Installed Inline Centrifugal Fans Not Performing ??

[michael333]

To Everyone,

I have a design where I'm using 2 inline centrifugal fans (each fan is Cook: Model GN-740) in a pull-pull arrangement for crossing airstreams via a static plate heat exchanger (Renewaire: Model CA2X). EF-3 exhausts air from public restrooms and a janitor's closet via the CA2X out the bldg. and SF-1 supplies outdoor fresh air via the CA2X to individual Mitsubishi ceiling cassettes.
It's a simple straight-forward design. Systems are installed.
EF-3 design = 525 CFM @ 0.75 ESP and SF-1 design = 500 CFM @ 0.875 ESP. Specified variable-speed controller for each fan.

Cook cutsheets and literature state the GN-740 can do ~500 CFM @ .875 ESP, 398 Watts, 1600 RPM.

I get a TAB report that states the following:
EF-3 = 374 CFM @ 0.24 in wc ESP actual, 1 amp. Fan is 29% low on airflow. Motor FLA = 2 amps.
SF-1 = 136 CFM @ 0.08 in wc ESP actual, 1 amp. Fan is 72% low on airflow. Motor FLA = 2 amps.
Direct Drive motor is on high speed for each fan according to the TAB report.
Do not know the actual RPM, only the actual amps.

I'm baffled at the low airflow CFM of these fans at such a low ESP.
EF-3 should be ~795 CFM @ 0.24 ESP according to Cook's literature.
SF-1 should be ~850 CFM @ 0.08 ESP according to their literature.

I and another colleague visited the job site and verified the following regarding both these systems:
-Inlet and outlet ductwork to each inline fan is good. No reason for system effect to cause the poor performance.
-Traverses were taken at fairly good locations in each system.
-Suction and discharge statics taken at good locations
-Variable speed controller wired up correctly, per Cook's installation manual, for each fan.
-Fans are on high speed
-We concluded that the fan wheels must be rotating in the correct direction because they're single-phase inline from the factory.
we did not physically check the fan rotation based on the above assumption.
-filters are in the correct location in the CA2X per the installation manual
-filters on the outside air inlet side of the CA2X were fairly dirty, but not that bad.
-airstreams cross correctly in the CA2X per the install manual
-turning vanes were installed in all 90 deg elbows of the ductwork

I'm even more baffled after my jobsite visit.

I'd welcome anyone's responses/advice for the following questions:
Why are these fans performing so low a airflow at a low ESP?? I'd expect to see a high ESP @ such low airflows!
Has anyone out there ran into issues with Cook's inline fans (GN-740) not performing according to their literature??
Is it possible that the fan rotation is in the wrong direction, even if they're single-phase from the factory??
Possible something is blocking airflow within the fan and motor housing itself?
Is it possible that both these fans came from a bad lot from the factory??
I'm going to put this issue back in the mech contractor's lap so that he and Cook can figure out why these fans are not performing.
Is this a good course of action??

Thank you for any advice that someone may afford on this,
Mike V P.E., CxA

 

[EnergyProfessional]

are you sure you included the pressure drop of the HX? Did you verify the measurement? Are you sure you read reading the spec sheets right? It sounds like you are deriving airflow from fan pressure gain?

not sure why you didn't use a Renewaire unit with the fans built in, which is the most common method. Would have been cheaper and you only needed to account for the ESP of the duct work and the rest of the system. In addition the cook fans will fall apart soon, they are the lowest quality one can find. .

 

[cry22]

you say you're in a pull-pull arrangement. This means draw-thru on both fans, right?
your static may be read at discharge of fans only without taking into account the HX, which can amount to 1" or more.
Your original static pressure looks low for flat plate heat exchanger application, HX SP is in the 0.8" to 1" by itself.
Did you approve the shop drawings?

Now on the other hand: why did you specify VSD motors on such a low power and constant volume application? what will throttle the flow to get your VSD's to slow down? if they do slow down, by how much? and when they do, aren't you reducing minimum required exhaust rates form the bathroom? aren't you reducing minimum OA to the space below code on SF-1? aren't you affecting your space pressurization? do you have controls in place tracking supply and exhaust rates for pressurization purposes?
I would've kept it simple - CV on both fans.

Herr:
I looked at Renewaire website. I am puzzled by their claim of reclaiming humidity with what looks like flat plate heat exchanger, which can do sensible recovery only. Am I missing something?

 

[SAK9]

You need to verify both direction of rotation and rpm before coming to any conclusions.If the actual system static is more than estimated,fan should ride up on the curve resulting in higher static and lower airflow.Since both airflow and static are low,the fan is operating on a different curve.This could be due to rpm being lower than design.

 

[EnergyProfessional]

Cry22: it is not a metal plate, it is osme type of "paper" that also trnafers mositure. We use them a lot and they are built very well and mantenance really like them since all parts are very well accessible. tha tis why I wonder why he chose separate fans.

Plate HX is a bit less efficient than a wheel.

 

[michael333]

Herr,
Internal Static Pressure drop of HX (CA2X) is approx .25 in. H2O @ 500 CFM according to Renewaire literature.
MERV 8 filters on inlet faces of the internal Lossnay core is .29 in wg according to filter literature.
Looking at ~0.55 across the HX. I'll direct the TAB to take actual PD readings across each airstream for my review.
Called for it in my spec and TAB did not provide it. Darn-it, I did not realize the Cook fans will fall apart.
I did look at Renewaire's HE1XINH and HE1XINV in design. With only the req'd inlet static to the most remote ceiling cassette + balancing damper + duct length losses + duct fitting losses + OA intake louver = maybe .80 ESP (vent air) and approx .60 ESP for exhaust air side. The HE1Xs are CV with no speed adjustment. I did not want a situation of too much airflow (750 to 850 CfM at .60 to .80 ESP) with the HE1X, so I went went the CA2X with remote inlines with factory-provided unit mounted variable speed controllers. My vent air and exhaust air systems are small systems.

cry22,
Yes, draw-thru on both fans from the HX. Yes, I approved the shop dwgs. Literature states .25 in H20 @ 500 CFM across the HX. Its not a VFD motor. Simply a variable speed controller that Cook provides with their CV inline DD fans if the ENR wants it as an accessory. Anyway, the speed controller is on High, with no varying it. TAB guy noted that.
I really need to get the vent air flow (SF-1) up to maintain, as you point out, the vent air rates to the ceiling cassettes.

SAK9,
Yes, I'm directing the TAB tech and mech guy to verify direction of rotation and provide RPM in the next TAB submittal.
Yes, I do realize the fan is operating on a different curve due to the rpm lower than design. Very good point.

Thanks guys,
Mike V

 

[EnergyProfessional]

you iften have to use a larger unit to get the required static. You can add VFD to the units.

measure the actual flow by traversing, measure yourself... don't trust TAB contractor

 

[MintJulep]

"I'm going to put this back on the mechanical contractor's lap...."

And thus starts the blame game.

You'll be better off getting yourself, the mechanical contractor and the TAB contractor all together on-site and promoting a "let's figure this out" attitude.

 

[willard3]

Has anybody plotted this on the fan curves?

It looks like FC fans. Where are you operating on the fan curve?

 

[chicopee]

As willard3 suggested plot the two fan performance curves for a series equivalent curve and then plot the system performance curve. At point of intersection is your appx. answer. If the fan performance data consist of one data point for each fan, then assume the performance curves to be quadratic of the form S.P.= K x cfm^2 from which K can be determine and be used for other calculated points before drawing the performance curves. The system performance curve is actually a pressure drop curve thru the ducting system; for equation use Darcy Weisbach equation which is also quadratic in nature, however develop that equation so that you have consistent units when plotting with the performance curves.

 

[ChasBean1]

ESPs are useless when evaluating fans. Redo your first post lining out all ESPs and replace them with TSPs - meaning the static pressure at the immediate fan outlet minus the static pressure at the immediate fan inlet.

 

[willard3]

Better to do a total pressure plot to diagnose fan problems.

 

[willard3]

What do these fans sound like when they are operating? Are they surging, ie, is the fan noise sinusoidal?