esp reading taken at blower?

[mnchapman]

Im still working on what seems to be low air flow to a kitchen in a public school. The blueprints for show two figures: Air Handler ESP= 0.87" RAF (return air fan) = ESP= 1.14. I've taken several readings and none of them match those numbers, nor even close.

Where, or what points did the installers take the readings that are printed on the blue prints? I have assumed the air handler esp reading is to be taken on the supply duct leaving the blower, but I get a reading of .27, not 0.87.

And I assume the raf reading is taken just after the return air fan, but I get a reading of .45, not 1.14".

 

[mnchapman]

The only documentation is the blue prints, with regards to cfm, sp, etc. The unit does have the model number, but no air flow specs.

I have a new thought about this problem of mine. While I wait for the pitot tube to arrive, I think I may have stumbled onto a cause. A clogged coil. I get a reading of +0.45" at the Return Air Fan (RAF) outlet. This fan is mounted on the ceiling above the air handler cabinet which is on the floor. About 15 feet of ductwork is between the two. I get a reading of -0.90" inside the cabinet- after the coil and at the supply blower inlet. Does this mean that I am getting a static pressure drop of 1.35" across my coil (and new filters)???

I look at the coil face and don't see any matted blankets of dirt that are restricting air flow. (I'm used to see these blanket type clogs on heat vav coils). However, I speculate that the coil could be clogged deeper in the coil. Would that be a common condition for a neglected unit?

Is there a rule of thumb for pressure drops across a coil?

 

[Yorkman]

I think that could be your problem, how many passes is your heating coil? The average pressure drop for a clean heating coil is aboout .027in. of water/number of rows. The way I read your post the sp. at the face of the coil and at the inlet to the supply fan is the same. So that the pressure drop of the duct work is minimal. The coil sounds like it could be dirty.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI

 

[Yorkman]

Mnchapman, the pressure drop of .027 in. of water/row is for a face velocity of 350 F.P.M. at a face velocity of
500 F.P.M. it climbs to .055 in. of water/row. It would be prudent to call the unit manufacturer to find the design pressure drop vs. face velocity. Either way 1.35 in. of water seems pretty steep.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI

 

[Yorkman]

Mnchapman,
To say that this question has been engrossing would be an understatement. I've beeen going through my A.S.H.A.E. manuals and it's suprizing the data you can find!!!
Just a fote note to pressure drop across your coil, the max value I've found for pressure drop is .15 in.of water/row at 800F.P.M. air face velocity. That still puts your 1.35 inches way up there. I don't want to mislead your investigation, so check with the manufacturer it will keep you from coming to the wrong conclusion. I would feel bad if I lead your in the wrong direction

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI

 

[mnchapman]

Good news. I found the problem with kitchen! I did not find it earlier because I was taking my manometer readings at the wrong locations, ( i.e. not at pitot reading locations, which I didn't even see one of them).

Where do I start? I dunno, so .... my return fan inlet ESP was 1.74" and the blue prints call for 1.17". Took me an hour to figure it out, then 30 min of kitchen ceiling return grid checking, but I found that the 3 kitchen ceiling return grids all had hidden (hard to see) louvers behind them. They louvers were all 95 percent closed! Can you believe that! THEY WERE ALL CLOSED! For at least 6 years, closed and maybe even 14 years since new!

Thanks a million for all who replied. I could never had solved this without the input from each and every poster. I was truely stumped. Maybe someday, I'll be able to post and help others.

Thank you gentlemen, ever so much!

 

[Yorkman]

Congradulations!!! Perseverance is often the key to success. Glad that you found the problem and a relatively easy one to fix.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI