Refrigerant - WikiHQ

Refrigerants are working fluids that carry heat from a cold environment to a warm environment while circulating between them. For example, the refrigerant in an air conditioner carries heat from a cool indoor environment to a hotter outdoor environment. Similarly, the refrigerant in a kitchen refrigerator carries heat from the inside the refrigerator out to the surrounding room. A wide range of fluids are used as refrigerants, with the specific choice depending on the temperature range needed and constraints related to the system involved.

Refrigerants are the basis of vapor compression refrigeration systems. The refrigerant is circulated in a loop between the cold and warm environments (see figure). In the low-temperature environment, the refrigerant absorbs heat at low pressure, causing it to evaporate. The gaseous refrigerant then enters a compressor, which raises its pressure and temperature. The pressurized refrigerant circulates through the warm environment, where it releases heat and condenses to liquid form. The high-pressure liquid is then depressurized and returned to the cold environment as a liquid-vapor mixture.

[[File:Air conditioning unit-en.svg|thumb|upright=2| A window air conditioner. The refrigerant circulates through the evaporator/cooling coil (blue), where it absorbs heat from the indoor air, making that air cooler. The refrigerant vapor then flows to the compressor, where an electric motor drives the vapor to higher pressure and temperature.

The vapor releases heat and liquefies in the condenser (red). The condensed liquid then flows through an expansion valve, depressurizing and cooling. After expansion, it returns to the evaporator as a cold liquid-vapor mixture.]]

Refrigerants are also used in heat pumps, which work like refrigeration systems. In the winter, a heat pump absorbs heat from the cold outdoor environment and releases it into the warm indoor environment. In summer, the direction of heat transfer is reversed.

Chillers are refrigeration systems that have a secondary loop which circulates a refrigerating liquid (as opposed to a refrigerant), with vapor compression refrigeration used to chill the secondary liquid. Absorption refrigeration systems operate by absorbing a gas, such as ammonia, into a liquid, such as water.

Thermophysical property requirements

In thermodynamic terms, refrigerants transport thermal energy, which is called enthalpy. Enthalpy greatly increases or decreases during evaporation or condensation. The difference between the enthalpy of the vapor and liquid phase is called the latent heat of vaporization. The latent heat of vaporization allows substantial energy to be absorbed or released, with minimal temperature change, in the evaporator or condenser. Engineers control the temperatures in the evaporator and condenser by changing the fluid's pressure. The evaporator pressure should be above atmospheric pressure to prevent air from leaking into it.

Similarly, the refrigerant must achieve a boiling point above the temperature of the warm environment, so that heat will flow out of the refrigerant as it condenses. Since boiling point rises with increasing pressure, the refrigerant in the condenser (on the warm side) will have an elevated pressure.

However, as the critical point temperature rises, the vapor density at the compressor inlet decreases. A lower density raises the volumetric flow rate of vapor needed for a given amount of cooling (in other words, the compressor must be larger to do the job). Thus, a trade-off between energy efficiency and volumetric efficiency underlies the selection of a refrigerant.

Refrigerants are sometimes blended to achieve a balance of desired properties. Pure refrigerants vaporize at a constant temperature when pressure is held constant (as it is in an evaporator or condenser). In contrast, blended refrigerants vaporize across a small range of temperature. This phenomenon is called temperature glide.

For safety, an ideal refrigerant should be non-toxic and non-flammable. For environmental protection, the refrigerant should have no ozone depletion potential, and a very low global warming potential. Refrigerants that are not naturally present in the atmosphere should have a short atmospheric lifetime and should decay into environmentally benign by-products.

Other requirements

The refrigerant must be chemically stable during use.

History

Diethyl ether molecule ]]

Vapor compression refrigeration was first described theoretically by Oliver Evans in 1805, using diethyl ether as the refrigerant. In 1834, Jacob Perkins patented a vapor compression system, also describing diethyl ether as the refrigerant. The first working prototype of that system was built by John Hague the same year, but used a rubber distillate, caoutchoucine, as the refrigerant. In the 1850s, James Harrison, working in Australia, developed a Perkins-type system also using diethyl ether. Ice making and meat packing were early applications of his technology.

Many more inventions followed during the second half of the 19th century. In the 1860s, Thaddeus Lowe developed a carbon dioxide system. The 1870s saw the introduction of systems based on ammonia, sulfur dioxide, dimethyl ether, and methyl chloride. Several 19th-century refrigerants continue in use to this day, but others have been discarded for safety or performance reasons. By start of the 20th century, ammonia was predominant in industrial systems.

The R- numbering system for refrigerants was developed by DuPont in the years that followed. The letter R is followed by a number that uniquely identifies the chemical structure of the refrigerant. The system has since become an international standard. Often, a more specific group of letters is used in place of R to denote the chemical family of the refrigerant. For example, R-12 may be called CFC-12 to indicate that it is a chlorofluorocarbon.

CFC and HCFC refrigerants were immensely successful, and they dominated the market for half a century. The process occurs when CFCs reach the stratosphere and absorb solar radiation. The absorbed radiation causes chlorine atoms to separate from CFCs, then catalyzing the breakdown of ozone (O3) into oxygen gas (O2). A decade later, researchers showed that CFCs had created a region of ozone depletionan ozone holeabove Antarctica. thumb|upright=2.2|Ozone (O3) in the stratosphere naturally cycles to oxgen gas (O2), and back, when it absorbs solar energy. If CFCs are present, solar energy can separate a chlorine atom, which breaks the cycle, forming O2 and ClO. The net result is [[ozone depletion#Ozone_cycle_overview | more oxygen and less ozone.]]

These discoveries led to the signing of the Montreal Protocol in 1987. This international agreement aimed to phase out CFCs and HCFCs to protect the ozone layer.

Under the Montreal Protocol, production of CFCs was scheduled to be banned in most countries by 1996. HCFCs were scheduled to phase out over a longer period because they have lower ozone depletion potentials (ODP) than CFCs. During this transition time, the adoption of HCFCs, such as R-22, was accelerated.

The search for alternatives to CFC and HCFC refrigerants, such as R-12 and R-22, began in the 1970s. By the time Montreal Protocol was signed, R-134a had been identified as a replacement for R-12 in automotive use and R-123 as a replacement for R-11 in large chillers. and CFCs were prohibited in new equipment starting in 1995.

US home air conditioners and industrial chillers moved toward HCFCs starting in the 1980s. Beginning on 14 November 1994, the US Environmental Protection Agency (EPA) restricted the sale, possession and use of refrigerants to only licensed technicians, per rules under the Clean Air Act. The US banned the production and import of CFCs on January 1, 1996. Stockpiled and reclaimed CFCs continued to be used while supplies were available.

Much later, governments began restricting HCFCs. For example, in 2000 the UK's Ozone Regulations came into force, banning ozone-depleting HCFC refrigerants such as R-22 in new systems. The regulations also banned the use of virgin R-22 as a "top-up" fluid for maintenance from 2010 and of recycled R-22 from 2015. In 2010, US EPA banned the use of R-22 (HCFC-22) in new equipment, much of which shifted to the HFC mixture, R-410A. All production and import of R-22 was banned on January 1, 2020.

The Montreal Protocol, which dealt with ozone depletion, did not aim to regulate the global warming impact of refrigerants. Even so, CFCs have much higher global warming potentials than the refrigerants that replaced them. As a result, the Montreal Protocol very significantly reduced global warming.

Renewed interest in natural refrigerants

Naturally-occurring refrigerants had been used prior to the introduction of CFCs in 1931. These included ammonia, carbon dioxide, isobutane, propane, among others. These refrigerants do not damage the ozone layer, and also have a very low global warming potential.

By 1996, Greenfreeze accounted for 35% of Western European production; and, by 2001, hydrocarbon refrigeration covered 100% of German production.

In 2004, Greenpeace worked with a group of multinational corporations, including Coca-Cola, Unilever, and later PepsiCo, to create a coalition called "Refrigerants Naturally!".

Corporations that manufactured synthetic refrigerants resisted the move toward hydrocarbons, however, citing the flammability and explosive properties of hydrocarbons. This resistance extended to attempts to block the approval of hydrocarbon refrigerants by the US EPA. Companies using refrigeration systems, particularly Unilever and its Ben & Jerry's ice-cream subsidiary, helped to overcome the regulatory barriers to hydrocarbon refrigerants. By 2010,

Japan had converted almost all refrigeration from R-134a to isobutane. By 2022, isobutane was used in more than 70% of new EU domestic refrigerators and, by 2025, in more than 60% of new US domestic refrigerators.

Carbon dioxide also gained new attention during this time. Despite its high operating pressure, CO2 was seen as a viable refrigerant in automobiles, as well as stationary systems.

Phase-down of HFCs (climate-change mitigation)

class=skin-invert-image|thumb|right|upright=.6| A [[1,1,1,2-Tetrafluoroethane molecule (HFC-134a or R-134a) has an atmospheric lifetime of 13.5 years

Different HFCs were adopted for different purposes. In domestic refrigerators and automobiles, R-134a replaced the CFC, R-12. In low-pressure chillers, R-123 replaced R-11. In small air conditioners, the blended refrigerant R-410A ultimately replaced R-22, following initial consideration of R-407C. And in low-temperature commercial refrigeration, the blend R-404A replaced R-502. The Kyoto Protocol was an agreement to cap emissions of certain greenhouse gases at a level 5% below 1990 emissions. These gases included HFCs.

In response, governments introduced new regulations. For example, in 2006, the EU adopted a regulation on fluorinated greenhouse gases (FCs and HFCs) to encourage to transition to natural refrigerants.

During the 2010s, new equipment increasingly used lower-GWP HFCs, hydrocarbons, and hydrofluoroolefins (HFO) as refrigerants. These refrigerants varied by sector of use, as described in contemporaneous press reports: R-600a (isobutane) for domestic refrigeration;

R-514A, R-1233zd(E), and R-1234ze(E) for chillers;

and R-32, R-290 (propane), R-407A, and R-744 (CO2) for commercial refrigeration. These choices reflected a range of trade-offs between established approaches, flammability, and reduced GWP. Some of these selections had a lower, but still high, GWP and were seen as transitional.

class=skin-invert-image|thumb|right|upright=.65| The [[2,3,3,3-Tetrafluoropropene (HFO-1234yf) molecule has an atmospheric lifetime of 12 days These regulatory decisions aligned with the opinion of the auto industry, which in 2010 had recommended R-1234yf for automotive air conditioning.

The lower GWP of R-1234yf relative to R-134a is primarily due to its very short atmospheric lifetime12 days vs. 13.5 years.

The Kigali Amendment to the Montreal Protocol was adopted in 2016. This international agreement implemented a gradual reduction in the consumption and production of HFCs. In 2019, the UNEP published new voluntary guidelines for air conditions and refrigerators.

At that time, researchers estimated that CFCs, HCFCs, and HFCs were responsible for about 10% of direct radiative forcing from all long-lived anthropogenic greenhouse gases.

The United States ratified the Kigali Amendment on October 31, 2022. The US Environmental Protection Agency has published phase-out schedules for HFCs,

with restrictions on GWP by sector of use.

By the mid-2020s, EU and US regulations on HFCs had resulted in broad adoption of some low GWP refrigerants, including R-600a (isobutane) in domestic refrigeration and R-1234yf in automotive applications. By 2022, more than 70% of new EU household refrigerators used isobutane (R-600a), and by 2025 more than 60% of new US domestic refrigerators also used isobutane. Each country may proceed differently, however. For example, China had widely adopted isobutane refrigerators long before the Kigali amendment, and it has banned HFCs from new refrigerators starting in 2026.

Refrigerant safety, environmental management, and reclamation

Refrigerants can pose both direct and indirect risks. Depending on their chemistry, they may be flammable, toxic, or environmentally damaging through ozone depletion or greenhouse effects. To standardize the safety hazards of refrigerants, ASHRAE Standard 34 assigns each one a letter–number code: letters "A" (lower toxicity) or "B" (higher toxicity), and numbers 1 through 3 to indicate flammability. A1 refrigerants are non-toxic and non-flammable, while A2L/A2 are non-toxic but flammable, and A3 refrigerants are non-toxic and highly flammable. B-class refrigerants have higher toxicity.

{| class="wikitable" style="float:right; width:50%; text-align:center; margin:1em"

|+ ASHRAE Safety Group Classifications

gas dusters with HFC-152a or hydrocarbon propellants,

metered-dose inhalers using HFC propellants, and disposable lighters containing the A3 refrigerant isobutane (R-600a).

To mitigate the environmental hazards, strict regulations apply to refrigerant handling. In the United States, Section 608 of the Clean Air Act requires certification for anyone servicing or disposing of stationary equipment, while Section 609 applies to technicians working on motor vehicle air conditioning. Similarly, the UK requires qualification C&G 2079 for fluorinated and ozone-depleting gases and recognizes C&G 6187-2 for handling hydrocarbons and flammable refrigerants. US law also prohibits knowingly venting most synthetic refrigerants, although it permits discharge of certain natural refrigerants, including ammonia (R-717), carbon dioxide (R-744), isobutane (R-600a), propane (R-290), and the hydrocarbon blend HCR-188C (R-441A).

To minimize emissions, used refrigerants must be recovered during service or decommissioning. Refrigerant reclamationprocessing used refrigerant so that it meets purity specifications of new gasmust be carried out in the US by EPA-licensed reclaimers, with recovery handled by certified technicians.

Comparative performance of refrigerants

ASHRAE

| 0.02

|R-600a ||HC(CH3)3 || Isobutane || <<1 || <<1 Used in most new US and EU vehicles by 2021, replacing R-134a.

|R-454B

|Mixture: R-32 (68.9%), R-1234yf (31.3%)

|1806

|R-513A || ||Mixture: R-1234yf (56%), R-134a (44%)

|1788

Banned or phasing-out CFCs, HCFCs, and HFCs

{| class="wikitable sortable"

! Code !! Chemical !! Name !! GWP 20yr!! GWP 100yr !! Status !! Notes

|R-11 CFC-11 ||CCl3F ||Trichlorofluoromethane ||8320

|R-134a HFC-134a

|CH2FCF3

|1,1,1,2-Tetrafluoroethane

|4140

| R-404A || || Mixture: R-125 (44%) / R-143a (52%) / R-134a (4%)

|| 7258

|R-410A|| || Mixture: R-32 (50%), R-125 (50%)

|| 4705

||2285 Most used in split heat pumps / AC in 2018, with almost 100% share in the US, but banned in new equipment starting January 1, 2025.

|R-514A

|Mixture: HFO-1336mzz(Z) (74.7%), HCO-1330E (25.3%)

|7 Being displaced by non-toxic HFO-1233zd(E).

Numbered classification of refrigerants

The R- numbering system, maintained by ASHRAE and ISO, uniquely identifies refrigerants according to their composition. The system originated for numbering halogenated hydrocarbons, but it encompasses blended refrigerants and inorganic refrigerants as well. thumb|upright=2|Disposable refrigerant gas cylinders, using different colors for different refrigerants. (Current guidelines discourage color-coded cylinders.)

Main numbering system

According to ISO: For example, the hydrofluoroolefin (HFO) R-1234yf is also called HFO-1234yf.

References

External links

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers
Green Cooling Initiative
What Are Refrigerants? Types, Uses & Their Environmental Impact
International Institute of Refrigeration