Posted: 6/1/2008 10:42:13 AM EDT
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Just a curiosity... how much power (in watts) does a central AC unit use in a house when it's running? I'm talking about the newest models in new houses. I've just been really curious about it. |
Well, I know mine is a Lennox unit, and I think it does have a variable speed blower, since when it starts up, it starts blowing, then increases volume. Ballpark? MOST efficient new units vs LEAST efficient new units? I'm also not really asking for how much total power (power * time), I'm just talking about instantaneous draw while it's running. |
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I've noticed that the amp draw on older hermetic compressors can range anywhere from 8 to 11 amps. Thats on an 8 or 10 SEER(Seasonal Energy Efficiency Rating). Many newer scroll compressor outdoor units have a 13 or 14 SEER rating. The amp draw on these can range from about 3.5 to 5 amps. (these are "rough" estimates based on a 2 to 2.5 ton AC unit) The higher the SEER rating, the more energy efficient it's going to be. |
Then there is at least that much in the air handling unit with the condensor fan. So 10 amps at 240 VAC (use that as the power factor is less than unity, meters count total power), you are looking at 2400 Watts. That is a small unit. Most wiring is 25 A minimum since 3 single phase motors starting up will easly pull double. |
2.5 ton is a pretty small unit. Yeah, start amps are going to be more than run amps. Eventhough it's on a dedicated 25A circuit, doesn't mean it's going to draw 25 amps. The air handling unit is on a seperate circuit than the outdoor unit. The air handling unit only sends 24v to the contactor which starts the compressor and the condenser fan. |
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Thanks for the replies. I'm really just curious because I'm hoping that in the next 5 years or so solar panels will go down in cost, and I'd like to know how much power I'd need to run the AC. When it comes to solar, I'd want to get 5+kW. Sounds like that would probably be enough capacity to run the AC system and more stuff. |
You will need a bit more than that. See how much AC you use at dusk and night. Yeah, 1000 square feet will get you about 10kW but only at peak sun. |
Volts x amps/1000 = kilovolt amp hours (KVA); amps is a measurement of current For single phase systems: Volts x amps x power factor/1000 = kilowatt hour; KW is a measurement of power. For three phase systems: 1.732 x Volts x amps x power factor/1000 = KW If you want to go solar; you'd need to know the starting current of both the air handler and compressor motors which will be substantially higher than their running current. |
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Anywhere from about 25 to 60+ amps for the condenser, depending on tonnage. Air handler fans are minimal. Usually 5-10 amps at best. Closer to 5, for residential units, generally speaking. I'm an electrician, btw. And the load can vary a lot, depending on things like variable/fixed speed air handlers, single/multi stage cooling, single/three phase systems, etc etc etc. |
Solar isn't at the price point, plus the house is new so I have no equity in it. 5 years down the road, that might be a different situation. What I'd really like a home power system to be is enough solar to generate 5-10kW, PLUS some manner of storing some of it. Possibly even storing enough to run everything after the sun is down. Someday, I bet it will be possible without breaking the bank. Again, I'm really just curious, since I never did know what kind of power the AC draws when it's on. |