Energy Management Trends: The Power Of Plugs.


Energy efficiency efforts in commercial facilities have historically by TFM.

Publicado por FAMASE el 07/10/2013 (ENG)

Energy efficiency efforts in commercial facilities have historically targeted lighting, heating and cooling systems, water heaters, and major appliances. Today’s office worker uses an ever growing suite of electronic devices, all drawing power and running up the utility bill. Gone are the days when equipment was simply turned “on” or “off.” Instead, modern electronic equipment operates in a variety of power levels, or modes.

Plug loads—items plugged into outlets by the user—are the fastest growing energy use item in commercial buildings1 and can represent as much as 50% of the energy use in an office building where other efficiency improvements have already been accomplished. Recent research led by New Buildings Institute (NBI)2 sheds light on office equipment3 energy use and savings strategies for cutting plug load impact.

Where’s The Waste?

Office equipment energy use naturally varies somewhat between facilities, but the lion’s share—95% of the total energy use of the loads studied in the NBI research—is typically concentrated in three areas: desktop computers, imaging equipment, and monitors, with desktop computers being the largest proportion at 69% (see Chart 1).

The research team metered hundreds of individual devices both before and after applying energy saving strategies. The metering disclosed key aspects of the energy use. In a small Oakland, CA office, 65% of desktop computers were often left operating overnight and on weekends (see Chart 2). Even at the best performing (most efficient) offices, nighttime energy use was as much as 50% of day use (this is referred to as the night ratio, so lower is better). For a “normal” office, the night ratio number is closer to 75% or 80%. The same is true when comparing energy use on workdays to non-workdays (Saturdays, Sundays, and holidays). These trends confirm a substantial amount of 24/7 plug load usage compared to plug loads that switch off or power down significantly.

Metrics Matter

To get a handle on plug load energy use, facility managers (fms) need to start with some base metrics. The most common energy use metric for plug loads is watts per square foot (W/sf) of space.

In standard design, it is not unusual to find 4 to 6+ W/sf specified while actual use is found to be less than 1 W/sf; high performance buildings have lowered this to .25 to .50 W/sf. When combined with time, this becomes the measure of energy consumption expressed as kilowatt hours (kWh).

Office space annual plug load energy usage ranges from around 1.0 to about 10.0 kWh/sf/year, so the average range of costs for the plug loads can be from $0.12/sf to $1.20/sf.4

Specified wattages for many items have changed in recent years, and overall office specs have evolved:


Typical Specification: 4 to 6 W/sf

Actual measured loads in 1990: ~<1.5 W/sf

Actual measured now:  <1 W/sf

Actual best practices possible now: .25 W/sf

Computers, a major contributor to plug loads, have also undergone changes.

Originally: 300+ watts

Early 1990s: 120 watts

EPA labeled mid-1990s: 75 watts/12 watts in sleep mode

Laptops now: 15 watts

Mini Desktop: 2 to 8 watts

Published and Graphics by TFM


>> Ver todas las noticias