Ventilation advice as I am confused

Old 08-19-15, 08:07 AM
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Ventilation advice as I am confused


I'm trying to see if the air pump being considered will deliver air thru a pipe. I've looked at the different calculations to do, did them and get answers I'm not clear how to assess.

But first what I'm trying to do: pump air thru a tube to vent a enclosed room. The tube is 20Meters long equivalent (it includes turns but have accounted for this with equivalent tube lengths). For simplicity sake lets assume sea level, 20degrees density at 1.2.

A pump yielding 330m3/hour of air is being considered with a duct tube of diameter 120mm with tube roughness at 0.04mm

My concern is the following math:

- my wind speed in the tube is 8.1 m/s
- calculated dynamic pressure at entry is 4.0 mmH20
- calculated dynamic pressure drop is 15.7 mmH20

So I conclude that the air will never reach the exit ?...
(this because the pressure drop is bigger than the entry pressure...)

Old 08-19-15, 08:24 AM
Join Date: Oct 2008
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LOL, you are way beyond me, but I do enjoy math. A simple observation is, the wind speed you selected will not be achieved, thus the resulting pressure drop is way too high. The air will flow, but how much I can't say.

I'll let the hvac guys untangle the metric terms since they are better with air flow than I am.

Note, will that air flow increase the pressure within the space where it exits?

Old 08-19-15, 10:54 AM
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lots of conversions for me but something like 84.95054 m3/h on normal HVAC

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