Health implications

A poorly maintained air-conditioning system can occasionally promote the growth and spread of microorganisms, such as Legionella pneumophila, the infectious agent responsible for Legionnaires' disease, or thermophilic actinomycetes.^[11] Conversely, air conditioning, including filtration, humidification, cooling, disinfection, etc., can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where an appropriate atmosphere is critical to patient safety and well-being. Air conditioning can have a positive effect on sufferers of allergies and asthma.^[12]

In serious heat waves, air conditioning can save the lives of the elderly. Some local authorities even set up public cooling centers for the benefit of those without air conditioning at home.

Poorly operating air conditioning systems can generate sound levels that contribute to hearing loss, if exposures are endured over a long term. These levels are similar to the exposure of living near a busy highway or airport for a considerable length of time. Properly functioning air conditioners are much quieter.

Energy use

It should be noted that in a thermodynamically closed system, 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 light bulb 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 200%. The air conditioner's energy consumption will increase by 50 watts to compensate for this, thus making the 100 W light bulb utilise a total of 150 W of energy.

Note that it is typical for air conditioners to operate at "efficiencies" of significantly greater than 100%, see Coefficient of performance.

Portable air conditioners

A portable air conditioner or portable A/C is an air conditioner on wheels that can be easily transported inside a home or office. They are currently available with capacities of about 6,000 to 60,000 BTU/h (1,800 to 18,000 watts output) and with and without electric resistance heaters. Portable air conditioners come in three forms, split, hose and evaporative:

A split system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit.

Hose systems Air-to-Air and Monoblock are vented to the outside via air ducts. A function of all cooling that use a compressor, is to create water as it cools the air. The "monoblock" version collects the water in a bucket or tray and stops when full. The Air-to-Air version, re-evaporates the water and discharges it through the ducted hose and can hence run continuously.

A single duct unit draws air out of the room to cool its condenser. This air is then replaced by hot air from outside or other rooms, thus reducing efficiency. However, modern units run on approximately 1 to 3 ratio i.e., to produce 3 kW of cooling this will use 1 kW of electricity. A dual duct unit will draw air from outside to cool its condenser instead of from inside the room, and thus is more efficient than most single duct units.

Air cooled portable air conditioners are compressor-based refrigerant system that uses air to exchange heat, similar to a car or typical household air conditioner. With this type of system the air is dehumidified as it is cooled.

Evaporative air conditioners do not have a compressor or condenser. Instead, liquid water is poured in and released as vapour. Because they do not have a condenser which needs cooling, they do not need hoses or pipes, allowing them to be truly portable.

As a rule of thumb, 400 square feet (37 m²) can be cooled per 12,000 BTU/h (3.5 kW or one ton of air conditioning) by a refrigerative air conditioner. However, other factors will affect the total heat load. Evaporative air conditioners use much less energy.