Reducing Plug-Load Energy Waste
- By Dr. Heidi Perry
- April 1st, 2011
When a school’s administration decides to tackle energy efficiency in the school building, they look first to lighting and HVAC systems to reap potential savings. These systems are the first target of most whole-building energy efficiency projects, but one major opportunity for savings is often overlooked — electricity wasted by plugged-in appliances. Even as major strides are made in more efficient lighting systems — utilizing CFL or LED bulbs and smart automatic switching — and in innovative low-energy heating and cooling systems, the quantity of electronics and other plugged-in devices is expanding rapidly.
Despite the rapid escalation of the number of electronic appliances and gadgets in use, the amount of energy used by these plugged-in appliances is often overlooked in energy efficiency plans. Plugged-in appliances are generally controlled by, and often brought in by, the occupants of the space and are out of the control of the owner and facilities manager. Additionally, appliances are often not considered to be a source of major savings because the energy use by a single appliance is small compared to the overall energy use of the building.
However, while the energy use of each individual appliance may be relatively small, the cumulative use of all the many plug-load appliances in a school building adds up. From the computers and smart boards in the classroom to the vending machines in the cafeteria and the copiers in the main office, these appliances are quietly using electricity at all times. During the school day we depend on these appliances to support the educational mission of the school. We expect them to be on and ready to use when we need them. What we are not always aware of, however, is how much energy these appliances are using when we don’t need them. Overnight and during weekends and vacations, all those appliances and electronics continue to use energy.
The energy drawn by appliances when not in use can be significant — in some cases up to 90 percent of the energy drawn by an appliance is used in standby mode, when the appliance is not being utilized. For example, consider two major energy wasters common in our schools — desktop computers and vending machines.
Desktop computers are rarely turned off overnight, and often do not have power-saving features enabled to put them into low-energy sleep or hibernate modes. Depending on the age and functionality of the computer, a CPU can draw an average power of 30-125 watts, all the time, whether being used or not.
Vending machines that dispense beverages are constantly running compressors to keep the drinks cold. These machines can use up to .3 kWh per hour, or 2,600 kWh per year. Water and soda are not harmed by coming up to room temperature, so there is no reason to keep the beverages cold when the school building is closed. If the building is only occupied during the day and not on weekends or holidays, 50 to 70 percent of the energy used by the vending machine is completely unnecessary.
Appliances with energy-saving standby modes may not be as big offenders as the desktop computers and vending machines that use the same amount of energy all the time, but they can still be major energy wasters. Large copier/printer/scanner multifunction machines enter stand-by mode in periods of non-use, but the average power in this mode is about 30 watts — still a significant power draw. Even appliances turned off by conscientious users may still be using energy all the time. This constant power draw, known as “phantom load” or “vampire power,” is used to power always-on features such as remote control sensors, digital clocks and display lights; but it is also sometimes completely wasted, such as by battery chargers left plugged in when the battery is already fully charged.
Unlike a light bulb left on in an empty room, glowing bright and obvious, the energy wasted by appliances is less visible. Instead of ignoring this invisible waste, a group of schools in New York City are using this overlooked energy sink as an educational opportunity for their students. An inter-disciplinary group of teachers from five schools around New York City have come together along with their students to measure the amount of energy used by appliances around their schools. Their goal is to make the energy wasted by plug-load appliances tangible to the students in order to shed light on which appliances are the most energy-intensive and to find which are the most energy efficient appliances by comparing the data across schools.
This interschool energy project employs a modlet to measure the power used by appliances in real-time. The modlet modernizes the electric outlet that is comprised of a two-socket outlet that measures in real-time the power drawn by plugged-in appliances and communicates the data wirelessly to the user’s computer. The data can be viewed graphically within the modlet’s power manager software or downloaded for further analysis. After initial baseline measurements, the modlet can be utilized to save on standby energy by automatically cutting power to appliances during periods of non-use.
The students find the visualization of the energy use enlightening. One student noted, “Before seeing the data, I thought that appliances plugged in and turned off used very little energy. But they waste a lot!”
Engaging students in learning about energy waste is a great opportunity to integrate energy efficiency goals with the educational mission of the school. The lessons being learned in the interschool project will translate to energy savings. The students’ and teachers’ new awareness of energy leaks by idle and unused devices will translate into energy saving behaviors — once they are aware of how energy is wasted, they are more likely to hit the “off” switch on the way out of the room. This will have a lasting impact far beyond the classroom.
Dr. Heidi Perry is director of Sustainability at ThinkEco in New York City