Understanding energy usage starts at home

Since Catherine and Max have written blog posts about their home heating, I thought I’d start the year with my own, equally geeky, piece on electricity use at home.

Electricity is probably the least salient thing we consume.  When we are buying groceries, gasoline, clothes, or tickets to a ball game, we are aware that we’re making a purchase and aware of what it costs.  But most of us don’t know how much electricity we use — or what we are doing to use it — as we move through life turning things on and off, or having them go on and off automatically.  If you read this blog regularly then you obviously care about energy use.  So, a fine New Year’s resolution would be to get to know your own electricity consumption.  To do so, all you need is $20 and less than an hour of your time.

The $20 is to buy a kill-a-watt, a watt meter that will tell you the electricity usage of anything that plugs into an outlet.  Just get the economy version.  The more expensive ones claim to translate kilowatt-hours to dollars, but they can’t handle complex electricity tariffs like we have in California where price increases with your monthly usage. (Some tool lending libraries also loan them out.  Or you can share one among friends.)  Once you get your watt meter, start plugging it in to everything that uses a plug.

Do the refrigerator first.  That is usually the largest plug load in your house, and often an easy place for efficiency improvement (by either cleaning the coils or, if the frig is old, getting a new one…your local utility is likely to give you a rebate on the purchase).  The nice thing about the kill-a-watt is that it will tell you the elapsed time as well as electricity use for things like refrigerators, which cycle on and off.  Leave the kill-a-watt there for a week and come back to see how much electricity it has gobbled up.

KillaWatt

My Kill-a-Watt measuring energy use of our washing machine (the plug was in a tight space so a short extension cord came in handy).

If you have a DVR, do that next.  You may be surprised at how much electricity it uses, in some cases as much as your refrigerator (if the DVR is oldish and the frig is pretty new).  We don’t have a DVR, but our high-definition cable box (without DVR) draws 15 watts all the time it’s on.  So I keep it on a power strip.

Then do your computers.  If you have a desktop/tower computer, notice how much the flow changes when the screen goes to sleep, cutting power use by half or more.  Then watch what happens if you put the computer into sleep mode (from which it wakes up much more quickly than a full shutdown).  If you use a laptop, you’ll see the same effect, but scaled down by more than 50%, so you can feel virtuous.

But so far we haven’t touched some of the biggest electricity hogs, things that don’t plug in (or the plug isn’t a standard 110v type that the watt meter is built for): furnace fan, air conditioner, stove, hot tub. (Yes, I cannot tell a lie.  I have a hot tub…and really enjoy it.)  The watt meter won’t help on those, but if you have a new smart meter, you can probably figure these out with the help of a friend.  Many of the new smart meters show, among other things, the real-time energy flow through the meter.  On the PG&E smart meter that I have, one area of the readout flashes different metrics in sequence.  Here’s a picture of my meter when it was showing that my house was using 1.45 kilowatts.

SmartMeter2

So, standing at the meter, have your friend turn on the A/C or the furnace fan or whatever you’d like to measure. Then, watch the change in the real-time readout.  (This isn’t as helpful for things that have uneven power use such as an electric water heater, which, if you have one, is probably the largest single source of your electricity use.)   Here’s what I found out:

Washing Machine: 0.12 kWh per load (using the kill-a-watt)

Electric dryer:  5500w (a good reason to use the drying rack, as we do for most things)

Furnace fan: 670w (that explains why our electric bill goes up when we run the gas furnace more)

A/C: 4700w (hardly ever use it where we live Orinda, so not a big problem)

Hot tub pump: 100w (but it runs all the time…probably worth putting it on a timer)

Hot tub heater: 6000w (we keep it off most of the time…luckily)

We are generally into the third tier on PG&E’s pricing, which means an incremental kilowatt-hour costs 32 cents.  So, that extra load of laundry costs about 3 cents in the washer, but running the dryer for 45 minutes costs about $1.32.  The dryer is nearly 20 years old, so we’ll have to replace it sometime; might be worth running a gas line and switching to gas, though I favor just using the drying rack more.  Heating the hot tub for an hour (which it takes if it hasn’t been used for a few days) costs almost $2.  I still don’t know how much gas my furnace uses when it is on for an hour (that’s next on my list), but the electricity it uses costs about 21 cents per hour.

You might be surprised at how expensive it is to use your appliances or, probably just as likely, surprised at how cheap it is.  Putting my computer into sleep mode (2w) at night saves about 11 cents a night compared to leaving it on with the screen off. Easy way to save money or hardly worth the hassle?  Or worth doing for the environment even if the savings are puny? You can decide for yourself.

Whatever you decide, as an energy researcher, policy maker, industry participant, or just someone interested in energy issues, becoming an informed consumer yourself is an important step towards understanding household energy use more generally.   I bet it will change your view of your own energy consumption and of public policy.

ADDENDUM: Writing this blog post prompted me to figure out the gas meter attachment that PG&E installed when they put in the smart electric meter.  The gas meter is analog dials, but pretty easy to read.  When our furnace is running, I figured out it uses 1.25 cubic feet per minute or 75 cubic feet per hour.  Our incremental (second tier) rate for natural gas from PG&E is $1.32 per hundred cubic feet (which is more than double the actual commodity cost of natural gas, but that’s a different subject), so running our furnace costs about $0.99 per hour for gas.  Adding in the $0.21/hour for electricity makes the total cost of the furnace running $1.20 per hour.  That still doesn’t tell me what it costs to keep the house heated to 68 degrees instead of 66 degrees, but it’s a step in the right direction.

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8 Responses to Understanding energy usage starts at home

  1. Grey Staples says:

    Interesting breakdown of costs … and not information the Nest or Home Energy Reports would easily provide. That said, there are an increasing number of outfits that claim to be able to tease information about individual electricity loads from smart meter data. I wonder about their accuracy but “smarter” appliances purport to do the same … just not sure when these will be mainstream (if ever).

  2. David Jacobowitz says:

    Severin, the dollar savings you’d get from switching all those electric heating appliances to gas is pretty straightforward (assuming you use them enough).

    I’m curious what you think the carbon impact would be?

    If you think of the marginal source of electricity in CA being, say, a 8000 btu/kWh machine, and ignoring transmisison, distribution, and potential efficiency differences in electric and gas appliances, and I’m sure a bunch more variables, then it’s a no-brainer that using gas-generated electricity to make heat is more than 2x the carbon of burning the gas at home to make heat. (I assume also these are all resistance heaters, not heat pumps.)

    However, you’d be making a decision about converting “permanent” loads, not whether to switch on your heater at some instant, so maybe the relevant comparison is the type of generation capacity being installed at the margin, not the current source of energy at the margin? In CA, for the time being, that’s mostly renewables. In which case you could be doing the world a (very small) favor by sticking with your electric appliances.

    • Another factor to consider when switching to gas for heating air and water and cooking is peak load issues. People cook around dusk and dawn. People bathe around dawn or at night. Furnaces run mostly at night. This is exactly the time that electricity sources like solar pv and wind are least able to deliver. So gas might still be a better choice for furnace, water heater and cooking.

  3. Pingback: Cap-and-Trade Throws a Wrench into the Gears of Green Consumerism | Energy Economics Exchange

  4. John Proctor says:

    Severin, you need a BPM motor for that furnace.

  5. Stephen St Marie says:

    I got a surprise from my basement dehumidifier. I connected it through a Kill-a-Watt for a full week and found it consumed 50.72 kWh. That translates to 217.4 kWh over a 30-day billing period. If all of that service were billed in the third tier, the cost would be about $70 per month. Wow!

  6. Howard Chong says:

    Great post. It challenge my students to think of things in terms of money (or carbon), and not just in the feel good aspect.

    A new fridge uses about 800 kWh in a year, or about $240. But the incremental savings of an energy star fridge may not recoup the cost. And the increased cost does include things that themselves take more energy to create (better compressors, etc.)

    For clothes drying, here in the rural NorthEast, my marginal electricity cost is about 10c/kWh. So the 55cents saved on line drying isn’t worth it for almost everyone (on purely economic grounds). Make it 30cents and the $1.65 makes it reasonable. (Also note the geographic variation: you can’t do this in humid places like the South.)

    For America’s most popular environmental activity, recycling, the cost savings are even more unlikely to be the best use of time/mental energy. The private costs savings of decreased garbage are miniscule. Then the materials must be transported; this kills the economic viability of many programs of heavy, low value materials that are not near recycling plants.

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