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Keepin' Cool June 3, 2007

Posted by truthspew in air conditioner.
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It’s been unusually warm for late May and early June in casa de Truthspew.

We had an air conditioner. It was a Frigidaire 8,800 btu unit. It could basically make a room arctic.

It even got struck by lightning but I was able to repair it. The electrical connections were all just blackened lumps but I carefully rewired it and it gave us another few years of service. But after a more than a decade of service, it finally lost its magic smoke and didn’t work anymore. Chances are I could have repaired it but my time wasn’t worth it when a new unit can be had for less than $100.

So we ended up with a Haier 5,200 btu air conditioner for $79.99. We already have a Haier tabletop dishwasher that works very well and we’ll probably end up buying this one to cover the office and middle room.

But the problem was power. The back of the building faces up against a brick wall with about a foot and a half clearance. So I was able to hang the unit in that window. But it’s little six foot power cord wouldn’t reach the outlets on the other side of the room. What to do, what to do.

The owners manual warns you not to use an extension cord. But those warning don’t apply to me as I know how to read power requirements and calculate the necessary parameters for an extension.

Some background info on the unit, it consume 4.8A at 115V. That’s a total of 552W (W=I*V where I is the current, V is the voltage. A better explanation of Ohm’s Law can be found here.)

Another neat trick is figuring out what it’ll cost to run this baby. I plan on running mine approximately twelve hours a day. During that twelve hours it’s duty cycle or time the compressor is running will be approximately one third of that twelve hours, or four hours. The remaining eight hours will require enough energy to run the fan which we’ll assume is 100W.

So 552W*4 hours = 2,208 Wh (Watt hours) , divide that by a thousand to get 2.208kWh (Kilo Watt hours). Then take the 100W*8 hours = 800Wh or .8kWh. So in a day this unit uses about 3kWh.

3kWh * 30 days = 90kWh. At an effective fourteen cents per kWh it means it’ll cost me $12.60 a month to run this unit.

Not too bad. You can do this with anything in your household so long as you know the power requirements. A microwave oven for example might require 10A to get up near 1200W of power, but it’s only used for minutes at a time so you have to average out over a time period to see the actual cost.

It’s a good way to cross check your electric bill.