Editing Heat pump (section)

===Refrigerant choice===
{{main|Refrigerant}}
Pure refrigerants can be divided into organic substances ([[hydrocarbons]] (HCs), [[chlorofluorocarbons]] (CFCs), [[hydrochlorofluorocarbons]] (HCFCs), [[hydrofluorocarbons]] (HFCs), [[hydrofluoroolefins]] (HFOs), and HCFOs), and inorganic substances ([[ammonia]] ({{chem|NH|3}}), [[carbon dioxide]] ({{chem|CO|2}}), and [[water]] ({{chem|H|2|O}})<ref>{{Cite journal |last1=Chamoun |first1=Marwan |last2=Rulliere |first2=Romuald |last3=Haberschill |first3=Philippe |last4=Berail |first4=Jean Francois |date=2012-06-01 |title=Dynamic model of an industrial heat pump using water as refrigerant |url=https://www.sciencedirect.com/science/article/pii/S0140700711003082 |journal=International Journal of Refrigeration |volume=35 |issue=4 |pages=1080–1091 |doi=10.1016/j.ijrefrig.2011.12.007 |issn=0140-7007}}</ref>).<ref>{{cite journal |last1=Wu |first1=Di |title=Vapor compression heat pumps with pure Low-GWP refrigerants |url=https://doi.org/10.1016/j.rser.2020.110571 |journal=Renewable and Sustainable Energy Reviews |date=2021 |volume=138 |page=110571 |doi=10.1016/j.rser.2020.110571 |bibcode=2021RSERv.13810571W |s2cid=229455137 |issn=1364-0321 |access-date=2022-11-17 |archive-date=2023-09-24 |archive-url=https://web.archive.org/web/20230924115906/https://www.sciencedirect.com/science/article/abs/pii/S136403212030856X?via%3Dihub |url-status=live }}</ref> Their boiling points are usually below −25&nbsp;°C.<ref>{{Cite web |title=Everything you need to know about the wild world of heat pumps |url=https://www.technologyreview.com/2023/02/14/1068582/everything-you-need-to-know-about-heat-pumps/ |access-date=2023-09-19 |website=MIT Technology Review |language=en |archive-date=2023-08-01 |archive-url=https://web.archive.org/web/20230801104352/https://www.technologyreview.com/2023/02/14/1068582/everything-you-need-to-know-about-heat-pumps/ |url-status=live }}</ref>

In the past 200 years, the standards and requirements for new refrigerants have changed. Nowadays low [[global warming potential]] (GWP) is required, in addition to all the previous requirements for safety, practicality, material compatibility, appropriate atmospheric life,{{Clarify|date=September 2023|reason=what does "appropriate atmospheric life" mean?}} and compatibility with high-efficiency products. By 2022, devices using refrigerants with a very low GWP still have a small market share but are expected to play an increasing role due to enforced regulations,<ref>{{cite web |last1=Miara |first1=Marek |title=Heat Pumps with Climate-Friendly Refrigerant Developed for Indoor Installation |url=https://www.ise.fraunhofer.de/en/press-media/press-releases/2019/heat-pumps-with-climate-friendly-refrigerant-developed-for-indoor-installation.html |publisher=Fraunhofer ISE |date=2019-10-22 |access-date=2022-02-21 |archive-date=2022-02-20 |archive-url=https://web.archive.org/web/20220220224636/https://www.ise.fraunhofer.de/en/press-media/press-releases/2019/heat-pumps-with-climate-friendly-refrigerant-developed-for-indoor-installation.html |url-status=live }}</ref> as most countries have now ratified the [[Kigali Amendment]] to ban HFCs.<ref>{{Cite web |last=Rabe |first=Barry G. |date=2022-09-23 |title=Pivoting from global climate laggard to leader: Kigali and American HFC policy |url=https://www.brookings.edu/blog/fixgov/2022/09/23/pivoting-from-global-climate-laggard-to-leader-kigali-and-american-hfc-policy/ |access-date=2022-10-04 |website=Brookings |language=en-US |archive-date=2022-10-04 |archive-url=https://web.archive.org/web/20221004135503/https://www.brookings.edu/blog/fixgov/2022/09/23/pivoting-from-global-climate-laggard-to-leader-kigali-and-american-hfc-policy/ |url-status=live }}</ref> [[Isobutane|Isobutane (R600A)]] and [[propane|propane (R290)]] are far less harmful to the environment than conventional hydrofluorocarbons (HFC) and are already being used in [[air source heat pump|air-source heat pump]]s.<ref>{{Cite book |url=https://books.google.com/books?id=LpStalb-tF4C&q=R600A+isobutane+ozone+environment&pg=PA77|title=Green Electricity and Global Warming|last=Itteilag|first=Richard L.|date=2012-08-09|publisher=AuthorHouse|isbn=9781477217405 |pages=77|language=en |access-date=2020-11-01|archive-date=2021-11-23|archive-url=https://web.archive.org/web/20211123223807/https://books.google.com/books?id=LpStalb-tF4C&q=R600A+isobutane+ozone+environment&pg=PA77|url-status=live}}</ref> Propane may be the most suitable for high temperature heat pumps.<ref name=":2" /> Ammonia (R717) and carbon dioxide ([[Carbon dioxide#Refrigerant|R-744]]) also have a low GWP. {{As of|2023}} smaller {{Chem|CO|2}} heat pumps are not widely available and research and development of them continues.<ref>{{Cite web |title=Smart CO2 Heat Pump |url=https://www.dti.dk/co2-heat-pump-20-200-kw/44672 |access-date=2023-09-17 |website=www.dti.dk |archive-date=2023-01-30 |archive-url=https://web.archive.org/web/20230130083759/https://www.dti.dk/co2-heat-pump-20-200-kw/44672 |url-status=live }}</ref> A 2024 report said that refrigerants with GWP are vulnerable to further international restrictions.<ref>{{Cite web |title=Annex 53 Advanced Cooling/Refrigeration Technologies 2 page summary |url=https://heatpumpingtechnologies.org/publications/annex-53-advanced-cooling-refrigeration-technologies-2-page-summary/ |access-date=2024-02-19 |website=HPT – Heat Pumping Technologies |language=en}}</ref>

Until the 1990s, heat pumps, along with fridges and other related products used [[chlorofluorocarbon]]s (CFCs) as refrigerants, which caused major damage to the [[ozone layer]] when released into the [[Earth's atmosphere|atmosphere]]. Use of these chemicals was banned or severely restricted by the [[Montreal Protocol]] of August 1987.<ref>{{cite web |year=2007 |title=Handbook for the Montreal Protocol on Substances that Deplete the Ozone Layer – 7th Edition |url=http://ozone.unep.org/Publications/MP_Handbook/Section_1.2_Control_measures/Annex_A_-_Group_I.shtml |url-status=dead |archive-url=https://web.archive.org/web/20160530171422/http://ozone.unep.org/Publications/MP_Handbook/Section_1.2_Control_measures/Annex_A_-_Group_I.shtml |archive-date=2016-05-30 |access-date=2016-12-18 |publisher=United Nations Environment Programme – Ozone Secretariat}}</ref>

Replacements, including [[R-134a]] and [[R-410A]], are hydrofluorocarbons (HFC) with similar thermodynamic properties with insignificant [[ozone depletion potential]] (ODP) but had problematic GWP.<ref>{{cite web |title=Refrigerants – Environmental Properties |url=http://www.engineeringtoolbox.com/Refrigerants-Environment-Properties-d_1220.html |url-status=live |archive-url=https://web.archive.org/web/20130314143622/http://www.engineeringtoolbox.com/Refrigerants-Environment-Properties-d_1220.html |archive-date=2013-03-14 |access-date=2016-09-12 |website=The Engineering ToolBox}}</ref> HFCs are powerful greenhouse gases which contribute to climate change.<ref name="R-410A">[[R-410A#Environmental effects]].</ref><ref>{{cite web|last1=Ecometrica.com|title=Calculation of green house gas potential of R-410A|date=27 June 2012| url=http://ecometrica.com/article/calculating-the-global-warming-potential-of-refrigerant-gas-mixes|access-date=2015-07-13 |ref=Calculation of green house gas potential of R-410A|archive-date=2015-07-13|archive-url=https://web.archive.org/web/20150713232735/http://ecometrica.com/article/calculating-the-global-warming-potential-of-refrigerant-gas-mixes|url-status=live}}</ref> [[Dimethyl ether]] (DME) also gained in popularity as a refrigerant in combination with R404a.<ref name="mecanica-dme">{{Cite web|url=http://www.mecanica.pub.ro/frigo-eco/R404A_DME.pdf |archive-url=https://web.archive.org/web/20120314211640/http://www.mecanica.pub.ro/frigo-eco/R404A_DME.pdf |title=R404 and DME Refrigerant blend as a new solution to limit global warming potential|url-status=dead|archive-date=March 14, 2012|date=March 14, 2012}}</ref> More recent refrigerants include [[Difluoromethane|difluoromethane (R32)]] with a lower GWP, but still over 600.

{| class="wikitable sortable"
|-
! refrigerant !! 20-year GWP !! 100-year GWP
|-
|[[R-290 (refrigerant)|R-290]] propane<ref name="ar6">{{Harvnb|IPCC_AR6_WG1_Ch7|2021|loc=7SM-26}}</ref> 
|0.072
|0.02
|-
|[[R-600a]] isobutane|| ||3<ref>{{Cite web |last=LearnMetrics |date=2023-05-12 |title=List of Low GWP Refrigerants: 69 Refrigerants Below 500 GWP |url=https://learnmetrics.com/low-gwp-refrigerants/ |access-date=2023-09-13 |website=LearnMetrics |language=en-GB |archive-date=2023-06-10 |archive-url=https://web.archive.org/web/20230610114014/https://learnmetrics.com/low-gwp-refrigerants/ |url-status=live }}</ref>
|-
|[[Difluoromethane|R-32]]<ref name="ar6"/>||491||136
|-
|[[R-410a]]<ref name=":1">{{Cite web |title=Global warming potential (GWP) of HFC refrigerants |url=https://iifiir.org/en/encyclopedia-of-refrigeration/global-warming-potential-gwp-of-hfc-refrigerants |access-date=2023-09-13 |website=iifiir.org |language=en |archive-date=2023-09-24 |archive-url=https://web.archive.org/web/20230924115907/https://iifiir.org/en/encyclopedia-of-refrigeration/global-warming-potential-gwp-of-hfc-refrigerants |url-status=live }}</ref>||4705||2285
|-
|[[R-134a]]<ref name=":1" />||4060||1470
|-
|[[R-404a]]<ref name=":1" />|| 7258||4808
|}

Devices with R-290 refrigerant (propane) are expected to play a key role in the future.<ref name=":2">{{Cite news |date=2023-09-06 |title=Propane-powered heat pumps are greener |newspaper=[[The Economist]] |url=https://www.economist.com/science-and-technology/2023/09/06/propane-powered-heat-pumps-are-greener |access-date=2023-09-17 |issn=0013-0613 |archive-date=2023-09-17 |archive-url=https://web.archive.org/web/20230917022901/https://www.economist.com/science-and-technology/2023/09/06/propane-powered-heat-pumps-are-greener |url-status=live }}</ref><ref>{{Cite web |last=Everitt |first=Neil |date=2023-09-15 |title=Qvantum plant has 1 million heat pump capacity |url=https://www.coolingpost.com/world-news/qvantum-plant-has-1-million-heat-pump-capacity/ |access-date=2023-09-17 |website=Cooling Post |language=en-GB |archive-date=2023-09-24 |archive-url=https://web.archive.org/web/20230924120053/https://www.coolingpost.com/world-news/qvantum-plant-has-1-million-heat-pump-capacity/ |url-status=live }}</ref> The 100-year GWP of propane, at 0.02, is extremely low and is approximately 7000 times less than R-32. However, the flammability of propane requires additional safety measures: the maximum safe charges have been set significantly lower than for lower flammability refrigerants (only allowing approximately 13.5 times less refrigerant in the system than R-32).<ref>{{cite web |last1=Miara |first1=Marek |title=Heat Pumps with Climate-Friendly Refrigerant Developed for Indoor Installation |url=https://www.ise.fraunhofer.de/en/press-media/press-releases/2019/heat-pumps-with-climate-friendly-refrigerant-developed-for-indoor-installation.html |publisher=Fraunhofer ISE |date=22 October 2019 |access-date=21 February 2022 |archive-date=20 February 2022 |archive-url=https://web.archive.org/web/20220220224636/https://www.ise.fraunhofer.de/en/press-media/press-releases/2019/heat-pumps-with-climate-friendly-refrigerant-developed-for-indoor-installation.html |url-status=live }}</ref><ref>{{Cite web |title=Refrigerant Safety – About Refrigerant Safety, Toxicity and Flammability |url=https://check-mark.co.uk/info/basics/refrigerant-safety/ |access-date=17 April 2024 |website=Checkmark}}</ref><ref>{{Cite web |date=2015-09-01 |title=A2L – Mildly Flammable Refrigerants |url=https://www.acrjournal.uk/features/a2l-mildly-flammable-refrigerants/ |access-date=2024-04-17 |website=ACR Journal}}</ref> This means that R-290 is not suitable for all situations or locations. Nonetheless, by 2022, an increasing number of devices with R-290 were offered for domestic use, especially in Europe.{{Cn|date=February 2024}}

At the same time,{{When|date=February 2024}} HFC refrigerants still dominate the market. Recent government mandates have seen the phase-out of [[Chlorodifluoromethane|R-22]] refrigerant. Replacements such as R-32 and R-410A are being promoted as environmentally friendly but still have a high GWP.<ref>{{Cite web |last=US Environmental Protection Agency |first=OAR |date=14 November 2014 |title=Phaseout of Ozone-Depleting Substances (ODS) |url=https://www.epa.gov/ods-phaseout |url-status=live |archive-url=https://web.archive.org/web/20150924132109/http://www.epa.gov/ozone/title6/phaseout/accfact.html |archive-date=24 September 2015 |access-date=16 February 2020 |website=US EPA |language=en}}</ref> A heat pump typically uses 3&nbsp;kg of refrigerant. With R-32 this amount still has a 20-year impact equivalent to 7 tons of {{CO2}}, which corresponds to two years of natural gas heating in an average household. Refrigerants with a high ODP have already been phased out.{{Cn|date=February 2024}}