Demand-controlled ventilation for multiple-zone HVAC systems—part 2: CO₂-based dynamic reset with zone primary airflow minimum set-point reset (RP-1547)

In Part 1 of this article, a CO₂-based dynamic reset was proposed and evaluated as an energy-saving demand-controlled ventilation strategy by reducing the outdoor airflow rate when the occupancy is under design occupancy. Further energy-saving potential still exists when the zone primary airflow rate ismodulated or reset instead of only resetting the outdoor airflow. Two new control strategies are presented: a CO₂-based dynamic reset, now combined with a zone primary airflow set-point reset in Part 2. The system level of these control strategies is the same as CO₂-based dynamic reset in Part 1. The additional control features are added at the zone level. The zone primary airflowrate minimumset-point will first be reset to increase system ventilation efficiency, whichwill lead to a reduced system outdoor airflow rate. With this proposed dynamic reset with zone primary airflow set-point reset, the design minimum zone primary airflow rate can be designed lower than the regular set-point used in variable air volume terminal box minimum set-points. This new setting reduces the energy consumption for the system supply fan as well as energy consumption for terminal reheating. Both energy simulation and airflow simulation were conducted in different locations of a building. In this article, the results show that the proposed strategies of CO₂-based dynamic reset with zone primary airflow set-point reset consume less energy when compared to CO₂-based dynamic reset presented in Part 1 and the baseline case “without demand-controlled ventilation.” The average annual system outdoor airflow rates for the two options of the proposed demand-controlled ventilation are 44. 1% and 45%, respectively, less than the outdoor airflow rate for the case without demand-controlled ventilation. Therefore, the proposed demand-controlled ventilation control strategies are suggested to consider for CO₂-based demand-controlled ventilation for multiple-zone single duct VAV systems with terminal reheat.