“An 18 percent boost in building energy efficiency by modifying a single factor is very, very good,” said team leader Michael Brambley. “The savings were much greater than we expected.”

The report is on a device that is capable of customizing the level of ventilation by sensing the number of people in different areas or zones of a building and then adjusting fan speed and air movement accordingly.

PNNL said that’s a big change from the way most sensor-based ventilation systems operate now: Currently, if there is even a single person in a room, ventilation runs full blast, as if the room is full.

But a room with just a few people doesn’t need nearly as much ventilation as a crowded room. Why have a fan pushing around air for ventilation for 100 people if there’s only one individual in the room?

“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 airflow is at maximum capacity nearly constantly. That creates a big demand to reheat the air before it enters the rooms. It takes a lot of energy to keep you comfortable under those circumstances.”

Current occupancy sensors have helped the nation save significant amounts of energy by automatically turning off lights when they’re not needed. But the team estimates that the more advanced versions still to come — which count the number of people in rooms — will save approximately 28 times as much energy, when used both for lighting and ventilation, compared to current sensors.

The project began three years ago when Liu began exploring the idea of adjusting airflow 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 variable air volume terminal box. The new sensors that count people are likely to become available within the next few years. While they are currently expensive, the technology is improving rapidly and the cost is expected to come down, Brambley noted.

“We undertook this study to try to determine if this is a technology worth pursuing vigorously. The answer, clearly, is yes. Using the number of people in a room as a factor in determining the level of airflow offers great promise for saving energy and money,” said Brambley.

To do its study, the team focused on a prototypical large commercial office building whose footprint is 160 feet by 240 feet — about 80 percent the size of a football field. The model building is 12 stories and also has a basement, giving it a total of about 500,000 square feet. Such buildings in the United States take up more than 4.4 billion square feet.

Brambley’s team programmed the simulation to heat a building if temperatures dipped below 70°F and to provide cooling at temperatures beginning at 75°. Numbers were set back 10° on the evenings and weekends. Occupancy patterns were estimated based on past studies.

In 13 of the nation’s 15 climate regions, the PNNL team estimates that the advanced ventilation control would save at least $40,000 annually for each building similar in size to the one modeled in the study. In two cities, Baltimore and Fairbanks, the savings stretch to more than $100,000 each year, because of the greatly reduced need to heat new air being pumped in from the cold outdoors. Even in the two cities where the savings would be the least, El Paso and Miami, estimated savings come to $33,400 and $23,500, respectively.

“While buildings have gotten much more efficient in the last two decades, there are still huge gains to be had,” noted Brambley.

Publication date: 7/1/2013

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