So it started out as a way of making people comfortable. Right? Well, not exactly. In 1882, thanks to Thomas Edison, the first electric power plant opened in New York making it possible for the first time to have an inexpensive source of energy for residential and commercial buildings. And by 1889, central station refrigeration was used in large cities to preserve foods and documents. It was well known that a cool surrounding could preserve foods and other perishables for a long time. But what was not well known was how humidity and heat were related. Then in 1902, Willis Carrier built the first air conditioner to combat humidity inside a printing company. Controlling the humidity in printing companies and textile mills was the start of environment management.

02/07/12

Refrigeration cycle

In the refrigeration cycle, a heat pump pumps heat from a lower temperature heat source into a higher temperature heat sink. Heat would naturally flow in the opposite direction. This is the most common type of air conditioning. A refrigerator works in much the same way, as it pumps the heat out of the interior into the room in which it stands.

This cycle takes advantage of the universal gas law PV = RT, where P is pressure, V is volume, R is the universal gas constant and T is temperature, where all quantities are in SI units).

The most common refrigeration cycle uses an electric motor to drive a compressor. In an automobile the compressor is driven by a pulley on the engine's crankshaft, with both using electric motors for air circulation. Since evaporation absorbs heat, and condensation releases it, air conditioners are designed to use a compressor to cause pressure changes between two compartments, and actively pump a refrigerant around. A refrigerant is pumped into the cooled compartment (the evaporator coil), where the low pressure and load temperature cause the refrigerant to evaporate into a vapour, taking heat with it. In the other compartment (the condenser), the refrigerant vapour is compressed and forced through another heat exchnage coil, condensing into a liquid, rejecting the heat previously absorbed from the cooled space.

Humidity

Refrigeration air conditioning equipment usually reduces the humidity of the air processed by the system. The relatively cold (below the dewpoint) evaporator coil condenses water vapor from the processed air, (much like an ice cold drink will condense water on the outside of a glass), sending the water to a drain and removing water vapor from the cooled space and lowering the relative humidity. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space.

Refrigerants

"Freon" is a trade name for a family of flourocarbon refrigerants manufactured by DuPont and other companies. These refrigerants were commonly used due to their superior stability and safety properties. Unfortunately, evidence has accumulated that these chlorine bearing refrigerants reach the upper atmosphere when they escape. The chemistry is poorly understood but general consensus seems to be that CFCs break up in the stratosphere due to UV-radiation, releasing their chlorine atoms. These chlorine atoms act as catalysts in the breakdown of ozone, which does severe damage to the ozone layer that shields the Earth's surface from the strong UV radiation. The chlorine will remain active as a catalyst until and unless it binds with another particle forming a stable molecule. CFC refrigerants in common but receding usage include R-11 and R-12. Newer and more environmentally-safe refrigerants include HCFCs (R-22, used in most homes today) and HFCs (R-134a, used in most cars) have replaced most CFC use.

Evaporation coolers

The aforementioned Persian cooling systems were evaporation coolers. In very dry climates, such affectionately called "swamp coolers" are popular for improving comfort during hot weather. The evaporative cooler is a device that draws outside air through a wet pad. The sensible heat of the incoming air, as measured by a dry bulb thermometer, is reduced. The total heat (sensible heat plus latent heat) of the entering air is unchanged. Some of the sensible heat of the entering air is converted to latent heat by the evaporation of water in the wet cooler pads. If the entering air is dry enough, the results can be quite comfortable. These coolers cost less and are mechanically simple to understand and maintain. An early type of cooler, using ice for a further effect, was patented by John Gorrie of Apalachicola, FL in 1842, who used the device to cool the patients of his malaria hospital.

Power

Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration". A "ton of refrigeration" is defined as the cooling power of one ton US (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. This is equal to 12,000 BTU per hour, or 3510 watts (). Residential "central air" systems are usually from 1 to 5 tons (3 to 20 kW) in capacity.

The use of electric/compressive air conditioning puts a major demand on the nation's electrical power grid in warm weather, when most units are operating under heavy load. In the aftermath of the 2003 North America blackout locals were asked to keep their air conditioning off. During peak demand, additional power plants must often be brought online, usually natural gas fired plants because of their rapid startup. A 1995 study of various utility studies of residential air conditioning concluded that the average air conditioner wasted 40% of the input energy. This energy is lost, ironically, in the form of heat, which must be pumped out.

There is a huge opportunity to reduce the need for new power plants and to conserve energy. In an automobile the A/C system will use around 5 hp (4 kW) of the engine's power.

Insulation

Insulation reduces the required power of the air conditioning system. Thick walls, reflective roofing materical, curtains and trees next to building also cut down on system and energy requirements.

<). Residential "central air" systems are usually from 1 to 5 tons (3 to 20 kW) in capacity.

The use of electric/compressive air conditioning puts a major demand on the nation's electrical power grid in warm weather, when most units are operating under heavy load. In the aftermath of the 2003 North America blackout locals were asked to keep their air conditioning off. During peak demand, additional power plants must often be brought online, usually natural gas fired plants because of their rapid startup. A 1995 study of various utility studies of residential air conditioning concluded that the average air conditioner wasted 40% of the input energy. This energy is lost, ironically, in the form of heat, which must be pumped out.

There is a huge opportunity to reduce the need for new power plants and to conserve energy. In an automobile the A/C system will use around 5 hp (4 kW) of the engine's power.

Insulation

Insulation reduces the required power of the air conditioning system. Thick walls, reflective roofing materical, curtains and trees next to building also cut down on system and energy requirements.