lea controls 2010 - university of hong kongwork6000/lea controls.pdf · 2010. 11. 23. · a lift...

MEBS6000 2010 Utilities Services M.Sc.(Eng) in Building Services

University of Hong Kong

K.F. Chan (Mr.) Ea of 2 Page Ea 1 of 8

Controls

A lift controller may be considered to comprise power control and traffic control.




The power controller must control the lift drive motion and operate the doors. Two factors make the task of moving a lift car in response to calls one of the most complex logic controllers:- � control options, � fail-safe operation The traffic controller must respond to passenger movement, hall/car calls, and to coordinate a group of cars. The rules on constraints of car movements include: 1) Car calls always take precedence over landing calls. 2) A lift must not reverse its direction of travel with passengers inside the car. 3) A lift must stop at a passenger destination floor. 4) With the exception of the main terminal floor and the parking floor, a lift must not

stop at any other floor where no passenger wishes to enter or leave the lift car. Among the most common control options are: a. car preference or independent operation of one lift car, b. rapid closing of doors, when a car call is registered, c. reduction in door open time, when passengers are detected d. differential door timing so that doors stay open longer at the main terminal floor

and / or vary according to the lift traffic, e. ‘door open’ button, f. ‘door close’ button, g. attendant operation (becoming less common), h. lift homing in the event of fire, i. emergency power operation, j. bed service (for hospitals) During uppeak or downpeak period, the traffic controller can also limit the door re-opening sequence to one on the re-registering of a landing call. Safety requirements are laid down by codes and regulations – single fault in the lift or the controller shall not cause a dangerous situation to arise for the lift user. However, note that the safety requirements and standards for lifts in home are less rigorous than those for lifts in public areas and work places. Types of traffic control � Automatic push button (APB) for single lift � Non-directional collective control (single call button per landing for both up

and down call, inconvenient) � Down-collective control – Up-distributive / down-collective control (single

call button per landing, does not allow interfloor traffic) - Down collective control for single lift (“Simplex” control) - Down collective control for two inter-connected lifts (“Duplex”

control) � Full collective – full directional collective control for two inter-connected lifts

(both up and down call buttons per landing) � Group control – automatic group supervisory control for multiple




inter-connected lifts � Computer-based traffic control algorithms All with automatic full load bypass Non-computer-based traffic control algorithms a. nearest car, b. fixed bi-sectional sectors, c. fixed unidirectional sectors, d. dynamic sectors. Computer-based algorithms a. estimated time of arrival. b. self-tuning systems, c. hall call allocation.

Hall call allocation panel

Each lift is given a designation




Panel indicating floor allocation to each lift on lobby side next to lift door

Panel indicating floor allocation to each lift inside respective lift car

Lift car operating panel – note that there is no destination button on the car panel

where hall call allocation control is adopted

Hall call allocation usually reduces the journey time at the cost of little longer waiting time. It provides very good interfloor traffic but the down peak is poorer because destination during down peak is all known! Caution on hall call allocation – as different passenger interface is provided, there is a need for familiarization by passengers.




Parking sectors The group control equipment may divide the building into sectors and ensures that at least one lift is parked in each sector when there is no traffic demand to be served. When traffic is present and there is no car available in a particular sector, a car may be returned to that sector as soon as one becomes idle. It was reported that this system is wasteful of energy, owing to unnecessary lift movement and changes in floor usage can result in poor service and long waiting times at some floors. It may be better to define the main terminal only as a parking floor and leave all other lifts at their last stopping floor.




Regenerative braking A fully loaded lift car moving downwards is able to do so by the weight of the lift car without driving power from the lift motor. The kinetic energy, if not recovered, is either dissipated as heat in the motor windings, or lost in the resistors or in the mechanical brake. It is possible to recover this energy by operating the motor in a generator mode while braking the lift – this is called regenerative braking. Likewise an empty lift car moving upwards (due to the counterweight) is able to drive the lift motor in a regenerative braking mode.

(Figure adopted from Barney, Elevator traffic handbook, theory and practice)

Type of drive Regeneration DC drive – motor generator (Ward Leonard drive)

Yes Regeneration takes place naturally – the DC motor becomes a DC generator, the DC generator becomes a motor driving the AC motor which becomes an ac generator.

DC drive – Thyristor Leonard drive

Possible Regeneration possible if equipped with the necessary power electronic circuit.

AC single speed AC 2-speed

Yes Regeneration takes place naturally via direct connection of motor to the mains power supply

Variable voltage AC drive with DC injection braking

No Energy dissipated as heat in the windings

VVVF AC drive Possible Regeneration possible if equipped with the necessary power electronic circuit.




Fireman’s lift � Lift shaft openings shall be provided with automatic self-closing fire-resisting

doors � 1.35m2 minimum � 680kg contract load � Fireman’s switch

→ Located at the landing of designated point of entry to enable the Fire Services personnel to gain immediate control over the lift and return it to designated floor.

→ When a Fireman’s Switch is operated the lift shall return to the landing of designated point of entry without stopping for car or landing calls.

→ Sole control of the lift shall be rested in the car control station, and the Fire Services personnel need only take 3 simple steps to operate the lift: � press the desired floor button or ‘door close’ button continuously to

close the lift door and register call; � on arrival at the desired floor, press ‘door open’ button continuously

until lift doors are fully open; � if another floor is desired, press floor button of that floor.

→ In case of power interruption or changeover from the normal power supply to the emergency power source after the Fireman’s Switch is operated, the fireman’s lift shall continue to be in the “fireman” control mode as soon as the power supply to the fireman’s lift is made available.




Illustration of bridgehead operation

Lobby of firemen’s lift must be protected from fire!

1) firefighter’s

lift 2) fire level 3) bridgehead 4) hot gases 5) water on

floor 6) fire

resistant door

7) fire protected lobby

8) stairway (escape route)

(Adopted from BSEN81-72) Home landing operation Usually lifts are provided with a facility to return to the designated point of entry in case of fire.

lea controls 2010 - university of hong kongwork6000/lea controls.pdf · 2010. 11. 23. · a lift...

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