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Honing in on CO2 to Determine Who’s in the 'House'

September 10, 2010 - 3:35pm


Heating and cooling a building seems like a straightforward task. But many buildings’ heating, ventilation and air conditioning (HVAC) systems waste energy and don’t pay any attention to indoor air quality.


“Commercial buildings’ HVAC systems are regulated by guidelines that dictate how much air flow is needed to provide adequate fresh air ventilation,” says Chuck McKinney of Newton, Mass.-based Aircuity. “But the number of people in a given building varies greatly throughout the day and night, and setting one fixed rate of air flow based on the theoretical occupancy usually results in over-ventilation and energy waste.”

From feds to NHL

To combat this common problem, Aircuity developed a demand control ventilation (DCV) system that increases the efficiency of commercial buildings’ HVAC systems and ensures high indoor environmental quality.

Aircuity’s DCV solution calculates a building’s occupancy level by measuring C02 levels in the air, which increase as more people enter the building and emit C02. The information is then transferred to a central server, which can integrate with a building’s HVAC system and increase ventilation when occupancy levels are high or decrease ventilation when levels are

Since 2006, Aircuity’s DCV solution has been installed in universities, hospitals, and the Prudential Center, home of the National Hockey League’s New Jersey Devils.

The Recovery Act is supporting the installation of the Aircuity’s DCV solution in two federal buildings: the McCoy Federal building in Jackson, Miss., and the Peck Federal building in Cincinnati, Ohio. Both facilities are undergoing renovations and energy retrofitting projects aimed at reducing their energy consumption and maintenance costs. Renovations to the McCoy building are projected to reduce the building’s fuel costs by 30 percent.

Fewer sensors increase efficiency

McKinney says there are a number of systems on the market that use similar principles to lower ventilation costs. Aircuity’s DCV system needs fewer CO2 sensors to get the job done.
“The idea of DCV had been around for some time, but it has traditionally been based on individual CO2 sensors being placed throughout a building,” says McKinney.

According to McKinney, Aircuity’s DCV solution can also measure air’s relative humidity, particulates, and the number of total volatile organic compounds (TVOCs), which can negatively impact the quality of the indoor environment. This has made the system particularly popular at universities, research facilities, schools and commercial office spaces that have variable occupancy rates.

He also notes, “Aircuity's approach is different; we pull air samples from different areas to a centralized suite of sensors, which measure the CO2 levels and compare it to the outside air. This greatly reduces the number of sensors needed and lowers the life cycle costs associated with calibrating the sensors.”