Elevator Traffic Handbook
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Elevator Traffic Handbook

Theory and Practice

Gina Barney, Lutfi Al-Sharif

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eBook - ePub

Elevator Traffic Handbook

Theory and Practice

Gina Barney, Lutfi Al-Sharif

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About This Book

This second edition of this well-respected book covers all aspects of the traffic design and control of vertical transportation systems in buildings, making it an essential reference for vertical transportation engineers, other members of the design team, and researchers. The book introduces the basic principles of circulation, outlines traffic design methods and examines and analyses traffic control using worked examples and case studies to illustrate key points. The latest analysis techniques are set out, and the book is up-to-date with current technology. A unique and well-established book, this much-needed new edition features extensive updates to technology and practice, drawing on the latest international research.

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1 Introduction

1.1 The importance of lifts

Lifts have always been essential to the successful operation of any building and have become especially important in the case of high rise buildings. It is not an exaggeration to state that without lifts, high rise building would not be viable. Lift traffic engineering involves the analysis, design and control of lift systems in order to deal with the passenger traffic flow in buildings.
This chapter sets the scene and presents some preliminary concepts that prepare the reader for the remaining chapters in the book.

1.2 The scope of the book: traffic design vs. engineering design

When discussing the term design in the context of lift systems, it is important to distinguish between two main areas of lift design: engineering design and traffic design.
Engineering design involves the electrical and mechanical design of the various components and systems in the lift.
Traffic design involves the design of the lift system such that it can transport the required number of passengers in a specified period of time under the stipulated performance conditions.
This book is concerned with the traffic design of lift systems, rather than the engineering design. However, it is necessary in certain cases to deal with certain engineering design topics inasmuch as they are closely linked to the traffic design aspects and have a significant impact on decisions made within the traffic design process. An example is the effect of shaft space on the selection of the rated speed of the lift, where the selection of the rated speed of the lift requires minimum clearances in the pit and the head of the shaft, referred to as pit depth and headroom, respectively.
Readers interested in a general view of the engineering of lifts (and escalators and moving walks) might consult CIBSE Guide D: 2015 ‘Transportation Systems in Buildings’.

1.3 The vertical transportation problem

In any engineering design, it is vital to clearly formulate the problem prior to attempting to solve it. This is no different in the case of the vertical transportation problem.
The vertical transportation problem can be summarised as the requirement to move a specific number of passengers from their origin floors to their respective destination floors with the minimum time for passenger waiting and travelling, using the minimum number of lifts, core space and cost, as well as using the smallest amount of energy.
The aim of lift traffic engineering is to achieve a compromise between cost and performance. A number of parameters have to be optimised such as the average passenger waiting time, the average passenger travelling time and the energy consumed by the lifts. The core space used must also be minimised in the building, in order not to take up valuable net usable area and reduce rental space. The solution of the vertical transportation problem identifies the number of the lifts to be used (as well as their rated speed and rated capacity) in the building in order to achieve the required performance. In effect, the vertical transportation problem is a multiple-constraint-multiple-objective problem that aims to produce a solution that is:
1 Safe.
2 Functional.
3 Reliable.
4 Cost effective.
5 Able to meet the passenger performance requirements (waiting time and travelling time).
6 Able to use the smallest possible core space of the building.
7 Energy efficient.
In order to solve the problem, it is necessary to identify demand and supply. Demand is represented by the arrival of passengers for service. Supply is represented by the number of lifts, their rated speed and rated capacity.
It is possible to think of the lift system as a processor of passengers. Escalators, moving walks, stairs or even corridors and doors can also be thought of as passenger processing devices. As the system is exposed to heavier demand (represented by more passengers arriving for service in a unit of time) the performance of the system changes. The system has handling capacity and is exposed to an arrival rate. The study of lift systems involves understanding how the system processes the passengers and the resulting quality of the performance.
A graphical representation of the vertical transportation design process is shown in Figure 1.1. The user requirements specification (URS) is shown as the input to the system on the left hand side of the figure. The URS usually comprises the quality of service element and the quantity of service element. In some cases, it could also comprise other criteria, such as the energy consumption. The building and passenger parameters are shown in the lower part of the figure.
Figure 1.1
Figure 1.1 Block diagram showing the overall design process
[The numbers shown on the figure represent corresponding chapter numbers]
The building and passenger parameters are combined with the user requirements by the design tool in order to produce a compliant lift traffic design. The design tool could be based on calculation or simulation. The output design is fully described by the following three components:
1 Number, speed and capacity of the lifts in the group.
2 The group control algorithm used.
3 The overall arrangement of the lift groups in the case of high rise buildings. This could include the zoning of the building into separate zones or the use of one or more sky lobbies.

1.4 The core space and the loss of net area

The lift shaft is a vertical space within the core of the building that contains the lift cars, the counterweights, the landing doors and any ancillary equipment. In addition to the core space that each lift takes up, the lift system also requires lobby space to provide an area for passengers to wait for the next lift and to access the lift when it arrives.
This core space (shaft space and lobby space) is a cost to the building developer, due to the loss of net usable area (and rent). This loss in net area is repeated on every floor. One of the main aims of lift system design is to minimise this space by finding the optimum number of lifts required for an optimum design. Zoning the building or using sky lobbies is another tool that reduces the loss in net usable area.

1.5 Peaks in demand for services and products

As is the case with many other services, demand for lift service is usually irregular, peaky, random and time dependent. This presents a problem for the designer of the lift system. Here are some examples of peaks in demand from other industries:
  • The demand for fireworks varies annually and peaks in the United Kingdom in November every year (bonfire night).
  • The demand for electricity follows a daily cycle, and usually peaks in the evenings just after sunset (especially in the winter) when people get back to their homes and turn the lighting and the electrical heating on.
  • The demand for public transportation systems also peaks in the morning rush hour (07:30–09:30) and the evening rush hour (16:30–18:30) when large numbers of passengers require the use of trains, metros and buses.
Peaks in demand are a major challenge for service providers, as they have to provide extra capacity (and the associated infrastructure) in order to meet the peak in demand, which is very costly.
One possible strategy is to try to manage demand by removing the peaks. Suppliers try to find ways of levelling the demand (i.e., move some of the demand from the peaks to the troughs). This can be done, for example, by providing financial incentives for users to use the service during the troughs in demand. For example, electricity providers design tariff structures that offer electricity at lower prices during low demand periods and at higher prices during peak demand periods. Another example is where public transportation providers offer cheaper off-peak train fares, or even different fares for different times of the day or the year.
Another possible strategy to meet the peaks in demand is to employ extra capacity during the peaks, such as a restaurant bringing in extra part-time staff during the peaks.
Nevertheless, peaks in demand will remain and suppliers have to be able to meet these peaks in demand. Designers have to design systems that can meet these expected peaks in demand.
Lift systems are designed based on the peak of the demand. The demand for the lift service is a daily cycle. For office buildings, it usually peaks at the start of the working day (for example, 08:00) when workers arrive for work. A significant peak in demand usually takes place in buildings that have a fixed starting time, and is less dominant in buildings that have a flexible starting time.
An additional complicating factor in the lift traffic design process is the random nature of the process. As will become clearer later in the book, the issue of the randomness of passenger arrivals and the randomness of passenger destinations present a serious complicating factor in the lift traffic design process and require special measures to deal with their effects (Alexandris, 1977).

1.6 Traffic in buildings

It will be noticed throughout the book that the types of traffic in the building have a significant effect on the design process. Thus, it is necessary to define the types of traffic in buildings in this chapter as preparation. In order to define the types of traffic in a building, it is first necessary to classify the types of floors.

1.6.1 Defining floors

It is necessary at this point to set the convention for the different types of floors. There are two types of floors in any building: occupant floors and entrance/exit floors. It is assumed that the building is sub-divided into groups of floors: exit/entrance floors and occupant floors.
An exit/entrance floor is a floor that allows passengers to enter or exit the building.
Most buildings have one exit/entrance floor, but some buildings might have multiple entrances. Some reasons for having multiple entrances are the presence of one or more floors of underground car parks, entrances at different street levels due to a sloping ground landscape, adjacent buildings or railway stations. It is usually assumed that no population or traffic demand exists on the entrance/exit floors.
An ...

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