Differential CO2 Based Demand Control Ventilation (Maximum Energy Savings & Optimized IAQ) HISTORY, THEORY AND MYTHS

Abstract

Demand control ventilation (DCV) utilizing continuous outdoor and indoor (differential) carbon dioxide (CO₂) measurements is an elegant closed loop feedback control methodology for determining damper position in a continuously changing HVAC system environment and subsequently maintaining a constant steady-state ventilation air (CFM) per person level. This article deals directly with the numerous misconceptions surrounding this technology as well as its applications as an energy conservation measure and commissioning tool. Summarized below are some of the benefits of adopting the DCV technology utilizing differential CO₂ measurements: DCV, when used as an HVAC VAV or CV mix air return system energy savings retrofit tool, can save energy when it functions in conjunction with existing (base case) energy savings control methodologies. This means that DCV control algorithms must be suspended, through computer programming, whenever normal free cooling opportunities exist-otherwise, energy consumption will increase. For example: If free cooling economizer controls exist in the base case, then the engineer must ensure that they continue to exist in the retrofit case.