Technical note on portable air conditioning

How Portable Air Conditioners Work. An air conditioner is basically a refrigerator without the insulated box. It uses the evaporation of a refrigerant, like Freon, to provide cooling. The mechanics of the Freon evaporation cycle are the same in a refrigerator as in an air conditioner. This is how the evaporation cycle in an air conditioner works: The compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon gas. This hot gas runs through a set of coils so it can dissipate its heat, and it condenses into a liquid. The air blown across this hot coil is discharged outside to the open air. The Freon liquid runs through an expansion valve, and in the process it evaporates to become cold, low-pressure Freon gas. This cold gas runs through a set of coils that allow the gas to absorb heat by the passage of room air across the coil. Mixed in with the Freon is a small amount of a lightweight oil. This oil lubricates the compressor. Most air conditioners have their capacity rate in British thermal units (BTU). Generally speaking, a BTU is the amount of heat required to raise the temperature of one pound (0.45 kg) of water 1 degree Fahrenheit (0.56 degrees Celsius). Specifically, 1 BTU equals 1,055 joules. In heating and cooling terms, 1 "ton" equals 12,000 BTU. A typical monobloc air conditioner might be rated at 10,000 BTU. For comparison, a typical 2,000-square-foot (185.8 m2) house might have a 5-ton (60,000-BTU) air conditioning system, implying that you might need perhaps 30 BTU per square foot or 100 watts per square metre. (Keep in mind that these are rough estimates. To size an air conditioner for your specific needs, contact us.) The energy efficiency rating (EER) of an air conditioner is its BTU rating over its wattage. For example, if a 10,000-BTU air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 BTU/1,200 watts). Obviously, you would like the EER to be as high as possible, but normally a higher EER is accompanied by a higher price. A portable air conditioner unit implements a complete air conditioner in a small space. The units are made small enough to move around a room on castors. You close the window down on the monobloc unit exhaust hose, plug the unit in and turn it on to get cool air. If you take the cover off of an unplugged monobloc unit, you will find that it contains: A compressor An expansion valve, A hot coil (condenser), A chilled coil (evaporator), Two fans, A control unit. The fans blow air over the coils to improve their ability to dissipate heat (to the outside air) and cold (to the room being cooled). In larger installed systems, air and water is used to dissipate the heat from the outside coil and the efficiency can be improved significantly by using a cooling tower. The cooling tower creates a stream of lower-temperature water. This water runs through the heat exchanger and cools the hot coils of the air conditioner unit. It costs more to buy the system initially, but the energy savings can be significant over time (especially in areas with low humidity), so the system pays for itself fairly quickly.

Evaporative cooling

The more simple evaporative cooler should not be confused with an air conditioner. It is simply a fan which blow air through a wet filter to evaporate water into the air flow from the fan and reduce it's temperature. Evaporative coolers should only be used in very well ventilated areas as they increase the humidity of the surrounding air very quickly. This makes them unsuitable for office or server room use. They are very useful to provide spot cooling of people working outside and for cooling areas such as marquees where the use of a large fan will not be a problem.