NATE Air Conditioning and Heat Pumps Practice Exam

External static pressure is the sum of the ____ and the ____.

1. Absolute static pressure entering the air filter, absolute static pressure leaving the air filter

2. Absolute static pressure entering the indoor blower, absolute static pressure leaving the indoor blower

3. Absolute supply static pressure, absolute return static pressure

4. Static pressure entering the evaporator coil, static pressure leaving the evaporator coil

The correct answer is: Absolute supply static pressure, absolute return static pressure

External static pressure refers to the total pressure exerted by the air in an HVAC system as it moves through the supply and return ducts. This pressure is important for ensuring that the air is properly distributed throughout the space being heated or cooled. The correct formulation of external static pressure includes both the absolute supply static pressure and the absolute return static pressure. In this context, absolute supply static pressure is the pressure of the air in the supply ducts pushing out into the conditioned space, while absolute return static pressure is the pressure of the air returning from the space back into the system. The combination of these two pressures gives a complete picture of the pressure needed to move air efficiently through the system, which is critical for optimal airflow and equipment performance. The other options focus on different components of the system but do not capture the overall pressure dynamics of supply and return airflow that contribute to external static pressure. Understanding external static pressure is essential for HVAC professionals to troubleshoot airflow issues and ensure the system operates efficiently.