The biggest energy load in most houses is space heating. When it comes to electricity, the list of major loads usually includes air conditioners, water heaters, and lighting.
Almost all other residential electrical loads are usually categorized as “plug loads.” According to a paper by Sam Rashkin, Glenn Chinery, and David Meisegeier, “plug loads are the fastest growing energy load in the residential sector.”
A grab bag of devices fall into this category, including televisions, set-top boxes, DVD players, music systems, computers, doorbells, alarm systems, toasters, coffee makers, hair dryers, garage door openers, and rechargeable tools. (Some, but not all, energy researchers include major appliances — refrigerators, clothes washers, clothes dryers, and dishwashers — with plug loads; others consider appliances to be a separate category.)
Appliances are easy
Designers of net-zero-energy homes are obviously interested in reducing electrical loads to a minimum. When it comes to major appliances, the task is fairly simple. For example, here are the steps required to minimize electrical use for a refrigerator:
- Convince the homeowners that they need no more than one refrigerator.
- Convince the homeowners to choose a relatively small refrigerator — ideally, not a side-by-side model, and ideally, one without a through-the-door ice-cube dispenser.
- Specify the most efficient available refrigerator that barely meets the homeowners’ size requirements.
Over the past couple of decades, appliance manufacturers, prodded in some cases by the federal government, have done a fairly good job of improving the electrical efficiency of most appliances. Anyone who wants to buy a really efficient air conditioner, refrigerator, or clothes washer can go out and buy one.
Losing the arms race
When it comes to plug loads, however, we are losing the arms race. For the most part, plug loads are not regulated by current energy codes. It’s discouraging that (for a variety of reasons) the average house built in the 1990s uses 17% more energy than the average house built in the 1980s and 18% more than one built in the 1970s.
While energy experts and regulators may direct their focus for a time at a particular device — televisions, for example — Chinese manufacturers continue to churn out dozens of inexpensive new gadgets that end up stacked to the ceiling at the local Wal-Mart. Unwary shoppers who stop by a megastore to buy school supplies for their kids have to pass a display of refrigerated wine-coolers on the way to the cash register — “only $99!” — and soon the struggle to keep down plug loads is lost.
The problem with a new $99 refrigerated wine cooler, of course, is that after a few years on your kitchen countertop, the cooler has used more than $99 of electricity. And the gadget is just one of dozens of items plugged into wall sockets throughout your home, from the electric toothbrush in your bathroom to the iPod recharging under your kid’s bed.
The plug-load problem is compounded by the fact that many electrical gadgets use a significant amount of electricity even when they are “off”:
- Televisions, set-top boxes, and DVRs stay warmed up constantly, waiting for someone to push a button on one of the remotes that fell between the seat cushions of your sofa.
- Recharging units keep humming long after the attached appliance is fully recharged.
- “Wall cubes” — those small transformers that convert 120 volts AC to 6, 9, or 12 volts DC — draw power 24 hours a day, as long as they remain plugged in.
Each year, average plug loads and standby loads have been creeping higher. Rob Dumont, an old hand at designing energy-efficient houses, measured the phantom loads — that is, the electrical loads when devices are turned “off” — at a near-zero-energy house (the Factor 9 house) in Regina, Saskatchewan. The loads were significantly higher than expected; for example, the home’s wireless router/modem consumed 10 watts when “off.”
Dumont’s measurements were reported in the October 2007 issue of Energy Design Update: “Although these appliances were all chosen with energy efficiency in mind, Dumont discovered that phantom loads in the Factor 9 house are drawing 65 watts, or 569 kWh per year. These loads amount to 10% of the anticipated annual electricity consumption required for the home’s appliances, lights, and miscellaneous electrical devices. Dumont points out that the phantom loads in the Factor 9 house are 73% higher than those reported in a 2001 Canadian study, “Stand-by Power Requirements for Household Appliances” (Aulenbach, Fung, Ferguson, and Ugursal), which determined that the average Canadian house had annual phantom loads of 329 kWh.”
Designers of net-zero-energy homes face a Sisyphean task
Paul Norton and Craig Christensen, two researchers from the National Renewable Energy Laboratory, reported monitoring data from a near-zero-energy house in Wheat Ridge, Colorado. “The energy used for space heating, water heating, and lighting has been dramatically reduced through superinsulation, passive solar tempering, solar water heating, compact florescent lights and other efficiency measures,” they wrote. “The energy used in the home is now dominated by appliance and plug loads determined by occupant choices and behavior. These loads constitute 58% of all the source energy used in the home. Because these loads are generally outside of the control of the home designer and vary considerably with different occupants, sizing a PV system to achieve zero net energy performance is challenging.”
A similar conclusion was reached in a report titled “Appliances, Lighting, Electronics, and Miscellaneous Equipment Electricity Use in New Homes” by Richard Brown, William Rittelmann, Danny Parker, and Gregory Homan. “Historically, most of the energy consumed by the U.S. residential sector has been for space heating, cooling, and water heating – what we call the ‘traditional’ end-uses. The ‘Other’ end-uses (appliances, lighting, electronics, and miscellaneous equipment), however, have grown to the point that they account for over half of residential electricity use (major appliances: 24%; lighting: 18%; miscellaneous equipment: 14%) and about 40% of total residential primary energy consumption. Moreover, miscellaneous energy is the fastest growing end-use in U.S. homes, projected to more than double in the next 20 years.”
The researchers continue, “We find that even homes designed for reduced whole-house energy consumption still have significant electricity consumption by the ‘Other’ end-uses, accounting for 60% of whole-house electricity use in low-energy houses, on average. For one low-energy house with more detailed sub-metered data, ‘Other’ electricity consumption is fairly evenly split between plug loads, lighting, and appliances.” Elsewhere in the same paper, the researchers report that plug loads represent “a significant barrier” for anyone hoping to design a net-zero-energy house because “$20,000 to $30,000 worth of PV capacity would need to be installed just to offset the consumption of miscellaneous devices.”
Don’t give up
Energy-conscious consumers can begin to tackle the plug-load problem, but any such campaign requires discipline. The necessary steps include:
- Make a ruthless inventory of your current plug load situation.
- Eliminate unnecessary appliances.
- Put as many gadgets as possible — especially gadgets with wall cubes — on power strips so that the devices can be easily disconnected.
- Avoid the temptation to acquire new electrical gadgets.
- Get your kids on board with the program.
There are no simple solutions to addressing our plug-load problem on a national scale. The two best solutions are stricter national efficiency standards for small appliances and rising energy prices. It seems to me that the latter solution will probably occur first.
Martin Holladay’s previous blog: “Designing a Good Ventilation System.”