Application of CO2-based demand-controlled ventilation using ASHRAE standard 62: optimising energy use and ventilation.

CO2-based demand-controlled ventilation (DCV), when properly applied in spaces where occupancies vary below design occupancy, can reduce unnecessary over ventilation while implementing target per-person ventilation rates. A recent interpretation of ANSI/ASHRAE Standard 62-1989, Interpretation IC 62-I989-27, has affirmed that carbon dioxide (CO2)-based demand-controlled ventilation (DCV) systems can use C02 as an occupancy indicator to modulate ventilation below the maximum total outdoor air intake rate while still maintaining the required ventilation rate per person, provided that certain conditions are met. This paper, co-written by the author of the interpretation, provides guidelines on the application of CO2-based DCV. In addition, a method is presented that allows reasonable estimates of the actual ventilation rate per person being effectively delivered to the space, based on comparing predicted CO2 ventilation levels with CO2 levels logged in an occupied space. Finally, a model is presented to evaluate various CO2-based DCV strategies to predict their delivery of target per-person ventilation rates within the lag times required by the standard.