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".

 

[imok2]

Sounds like the fan is running backwards or the unit is installed backwards normally the supply side static pressure is higher then the return side, you show just the opposite?

 

[Ashereng]

It could also be that the numbers on the "blue print" is a design pressure, and what you are reading would be "installed", or "as-built" pressures.



"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[mnchapman]

The belts have been ignored for so long on these units, that they are streched, running very loose for perhaps years and maybe they became glazed and unable to grip the pulley anymore, even after I tightned them. hmmm, just grasping for straws, but I wish I had a tachometer to read the blower rpms directly. I'm gonna look at this unit again tomorrow.

 

[willard3]

See if you can find the balance report from when the building was commissioned.....that should have realistic pressures.

There are a million reasons RA pressure is higher than SA pressure.

 

[cme]

clogged filters?

 

[walkes]

change in system configuration since installation?

 

[mnchapman]

Well, I took another close look today. It still a mystery to me. The figures I posted were after I installed new filters and tightened both belts. When I opened the cabinet door on the blower side, the reading increased from 0.27 to 0.44" on the supply duct, just after the blower. I was hoping it would shoot up to 0.87", but alas, nope. I checked the blower fins today, there is no dirt build up and they look relatively clean. Belt is still tight and all looks great to the naked eye. I even checked all 3 return grills and they sucked up a paper towel in a heartbeat.

What next? Check voltage on this 1 hp motor, check amps, tighten belt some more, replace the belt? There are a set of as-builts but they do not include pressure readings, except for the proofing switches on the cabinet and raf. The proof switch on the cabinet is stated to be 0.5" to 1.0". I get 1.20" reading (twin tube input reading, cab before blower, duct after blower). The blueprints with the ESP spec's does not state if it is a design or commissioning spec.

I think I am at the point to buy me my first pitot tube, but I fear if will only confirm my findings. This is bugging me to death. Im spending too many hours on this unit, but I just have to figure it out somehow. The 1 hp motor is blueprinted for 1850 cfm (close enought) and I want to prove it is doing its job.

 

[Ashereng]

Welcome to the real world. Hee Hee. ;-)

The next time you comission something, keep in mind your current frustrations, and red line the as-built drawing so that it will elimiate the frustration of the next guy to use those drawings.

We all thank you in advance.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[Yorkman]

Mnchapman,
You didn't say how your amperage looked, when you checked it. It sounds like you may be starving the return fan or just turning the supply or return fan sheeves too slow. Is there a way to open a door at the inlet side of the return fan and then check the discharge static pressure of the return and supply?. It might indicate whether your getting enough air to the return fan or not. If the static doesn't rise close to your design on the return then it could be the return fan is turning too slow. If it does go up substantialy the the problem maybe on the return side ducting.



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

 

[mnchapman]

Yorkman, I've been thinking along those same lines. There is no inlet door that I've seen, but tommorrow I will track the duct to find one. Most our ducts do have doors, so you have gave me something to look for tomorrow. Out of desparation, I might cut an opening myself and then close it with Z strips. Looks like I might be buying me a pair of the metal snips that cut and remove a 1/4" gulley.

This is good, I have something to follow up on tomorrow.
I haven't checked amps yet cause the rating will be hard to see where the motor is mounted, but I will do that too.

 

[walkes]

mnchapman, did you take readings across each blower? Inlet and discharge pressures to get your blower sp, instead of discharge alone. Or did I misread your post?
Get the serial number from the unit, get the blower curves from the original supplier and compare the pressure differential across each blower to their respective fan curves.

 

[mnchapman]

I did take readings on both sides of both blowers and have all the numbers written down at work. But the .027 reading I cited is from the outlet of the supply blower.

Have I committed an error in measurements?

If so, let me think. I recall: +0.27" blower outlet.

And when I connect the twin pipes of my monometer to both the blower outlet static probe and the cabinet static probe (blower inlet, although not same size duct since its the cabinet); I get reading of 1.17". But I believe that is -1.17". According to the specs, that twin pipe reading should be between 0.5 and 1.0". Hence not 1.17.

Today, I put on a new belt and got same readings. I checked amps and got 1.3 amps. The motor rating is 1.7.

 

[imok2]

There are hundreds of combinations of different static pressure readings. The basic premise is that if static pressure is high, there may be blockage, or the duct may be undersized.

If static pressure is low, there's a good chance that there may be duct leakage, or that the fan is dirty or damaged, also be certain to always read the nameplate data to determine the total static pressure that the unit was manufactured for. Also, obtaining a copy of the manufacturer's fan curve data can be very helpful in interpreting static pressure and airflow reading.
You need to take two readings: one on the supply side of the fan, and one on the return side of the fan.

 

[mnchapman]

Nameplate data? There are labels on the units, but no specs supplied nor printed on the units themselves. (1992 origin). Fan curve data? How do I go about getting this information? Do I pay for a vendor rep visit?

Supply side verses return side. Those 2 points are but a few of the points in the system. Not sure where to take readings. This is a simple air handler. It is the smallest one in the school, without any variable factors such as vortex, etc. I got: Return register. return duct. return air fan. then on to: cabinet filters, cabinet coils, cabinet supply inlet, cabinet supply blower, cabinet blower outlet/duct.

My 0.27 reading is the cabinet blower outlet/duct (12x12 inch)

 

[imok2]

Whenever you need information you need to get and post every bit of information you have. For example you mention labels what does it say, who's the mfg.? and to get total ESP for any fan you need to read the fan inlet pressure and the outlet pressure. To get the velocity pressure you need a pitot tube then you need to convert it to FPM and multiply this by the duct cubic feet. This may be of value to you:

http://www.dwyer-inst.com/htdocs/airvelocity/AirVelocityIntroduction.cfm

 

[mnchapman]

Not Total ESP,just esp. Labels have no information on them,, that was the point I was making.

 

[Yorkman]

Mnchapman,
At this point I would just break down and do the traverse of the supply duct it will tell you where you are at. You could be grinding away at this and may be with in 10% of the spec and not even know it.

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

 

[mnchapman]

Yorkman, you are right again. I took several other units sp's today and could not determine anything useful. I'm gonna break down and buy me a pitot tube.

 

[walkes]

mnchapman, by chance did anyone leave the operations and maintenance books lying around? Or did they get thrown out over time. They may have the model number and manufacturer listed.
If not contact your local rep to see if they or the factory have the records on the units. I have at times done this and received info on equipment 30 years old.