Today we will start explaining the lift traffic design
calculations. In article “Vertical Transportation Design and Traffic Calculations – Part Two”, we listed the (4) methods of Traffic Design
Calculations, which were:
First: Calculation methods,
which includes:
1 The FormulaBased Method (Classical
Method Method),
2 The Monte Carlo Simulation Method.
Second: Simulation methods,
which includes:
3 Discrete Event Simulation Method,
4 Time Slice Simulation Method.
Also, we indicted that in this course, we
will explain only the first method which is The FormulaBased Method (Classical
Method) applied to commercial office buildings.
Traffic Design Calculations

Introduction

In order to get a better
understanding of the traffic design calculations by The FormulaBased Method
(Classical Method). We need to know the following:

1 The
Daily Routine Work of an Elevator
Fig.1:
Passenger demand rate for an office building
The daily routine work of
an elevator can be called simply the daily traffic patterns of an elevator.
Fig.1 illustrates a possible traffic pattern and shows the number of up
landing calls and down landing calls registered during the working day in a
fixed time company where employers must start and leave the work in
predetermined time, these daily traffic patterns can be divided to:
1 Morning uppeak:
At the start of the day
there is a larger than average number of uphall calls. This is due to the
building’s occupants arriving to start work.
2 Evening downpeak:
Late in the day there is
a larger than average number of downhall calls. These are due to the
building’s population leaving the building at the end of the working day.
3 Midday traffic:
In the middle of the day
there are two separate sets of uppeaks and two down peaks. This represents a
situation where the occupants of the building take two distinct lunch periods
(ie: 12.00 to 13.00 and 13.00 to 14.00). This pattern is sometimes called twoway
traffic.
4 Random (balanced)
interfloor traffic:
During the rest of the
day the numbers of uphall and downhall calls are similar in size and over a
period are equal.
Note:
The above traffic
patterns will not be observed in a flextime company where employers can start
and leave the work as per their choice.
From above explanation of
the daily routine work of an elevator in a commercial office building, we can
list the different traffic conditions as follows:
And as we indicated
above, we will be interested only in the Uppeak traffic condition used with
the FormulaBased Method (Classical Method Method).
1.1 Uppeak
Traffic
An uppeak traffic
condition exists when the traffic flow is in an upward direction, with all,
or the majority of, passengers entering the lift system at the main terminal
of the building.
Fig.2: the
up peak traffic profile
Fig.2 reveals the detail
that the up peak traffic profile is slow to rise and quick to fall. The lift
installation must be able to handle the peak if a satisfactory service is to
be provided. From fig. , we have observed (3) nos. handling capacities as
follows:
A 5 minutes handling
capacity
To size a lift
installation to handle the number of passengers requesting service during the
heaviest five minutes of the up peak traffic condition as recommended by
Industry practice.
B One hour handling
capacity
To size the lift system
to handle the actual peak would require too large a system, which would be
very expensive and much of the equipment would be underutilized during large
periods of the working day.
C 30minute handling
capacity
To size a lift
installation to handle the peak in a 30minute of the up peak traffic
condition and this would result in a totally inadequate installation, not
only for up peak traffic but also for the other traffic conditions.
Notes:

2 The
Round Trip Cycle of an Elevator
A single lift car
circulates around a building during the uppeak traffic condition in the
following cycle:
Based on this
cycle, we can define The Round Trip Time (RTT) as follows:
It is the time in
seconds for a single car trip around a building from the time the car doors
open at the main terminal, until the doors reopen, when the car has returned
to the main terminal floor, after its trip around the building.
In the next article, we
will explain the Round Trip Time (RTT) in detail.

Important
Traffic Design Calculations

Now, we are going to
learn how to get the most efficient and economic traffic design solution by using
one of the following methods:
And before explaining
the above two methods, we need to understand and learn how to perform the
following important Traffic design calculations:

1
Calculation of the Number of Round Trips for a Single Car
To calculate how many
round trips a single lift car can complete during the peak 5minute period,
equation#1 will be used.
Number of
round trips for a single car = 5 minutes / RTT = 300 / RTT equation#1

2
Estimation of Population
The number of passengers
that can use the lift will be comprised of one or more of the following
passenger data sets:
Since we are dealing
only with the uppeak traffic, these data are simplified to be:
To determine the number
of passengers, who will board and what their demand will be, depends on the
building population.
2.1 The factors
affecting the estimation of building population
The number of occupants
will vary according to:
Note:
The size of the intended
population should be obtained from the building owner or proposed occupier,
if possible (and in writing). However, it may be that the population size is
not available, or the building is a speculative one, when an estimation must
be made.
A Purpose of a Building
The buildings are
generally defined as:
B The quality of the
accommodation
The more prestigious the
building, eg: a head office, the more space is available to each occupant.
C The type of occupancy
There are three main
types of tenancy:
1 Diversified tenancy:
It is a building
occupancy condition, where no single tenant occupies more than a single floor
and no more than one quarter of the tenants of the building are engaged in
the same type of business activity.
2 Mixed tenancy:
It anticipates the
possibility of multifloor occupancy by a single tenant or multiple tenants
with the same business activity.
3 Single tenancy:
It is a building
occupancy condition where a single tenant occupies a substantial portion or
zone of the building (say 80%). The single tenancy situation can present a
severe traffic design condition. The group handling capacity with such
occupancy can be high (about 14%) for calculation purposes. And some
singletenant insurance companies, government entities, or utilities, with
large numbers of clerical workers can have handling capacity requirements of
substantially more than 15% of the population in five minutes, if they
operate a fixed starting time regime. In these cases, it would be important
to establish this demand from the prospective building owner before carrying
out any calculations.
2.2 Main Terminal
Population
The main terminal
population is not normally included in the design population for the
following reasons:
The main terminal
population may be included in the building population in the following
situation. There are underground parking levels served by the same group of
lifts that serve the upper floors of the building. Thus persons who work on
the main terminal floor and who park in the underground levels would use this
group of lifts.
2.3 Usable Area and Rentable area
Most population
estimates start from knowledge of the net usable area, ie: the area which can
be usefully occupied and which excludes circulation space (stairs, corridors,
waiting areas), structural intrusions (steelwork, space heating,
architectural features, etc.), toilet facilities, cleaners’ areas, etc.
The American National
Standard ANSI Z65.1–1980 “Standard Method for Measuring Floor Area in Office
Buildings” gives a useful guide to calculating areas in office buildings. It
defines two important terms:
Rentable area Definition:
Usable area Definition:
In most traffic design
cases, we can calculate and project the building population from the
following equation:
The
estimated population = the usable area of the building / the area allocated
per person (in m2)
Where architectural
drawings are too schematic to make an accurate estimate of areas, one of the
following approximate rule of thumb relationships may be used, when the gross
area is known:
Rentable
area=90–95% of gross area
Usable
area=75–80% of gross area
or the relationship
below if the rentable area is known:
Usable
area=80–85% of rentable area
Notes:
Example#1:
Using rules of thumb
above, what are the rentable and usable areas of
(a) a tall/slender
building and
(b) a low/squat
building, each having a gross area 5000 m2?
Solution:
(a) This will have a
large core compared to the footprint, but the occupants will always be close
to a lift.
Rentable area=90% of
gross area, ie: 4500 m2
Usable area=75% of gross
area, ie: 3750 m2
(b) This will have a
small core compared to the footprint, and the occupants may be far from a
lift.
Rentable area=95% of
gross area, ie: 4750 m2
Usable area=80% of gross
area, ie: 4000 m2
2.4 Practical Population
Estimations
Table2 gives guidance
for a variety of buildings based on surveys and experience of the population to
be accommodated.
* Patient plus three others (doctors, nurses, porters, etc.).
Table2: Estimation of population

3
Calculation of the Average Number of Passengers per Trip (P)
As each car has a
defined rated car capacity (CC) that it can accommodate, but the number of
passengers assumed to be carried on each trip is taken as 80% of rated car
capacity. This does not mean cars are assumed to fill only to 80% of rated
car capacity each trip but that the average load is 80% of rated car
capacity.
Therefore,
Industry practice assumes a car loading of 80% of rated capacity. Values less
than 80% do not fully utilize the installation, and values above 80% quickly
result in poor service times.
P = CC x
80/100 equation#2

4
Calculation of the Uppeak Handling Capacity (UPPHC)
The handling capacity
(UPPHC) of a lift system is the total number of passengers that it can
transport in a period of 5 minutes during the uppeak traffic condition with a
specified average car loading.
A period of 5 minutes
for the handling capacity definition has achieved general acceptance as it
lies between one hour and a reasonable average waiting time, typically 30 s.
Therefore the 5minute handling capacity (UPPHC) for a single car is:
UPPHC =
average number of passengers per trip x 300 / RTT equation#3
So, from equation#2:
UPPHC =
P x 300/RTT equation#4
In installations with more than one car, Equations #4 become:
UPPHC =
P x L x 300/RTT equation#5
Where L is the number of
lift cars.

5
Calculation of the Waiting Interval (Passenger Waiting Time)
Interval (INT) is the
average time between successive lift car arrivals at the main terminal floor
with cars loaded to any level.
With a single car the
interval between successive arrivals is the round trip time.
Interval
= RTT equation#6 for a single
car
However, where a lift
system contains more than one car the interval becomes:
Interval
= RTT / L equation#7
for L number of cars
Fig.3 illustrates the relationships between round trip and interval.
Fig.3:
Relationship between round trip time and interval
Uppeak
interval (UPPINT)
Uppeak interval (UPPINT)
is the average time between successive lift car arrivals at the main terminal
floor with cars loaded to 80% of rated car capacity during uppeak traffic
conditions.
Equation#5 can now be rearranged,
using Equation#7, to give the handling capacity of a group of L lifts:
UPPHC =
P x 300/ UPPINT equation#8
Notes:

6 Calculation
of The percentage population served (%POP)
The percentage
population served (%POP) is the number of passengers who arrive, at the main
terminal of a building, for transportation to the upper floors over the worst
5 minute period expressed as a percentage of the total building population.
%POP =
UPPHC x 100 / building population equation#9
uppeak handling
capacity, uppeak interval and uppeak percentage population served, are the
parameters most often quoted by a lift supplier.
Example#2:
A building is served by
three lifts with a round trip time of 150 s. The building population is 400
persons and each car has a rated car capacity of 10 passengers. Calculate the
uppeak interval, uppeak handling capacity and percentage population served.
Solution:
From equation#7
Interval
= RTT / L = 150 / 3 = 50 s
From equation#2
P = CC x
80/100 = 10 x 80 / 100 = 8 persons
Then, from equation#5
UPPHC = P
x L x 300/RTT = 8 x 3 x 300 / 150 = 48 persons / 5 minutes
From equation#9
%POP =
UPPHC x 100 / building population = 48 x 100 / 400 = 12%

In the next article, we will continue
explaining other Important Traffic design calculations. Please, keep following.
The
previous and related articles are listed in below table:
Subject Of Previous Article

Article

Applicable Standards and Codes Used In This Course,
The Need for Lifts,
The Efficient Elevator Design Solution
Parts of Elevator System Design Process
Overview of Elevator Design and Supply Chain
Process.


The Concept of Traffic Planning,
The (4) Methods of Traffic Design Calculations,
Principles of Interior Building Circulation:
A Efficiency of Interior Circulation


B Human Factors


C Circulation and Handling Capacity Factors:
Corridor handling
capacity,
Portal handling capacity,
Stairway handling
capacity,
Escalator handling
capacity,


Passenger Conveyors
(Moving Walkways and Ramps) handling capacity,
Lifts Handling Capacity.
D Location And
Arrangement Of Transportation Facilities


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