How to Use a Kill-a-Watt Meter
An introduction to killing watts with this fun toy!
This week’s issue of The Free Weekly (which came out last Thursday, sorry for the delay) is worth a look. If you haven’t used one before, Making Ripples column talks about using a Kill-a-Watt meter to reduce energy consumption from entertainment appliances like the TV and video games.
Hey all, this is Ryan finally hoppin’ in here to add some detail to this post. Measuring appliance energy consumption can be tricky. The easiest appliances are those that pull a steady amount of power as long as they’re plugged in. These include things like TVs, stereos, and other items that are not pulling energy to simultaneously power the device and charge a battery – they run, pure and simple, on wall power while powered on. However, as you’ve probably heard, these devices also usually draw energy while powered off, to maintain various internal functions like clocks, “instant turn on” functions, and other things. This is often know as a device’s “phantom pull,” though I’ve also heard it called “vampire power.”
The more intriguing appliances include refrigerators, laptops, and other devices that draw power sporadically or consume varying levels of energy depending on at what stage in the recharge cycle their batteries happen to be.
Our old apartment was 100% electric, meaning that not a single appliance used gas or any other form of energy. By watching the movements of the meter, I could determine that we would use, when we avoided using the heating/cooling wall unit, between 3.0 and 4.5 kWh of energy per day. This apartment provides a more useful comparison to the kind of living conditions we’ll have in the off-grid earthbag house.
That all said, let’s look at a few of our devices:
- Our “entertainment center,” which consists of an ancient 13″ CRT television, DVD player, and VCR (which mostly just acts as an RF modulator for the DVD player) varies between 60 – 80 watts while fully powered on, and has a phantom pull of 13 watts when everything is powered off but the power strip remains active. This series of devices would leach nearly 1/3 of a kWh every day if we didn’t turn off our power strip when finished with it.
- Our refrigerator uses 13o watts while running, and the frequency it kicks on depends on how often it’s opened, how good the seals are, how much/little is inside of it (actually having more is better since the items inside store and radiate cold, which helps modulate the internal temperature), how hot it is in the house, and how clogged the air intake filters are. On average, during a warm day, ours would run for about 16 hours per 24-hour period. This equals just over 2 kWh of power consumed. This actually accounted for, generally, more than half of the power we would use day to day.
- In our old apartment, we used to have an electric stove. Classically, converting electric power to heat is one of the most inefficient ways to use it. Every bit of heat you feel radiate off of something hot is “lost” power, which is not being channeled into your food. This is why one coil on an electric range uses 1000 watts, a full kilowatt of power at all times while active.
- In the same vein, our old heating/cooling unit would use 6,000 watts of power, which blew my mind so much that we made every effort (most of them involving shivering like crazy) to avoid using it. That used to floor me until my dad told me about the industrial-strength heating units hanging from the ceilings of some parking garages. Each unit, spaced about 20-feet apart, and totaling perhaps 50 or more for the whole garage, used between 20,000 and 30,000 watts. EACH UNIT! This is 1,000 and 1,500 kilowatts of power, which would consume 1.0 to 1.5 MEGAWATTS of power every hour. I am humbled, and slightly sickened, I must admit.
- Our various laptops use anywhere from 25 – 75 watts of power. The netbook, from ASUS, uses the least, charging at around 40 watts to start, decreasing to 10 when the battery is almost full. When shopping computers, I always look for the EPEAT designation, which means the device is made with many environmental considerations in mind.
And that’s just a snapshot. If you’re curious about anything else, just let us know!