Which of the following would regulate the amount of air that enters a structure based on Demand Control Ventilation (DCV)?

The correct choice is based on the principle of Demand Control Ventilation (DCV), which adjusts the amount of ventilation based on the occupancy and air quality needs of a space. Monitoring carbon dioxide levels is crucial because they indicate the number of occupants and their activity level within the space. As occupancy increases, carbon dioxide levels rise, signaling that more fresh air is needed to maintain adequate indoor air quality. Consequently, the ventilation system can regulate air intake appropriately to ensure that carbon dioxide concentrations remain within acceptable limits, promoting a healthy environment.

In contrast, humidity levels, while important for comfort, do not directly reflect the necessity for increased ventilation related to occupancy. Indoor temperature can influence comfort and energy use but does not serve as a direct measure of how many people are in a space. Outdoor temperature primarily affects heating and cooling loads rather than ventilation requirements based on air quality or occupancy. Thus, using carbon dioxide levels as a regulator aligns perfectly with the objectives of Demand Control Ventilation, making it the most appropriate choice.