Assessing the feasibility of controlling indoor CO2 in air conditioning retrofits (ASHRAE Journal. November. 2002. p. 34-43)

In traditional air conditioning systems (AHAC), the supply of fresh outdoor air to the premises is determined by sanitary standards according to the number of people in them and is not controlled by changes in their actual number. When modernizing the RAC, it is energetically expedient to change the supply of outside air taking into account the actual number of people in the room by controlling the CО₂ content in it. This applies primarily to the buildings of cinemas, theaters, conference rooms, school classrooms, and hospitals. The Direct Digital Control (DDC) system includes zone control sensors for controlling the CО₂ content installed at the exhaust air quantity control dampers.