This routine estimates the approx size of a fan (squirrel cage type) to
supply the volume of air you want at the back pressure you need. Obviously
manufacturers data is the best, but in the event that you have a surplus fan
with no data, this is a reasonable method of approximation. Note that this
data was generated from manufacturers data.
Note: If you use option 23, concerned with determining the spec for a fan to
cool a valve, it will automatically set the default flow rate and back pressure
to the correct figures.
These routines are *not* accurate representations of the original manufactures
data since they assume a very simple relationship between back-pressure and flow,
which is not perfect. Hence the actual flow will be higher or lower than
program tells you. If you have manufacturers data, trust that - not this
program. I hope these flows are pessimistic, but they may be optimistic!!