Saturday, June 02, 2007

"Mind" -> Kill A Watt

This is undoubtedly one of the coolest gadgets on the planet today.

Kill-A-Watt
is a meter that you pull between the wall and whatever appliance that you want to measure. If you click on the hot link above, you can see that Amazon has it for a mere $23.

Electricity is measure in something called KiloWatt Hours. This is often abbreviated kwh. Now what is a kilowatt hour? The easiest way of thinking about a kwh is "as a measure of work." Let's say that you were paying somebody to carry books upstairs in your house. Would you pay them by the hour? Well that isn't very fair. What if they don't work hard?

Would you pay them by the book? Again, maybe they'd just grab all the small books.

The answer is paying them by how many pounds of books times the number of steps they carry them up. The more weight or the more steps, the more they get paid.

Kilowatt Hours are like that. A kilo*watt*hour (to use the right math term) is how much electricity you used. By plugging in Kill-A-Watt, you can see how many kwh you are using on any appliance.

Now, you may want a simple answer to how much electricity costs you. In our area, the cheapest electricity cost .12 for every kilowatt hour. However, this isn't a very easy thing to remember.

At .12 per kwh, you will pay $1 every year if you leave a 1 watt appliance on 24 hours for 365 days per year. Each year has 8760 hours. So, if you don't running it all the time, you can simply take a fraction of this.

For instance, we have somebody at work who is cold, even in summer. So, he has brought in a electric heater. It is a 2000 watt heater. Remember that I said it was $1 per watt for the year? So, if he leaves it on all the time, it is a $2000 bill for electricity every year!

However, he doesn't. He just has it running when he is in the office. If he runs it 8 hours per day for 50 weeks at 5 days per year, he will be running it for 2000 hours per year. 2000 hours is a fraction of all of the hours in a year (1 year = 8760 hours).

He actually runs it $2000 * 2000/8760 hours = $457 per year.

How about that 300 watt halogen lamp you have? If you left it on all the time, it would be $300. If you leave it on 8 hours per night, then then you leave it on for 1/3 of the day (which will be 1/3 of the year). This is $100 dollars.

You can buy florescent floor lamps, which put out the same light in only 50 watts. This will cut your bill from $100 down to just $17 per year! You end up with another $83 dollars.

The big offender in a house is lights, refrigerators, and air conditioning.

Now, you may have a PC with a 200W power supply that you leave on all the time. You do the math, and this would mean that you are paying $200 per year in electricity!

Fortunately, it isn't that bad. PCs use "switching power" supplies. This means that you only convert what you need (plus about 20% because it isn't perfect). For instance, my PC at work with a 400W power supply "only" pulls 110 watts. However, it does cost my company $110 per year if I leave it on all the time.

Interesting, my portable PC only pulls 17W. So, by using my portable PC, I could save my company $93 per year.

Now, I've found out all these numbers by plugging in the Kill-A-Watt meter. If you do the same, I'm sure you'll find out a lot of interesting data that will cause you think about what items you leave running.

1 comment:

tmm said...

I didn't know you run on a crushed ankle until a day ago.