Refrigerants and their Contribution to Global Warming

Seven main GHGs are included in the Greenhouse Gas Protocol’s Corporate and Reporting Standard. These GHGs were originally set out for control in the 1997 Kyoto Protocol, they are:

• Carbon dioxide (CO₂)
• Methane (CH₄)
• Nitrous oxide (N₂O)
• Hydrofluorocarbons (HFCs)
• Perfluorocarbons (PFCs)
• Sulphur hexafluoride (SF₆)
• Nitrogen trifluoride (NF₃)

It’s common for people use the term “carbon emissions” when referring to GHG gas emissions. CO^₂ is the most common GHG but “carbon emissions” is shorthand for equivalent carbon dioxide (CO_2e) emissions. At the building or corporate scale, CO_2e is usually measured in tonnes or kilograms and is a measure of the combined global warming potential of a group of different GHG emissions expressed as the equivalent amount of CO^₂ emissions.

There are also many other GHGs. Water vapour is considered one of the most potent GHGs, however it is not on the list of regulated GHGs because atmospheric water vapour levels are difficult to attribute directly to human activities. Water vapour is often referred to as a “global warming accelerator” because rising global temperatures increase evaporation rates, adding more water vapour to the atmosphere and amplifying the effect of global warming which is directly attributable to human activities.

The global warming potential (GWP) of a GHG measures its contribution to global warming compared to an equivalent mass of CO_2. CO₂ has a GWP equal to 1. Once released, CO₂ spends hundreds of years in the atmosphere. This means today’s emissions will continue to affect the planet’s climate for many generations to come, even if we can reduce CO₂ emissions in the near future. The GWP of a GHG is conventionally expressed over a 100-year period to allow ease of comparison with CO₂.

More reactive GHGs have shorter atmospheric lifetimes; that is, they spend less time in the atmosphere and have a greater impact on global warming in the short term. Methane, for instance, has an atmospheric lifetime of around 20 years - measured over this time frame, its GWP is 86 times that of CO₂. Over 100 years, the GWP of Methane is around 28 times that of CO₂ and is referred to a GWP = 28.

Fluorinated GHGs (F-gases) are a family of gases containing fluorine. They are very powerful GHGs with a high GWP.

Of the controlled GHG, three are types of F-gases:

• hydrofluorocarbons (HFCs)
• perfluorocarbons (PFCs)
• sulphur hexafluoride (SF₆)

HFCs are F-gases and are the most commonly used refrigerant gases. HFCs are used within home and commercial cooling systems, VRF systems, heat pumps, fridges and freezers, and vehicle air conditioning systems. If accidentally released into the atmosphere through leaky systems or illegally and deliberately vented, HFCs are harmful greenhouse gases. HFCs have a very high GWP: 1kg of the common (HFC) refrigerant gas R-410A has a GWP equivalent to 2,088kgCO_2e.

The use of F-gases is currently being curtailed. Legislation to reduce F-gas use has been put in place internationally, including in the EU and the UK following the Kigali Amendment to the UN’s Montreal Protocol. The new rules limit the use of HFCs, and are expected to prevent emissions equivalent to 105 million tonnes of CO_2e by 2047.

Leakage of refrigerants can account for a significant proportion of a building’s total whole-life carbon emissions. Refrigerants add to a building’s whole-life carbon emissions if they are allowed to leak out of equipment or pipe work into the atmosphere. The risk of such leakage varies depending on the type of refrigerant system installed and the quality of its installation, maintenance regime, and refrigerant recovery and disposal at the end of the equipment's life. The atmospheric damage that refrigerant leaks cause depends on the type of refrigerant used and its properties including GWP.

Variable Refrigerant Flow (VRF) heating and cooling systems circulate high quantities of refrigerant through a pipe network between indoor fan coil units and outdoor air source units. The Chartered Institute of Building Services Engineers (CIBSE) have produced a technical memorandum, CIBSE TM65, which sets out annual leakage rates to be assumed in assessments lifecycle carbon emissions. For VRF systems CIBSE suggest using an annual leakage rate of 6% and an end-of-life recovery rate of 97%. The higher risk of leakage coupled with the larger quantities of refrigerant mean that VRF systems can contribute significantly to the whole-life carbon emissions of the buildings in which they are installed. Their contribution could be as high as 13% for a typical VRF system using R-410A refrigerant.

Reducing the risk of leakage and choosing systems with low GWP refrigerants are the two main steps we can take to lower the contribution which refrigerants make to whole-life carbon emissions. CIBSE TM65 sets out the following steps:

• Reduce the volume of refrigerant used

- Optimise the passive design of buildings to limit the need for heating and cooling systems

- Minimise the lengths of refrigerant pipes between components in distributed refrigerant systems such as VRF or split air conditioning systems

- Consider alternatives to distributed refrigerant systems. These might include central packaged heat pumps or chillers, conventional water-based distribution systems, or “hybrid” VRF systems where refrigerant distribution is reduced, and water is used to convey heating and cooling to final devices

• Select equipment with low GWP refrigerant

- Avoid high GWP refrigerants (such as HFC) where possible. Manufacturers are increasingly providing alternative solutions utilising lower GWP refrigerants. Hydrocarbon and natural refrigerants are increasingly common in self-contained heat pump and chiller systems. Large central plant is also available with new HFO (Hydrofluoroolefin) types of refrigerant developed by manufacturers such as Honeywell, which have a very low GWP.

• Use best installation practice, planned preventative maintenance, and leak testing and detection
• Recover 100% of refrigerant from the systems at their end of life

The table below highlights the GWP and typical building system applications of some common refrigerant gases. Selecting a lower GWP refrigerant can help reduce the whole life carbon emissions of our buildings and help combat global warming.

* The quantity of flammable or toxicity of refrigerant and the ventilation of refrigerant containing equipment and pipelines needs to be considered during design development.