Cooling Load and Capacity

• Cooling load is the maximum amount of heat, according to design conditions, that will build up in a space that is not equipped for cooling. This measurement is expressed in BTU/h. Cooling load determines the size of air conditioner required to effectively deal with the heat buildup -- the air conditioning unit's cooling capacity. Air conditioners must be correctly sized for the spaces they will be cooling to avoid inefficient or wasteful under or oversizing.
  
  

Importance of Correct Sizing

• Room air conditioners generally range from 5,000 to 30,000 BTUs. Units larger than these are usually designed for central air conditioning. An air conditioner that has a higher BTU rating than required will cycle off prematurely and fail to remove moisture from the air. An undersized air conditioner may run continuously and fail to provide adequate cooling. Both scenarios result in bothersome and costly energy inefficiency.
  
  

Additional Sizing Considerations

• Air conditioner size should be adjusted to meet the specific cooling needs of an interior space. A commercial building that must be cooled quickly to avoid damage to electrical equipment or perishables may require a larger unit than one designed for a residential space of the same size. BTUs should be increased by 10 percent in areas with two storey or higher ceilings. Kitchen space requires a BTU increase of 4,000 to counteract the heat produced by cooking.
  
  

Site and Occupancy Considerations

• BTUs should be increased by 600 for each additional occupant of a space. Sunny areas that do not have the cooling benefit of shade trees require a BTU increase of 10 percent. Air conditioning must be adjusted for extremes of climate. An area that experiences extreme heat and humidity will require a larger unit than one that does not. An area that requires a slow replace rate of hot air for cool needs about 2,000 BTUs per 1,000 cubic feet of space. Commercial buildings may require 4,000 BTUs per 1,000 cubic feet of space.