3 facts about plug loads you need to know

October 8, 2013

By Michael Murray

As we say goodbye to the summer, air conditioners are retired for the season. Much of the United States rejoices in that fact, because outdoor temperatures are finally comfortable, particularly for the middle of the country that was ravaged by heat and drought just a few weeks ago. There’s no doubt that turning off those A/C units is great for your utility bills. But unfortunately for your budget, your tenants or occupants may turn to other electricity-guzzling devices for comfort and entertainment as the season changes. These bad habits will eat away at the savings from mild weather.

Reducing non-HVAC power densities in buildings is becoming a difficult task, as illustrated by the American Council for an Energy Efficiency Economy’s (ACEEE) July report on plug loads. Plug loads are the electricity-consuming devices and appliances in buildings that, generally speaking, are plugged into wall outlets, as opposed to overhead lighting or HVAC equipment. The share of electricity usage in commercial buildings that is not associated with lighting or HVAC is set to grow dramatically in the next ten or twenty years. As you consider efficiency efforts as well as utility budgets for next year, consider these findings from ACEEE’s thorough research.

Miscellaneous electric loads are likely to be the biggest impediment to achieving high efficiency / net zero energy buildings.

1) Plug loads (also called miscellaneous electric loads, or MELs) are growing faster than any other category at 2.2% per year. Why? Trends in computing, comfort expectations and energy illiteracy are all to blame. Facility managers at universities, for instance, have long been critical of college students bringing their own small refrigerator into dorm rooms because of the increased power usage over a communal refrigerator, to say nothing of the extra computers plugged in for gaming and file sharing. In office buildings, the energy savings from replacing cathode-ray tube (CRT) monitors with LCDs has arguably been wiped out by the modern workplace’s expectation that each employee should have two to three LCDs instead of one, two PCs, and now an iPad or Android tablet. Efficiency gains are being eaten away by the sheer number of devices.

2.2% per year may not seem like much, but (2) by 2035, MELs will constitute the majority of U.S. electricity use. HVAC and lighting are regulated by building codes, and so total energy used by those categories is projected to remain flat despite increases in floorspace. In the long run, “MELs are likely to be the biggest impediment to achieving high efficiency / net zero energy buildings.”

Perhaps the most interesting contribution of ACEEE’s report is the calculation of potential energy savings. With lighting, humans’ desired brightness level can be satisfied with a set amount of energy, and exceeding that level can lead to glare or discomfort. It is fairly straightforward to calculate energy savings potential from lighting by quantifying the difference between current energy usage and that associated with high-efficiency lighting that meets biologically optimal brightnesses (given the tasks to be completed in a given space). But what is our equivalent biological limit to plug loads? When does the “glare” of plug loads become too bright, reducing comfort or productivity? There does not appear to be a limit. The number of LCD screens, communication devices, music players, and other nifty gadgets can increase almost indefinitely, it seems, without harm. Thus identifying what plug loads are excessive versus those that are necessary in today’s world is anything but objective.

How one estimates potential plug load savings has a large influence on how one thinks about possible solutions. Plug loads can be replaced with efficient alternatives, turned off more frequently, or never purchased in the first place. One’s policy of choice (government-mandated standards, behavioral marketing, or wholesale societal changes, respectively) will vary depending upon one’s assumptions of the effectiveness of each. Government standards’ impact is perhaps the easiest to evaluate, because one can estimate savings from new standards over today’s, and then make assumptions about the timeframe for device replacement (two years for computers, twelve for refrigerators, etc.). But behavioral potential is much more subjective. Plug loads could be eliminated tomorrow if everyone made implausibly radical lifestyle changes (or if there were prolonged power outages). Since neither are likely, one must choose, somewhat arbitrarily, a place on the spectrum of Americans’ behavioral malleability, with no-chance-in-hell cynicism on one side and surely-we’ll-come-around humanism on the other. Skeptics might argue for 0-2% savings; optimists, including some behavioral economists, would argue for a much higher number, perhaps in the 10% to 20% range. (In one compelling example, the city of Juneau, Alaska saw 30% savings after an avalanche knocked out a transmission line, and residents made significant electricity cut-backs in order to avoid rolling blackouts. One wonders if those results can be replicated without needing a natural disaster.)

I tend to be on the optimistic side, but in any event, ACEEE avoided behavioral savings altogether and estimated potential plug load savings by comparing today’s usage to the most efficient, commercially-available alternatives across 20 of the largest MELs. Even though the study’s authors essentially valued the behavioral potential at zero, the potential savings are still tremendous: 47% of plug loads, or more than three (3) quadrillion BTUs (quads) per year (assuming all plug loads are “turned over” to efficient alternatives). (3) A 47% reduction in plug loads is equivalent to saving the power output of all U.S. nuclear power plants, or all Middle Eastern oil imports.

For more information, see ACEEE’s 95-page report, “Miscellaneous Energy Loads in Buildings” (free account required).

Michael Murray