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July 12, 2008

Green Gadgets: An Introduction to the Kill A Watt™

This is another article in our "Green Gadgets" column written by Shane Conder, a guest blogger.

Today I'm writing about a gadget you may have already heard about. Have you ever wondered how much electricity something you plug into the outlet really uses? You read on the label the peak power that an appliance might use, but does it use that much power all the time? How much power does something use over a given amount of time when there are variable power requirements?

All of these questions can be answered with a simple and inexpensive gadget called the Kill-A-Watt from P3 International. This device will show a lot of different pieces of information. The pieces we are interested in, though, are the Watt measurement and a sum of the Watt-Hours that the device has measured.

The first measurement, Watts, will tell you how much power is being used by a device in it's current state. For instance, if you were to plug in a lamp that had a 100 watt light bulb in it, the Kill a Watt will likely read 100 watts as these bulbs are usually pretty close to their rated power. What can you do with this? Well, you now know that if you leave this particular device on for one hour it will use that many watt-hours (Wh) of power. In our example here, one hour would result in 100 watt-hours. Your electric company likely measures electricity consumption in kilowatt-hours (kWh). Just divide your watt-hours by 1,000 to get the amount of kilowatt-hours that can be used for calculating costs. In this example, that results in 0.1 kWh for using the lamp for one hour. (Quick science note: Kilowatt-hours is a measurement used by the electric utilities in many countries, including the United States. In your science class, you'll learn that one Watt for one second is a Joule, a more common measurement of power used over time in science. One kWh is 3.6 megajoules. Although it's referred to as power used, it's more accurately the amount of work performed.)

The second measurement on our Kill a Watt shows the actual number of kilowatt-hours (shown as kWHr) of power that has been measured. Since this is already in the units that your electric company probably uses it can be used directly. This number is typically lost when you unplug the basic Kill a Watt. However, some versions will keep this information when they aren't plugged in.

Now you can go around your house and measure the electricity being used by all of your devices. Try it out even when a device is off. You might be surprised at the results! Let us know what you find.

This is the first of a series of articles on power usage. In the next article, we'll talk about how to calculate how much your devices electricity will cost. Then we'll talk about some common devices and how much electricity they use, even when supposedly powered off.

Posted by shane at July 12, 2008 10:52 AM