Getting to the Bottom of Home Energy Use

July 01, 2011
July/August 2011
A version of this article appears in the July/August 2011 issue of Home Energy Magazine.
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In 1949, according to DOE’s Energy Information Administration (EIA), residential electricity consumption was 5% of total residential energy consumption. By 2009, it was 40%. This rise is attributable to many factors—appliance and equipment saturation, innovations in electronic technology, larger houses, and greater disposable income, among others. According to DOE, end-use electricity consumption will continue to grow as a percentage of total household energy consumption. As electricity consumption grows, so does base-load household electricity consumption—that year-round electrical load upon which seasonal electrical loads, like air-conditioning and space heating, are stacked. Water heating, refrigerators and freezers, lighting, laundry and kitchen appliances, electronics and entertainment devices, pumps, and miscellaneous plugged-in loads are common base-load end uses. All additional electricity use—from occasionally used devices, tools, or equipment; visitors; short-term construction jobs; and so on—is consumed on top of base-load use. And the fervent appetite for new and as-yet-unimagined appliances and electronic devices is expected to climb. Growth is why base-load end use is an important topic.

The most common way to separate a household’s base-load electricity use from its total annual kWh use is to review the last 12 months of electricity use, as shown on the utility bills. You will see that annual electricity use moves in cycles. Some of these annual cycles have only one peak season—a winter peak heating season. Others have two peak seasons—a winter peak heating season and a summer peak cooling season—and two low-use (base-load) seasons, in the spring and fall. To get an average base-load month in kWh, add kWh use for the three or four lowest-use months and divide the sum by the number of months in question. Multiply the result by 12 to get an annual base load for the household.

Benchmarking Base-Load Use

In general, we in the United States consume more electricity than we need to subsist comfortably, compared to the rest of the world. By this standard, most base-load use in the United States could be considered high. However, by other, more complex standards, the answer to whether base-load use is normal turns out to be “It depends.” Fluctuating variables, such as regional climate, house size, number and age of occupants, income level, energy standards, and utility rates, all contribute to base-load use, and to what constitutes normal use for a given household. Various benchmarks can be used to determine a base-load benchmark for electricity use. I often use a regional base-load benchmark calculated using electricity consumption by all households in my region in the Alaska interior. I calculate this benchmark using a publicly available document called RUS Form 7. This document is a monthly financial and statistical report published by the U.S. Department of Agriculture (USDA) Rural Utility Service and updated by the utility. RUS Form 7 provides the information needed to calculate average annual residential use within the utility’s service area.

In 2010, according to the RUS Form 7 of our interior Alaska electric cooperative utility, the average total residential consumption in the service area was 8,026 kWh per household per year, or 22 kWh per household per day. That average includes all electricity use—base load and seasonal—but it provides a general average use profile of the approximately 37,530 residential accounts our electric utility serves.

The calculation that was used to obtain household base-load use can be applied to the utility’s service area base-load use, using the monthly reported numbers. Add kWh use for the four lowest-use months for all residential accounts, and divide the sum by 4 to get an average base-load month in kWh for all residential accounts. Multiply the result by 12 to get an annual base-load average for the region in kWh. In the example given above, the result is 6,677 kWh per household per year, or 18.3 kWh per household per day. This constitutes 82.4% of total residential electricity use (see Table 1).

Table 1: Benchmarking Regional kWh Base-load Use

Any utility in the country should be able to provide the number of residential accounts, the total monthly residential kWh sales, and the average residential consumption across the service area. But based on my experience, base-load end use in a small, dry cabin in the woods in my area could run as low as 2,600 kWh per year, or 7.1 kWh per day. In contrast, base-load end use in a large house with many occupants might run as high as 16,200 kWh per year, or 44.4 kWh per day. Most energy raters intuitively understand which household has high-base-load or above-normal use. However, the person in the cabin is much more likely to wonder why his use is inexplicably high. For him, any small change in base-load use might constitute a large percentage change in total use. Still, on average, my region’s base-load benchmark of 6,677 kWh per year, or 18.3 kWh per day, is an acceptable benchmark.

Choosing a regional benchmark equalizes a few of the variances normally caused by differences in climate, fuel, and utility rates. In addition, my experience as a local resident, housing specialist, and energy rater in the area has made me familiar with different types of houses and different lifestyles. This, too, can help the rater get a good perspective on a particular household’s energy use.

The EIA collects data on electricity consumption in each state. Based on these data, which are available on the EIA web site, you can extrapolate and estimate a statewide benchmark. This is one more way to obtain a comparative benchmark on electricity use, although it may be much broader and less specific than the regional benchmark. For example, Tennessee households have the highest annual electricity use, averaging over 15,600 kWh; Maine has the lowest annual electricity use, averaging 6,200 kWh. However, many factors—including variable seasonal use, different rate structures, and differences in income—may cause large differences in consumption across each state.

According to the EIA 2008 residential electric use data, the average annual electricity consumption for a U.S. residential utility customer is 11,040 kWh. Assuming that space cooling and heating are seasonal, and therefore are not considered base-load use, this gives a national base-load use benchmark of about 8,236 kWh a year, or about 23 kWh per day (see Table 2).

Table 2: National Daily kWh Averages for Base-load Appliances

Auditing, Monitoring, Measuring, and Logging Base Load

The purpose of establishing some base-load use benchmark is to create a starting point in any assessment of a household’s energy use. It is necessary to establish this benchmark because average annual electricity use varies from state to state, from region to region, and from household to household, depending on the wide range of variables mentioned above. In the previous examples, regional utility data reported to the USDA and state and national data collected from the EIA are used to set up base-load use benchmarks. From the examples cited, the base-load use averages range from 23 kWh per day (national) to 19 kWh per day (regional) to 11 kWh per day (my household energy use), which establishes some general guidelines.

Individual household base-load appliance or electronic device energy use can be measured, and the findings logged, to analyze base-load use in even greater detail. Calculating or measuring use and then logging the results for each household base-load device will take time and some math, but it is worth the effort if you want to understand where the electricity is going.

To find out how much power a device draws, look for the wattage rating on the manufacturer’s nameplate, stamp, or label. If no plate or label can be found, DOE publishes lists of typical wattages for various commonly used devices. The wattage printed on the nameplate is the maximum power the device draws. Note that a motor may use up to 3 times more current during startup than it uses when it is operating continuously. After you determine the power of a device, you can calculate about how much electricity it uses by multiplying the kW it draws by the hours the device operates per day. (At best, this last might be an educated guess.) Record this use and continue the audit until you have inventoried all the base-load devices in the house and have recorded electricity use for each. Of course, the most basic, accurate, and affordable monitor we all have access to is our utility meter. Using the utility meter, you’ll probably have to do your own data logging (if you don’t have a smart meter and supporting utility). You’ll need a timepiece, pencil, paper, and a devoted block of auditing time to log the daily differences in use and associated activities to isolate individual energy users, such as the water heater or pumps.

To isolate a particular device or appliance for measuring energy consumption, you can record the kWh over a period of time when you know the device is on, and again over a period of time when you know the device is off. For example, I often tell people who want to know if their water heater is operating normally, and who don’t have an amp meter, to read the meter at the same time over several days. I recommend leaving the water heater on, but don’t distort the reads with additional loads—by using tools, doing laundry, vacuuming, and so on. After several 24-hour reads, open the water heater circuit breaker to prevent electricity from reaching the water heater. After 24 hours take a final meter read before closing the water heater breaker and reenergizing it. This method is not exact, because other devices in the house are using electricity, so the water heater is not isolated. However, if the water heater is working abnormally high, this method may indicate that.

A more accurate auditing method is to measure residential base-load devices with an energy-monitoring tool that records both kWh and monitoring time. Portable plug-in energy monitors are available for 120V plug load devices; they include the WattsUp? PRO and the Kill-A-Watt. The Kill-A-Watt monitor is the most affordable, and you can use it to do the basic first-step measuring to determine many base-load uses in the household.

After you inventory the base-load uses, an approximate household profile emerges that you can compare to the base-load benchmark you’ve selected. This is a starting point for determining what constitutes normal base-load use. Now you can make some broad generalizations, perhaps comparing the base-load use to that of other similar buildings with a similar number of occupants in a similar climate zone and with a similar utility structure. It now becomes easier for you to evaluate whether an appliance or device is functioning inefficiently, or if it can be turned off when not in use. Once you have audited and inventoried the energy use of individual appliances and electronic devices, you can compare the base-load use to the average use listed in several tables and charts available through DOE or local utilities.

The Poster Child of Base-Load Use

Appliances and electronic devices have two price tags. One tag is the purchase price, or the capital cost. The other is the operating cost, which is paid monthly in the form of an electricity bill. The operating cost is always the higher cost. An energy-efficient capital purchase reduces the operating cost and has a faster payback on the capital cost.

The refrigerator is the classic example. As a result, it has become the poster child of base-load use. The refrigerator and its cousin, the freezer, have been singled out for this position because nearly 100% of households have a refrigerator and a freezer. These appliances are always working, and the refrigerator manufacturers and energy efficiency advocates have a long history of working together to improve efficiency standards.

The first step in deciding whether to keep or replace a refrigerator or freezer for energy- and cost-saving reasons is to find out how much electricity the refrigerator uses. The Association of Home Appliance Manufacturers (AHAM) maintains an online searchable directory of energy ratings for refrigerators, listed by make and model number. I have found, however, that the Home Energy refrigerator search site and replacement calculator is easier to use than the AHAM site. You can also use a plug-in power monitor to track electricity use, as described above.

Be aware that variables, like the age or state of an appliance or the conditions under which it operates, can affect data collection and energy use. When I monitored my 1995 GE 20 ft3 top-freezer refrigerator for two one-week periods, using both a Kill-A-Watt and a WattsUP? PRO monitor, the readings were 625 kWh and 655 kWh per year, respectively. Both monitors measured about 15% less than the AHAM energy rating for this refrigerator, which is listed at 745 kWh per year.

Once you evaluate base-load electricity use, open one of the many online energy savings or simple payback calculators available and consider whether a replacement is merited. DOE publishes unit energy consumption standards for new refrigerators and freezers of typical sizes. This allows you to compare an existing unit’s monitored energy use, or its energy-rated use, against what is available to purchase new, using the Home Energy replacement calculator or another tool.

It is useful to know how much refrigerator electricity use contributes to household base-load use (or the regional base-load benchmark). This can help you to prioritize and target appliances and devices for making energy saving changes in your household. My total household base-load is about 4,002 kWh per year (see Figure 1). From monitoring, I now know that the refrigerator uses about 15.9% of that total.

Actively Implementing Lower Use Goals Produces Long-Term Savings
Actively Implementing Lower Use Goals Produces Long-Term SavingsFigure 1. This is my household average daily kWh use per month from 2000 to 2010. It shows the results of focusing on reducing base-load use. Financially, this reflects a respectable rate of return on our energy efficiency and conservation investments.

Whole-House Monitoring Comes of Age

Whole-house power monitors show how much electricity a household uses in real time, and how efficiently it uses it. Some monitors have a wide range of additional functions. I’ve tried several, including The Energy Detective (TED) 5000, by Energy, Incorporated, and the Blue Line PowerCost Monitor (PCM).

The TED 5000 connects to the circuit breaker distribution panel with two current transformers, which are connected to a measuring transmitting unit. This transmitting unit sends a wireless signal to a gateway device that connects to a wireless router and, with TED 5000 Footprint software, allows electricity use to be displayed on a display screen. The software also installs an energy dashboard program that allows use to be displayed on your computer as well.

learn more

National and state statistics are available from the DOE Energy Information Administration, at www.eia.doe.gov.

Rural utility data (RUS Form 7) are available from USDA’s Rural Utility Service, at www.usda.gov/rus.

For average appliance energy use, go to www.eia.doe.gov/emeu/reps/enduse/er01_us.html.

To view the AHAM refrigerator database, go to http://rfdirectory.aham.org/AdvancedSearch.aspx.

For the Home Energy refrigerator search site and replacement calculator, go to www.homeenergy.org/consumerinfo/refrigeration2.php.

The Kill-A-Watt is available from P3 International at www.p3international.com/products/.

WattsUp? PRO is available at www.wattsupmeters.com/secure/products.php?pn=0.

Purchase The Energy Detective (TED) 5000 at www.theenergydetective.com.

The PowerCost Monitor (PCM) is available from Blueline Innovations at www.bluelineinnovations.com.

Both power monitors provide power load data in kWh, electricity use in kWh, and electric costs when you input the rate. Both devices store data and can perform other functions. I use the TED more often, because it connects to my circuit breaker panel. Blue Line’s PCM is good—I like the fact that it provides outside temperature information—but because my meter is located at the limit of reception, I do not get a reliable signal. Sometimes I’ll walk by the monitor in the quiet of the night. I’ll check the TED display and see that the house is silently using 200 watts—somewhere. It must be the red and green lights I see scattered in the dark powering standby loads (though I control many standby loads with power saver strips). From TED data, I’ve learned that the house always has a measured load of 0.1 kW to 0.2 kW. Obviously there is a continuous and uninterrupted subbase that adds to the normal base load; much of this subbase must be standby use or small devices, such as clocks, chargers, and indicator lights. The power monitors can also profile the electricity use of major appliances, like refrigerators and water heaters, and can chart duty cycles.

Online programs, such as Google’s PowerMeter or Microsoft’s Hohm, allow remote monitoring via web sites and track and display near real-time energy use. You can budget for energy use, set reduction goals, project trends, and receive progress reports and feedback via e-mail. Hohm can provide an energy score for the residence and, depending on how many others are participating in the region or the utility, let the user compare energy between households. Price—and time devoted to monitoring use—should help you decide how much you want to spend on monitoring devices. Data-logging and feedback monitors are great tools. I get a daily readout showing where my real electricity use is for the day compared to an allotment that the PowerMeter has calculated based on my historical use and my reduction goals. At the end of the week, PowerMeter e-mails me a progress report. I wish electric use monitors were standard measuring devices inside every house, like clocks, hygrometers, barometers, and thermometers.

Back in my office sits a cardboard box with 45 pounds of locally mined coal. It represents the fossil fuel necessary to generate our region’s residential 22 kWh daily average use. Over the last decade, I have reduced my household average electricity use about 5% each year, deliberately and methodically clamping down on base-load electric use (Figure 1). The reduction has resulted in a respectable rate of return—tax-free—considering that electricity rates have gone up over those years and in light of current economy conditions. Such efforts everywhere—changes in behavior, investments in efficiency—not only save money, but also help lessen environmental impacts and slow the coal trains. It’s may seem hard to halt a moving coal train, but there may be little choice, especially if the tracks stray far from what we seek for our future.

Todd Hoener is an energy specialist and renewable energy program administrator for an electric utility in Alaska.

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