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.