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Results of Laboratory Testing of Advanced Power Strips

Lieko Earle and Bethany Sparn, National Renewable Energy Laboratory

ABSTRACT

The ever-increasing inventory of miscellaneous electric loads (MELs) in U.S. homes

results in wasteful electricity consumption in the form of 'vampire' loads. The emerging

technology class of products called the advanced power strip (APS) seeks to mitigate this

problem via auto-switching capabilities, where supply power is automatically shut off when the

end-use appliance is detected to be in an unused state. These products are relatively new and

untested; as such, there is a dearth of quantitative data on how effective they are at energy

abatement and whether they impact the functionalities of the end-use appliances they serve. For

utility efficiency programs to incorporate plug load reduction via APS, concrete numbers are

required to document cost-effectiveness of the strategy, but this cannot be quantified without first

demonstrating that these devices perform their basic functions reliably. To address this need, we

have conducted a focused study to evaluate the technical performance of APS devices when

subjected to a range of home entertainment center and home office usage scenarios. Guided by

the test specification and minimum functional standards developed by the Northeast Energy

Efficiency Partnerships' (NEEP's) APS Working Group, we have tested 20 currently available

APS products in the laboratory to determine whether each works as designed and what, if any,

actions or habit changes are required for the user. We report on the results of this laboratory

investigation.

Introduction

As increasingly stringent residential building energy codes improve thermal envelopes,

and mechanical system efficiencies increase due to advances in technology and standards,

occupants continue to introduce more and more appliances and electronics into the home,

creating a moving target for plug-load energy reduction. From televisions to toasters, cell phone

chargers to pool pumps, plug loads are as diverse as they are ubiquitous, and as a class continue

to expand their fractional share in the electrical energy budget of the modern American home.

With so many appliances throughout the house, it is easy for busy people to leave things like

TVs and computers switched on inadvertently when they are not in use, resulting in substantial

'active' power waste. Moreover, this increase in miscellaneous electric loads (MELs) also

consumes energy in the form of 'vampire' or 'phantom' loads: many devices continue to draw

current as long as they remain plugged into receptacles, even after the appliances are switched

off (Hendron & Eastment 2006). In a typical home with 40 plug loads, vampire loads can

account for nearly 10% of household electricity use (standby.lbl.gov). Plug-load energy waste is

pernicious; each individual device may require only a low level of power to be in standby mode

(and even less in off mode), so there is little incentive for the homeowner to walk around and

switch off power strips, much less unplug each device that is not in use. Effective reduction of

both vampire and active loads will require a more convenient solution.

Recent years have seen growing interest in quantifying plug-load energy consumption via

sub-metering, and early studies have focused largely on creating an inventory of household

MELs and their associated power draw characteristics for on, off, and standby states to identify

Summary of content (13 pages)

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Results of Laboratory Testing of Advanced Power Strips Lieko Earle and Bethany Sparn, National Renewable Energy Laboratory ABSTRACT The ever-increasing inventory of miscellaneous electric loads (MELs) in U.S. homes results in wasteful electricity consumption in the form of 'vampire' loads.
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savings opportunities (Meier et al. 2008; Porter et al. 2006; Roth et al. 2007). Field test results indicate that typically occupants do not take the time to unplug unused appliances (Bensch et al. 2010). Given these findings, automation seems an ideal solution to curbing vampire loads without interfering with how people use their plug loads. Advanced power strips (APS) may provide the appropriate balance of intelligent control and convenience to meet this need.
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Table 1. Categories of APS Technology Category Control Strategy Current-Sensing Current-sensing power strips monitor the current draw of the controlled outlets to determine when the connected devices are not turned on. Supply power to the controlled outlets is then shut off. Some action must be taken to restore power to those outlets. In an AV setting, an infrared (IR) signal is usually used to 'wake up' the power strip.
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guided by the February 2012 draft of the test specification authored by the APS Working Group. That document is still under development, and the final version will incorporate practical lessons learned from the work presented here.1 For example, the procedures in the current draft consider only a limited number of use-case configurations and the test plan is difficult to tailor to different variations of APS products.
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Table 2. Summary of APS Products Tested ID Brand Model 1 APC 2 Belkin 3 Bits Limited 4 Bits Limited 5 Coleman Cable Inc. Power-saving Surge Protector P8GT Conserve Smart AV Surge Protector Smart Strip Surge LCG3 Wireless Smart Surge Protector SUG7 Smart Strip FMH6-6MS-SR 6 EcoStrip USB Ecostrip 2.
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load and for the power strip at a sample rate of 0.25 Hz, which was limited by the time required for each Modbus query. The approximate time delay of power shut-off and power restore were also recorded. In addition, the standby power consumption of each APS alone (with no appliances connected to it) was recorded using an Ohio Semitronic AC Watt Transducer (GW5106E), which has a superior accuracy level to the CCS system, but was inconvenient to employ for the entire testing program.
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For all of the configurations, the computer and the connected appliances were put through a sequence of power states. Each test set began with all the appliances off. The computer was turned on first, preceded by any action required to wake up the power strip. Then the monitor, printer, and desk lamp were turned on. The power settings on the computer were adjusted for the tests so that after two minutes of inactivity, the computer would enter sleep mode.
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    Start with perfect score of 5. Subtract 1 point for each additional step required in the initial set-up beyond simply plugging the appliances into the sockets (e.g. need to adjust threshold, need to pair with TV remote). Subtract 1 point for each additional step needed to operate the equipment (e.g. waking the power strip by pressing a button before the master appliance is turned on).
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misleading to the user, who may intend to turn off the entire power strip, and instead end up just turning off the TV. In this case it would not be immediately clear to the user that only the TV was turned off. These difficulties resulted in a low usability score for this device. Device 8 has a USB sensor on a tether. Similar to Device 6, the USB failed to recognize when the desktop computer entered standby mode.
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Device 9 is an IR-sensing APS that is intended for AV use. Power to the peripherals is shut off automatically if the APS does not detect a remote control event (i.e. volume change, channel change) over a specified time period, which can be adjusted by the user to be 1, 2, or 3 hours. A green LED light flashes to warn the user when the time limit is approaching. The automation works reliably.
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computer is detected via USB alone. However, using a USB port for power sensing does not reliably detect standby mode for all types of computers. Conclusions and Future Work This work should be interpreted as a snapshot of the state of APS technology, and a first pass at evaluating APS technologies and creating a means for future evaluations. New APS products are continually being introduced into the market, making it difficult to do an exhaustive study.
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Plans for further testing in our laboratory are underway, including expanding the variety of master devices (different computers, different television units, and using the stereo receiver as master), and measurement of actual threshold levels. A possible configuration for the AV environment is to designate the stereo receiver as the master and plug the TV, DVD player, game console, and any other accessory electronics into the controlled outlets.
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Porter, Suzanne F.; Moorefield, Laura; May-Ostendorp, Peter. 2006. Final Field Research Report. California Energy Commission Roth, Kurt; Mckenney, Kurtis; Paetsch, Chris; Ponoum, Ratcharit. 2007. U.S. Residential Miscellaneous Electric Loads Electricity Consumption. Washington, D.C.