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Air Conditioning SEER Energy Efficiency Ratings Explained AirCondAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• What are air conditioning SEER energy efficiency ratings?
• How do we compare differences in seasonal energy efficiency or operating costs of different brands or models of air conditioners?
• What is a BTU or British Thermal Unit? How do we convert Watts to Joules?

This article explains air conditioning SEER energy efficiency ratings along with related terms like Watts and hourly operating cost, in easy to understand language. This website answers most questions about air conditioning systems. We continue to add to and update this text as new details are provided. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

SEER RATINGS EXPLAINED - determining Seasonal Energy Efficiency of Air Conditioning Systems

SEER stands for "Seasonal Energy Efficiency Ratio. This is a measure of the energy efficiency of the air conditioning system. SEER ratings permit consumers to compare operating costs of various cooling systems and products.

SEER = [Total Cooling Output Over the Cooling Season] / [Total Electrical Energy Input Over the Cooling Season]

Higher air conditioning SEER rating means more efficient, or in other words lower energy cost to cool the building. Older air conditioning systems are likely to have a lower SEER (perhaps 5 or 6) than a newer more efficient system (perhaps SEER=10). But beyond comparing SEER ratings, a look at the building insulation, air leakage, and the layout, insulation, and adequacy of the air conditioning duct system are likely to have a very large, usually determining effect, on the operating cost of air conditioning systems in buildings.

How Much Energy Does an Air Conditioning System Use?

How to Calculate Energy Usage using an Air Conditioner's SEER rating

A concise way to translate SEER number directly into energy cost is SEER 10 = 10 BTUs/WattHour. In other words, an air conditioner that has a SEER rating of 10 will provide 10 BTUs of cooling per WattHour (Wh) of operation. So if our air conditioner has a SEER of 9, it is less efficient than an A/C unit with a SEER of 10 because our SEER 9 air conditioner produces 9 BTUs of cooling for the same Wh of operation. That is, we've kept the energy consumpation (one Wh) the same, but we got less cooling output.

Let's define Watts and BTUs so we can better understand these air conditioner figures of SEER efficiency, BTUs, Watts, and air conditioning operating cost calculations.

What is a Watt Hour or Wh?

What's a WattHour? Watt hours (Wh), sometimes written W.h, can measure either electrical energy produced, say by a power station, or Watts can measure the amount of electrical energy consumed (say at a light bulb or an air conditioner in our home). For air conditioners, the A/C units' total Wh is the energy used in running the air conditioning system for an hour.

If you turn on a 100-watt light bulb for an hour, you've used 100 Wh of energy. Or if you had a one-watt bulb and lit it for an hour, it'd use 1 Wh of energy. Thank James Watt (1736-1819), credited with developing a useable steam engine, for WATT which was named for him in 1882.

What is a BTU or British Thermal Unit? What is a Joule?

Definition of BTU

A BTU is a measure of heat energy. One BTU is the amount of heat energy we need to raise the temperature of one pound of water by one degree Farenehight. One BTU also is definded as 252 heat calories (this is not the same as food calories). When talking about air conditioners or heaters, we talk about the A/C unit's BTUh capacity - the number of BTUs of cooling (lowering rather than raising temperature) it can produce in an hour of running.

Definition of Joule

Note: Outside of the U.S. and some other places, BTUs is being replaced with the SI unit of energy, the Joule. (J). The English have beaten out the Scots by James Prescott Joule who defined this value. since there are 3600 seconds in an hour) the following formulas equating Watts, Joules, and Newton meters can be written:

1 Watt second (Ws) = 1 joule (J) = 1 newton meter
1 Watt hour (Wh) = 3600 Joules

1 kilowatt hour = 3.6 x 10⁶ Joules, since there are 1000 watts in a kilowatt.

We can think of an air conditioner's "efficiency" as expressed either in the total operating cost for a season of use, or you may prefer to just express the air conditioner's efficiency as its operating cost to run the system for one hour.

The equation shown at page top is designed to reduce all of the parameters describing air conditioning efficiency to a single efficiency number, SEER. SEER numbers are useful when we're comparing one air conditioner with another. But suppose we want to know the actual air conditioning cost per season, or air conditioning cost per operating hour to operate our air conditioner?

To translate our air conditioners SEER rating into actual air conditioning operating costs we need to know:

How Much Electricity Does An Air Conditioner Use Per Hour?

How much electricity our air conditioner uses per hour is easy to calculate. Let's assume that the data tag on our air conditioner says that the unit is a 5000 BTUh device with a SEER rating of 10. This means our A/C unit will produce 5000 BTUs of cooling in an hour of running. Since SEER=10 means that 10 BTUs used per Wh, then
5000 BTUh / 10 SEER = 500 Watts per hour that our A/C unit will use.

How Much Electricity Does An Air Conditioner Use in one Cooling Season?

A common example we use (because the math is easy) is to assume we have 125 days of cooling season during which we run the air conditioner for eight hours per day.
8 x 125 = 1000 hours of cooling operation over a season
500 Wh (watts used per hour) x 1000 (hours per season) = 500,000 Wh per season
So we are using 500,000 WattHours of energy (electricity) per cooling season. We divide this by 1000 to convert to Kilowatts since that's how our electrical bill will express our electricity usage.
500,000 Wh / 1000 = 500 kWh or kilowatt hours per season of use
That's how much electricity we're using over the cooling season.

In the next section of this article we determine the actual dollar cost of running an air conditioner either by the hour of by the season of use. It's easy to get from that data to actual air conditioning operating costs in dollars.

AIR CONDITIONING SYSTEMS Chapter Index

To continue reading this air conditioning inspection guide, use links to the document chapters at left or below. Links shown in green font indicate where you are in this document.

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