Energy Savings for Occupancy-Based Control (OBC) of Variable-Air-Volume (VAV) Systems.

摘要

Terminal boxes usually serve a single building zone, controlling the air-flow rate to the zone and reheating the air when it is too cool. Each terminal box has a minimum air-flow rate that ensures the ventilation requirements of the occupants of the zone served are met. This minimum air-flow rate is maintained at a constant value based on the design occupancy of the zone, which often corresponds to the maximum occupancy, because measurements of actual occupancy are not currently used to adjust the flow rate. Therefore, the minimum flow rate must meet the ventilation needs of the fully occupied zone. The total flow rate may be higher than the minimum to provide adequate cooling or heating, but the minimum for ventilation should always be met. In practice, control system integrators and installers often set the cooling minimum air-flow rate for ventilation to between 30% and 50% of the maximum air-flow rate of the terminal box. Building occupancy, however, varies dynamically. Conference rooms, cafeterias, auditoriums, and other assembly spaces are often unoccupied for significant periods of time. Office occupancy varies during the course of a work day, from day to day, and over the longer term because of attendance of meetings elsewhere, business travel, changing room functions, and variations in staffing. The resulting over-ventilation, during times when the space has less than maximum occupancy or is unoccupied, wastes significant fan energy and causes discomfort for occupants in some spaces (e.g., conference rooms) from overcooling or overheating, especially in interior zones that do not have reheat in the terminal boxes.