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Any Potential Savings For Large Motors


cdroot4383

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Hello everyone,

 

First of all, I wanted to say this is an excellent forum, and even though the terminology is a little different in the states (metric instead of US standard) all the concepts are the same. Anyways, I am part of a team to begin saving money with our large motors (2000Hp) and fans (102" blades). The system consists of four motors and fans in parallel with one set on backup. The system consists of numerous dampers throughout to limit the air flow depending upon the application. Unfortunately, our power company and EPA have some stringent regulations on our plant:

 

1) while the fans are in operation, they must draw minimum kWhr rate, regardless of system needs (imposed by the EPA)

2) the power utility does not charge for poor power factor

3) the kWhr price does fluctuate, but that is dependent upon the supply and demand of the community needs and are not any increases in price during high surge applications

 

thankfully, I read the website wasting a lot of time investigating these so called "energy saver" devices since they would appear to work in this application. We looked into the soft starters and VFD, but the soft starters seem to only help with the mechanical wear and tear of starting the load and the VFD would allow the system to be properly controlled, but would reduce the minimum kWhr draw get us in trouble with the EPA

 

Basically, is there any way to have energy savings when the EPA regulates the minimum power draw required and when the system operates at this range continuously.

 

thanks in advance,

chris

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Dear cdroot4383,

I'm happy when someone want to save energy!

 

First of all, look to the load. Are there some aerodynamic obstacles that could be removed? Is there some right-angle deviation that could be smoothed? You could save hundreds of kW if actual shapes are not perfect.

 

Additionally, you could improve the lubrication using special oils or greases. You could improve the belt transmission, if possible.

 

On some applications, fans rotors could be painted to have less aerodynamic losses.

 

After that, if you will give the data of your motors (DC? AC? Which type?) , we will give you also electrical suggestions.

 

Regards

Mario

Mario Maggi - Italy - http://www.evlist.it - https://www.axu.it

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mariomaggi,

 

Energy savings has been the top of the mission statement at the plant for sometime here at our plant, especially since our entire energy costs almost $2,000,000 per month (thats only electrical).

 

I personally could not figure out a way to justify upgrading the system if the Environmental Protection Agency (EPA) requires a minimum power draw (kWhr rate). I think upgrading the system would improve the flow to the system, but would not reduce any costs and save energy because of the minimum kWhr, but i may be wrong. I definitely agree that improving the lubrication on the system will help with the premature failure to the mechanical aspects, which would lead to lower maintenance costs and save money, but how does that save on the electrical power with the EPA restriction?

 

I havent had an opportunity to look at the system in detail, other than there are dampers used in the system at certain times (during maintenance to exhaust fumes). Here are some of the specs for the motor and fans

 

motors:

2000HP

70% efficiency (seemed awfully low for a motor of this size, i think there may have been a typo on the paper, did not have the opportunity to check name plate data)

2300V

400A

 

Fans:

98" impeller (not the 102")

720 RPM

forward curve, radially tipped

other gases besides air in stream, argon, nitrogen, oxygen

Air temperature = 310 degF

 

thanks in advance,

Chris

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Hello Chris

 

In broad terms, I would not expect to save energy with large motors, but you can commonly save energy by altering the way that they are used.

Large motors are usually inherently pretty efficient and only exhibit "low efficiencies" at very low shaft loads. The losses are still small relative to the motor rating. Flawed logic is typically applied to the concept of saving energy with induction motors with many claims made about oversized motors etc, but although the expectation of the uninitiated is that the large motor will draw large power under light loads, the reality is that the motor reduces power consumption to match the load by the very way that it operates.

 

Many applications employing these large motors operate inefficiently, even though the motor it self is operating efficiently.

A common application that drops system efficiency, is a centrifugal pump operating against a closed valve or variable flow with the pump operating at full speed. The pump will absorb a lot of power when it is "dead headed". Slowing the pump down so that the speed is in synch with the flow requirement will keep the pump operating at maximum efficiency.

Similarly, a fan where the air or gas flow is controlled by shutters or dampers can wast a lot of energy spinning the gas rather than moving it. Slowing the fan down so that it can operate without any throttling will reduce the fan losses (not the motor losses).

 

To save energy, you need to determine where the energy is being wasted and find ways to reduce the wastage.

 

Best regards,

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Hi Chris, could you please clarify some thing? Are you saying that the EPA is insisting that you must draw a minimum amount of power at all times? This seems fairly counterproductive for an enviromental protection agency <_< Is it possable that they insist on minimum FLOW rates? If the EPA is insisting on a minimum energy draw then there is no point in attempting to install energy saving devices. :(

 

Ken

An expert is one who knows more and more about less and less until he knows absolutely everything about nothing
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Chris,

70% efficiency

this is a very bad figure, probably it is wrong! Is a wound rotor motor?

Efficiency must be over 96%. Probably your motor has different motor data.

 

Let us know.

Regards

Mario

 

In which country are you working?

 

Mario Maggi - Italy - http://www.evlist.it - https://www.axu.it

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kens,

 

That EPA regulation to require minimum power consumption was something that had to be explained to me a couple of times, because it didnt make any sense. The flow rate is the important parameter in determining that the system is working properly to ensure a safe work environment for all of the employees. With the minimum power consumption restriction, I wanted to be sure that I did not overlook a simple to save energy, but I wanted some other opinions. I could not see a way to save money if there was a minimum power consumption rate and we operate at that rate most (if not all) of the time.

 

mariomaggi,

 

I definitely agree that the low efficiency did not make any sense. I have a feeling that the 70% is the efficiency of the system. According to the fan curves from the manufacturer, the fan itself is efficient (high 70%). I am working in the United States.

 

marke,

 

I think the next step is to find the flaws in the system and come up with a report that could show (and prove financially) that the true deciding factor to the system performance is the flow rate and not the minimum power consumption. I'll talk with my supervisors and see which route we can take to minimize the amount of energy used in our system

 

thanks again for everyone's help,

chris

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Hello Chris

 

As I understand it, the EPA have specified a minimum air flow rate and that this has then been converted to power input?

If the air flow rate is being reduced by dampers, then the fan efficiency will be reducing. There will be power dissipated in the air circulated by the fans. If you look at the input energy, you can separate that out to work being done in creating the air flow and power lost in circulating the air, so input power is not a good indicator of flow rate.

If you measure the rate of air flow, and the pressure differential across the fan (input to output before the dampers), you should be able to get an indication of the fan efficiency from the manufacturers. Compare this to the efficiency unrestricted and that will give you an indication of the losses. If you slow the fans down, you will improve the fan efficiencies and save energy.

 

Best regards,

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Hi Chris, as Mark has said measuring input power is an poor method of measuring flow. If the reason for the EPA regulation is to ensure minimum flow rates then there is a great potential for energy savings . The idea would be to install flow measuring stations to accuratly measure flow and use a VSD to vary fan speed and therefore flow. It is a simple matter to set a minimum fan speed , therefore minimum flow, into the VSD and also to have a bypass system so should there be a VSD fault the fan can run full speed. The financial proof will come naturally once you run some numbers through. Remember the centrifugal fan laws - 20% speed reduction = 50% energy reduction. Flow is proportional to speed.

 

There are a few clever members of this forum who are based in the US. I know its a pretty small place so you probably know them :D , at least they may be a little more familiar with the bureaucracy over there regarding the EPA.

 

Good luck and let us know how you get on.

 

Ken

An expert is one who knows more and more about less and less until he knows absolutely everything about nothing
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cdroot4383,

 

I certainly appreciate the utterly ironic and ridiculous nature of this minimum energy consumption issue, but I hope you realize that you are saying that you want to "save energy" yet you are not allowed to reduce your kWh. Energy use is MEASURED in kWh! So you cannot save kWh and keep kWh the same, that statement makes no sense.

 

So I agree with Marke and kens, the first step is to get to the root of what this EPA requirement is all about. If their insistence on a kWh usage is a crude way of determining total flow, then someone needs to engage them into rethinking a more accurate method of measurement, i.e. real flow instrumentation with totalizing. That is typically done with a strip recorder or chart recorder. Then you can optimize your energy consumption while maintaining the flow requirement they want. Once you get to that point, there are a lot of different ways to approach the savings, both mechanical and electrical.

 

That said, I have seen sometimes where power measurement is used because it is difficult to cheat on it, i.e. maybe the EPA has caught your employer or a competitor in falsifying records in the past. They may have come up with this method because they know the utility will not let them get away with trying to cheat on power use, and the utility is already a watchdog so the EPA doesn't need to do that themselves. If that is the case, you are wasting your time trying to "save kWh and keep kWh the same". Start concentrating on maximizing your up-time by reducing maintenance and mechanical breakdowns, in which case the soft starters may play a pivotal role.

"He's not dead, he's just pinin' for the fjords!"
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hello again,

 

I definitely agree with everyone here that having a minimum input power for operation is a poor and inefficient way of handling the system. Ever since I have been working here, everyone who is responisble for the energy in the plant has stated that the EPA regulates the input power to the system and not the flow rate. Basically, you could close all the dampers in the system and as long as the motors and fans are using the minimum kWhr rate, the EPA would be happy.

 

I decided to post this question here and I got the answer I was hoping for in that:

1) I wasnt the only one confused why the EPA would have a restriction on the minimum input power instead of the flow rate

2) It is impossible to have any savings if the system is operating at the minimum input power rate.

 

I'll try to discuss this with my supervisors and see if there is a way to get this regulation changed to a minimum air flow rate, which is the true deciding factor if a fan is working properly. As soon as I find out anything else i'll let everyone know

 

thanks again for your help,

chris

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  • 2 weeks later...

Hello Again,

 

After a couple of weeks of pure confusion about the EPA standard, we finally got some clarification on this minimum input power restriction. It was music to my ears to hear that the EPA does not require a minimum amount of input power draw. After going through a couple of layers of management, the minimum input power draw has been self imposed by our facility. This was done to ensure that our shop floor area was free from toxic fumes and this minimum power draw was a value that ensures a safe work environment 24/7/365.

 

Currently, we are planning to improve all of our vent hoods and inspect the duct work to minimize the losses. Once this part is fixed, we are going to look into purchasing some NEMA premium motors (current motors are 25+ yrs old) with VFD's to fine tune our system.

 

Thanks again for everyone's help,

Chris

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Hi Chris, thanks for the update. Perhaps you could let us know your results when the project compleated.

 

Ken

An expert is one who knows more and more about less and less until he knows absolutely everything about nothing
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