Hello Forum. I am new to the site, so thank you in advance for creating such a open forum to discuss the industry. I am trying to understand the frictional losses for a standard fixed grip lift system, and any help would be greatly appreciated. Presumably, there are losses transfering power from the engine to the rope, and then losses as the chair moves over the sheave wheels on the towers and around the bull-wheel. If coefficents for each step are available, that would be great, or just an estimated % losses for an entire system. Thank you.
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Frictional Losses
Started by lift-tech, Jul 26 2010 02:42 PM
7 replies to this topic
#2
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Posted 26 July 2010 - 02:59 PM
Others will no doubt have more specific data, but my experience shows that an empty fixed-grip lift (of any horsepower) requires about 20 t0 25% of the machine's normal "full load" requirement.
This post has been edited by Emax: 26 July 2010 - 02:59 PM
There are three roads to ruin; women, gambling and technicians. The most pleasant is with women, the quickest is with gambling, but the surest is with technicians. Georges Pompidou
#3
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Posted 27 July 2010 - 01:19 PM
Thanks Emax. Any ideas on how much of this loss is attribtuable to the gearbox/engine/drive and how much is attributable to the towers/wheels or anything sources? Thanks again.
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Posted 27 July 2010 - 02:25 PM
lift-tech, on 27 July 2010 - 01:19 PM, said:
Thanks Emax. Any ideas on how much of this loss is attribtuable to the gearbox/engine/drive and how much is attributable to the towers/wheels or anything sources? Thanks again.
I would expect that the majority is the result of the line friction / cable flexure. The motors and (most) gearboxes are quite efficient.
There are three roads to ruin; women, gambling and technicians. The most pleasant is with women, the quickest is with gambling, but the surest is with technicians. Georges Pompidou
#5
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Posted 28 July 2010 - 05:36 PM
20-25% for a fixed-grip seems a bit right. I have experience logging kW load on detachable ski-lifts, which generally pulled 25-30% kW load, empty, when running at near full speed (typical 90%, 4.5m/s on lifts designed for 5.0m/s). Higher empty kW when very cold.
Empty kW load was higher in the morning, and perhaps 5% lower late in the afternoon (same ambient temperature).
All my data was for top-drive lifts. Others have studied top-drive vs bottom-drive, with top drives 10-15% more efficient then bottom drive. (I can dig up the info if any interest)
The difference between fixed-grip and detachable is likely due to the power requirements of the accelerator/decelerator & turnabout machinery. Obviously there is a lot of friction losses in these systems. Rubber belts & tires like to be warm, and that requires energy input of one form or another.
Many ski-lifts use more energy to heat the stations & machinery, then to actually turn the lift & move customers. Effort focused on energy efficient heating controls pays back many $$. Of course you want your machinery warm for start-up... but why are your unit heaters running at midnight? Point heat, on hydraulic systems, motors, gearboxes & controls, is important to keep the moisture & condensation out, but why heat the entire station (& planet) when not needed. Heat-lamps work great on tires & belts to get them quickly supple for cold morning start-ups.
Empty kW load was higher in the morning, and perhaps 5% lower late in the afternoon (same ambient temperature).
All my data was for top-drive lifts. Others have studied top-drive vs bottom-drive, with top drives 10-15% more efficient then bottom drive. (I can dig up the info if any interest)
The difference between fixed-grip and detachable is likely due to the power requirements of the accelerator/decelerator & turnabout machinery. Obviously there is a lot of friction losses in these systems. Rubber belts & tires like to be warm, and that requires energy input of one form or another.
Many ski-lifts use more energy to heat the stations & machinery, then to actually turn the lift & move customers. Effort focused on energy efficient heating controls pays back many $$. Of course you want your machinery warm for start-up... but why are your unit heaters running at midnight? Point heat, on hydraulic systems, motors, gearboxes & controls, is important to keep the moisture & condensation out, but why heat the entire station (& planet) when not needed. Heat-lamps work great on tires & belts to get them quickly supple for cold morning start-ups.
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Posted 29 July 2010 - 12:11 PM
mthornton, on 28 July 2010 - 05:36 PM, said:
Others have studied top-drive vs bottom-drive, with top drives 10-15% more efficient then bottom drive. (I can dig up the info if any interest)
Yes, I'm interested. Thank you.
This post has been edited by Razvan: 29 July 2010 - 12:12 PM
#7
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Posted 29 July 2010 - 05:29 PM
Razvan, on 29 July 2010 - 12:11 PM, said:
Yes, I'm interested. Thank you.
From Greening Your Ski-Area, A pollution Prevention Handbook
from chapter 8
Top drive vs botton drive energy efficiency go to section 8,1
The entire chapter 8 is pretty good reading, but don't believe everything you read on the internet. For example, the section on harmonics mitigation reads like a sales-pitch for active harmonics filters. Proper transformer selection & good electrical distribution design is greatly preferable to active filters (a desparate last resort.)
#8
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Posted 26 August 2010 - 06:36 PM
Generally, frictional losses between the ropes and the elastomer sheave liners are assumed to be between 2% and 3% of the supported pressure. For the bullwheels, it is anywhere from 0.3% to 2%. There are differing opinions on this, and a lot of research.
The driveline efficiences tend to be about 10 to 15%. This varies according to the type of drive and gearbox used and whether there are tire drives (for detachables).
As far as the differences between top drive and bottom drive lifts, in my opinion, there is very little advantage when lifts are 150HP or less. This is because a minimum tension must be maintained at the lower terminal regardless of lift size. So the ropes tend to be the same size for top or bottom drives for these smaller lifts. A bottom drive and tension is usually the cleanest arrangement for a fixed grip and rope tensions are easier to optimize. The worst is a top drive and top tension. Of course there will always be a suitable application for any particular arrangement.
The driveline efficiences tend to be about 10 to 15%. This varies according to the type of drive and gearbox used and whether there are tire drives (for detachables).
As far as the differences between top drive and bottom drive lifts, in my opinion, there is very little advantage when lifts are 150HP or less. This is because a minimum tension must be maintained at the lower terminal regardless of lift size. So the ropes tend to be the same size for top or bottom drives for these smaller lifts. A bottom drive and tension is usually the cleanest arrangement for a fixed grip and rope tensions are easier to optimize. The worst is a top drive and top tension. Of course there will always be a suitable application for any particular arrangement.
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