Speed control of escalators 1

[Marke]

There seems to be a move towards speed control of escalators such that they are slowed down when not in use. I understand that this is an effort to reduce the power consumed by the escalator. Anybody had experience with this and care to suggest actual savings?

Best regards

Mark Empson

http://www.lmphotonics.com

 

[ozmosis]

A few years (about 4) I got involved with a project where Otis were investigating the prospect of adding variable speed control onto escalators. The main benefit of this for the end users is to control the flow of people rather than use them for energy savings. Where escalators are used in 'exhibition area' such as one in Madam Tussauds we did where they wanted to restrict hundreds of people spilling out into the area below and also to provide better viewing of exhibits on the way down. It is not energy saving as it is more beneficial to switch them off than just slow them down (most airports do this and simply use sensors to start/stop). You will save more energy running at lower speed than maximum speed but the economics do not work too well when you can just switch off easily.

 

[jbartos]

Comment: This appears to be an alternative to an escalator time out during the slow traffic hours. The passenger must actually start the escallator, perhaps by a photocell. The principle is similar to the apartment building stairway lights in Europe being timed during the night. Anyone using the stairway has to turn timed stairway lights on during the night. This means that stairways are actually dark during night thus saving electricity.
Now, the escalators running slow during the slow traffic would have to be accelerated if the passenger arrives. There will some energy savings and a reduction of escallator wear. By letting the escallator time out (or sleep), there will be energy savings even higher and no expensive VFD required.

Also, visit

http://www.emsd.gov.hk/emsd/e_download/pee/guidelines on ee of lift & escalator installations.pdf

for:
5.4.2 Standby Mode of Escalators and Conveyors

 

[jraef]

It would seem to me that an escalator would be a constant torque load if it were carrying an equal number of passengers at a reduced speed, so the input power would be the same regardless: no energy savings.

The only thing I would guess at is that they slow it down when there are fewer riders, but that seems counterintuitive. If I was the only one on an escalator and it ran slower, I would not be happy.



"Venditori de oleum-vipera non vigere excordis populi"

 

[jraef]

Ah-ha!
If NOBODY was on the escalator it may look very similar to a centrifugal load: less work and lower speed means less energy consumed. You could of course shut it off, but if it was not moving everyone would think it was broken and being a "staircase", users would simply avoid it.

By running it slow the users understand that it works and get on. Then the motor drive could gently increase speed as it becomes loaded. A decent vector drive could monitor load kW and use that as the criterea for speed increase, so a photoeye would not even be necessary. The trick would be to entice the user onto the escalator so that it knows it needs to speed up, hence the slow unloaded speed!

One would save energy during the unloaded times but avoid having the users think it was inoperable.

Problem solved.

"Venditori de oleum-vipera non vigere excordis populi"

 

[busbar]

At zero speed, don’t escalators become “stairs”?

 

[ozmosis]

Energy saving stairs though!

 

[aolalde]

"jraef (Electrical) Mar 11, 2004
It would seem to me that an escalator would be a constant torque load if it were carrying an equal number of passengers at a reduced speed, so the input power would be the same regardless: no energy savings."

Please verify that;

E= P*t
P= 0.746*T*n/5250

Were:
E= energy (kw*hr) what you pay.
t= Time (Hrs)
P= Power (kW)
T= Torque (Lb*Ft)
n= speed (rpm)

If speed is reduced, (at constant torque) the Power is proportionally reduced and so is the energy consumption.

 

[jbartos]

Comment: The escalators save people energy since it takes some calories to walk up stairs. Also, they enable a smooth and predictable flow of the people traffic.

 

[aolalde]

So, may be the speed is reduced when the traffic increases?

 

[jarvis]

First they just need to make them safe for kids. My cousin who is only like four, lost his ballance at the bottom of one and got his hand pulled in with the stairs. His mom could hardly get his hand out and when she did the skin had been ripped off of it. The shop nearby said that he requested the mall get it fixed many times, but it went undone. I guess a screw was out of one of the cover plates so it was loose. This happened at the Mall-Of-America.

Ben Englund

 

[jbartos]

Comment on Marke (Electrical) Feb 28, 2004 marked ///\\There seems to be a move towards speed control of escalators such that they are slowed down when not in use. I understand that this is an effort to reduce the power consumed by the escalator. Anybody had experience with this and care to suggest actual savings?
///Assume 10HP motor (HP varies with the length of escalators) that is loaded lightly with no one on the escalator. It may easily be loaded about 1/20 of rated HP, e.g. 20HP/20=1 HP. 1HP=746Watts. During several night hours, e.g. 8hours, the savings will be .746kW x 8hour x .1$/kWhr=0.6$ or 60cents.\\\

 

[ozmosis]

I was on an escalator recently going up, looking at the other escalator right next to me going down. It got me thinking about this thread. I think we've established that there is little in the way of energy savings to be had on an escalator. However, if you were to link on a common DC bus one inverter for driving and one inverter for regenerating, the potential is there to have one inverter feeding the other and therefore drastically reduce the rectifier feeding the two inverters. It's a common application in winding applications where the regen energy is used to feed the driven and thus reduce the overall cost of a system and therefore cost of energy drawn from the supply.
I can't say I've done it on an escalator but it would make an interesting engineering exercise.

 

[jraef]

sed2developer,
Interesting point, I wonder if it has been investigated. The only thing about it is that I know that escalators must be motored even going down. I'm not sure if it is friction in the drive system being more than the force that the load (people standing on it) can exert, or if they use the motor as a governor to keep it from free-wheeling down. If it is the latter, your idea may have merit.

"Venditori de oleum-vipera non vigere excordis populi"

 

[jbartos]

Comment on sed2developer (Electrical) Apr 1, 2004 marked ///\\However, if you were to link on a common DC bus one inverter for driving and one inverter for regenerating, the potential is there to have one inverter feeding the other and therefore drastically reduce the rectifier feeding the two inverters.
///Please, would you elaborate on this?\\///Normally, two sided VFD (with Active Front End (AFE)) does not have the direct rectifier feeding. It uses the front AC-DC converter in reverse way as a DC-AC inverter.\\\

 

[ozmosis]

jabartos
I wasn't thinking of a regenerative front end (either active or back to back diodes) although this could be used. My theory was based on using one stand-alone 6-pulse rectifier rated for (probably) about 1.25 of the driven and regen load. This assumption is based on the theory that one of the inverters is driving the escalator UP and one is being 'driven' DOWN. If this is the case then the inverter driving UP(the term inverter is being used correctly in this case as the DC fed converter of DC volts to a PWM AC output)could (theoretically) use the regenerated energy from the 'driven' inverter to feed it rather than dumping it into resistors or dumping it back into the supply (as with an AFE/4 Quad drive). The benefits are that you only take power from the main AC supply to start the UP escalator and thus you don't need 2 x full 'converters' to drive and be driven. You save cost, physical room (important to escalator manufacturers) and energy, as you are not drawing on the supply. Another saving is that you only need one set of AC cables.
Obviously this is just theory, as jraef points out, the DOWN escalator may not actually be regenerating. I've seen the gearboxes on these escalators and they are large inefficient worm&wheel gearboxes that proabably lose any regen energy in their efficiency losses.

 

[ScottyUK]

sed2developer,

You might have hit a possible snag with the scheme: a worm and wheel is inherently a non-regenerative device because the worm can drive the wheel, but the wheel can not drive the worm. I guess this could rule out retrofit to some designs of escalator.






-----------------------------------

Start each new day with a smile.

Get it over with.

 

[digitrex]

I have seen escalators (or horizontal converyors like those in airports) that stop when nobody is on them.

There they install some sensors to pick up approaching person and start the escalator automatically.

 

[edison123]

When lifts and hoists are free falling (with brkaes released) enabling regeneration, can escalators, running at an angle, be considered in the same class for regeneration ?

 

[jbartos]

Comment on sed2developer (Electrical) Apr 4, 2004 marked ///\\jabartos
I wasn't thinking of a regenerative front end (either active or back to back diodes) although this could be used. My theory was based on using one stand-alone 6-pulse rectifier rated for (probably) about 1.25 of the driven and regen load. This assumption is based on the theory that one of the inverters is driving the escalator UP and one is being 'driven' DOWN.
///Please, would you clarify how "...one is being 'driven' DOWN." Specifically, if you could clarify the architecture how for the inverter being "driven" down.\\\