Watt-meters

Yolo Energy Watch has donated watt-meters to all libraries in Yolo County, where patrons can borrow them for free--just like checking out a book!  

Watt-meters are devices that can measure how much electricity standard household devices and appliances use. While there are a range of different types of watt-meters with varying levels of complexity, all of them will measure the amount power, or electricity, being consumed in any given moment. Electrical power is measured in "watts" for most of our devices, but when you start talking about your entire house you would be measuring in "kilowatts," which are 1,000 watts. Most watt-meters can also measure other characteristics of electricity, such as amps and volts.

WARNING: Most watt-meters are made for low- to medium-power, 110-volt devices. Plugging in a 220V clothes dryer or similarly large device may overload and break the watt-meter (thankfully, 220V plugs usually won't fit in the 110V plug receptacle).  The Kill A Watt P4400 has a maximum power rating of 1,875 watts.

For more information regarding national energy use averages visit: http://visualization.geblogs.com/visualization/appliances/
 
Measuring power with the Kill A Watt P4400:
  1. Plug one end of the watt-meter into the wall (you may want to use a  short extension cord)
  2. Plug the device into the watt-meter
  3. Press the button "Watts" until the display shows a number and "watts" in the lower right corner
  4. The display on the meter will show you the amount of electricity, in watts, that are being used in that instant
Calculating total energy use:
Once you know the power that a device is using, you can calculate the total amount of energy that it uses by multiplying the power in watts by the number of hours that you use it. For example, if your TV uses 45 watts, and you watch it 2 hours a day, 7 days a week, the calculation for monthly usage would be:

45 watts x 2 hours x 7 days x 4 weeks = 2520 watt-hours = 2.52 kilowatt-hours (kWh)

However, some devices, like refrigerators, microwaves, and air conditioning units, cycle through different power levels as a part of normal operation, which means if you take one reading with the watt-meter you won't get an accurate measurement of total usage. For these appliances, the watt-meter has a data-logging function that will record the power being used up to 9999 hours, or 9999 kWh, whichever comes first. 

Measuring total energy used:
  1. Plug one end of the watt-meter into the wall (you may want to use a  short extension cord)
  2. Plug the device into the watt-meter
  3. Press the red "KWH/Hour" button. Press once to see the kilowatt-hours (total energy) used since the device was plugged in. Press again to see the amount of time elapsed since the device was plugged in.