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How to Compare the Energy Efficiency of Air Conditioners

Updated on March 28, 2016
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In residential and commercial buildings, air conditioning can represent a very large portion of the electric utility bill. If you live in a place with hot and humid climate, air conditioning expenses can be higher than those of all other electrical devices combined! For this reason, upgrading your air conditioning equipment to higher performance models can be a very good investment that will save you thousands of dollars in the long run.

Seasonal Energy Efficiency Ratio

The energy efficiency of air conditioners is rated by the Seasonal Energy Efficiency Ratio, or SEER. Basically, the SEER is a ratio of cooling output to electric input. This means that, among two air conditioners of the same cooling capacity, the one with the higher SEER will consume less energy.

It is important to keep in mind that the SEER considers cooling output in BTU/hour and electric input in watts. If you know the cooling output of an air conditioning device and the SEER rating, you can use the following formula:

  • ELECTRIC INPUT (WATTS) = COOLING OUTPUT / SEER

This means that if you have two air conditioning units with 12,000 BTU/hour of cooling capacity, but one is SEER 10 and the other is SEER 24, their respective power inputs will be:

  • Unit 1 = (12,000 BTU/hour) / 10 = 1,200 watts
  • Unit 2 = (12,000 BTU/hour) / 24 = 500 watts

Energy Savings with an Air Conditioner Upgrade

In this scenario, you are saving 700 watts of power by upgrading the air conditioning unit! If you want to calculate savings as a percentage, you simply have to subtract the two SEER ratings and divide the difference by the largest SEER. For example, in the example above:

  • Difference = 24 - 10 = 14
  • Percentage savings = 14 / 24 = 58.33%
  • 700 watts is 58.33% of 1200 watts. This form is practical if you want to calculate the savings directly from the SEER values.

Sometimes, you will not know the SEER rating for your current unit but the following assumptions will be adequate in most cases:

  • Window type air conditioner = SEER 8
  • Old model of split type air conditioner = SEER 10
  • If the model displays the value as a COP (Coefficient of Performance), multiply it by 3.412 and it will be converted to a SEER value.

The following chart shows estimated savings when upgrading a SEER 10 unit to units of higher SEER ratings:

Achieving Further Savings

Keep in mind that there are complementary measures you can carry out to further reduce air conditioning expenses after purchasing a high efficiency unit.

  • Upgrading the lighting to LED reduces the heat that is released into indoor spaces, which is subtracted from the air conditioning load.
  • Installing the condenser unit in the north wall of your building will reduce the incident sunlight, allowing it to operate more efficiently. Make use of natural shading if possible... but don't cram the unit into a tight space because that actually makes it work harder.

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