This article is intended an overview for architects, contractors and property owners on the subject of refrigerants used in HVAC equipment. It is not intended to replace manufacturer guidelines or governmental advice which should be strictly adhered to.
What is a Refrigerant?
A refrigerant is a substance, often a fluid, used in a refrigeration cycle to cool a space. Refrigerants capture heat and then release it to another space by using the thermodynamic phenomena of phase changes, in which a fluid changes to a gas or vice-versa.
For more information on the refrigeration cycle be sure to check out our article about how air conditioners work.
Refrigerants are used in various building equipment including air conditioners, refrigerators, freezers, walk-in coolers, etc.
Refrigerant Effects on the Environment
Many refrigerants are known to have a negative effect on the environment because they contribute to global warming and they deplete the ozone layer.
Global Warming Potential (GWP)
Greenhouse gases such as carbon dioxide and the emissions from some refrigerants contribute to global warming by absorbing infrared radiation and holding it in the atmosphere, which is often referred to as the greenhouse effect.
The GWP of a refrigerant is a measure of the amount of heat a gas will trap in the atmosphere over time as compared to carbon dioxide, which has a baseline GWP of 1. Thus, a gas with a GWP higher than 1 traps more heat than CO2.
Ozone Depletion Potential (ODP)
Some chemical compounds, including refrigerants can contribute to the depletion of the ozone layer, which protects the earth and its occupants from the deadly effects of the sun’s rays.
The ODP of a chemical is the measure of how much it causes degradation of the ozone layer as compared to trichlorofluoromethane (CFC-11), which has a baseline ODP of 1.0. Thus, a chemical with an ODP over 1.0 will degrade the ozone layer more than CFC-11.
Types of Refrigerants
Refrigerants fall into one of following four main categories:
CFCs are an excellent unreactive refrigerant with a low boiling point. They have low toxicity, no fire risk, are inexpensive, and easy to store. However, CFCs are ozone-depleting greenhouse gases that contain fluorine so they are highly detrimental to the environment.
Most countries stopped producing CFCs in 1994. Developing countries will have eliminated all CFC stock by 2020 and developing nations will eliminate all stock of CFCs by 2030.
Freon, a DuPont brand, is a CFC commonly used for refrigeration.
HCFCs are currently being used as a replacement for CFCs, but they will also be phased out over time. HCFCs are more ozone-friendly than CFCs, however they still deplete the ozone, albeit at a slower rate.
Unfortunately, HCFCs are a potent greenhouse gas, many times more potent than carbon dioxide. In addition, HCFCs have contributed to a build-up of chlorine in the atmosphere.
HFCs are a popular choice by refrigeration manufacturers because they are a suitable replacement substance for CFCs and do not deplete the ozone as much as CFCs or HCFCs. However, HFCs are potent greenhouse gas sources so they have a high global warming potential.
A UNEP report offers a range of recommendations, including use of HFCs with a very short atmospheric lifespan (days or weeks, instead of the dozens of years for a few HFCs now in use). Others, such as Greenpeace, are calling for their phase out as well due to their contribution to global warming.
Natural refrigerants occur naturally – they are not man-made like the other refrigerants we have discussed. They can be used as cooling agents in refrigerators and air conditioners. Popular choices for natural refrigerants are hydrocarbons (isobutane – R-600A), ammonia, carbon dioxide, and water.
Hydrocarbons (HC) do contain carbon dioxide but this has a Global Warming Potential of 1 and the HCFCs and HFCs currently popular on the market have a GWP in the thousands. This makes hydrocarbon use as a refrigerant the most environmentally-friendly option available today.
Comparison of Refrigerants – Global Warming Potential and Ozone Depletion Potential
The table below compares the various refrigerants and the effect they have on the environment.
|Refrigerant Type||Class||Ozone Depletion Potential||Global Warming Potential|
|HCFC||Synthetic||Very Low||Very High|
Fighting Climate Change Due to Refrigerants
There have been a number of international acts with a focus on eliminating the use of refrigerants that are detrimental to our environment.
Montreal Protocol on Substances that Deplete the Ozone Layer
The 1987 Montreal Protocol established requirements that led to the worldwide phase out of ozone depleting chlorofluorocarbons (CFCs). Amendments then led to the phasing out of CFC production in all developed nations.
In 1992 it was then amended to establish a schedule for the phasing out of hydrochlorofluorocarbons (HCFCs) by 2030. These are less damaging to the ozone layer than CFCs but still contain chlorine which destroys ozone.
The Montreal Protocol as amended is now implemented through the US Clean Air Act (see below) via the US Environment Protection Agency (EPA).
The United States Clean Air Act
Along with prohibiting the production of ozone-depleting refrigerants, the US Clean Air Act mandates the use of common sense in handling refrigerants. By containing and using refrigerants responsibly through recovery, recycling, reclaiming, and by reducing leaks ozone depletion and global warming consequences are reduced. The Act outlines specific refrigerant containment and management practices for HVAC manufacturers, distributors, dealers and technicians.
The Clean Air Act does not allow refrigerants to be vented into the atmosphere during installation, service, or retirement of equipment.
One thing a HVAC specifier or purchaser can do for the environment, regardless of the refrigerant used, is to select a reputable dealer that employs EPA-certified technicians to use refrigerants. This is known as "Section 608 certification" and refers to the Clean Air Act.
The Kyoto Protocol, signed in 1997, is an international treaty that seeks to reduce greenhouse gas emissions. The premise of the protocol is that human activities are responsible for global warming and the global temperature will continue to rise unless humans alter their behavior. The main goal of the protocol is to contain greenhouse gas emissions with a focus on carbon dioxide emissions.
The United States has not ratified its agreement to the Kyoto Protocol. The US argues that developing countries have not committed to the reduction in emissions.
Common Refrigerants Used in Buildings
HCFC-22 (R-22) has been the most popular refrigerant for residential heat pump and air-conditioning systems for over four decades. Unfortunately, if it leaks it contributes to ozone depletion. It is also a greenhouse gas and its manufacture gives a by-product HFC-23 that contributes to global warming. It is often known by a brand name, such as Freon.
As of 2010, HCFC-22 was discontinued for use in new air conditioning systems, however it can still be used to service existing systems. Starting in 2020, HCFC-22 can only be used if it is recovered and recycled for reuse in the same system. Air conditioner manufacturers are now offering alternatives to HCFC-22 that use non-ozone depleting refrigerants.
For now existing HVAC units using HCFC-22 can continue to be serviced with it. After 2020, the servicing of R-22-based systems will rely solely on recycled or reclaimed refrigerants. It is expected that this will ensure that existing supplies of it will last longer and be available to service a greater number of systems.
R-400 Series Refrigerants
The R-400 series is made up of hydro-fluorocarbon (HFC) zeotropic blends. The most popular is R-410A, which does not contribute to depletion of the ozone layer, but, like R-22, contributes to global warming. R-410A is the most common refrigerant for new light commercial A/C systems, but operating pressures are more than 50% higher than R-22 so R-410A systems require components capable of working at these higher pressures. R-410A is manufactured and sold under various trade names, including GENETRON AZ-20, SUVA 9100, Forane 410A, and Puron.
The transition away from ozone depleting R-22 to systems that rely on replacement refrigerants like R-410A has also required redesign of heat pump and A/C systems. New systems incorporate compressors and other components specifically designed for use with these replacement refrigerants.
R-600 Series Refrigerants
The most popular of the R-600 series refrigerants is R-600a, which is also called isobutane. R-600a, which comes from natural sources, has zero ozone depletion potential and negligible global warming potential. The biggest downfall is that isobutane is flammable so systems must be designed with that in mind and technicians must be trained to properly handle it.
R-600a is most commonly used in domestic refrigerators in Europe (primarily in Germany), but it has been used in commercial refrigerators in the United States, albeit in very limited numbers.
Refrigeration Management and LEED
Tax incentives or rebates are offered by some US State governments or local utilities for buildings and systems that meet green codes such as the Leadership in Energy and Environmental Design (LEED) Green Building Rating System developed by the US Green Building Council (USGBC).
Points toward LEED certification can be achieved in various ways including through enhancements to an HVAC system and multiple levels of refrigeration management.
Passive Cooling – an Alternative to Refrigerant Use?
Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building to improve the indoor thermal comfort with little or no energy consumption.
Natural ventilation forms part of a passive cooling process and allows for the ventilation of internal space without using mechanical systems. While passive cooling methods use little energy, care must be taken to ensure thermal comfort. In many climates during warm or humid periods, maintaining thermal comfort solely via natural ventilation may be impossible so conventional A/C systems are used as backups.
It is more common in residential and small scale buildings, but research and development in this area is challenging mainstream thinking on how and where it can be employed in larger buildings by utilizing cross ventilation, the stack effect, and night flush cooling to minimize energy consumption and refrigerant use.