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.
I've kept track a few times and during a hot 90F days with lows of 70F
it runs between 8 to 10 hours/day. That may be a low estimate, I'm
going to put a time meter on it for a much more accurate figure.
No delays here. Anyway that doesn't sound like it would increase
efficiency much, if any. I wouldn't like it blowing all that moisture
from the evaporator back into the house again as it warms up. If it's
cold when it turns off as it warms up it is still taking heat away from
what ever is around it. And if it doesn't cool off much in between
cycles, then it blows cooler air faster when it kicks on again.
Time wont do it nor will ratings on the fan or compressor take into
account the controll board, other components in the condensor and how
age and condition of unit play a big part in total useage. Use a clamp
on amp meter at the circuit panel, an old fan or compressor near
failure can use alot more power, air restrictions you are unaware of
will also affect everything.
Depends on the weeks. This week, we had most days high 80s to mid-90s.
Next week the forecast is calling for at least 3 days with highs in the
mid 70s to low 80s. So just turning or now tells you next nothing by
I want to find a voracious, small-minded predator
and name it after the IRS.
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.
A couple of years ago, I hooked up an amprobe to my 3 ton carrier unit
outside and it read 16 amps (220V).
My inside fan blower I think used 5 amps (120V).
So that's about 4,120 watts total full load. Keep in mind I usually
keep my inside fan on continuosly, and my outside unit cycles on and
off throughout the day.
Find an old mechnical clock that has time and date. Those ones with
the litte flip numbers work well. Set it to 1/1/2000 midnight and
hook it into the blower circuit. At the end of a month you'll have
the number of days and hours the unit ran.
You could also buy an old meter and run a circuit through it. You'll
need a subpanel though.
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.
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
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