Numbers, numbers everywhere but what do they mean? Look at tonnage, a number that refers to the cooling capacity of the unit. Tonnage is compared to the square footage of area to be cooled. Another factor is ambient outside temperature. The tonnage is related to the melting of ice. A one ton is related to the amount of heat (288,000 Btu) to melt one ton of ice in 24 hours. A one-ton air conditioner is rated at 12,000 Btu’s per hour. A 4-ton AC unit will remove about 48,000 Btu’s per hour.
So, what’s a BTU? A BTU is the amount of heat needed to raise the temperature of one pound of water by one-degree Fahrenheit. A BTU in SI (Society International in English more commonly known as ‘metric system’) is 1.054 to 1.060 kJ or kilojoules, or 252-252 little calories, food calories are actually a kilocalorie or 1000 little calories. BTU in AC is more accurately Btu’s per hour. A thousand BTU / hour is about 293 watts. AC units refer to 12,000 BTU an hour or the amount of heat transfer to freeze one short ton (2000 lbs) of water in 24 hours. Now you know. Calculated on the square footage in takes about 2.5 tons of AC to keep up with 750 to 1,000 square feet. High ceilings increases the amount of air and can affect the calculation. Most calculations are based on 8 foot ceilings. Your region affects the tonnage. In the southwest the area drops per ton. Like 1.5 tons for up to 900 square feet of living area. The same tonnage can handle in the northern regions a 1.5 ton AC/Heat-pump can handle up to 1,100 square feet.
SEER rating or Seasonal Energy Efficiency Rating compares the cooling per unit of energy used. But is the SEER rating accurate. Factually it is not, AC units are tested at 82 degrees Fahrenheit. But up the ambient temperature to a more commonly encountered temperature of 95 degrees you lose about a ton in actual operation. SEER is a marketing term used by the AC industry.
The best method for comparison of AC units is the EER or Energy Efficiency Ratio. EER is calculated by taking the total Btu’s of heat that is ejected and dividing by the watts of electrical power used. Most unbiased experts believe the EER, though calculated in a controlled environment is more accurate than the SEER rating. However, the rule of thumb is the higher the SEER the better, but high SEER rated AC units cost quite a bit more. Currently the general trend is up for SEER rated AC units. 13 SEER was high a few years ago, but units are a minimum of 13 SEER or higher. But the price on 14-16 SEER is coming down making these units more attractive.
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Heat pumps used for heating are good down to 25-30 degrees Fahrenheit. Lower than that you need gas or heat strips for the all electric home. Split units put an air handler in the attic and the compressor unit on the ground outside. Roof mounted air conditioners combine all the functions in one unit. We’ve but touched on all the numbers that are related to air conditioning. Air Supply Heating and Air Conditioning can meet all your air conditioning and heating needs. Contact us today!