The enthalpy difference method is used to measure the air volume in the enthalpy difference chamber. How is the air volume calculated? Why should the static pressure be adjusted to zero?

In the appendices of GB/T7725 and GB/T 17758, the calculation formula of air volume is introduced in detail, or refer to GB/T1236;

Did not say that the static pressure is zero;

For home wall hanging machine, home cabinet machine, four-sided air outlet ceiling machine, seat-crane dual-purpose machine and other machines that are not connected with air duct in actual use, the static pressure of air outlet is adjusted to 0 Pa during testing;

For air conditioners with wind static pressure such as pipeline machines and chillers, the wind static pressure controlled during the test is not zero.