Smart Plug Load Controls Integrated With Building Energy Management Systems

Plug loads comprise more than 50 percent of energy consumption in high-efficiency buildings. Applying intelligent controls to turn off plug loads when unused can provide dynamic load reduction and flexibility. Integration of plug load controls with building energy management systems promises additional energy savings and flexibility. The effectiveness of various control strategies is presented, along with the operational lessons that informed their design. During a 3-year period, more than 600 smart outlets in 12 University of California, San Diego office buildings were operated. The attached plug loads consisted primarily of printers, TVs, water dispensers, and copiers. After recording baseline power measurements for a year, the project team defined plug load control strategies for each plug load type and use, and for different risk tolerance levels, because plug load control can potentially be disruptive to daily work. For advanced controls, smart plugs were integrated with heating, ventilation, and air conditioning systems through the campus building energy management system. The team found static schedules to be the least disruptive and most predictable for occupants, resulting in 38 percent and 66 percent energy savings in two field studies for this project. For printers, print server-triggered plug load control produced 86 percent energy savings, the highest of all strategies, with minimal occupant impact. Scheduling of water dispenser temperature controls, based on occupancy measurements, produced 32 percent savings, which can yield a simple payback of 3 years.