Determine if smart power strips are cost-effective. Many buyers base their purchase decision on a simple visual observation that office equipment is left on longer than necessary. But to determine whether an investment in this type of equipment will really be cost-effective, you can monitor particular groups of equipment to see how much power they draw, how many hours they are left on, and how often they could be turned off. Several companies now offer standalone devices for measuring plug load power draw. Data from this type of device can be combined with a sensor to track energy usage and occupancy and estimate the savings that can be achieved through control of plug loads. Energy loggers can also be used to determine office equipment power draw and time of use. Once the equipment power draw, times of use, and occupancy schedules are known, a simple calculation (see sidebar) can be performed to determine the payback period of a smart power strip.
Alternatively, some newer Internet-connected smart power strips have built-in energy-tracking functionality. In certain applications, it may be economical to purchase a small number of this type of power strip, use them to identify the best applications, and see if it makes sense to purchase more to control the various plug loads in the facility.
Pick the right control strategy. Smart power strips equipped with ultrasonic or PIR occupancy sensors will work in a typical office setting if they are installed correctly. However, each type has limitations. Ultrasonic sensors are more sensitive to movement than PIR devices, but they’re also more prone to false triggering; PIR sensors experience dead spots but are generally a better choice in a typical workstation where the line-of-sight requirement of a PIR sensor can be easily met. Strips that use equipment power monitors or timers may require less effort to install initially and might be a better solution in areas where a number of plug loads interact with each other in some way (such as computer peripherals), in spaces with low occupancy, where a usage schedule is well established (for example, a water cooler that can be turned off every night), or in areas where frequent foot traffic might lead to false triggers with occupancy sensing.
The National Renewable Energy Laboratory report, Plug-Load Control and Behavioral Change Research in GSA Office Buildings (PDF), shows actual measured savings from smart power strips. Researchers compared timer-based, load sensing, and combination approaches and their overall performance across several federal buildings (Table 2).
Table 2: Electricity use reduction by device type for three different control types
Energy reductions from smart power strips can be highly variable depending on building specifics and behavior. Total average savings across equipment type and with varied approaches were about 27 percent.
Interestingly, the study found that schedule timer controls often outperformed load-sensing controls. The small negative savings could be attributed to normal usage variation coupled with disabled or broken load-sensing controls.
Consider Internet connectivity. A variety of products now feature the ability to connect to a Wi-Fi network. This allows users to adjust control settings and on/off schedules through a web portal while also monitoring real-time energy consumption. For facilities managers, this can offer a significant benefit because all the strips in a facility can be set up and monitored from a single location. These units also tend to have built-in power sensors, which can help identify plug loads that may yield the largest energy savings, provide a straightforward way to track actual energy savings, ensure persistence of savings (since a facilities manager can easily see if any smart strips have been unplugged or otherwise adjusted by employees), and open the door to employee engagement and awareness efforts. Although Internet-enabled smart strips can be around 2 to 5 times more expensive than nonconnected smart strips, the unique benefits they offer may nonetheless make them worth considering for many facilities.
Optimize occupancy sensors. Some smart power strips come with small-range occupancy sensors that only sense a presence in the workstation; others cover a wider area and detect the presence of people in the office around the workstation. Choose the latter if you want equipment to turn off less frequently and turn on sooner.
As is the case for wall- and ceiling-mounted occupancy sensors, the sensors that come with smart power strips are easily visible and can potentially be improperly adjusted, stolen, vandalized, or fooled into perceiving a human presence when a space is unoccupied. For continued energy savings, take the following precautions:
- Involve building personnel in planning for the sensors.
- Train maintenance personnel and office occupants to keep sensors operational rather than disconnecting them when problems occur.
- Position sensors carefully so that they only see the area that you want them to see; the biggest cause of false triggering is incorrect sensor positioning.
Pick a product with an adjustable time delay. Smart power strip products may come with either adjustable or factory-set time delays that determine how long a period of nonoccupancy or inactivity must be before the equipment is turned off. A product with an adjustable time delay allows you to customize the device to suit individual work habits.
Target devices with large plug loads. Large plug load devices such as vending machines, mini refrigerators, and water dispensers will contribute the most energy-use reduction when plugged into a smart power strip.