All humans and animals breathe in oxygen, then release carbon dioxide and other metabolic byproducts. Too much carbon dioxide and too little oxygen in a building can result in poor air quality, which leads to a phenomenon known as "sick building syndrome." By using carbon dioxide detectors to monitor air quality, building managers ensure the proper level of ventilation to accommodate occupants, workers and visitors.
Function
HVAC technicians install carbon dioxide sensors within the building's air ducts. These sensors measure carbon dioxide levels produced by the occupants in the building, then automatically adjust ventilation levels based on these readings. The sensors may send an electronic signal to dampers within the ducts, which open or close to increase or decrease airflow. They may also send a signal to the central furnace or air conditioner, instructing the unit to increase or decrease airflow or adjust fan speeds as needed to achieve proper ventilation levels.
Benefits
Carbon dioxide sensors help building owners balance the need for adequate ventilation with the need to maximize energy efficiency. Too much ventilation ensures healthy air quality but wastes energy due to increased heating and cooling needs. Too little ventilation keeps energy efficiency high, but may lead to unhealthy occupants. Properly installed sensors also reduce energy costs and help protect the environment from the effects of wasted energy.
Applications
According to the Oregon Office of Energy, carbon dioxide sensors operate most effectively in large assembly areas, including gymnasiums, auditoriums and churches. These buildings are designed to provide enough ventilation for a full-capacity crowd. In most cases, this amount of ventilation is largely unnecessary, as these buildings may be empty much of the time. By using carbon dioxide detectors, the Oregon Office of Energy estimates that building managers in these types of facilities can cut energy consumption by as much as 60 percent.
Considerations
Before investing in carbon dioxide detectors, it's important to understand the potential drawbacks or limitations to these devices. The Oregon Office of Energy estimates that these sensors can cost as much as $1,000 each, including installation and materials. They must be carefully placed within the ducts, as improper placement can lead to incorrect readings and inadequate ventilation. Finally, these sensors take time to adjust to changing carbon dioxide levels, and may not be as effective in applications in which the occupant load changes rapidly.
Alternatives
Some simple alternative technologies offer an effective replacement or complement to standard carbon dioxide detectors. Occupancy sensors use infrared lights to measure changing occupant load, and they deliver signals to duct dampers or fans to modify ventilation levels as needed. Some buildings may also benefit from manual adjustments made by counting ticket sales or by using a turnstile to count total occupants throughout the day.
