Building Services Engineering Design 2 Module BNEE483 • Hugo Gallagher • Room M709 • email@example.com • firstname.lastname@example.org • Tel: 0141 331 8836 • Lecture 7
Lifts, Escalators and Paternosters
Planning Lift Installations • To function efficiently and to provide access for the elderly and disabled, modern offices and public buildings are provided with suitably designed lift installations. • Planning should commence early in the design programme. • Priority given to locating lifts centrally within a building to min. horizontal travel distance. • Consideration also given to position, relative to entrances and stairs. • Where the building size justifies several passenger lifts, they should be grouped together.
Planning Lift Installations – Large Buildings • In large buildings - usual to provide a group of lifts near main entrance and single lifts at the ends of the building. • Lift lobby must be wide enough to allow pedestrian traffic to circulate and pass through the lift area without causing congestion. • Tall buildings in excess of 15 storey’s, high speed express lifts may be used which by-pass the lower floors.
Building with a main group of lifts + single lift serving interfloor traffic
Requirements: • Necessary in all buildings over 3 storeys high • Essential in all buildings over a single storey if they are accessed by the elderly or disabled • Min. standard - one lift per four storeys • Min. walking distance to access a lift - 45 m • Floor space and lift car capacity can be estimated at 0 - 2 m2 per person.
Express Lift • Does not stop at the lower floor levels • Upper speed limit is 7 m/s because of the inability of the human ear to adapt to rapid changing atmospheric conditions. • Overall theoretical max. travel distance is 21 m vertically, therefore limited to four or five storeys.
Electric Motor • Low speed lifts operate quite comfortably with an a.c. motor to drive the traction sheave through a worm gear. • For faster speed applications a d.c. motor is preferable. • Supplied via a mains generator for each lift motor. • D.C. motors have historically provided better variable voltage controls, more rapid and smoother acceleration, quieter operation, better floor levelling and greater durability in resisting variable demands. • Recent developments with a.c. motors have made them more acceptable • Now becoming more widely used.
BS Standards • Refs: • BS 5655: Lifts and service lifts. • BS 5656: Safety rules for the construction and installation of escalators and passenger conveyors.
Roping Systems for Electric Lifts • High tensile steel ropes are used to suspend lift cars. • Design factor of safety of 10 and are usually at least 4 in number. • Ropes travel over grooved driving or traction sheaves and pulleys. • A counterweight balances the load on the electric motor and traction gear.
Methods for Roping • Single wrap 1:1 • - most economical and efficient of roping systems but is limited in use to small capacity cars. • Single wrap 1:1 with diverter pulley • - required for larger capacity cars. It diverts the counterweight away from the car. To prevent rope slip, the sheave and pulley may be double wrapped. • Single wrap 2:1 • - an alternative for use with larger cars. This system doubles the load carrying capacity of the machinery but requires more rope and also reduces the car speed by 50% • Double wrap • - used to improve traction between the counterweight, driving sheave and steel ropes.
Single Wrap 3:1 • Used for heavy goods lifts where it is necessary to reduce the force acting upon the machinery bearings and counterweight. • Load carrying capacity is increased by up to 3 times that of uniform ratio, but capital costs are higher with increased pulleys and greater length of rope. • By comparison, car speed is also reduced to 1/3.
Drum Drive • A system with one set of ropes wound clockwise around the drum and another set anti-clockwise. • It is equally balanced, as one set unwinds the other winds. • Disadvantage of the drum drive is that as height increases, the drum becomes less controllable, limiting its application to rises of about 30 m. • Compensating rope and pulley - used in tall buildings where the weight of the ropes in suspension will cause an imbalance on the driving gear and also a possible bouncing effect on the car. • Compensating ropes attach to the underside of car and counterweight to pass around a large compensating pulley at low level.
Making Space – Miconic 10 ID System • In the modern building, needs of the handicapped must be considered, but also VIPs (very important people) and CIPs (commercially important people). • All these groups need more space in the lift cars, for reasons of physical space requirements, individual security or confidentiality. • Miconic 10 ID system, this is now achievable by the use of smart cards, PIN codes, key rings, watches or combinations of these methods of individual identification. • Occupants of the building or visitors are security checked prior to the journey, and the call station assigns the right lift car based on the intending passenger’s needs and security rights.
Lift Controls (1) • Single automatic push button system is the simplest and least sophisticated of controls • Lift car can be called and used by only one person or group of people at a time • When the lift car is called to a floor, the signal lights engraved “in use” are illuminated on every floor • The car will not respond to any subsequent landing calls, nor will these calls be recorded and stored.
Lift Controls (2) • Car is under complete control of the occupants until they reach the required floor and have departed the lift • The “in use” indicator is now switched off and the car is available to respond to the next landing call • Although the control system is simple and inexpensive by comparison with other systems, it has its limitations for user convenience • Most suited to light traffic conditions in low rise buildings such as nursing homes, small hospitals and flats.
Ref. BS 5655-7: • Specification for manual control devices, indicators and additional fittings • Down collective - stores calls made by passengers in the car and those made from the landings • As the car descends, landing calls are answered in floor sequence to optimise car movement • If the car is moving upwards, the lift responds to calls made inside the car in floor sequence • After satisfying the highest registered call, the car automatically descends to answer all the landing calls in floor sequence • Only one call button is provided at landings • This system - most suited to flats and small hotels, where the traffic is mainly between the entrance lobby and specific floors.
Full or Directional Collective • A variation in which car and landing calls are immediately stored in any number. • Upward and downward intermediate landing calls are registered from one of two directional buttons. • Uppermost and lowest floors only require one button. • Lift responds to calls in floor order independent of call sequence, first in one direction and then the other. • It has greater flexibility than the down collective system • Appropriate for offices and departmental stores where there is more movement between intermediate floors.
Central Processor (1) • Two cars may be co-ordinated by a central processor to optimize efficiency of the lifts. • Each car operates individually on a full or down collective control system. • When cars are at rest, one is stationed at main entrance lobby and the other, which has call priority, at a mid point within the building or at another convenient floor level. • Priority car will answer landing calls from any floor except the entrance lobby. • If the priority car is unable to answer all call demands within a specific time, the other car if available will respond.
Central Processor (2) • A similar system may also apply to 3 cars, 2 stationary at entrance lobby and one available at mid point or top floor. • Supervisory control system, each car operates on full collective control and will respond to calls within a dedicated zone. • A microprocessor determines traffic demand and locates cars accordingly to each operating zone.