How Much Electricity are You Using?
October 11, 2008
How Much Electricity are You Using?
by Brad Grieve
If last weeks article on the Cost of Electricity here at Lake Chapala wet your appetite I hope this article gives you some more to chew on.
One of the questions I often receive is how to determine the quantity of electricity each of the apparatus in a typical house uses. You can use a Watt Meter, but these are a bit hard to find here at Lake Chapala. However each house here at Lake Chapala already has a wattmeter pre-installed; it is your CFE electricity meter. A bonus is using it to determine how many watts a given appliance is using is free.
First look at the front of your electric meter and look for the specification Kh which is immediately followed by a number. Many of the new meters will have the specification of Kh 3 1/33, which means the Kh factor is equal to 3 1/33 or 3.0303.
The next thing you look at is the spinning wheel on the front of the meter. This is the silver disk that is rotating like an old LP record or for those of you, who don’t remember LP records, is spinning like a Compact Disc, only slower.
On the top of the rotating disk are a series of numbers but what we want to do is take note of one point on the disk and count the number of seconds it takes to complete one revolution. If you are using a lot of electricity, the disk will be spinning very fast and if you are using a little electricity, the disk will be rotating slowly. You can count the seconds to complete one revolution of the disk using a stopwatch or other time device (wristwatch) to count the number of seconds.
Now comes the time to pull out the calculator and do some math. The best way to demonstrate this is by using an example. The Kh factor for the meter of my office is 3.0303 (as described above). The number of seconds it took to do one revolution is 72 seconds.
First multiply the Kh factor by 3600. Then divide the result of this multiplication by the number of seconds for one revolution. The final result will produce the number watts consumed. Using the above information for my office the calculation is as follows:
3600 x 3.0303 / 72 = 152 watts
Sounds like a lot, however this accounts for all the office equipment I have connected to all the various outlets in the walls of my office and all together they are consuming 151 watts. This would mean if I left them on all day and all night for two months (61 days) my electricity bill would be 223 kWh (kilowatt hours).
However, the reality is my electricity bill is less than half of that since I turn off my computer etc. at night when I leave the office.
What is interesting about this procedure is now I can turn on the lights in my office and by counting the seconds for one revolution on the electric meter, determine my new rate of electricity consumption. With the lights on, the number of seconds for one revolution was 27 seconds. Therefore the new consumption rate was as follows:
3600 x 3.0303/27 = 404 watts with the lights on
Now knowing the before and after calculations of my electricity consumption I know that with the lights on I consume (404-152 =) 252 watts more which means my lights in the office consume 252 watts when turned on. Considering the slight error in measuring the seconds with a small clock and any loses in the electrical distribution in the walls of my old office, it is very close to the total wattage of the five 50 watt bulbs in the fixture which add up to 250 watts.
You could repeat this experiment with this in your own home by turning on and off various appliances in your own home to determine the difference in electricity consumption of every appliance.
