2 Refrigerant Types and Environmental Properties

How refrigerants work

Refrigerants absorb heat as they evaporate and release heat as they condense. A suitable refrigerant must operate at practical pressures and temperatures, transfer heat effectively, and be compatible with the equipment and materials used.

Refrigerant families

Refrigerant families are often grouped by chemical composition. A family can offer clues about environmental effects, but the actual properties depend on the specific molecule or blend.

• CFCs (chlorofluorocarbons), such as R-11 and R-12, contain chlorine; many have high ODP and high GWP.

• HCFCs (hydrochlorofluorocarbons), such as R-22, contain chlorine and hydrogen. They generally have lower ODP than CFCs but still contribute to ozone depletion.

• HFCs (hydrofluorocarbons), such as R-32, R-134a, and R-410A, do not contain chlorine and have zero ODP, but many have substantial GWP.

• HFOs (hydrofluoroolefins), such as R-1234yf, are unsaturated fluorinated compounds. Many have very low GWP and zero or near-zero ODP; some are mildly flammable.

• Natural refrigerants include ammonia (R-717), carbon dioxide (R-744), propane (R-290), and isobutane (R-600a). They often have low GWP and zero ODP, but their safety and operating properties vary: ammonia is toxic, hydrocarbons are flammable, and CO₂ systems operate at high pressure.

Changes among refrigerant families reflect changes in environmental priorities, not a simple progression toward substances that are safest or best in every system. For example, HFCs addressed the ozone-depletion problem associated with many CFCs and HCFCs, but some HFCs still have high climate impact.

Operating properties and blends

Several physical and operating properties affect how a refrigerant performs in an application:

• Boiling point and saturation pressure determine the pressures and temperatures at which the refrigerant evaporates and condenses.

• Heat-transfer capacity affects how much heat the system can move for a given flow rate and equipment size.

• Critical temperature and pressure help define the conditions under which ordinary condensation is possible.

• Compatibility concerns whether the refrigerant works with system materials, lubricants, seals, and components.

• Environmental properties include ODP and GWP, which describe different atmospheric effects.

• Safety properties, including toxicity and flammability, affect system design and handling requirements.

A Refrigerant blend combines two or more refrigerants to obtain a useful balance of properties. Some blends have Temperature glide: their temperature changes as they evaporate or condense at a given pressure. The amount of glide and the blend’s behavior depend on its composition.

Environmental indicators

Ozone-depletion potential (ODP) compares a substance’s capacity to deplete stratospheric ozone with that of CFC-11, which is assigned an ODP of 1. Chlorine- or bromine-containing compounds can release ozone-depleting atoms after reaching the stratosphere. CFCs and HCFCs therefore have ODP greater than zero, while HFCs do not contain chlorine and have zero ODP.

Global-warming potential (GWP) compares the heat-trapping effect of a mass of gas with that of the same mass of carbon dioxide over a specified time period. CO₂ is assigned a GWP of 1. If a refrigerant escapes to the atmosphere, a higher GWP can mean a larger direct climate impact. GWP values depend on the assessment and time horizon, so comparisons should use values based on the same standard.

ODP and GWP describe different effects. A refrigerant can have zero ODP but still have high GWP, as is true of many HFCs. Conversely, several HFOs and natural refrigerants have low GWP.

Environmental assessment also includes Indirect emissions: greenhouse gases emitted when electricity is generated to operate equipment. A low-GWP refrigerant is not automatically the lowest-impact choice if a system using it consumes substantially more energy. Leakage prevention and efficient equipment therefore matter alongside refrigerant selection.

Safety classifications

ASHRAE Standard 34 classifies refrigerants using a letter for toxicity and a numeral or numeral-letter combination for flammability:

• A indicates lower toxicity under the standard’s criteria; B indicates higher toxicity.

• 1 means no flame propagation under the specified test conditions.

• 2 indicates lower flammability; 2L identifies a lower-flammability refrigerant with low burning velocity.

• 3 indicates higher flammability.

Examples are R-134a (A1), R-32 (A2L), propane R-290 (A3), and ammonia R-717 (B2L). These classifications describe particular hazards; they do not mean a refrigerant is harmless. Even an A1 refrigerant can create risks through oxygen displacement, cold burns, high pressure, or harmful decomposition products in a fire. A safety group is not, by itself, an instruction for installing or servicing a system.

Comparing refrigerants

Compare refrigerants by keeping the questions about environmental effects, hazards, and system performance distinct:

1. Ozone depletion: Check the refrigerant’s ODP.

2. Warming if released: Compare GWP values using the same time horizon and assessment basis.

3. Hazards: Check the ASHRAE safety classification and the equipment’s requirements.

4. Complete-system performance: Consider energy use, leakage, and application suitability as well as the refrigerant itself.

No single refrigerant is ideal for every application. Environmental impact, energy efficiency, cost, and safety all matter, and the best choice depends on the refrigerant and the performance, environmental impact, and safety of the complete system.