As with anything having to do with energy conservation SEER is probably the least understood concept by homeowners. Simply put, SEER stands for Seasonal Energy Efficiency Ratio. The resulting SEER number that is applied to an air conditioner is called its SEER rating. The higher the AC SEER rating the more energy efficient a given air conditioner is. We’re assuming for comparison purposes that all other variables are the same between the AC systems compared.
Think of AC SEER ratings the same way you do MPG ratings for automobiles, but instead think of BTU’s per watt.AC SEER is simply a formula that is described by the outcome of the following:
BTU’s / SEER = Watts/hr
Divide the AC system’s rated BTU’s by its stated AC SEER rating to determine how many
watts it consumes per hour, (Kwh stands for kilo-watt hour).
Here’s the formula (we’ll use a 3 ton, 15 SEER AC system for this comparison):
36,000 BTU’s (3 tons) divided by 15 SEER = 2,400 watts/hr
This is simply the number of watts consumed each operating hour by the AC system.
The last step is to determine your annual AC system operating cost to use as a basis of comparison to determine which of the multiple AC SEER rating choices you’ve been offered is best. To do that we need to know how many hours, on average, your AC system will operate. While many factors are involved here let’s assume that you operate your AC system the same way most people in your geographical area do. This assumes that you: set your thermostat at or near 78 most of the time, turn up/off your AC system when you’re gone for 4 hours or more, have the AC system tuned up periodically, and live in a home of average insulation and have average quality windows.
Fortunately, a lot of study has been done to tell us how many hours our air conditioner will operate based on our geographical area and using the assumptions listed above. To keep it simple, we’ll use an average in Texas, or 2,500 hours of operation hours annually.
Remember the number 2,400 watts/hr from above? That was the amount of watts our example 15 seer air conditioner consumed each hour it operated. Now that we know our number of operating hours annually (2,500) we simply multiply these two numbers to get the total numbers of watts consumed on an annual basis.
2,500 hours of operation X 2,400 watts consumed per hour = 6,000,0000 watts= 6,000 Kwh Annually
Now all that is left is to convert these numbers to an annual cost. To do that lets look again at your power bill and determine the total cost per Kwh. This is your cost for each Kwh your air conditioner consumes. Let’s use 12 cents per Kwh, including taxes, franchise fees, peak usage, feudalistic surcharges, etc.
6,000 Kwh consumed annually X 12 cents per Kwh = $720 per year