Belt slipping on AHU waisting KW

[hurk27]

I haven't seen anything in writing that it is guaranteed but this is why they are doing this test and recording the KW with a meter. This unit was a free-bee to change over in hopes they can prove the change will save money.

Yes we would have seen an increase in KW but the funniest part is there is a chance the fan would not have lasted long at 2200 RMP. She was a screaming when it was first started.

I already see one problem, the fact that the mechanical ratio between the motor and fan has changed, this will affect start up of motor as well as any ability of running it in bypass mode if ever needed in case of drive failure, they should have been better at making sure the ratio between the motor and fan was not changed, if they had any understanding of what it would cause this should have been part of their design, who are these guys??? sounds sloppy to me, in any constant torque application RMPs of the load can make a big difference as well as start up load on the motor if the ratio is less then what it was to start with?

 

[hurk27]

It was a bum rap................

I don't know some count years and some count rears, sounds like more fun

 

[Microwatt]

I already see one problem, the fact that the mechanical ratio between the motor and fan has changed, this will affect start up of motor as well as any ability of running it in bypass mode if ever needed in case of drive failure, they should have been better at making sure the ratio between the motor and fan was not changed, if they had any understanding of what it would cause this should have been part of their design, who are these guys??? sounds sloppy to me, in any constant torque application RMPs of the load can make a big difference as well as start up load on the motor if the ratio is less then what it was to start with?

There guys are just salesmen trying to make a sale. I would give the name of the company but I don't think that would be fair.

When the HVAC guy first saw the pulleys weren't the same size he brought that up to them and their response was "close enough". There was no design involved at all with this. They came in to our boss with a fancy power point presentation and some thermal imaging pictures and told him thousands of dollars could be saved. They said they would even install the system on one of our units and record KW before and after to prove it. So here we sit. I just don't think they expected to run in a couple of us that could see the flaws in what they were presenting.

They didn't even know how to use the KW meter. They needed me to set it up for them.

 

[gar]

130411-1040 EDT

Unless you had exactly the same , or extremely close, mechanical ratio to the actual application the motor would have a different efficiency and no meaningful change up or down could be shown.

To run this test an accurate dynamometer load, and stable voltage source are required. Then the cogged belt ratio has to be determined, and the V-belt ratio adjusted to be the same. Mechanical loading should be approximately the expected operating level.

.

 

[kwired]

There guys are just salesmen trying to make a sale. I would give the name of the company but I don't think that would be fair.

When the HVAC guy first saw the pulleys weren't the same size he brought that up to them and their response was "close enough". There was no design involved at all with this. They came in to our boss with a fancy power point presentation and some thermal imaging pictures and told him thousands of dollars could be saved. They said they would even install the system on one of our units and record KW before and after to prove it. So here we sit. I just don't think they expected to run in a couple of us that could see the flaws in what they were presenting.

They didn't even know how to use the KW meter. They needed me to set it up for them.

But had you not readjusted the speed with the VFD, you in fact would be using more energy before losses are even looked upon, as the actual blower output would be demanding more energy. If you had no VFD and the motor was originally sized to near output you would also be having overload problems with this motor after their change.

Close enough doesn't cut it with gears and pulleys. Small changes in sizes can make a big difference in output. Fractions of an inch at several hundred rpm ends up being a big change to the final output.

Problem is these guys are trying to make a sale to someone who knows more about what they are doing than they do. Interesting to see how long they keep trying to make a sale to your company, and what kind of BS they will come up with to try to make the sale.

 

[renosteinke]

Every means of transferring power has some inefficiencies, and various products have been invented to address specific requirements.

Heck, there's a case to be made for replacing the belts with chains and sprockets!

Sometimes you just have to back off, and trust the engineers at the factory to do their jobs!

Sure, V-belts slip, especially at start-up. That's not a bad thing; it's one reason V-belts are better for handling 'shock' loadings.

The cogged belts have a name that suggests their proper use: timing belts. There's nothing in the usual motor / fan arrangement that would benefit from keeping the motor perfectly timed to the fan.

The company is selling snake oil. IMO, they're doing unnecessary work, and lying like a carpet to make the sale.

If you REALLY want to save energy, you'll put a VFD on the motor, and adjust the motor speed to get exactly the desired air flow. "Extra" air flow only gets lost as friction within the ducts, anyway. Or, use larger ducts.

 

[GoldDigger]

If you REALLY want to save energy, you'll put a VFD on the motor, and adjust the motor speed to get exactly the desired air flow. "Extra" air flow only gets lost as friction within the ducts, anyway. Or, use larger ducts.

Which the OP already has, and used to adjust the fan speed to be the same after the drive change before making the new power measurements.
It sounds like they had already decided on (engineered?) the fan speed they want, so no room for savings there. But good advice for general consumption.