A refrigerant is a chemical substance used in heat pumps and refrigeration cycles.  The job of a refrigerant is to transport enthalpy (i.e. heat energy) from the evaporator of a refrigeration or air conditioning system to the environment.

What is a Refrigerant?

The difference between a simple coolant and a refrigerant is that a refrigerant in a refrigeration cycle can transport heat energy against a temperature gradient, so that the ambient temperature may even be higher than the temperature of the target to be cooled.

A coolant is only able to transport enthalpy along a temperature gradient to a point of lower temperature.

Each chemical substance may exist in different physical states (phases): solid – liquid – gaseous.  Between such states there exist phase transitions e.g. from a liquid to a gas and back again.  Many working fluids have been used for such purposes but the operation of initial chillers often resulted in deaths because the refrigerants used were toxic, examples are SO2, CH3Cl, ammonia (NH3).

Refrigerant Timeline

  • 1930 – CFCs Freon (R11) & Frigen (R12) manufactured.  Used as refrigerants
  • 1974   CFC ozone hypothesis
  • 1978   Confirmation of the hypothesis
  • 1995   Ban on the production and use of CFCs in new installations
  • 1998   Montreal Protocol
  • 1998   R12 is withdrawn from the market
  • 2000   Prohibition of HCFCs (R22)
  • 2006   First F-Gas Regulation 842/2006
  • 2015   Ban on the use of HCFCs
  • 2016   Kigali Amendment to the Montreal Protocol

A Bit of Chemistry

A look at the periodic table of the elements shows that almost all elements have one of the following properties:

  • solid
  • radioactive
  • unstable
  • noble gas
  • venomous or toxic

All these properties exclude such elements from being considered as a candidate for a refrigerant.

So what is left over…?

The answer is hydrocarbons i.e. compounds of carbon C and hydrogen H, such as methane, ethane, propane.

What are the requirements for an ‘ideal’ refrigerant?

  • large specific evaporation enthalpy
  • high volumetric cooling capacity
  • high thermal conductivity
  • high critical temperature
  • no temperature glide
  • low viscosity
  • non-flammable or explosive
  • no ozone depletion potential (no ODP)
  • no greenhouse effect (no or low GWP)
  • non-toxic
  • perceptible by odour on leaving
  • non-corrosive
  • compatible with lubricants

The table below shows the hydrocarbon elements with their halogenation, designation and gives examples of the refrigerants that have been in common use over recent years.

C, Hnon-halogenatedhydrocarbonsHCsnaturalR290, CO2
C, Ffully-halogenatedhydrofluorocarbonsHFCsF-Gas regulationsR134A
C, F, Clfully-halogenatedchlorofluorocarbonsCFCsMontreal protocolR11
C, F, Hpartly-halogenatedhydrofluorocarbonsHCFCsF-Gas regulationsR407c, R410a
C, F, C, Cl, Hpartly-halogenatedhydrogen-fluoro-chloro-hydrocarbonHCFCsMontreal protocolR22

Methane CH4

CFCs, HCFCs and HFCs can be produced from the methane molecule CH4 by replacing the H-atoms with one of the halogen elements i.e. Fluorine, Chlorine, Bromine, Iodine

Petra UK - R11

CFC (R11)


1 atom Carbon / 3 atoms Chlorine / 1 atom Fluorine

Petra UK - R22

HCFC (R22)

partly – halogenated

1 atom each Carbon /  Chlorine / Hydrogen / 2 atoms Fluorine

Petra UK - R134a

HCFC (R134a)


2 atoms Carbon / 4 atoms Hydrogen / 2 atoms Fluorine

Petra UK - R290

HC R290


3 atoms Carbon / 8 atoms Hydrogen

Refrigeration – Environmental Metrics

Environmental concerns have long been the driving force for the development of environmental friendly refrigerants.  Ongoing research in the fields of system design optimisation, energy efficiency improvements,and the search for new refrigerants, is important for both heat pump and refrigeration systems.  It is therefore helpful to have a transparent and easy to use reference protocol when designing air conditioning or refrigeration systems with low environmental impacts.

Three environmental metrics can be used when comparing the environmental impact of various refrigerants and refrigeration systems:

  • Global Warming Potential (GWP)
  • Total Equivalent Warming Impact (TEWI)
  • Life-Cycle Climate Performance (LCCP)

Each serves the similar aim of quantifying the impact of refrigerants on global warming.  Whilst not directly having a bearing on the environmental impact of the refrigerant, it is also important to be aware of the flammability class of a refrigerant as this will determine other areas of regulatory compliance.

In the tables below we consider the environmental impacts of the refrigerants that we currently use:


GWP is perhaps the most commonly used environmental metric. GWP is the index used to compare the global warming impact of an emission of a greenhouse gas in relation to the impact from the emission of similar amount of CO2. The impact is estimated over a time horizon of 100 years.  GWP is an easy metric to use. The smaller the GWP, the lower the contribution of a substance to global warming.

RefrigerantTypeOzone Depletion PotentialGlobal Warming Potential
R513aHFO/HFC blend0631
R452bHFO/HFC blend0698

Read more about Ozone Depletion Potential (ODP) here


TEWI accounts for the global warming impact from both direct and indirect emissions and is calculated as a sum of both the direct effect of refrigerant released during the lifetime of the equipment, and the indirect impact of CO2 emissions from the fossil fuels used to generate the energy needed to operate the equipment throughout its lifetime. TEWI can be calculated using the equation below (UNIDO 2009):

TEWI = direct emissions + indirect emissions = (GWP×L×N)+(Ea×β×n) where:

L = annual leakage rate in the system, kg (3% of refrigerant charge annually)
N = life of the system, years
n = system running time, years
Ea – energy consumption, kWh per year ,
β – carbon dioxide emission factor, CO2-eq. emissions per kWh


The LCCP indicator is used to measure all GWP data related to the refrigeration system’s operation, including the environmental impact of substances emitted during the process of refrigerant production and transportation.

This environmental effect, together with environmental effects already accounted in TEWI, is known as the life-cycle climate performance (LCCP) and is intended to provide an overall picture of the environmental impact of different refrigerants.

LCCP is a holistic metric to quantify the effect of the refrigerant on the total lifetime system emissions.


In practice, the LCCP is more complex than the TEWI metric to calculate, and an additional contribution of LCCP compared to the TEWI is negligible as can be seen from the table below which show a comparison between R290 and R410 for the same unit under identical operating conditions.

TEWI/LCCP ComparisonR290R410A
TEWI, kg CO2 equivalent37,77543,551
% of R410a87.14%100%
Direct emissions contribution to total TEWI%0.01%9.42%
LCCP, kg CO2 equivalent37,78045,398
% of R410a83,22%100%
% of TEWI0.01%4.72%


Pavel Makhnatch and Rahmatollah Khodabandeh / Energy Procedia 61 ( 2014 ) 2460 – 2463

Toxicity & Flammability


Toxicity and flammability

The safety classification of refrigerants consists of two alphanumeric characters (e.g. A2); the capital letter corresponds to toxicity and the digit to flammability.

Toxicity classification

Refrigerants are divided into two groups according to toxicity:

Class A – Refrigerants for which toxicity has not been identified at concentrations less than or equal to 400 ppm

Class B – Refrigerants for which there is evidence of toxicity at concentrations below 400 ppm.

Flammability classification

Refrigerants are divided into three groups according to flammability:

Class 1 – Refrigerants that do not show flame propagation when tested in air at 21°C/101kPa
Class 2 – Refrigerants having a lower flammability limit of more than 0.10 kg/m3 at 21°C/101kPa and a heat of combustion of less than 19 kJ/kg;
Class 3 – Refrigerants that are highly flammable as defined by a lower flammability limit of less than or equal to 0.10 kg/m3 at 21°C/101 kPa or a heat of combustion greater than or equal to 19 kJ/kg.

RefFlammability ClassLower Flammability Limit kg/m3Heat of Combustion MJ/kg
R290A3 Highly Flammable<0.1or   >19
R513aA1 Non-FlammableCannot be ignited
R452bA2L* Mildly Flammable>0.3and<19
R1234zeA2L* Mildly Flammable>0.3and<19
R410aA1 Non-FlammableCannot be ignited
R407cA1 Non-FlammableCannot be ignited
R134aA1 Non-FlammableCannot be ignited

* For EN 378 the 2L category is a proposal that is still under discussion.  However, the 2L category is used in ISO 817:2014 “Refrigerants — Designation and safety classification”


Petra UK - R452b


  • Blend of R32 (67%), R125 (7%) and R1234yf (26%)
  • GWP – 675
  • Flammability class  – A2L
  • Low GWP replacement for R410a
  • Used in scroll compressors
Petra UK - R513a


  • Blend of R1234yf (56%), R134a (44%)
  • GWP – 631
  • Flammability class  – A2L
  • Low GWP replacement for R134a
  • Used in screw and centrifugal compressors
Petra UK - R1234ze


  • Chemical composition C3H2F4
  • HFO
  • GWP – 7
  • Flammability class  – A2L
  • Low GWP replacement for R134a
  • Used in screw and centrifugal compressors
Petra UK - R290


  • Naturally occuring element
  • Chemical composition C3H8
  • GWP – 3
  • Flammability class  – A3
  • Can be used in all types of compressors
Petra UK - R134a


    • Chemical composition C2H4F2
    • HFC
    • GWP – 1,430
    • Flammability class  – A1
    • Used in screw and centrifugal compressors
Petra UK - R410a


  • Blend of R32 (50%) and R125 (50%)
  • HFC
  • GWP – 2,088
  • Flammability class  – A1
  • Used in scroll compressors

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