Restrain Rising Plug Loads

01/01/2016 |

These loads pose different challenges than central energy loads

Energy efficient workstation

Low-Demand Workstation

In the quest for whole building energy efficiency, FMs cannot ignore plug loads, which account for a growing share of commercial building consumption. These loads pose some different challenges than those of central energy loads like lighting and HVAC.

The Department of Energy (DOE) reports that plug loads are rising at roughly twice the rate of total building energy use. By 2030 they will increase some 49% while other building loads will increase only 24%. The projection is based on increases in the number of plug-in devices and their energy intensity. Plug loads currently represent 33% of commercial building energy use.

What tools and techniques do FMs have to roll back these loads?

Procurement Practices
A clear starting point is being rigorous about unnecessary and inefficient equipment. “If you’re going to bring in new equipment, be sure that you need it and don’t have other alternatives,” says Cynthia Putnam, Project Director of the National Building Operator Certification Program at the Northwest Energy Efficiency Council (NEEC). For example, if a single printer/copier can be shared among more users instead of purchasing an additional one, energy usage would likely be less. When new equipment does become inevitable, efficiency should be a factor in the purchasing decision.

But once the equipment is installed, the focus moves to the individuals who directly operate – and share – the equipment. Because shared equipment has no particular “owner,” equipment like printers and copiers are often operated inefficiently and have some of the greatest potential for savings.

Initiatives to promote occupant awareness and acceptance are key. To improve energy management, the NEEC operator certification program has increased its focus on how to communicate effectively with occupants, Putnam says.

A tactic that helps with communication is selecting a facility “plug load champion” who coordinates communication with occupants and managers. (See “Six Steps to Good Plug Load Management” at left.)

Submetering Connects Users to Their Usage
Submetering is a vital tool to encourage users to recognize their usage and change their behaviors. It accommodates benchmarking and continuous monitoring that gauges outcomes and provides feedback.

Submeters vary in cost and complexity. Simple units measure instantaneous power and cumulative energy but require manual reading and recording of the data on the instrument. More advanced submeters measure and record interval data for manual download by the user. The most advanced units send interval data automatically to remote locations, where it can be used in building management systems.

Power Strips That Control and Monitor
Both metering functions and power control can be provided by a single device – advanced power strips (APS). APS have metering capabilities that allow users to quantify the power usage of each plugged-in device. They can also supply data to web-based dashboards where users can control power remotely and FMs can monitor usage across a facility. Some APS can control plugged-in devices by a preset schedule or occupancy sensors. Others turn off power if a device draws more than a preset threshold.

The Center for Integrated Design (CID), part of the Department of Architecture at the University of Washington (UW), has investigated and implemented APS. According to Heather Burpee, Research Assistant Professor and Director of the CID’s UW Discovery Commons, the CID has used APS outfitted with wireless bridges. Each of the four ports in the APS has its own IP address so that the energy usage of each plugged-in device can be tracked remotely through a web interface.

The APS usage data has helped the department to identify energy hogs, which Burpee says includes some printers/copiers that reduce power by only 20% in standby or hibernation mode. As a tenant in Seattle’s Bullitt Center, the first office building to earn Living Building certification, the CID has a lease requiring it to use no more than 5 watts per square foot for plug loads, lighting and servers.
Another user of APS is the Naval Facilities Engineering Command, which deployed off-the-shelf devices at workstations, print rooms and break rooms of a 100-occupant office building. The strips cut power according to a user-defined, preset schedule. A report prepared by NREL on the NAVFAC application found that plug loads were reduced by 28%, which represented 8% of the office building’s total consumption.

How to Use Advanced Power Strips (APS) in an Office
Each APS has three outlet types for equipment with various electricity needs:
Primary Outlet

The primary outlet acts as the “control” or “master” outlet because it turns off the power to secondary outlets when the device connected to it is turned off. The primary outlet typically powers your computer’s central procesing unit because most other devices connected to the power strip at an office desk depend on your computer for their functionality. For example, you need to turn on your computer to use your monitor and print documents.
Secondary Outlet
Monitor, printer, desk lamp

The secondary outlets act as the “controlled” outlets and typically power peripheral devices, such as your computer monitor(s), desk lamp and printer. When the device connected to the primary outlet is turned off, the power will automatically be shut off to the device connected to the secondary outlets. For example, turning off your computer automatically shuts off the power to your monitor or printer. The amount of energy you save with an advanced power strip depends on the energy usage of the devices connected to the secondary outlets.

Always-On Outlet
Landline phone, fax, mini fridge

The always-on outlets are not controlled by the primary outlet. Important office desk devices, such as landline phones and fax machines, that are plugged into the always-on outlet will recieve constant power regardless of the primary outlet device.




Source: NREL

Best Practices for Power Strips
Among the report’s recommendations is that users not be allowed to program devices by themselves, as this practice leads to devices that are uninstalled or installed incorrectly. Training and occupant buy-in are critical, and occupants should be informed about how the APS system works, how to schedule devices and how to override them. It is also important for implementers to anticipate off-hours software updates that require overriding APS schedules.

A GSA study of plug loads and behavioral change found that schedule timer controls on strips provided more energy savings than load-sensing controls. The study also advised that once plug strips have been implemented, checkups should be done to ensure that occupants haven’t reverted to their previous behaviors.

Federal Resources on Plug Load Management
These resources cited in the article provide more information.

Assessing and Reducing Plug and Process Loads in Office Buildings, a report by the National Renewable Energy Laboratory (NREL).

Plug & Process Loads. Web pages from the DOE’s Better Buildings Alliance program.

Plug-Load Control and Behavioral Change Research in GSA Office Buildings. Prepared for the U.S. General Services Administration (GSA) by NREL.

Reducing Plug Loads in Office Spaces. Produced under direction of Naval Facilities Engineering Command (NAVFAC) by NREL.

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