Cooling capacity refers to the rate heat is removed from a space, under standard conditions. These conditions take into account such factors as the volume of the space being cooled and the air temperatures both inside and outside the space. Typically, the cooling capacity of a modern air conditioner is printed on the outside of the unit.
Generally, cooling capacities are rated in British Thermal Units (BTUs) per hour, or in tons. A ton of cooling capacity is the same as 12,000 BTUs per hour, and the term has its origin in the cooling effect of a ton of ice. Often, capacity measurements are given in tonnage for cooling units and BTUs for heating units. Broken down, a BTU is based on the amount of energy it takes to raise the temperature of a pound of water by just one degree Fahrenheit.
Cooling capacity is directly related to the size of the area being cooled. As an illustration, a typical 2,000-square-foot home, depending on the climate it is in, may require an air conditioning system with a cooling capacity of 48,000 BTUs per hour. In contrast, an average 150-square-foot bedroom may be able to get by with a unit rated at 5,000 BTUs per hour.
Air conditioners cool a heated room by transferring the heat to the fluid-filled evaporator coils of the unit. The units condense some of the moisture in the air, too. That makes the atmosphere in the room not only cooler, but less humid and more comfortable as well.
Cooling capacity ratings are usually printed directly on the sticker of newer air conditioning units. On older models, the capacity is sometimes coded within the serial numbers. These ratings apply not only to residential and commercial air conditioning systems – including heat pumps that operate in the air conditioning mode – but also to industrial chillers, cooling towers, and other cooling equipment.
The Air-Conditioning, Heating and Refrigeration Institute (AHRI) independently certifies heating, ventilating, air conditioning, and refrigeration (HVACR) equipment and components to ensure these systems meet industry efficiency standards. Generally, the Institute – known as the Air-Conditioning and Refrigeration Institute (ARI) prior to 2009 – works with manufacturers to develop standards and guidelines that result in uniform ratings, including cooling capacity ratings, to give consumers a basis of comparison. An ARI number on a heating or air conditioning unit is a guarantee that its cooling or heating capacity has been properly tested.
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