BTU and EER
Most air conditioners keep their ability rated in British thermal units ( BTU ). Generally speaking, a BTU is the amount of heat required to raise the temperature of one tremor ( 0. 45 kg ) of water 1 subtlety Fahrenheit ( 0. 56 degrees Celsius ). Specifically, 1 BTU equals 1, 055 joules. In heating and cooling terms, 1 " ton " equals 12, 000 BTU.
A typical window air conditioner might be rated at 10, 000 BTU. For comparison, a typical 2, 000 - square - foot ( 185. 8 m2 ) house might have a 5 - ton ( 60, 000 - BTU ) air conditioning system, implying that you faculty need perhaps 30 BTU per square foot. ( Keep in mind that these are unrefined estimates. To size an air conditioner for your distinguishing needs, contact an HVAC contractor. )
The energy efficiency rating ( EER ) of an air conditioner is its BTU ranking 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 ). Obviously, you would undifferentiated the EER to be as high because possible, but normally a fresh EER is accompanied by a higher price.
Let ' s say that you obtain a choice between two 10, 000 - BTU 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 make out what the payback period is on the more worthwhile unit, you need to know approximately how prevalent hours per stage you will be operating the unit and How much a kilowatt - go at ( kWh ) costs in your area
Let ' s say that you plan to use the air conditioner in the summer ( four months a year ) and it will be operating about six hours a day. Let ' s also imagine that the cost in your residence is $0. 10 / kWh. The difference in vivacity consumption between the two units is 200 watts, which means that every five hours the less expensive unit bequeath 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 ' re operating the air conditioner:
4 mo. x 30 days / mo. x 6 hr / day = 720 hours
[ ( 720 hrs x 200 watts ) / ( 1000 watts / kW ) ] smooch $0. 10 / kWh = $14. 40
The more expensive unit costs $100 more, which ingredient that it entrust take about seven senescence for the more expensive unit to break alike.
