Air Conditioners: Polluters Or Climate Comfort?

As global temperatures continue to rise due to climate change, the demand for electricity to power air conditioners to keep people cool and safe from extreme heat will also increase. While air conditioners provide relief from sweltering heat, they also contribute to air pollution and have adverse effects on human health and the environment. This is mainly due to the large amount of energy they consume, which often comes from burning fossil fuels, leading to the emission of greenhouse gases and other pollutants.

Energy Consumption

Air conditioning units require a lot of energy to function. The energy used to power air conditioning comes from the combustion of fossil fuels, which contributes to ozone depletion.

In 2022, air conditioning ("space cooling") consumed around 2,100 terawatt-hours (TWh) of power, accounting for approximately 7% of global electricity usage. This equates to 3% of carbon emissions, or 1 billion tonnes of CO2 from electricity use. When the refrigerants used in AC units are taken into account, the carbon emissions rise to 1,750 million tonnes of carbon dioxide equivalents (CO2eq), or 3.2% of all greenhouse gas emissions.

In the US, air conditioning accounts for 10% of the country's total electricity consumption, with the average US home using 2,000 kWh/year of electricity for air conditioning, or 17% of their total household electricity consumption. This is a significant amount of energy, and it is important to consider ways to reduce AC energy demand and CO2 emissions.

One way to reduce energy consumption is to improve the energy performance of AC units. This can be achieved through higher coefficients of performance (COP), improved home insulation, and smart controls to optimise cooling. Next-generation technologies, such as adsorbing water onto sorbents, may also help to improve energy intensity. Additionally, increasing the use of renewable energy sources, such as solar, wind, hydro, and nuclear power, can lower the CO2 intensity of the power grid.

Greenhouse Gas Emissions

Air conditioning currently accounts for a large portion of global greenhouse gas emissions, with estimates ranging from 3.9% to 4%. By 2050, researchers expect the number of air conditioners on Earth to quadruple to 4.5 billion, becoming as ubiquitous as cell phones. This increase in air conditioner usage will have a significant impact on global temperatures, contributing to a rise of up to 0.5-degree Celsius by the end of the century.

The basic cooling technology behind air conditioning has not changed significantly since its invention in 1902. Air conditioners use a vapor-compression cycle, in which a liquid refrigerant circulates through two metal coils, one located inside the space to be cooled and one outside. The refrigerant evaporates and condenses under varying pressure, absorbing and ejecting heat from the indoor and outdoor coils, respectively. This process requires a significant amount of electricity, which is typically generated by the combustion of fossil fuels, contributing to greenhouse gas emissions.

In addition to the energy consumption of air conditioners, the refrigerants used in these systems can also contribute to greenhouse gas emissions. Chlorofluorocarbons (CFCs) were commonly used in the past but were banned due to their damaging effects on the environment, particularly the ozone layer. While the current refrigerant of choice, hydrofluorocarbons (HFCs), do not deplete the ozone layer, they still contribute to global warming. HFCs are highly potent greenhouse gases, trapping thousands of times more heat in the atmosphere than carbon dioxide. While a properly functioning air conditioner should not release HFCs, leaks and improper disposal of old units can result in these chemicals escaping into the atmosphere.

The impact of air conditioning on greenhouse gas emissions is not limited to the direct emissions from the units themselves. The manufacturing process of air conditioners can also result in the release of HFCs into the atmosphere. Additionally, the energy-intensive nature of air conditioning contributes to the demand for electricity, which is often generated by burning fossil fuels. This, in turn, leads to increased greenhouse gas emissions from power plants.

To mitigate the impact of air conditioning on greenhouse gas emissions, manufacturers are competing to develop more efficient and environmentally friendly cooling technologies. The Global Cooling Prize, for example, aims to incentivize the development of air conditioners that produce significantly less greenhouse gas emissions over their lifetime compared to standard units. Innovations in refrigerants and efficiency-boosting technologies are being explored, with some teams focusing on combining climate-friendly refrigerants with smart controls and solar panels.

Ozone Layer Depletion

Air conditioners have been found to contribute to ozone layer depletion. This is due to the release of ozone-depleting pollutants, such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs). CFCs, used in older air conditioning units, were found to be incredibly damaging to the environment, and have since been banned. HFCs, which are now used in modern units, do not contain ozone-depleting chlorine and have very low global warming potential (GWP).

The ozone layer acts as an invisible filter, allowing some energy in and some out, protecting the Earth from harmful UV rays. Ozone depletion is the thinning and loss of this protective layer. In the 1970s, scientists discovered a shocking overall reduction in ozone concentration at a rate of 4% per decade, as well as severe annual springtime depletion over the polar regions.

The cause of this depletion was identified as man-made chemicals used in refrigerants and aerosols. CFCs, when broken down by sunlight, release chlorine and bromine, which destroy ozone molecules. The Montreal Protocol treaty was introduced in 1987 to outline the phasing out of these ozone-depleting refrigerants, and it has since been signed by 197 states.

Today, the most common substances used in refrigeration and air conditioning are HCFCs and HFCs, which are non-ozone-depleting alternatives. However, these substances still have very high GWP, with some alternatives having higher flammability, toxicity, and pressure, requiring a different approach to safety.

While air conditioners contribute to ozone depletion, modern units are more environmentally friendly than older ones. It is important for consumers to be mindful of the substances their appliances release into the atmosphere and to consider energy-saving practices to reduce their environmental impact.

Materials Used in AC Units

Air conditioning units are made from a variety of materials, including metals, plastics, and other non-traditional materials. The most common metals used are copper, aluminium, stainless steel, and other corrosion-resistant metals. Copper and aluminium are chosen for their superior thermal properties and positive influence on system efficiency. Copper tubing is a critical ingredient in many AC components.

The use of plastic and other non-traditional materials is becoming more common as manufacturers aim to reduce weight and costs.

The working fluid, or refrigerant, is typically a liquid with strong thermodynamic characteristics, such as freon, hydrocarbons, ammonia, or water. However, due to the hazardous effects of freon on the environment, it has been phased out of more modern units.

The outer encasement of AC units is usually made from sheet metal, which is protected from environmental conditions by a paint or powder coating. The sheet metal is typically galvanized to prevent corrosion and is formed into the unit's wrapper, bottom pan, face plates, and support brackets.

The condenser and evaporator, which act as heat exchangers, are made from copper or aluminium tubing bent into a coil form to maximize the distance the working fluid travels. The opposing fluid, or cooling fluid, passes through or around these tubes, with the working fluid drawing away its heat.

The pump, another essential component of an AC unit, is purchased from an outside supplier. It is designed to increase system pressure and circulate the working fluid. It is connected to the system with fittings and anchored in place with support brackets and a base.

Overall, the materials used in AC units are chosen for their thermal properties, durability, and cost-effectiveness, with a growing focus on reducing weight and environmental impact.

Indoor Air Quality

Air conditioning units can be a helpful tool to improve indoor air quality, but this depends on the type of unit and how well it is maintained.

How Air Conditioners Work

Air conditioners recycle air that is already present in your home. They use refrigerants, fans, and evaporator coils to cool the air. The fans in an air conditioning unit draw warm air in through a vent and blow it over the evaporator coil, which is filled with refrigerant to remove heat from the air. The refrigerant then travels to the compressor, which increases the temperature and pressure, before moving to the condenser located outside of the home. The heat is then released into the outdoor air, and the refrigerant returns to the evaporator coil to start the process again.

Air Conditioners and Indoor Air Quality

The main purpose of air conditioning is to improve comfort by cooling the air and regulating temperature. However, air conditioners do not actively improve indoor air quality, and in some cases, they can worsen it. When using an air conditioner, it is common to close all windows and doors, which can trap indoor contaminants. Additionally, if an air conditioning unit is not properly maintained or is used more often than necessary, indoor air quality can suffer.

Improving Indoor Air Quality with Air Conditioners

To improve indoor air quality, it is recommended to use air conditioners that recirculate indoor air rather than using fresh air intake from the exterior. Central air conditioning and split air conditioning systems (wall units that don't require window access) are better for indoor air quality than window units, as they circulate air without pulling in polluted air from outdoors. It is also important to regularly change the air conditioner's filter to ensure it is working effectively.

Other Strategies for Improving Indoor Air Quality

In addition to using air conditioners, there are other strategies to improve indoor air quality. These include:

• Improving ventilation by opening windows and doors or using fans.
• Using air cleaners or filtration systems to remove pollutants from the air.
• Sealing or enclosing sources of pollution, such as asbestos, or adjusting them to decrease emissions, such as with gas stoves.
• Avoiding activities that can generate high levels of pollutants, such as painting, welding, or cooking.

Frequently asked questions