Cost to run central A/C

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Tony Hwang wrote:

I think I wrote that a bit misleading. I was talking about the kwh meter from the electric company. I do however have a clamp around ammeter on my shopping list. I'd like to get one that reads DC current also, of course they are more expensive.
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On Sat, 26 Jun 2010 13:31:37 -0400, Tony wrote:

Best method. After they read the meter start using it for a month. Next time they read the meter, stop using it for a month until the next reading. They usually read it the same day of the month. Take it your self to make sure they are not estimating your bill and the reading is actual. You could also take your own reading daily and run it one day and not the next to get an idea of daily usage. Using stamped values and ideal math is not accurate and won't count load, wear, age and your comfortable temperature setting. You can also get an amp clamp and check one leg of the supply power from the box which will vary when the fan/ compressor cycle on/off. (Is the inside fan on the same circuit?)
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ultimately is the comfort you gain worth the larger electric bill?
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snipped-for-privacy@aol.com wrote:

I want to compare what 1 or 2 8,000 BTU window units use compared to the central AC. I'm almost positive the window units are much more energy efficient than the central air.
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The real factors are how clean the units are, and what type of compressor. Rotary scroll is far more efficient than an old piston compressor.
I've seen outdoor AC unit drawing about 4.5 amps at 220 volt. (2 or 2.5 ton, can't remember). Rotary scroll compressor.
Dirty units draw a lot more power.
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Van Chocstraw wrote:

I can guess the date they read the meter give or take a day or two. They read it from their office, no more meter man. Besides, I think I'd die without AC for a day. Also, with my meter I could be off almost 20 kwh's a day without knowing it. My meter reading must be multiplied by 20 for actual kwh's.
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"Tony" wrote in message

If your heating is other than electric, then the cost is the difference in your electric bill from the winter to the summer.
Or if there is a month in the spring when you don't use heating or A/C, then the difference in the electric bill from that month and a summer month.
Hint: If you get a couple of window air conditioners and just cool the room(s) you are using, the cost will be lower. So just cool the living room during the day and just cool the bedroom at night. If you have 6 kids and 7 bedrooms, then not much savings of course!
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Bill wrote:

That's exactly what I getting at. I'm almost positive it costs less to run 1 or 2 8,000 BTu window units than the central ac, even if I close off the rooms not being used.
I suppose if I compared oranges to oranges and converted both central and window rattler to a basic BTU's/watt that would be very helpful, but I still need the specs on my compressor.
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Tony wrote:

Have you sought help from your electric company?
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Have you looked on your bill and read the $/kwh? Compared the chart for month to month, and this year vs. last year comparisons?
AC, in my estimation, has to do with keeping things cool. Once a room is cool, it takes less power to keep it cool than to cool it down from warm. With central units, they will do this better than room units that have to cool a warm room. Up. Down. Up. Down.
But, then, the only way you find out is to install central, and do a post mortem analysis.
Sometimes a large central AC won't have to work as hard as several smaller ones. But then, there's the thing of cooling unused space ......... It's hard to say.
Steve
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A fool shows his annoyance at once, but a prudent man overlooks an insult.
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Steve B wrote:

Yes. But comparing last years to this years has too many variables.

I'm with you there.

No up down up down here. In this 93F weather the little 8000 BTU unit runs on high 24/7 unless it gets too cool, then I turn it down. Cycling it makes it less efficient.

I have central. I believe it costs much more to operate than a window unit or two, but it's hard to say without the right numbers.
Right now I have one 8000 BTU unit and one fan to circulate the air. Running it 24/7 30 days would cost me less than $60. It never runs all night so it's maybe $45-$50 a month to cool 960 sq ft. Forgot the fan to circulate the air, add about $4. per month.

I always considered "work as hard" an odd expression in this context. I had a Fedders, maybe 7000 btu run pracically 24/7 each summer for 15 years and it never stopped working. I left it at my old house because it wasn't nearly as efficient as the newer ones.
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But as you say, there are so many variables ...... insulation, reflectivity of roof, roof venting, single or dual pane windows, airtightness of the structure, even natural shade tree placement. You have asked a complicated question with no answers, and are shooting down people who are answering you. If you know all these things, just go ahead and do whatever it is you were going to do from the get go. Unless it is new construction where you can control the variables, you're pretty much stuck with a WYSIWYG situation.
Steve
visit my blog at http://cabgbypasssurgery.com watch for the book
A fool shows his annoyance at once, but a prudent man overlooks an insult.
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Steve B wrote:

No wonder you say it's complicated! I'm talking about using the same house for both *tests*, factoring in the weathers "cooling degree days".

I didn't think my question was so complicated. What is the rated current draw on the compressor I listed? That's all.
It seemed like somewhere there would be an easy answer, another web page maybe? I guess not.
and are shooting down people who are answering

I'm trying to use the abilities I have to do a simple comparison. Using my electric companies meter isn't very accurate as I explained. It's presision is +/- 19Kwh.
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The answer as to how many amps the compressor is rated out may not be complicated, but it also doesn't answer the question you are seeking, which is how much it cost to run your AC.
If you want to know how many amps the compressor is actually drawing, just buy a cheap clamp-on amp meter from HarborFreight or similar. They have them for around $12. But that leaves out power factor and how much the rest of the system, eg blower is using.
As I and others suggested, why can't you turn off any loads that might come on, eg electric water heater, attic fan. refrigerator, etc, then run the house for a couple hours of continuos AC and a couple hours without AC and record the electric meter readings. That will give you how many Kwh it takes to run and you'll be way ahead of where you would be with the amp rating of the compressor.

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snipped-for-privacy@optonline.net wrote:

Like I said before... A couple hours run time using a kwh meter with an accuracy of +/- 19Kwh??? That may show my AC runs for free.
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Have you even taken a look at your electric meter? When that AC is running, the meter is going to be flying and in a couple of hours you will indeed have enough usage to increase the least significant digit or two digits, substantially. Certainly enough to get a good enough reading to determine the approx cost of running the AC continuosly for those two hours. There is no way you could falsely conclude that it's "running for free." Assuming you did what I suggested, which is to turn off any other large loads that might come on, ie electric water heater, pool pumps, etc. just taking the entire usage during that test period and counting it as AC usage isn't going to be too far off. Think about how big your ENTIRE bill is during months with no large loads, ie no heating, no AC. Divide that down to 2 hours, and it isn't much compared to what the AC will use.
If you want to get a better read on the low usage from the rest of the house when the AC isn't running, measure it for 8 hours, or whatever it takes to move the meter enough to get a good reading. Or better yet, just open all the other freaking breakers so there is no other load other than the AC for two hours.
This ain't rocket science.
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snipped-for-privacy@optonline.net wrote:

Yes many times.
When that AC is

Sorry, my meter doesn't do anything fast. It's not mechanical and the little fake LCD "spinner" thing doesn't move fast either. To read my meter you must multiply by 20. If I stand in front of it watching, the number changes 1kWh for every 20kwh's used.
There is no way you could falsely conclude that

If I read it only an hour apart it may very well have the same reading. It may have the same reading for hours! If the reading just turned to 0003777, it takes the use of 20 kwh's to change to 0003778. So if it's been a few hours, it may very well have the same reading it did when first checked. That is why I said it's accuracy is +- 19kWh. It all averages out in the long run, but for less than a few days or more, it's not very accurate at all.
Assuming you did what I suggested, which is

Two hours isn't nearly long enough and it would be tough to turn off everything else for a couple of days.

It seems to be, since no one seems to understand how my electric meter works.
All I asked was how much power does my compressor draw. I already figured in the fan and blower motors, I just needed to know what the compressor draws.
As someone suggested, I didn't buy it yet, but I put an "amp clamp" meter on my Harbor Freight shopping list. So thank you to everyone who replied and I will take the advice of getting an ammeter (and an hour meter to keep track of how long the AC is actually running).
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To read my

OK, so your meter moves slower than the meters I have had.
But, it would seem that fake LCD spinner thing must move at some rate substantially faster than the speed with which the lowest digit on the meter increases. Mine moves very fast, easily 20X or more for one increase of the lowest digit. You say the lowest digit on yours equals 20Kwh. If it takes just 10 rotations of the spinner to make the lowest digit increase by 1, that means one rotation is 2Kwh. An AC unit is probably using on the order of 6KW. So, in an hour the spinner should be rotating about 3 times. If it's 20 rotations to increase the digit by 1, which I would think is more likely, then the spinner will rotate 6 times in an hour.
Given that, I don;t see why this procedure wouldn't work:
Turn on the AC and as many other large loads as you can, eg ovens, dryer, stove, water heater, etc. That will get you an increase in the lowest digit in under an hour. Keep an eye on the meter or pay your kid to watch it until the lowest digit changes once. Then count the rotations of the spinner until it changes again, which will be 20kwh. You probably don't need to watch it the whole time. Just record the time the meter digit changed and how long it takes for one spinner revolution. Then record the time when the lowest digit increases by one again. Based on how long it takes for one rev and how long it takes to increase one full digit, you can calculate the multiplier. As an alternative, you could call up the electric company and maybe they can tell you if you find the right person.
Knowing that, just turn on the AC with all the other loads turned off and record how long it takes the spinner to make a full revolution and you can calculate the cost to run the AC per hour of use.
I don't know why you need to know, nor how exactly you want it, but for any purposes I would have, I could just look at my electric bill for April and May, compare it to July and August and know close enough without doing anything else.

Next you'll be worrying that the amp meter only records amps and without knowing the power factor of the motors involved, you still won't have the true energy used.
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snipped-for-privacy@optonline.net wrote:

Thanks, that is what I'll be doing. Harbor Freight is about 60 miles away so it will be a little while until I can get there again. (I was a Harbor Freight virgin until last week. I see what people meant about not leaving the store with only the item I intended to buy!)
Thanks again, amp clamp is the way to go.
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LouB wrote:

I don't see how they can help, what kind of help would I be seeking?
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