OT:Fan & filter air flow calculation

[rich_p]

Hi All!
We have a control panel that houses a VSD in an old shipping container. The control panel will be cooled with a fan and filter unit. So that the hot air from the control panel is not recirculated inside the shipping container we want to ditch the filter unit and pipe an outlet from the top of the control panel to the outside of the shipping container.

We have some spare 150mm pipe (area 17662mm^2) however the filter hole would have had an outlet of 31329mm^2. Is there are formula to calculate the reduction of airflow if using 1 piped outlet or the increase in airflow if we were to have two piped outlets?

Any help/ideas appreciated!

Cheers

 

[Tom Jenkins]

This is a complex analysis. The air flow reduction depends on the characteristics of the fan (pressure vs. flow fan curve). To do this properly you need to calculate the pressure drop vs. flow for your pipes and plot it over the top of the fan curve. The intesection of the two shows the operating point.

If you aren't familiar with fluid mechanics perhaps your fan supplier can offer assistance.

 

[leitmotif]

This is a complex analysis. The air flow reduction depends on the characteristics of the fan (pressure vs. flow fan curve). To do this properly you need to calculate the pressure drop vs. flow for your pipes and plot it over the top of the fan curve. The intesection of the two shows the operating point.

If you aren't familiar with fluid mechanics perhaps your fan supplier can offer assistance.

Tom is right. But I see one more problem. What is the heat load of the panel? You must know how many BTU you need to get rid of to keep panel at temp X. You also need to know what ambient temperature is and what effect solar radiation heating may be. In addition you need to know what the altitude is.
Then you can do Q = MC dT
M = flow rate
C = constant ie BTU / lb
dT temp difference between cabinet and ambient.


Hoffman has some good guides for making these calcs.

If mine I would filter fan intake (keeps fan clean) then discharge fan to cabinet to pressurize cabinet to keep dust loading to minimum.

ACGIH has "recommended industrial Ventilation" manual much of which applies to this.

Dan Bentler