What two variables are compared when controlling outside air and return air?

What two variables are compared when controlling outside air and return air?

• A. Outside temp, airflow
• B. Inside temp, humidity
• C. CO2 concentration, occupancy
• D. Air pressure, humidity

Answer: (A)

When a system controls outside air and return air, it uses outdoor conditions as the driver and adjusts how much air actually flows into the space. The key idea is economizer logic: if the outdoor air is favorable (usually cooler) compared to what’s inside, you want more of that air to mix in to meet cooling needs without overworking the mechanical cooling. That decision is made by comparing the outdoor temperature to the indoor/return air conditions, and the result is the amount of outside air flowing into the system—the damper position and thus the actual airflow. So the two variables involved are the outside temperature and the airflow (the amount of outside air entering the system). The other factors listed—indoor temperature/humidity, CO2 or occupancy, and air pressure—are important in different control schemes, but they aren’t the primary pair used to determine how much outside air to bring in for typical outside-air/return-air control.

When a system controls outside air and return air, it uses outdoor conditions as the driver and adjusts how much air actually flows into the space. The key idea is economizer logic: if the outdoor air is favorable (usually cooler) compared to what’s inside, you want more of that air to mix in to meet cooling needs without overworking the mechanical cooling. That decision is made by comparing the outdoor temperature to the indoor/return air conditions, and the result is the amount of outside air flowing into the system—the damper position and thus the actual airflow.

So the two variables involved are the outside temperature and the airflow (the amount of outside air entering the system). The other factors listed—indoor temperature/humidity, CO2 or occupancy, and air pressure—are important in different control schemes, but they aren’t the primary pair used to determine how much outside air to bring in for typical outside-air/return-air control.