Until the recent growth of the green building industry under the LEED® program, the cost and time involved with using carbon dioxide sensors in commercial buildings often outweighed the perceived benefits. “Today, building owners and designers see more reasons than ever to include CO2 sensors in building design and remodels, as the cost and reliability have improved with the maturation of the technology over the last two decades,” says Jeff Hartnett, commercial split systems product manager for Lennox Industries.
While a certain level of CO2 is natural in buildings – humans produce it with every breath exhaled – high levels can cause a building’s occupants to become sluggish, tired and less productive. High CO2 levels may also indicate that a ventilation system is not operating properly and is allowing the buildup of high levels of pollutants such as volatile organic compounds.
When CO2 sensors are used with Demand Control Ventilation (DCV) systems, the amount of fresh-air ventilation is controlled based on how many people are actually in a space at any given time. When CO2 levels rise with increased occupancy, more fresh air is introduced by opening dampers. CO2 levels fall as people leave, so the dampers close to reduce the amount of air that must be heated or cooled and the costs associated with treating excess air. (Carbon dioxide is usually measured in parts per million, with outdoor levels typically around 400 to 450 ppm*, but ASHRAE Standard 62 should be consulted to calculate appropriate CO2 levels.)
Several considerations can help achieve the best results with CO2 sensing and Demand Control Ventilation:
Use of CO2 monitoring and Demand Control Ventilation can play an important part in an energy-efficient building design, and can help building professionals earn LEED credits for their projects.
*Federal Energy Management Program Federal Technology Alert: Demand-Controlled Ventilation Using CO2 Sensors, 2004.
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