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Explanation of the Energy Efficiency Ratio (EER) ratings for air conditioning systems. How they are calculated, what you need to know, how to know which rating is best and what to look for.
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Portable Air Conditioner Efficiency Information Page
Each air conditioner has an energy-efficiency rating that lists how many BTUs per hour are used for each watt of power it draws. For room air conditioners, this rating is the Energy Efficiency Ratio, or EER. For central air conditioners, it is the Seasonal Energy Efficiency Ratio, or SEER. These ratings are posted on an Energy Guide Label, which must be attached in a visible place on all new air conditioners. Many air conditioner manufacturers are voluntary participants in the EnergyStar labeling program. EnergyStar-labeled appliances mean that they have high EER and SEER ratings.
How is EER Calculated?
The EER of an air conditioner is its British thermal units (BTU) rating over its wattage. For example, if a 10,000-BTU air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 BTU/1,200 watts). The higher the EER is, the more efficient the air conditioning unit is. However, normally a higher EER is accompanied by a higher price.
Would the Higher Portable Air Conditioner EER Rating be Worth the Extra Cost?
Let’s say that you are given a choice between two 10,000-BTU air conditioning units. One has an EER of 8.3 and consumes 1,200 watts, and the other has an EER of 10 and consumes 1,000 watts. Let’s also say that the price difference is $100. To calculate what the payback period is on the more expensive unit, you need to know:
1. About how many hours per year the unit will be operating
2. What the rate of a kilowatt-hour (kWh) is in your area
Let’s say that you plan to use the air conditioner in the summer (approximately five months a year, depending on where you live) and it will be operating about 8 hours a day. Let’s also say that the cost of a kilowatt-hour in your area is approximately $0.10. The difference in energy consumption between the two units is 200 watts, which means that every five hours the less expensive unit will consume 1 additional kWh (and therefore $0.10 more) than the more expensive unit.
Assuming that there are 30 days in a month, you find that during the summer you are operating the air conditioner:
5 mo. x 30 days/mo. x 8 hr/day = 1200 hours
[(1200 hrs x 200 watts) / (1000 watts/kW)] x $0.10/kWh = $24.00
Since the more expensive unit costs approximately $100 more, this means that it will take about four years for the more expensive unit to break even.
Not all BTU ratings can be trusted. Just because the BTU’s are stated to be high on specific air conditioning units, it does not mean it is necessarily true. Some manufacturers will exaggerate the BTU’s on units to raise the possibility of selling the them and others will be more conservative in regards to the BTUs, which will cause the EER rating to be lower so a lower portable air conditioner EER may be misleading. It is best not to allow the EER energy rating to be your only criteria for choosing an air conditioning unit. Do the research on whatever unit you are considering for your home and you will be happier with your purchase.