Demand Control Ventilation Retrofits Provide Fast ROI

March 18, 2015 By Karen Henry

empty conference room Energy ManageDepending on the building’s size, existing infrastructure and control requirements, a demand control ventilation (DCV) retrofit can provide an energy savings payback in five years or fewer, according to an article in Buildings. A DCV retrofit of a single classroom at the University of Georgia, for example, achieved payback in less than two years.

Traditional ventilation supplies air at fixed rates based on square footage and peak occupancy. When demand response is used, ventilation drops automatically if occupancy sensors detect that there are fewer people in a room, and energy is conserved. When the occupancy in a room using DCV drops from one to zero, air supply decreases by about 25 percent. Multiple rooms compound the savings.

For buildings with fairly predictable occupancy rates, DCV can be scheduled via the facility’s building management system. Buildings with irregular or unpredictable occupancy rates require sensors to detect how many people are in a space. Carbon dioxide is the most common method for determining occupancy, but occupancy sensors, such as infrared sensors that are paired with lighting controls, can also be used. However, infrared sensors can only detect if someone is in a room; it cannot calculate the total number of occupants.

Switching to DCV typically requires additional building management system points, new setpoints and new control codes for dampers. Outdoor dampers should not be stuck or blocked,  and sensors are typically placed in the space itself rather than in ductwork because return air is an average of all conditioned spaces rather than an individual area.

Once the DCV sequencing has been established, the system requires minimal maintenance. The system should be recalibrated at regular intervals according to the manufacturer’s guidelines.

Photograph via Shutterstock.

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