How do you calculate the temperature drop in an HVAC system?

To determine the temperature drop in an HVAC system, you look at the difference between the temperature of the air supplied by the system and the temperature of the air returning to it. The correct calculation is based on the premise that the temperature drop reflects how much the air has cooled (or heated) as it travels through the system.

In this context, the supply temperature is the temperature of the air being delivered into the conditioned space, while the return temperature is the air that is returning to the HVAC unit after circulating through the environment. By subtracting the return temperature from the supply temperature, you can accurately quantify how much the air has cooled (for cooling systems) or heated (for heating systems) as it travels through the system.

Thus, the equation that correctly describes how to calculate the temperature drop is by taking the difference between these two temperatures: Supply Temp minus Return Temp. This gives you the temperature drop that indicates the effectiveness of the HVAC system in conditioning the air.