Energy Manager

HVAC occupancy sensors count occupants and adjust air accordingly

June 18, 2013 - A single advanced building control now in development could slash 18% off the overall annual energy bill of the average large office building—with no loss of comfort—according to a report by researchers at the U.S. Department of Energy’s (DoE’s) Pacific Northwest National Laboratory.

June 19, 2013  By  Anthony Capkun

The report is based on simulations of the impact of one type of advanced building control now available in the building industry: a device is capable of customizing the level of ventilation by sensing the number of people in different areas or zones of a building, then adjusting fan speed and air movement accordingly.

“This is the reason you often feel cold when you’re in a big space like a conference room or cafeteria without a lot of people,” said engineer Guopeng Liu, the lead author of the report. “Technology available today doesn’t detect how many people are in a room, and so air flow is at maximum capacity nearly constantly. That creates a big demand to re-heat the air before it enters the rooms. It takes a lot of energy to keep you comfortable under those circumstances.”

Researchers estimate that advanced occupancy sensors on the horizon—which count the number of people in rooms—will save about 28 times as much energy as today’s occupancy sensors when used both for lighting and ventilation.

The project began three years ago when Liu began exploring the idea of adjusting air flow to different zones of a building based on the precise number of people in a room. That ‘decision’ of how much air to move takes place in a piece of equipment known as a variable air volume terminal box. The new sensors that count people are likely to become available within the next few years.


Since heating, cooling and related equipment usually draw much more energy than lighting, researchers say those systems offer a greater opportunity for savings. The team found that advanced controls for ventilation offer about eight times as much savings as advanced controls for lighting, where lights are turned Off more quickly than is now common after everyone leaves a room. When the HVAC system alone is considered, the advanced controls cut energy usage by nearly 40%.

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