What is the difference between absolute pressure and gauge pressure?

Absolute pressure refers to the total pressure exerted on a system, including atmospheric pressure, while gauge pressure measures pressure relative to the ambient atmospheric pressure. This means that gauge pressure can be considered as the pressure read on a gauge which does not take atmospheric pressure into account.

The correct answer of 14.7 psi represents the standard atmospheric pressure at sea level. This value is significant because it sets the baseline for gauge pressure calculations. When measuring gauge pressure, any reading taken will be the difference between the absolute pressure and this atmospheric pressure.

In practical terms, when you have a gauge pressure reading and want to find the absolute pressure, you simply add this standard atmospheric pressure (14.7 psi) to the gauge pressure reading. This relationship forms the foundation for understanding how pressure readings are taken in various applications, including HVAC and A/C systems.