Energy Management Trends: The Power Of Plug Load Management
By Cathy Higgins and Dan Harris, P.E.
From the September 2013 issue of Today’s Facility Manager
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.
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
Approaches to reducing equipment energy use at minimum cost can be grouped into three categories: software, hardware, and people.
Software. Most new devices have been engineered to allow reduced electricity use by switching internal software settings from a higher to a lower power mode; this is an essential step to save energy. The most effective practice is to make sure devices are turned off when not in use for extended periods. Another software related solution is power management controlled at the information technology (IT) department level. There are products that allow for the security and access required by IT staff while automatically ramping computers and monitors down, or turning them off during idle periods.
Hardware. Options here include advanced power strips and timers that automatically control loads after business hours and on weekends. The single largest savings can be the difference between an older device and newer equipment, but changing equipment only for energy efficiency is not cost-effective. When it is time to procure additional or replacement equipment, fms should strive to purchase and install options with the best efficiency reviews. The recent NBI study found very little or no increased cost for the most efficient options5 at the time of purchase.
People. Engaging facility occupants is critical to any effort to impact the energy use of plug loads. Ways to accomplish this include e-reminders, posters, displays, prompts, green teams, and competitions. The information must be simple and easy to understand, with feedback that encourages users to change personal practices that will result in more efficient use of equipment.
One company on the research team, Portland Energy Conservation, Inc. (PECI), decided to meter several floors of its own high efficiency leased office space and initiate competitions aimed at reducing the overnight ratio. This approach netted a 23% reduction in their weekday night ratio and input from staff that having targets helped them engage in the necessary changes. Continued focus on the issue and strong initial participation will ensure a competition event becomes standard practice.
The amount of savings achieved through these combined methods can vary widely, but the study sites showed reductions of 20% to 40% in office equipment energy use. Key to these results were aggressive power management settings, the installation and use of plug strips and timers, and occupant reminders and prompts. Fms can begin with the five “R” steps.
Review: Identify needs, inventory equipment, and focus on devices that use the most energy; this is usually the equipment that is used most.
Remove: Eliminate or unplug unnecessary devices.
Replace: When it’s time to replace, purchase the most energy efficient devices for the job.
Reduce: Turn it off or power it down when not in use.
Retrain: Make sure staff understands why, when, and how to power down.
The increased attention being paid to this source of energy use in facilities is resulting in new technologies, methods, and resources for fms who aim to put plug loads in their place.
1Energy Information Agency; 2008 Annual Energy Outlook.
2Research in conjunction with PECI and Ecova on behalf of the California Energy Commission; 2012.
3Large appliances (refrigerators), water coolers, vending machines, and server closets were not a part of the study.
4Based on the national average cost of electricity at $0.12 per kWh.