the difference between "draw through" and "blow through" configurations in Air Handling Units (AHU). In the top diagram, the "draw through" setup shows the fan pulling the return air through the air filter and cooling or heating coil before supplying it to the space. In this configuration, the fan is located after the filter and coil, ensuring that air is drawn through them for conditioning. The lower diagram shows the "blow through" configuration, where the fan is placed before the cooling/heating coil, pushing the conditioned air through to the space. The key difference lies in the fan's position relative to the coil, which affects airflow dynamics and system efficiency. These two setups are used depending on the design and specific requirements of the HVAC system.