Energy Vampires Beware! The Kill-A-Watt Meter Is Here!   Leave a comment

This week wraps up my personal energy audit and I have to say it has been eye opening. I’m in love with my Kill-a-Watt meter now (yes I am a nerd). I think I’ll probably keep using it to take some longer term measurements here and there, and I’ll make it available to any of my friends who want to borrow it as well. In a future post I’ll get into some of the surprising results that we got, but I’m still measuring my computer’s usage as I type this. What I have done is an analysis of what percentage of our home energy usage is heating, cooling, water heater, passive appliances, and active appliances. I did this through a combination of meter reading, bill analysis, and direct measurements. This is based on only one year, and I didn’t take into account heating degree days or cooling degree days, so the HVAC numbers have a rather high error rate.

I described in a previous post a simple method for estimating how much energy use use for heating and cooling. I forgot to mention that if you have both gas and electricity, you’ll need to convert therms into kWh. For the analysis at our old house I used the converter at convertme.com. For us: heating was 16% of the annual total and cooling was 20%.

The next task was a bit more challenging, and that was determining the passive electric load. The first step is really easy: read the meter. For a couple of weeks, every night right before I went to bed I grabbed a flashlight, pad, and pen and walked out to the electric meter to record the kWh display. And the next day my husband did the same as soon as he got home from work in the afternoon. During that time we had (almost) no active electricity use. I figure that the garage door, toaster, etc. are minor enough compared to 15 hours of passive usage that it didn’t significantly affect the readings. After dividing the difference between the two readings by the elapsed time, you get kWh/hr. Ours came to just over 5 kWh per day. That is our passive load, aka energy vampires, and includes things like the water heater, cable box, refrigerator, microwave and stove clocks, cell phone chargers, etc.

The second step was the step that I found so exciting this year, and that was measuring the contributions to the passive load from all of the applicable appliances with plugs. For several weeks I’ve been using my Kill-a-Watt meter to measure the daily electric usage for many of our appliances, including everything that is plugged in all the time. By subtracting out this measured total from the passive usage I calculated from the meter, I was able to estimate how much electricity the water heater uses and the non-water heater passive usage. For us: water heater uses 18% of the annual total and passive appliance use 13% (which means active appliance use is 33% of the total).

It is really nice to know that heating and cooling use less electricity than our appliances. Unfortunately it is probably easier to reduce energy used for heating and cooling (shade, insulation, sweaters, etc.) than appliances (turn of the TV and computer?). I did take a closer look at our passive load and I think we can reduce it by 15% by moving a few more things to power strips that get turned off at night. We found some surprising energy hogs that I’ll save for a later post.

Note that I didn’t bother using my electric rate to calculate $ spent on heating/cooling/water heating/passive/active appliances once I had the kWh, but for a lot of people that would be the desired end number.

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Posted September 28, 2011 by mayakey in energy use, home

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