How we use air conditioning ?

For comfort.  When the weather is hot, most people prefer eating in cool, air-conditioned restaurants.  They sleep better in air-conditioned bedrooms.  Air-conditioned aeroplanes, trains, ships, buses, and cars make travelling more pleasant and less tiring in hot weather.  Air conditioning helps keep homes clean by taking dirt from the air.  Air-conditioned hospitals protect the health and improve the comfort of patients and hospital staffs. 

During cold weather, air conditioning performs much the same services.  It supplies clean, moist air that is warmed to the most comfortable temperatures for working and sleeping. 

In business and industry, air conditioning improves the efficiency of workers.  Employees stay more alert and become less tired in air-conditioned offices and factories.  They make fewer mistakes and have fewer accidents.  Air conditioning also protects workers against high temperatures and harmful dust, smoke, and fumes.  In stores and shops, air conditioning keeps merchandise clean.  It also increases sales, because people like to shop in comfort. 

Several industries that work with delicate parts have air-conditioned clean rooms, which are free of dust or germs.  These companies include aeronautics and electronics firms.  They make or assemble equipment in such rooms because the tiniest speck of dust could prevent the equipment from working properly.  Also, large electronic computers become warm when in use.  A computer may break down unless air conditioning removes this heat. 

Metals and other materials expand as the temperature rises, and contract as the temperature drops.  For this reason, air conditioning is used to control the temperature in factories that manufacture tools or parts for instruments, watches, cameras, and other precision products.  Changes in temperature would change the size of such products. 

Many nonmetallic materials, including textiles, paper, and tobacco, absorb moisture from the air.  Too much moisture may make these materials stretch out of shape.  Too little moisture in the air makes them dry and brittle. 

Almost all textile mills use air conditioning to control moisture so they can produce strong, uniform threads and fabrics.  Some fibres, such as nylon and rayon, could not be made and woven into cloth without air conditioning.  Even the sewing machines that mass-produce nylon stockings require proper temperature control.  The needles of these machines are so small, and operate in such tiny spaces, that sudden temperature changes could cause them to jam and break. 

Paper stretches in wet weather, and becomes brittle in dry weather.  Air conditioning helps control moisture in printing plants so the paper will remain flexible and stay the same size.  This makes possible high-speed printing of newspapers, magazines, and books throughout the year. 

The food industry uses air conditioning to remove dust and other impurities from the air, and to control temperature and moisture.  Air conditioning makes it possible to store fruits, vegetables, fish, eggs, and other foods throughout the year by preventing the growth of bacteria that spoil foods.  Chocolate melts in warm weather, but air-conditioned factories can make it all year round. 

Air conditioning can slow down or speed up the curing of cheese by changing the temperature and moisture of air.  At one time, Roquefort cheese could be made only in certain caves in France that had cool, moist air.  Air conditioning duplicates the air in the caves so similar cheeses can be made elsewhere.  In bakeries, air conditioning controls the rising of bread dough and keeps flour from moulding.  Bread that is cooled in air-conditioned rooms has crack-free crusts. 

In pharmaceutical and chemical plants, air conditioning not only provides dirt-free air, but also removes germs from the air.  Air conditioning keeps moisture at the proper level so that powders, salts, and other chemical substances stay dry. 
 
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How air conditioners work ?

Air-conditioning can be best said to do the following functions:

Control the temperature

Human body is most comfortable between 22 °C and 26 °C. Most air conditioners blow the air over coils (large groups of tubes) that are filled with cold water or a chemical refrigerant (eg. Freon).  To cool the air, some air conditioners blow it through sprays of cold water ( is this not what our poor cousin - the Desert Cooler does to cool the air). In large air conditioning plants for large buildings Refrigeration machines may be used to chill the water or refrigerant that flows through these coils . 
In cold climate regions Air conditioners used in large buildings heat air by blowing it over coils filled with hot water or steam.  A boiler heated by a coal, gas, or oil burner produces the hot water or steam.  In some air conditioners, electric heaters warm the air.  These heaters have a screen of wires heated by electricity.  The air is warmed as it passes through the screen.  
 

Control the humidity

The evaporation of moisture from our skin helps cool our bodies.  But in summer, air often becomes humid (moist). Humidity is also high in coastal areas as ocean water evaporates into the air blowing over the coastal regions.  Humid air cannot pick up as much extra moisture as dry air can. (That would explain why we feel sultry and perspire more in Mumbai than in New Delhi with the same temperature). We find it difficult to cool off in humid weather, because the air does not absorb the perspiration from our bodies.  The amount of moisture that people lose as perspiration depends on their activities and emotions.  For example, a crowd at a cricket stadium perspires more than an audience in a cinema.  An air conditioner removes warm, moist air from a room and supplies cool, dry air.  Otherwise, the air becomes sticky and we soon start to feel uncomfortable.  

The amount of moisture in air compared with the amount it can hold is called the relative humidity. People usually feel most comfortable when the relative humidity is kept between 30 and 60 per cent. This range of temperature and humidity is called the comfort zone.

Air conditioners can dehumidify (remove moisture) from air in several ways.  Cold air cannot hold as much moisture as warm air can.  When air conditioners cool air by passing it over cooling coils, the water or refrigerant in the coils can be made cold enough to cause the moisture in the air to condense (turn into a liquid).  The same process occurs when the outside of a drinking glass becomes moist as it is filled with ice water. Ever noticed water droplets dropping out of outside of Window ACs.

It may also be required to add moisture where it is severely dry. In places like New Delhi , Hyderabad and Nagpur the summer conditions get very high temperatures and dry air. Thus moisture is added into the air by blowing it through a stream of water. Some of the water evaporates in the heat to humidify the air. Our Desert Cooler does exactly this. Also notice that excessive use of cooler in a closed room makes you sultry and uncomfortable. Can you tell why?

In cold countries Moisture control is important in winter, too.  Cold outside air contains little moisture as the moisture also freezes.  When this air is heated, it becomes extremely dry.  Such air dries the skin and may irritate the nose, throat, and lungs.  To prevent these discomforts, air conditioners add moisture to the air in cold weather.  They do this by passing air through sprays of water or over pans of heated water.  The water evaporates into the air.  
 

Clean and filter the air.

Cleaning the air can be done in several ways.  Some air conditioners force the air through filters.  The filters usually consist of closely packed fibreglass wool or metal fibres that have been coated with a sticky oil or some other type of adhesive .  As the air passes through, the dirt, dust, and soot in the air stick to the fibres.  This is the most popular type of system in residential systems. Air can also be cleaned by blowing it through sprays of water called air washers.  An air conditioner that uses this method has a row of nozzles that squirt a fine mist of water into the air.  The water rinses out the dirt.  Air conditioners may also be equipped with electrostatic filters, or electrostatic precipitators.  These devices put a positive electric charge on the particles of dirt in the air.  Negatively charged collector plates attract the positive particles out of the air.  Many air conditioners force the air through porous pieces of carbon, which absorb odours.  

Pharmaceutical firms and hospitals require extremely pure air.  They usually have air conditioners equipped with special filters.  These filters remove all dirt particles down to a size of 0.0003 millimetre.  Air conditioners may also have special UV lamps that kill germs in the air with ultraviolet rays.
 

Distribute the air uniformly.

Circulating the air is important because most people feel uncomfortable in motionless air. You would not cold air to be thrown at you like a bucket of water.  Thus spreading the air in the room UNIFORMLY is as important as all the other processes in air conditioners. Fans blow conditioned air through the room.  The air may be blown in directly or through ducts (pipes) that lead to various parts of a building.  At the same time, used air is sucked out.  To eliminate smoke and odours, the fans exhaust some of the used air by blowing it out of the building.  The remaining used air is returned to the air conditioner, where it is mixed with ventilation air drawn in from outside.  This mixture of inside and outside air is then conditioned and circulated.  Eventually, an air conditioner replaces all the air in a room or building with ventilation air drawn in from outside. The velocity of this flowing air is also important and it should not be too slow nor should it be a violent wind in the room. The amount of air circulated through a room depends on the size and speed of the fan used in the air conditioner. 
 
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Kinds of air conditioners?

Room air conditioners operate on electricity or gas, and are located partly in the room to be cooled.  They are enclosed in a single cabinet.  They blow the conditioned air directly into the room and do not have air ducts leading to and from them.  The three chief types are (1) window air conditioners, (2) consoles, and (3) self-contained air conditioners. 

Window air conditioners fit into the lower part of a window, and can be moved from window to window. 

Consoles are larger than window air conditioners and stand on the floor in the room.  They must be near a window or a wall opening in order to obtain outside air. 

Self-contained air conditioners are the largest room air conditioners.  They may stand 2 metres tall, and can cool an entire large room, such as a restaurant. 

Central air conditioners use electricity or gas.  They can supply conditioned air to a number of rooms or to an entire building from one central source.  Fans blow the conditioned air through air ducts from the air conditioner to the rooms. 

Central conditioners have a number of advantages over other kinds.  For example, all the equipment for air conditioning a large area is located in one place.  This reduces the cost of cleaning and repairing.  Central conditioners can also be zoned.  That is, they can supply air of different temperatures to different parts of a building.  A doctor with a crowded waiting room might want cooler air than a lawyer in a smaller office.  Zoning makes it possible to serve both their needs. 

Combination room and central air conditioners are used in large buildings.  They combine the advantages of both types.  One kind of combination system has a central conditioner to condition outside air.  It circulates the conditioned air to a unit in each room.  The room unit controls the temperature and moisture-content of the air. 

Another type of combination system furnishes cold water or a refrigerant from a central refrigeration machine to a conditioner in every room.  Each room conditioner has a fan, filter, and cooling coils to condition and circulate the air. 

A third variety of combination system conditions a mixture of outside and inside air.  This system supplies each room with cool, conditioned air through one duct, and warmed, conditioned air through another duct.  A mixing-box unit in each room mixes the two air streams to provide the right temperature.  Combination systems have the advantage of supplying conditioned air or a cooling fluid from a central source.  This cuts the cost of maintaining them.  At the same time, the individual room units allow the persons in each room to adjust the temperature to suit their wishes. 

Air conditioners for vehicles.  In cars, the refrigeration unit is located under the bonnet near the engine.  The engine drives the unit by means of a belt connected to the engine.  Air ducts feed the conditioned air into the car. 

Buses often have a separate motor to drive the refrigerating equipment.  This equipment may be located either in the rear of the bus or under one side near the luggage compartment.  The air conditioner is in the roof of the bus.  It supplies cool, conditioned air to the seats through ducts running along the roof. 

In a railway carriage, an electric motor or a petrol engine drives a refrigeration unit located under the carriage.  The air conditioner is mounted over the entrance at one end of the carriage.  Fans in the conditioner blow the air through ducts to outlets that are located in the carriage. 

Aeroplanes require special air-conditioning units.  Much of the equipment is made of aluminium to save weight.  The refrigeration and air-conditioning units for large aeroplanes are usually located in the wings.  In smaller aircraft, these units may be in the body of the aeroplane.  Air turbines drive the refrigeration equipment.  Air ducts feed the conditioned air to different parts of the aeroplane. 

On ships, the refrigeration equipment is installed in the engine room or in a mechanical equipment room.  The air-conditioning units are located throughout the ship.  Air-conditioning equipment for ships must be extra strong to withstand the rolling and pitching motion of the water.  Special metals are used to resist corrosion by sea water. 
 
 
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Choosing a room air conditioner ?

Two facts should be kept in mind when selecting a room air conditioner. (1) The capacity (cooling power) of the air conditioner should be suitable for the room. (2) The electric power requirements for the air conditioner must match the electric system available for it. 

Capacity of air conditioners.  The size of a room and the number of people using it help determine the capacity of the air conditioner needed.  So do the number, size, and direction of the windows in a room, the wattage of appliances and lights, and the amount of wall insulation. 

An air conditioner that has a lower capacity than needed will not keep a room cool.  An oversized unit will control the temperature, but it may not reduce excess humidity.  Such a unit will run only a short time before the temperature falls.  It may not even run long enough to remove much moisture from the air. 

Manufacturers rate the capacity of air conditioners in four ways: (1) British thermal units, (2) watts and kilowatts, (3) tons of refrigeration, and (4) horsepower. 

British thermal units.  One British thermal unit (B.T.U.) equals the amount of heat needed to raise the temperature of 1 pound (0.5 kilogram) of water one degree Fahrenheit (0.6 degree Celsius).  The B.T.U. per hour rating is the basic measurement for air conditioning, and should always be used

specify the capacity of an air conditioner.  An air conditioner with a capacity of 12,000 B.T.U.'s per hour can remove enough heat from the air it is conditioning to raise 12,000 pounds (5,440 kilograms) of water one degree Fahrenheit each hour.  Watts and kilowatts are the units used to measure air conditioner capacity in the metric system.  One watt equals 3.4 B.T.U.'s per hour.  Tons of refrigeration.  One ton of refrigeration removes the amount of heat needed to melt 0.9 metric ton of ice in 24 hours.  A one-ton air conditioning unit can remove 288,000 B.T.U.'s of heat in 24 hours, or 12,000 B.T.U.'s per hour (3,510 watts).  A two-ton unit can remove twice this amount, and so on.  Horsepower measures the power needed to run the refrigeration equipment that cools the air.  Air conditioners may range from 1/4 horsepower (190 watts) to as high as 3,000 horsepower (2,200 kilowatts) for units that air-condition entire buildings.  Electric power requirements.  Local electrical codes govern the kind of motor that can be connected to different kinds of electrical systems.  Most air conditioners with motors of 1 horsepower (750 watts), or less, operate on 110-volt, single-phase current.  Larger air conditioners need either 220-volt or 220-440-volt, three-phase current.  Different air conditioners use various amounts of electricity to remove the same amount of heat.  Engineers use a number, called the Energy Efficiency Ratio (EER), to measure how economically an air conditioner uses electricity.  To find an air conditioner's EER, its B.T.U. per hour rating is divided by the number of watts of electricity used by the unit.  For example, an air conditioner that uses 600 watts to remove 5,000 B.T.U.'s per hour has an EER of 5,000 divided by 600, or 8.33.  Most air conditioners have an EER of from 4 to 8.  The higher the EER of a unit, the less electricity it uses--and the less it costs to operate.        Top History  The ancient Egyptians, Greeks, and Romans used wet mats to cool indoor air.  They hung the mats over the doors to their dwellings.  When wind blew through the mats, evaporation of the water cooled the air.  About 1500, Leonardo da Vinci, the great Italian artist and scientist, built the first mechanical fan to provide ventilation.  Water power turned the fan.  In 1553, the English developed a rotary fan to ventilate mines.  Textile manufacturers made the first attempts at air conditioning.  In 1719, a silk company in Derwent, England, installed a central system to heat and ventilate its mill.  Early cloth makers in New England, U.S.A., boiled water in huge pots near their looms to keep the air moist.  Unfortunately, the heat injured the health of the workers and this method was discontinued.  About 1838, David B. Reid, an English scientist, provided the British House of Commons with a system to ventilate and humidify the air.  In the mid-1800's, John Gorrie, an American, invented a cold-air machine to cool hospital rooms.  During the late 1800's, textile manufacturers in New England began using sprays of water to condition the air in their mills.  In 1897, Joseph McCreery of Toledo, Ohio, U.S.A., received a patent for the type of spray now used in air conditioners.  By 1902, Alfred R. Wolff, a consulting engineer, had designed air-cooling systems for Carnegie Hall and several other buildings in New York City.  That same year, Willis H. Carrier, a research engineer, designed the first scientific system to clean, circulate, and control the temperature and humidity of air.  In 1906, Stuart W. Cramer, a textile engineer from Charlotte, North Carolina, U.S.A., used the term air conditioning for the first time.  Air conditioning became a recognized branch of engineering in 1911.  The first mine to be air conditioned was one at Morro Velho, Brazil.  In 1933, the Cumberland Hotel in London introduced air conditioning into its building.  Japan began to equip its trains with air conditioning in 1934 and by 1935, a cigarette factory in Calcutta, India, had air conditioning.  Between 1935 and 1938, trains were equipped with air conditioning for use in Africa, Australia, India, Malaysia, the Middle East, and South America.  The Greyhound Corporation in America installed the first bus air-conditioning systems in 1940     Top Power Saving Tips for Airconditioners A well known maxim : maintaining an A.C is more difficult than buying one. True to certain extent. Competition and entry of world renowned players in the A.C industry has brought down the prices of the air-conditioner to the level of a Television or an audio system. But the general fear about the recurring power bills causes many families to shy away from buying one and thus denying oneself of a fundamental desire - comfort. Presented here are some tips which would ensure that your power bills remain under control 1)   Design the system optimally:   Lower than required tonnage shall stress the compressor and cause it to age faster Higher than required tonnage shall cause the compressor to cut-off more often - something that affects its health adversely apart from consuming more power. 2)   Insulate an exposed roof with appropriate insulation - glass-wool/ thermocole etc.- Tonnage reduces by app. 25% The initial cost (Rs 25-40 per sq.ft) more than compensates the additional power bill you would have to shell out otherwise. 3)   Cover the West/ East facing Windows with heavy drapery or blinds. Maximum heat gain in a room occurs from West facing glass. 4)   If possible install awnings outside windows to prevent sunlight from falling directly on the glass. 5)   Seal the room adequately. Crevices under doors, poorly fitted windows, aluminium sliding windows and ventilators provide ample scope for air leakage. Cool air can escape through these or outside air can creep in causing the A.C to work harder to be able to maintain the room conditions. Use foam or rubber to seal these leakage points. 6)    Buy a brand of A.C that gives you an accurate thermostat. This will not only save you power, it will also give you stable and comfortable room conditions so that you wont find yourself shivering in the middle of the night. 7)    Maintain your A.C well   Clean the filters regularly. Most A.Cs now come with a removable filter and thus cleaning it fortnightly would prevent the cooling coil from choking. This small activity would reward you with lower power consumption as well as consistent cooling performance. Quarterly preventive maintenance service is an absolute must. Ensure that the A.C is serviced thoroughly on a quarterly basis. The A.C technicians blow off and clean the dirt off the condensor coil ,lubricate the other parts and carry out other preventive maintenance activities to ensure smooth functioning of your A.C and thus slower aging, consistent performance and lower power consumption. Quarterly preventive maintenance is almost always a part of the standard warranty/ maintenance contracts.  A comprehensive preventive maintenance contract with a reputed service franchisee (preferably of the manufacturer) is a very small price to pay for hassles and costs you would have to undergo otherwise. 8)    Do not load your A.C suddenly. If you expect a gathering in the evening, it is prudent to switch on the A.C a good half an hour before the guests arrive. This way the room will be cooled down when the guests arrive and the A.C will not see a sudden surge in the load. Remember that half an hour of pre-cooling will not increase the consumption as much as without it. Because your A.C would have drawn much more power to offset the sudden load thrust upon it. Finally - treat the machine with respect. Frequent tampering with controls, settings, irregular maintenance and imbalanced load conditions can do more harm to the machine and your power bills than anything else. This article was submitted upon request to Essar Power and was Published in their Newsletter "Power Buzzz"     Top