Page 9 - FANS. Aerodynamic _Selection Meethod__Combine_part2

The designation and application of the dynamic pressure of the fan Pv on
the aerodynamic characteristics, when selecting a fan, is also doubtful in
understanding the process of air movement - it is reflected in the fan

catalogs, i.e. All reasoning is conducted around static Ps and dynamic Pv
fan pressures.

The author rejects the artificial separation of the total pressure of the fan to
the static pressure of the fan and the dynamic pressure of the fan, since the
dynamic pressure of the fan depends on the configuration (length, cross
section, local resistance) of the discharge duct, and can show a value of 3-8
(see Fig.1), and the static pressure of the fan should be equal to the value of

8-1, with a total pressure of 3-1. Practical measurement of the static
pressure of the fan will not confirm its value equal to 8-1, but will show
another value, for example 10-1.

Thus, according to the existing theory, it is impossible to accurately (or with
high accuracy) select a fan, since You can`t rely on the dynamic pressure of
the fan, calculated for the injection pipe using the well-known formula:

Pv = ( ² )/ 2 Dynamic pressure = (Density)x(Velocity)²/2

The author proposes a new theory and a new fan selection method that
significantly improves the selection accuracy, which is confirmed by

aerodynamic tests (instrumental measurements), which will lead to
minimal energy consumption, other related costs (metals and alloys,
electric wire, electrical installation fittings, etc.), non-use throttling devices
and frequency converters without technological need.

The theory provides a method that allows you to actually compare the

design data with the results of aerodynamic measurements, to assess the
possible errors in the design and installation of the ventilation unit.

The theory (and method) makes it possible to make an exact replacement of
the fan with another optimal fan - if the need arises to change the
parameters of the same ventilation unit.