Archive for the ‘electricity’ Tag

Wait, My Refrigerator Uses Less Electric Power Than An Old Fashioned Lightbulb?   Leave a comment

So I started this post to list out some of the interesting results that came from my energy audit, but it quickly changed into something else. I figured it would be easier to talk about appliances in terms of watts, not thousands of a killwatt-hours per hour, so I did the conversion. Then I stared at the list for a while thinking, “Wait but didn’t we used to commonly use 40- to 100-watt lightbulbs? My refrigerator uses 46 watts! How on earth can a big refrigerator use less electricity than a little light bulb? Really?!” No wonder lighting is often separated out from appliances in statistics. In fact, the only appliance that I measured to be more than 100 watts was our washing machine!

Speaking of the washing machine. I measured 3 loads and they all came out to 110 W per load. Out of curiosity I compared that to the Energy Star EnergyGuide. According to Energy Star, our model washing machine is projected to use 130 kWh per year based on eight wash loads per week. That calculates to 312 W per load. Is that discrepancy due to use of only cold water? I always thought the energy savings from washing with cold water was energy savings at the water heater, not the washing machine. More research will be done…

So what were the other surprises?

  • Cell phones are pretty efficient! Our two cell phones averaged 0.07 W, which is less than 1 kW for an entire year. This is less than the doorbell and digital alarm clock.
  • But Dust Busters are not. At 3.3 W, that’s comparable to the cable modem and router. And that’s just for keeping it charged, and not having been used prior to measuring the electric consumption. The battery charger, keeping a few AA batteries ready to use, only used 2.5 W.
  • The TV uses more electricity (63 W) than the refrigerator (46 W). It’s an old TV, so I don’t know how modern TVs compare.
  • A Playstation 2 (8 W) uses more electricity than a DVD player playing a DVD (10.6 W). But the cable box uses twice as much (16.5 W)
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Posted October 1, 2011 by mayakey in energy use, home

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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.

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

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Calculating Baseline Energy Use   1 comment

The easiest task in a personal home energy audit is to analyze electric and gas bills to observe patterns. If there’s a time of year, like spring or fall, when for an entire billing cycle neither cooling nor heating is needed than it’s pretty easy to determine an average typical non-HVAC daily and annual energy use. Then it is pretty easy to subtract and  determine how much cooling and heating increase energy demand during the appropriate season. It’s a rough calculation, since there may be seasonal fluctuations to the “typical” energy demand like more lights on during winter, but it’s a good start. I calculate that we typically use 10-11 kWh per day non-HVAC, which comes to 3,840 non-HVAC kWh over the course of a year (65% of total). Heating required approximately 990 kWh for the year (15% of total), and cooling required approximately 1,200 kWh for the year (20% of total).

The next task is to break down that “typical” energy use a bit, but this requires a bit more effort since you have to read the meters. Reading the meters isn’t challenging, especially now that digital smart meters are being rolled out. I hear that some utilities are already using the smart meters to provide customers with real-time tracking ability from their computers, but walking into the back yard and reading the meter really isn’t much work. There are a few different strategies for meter reading schedules. You can read it once per day to get a feel for your real “typical” energy use and the fluctuations, you can read it twice per day to differentiation baseline and active use, or you can read it many times per day to track specific appliances.  The latter is what I did last time I did a home energy audit, and it is a BIG PAIN! So this time I have a Kill-a-Watt to do the measuring for me, and we did twice per day readings. For a couple of weeks I read the meter immediately before going to bed, and Mike read the meter as soon as he got home. During that time there was very little active use of electricity: a toaster or blender for breakfast, a brief light on in the pre-dawn, and the garage door. I consider those to most likely be negligible over the 15 or so hours of baseline energy use. What I mean by baseline is the stuff that is always on: refrigerator, cable box, thermostat, etc. It’s the baseline because even if you eliminate all active energy demand the house will still draw this baseline amount. It’s relatively constant, with minor fluctuations like water heater working harder in winter and fridge in summer. So now I know that our baseline home energy use is approximately 4.8 kWh per day, which is almost half of our typical daily energy usage.

There’s very little that I can do to reduce that baseline energy usage. I’m not getting rid of the fridge or the alarm, and while I would love to turn off the cable box I can’t without breaking it. What I want to know is how much of that baseline goes to the water heater. By using the Kill-a-Watt I’m measuring as many of these baseline contributors as I can and then I’ll be able to calculate an estimate of how much hot water contributes to our energy usage. My guess is that it is most of the baseline.

Posted September 2, 2011 by mayakey in energy use, home

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Long Term Household Energy Profile   Leave a comment

The first thing that I did as part of my personal energy audit was update my household energy usage log. Since 2005 I’ve meant to get into the habit of logging gas/electrical usage when I pay the bills the same way I log gasoline usage after I enter receipts into Quicken. However, I just never got around to it. After spending a couple of hours entering in six years worth of data, I think I’ve received the appropriate self-kick in the butt and will start dutifully logging each month from here on out. This is one step to the audit that is really easy to skip by just logging onto your gas/electric account online since I think most companies give you easy access to one or two years of usage in a simple table and/or graph. The benefit of entering it into my own spreadsheet is that I can play with the data. For instance, at the old house we did have gas, which was billed in therms. Using my spreadsheet I can really easily convert therms into kilowatt-hours and add them together. It was actually astonishing when I did that because 1 therm is approximately 29 kWhr, so the blips for summer cooling almost disappeared under the magnitude of the winter heating peaks. Another benefit of the spreadsheet is developing a long term profile:

Annual Household Energy Usage Comparison Chart

Annual Household Energy Usage Comparison

 

Analyzing our profile like this provides a lot of good information. For one thing I had been thinking for the last seven years that in Sacramento where it regularly tops 100 degrees in summer and rarely drops much below freezing even at night in the winter it would make more sense to focus on cooling rather than heating improvements. But that is not necessarily true, as the energy used to heat that uninsulated leak-bucket where we used to live dwarfed the energy used to run the two window air conditioners and a passel of fans in the summer. Speaking of fans, the second summer that I lived in Sacramento I went without air conditioning just to prove to myself that I could (I love heat, the question was if I still loved it when there wasn’t a cool room to retreat to). According to my energy profile I used MORE electricity the summer that I DIDN’T use any air conditioning. Granted it’s not a big difference, so it might not be statistically significant, but it does mean that I can absolutely say that turning off the air conditioner didn’t save me anything. I did have a fan running either on/near me or drawing cool air into the house almost every minute that I was home that summer, so apparently a fan can actually use as much electricity as an air conditioner. And compared to subsequent years when my husband (then-fiancee) insisted on air conditioning, I just use less electricity in summer period.

Oh, and not that we needed the confirmation that our new house is better construction/more energy efficient than the old, but the thick black line is the energy usage for the new house. (Note that the August point is for the month we were cleaning the house and not yet living in it.) That graph got a happy dance from me.

I’m curious if anyone else ever studies their long term energy profile like this.

Posted July 27, 2011 by mayakey in energy use, home

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2011 Summer Project: Energy Audit   1 comment

Every summer I do some kind of environmental self-audit or equivalent on a rotating schedule (with interruptions). I started doing this back in 2001 when I was first living on my own after college. I was originally inspired by two things. The first was my participation in a college-wide trash sort. It was the university’s way to prove the effectiveness of measures to promote recycling. So they got a bunch of volunteers, gave us Tyvek suits, gloves, and face shields, and sent us into a room with large sorting tables where bags of garbage from all over the campus were placed for us to sort through. In the end they measured the weight or volume (I don’t remember) of recyclable material for comparison with previous measurements. I was crazy enough to be one of those volunteers. And I learned a lot about American’s trash habits, most of it sad. (That’s a story for another day, though.) The second source of inspiration was a class that I took in which we did one week audits of our direct water and energy usage. These experiences made me realize how useful it is to actually measure and not just guess when it comes to something you want to improve, in this case my “global footprint”. Not only can you be surprised by the results, but it also means that you have a way to see progress, which feels really good.

So that first year I started by doing my own trash sort. I saved all of my trash for a month and then took it down to my mom’s house at the end of the month to sort and weigh. Kitchen waste got weighed throughout the month so that I didn’t have horrible smelling garbage to sort through. The following year I attempted to do a water use audit, during which I realized that human return flow is not insignificant. In 2003 I evaluated the ingredients my personal care products for potential exposure problems. 2004 was when I moved to Sacramento and in the upheaval skipped a year. In 2005 I was able to do my first direct energy use audit. It was quite involved, with me reading my gas and electric meters four times a day on weekdays (when I woke, left for work, returned from work, and went to bed), and before/after any major changes on weekends (like turning on the dryer or taking a shower). I was trying to figure out how to determine my baseline electric and gas usage, as well as electrical demand of the various electrical items in my house. That was mostly not successful. I did get a pretty good estimate of the baseline, though. Since that was also the year I went without air conditioning all summer that baseline does not include air conditioning or winter heating, so it’s what I would consider a true baseline: the measure of phantom energy and structural demand.

This year’s energy audit should be a little easier. I got a relatively comprehensive energy audit done on the house, and I bought a Kill-a-Watt monitor. A Kill-a-Watt monitor is a monitor that plugs into a socket and then measures the electricity usage of anything that you plug into it. This way I’ll actually be able to directly measure how much electricity is consumed by my computer, the TV, the refrigerator, etc. I’ll be using this blog to help me work through this energy audit throughout the summer.

It is worth noting that this is really only a partial energy audit, since I can only measure direct usage. I can’t measure my portion of communal energy usages like municipal (street lights, traffic lights, etc.) or commercial (lighting in my office, air conditioning in the grocery store, etc.). Nor can I measure/estimate the embedded energy in my water, food, and various stuff that I use/buy.

Posted July 25, 2011 by mayakey in conscious living, energy use

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