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Why Low GWP and Natural Refrigerants

Ozone-depleting refrigerants (high ODP refrigerants) have in the past been increasingly replaced by HFC refrigerants. Although these refrigerants have an ODP of zero, they still have a high global warming potential (GWP) of over 700 to 2000 and above. Whereas synthetic HFO refrigerants such as R1234ze are now available with a much lower GWP level of 1 (AR5). Alongside these Low GWP synthetic refrigerants Natural Refrigerants such as hydrocarbons and CO₂ are also being increasingly applied, which have GWP levels of 3 & 1, respectively. This means that it is now not at all impractical to utilise either a natural refrigerant or Low GWP F-gas refrigerant and deliver a system that is not only low carbon in operation but is also low carbon in terms of the working fluid/refrigerant utilised within the heat pump or chiller.

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    The GWP level of refrigerants is becoming much more relevant, as it is now recognised that the lifetime carbon emissions of a Heat Pump or Chiller installation are directly related to the refrigerant selection within the unit. This is where best practice advice should always point towards the use of a refrigerant with a sub-700 GWP regardless of the application and a sub-10 GWP where practical to do so.

    Alongside the increasingly important focus on carbon emissions, F-Gas legislation is also driving down the use of High Global Warming Refrigerants.

    As early as 2014, a revision or sharper tightening of the F-Gas Regulation took place, with the result that HFC refrigerants with a GWP > 2500 were banned in new plants from 01.01.2020. As of 01.01.2022, this prohibition also became applicable to refrigerants with a GWP > 1500, as far as they are used in commercial refrigeration systems with an output of more than 40 kW. In order to achieve the set climate protection targets, further tightening or revisions of the F-gas regulation are to be implemented over the coming years.

    In October 2023 European legislation was introduced that stipulates chillers will be required to operate with 750 GWP and below from 2027, with commercial Heat Pumps operating with 150 GWP or 750GWP and below where necessary from 2030. Since Brexit the UK has its own F-Gas legislation, which will provide the same low-GWP focus as the European legislation.

    Performance characteristics and relevant advantages of the two most used Hydrocarbons

    Natural refrigerants, such as propane and isobutane, are gaining more and more popularity due to their low environmental impact and exceptional thermodynamic properties, which promise to make the refrigeration and heating industries increasingly sustainable and ready to meet future demands.

    Hydrocarbon refrigerants include propane, isobutane and isopentane. The latter is used in heat pumps that reach very high temperatures, up to 160°C, although it is still the subject of studies for its full application. In addition, some of the most used hydrocarbons also include R1270 (propylene), remarkable for its effectiveness in low-temperature contexts for excellent performance up to -45°C, and R170 (ethane), ideal for systems operating at very low temperatures, that is, up to -90°C.

    Propane

    Propane is renowned for its guarantee of high performance, with operating pressures similar to HFC or HFO refrigerants and a significantly lower environmental impact. Its wide availability on the market facilitates its adoption in multiple sectors such as refrigerated transport, process refrigeration, air conditioning and heating, as in the case of heat pumps, confirming that it is a valid choice in terms of efficiency and sustainability.

    Isobutane

    R600a refrigerant gas, commonly known as isobutane, is renowned for its good thermodynamic properties that make it particularly efficient in numerous refrigeration cycles. A valid alternative to high GWP refrigerants, this gas is often used in high-temperature heat pumps (up to 80-85°C) of the water-water type. In addition, besides being non-toxic, it is a safe gas, with a low global warming potential as it lacks ozone depletion potential.

    Discover the differences between R290 and R600

    The main differences between propane and isobutane affect their performance in different applications. Propane is beneficial for its ability to reach atmospheric pressure at much lower evaporation temperatures compared to isobutane, evaporating at about -42°C. Conversely, isobutane requires higher evaporation temperatures, which are around -10°C. Propane is particularly suitable for applications that require low temperature operations, such as air-water heat pumps, used during the winter. In detail, given that the evaporation temperature of these heating systems is influenced by the environment, propane is an optimal choice to maintain high performance, even in cold weather conditions. Isobutane, on the other hand has a lower density compared to propane and can condense at higher temperatures. This trait makes the refrigerant suitable for SINGLE-STAGE high-temperature heat pumps or for a SECOND STAGE of a TWO-STAGE system. Under these conditions, isobutane can be used to heat fluids up to 80-85°C efficiently and effectively.

    Regulations for the use of hydrocarbons

    The European standard EN 378 and the ATEX Directive regulate the use of R290 and R600. The former addresses safety and environmental requirements of the entire life cycle of refrigeration systems, from their design to disposal. A point of reference for refrigeration technicians at any level in the plant construction and management chain. The latter, the ATEX 1999/92/EC standard, acronym of “ATmosphere EXplosible”, was designed to establish the minimum requirements to protect the occupational health and safety of users where there is a potentially explosive atmosphere due to flammable mixtures of gases, vapours, mists or combustible dust in the air.

    It is now becoming an accepted best practice to apply refrigerants within Cooling & Heating Plant that have a Global Warming Potential (GWP) at the lowest practical level to meet the needs of the application.

    An application requirement will dictate the refrigerant options available, and this will always be the design/specification driver, but with the choice of plant now available, it is not impractical at all to achieve a project specification to include either Natural Refrigerant or low GWP F-gas refrigerant and deliver a system that is not only low carbon in operation but is also low carbon in terms of the working fluid/refrigerant utilised within the Heat Pump or Chiller.

    • Refrigerant environmental impact is classified by GWP
    • Global warming potential (GWP) quantifies the impact of a refrigerant as a factor of carbon dioxide
    • GWP compares each refrigerant to an equivalent mass of CO₂..

    Refrigerant selection is key to ensuring an application is both F-gas future-proof and also delivering the lowest carbon impact.

    The illustration below shows a range of refrigerants with their respective Global Warming Potential