Smart Energy Today

Reducing electricity consumption is easy once you determine the main energy hogs in your home. So how can you determine how much energy a device is using? One way is to use a Meter like the Kill-A-Watt meter, which will tell you the power consumption of any appliance plugged into the meter. Another way is to simply use your electric meter, which will provide allow you to take measurements of your entire home. Using the following method you can use your electric meter to determine how much electricity a device or set of devices (i.e. entertainment center) are using.

This method only works with the electro-mechanical type meters - the ones with a spinning aluminum disc and a series of dials. If your meter is one of the new solid-state types with an LCD display, you will not be able to use this method.

An electromechanical meter operates by counting the revolutions of an aluminum disc which is made to rotate at a speed proportional to the power (watts) flowing through the meter. Each revolution of the disc represents a given amount of energy in watt-hours, and can be determined by finding the Kh factor displayed somewhere on the face of the meter. This Kh factor tells you the number of watt-hours used for every revolution of the disc (7.2 is a common Kh facter.)

Once you find the Kh factor for your meter, you can now determine the power consumption at any time by simply using a stop watch to time the number of seconds it takes the disc to complete one revolution. Then use the following formula to calculate power (P) in watts, where Kh is the factor for your meter and t is the time in seconds for the disc to complete one revolution.

P = ( 3600 x Kh ) / t

Example: On a meter with a Kh factor of 7.2, and one revolution of the disc takes 27 seconds gives you a value of 960 watts.

P = ( 3600 x 7.2 ) / 27 = 960 watts

This tells you that the devices and fixtures running during the time of your test are using 960 watts of power. To measure a specific device(s), turn off everything including the device(s) you are testing and take a measurement to get a baseline. Then turn on the device(s) to test and take another measurement. Now subtract the baseline measurement to determine the power consumption of the device(s).

NOTE: Make sure that the refrigerator or freezer compressors do not kick on in between the two measurements, or you will get an incorrect power value.