Computers and Sensors Curb Electricity Use in Buildings

UCSD Jacobs School of EngineeringUCSD research scientist Yuvraj Agarwal has discovered a better way to regulate HVAC systems in buildings using ‘occupancy sensors’. Based on early test results, the software- and sensor-based solution produced electrical energy savings of between 9.54 and 15.73 percent on their test deployment on one floor of a 5-floor campus building.

Buildings account for nearly 40 percent of primary energy use in the United States, and three-quarters of that consumption is electrical—half in residential buildings, half in commercial. Improving the efficency of HVAC systems in commercial buildings is, therefore, a prime target for cost savings.

Gupta, Agarwal and their colleagues had to look no further than the building where they work, and where HVAC systems usually account for between 25 and 40 percent of total annual electricity bill. Like in most commercial buildings, the campus Energy Management System sets HVAC systems on a “static occupancy schedule,” i.e., timed to coincide with standard working hours (for the CSE building, from 5:15 a.m. to 10 p.m. on weekdays). This is done because there is currently no easy and cost-effective way of knowing when individual occupants are in their offices.

To test their system, the UCSD researchers deployed an occupancy sensor network across an entire floor of the building. The sensors detected several periods of low occupancy when HVAC systems were operating at full steam – and therefore wasting energy.

Working with administrators of the campus EMS, the researchers used the real-time occupancy information from each sensor node to turn the floor’s HVAC systems on or off. This so-called “aggressive duty-cycling” of HVAC systems saved energy while still meeting building performance requirements.

The cost of sensors and their deployment is a significant barrier that the team overcame with an in-house design that brought the cost of the sensor to below $10 – one-tenth the price of the cheapest commercial sensor. At that cost, the sensor network can make widespread monitoring and control possible inside buildings.

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