Non laboratory applications
Houghton emphasizes the benefits of Demand Controlled Ventilation (DCV):
For many building operators, improving air quality by correcting under ventilation is the most important benefit of demand-controlled ventilation. But correcting over ventilation also can provide large energy savings—in some cases up to 80 percent of HVAC energy. DCV offers the greatest potential for energy savings on buildings with wide or unpredictable swings in occupancy such as auditoriums, cafeterias, theaters, retail stores, classrooms, and conference rooms. Potential energy savings from DCV depend on several factors, including:
- Baseline ventilation rate. Most buildings are set up to supply enough fresh air to satisfy the design occupancy whenever the building is occupied. (In practice, it is difficult to measure how well this is achieved.) Compared to this arrangement, DCV will reduce energy whenever actual occupancy is less than design occupancy—as long as outdoor air requires heating or cooling. If a building is under supplying outside air, a DCV system may actually increase energy use—but it will also bring the building into compliance with accepted practice, and do so more efficiently than a simple increase in the constant ventilation rate.
- Occupancy. Buildings with predictable near-design occupancy will save less energy from a DCV system than buildings with highly variable occupancy, or buildings which never reach design occupancy.
- Climate. Buildings in extreme heating or cooling climates will benefit most from DCV, while those in moderate climates where economizer operation is common will achieve relatively little benefit. However, it may be worthwhile to install CO2 sensors in buildings in moderate climates to document ventilation performance.
- Control setpoint. Building operators can choose to keep indoor CO2 concentrations very close to the 1,000 parts per million (PPM) target referenced in ASHRAE Standard 62-1989, or use a lower setpoint, such as 700 PPM, to intentionally provide more outside air per person. Lower setpoints will yield less energy savings than higher setpoints, but may still save energy compared to constant ventilation.