Demand Controlled Ventilation (DCV)

DCV can be achieved by various means, the most effective of which is by determining air quality by the amount of CO2. The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) has determined that the acceptable CO2 level of air in commercial and institutional buildings is 1000 parts per million (ppm), with outdoor air concentrations at about 400 ppm. A typical control setpoint would be 800 to 900 ppm. CO2 concentrations are measured in the return air duct for areas with similar occupancy and use, or in the controlled space. If only one sensor is used for a large area, it should be placed in the zone that is likely to have the highest occupancy. Occupancy sensors can be used as override switches to turn on the fan for a short time during a normally unoccupied period, or as indicators of occupancy during occupied periods. In an unoccupied auditorium or a gymnasium, the air system might simply maintain a minimum temperature with no ventilation. When the space is occupied, the CO2 measurement will be used to control ventilation air quantities by modulating the outside air damper from fully closed to fully open to maintain the desired CO2 level.

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