# Anyone have experience with fanwall technology?



## Shorty Circuit (Jun 26, 2010)

I've got a submittal from a vendor for a single VFD for a 6 fan 5HP each fanwall technology application. The mechanical engineer's spec calls for a complete system. These are referred to I think in article 420 as grouped motors. I'm specifically concerned about 420.52 and 420.53. It appears to me that each motor must have its own overload rated for the specific motor. The MOP should probably be within the guidelines in the chart. Does anyone have any experience with fanwall technology especially using one VFD for multiple motors? The VFD looks to have a bypass breaker (no redundant VFD) but it doesn't say if it will work automatically on VFD failure.


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## John Valdes (May 17, 2007)

Shorty Circuit said:


> I've got a submittal from a vendor for a single VFD for a 6 fan 5HP each fanwall technology application. The mechanical engineer's spec calls for a complete system. These are referred to I think in article 420 as grouped motors. I'm specifically concerned about 420.52 and 420.53. It appears to me that each motor must have its own overload rated for the specific motor. The MOP should probably be within the guidelines in the chart. Does anyone have any experience with fanwall technology especially using one VFD for multiple motors? The VFD looks to have a bypass breaker (no redundant VFD) but it doesn't say if it will work automatically on VFD failure.


I do not know about "fanwall" technology? Is fanwall the name of the system or the concept? 
I do know a little about VFD's.

When using a single VFD to operate more than on motor you must use individual OLR's for each motor. OLR's only. No contactors should ever be installed on the load side of a VFD.. The bypass is used in case of VFD failure. So you can bypass to line voltage. This is usually accomplished with contactors, not breakers.
A manual bypass requires operator intervention where an automatic bypass does not. Usually a switch is used to operate the contactors for bypass. This is the best way as someone should know if the drive has stopped operating. An automatic bypass can also be dangerous and I would only use one if the application was designed for it. I generally never use automatic bypass.

I am really not sure what your question is. I hope I have helped some. It does not look as if I have. Sorry.


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## Shorty Circuit (Jun 26, 2010)

John Valdes said:


> I do not know about "fanwall" technology? Is fanwall the name of the system or the concept?
> I do know a little about VFD's.
> 
> When using a single VFD to operate more than on motor you must use individual OLR's for each motor. OLR's only. No contactors should ever be installed on the load side of a VFD.. The bypass is used in case of VFD failure. So you can bypass to line voltage. This is usually accomplished with contactors, not breakers.
> ...


Thanks for the advice, that's exactly what I was looking for. I was concerned about the individual overloads. I was also wondering about the desirability of automatic versus manual bypass. 

Fanwall technology substitutes several to many small fans for one large one in line with a duct. The supposed advantages are that if one fan fails, the VFD ramps up the remaining fans. I've seen VFDs on the internet specifically designed for them, one control circuit with multiple VFDs, one for each fan. Each VFD has built in protection and you can tweak the relative speed of each fan motor. The submittal wasn't one of them, it was intended for a single motor of up to 30 hp. One mechanical engineer friend tells me the supposed energy savings is marginal, not worth the added cost. People always invent new gimmicks to sell.

There are plenty of links to fanwall technology sites on Google.


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## Wirenuting (Sep 12, 2010)

Careful with the new slim line ABB drives. 
The disconnect on them has a small circuit board that dies after a few uses. Then you can't even use the bypass function.


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## John Valdes (May 17, 2007)

One more thing about VFD's and fan motors. Make sure the VFD has an "start on fly" option/parameter or parameters. This is real important as normal air circulation can cause the fans to turn opposite of the intended direction. Should the VFD have to start a motor that is turning in the wrong direction and at a decent RPM it will trip on overload. "Flying Start" is a parameter function that takes into account this possible condition. 
I have seen these fan walls before. I just did not put two and two together until you explained. Who's drive are you using? Motors? Thanks and good luck.


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## JRaef (Mar 23, 2009)

I've done this many times. The intent is that if the flow requirement is variable, as in a tunnel freezer for example, then varying the speed of 6 fans uses less energy than running all 6 across-the-line and choking off the flow with another device such as a VAV box. But as you said, it also maintains the ability for the system to compensate if one fan fails. 

But if your situation calls for just having 6 OL relays down stream from the VFD, *it will NOT accomplish that* compensatory ability. OL relays do not disconnect a load, they just open a control contact, which must be wired back to the VFD to shut down the entire thing. So if one motor overloads, all 6 will be shut down in your system design.

Then there is the issue of Short Circuit protection for the motor circuits. The breaker protecting the VFD is NOT considered the SCPD for the motor any longer, it is only the SCPD for the VFD. The VFDs are then UL listed to provide SC protection for ONE motor down stream of them, but there is no way they can protect a motor that is essentially 1/6th the rating of the drive or less. So you would also need to put in circuit breakers or fuses on each motor circuit. Fuses are a really bad idea because you cause a severe current imbalance on the output of the VFD and it will likely shut down to prevent damage to itself. Circuit breakers are expensive but one of two possible remedies.

The better way to do this is to use the IEC style Motor Protector Switches that have the OL and SC protection you need for each motor circuit, plus they open up when they trip, which will disconnect the overloaded motor and allow the VFD to speed up the remaining ones to maintain the air flow. While generally true that it's not a good idea to have a switching device down stream of the VFD, that is because of rapid changes in total current if you switch off (or on) the entire load at once, called dI/dt for delta I (current) / delta t (time). But switching off one small motor in an overload condition out of a group is not going to cause harm to modern VFDs. It's done all the time.


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## Shorty Circuit (Jun 26, 2010)

John Valdes said:


> One more thing about VFD's and fan motors. Make sure the VFD has an "start on fly" option/parameter or parameters. This is real important as normal air circulation can cause the fans to turn opposite of the intended direction. Should the VFD have to start a motor that is turning in the wrong direction and at a decent RPM it will trip on overload. "Flying Start" is a parameter function that takes into account this possible condition.
> I have seen these fan walls before. I just did not put two and two together until you explained. Who's drive are you using? Motors? Thanks and good luck.


Not my spec, not my decision. You guessed it. Bad news according to the previous posting. But what can I do. The owner "went shopping" for a bargain I guess. This is the first and only report I ever got but I'm not surprised. After ABB bought the drawout switchgear product line at the breakup of ITE, I was forced to bid out a 5000KVA double ended sub with duplex switching. Good thing I bought all cubicles filled. The breakers would break if they were over cranked. One day after I left, I got word that the HV bushings on one of the Wesgtinghouse transformers sprung a leak. There wasn't enough clearance to remove it. GE repaired it I think by sealing it.


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## John Valdes (May 17, 2007)

JRaef said:


> I've done this many times. The intent is that if the flow requirement is variable, as in a tunnel freezer for example, then varying the speed of 6 fans uses less energy than running all 6 across-the-line and choking off the flow with another device such as a VAV box. But as you said, it also maintains the ability for the system to compensate if one fan fails.
> 
> But if your situation calls for just having 6 OL relays down stream from the VFD, *it will NOT accomplish that* compensatory ability. OL relays do not disconnect a load, they just open a control contact, which must be wired back to the VFD to shut down the entire thing. So if one motor overloads, all 6 will be shut down in your system design.
> 
> ...


Great point JRaef. Single OLR's would not shut down individual fans on a single system drive. Glad you caught that mistake on my end.
The manual OLR/starter makes much more sense. We do not want to loose all the fans if one f's up. Thanks.

Shorty. Take note.


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## Shorty Circuit (Jun 26, 2010)

John Valdes said:


> Great point JRaef. Single OLR's would not shut down individual fans on a single system drive. Glad you caught that mistake on my end.
> The manual OLR/starter makes much more sense. We do not want to loose all the fans if one f's up. Thanks.
> 
> Shorty. Take note.


Clearly each motor nees an individual overload but the chart allows 800% for the OPD if it's a CB, in this case probably a 50 or 60 amp CB to protect 6 motors with an FLA of 6.7 amps each. The question isn't whether or not this is a smart thing to do, it's whether or not it's code legal. The VFD has protection against short circuits so a failed single fan motor will likely not take it out if the overload works. I've never liked fuses on three phase motors, too much chance of single phasing them and burning them up. 

It's interesting that the spec for VFDs and motor starters is in Division 15 (now something like Division 25 in the revised AIA scheme) and not in Division 16. Generally the Mechanical Engineer specifies how the system is to perform and the contractor essentially designs it and submits it to the ME for approval. All I do is bring power to a disconnect switch and provide power for a PLC. At worst an I&C engineer will look at it and decide what he wants.


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## JRaef (Mar 23, 2009)

My experience is that it's about 50-50 as to whether the VFD spec is in Div. 15 or 16. When it's in 15, it's usually associated with being part of a mechanical system that has an overall performance spec for the entire system. So they don't want to create a finger-pointing scenario because the EC chose a VFD that prevents the MC's equipment from meeting the performance requirements. But when the CE knows what they are doing, they will include the VFDs in Div. 16, and _especially _if they are to be mounted in MCCs.


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## Shorty Circuit (Jun 26, 2010)

John Valdes said:


> Great point JRaef. Single OLR's would not shut down individual fans on a single system drive. Glad you caught that mistake on my end.
> The manual OLR/starter makes much more sense. We do not want to loose all the fans if one f's up. Thanks.
> 
> Shorty. Take note.


This is true about the OLRs IF there is no other control. In my case there will be an air flow monitor that will ramp up the speed of the surviving five to compensate for the loss of one fan achieving the set point. One question for the ME has to be what happens if the unit operates in bypass, will the fans overpressurize the duct? If the set point is at say 80% of maximum fan hp output to achieve the desired flow anticipating a 16% loss if one of six fans fails, there should be no problem. But what if it's at say 30%? Then the airflow would be over 300% its set point. 

It seems that for 6 fans the 800% MOP in the chart is just adequate for a single breaker to handle all six and still meet the requirements of 430.53. Any more an there would be a problem.


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## John Valdes (May 17, 2007)

The designer should be able to answer those questions, especially about the bypass.
Is there a damper on the suction end of the duct work? This could be adjusted for bypass operation if fan speed (vacuum/pressure)is an issue.

I did see a 50" duct collapse one time as it drew way to much air and turned the ductwork into a used beer can.

800%? If you are using an inverse time delay (everyday type) breaker, your multiplier is 250%. What am I missing?


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## McClary’s Electrical (Feb 21, 2009)

Jraef, we did a fan shed with (64) 5 HP fans. (32) on each end. (2) VFD's.
The overloads we used do not open a control circuit. They opened line voltage. Each opens and operates independantly of the other 63 motors.


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## JRaef (Mar 23, 2009)

mcclary's electrical said:


> Jraef, we did a fan shed with (64) 5 HP fans. (32) on each end. (2) VFD's.
> The overloads we used do not open a control circuit. They opened line voltage. Each opens and operates independantly of the other 63 motors.


You must have used manual motor starters then. If it has contacts that open the power circuit, that makes it a starter.


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## McClary’s Electrical (Feb 21, 2009)

JRaef said:


> You must have used manual motor starters then. If it has contacts that open the power circuit, that makes it a starter.


 

No, a starter needs control voltage to operate an engage. These were overloads connected to a central bus connected to a VFD. 32 taps off of buss to overloads. No starter.


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## Shorty Circuit (Jun 26, 2010)

mcclary's electrical said:


> No, a starter needs control voltage to operate an engage. These were overloads connected to a central bus connected to a VFD. 32 taps off of buss to overloads. No starter.


The control voltage comes either from the built in microprocessor or from an external command such as a PLC. (There are manual across the line starters which simply use pushbuttons. It's the cheapest starter you can get.)

The MOP circuit breaker for grouped motors over 1HP is given in table 430.53. It should be a magnetic breaker or an HACR breaker of no more than 800% of an individual motor. This recognizes the need to ride through the inrush current of all motors starting at full voltage at the same time. Individual protection is provided by the OLRs on each individual motor. There are VFDs where each motor has its own separate speed control circuit but using one VFD controller for all of them is the cheap way out. It does not offer the level of monitoring and protection for all motors as it would for one individual motor however.

It isn't what I would have chosen but my only concern is whether or not it is code legal and it appears to be IF these criteria are met. The cut sheets submitted also didn't qualify the equipment for EMI/RFI protection nor for THD both at the input to prevent reflected harmonics generated back at the distribution network nor at the output to prevent waveform performance from compromising the lifespan of the motor. It's my hunch that the manufacturer will be able to provide satisfactory responses to requests for this information.


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## JRaef (Mar 23, 2009)

mcclary's electrical said:


> No, a starter needs control voltage to operate an engage. These were overloads connected to a central bus connected to a VFD. 32 taps off of buss to overloads. No starter.


I'm not trying to be argumentative, but there are some finer distinctions to be understood here, if not for you, for others who are looking to learn. It's just semantics really, but although I'm sure you did it right, if someone unfamiliar reads "overload relay" and does it that way, they end up with the problem the OP now has.

A "Motor Starter" is a switching device plus an overload. 

The switching device can be a magnetically operated contactor with a control circuit, but it can also be a mechanical device that is directly engaged by the operator and disengaged by the overload trip mechanism.

If the switching device is a magnetically operated contactor where the overload relay opens the contactor coil control circuit to drop it out, we call that a "Magnetic Starter", or shortened to "Mag Starter".

If the switching device is a mechanical device that is engaged by the operator and disengaged by the overload trip mechanism, we call that a "Manual Motor Starter", often shortened to MMS but also called a "Motor Switch". There is no control circuit necessary for that.

There are two styles of MMS, one is the more traditional NEMA design with a large set of NEMA rated contacts and two push buttons, and an IEC style that is sized specifically for the motor FLA and can have push buttons or a rotary switch mechanism. The main difference though is that the IEC styles ALSO include the Short Circuit Protective Device necessary for a complete motor circuit. So a NEMA style MMS still has to have a SCPD added to the circuit, i.e. a circuit breaker or fuses, but the IEC style already includes it, along with a legal LOTO provision, not found on the NEMA version.

An Overload Relay is strictly a sensing device that has a *pilot duty auxiliary contact* that is used in the control circuit of a mag starter. There is no device in an overload relay that interrupts the flow the motor power circuit. If there is, and there is no control circuit, that means it is a manual motor starter.

Mag Stater:









NEMA style Manual Motor Starter:









IEC Motor Protective Switch / Manual Motor Starter:









Overload Relay (IEC style), no power switching capability:


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## McClary’s Electrical (Feb 21, 2009)

JRaef said:


> I'm not trying to be argumentative, but there are some finer distinctions to be understood here, if not for you, for others who are looking to learn. It's just semantics really, but although I'm sure you did it right, if someone unfamiliar reads "overload relay" and does it that way, they end up with the problem the OP now has.
> 
> A "Motor Starter" is a switching device plus an overload.
> 
> ...


 
Thanks Jraef, as usual, you're the best. I didn't realize what I said wasn't what I meant:laughing:. Mine were manual starters/overloads.


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## miller_elex (Jan 25, 2008)

Yes I've done at least fifty fanwalls.


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## McClary’s Electrical (Feb 21, 2009)

JRaef said:


> I'm not trying to be argumentative, but there are some finer distinctions to be understood here, if not for you, for others who are looking to learn. It's just semantics really, but although I'm sure you did it right, if someone unfamiliar reads "overload relay" and does it that way, they end up with the problem the OP now has.
> 
> A "Motor Starter" is a switching device plus an overload.
> 
> ...


 
I figured I'd expand on this further with some pictures:









(32) (5) HP motors on each side. 64 total








Common VFD for each side








Idividual overloads tapped








Just like Jaraef said


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