Cost to run central A/C

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Tony wrote:

Part of their biz need is estimating electric usage. Its not going to cost anything to ask so why not?
Also, tried google? Here is a start: http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=comparing+central+air+versus+window+units which got About 396,000 results (0.35 seconds)
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On Sat, 26 Jun 2010 13:31:37 -0400, Tony wrote:

Run it one month and then look at your electric bill.
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I see two approaches. For the macro view, as per the above, just comparing electric bills for summer with months in Spring or Fall with no AC or electric heat use would give a decent approximation. My utility bills show usage by month over the last year. I can easily see the effects of running the AC. Of course, if you had some other seasonal load, like pool pumps, etc, that could complicate things.
For the micro view, as someone else suggested, record the electric meter for a time period on a day with no usage and then do the same with the AC on.
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snipped-for-privacy@optonline.net wrote:

What I did for the zone room (this is the room where I spend 99% of my time) stick a plain Jane window unit through the wall, make that a quiet Plain Jane unit. Get a thermostat, relay and transformer. Wire them up to feed the outlet serving the window unit. Set the thermostat and forget it.
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FatterDumber& Happier Moe wrote:

Yes I like remote temperature controls on window units. I can't find the one I made. It was an electric heat thermostat with the generic snap action switch replaced with one that was the opposite as new, meaning I don't remember if new it had a NO or NC switch, but I changed it to be used for cooling instead of heating.
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Tony wrote:

If ever a thread needed a summary....
No clamp-on meter will do what you want. You need to know the phase angle between the current and voltage 'cause you're billed by the watt-hour. Amps times volts is volt-amps. Different by the power factor.
I've been logging my AC consumption for several days to determine how much it costs to run. It's not rocket science. You use the power company meter. Old meters have a wheel that goes around. They count the number of times it goes around and send you a bill. This is 100% accurate. Any uncertainty in your measurement is due to your ability to operate a stop-watch. Newer meters have a row of numbers with an underline that moves left to right to simulate the wheel. Mine also emits an IR pulse for every movement of the underline. Calibration varies. It's written on the face of the meter in terms you probably don't understand. Mine is one watt-hour per blink of the IR pulse..You can call the power company and get the factor to multiply the readings to get kwh.
I programmed my palm pilot to read the IR pulses and readout in watts then graph that vs time. But that's another story.
Put your house in a stable power configuration with the air conditioner on. Go measure how long it takes for the wheel to go around. Timing multiple rotations can increase the precision by spreading your timing error over several rotations. Turn off the AC and repeat the measurement. A little math later, you have your answer.
Go repeat the entire measurement with some load you KNOW...like the water heater. If you get the right answer, your math is probably correct.
Now you know the power consumption of the part of the system you turned on/off.
Might want to repeat the measurement to make sure you get the same answer...just in case the fridge or water heater or something else came on.
You still need to time the on/off cycles.
As previously suggested, you can take a battery operated clock. My first endeavor used a cardboard flap on a microswitch placed over an air outlet. Air comes on, switch closes, clock runs till the air goes off. Second generation uses a palm pilot to sense the swtich and graph the data. I can tell you exactly how much it costs to run my air conditioner.
But if you run the fan continuously, you need a different system. BlueLine Innovations makes a wireless sensor that straps on your power company meter and reads out on a remote unit. Resolution is not so good, but close enough. YOu can buy 'em on ebay for about $35 shipped. I got mine at a garage sale.
If you can find a place to clamp it, a clamp-on meter into a DVM into a computer can provide the on/off logging function.
Knowing is only the first step. Now, what are you gonna do about it? By watching the percent-on-time over the day, I'm indentifying situations where solar heat gain is a significant factor and taking steps to reduce the cost significantly.
mike
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