Air conditioning, often abbreviated as A/C or AC, is the process of removing heat and controlling the humidity of air in an enclosed space to achieve a more comfortable interior environment by use of powered "air conditioners" or a variety of other methods, including 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).
Air conditioners, which typically use vapor-compression refrigeration, range in size from small units used within 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), as of 2018, 1.6 billion air conditioning units were installed, which accounted for an estimated 20% of energy usage in buildings globally with the number expected to grow to 5.6 billion by 2050. The United Nations called for the technology to be made more sustainable to mitigate climate change using techniques including passive cooling, evaporative cooling, selective shading, windcatchers and better thermal insulation. CFC and HCFC refrigerants such as R-12 and R-22, respectively, used within air conditioners have caused damage to the ozone layer, and HFC refrigerants such as R-410a and R-404a, which were designed to replace CFCs and HCFCs, are instead exacerbating climate change. Both issues happen due to venting of refrigerant to the atmosphere, such as during repairs. HFO refrigerants, used in some if not most new equipment, solve both issues with an ozone damage potential (ODP) of zero and a much lower global warming potential (GWP) in the single or double digits vs. the three or four digits of HFCs.
Energy use[edit | edit source]
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.
Counteracting heat from appliances[edit | edit source]
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 systemW, 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[edit | edit source]
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.
- 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[edit | edit source]
Using a diffuserW 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]).
- In air conditioning the Coandă effect is exploited to increase the throw of a ceiling mounted diffuserW. 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[edit | edit source]
Reverse cycle air conditioners[edit | edit source]
Reverse cycle air conditionersW 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.)