On Jun 29, 12:57*pm, Tony wrote:
wrote:
On Jun 28, 5:42 pm, Tony wrote:
wrote:
On Jun 28, 12:39 pm, Tony wrote:
Steve B wrote:
"Tony" wrote in message
...
Steve B wrote:
"LouB" wrote in message
...
Tony wrote:
Bill wrote:
"Tony" *wrote in message
I'm trying to figure the cost of running the central AC in my house.
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!
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.
Have you sought help from your electric company?
Have you looked on your bill and read the $/kwh? *Compared the chart for
month to month, and this year vs. last year comparisons?
Yes. *But comparing last years to this years has too many variables.
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.
I'm with you there.
With central units, they will do this better than room units that have to
cool a warm room. *Up. *Down. *Up. *Down.
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.
But, then, the only way you find out is to install central, and do a post
mortem analysis.
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.

Tony wrote:
cjt wrote:
Tony wrote:
cjt wrote:
Ed Pawlowski wrote:

"Art Todesco" wrote

http://www.nordyne.com/literature/8569%20Compr.pdf
The best would be to compare the electric meter with the unit
running and not running. This way you will have actual watt-hours
and you don't have to think of things like power factor, etc. But,
it will change depending on temperature. And the run time will
vary when the temperatures are cooler than when it is just plain
hot outside.

Many electric bills give a 13 month use history. Mine even gives
the average temperature for the month. Look at months like April
and October when neither heat or AC is used much and compare to
July and August and you get a pretty good idea. Aside from that,
the only accurate method is a recording ammeter over time.



I think you mean a recording watt-meter. Amps don't account for
power factor.

Another question maybe you can help? If I buy a clamp on type
ammeter that plugs into my DMM to display the current... if my DMM
measures AC with true RMS, will that fix the problem of the power
factor?

No. Power factor arises from the phase relationship between the voltage
and current. For purely resistive loads, they are in phase and the
power factor is one. For reactive loads, they are not in phase. It's
not a question of RMS vs something else.

BTW, if you're willing to try something a bit more interesting, you can
measure total daily power use and minutes your A/C is on each day over a
period of time. Plot the two against each other and fit a line to the
data using a least-squares fit. Done correctly (including scaling
minutes to hours, making the correct choice of axes, etc.), the slope
will be A/C watts and the intercept will be your background use (i.e.
the average energy consumed by the rest of your appliances) within a
margin of error that you might even be able to quantify statistically
(although if your background use varies too dramatically or is
correlated to A/C use, the analysis might fall apart or at least become
difficult). The longer the time period you incorporate in your analysis
(within reason -- you don't want seasonal changes in efficiency, etc. to
get involved), the more accurate you can be.

:-)


Not sure I understand all that. But if you mean to use the power
companies kwh meter, keep in mind that it only changes one kilowatt hour
for each 20 KWh used. This makes it difficult to estimate usage since
it can display the same number for hours even if I am using electric. It
wont add 1 kwh at a time, only 20 kwh at a time.

So take your readings several days apart.

Tony wrote:
Art Todesco wrote:
On 6/26/2010 1:31 PM, Tony wrote:
I'm trying to figure the cost of running the central AC in my house.
Inside was fairly easy, a 1/2hp fan motor. Outside the numbers on the
plate from the factory are long gone. I found on the fan motor that it
is 1/8hp. Now the compressor.... On it is listed the voltage but not the
amps or watts but it does list the LRA (locked rotor amps) of 105.0 It
is a Copeland CR38K6-PFV-370.

I found this site but even this isn't very useful to me only giving me
the RLA of 19. I read the RLA is "rated load amps" and does not mean
"Running Load Amps". RLA being the most current it should draw under the
harshest conditions.

http://www.nordyne.com/literature/8569%20Compr.pdf
The best would be to compare the electric meter with the unit running
and not running. This way you will have actual watt-hours and you
don't have to think of things like power factor, etc. But, it will
change depending on temperature. And the run time will vary when the
temperatures are cooler than when it is just plain hot outside.

That is very difficult with the newer digital electronic meter I have
and the way it's set up. With it on a current transformer the meter
hardly moves at all. The readings have to be multiplied by 20 for the
actual usage.
Hmmm,
I have an Amprobe DMM with built in true RMS reading. IUt has a clamp.
Just set the switch to lo or hi response and clamp, it reads the current
at the moment.

Tony Hwang wrote:
Tony wrote:
Art Todesco wrote:
On 6/26/2010 1:31 PM, Tony wrote:
I'm trying to figure the cost of running the central AC in my house.
Inside was fairly easy, a 1/2hp fan motor. Outside the numbers on the
plate from the factory are long gone. I found on the fan motor that it
is 1/8hp. Now the compressor.... On it is listed the voltage but not
the
amps or watts but it does list the LRA (locked rotor amps) of 105.0 It
is a Copeland CR38K6-PFV-370.

I found this site but even this isn't very useful to me only giving me
the RLA of 19. I read the RLA is "rated load amps" and does not mean
"Running Load Amps". RLA being the most current it should draw under
the
harshest conditions.

http://www.nordyne.com/literature/8569%20Compr.pdf
The best would be to compare the electric meter with the unit running
and not running. This way you will have actual watt-hours and you
don't have to think of things like power factor, etc. But, it will
change depending on temperature. And the run time will vary when the
temperatures are cooler than when it is just plain hot outside.

That is very difficult with the newer digital electronic meter I have
and the way it's set up. With it on a current transformer the meter
hardly moves at all. The readings have to be multiplied by 20 for the
actual usage.
Hmmm,
I have an Amprobe DMM with built in true RMS reading. IUt has a clamp.
Just set the switch to lo or hi response and clamp, it reads the current
at the moment.

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.

Tony wrote:
FatterDumber& Happier Moe wrote:
wrote:
On Jun 27, 10:21 am, Chief Two Eagles wrote:
On Sat, 26 Jun 2010 13:31:37 -0400, Tony wrote:
I'm trying to figure the cost of running the central AC in my house.
Run it one month and then look at your electric bill.

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.

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.

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.

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