biofilter pressure measurement

[swazimatt]

I was involved in a wastewater pumpstation design that had a fan forced ventilation through a biofilter (a bark and lime chip bed hat removes the SO2 odours from the WWPS see attached plan). Unfortunately the biofilter designer is no longer working for our company.

The design required a "Pressure drop generally less than 100 mm water gauge" across the media
My question is how would this be measured? would you have a pressure sensor after the fan (before it enters the media) and compare it to atmospheric pressure? or measure the pressure in the duct before and after the fan

The plan just shows a pressure sensor after the fan and a second sensor in the duct just before it enters the biofilter, but i am not sure how that will measure a pressure drop. As this is effectively the same portion of pipe surely the only pressure drop measured here will be a result of friction?

(i have shown the current sensor locations on the snip attached)

 

[swazimatt]

this is a section through the biofilter

 

[IRstuff]

There should be a pressure sensor before and after the media to measure the pressure drop across the media.

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[HVAC-Novice]

You usually use a single sensor (or gauge) with hoses going up and downstream of the filter.

You could use 2 sensors (or gauges), but then you have to manually subtract the values and you add sensor inaccuracies.

none of the 2 pressures will equal atmospheric pressure, so you can't use that as a reference (like a regulars sensor would). Google absolute and gauge pressure.