- Chelsea Green Publishing - http://www.chelseagreen.com/blogs -

Thoughts inspired by the release of our other co-latest Green Guide: Greening Your Office

Inspired by our new Green Guide, Greening Your Office, I’ve conducted a little experiment with the power consumption of our office water cooler. We’ve got two of them, one in our main office and one in the set of satellite offices down the hallway.

Last year for my birthday, when my parents asked me what I wanted as a gift, I asked for a Kill-A-Watt electric usage meter [1]. (Yes, I’m a green geek.) This is a nifty little thing that plugs into any regular 3-prong outlet. You plug your appliances into it, and it tells you how much energy the appliance is using. It’ll give you measurements for a moment in time or cumulative over time.

So I brought the Kill-A-Watt in to work and plugged our main office water cooler into it. (The cooler also has a hot water faucet, but for simplicity I’ll just call it a cooler instead of a cooler/heater.) The thing normally is plugged in and on all the time, including at night and weekends when the office is empty.

Our water cooler doesn’t get a lot of use, relatively speaking. Not many people in the office are heavy tea drinkers, so don’t rely on it for hot water, and I haven’t noticed heavy reliance on it for cold drinking water. It gets used for sure and I’m glad to have it in the office, but I’m sure that in other offices there are greater demands on the water cooler.

Anyhow, I left if plugged in to the Kill-A-Watt for 13 days, and here’s my estimates and conclusions about whether it makes sense to install one of those outlet timers so that the cooler is automatically shut off each night.

I’ve tried to be conservative in my estimate about how much power the cooler draws and how quickly an outlet timer will pay back.

Assumption #1: Nighttime power use (7pm to 7am) is 1/2 of daytime use (7am to 7pm) because nobody is getting water out of the cooler, so it doesn’t have to cool or heat new water. In other words, in a 24-hour period, one-third of the electricity used is at night and two-thirds is during the day.

Assumption #2: The landlord is paying 12 cents per kWh for power to this building. (I don’t know what the commercial rate is for electricity here. Green Mountain Power charges me about 18 cents/kWh for my residential use, so I think cutting that rate by a third counts as a conservative assumption.)

Results: Based on my measurements of total draw by the cooler over 13 days combined with assumption #1, the cooler draws about 0.58 kWh per night. Applying assumption #2 gives us a cost for leaving the cooler on of 6.96 cents per night. An outlet timer costs $10 at the local Home Depot, though I’ve seen them for as little as $6.88 on Amazon.com [2]. Going with the $10 timer, it would therefore pay for itself in 144 days, or a little under 5 months. Going with the Amazon.com cheapo timer (and ignoring shipping costs), it would pay for itself in 99 days, or about 3 months and a week.

If the rate for electricity is more than 12 cents/kWh, or if I was too conservative in my assumption about nighttime power consumption of the cooler, then the payback period would be shorter. (An additional conservative aspect of my estimate is that I treated weekends like regular work days, even though a timer could be set to turn the coolers off for the full duration of the weekends.) If my assumptions were not conservative enough, then payback would be longer. Either way, the payback period seems pretty good as investments in equipment go, dontcha think? I’m hoping our landlord sees the light and installs timers for the two water coolers in our offices and other offices in the building.