Remember the ABB invertors story?

Goody

Member
Join Date
Apr 2002
Location
Huddersfield W Yorks UK
Posts
1,081
Can you remember the post of mine back last year when ABB sold a customer of mine thousands of pounds worth of invertors to save them thousands of pounds of electricity?

Well, its raised its head again.
There have been meetings with ABB specialists and for whatever reason I was not included.

If you can recall, the first machine where these invertors were fitted by me was a fabric drying/treatment machine and when the circulation fans were slowed 10%, the fabric was not treated or dried properly.

ABB came up with lots of ideas and excuses and I think they are still doing the same.

Its moved on now to the customer fitting F1 fan motors with newly designed fan blades.
I have to wire a binary rotary switch to allow the invertors to run at 6 or 7 separate speeds.
These speeds are only going to be 1HZ apart (I think) and different fabrics are going to be monitored by the management at different speeds.
Meanwhile ABB are going to fit a KWH monitoring device to show the customer just how much money they are saving.

I will fit the switch and play along, my advice and thoughts seem to be of no consequence to them.
I will do the work and get paid. I just thought I would give you an update and would appreciate any comments especially from our resident and much revered ABB motor guru.
 
1'stly important phase is PROCESS engineering and dimensioning.
2'ndly mechanical dimensioning must be as process engineers have plant, not over or under dimensioning !
3'rdly important thing is electrical engineering for energy saving.

Fans, pumps etc. must work on their nominal curve and this is mechanical engineering plant.
It means that wrong pump- or fan construction mainly 'cavitate' and needs more power than with correctly pump or fan. If it is so, we can't save energy with VFDs etc. as much as possible becourse motor itself not work in its best nominal value.
If pump or fan load is continiously under 60%, (even 10%, I have seen)it means a lot energy lost in the motor winding and iron. Motor takes reactive current who is ~50% of nominal current even without load.

Motor must be winding as near as possible of the used main voltage, 400V for 400V (not 380V) etc.
Motor efficiency factors are very diffrent today, becourse old motor could have bad efficiency.
 
Goody,

When properly sized and installed a VFD will save a ton of money on energy cost. First by helping with demand, if the customer is billed this way, which most here in the US are. Second by the amount of power consumption used by a motor not running full speed on a variable torque application such as a fan or pump.

If you have a 100HP motor on a fan or a pump application and reduce the speed by 10%, you have effectively reduced your 100 hp load to about a 73HP load, which equates to a 27% energy savings. If I remember correctly, current is = to the inverse of speed cubed or something like that (I don't remember the exact formula for this, I cheat with one of several energy savings software’s I have from different vendors).

The point is the slower you run the pump or fan in your case the greater the savings, for example if you dropped the speed to 80% the effective load would be a 53HP motor, for a 47% energy savings.

With that being said if your fans running at 90% speed are not moving enough air to properly dry the fabric, then the only benefit for energy saving on your project is to help lower the demand at the plant, there would be no energy saving at all as ohms law applies. While you may lower the starting current of the motor, you are stretching it out over a longer period of time, so the power consumed is the exact same, so you have no energy savings what so ever. This same benefit can be achieved by using a soft starter at a greatly reduced cost savings.

While the ABB guy’s in your mind are selling a ton of BS the truth is that you can achieve a tremendous amount of money using a VFD on a variable torque application, when you do your homework and know that you can get the same results running at a slower speed. If you don’t do your homework then you could be throwing good money after bad, as it appears to be in your case.

Mike
 
Seppo and Mike and anybody else who's joined the forum in the last couple of months.

Goody started this saga back in November. Here's a link to the original.

http://www.plctalk.net/qanda/showthread.php?s=&threadid=1656

It's very interesting reading.

Goody, I'm wondering now if there were discussions that you weren't privy to before the customer bought these 30 drives. It's beginning to sound like the customer is embarking on a program to improve the entire process. Installing new fan blades is not a trivial expense, and it's hard to imagine ABB going to that expense to prevent having the drives returned because they didn't live up to the original estimates of energy savings. It's equally hard to imagine the customer paying for the new blades unless it was part of the original plan. I say it's hard to imagine, but not that it's impossible to imagine. I've seen people implement some elaborate schemes to cover their blunders.

Thanks for the update and please continue to keep us posted. This could get very interesting.
 
Steve,

I am sorry I was a member back in November but I did not remember this post, thanks for the link it was very informative.

Mike
 
I have a very similar situation to the customer of Goody, I have in excess of 50 inverters on water pumps that have between 1 and 37kW motors. I use the variable speed with a PID loop to maintain a pressure of about 3 bar on most pumps and it works very well. Before I had pumps that were sized on maximum demand so we had a huge bypass valve that was open the majority of the time otherwise the pressure would raise to 6 bar and wreck my heating jackets etc.
I would say this though if you have a situation where you want to slow pumps or fans by 10% and not actually vary the speed, inverters are a waste of money and you should engineer your system propely and install pumps, fans and motors of the right size! This will save you far more money than an inverter ever will!
 
At the risk of repeating some of the comments in the earlier thread, there is no such thing as a magic bullet for energy savings or anything else in the industrial automation field. You have to understand the process and how each piece functions in the process to identify waste and potential savings.

The fundamental problem with Goody's customer's process is that it appears that all of the fan output at full speed is required all the time. No amount of snake oil or crafty salesmanship is going to get any savings with a VFD or anything else, if that is truly the case.

That reminds me of a situation I ran into a couple of years ago where a softstarter had been installed on a machine that required ALL of the motor's starting torque to get moving from stop. I could barely suppress a few cheap giggles when the customer expressed his frustration in not reducing his inrush current with the new softstarter.

Really, now, everyone, the laws of physics and conservation of energy aren't called LAWS for nuthin'!!!!!
 
It is an ill wind indeed that blows no one good

Well, Goody, I'm glad that you are at least earning something from this fiasco.

As previously stated, The first LAW of thermodynamics is conservation of energy. If the new fans save money it's because they are higher efficiency than the old ones.

Here is a link that shows how a successful installation is engineered to use VFDs and reduce the energy required to move air:

http://ecmweb.com/ar/electric_retrofitting_vfd_motors/index.htm
(You may have to register to see the article.)

Here is a graph that doesn't show up on the article:

There is no magic bullet! These are higher pressure than a typical fan, but the same engineering principles apply.

uniontow.jpg
 
And now for the rest of the story

Here is the actual field test data from this application. The energy savings is considerable, BUT in order to achieve them you have to be able to reduce flow. The savings in this application, as in most of the good applications for VFDs, is the result of the air moving equipment having higher pressure and flow capacity than the process demands. In addition the application is one with varying demand for air flow, so as the blowers are controlled to reduce output the savings are increased.

In your application, Goody, it seems that the fans are providing the precise capacity the process demands, and they cannot be turned down to lower output. Savings from using of VFDs will therefore be non-existant.

unpwr.jpg
 
Tom, the airflow/hp curve you provided on the Lamson blower isn't what I would expect from most fans. I'm not contesting your data here; the fan may well have a non-conventional characteristic curve.

My question comes with regard to the shape of the VFD curve. Since most fans follow the rule of flow being proportional to speed, shaft torque being proportional to the speed squared, and horsepower being proportional to the speed cubed, it seems that the curve should have much more vertical curvature to it.

For example, on your curve, the hp at 3500 cfm is about 120 and the hp at 7000 cfm is only 230. I would normally expect a shaft speed change of 2/1 over that flow change, a torque change of 4/1, and a horsepower change of 8/1. Your fan curve is radically different.

Is there an explanation for this that you know of.
 
Turboblower is an one specific kind of blower where the air flow is not proportional to the rotational speed, 'output' will vary much regarding the wing parameters.

Turbo is also more efficient than radial blower they also can generate substantially more dynamic pressure than radial fan because they are pumps in their nature.

I suggest that you introduce yourself to the turboblower technology it might help to provide an energy saving solution on this question in hand.
 
Hey, Goody. Did I miss it or is your customer using a conventional fan. Seems some turbo blower data has gotten involved in this thread and may or may not be applicable.

Please advise since there is a huge difference between the types in how an inverter is properly applied for energy savings.
 
They were just conventional aeroplane type propeller fans (4) but I don’t know now for sure as I am being phased out of the equation. Apart, that is, from the fitting of any new electrical control ideas.

I have become passive now with them – what can you do if they won’t listen.
I sincerely think that my customer is being seduced by all the techno-babble they are getting.

I know that they have always been very keen to save any electricity in any form. (no bad thing)
We have fitted all sorts of power saving devices in the past even down to a single PIR sensor for a single 100W incandescent lamp.
(I am not joking and it cost them £300 for it too)
If the boss hears the words, ‘this will save you money’ that’s all it takes.

But all the same, I shall keep everyone posted as the events nfurl.

This 6 or 7 position switch I am fitting is making me laugh.
I am going to have to make it select 46HZ – 47HZ etc up to 50HZ. Unbelievable.
But maybe there is a little voice somewhere in the back of my mind saying maybe they will pull it off.
 
It sounds like you people are all of an engineering background.
I am a 30 year industrial electrician.
The past 15 years I have been working quite a bit on AB VFDs, mostly larger ones because they seem to fail quite often.
I can understand installing a vfd for energy savings on start-up and continous duty. The thing I don't understand is that nobody seems to monitor before and after cost of running equipment, at least at my plant.
Why would want to install VFDs on multiple systems without knowing for sure if it is going to work on a single system?
 

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