From Wikipedia:Air conditioning

Air conditioning, often abbreviated as A/C (US) or air con (UK), is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature and, in some cases, controlling the humidity of internal air. Air conditioning can be achieved using a mechanical air conditioner or through other methods, such as passive cooling and ventilative cooling. Air conditioning is a member of a family of systems and techniques that provide heating, ventilation, and air conditioning (HVAC). Heat pumps are similar in many ways to air conditioners but use a reversing valve, allowing them to both heat and cool an enclosed space.

In hot weather, air conditioning can prevent heat stroke, dehydration due to excessive sweating, electrolyte imbalance, kidney failure, and other issues due to hyperthermia. An estimated 190,000 heat-related deaths are averted annually owing to air conditioning. Air conditioners increase productivity in hot climates, and historians rank air conditioning as a key factor that shaped postwar metropolitan growth, alongside highways, automobiles, shopping malls, and suburban housing. As of 2022, air conditioning used about 7% of global electricity and emitted 3% of greenhouse gas.

Air conditioners, which typically use vapor-compression refrigeration, range in size from small units used in vehicles or single rooms to massive units that can cool large buildings. Air source heat pumps, which can be used for heating as well as cooling, are becoming increasingly common in cooler climates. According to the International Energy Agency (IEA) 1.6 billion air conditioning units were used globally in 2016. The United Nations has called for the technology to be made more sustainable to mitigate climate change and for the use of alternatives, such as passive cooling, evaporative cooling, selective shading, windcatchers, and thermal insulation.

Energy use

Air conditioners are one of the most intensive users of electricity - although they do not need to be operated all day, nor all year, in most climates.

The need for air conditioning can be greatly reduced through building design, notably passive solar^W and good insulation. See Alternative building

Counteracting heat from appliances

Extra energy is used when using heat-producing appliances in an air conditioned room or building. There is not only the energy used by the appliance, but a greater amount of energy to remove the heat from that appliance. Wikipedia:Air conditioning#Energy use states:

It should be noted that in a thermodynamically closed system^W, any energy input into the system that is being maintained at a set temperature (which is a standard mode of operation for modern air conditioners) requires that the energy removal rate from the air conditioner increase. This increase has the effect that for each unit of energy input into the system (say to power a lightbulb in the closed system) requires the air conditioner to remove that energy. In order to do that the air conditioner must increase its consumption by the inverse of its efficiency times the input unit of energy. As an example presume that inside the closed system a 100 Watt light bulb is activated, and the air conditioner has an efficiency of 50%. The air conditioners energy consumption will increase by 200 Watts to compensate for this, thus making the 100W light bulb utilise a total of 300W of energy.

Peak load

Air conditioners being turned on during the hottest days of summer account for the highest peak loads experienced by many cities' electricity infrastructure.^{[verification needed]} Thus much extra capacity needs to be built into the generating equipment, at the expense of many millions of dollars, and it is then only used for a few days per year.

Suggested solutions:

• Ban air conditioners. This could lead to heat stroke and even death by elderly and susceptible people during a heat wave.
• Peak pricing: charging a higher price for electricity during certain hours of the day in summer. This requires specialized meters to measure the eletricity used in different time periods (similar to off-peak hot water heaters). This has the advantage of not restricting use when needed, but discouraging wastefulness.
• Rely more on solar energy, which provides most power at the time when air conditioning is most needed.
• Encourage retrofitting of cooling, energy-saving design features such as awnings, insulation, and roof ventilation.
• Re-use cooled air by integrating an Air decohesion processor (ADP) into the system. This low-energy consuming device cleans used and already cooled/(heated) air, leaving the temperature at the desired level and destroying unwanted substances.

Quieter operation

Using a diffuser^W which sends air along the ceiling results in the same spread of air for less discharge velocity - meaning a smaller fan and less noise (and we might guess it would give a very slight saving in power usage - unless the air is heated by contact with the ceiling, in certain circumstances^{[expansion needed]}).

Wikipedia:Coandă effect#Air conditioning states:

In air conditioning the Coandă effect is exploited to increase the throw of a ceiling mounted diffuser^W. Because the Coandă effect causes air discharged from the diffuser to "stick" to the ceiling, it travels further before dropping for the same discharge velocity than it would if the diffuser was mounted in free air, without the neighbouring ceiling. Lower discharge velocity means lower noise levels and, in the case of variable air volume (VAV) air conditioning systems, permits greater turn-down ratios. Linear diffusers and slot diffusers that present a greater length of contact with the ceiling exhibit greater Coandă effect.

Solar powered air conditioning

From Solar powered air conditioner

Solar-powered air conditioning is an incredibly practical and efficient solution. Air conditioning is needed most during hot, sunny days—the same conditions when solar power is most effective. Since air conditioners place a heavy load on the power grid, switching to solar can significantly reduce energy costs and consumption. Modern solar air conditioners even work on cloudy days, thanks to batteries that store energy for 12–24 hours.

Reverse cycle air conditioners

Reverse cycle air conditioners^W can also be operated as a highly efficient heater. As they are a heat pump rather than a heat generator, they can bring more heat energy into a room or building than the energy consumed by the appliance. Do reverse cycle air conditioners have a different name? (Also asked here.)

See also

• Evaporative cooling