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| apsnyone.com | Home appliances | Major appliances | Small appliances | Air conditioning | Dishwasher | Freezer and Refrigerator | Vacuum cleaner and Washing machine |
Air conditioning
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An air conditioner (often abbreviated to A/C in the United States
and Canada, and air-con in Britain and Japan) is an appliance,
system or mechanism designed to extract heat from an area using a
refrigeration cycle. In construction, a complete system of heating,
ventilation and air conditioning is referred to as HVAC. Air conditioning engineers broadly divide air conditioning applications into comfort and process. |
Comfort applications aim to provide an indoor environment that
remains relatively constant in a range preferred by humans despite
changes in external weather conditions or in internal heat loads.
Some have claimed that comfort air conditioning increases worker
productivity but this claim is disputed, one counter argument being
that apparent increases in productivity can be explained as
resulting from workers perceiving that their employer shows an
interest in their welfare. (See Hawthorne effect). What is certain
is that comfort air conditioning makes deep plan buildings feasible.
Without air conditioning, buildings must be built narrower or with
light wells so that inner spaces receive sufficient fresh air. Air
conditioning also allows building to be taller since wind speed
increases significantly with altitude making natural ventilation
impractical for very tall buildings.
Process applications aim to provide an indoor environment suit a
process being carried out that remains relatively constant despite
changes in external weather conditions or in internal heat loads.
Although often in the comfort range it is the process that
determines conditions not human preference. Process applications
include:
Hospital operating theatres in which air is filtered to high levels
to reduce infection risk and the humidity controlled to limit
patient dehydration. Although temperatures are often in the comfort
range, some specialist procedures such as open heart surgery require
low temperatures (about 18°C, 64°F) and others such as neonatal
relatively high temperatures (about 28°C, 82°F).
Clean rooms for the production of integrated circuits,
pharmaceuticals and the like in which very high levels of air
cleanliness and control of temperature and humidity are required for
the success of the process.
Facilities for breeding laboratory animals. Since many animals
normally only reproduce in spring, holding them in rooms at which
conditions mirror spring all year can cause them to reproduce year
round.
Aircraft air conditioning. Although nominally aimed at providing
comfort for passengers and cooling of equipment, aircraft air
conditioning presents a special process because of the low air
pressure outside the aircraft.
In both comfort and process applications not only is the objective
to control temperature (although in some comfort applications this
is all that is controlled) but other factors including humidity, air
movement and air quality.
Efficiency
The efficiency of air conditioners are usually rated by the SEER (Seasonal Energy Efficiency Ratio) rating system. The SEER rating is calculated by dividing the total number of BTUs of heat removed from the air by the total amount of energy required by the air conditioner in watt-hours. The higher the ratio, the more energy efficient the air conditioner.Looking at it on a power basis, the SEER ratio relates the cooling power of the air conditioner (in BTU per hour) to the electrical power consumption (in watts). For example if an air conditioner has a cooling power of 5000 BTU/hour, and an SEER rating of 10, then on average it will consume 500 watts of electric power (5000 divided by 10).
Today, it is rare to see systems rated below SEER 9 in the United States, as people there are increasingly using higher efficiency units. In addition some countries set minimum values for energy efficiency, although not always in terms of SEER. (For example, the United States [4] requires new systems to have a minimum SEER rating of 13.) Substantial energy savings can be obtained from more efficient systems. For example by upgrading from SEER 9 to SEER 13, the power consumption is reduced by over 30% (equal to 1 - 9/13). It is claimed that this can result in an energy cost saving of $US 300 per year, depending on energy tariffs, usage and climate. A common misconception held by people is that the SEER rating system also applies to the efficiency of heating systems. This however is not true, as SEER ratings only apply to air conditioning.
Air conditioners (for cooling) and heat pumps (for heating) both work similarly in that heat is transferred or "pumped" from a cooler "heat-source" to a warmer "heat-sink". (Note: This process requires energy input according to the second law of thermodynamics)
Air conditioners and heat pumps usually operate most effectively at temperatures around 50-55 degrees Fahrenheit. Typically when the heat source temperature falls below 40 deg F, the system begins to reach a point called the "balance point", where the system is not able to "pull" any more heat out of the heat-source. Similarly, when the heat-sink temperature rises, the system will also operate less effectively, and the system will not be able to "push" out any more heat typically when the heat-sink temperature reaches about 120 deg F.
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