Are Energy Management Systems Cost Effective?

While the market for energy management systems (EMS) has been exploding, there are many indications that the pendulum of high expectations may have swung too far. A simple seven-day time clock can usually provide 80-95 percent of the potential savings of many EMS features. For several hundred additional dollars, a small microprocessor based time clock with features such as automatic holiday and daylight savings adjustments, optimal start, and four separate load stop/start schedules (ventilation, heating, and air conditioning, indoor lights, and outdoor lights) can be purchased which can increase the savings an additional 5-20 percent on most buildings. Owners of multiple building systems or large commercial and industrial buildings can often justify a complex EMS with increased load scheduling capability. However, EMS features such as duty-cycling and demand limiting are usually overrated in their energy savings capability, not only because slowing down the fans can save more energy than cycling them, but also because duty cycling can cause personnel discomfort and equipment maintenance problems. Moreover, any temperature control modifications which save energy can usually be installed without an EMS for less initial cost and with an equivalent energy savings. Additional expenses for EMS features such as temperature monitoring and remote set point adjustment are not usually of value if a building's heating, ventilating, and air conditioning (HVAC) system is operating properly. EMS features such as metering and report logs can be useful diagnostic tools in the hands of a qualified individual, but often they provide data diarrhea.