year GWP horizon accordingly, because the 100 year outlook might be too late.
3. GWP values for most refrigerants and their associated blends require revision, and likely will be significantly higher than stated under current regulations. This means that there is a risk of current solutions being out of date, and not because the thresholds have been moved, but simply because the latest science says the refrigerant has more radiative forcing than we initially though.

Stakeholders should prioritise accordingly, and whilst we might be dead in the long run, we can still make useful and beneficial changes for the future.

K2 Engineering

If you found this article useful and you need advice, engineering consultancy, or project management in decarbonising your refrigeration or heating systems large or small, give K2 engineering a call.

https://www.k2engineering.co.uk/