In article “Vertical Transportation Design and Traffic Calculations – Part Six”, we started
explaining how to perform the following lift
traffic design calculations:
1
Calculation of the Number of Round Trips for a Single Car,
2
Estimation of Population,
3
Calculation of the Average Number of Passengers per Trip (P),
4
Calculation of the Uppeak Handling Capacity (UPPHC),
5
Calculation of the Waiting Interval (Passenger Waiting Time),
6
Calculation of The percentage population served (%POP),
Today we will continue explaining other lift traffic design calculations, which will be:
7
Estimation of Arrival Rate,
8
Calculation of the Round Trip Time RTT,
7 Estimation Of Arrival Rate

In many buildings it is unlikely that all the total population
is present on any day. Thus, in design calculations, the total building
population can be reduced by 1020% to account for:
And the reduced building population
can be called the effective building population.
Here we need to differentiate between the
percentage population served (%POP) and the Arrival rate (%) as follows:
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. It is
calculated from the following equation:
%POP = UPPHC x
100 / building population
Arrival rate
(%): 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
effective building population.
Table1 gives guidance of probable peak arrival rates of many
building types.
Table1: Percentage arrival rates and uppeak intervals
The up peak intervals
will vary from building to another due to effects such as:

8 Calculation of the Round Trip Time RTT

In Article “Vertical Transportation Design and Traffic Calculations – Part Six”. We explained that 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. Fig.1 shows The elements
of a round trip time.
Fig.1: The elements of a round trip time
Note:
Therefore a round trip consists of a number of elements as
follows:
First: elevator standing times:
Second: elevator running times:
The following Table2 gives full definitions of the elevator‘s
round trip time parameters
Table2
It is now possible to deduce an expression for round trip time
as follows:
RTT = Passenger transfer time + door operating time + time to
accelerate, deaccelerate, level, etc. the car (S+1) times + time to travel
remaining floors at rated speed to the highest call reversal floor (H) + time
to express run from the highest floor (H) to the main terminal (MT)
RTT = (P t_{t} + P t_{u}) +
(S+1)(t_{c}+t_{o}) + (S+1) t_{f}(1) + (HS) t_{v}
+ (H1) t_{v}
So,
RTT = 2Ht_{v} + (S+1)t_{s} +
2Pt_{p}
_{}
The term (S+1) occurs to account for the stop at the main
terminal floor.
From the above equations, The Round trip time of the lift is
much affected by the following six parameters:
In the next paragraphs, we will know
how to calculate each one of these six parameters.

8.1 Calculation of the Average Number of
Passengers per Trip (P)
P = CC x 80/100

8.2 The Average Highest Floor Reached (H)
The Average Highest Floor Reached H can be determined from the
following equation:
Where:
Also, Table3 gives values for H for a number of standard car
sizes and a typical range of floors above the main terminal with P assumed to
be 80% of rated capacity.
Table3: Values of H and S for rated capacity (cc) values from 6
to 33 persons
Number of floors N, above MT
80% capacity shown in parentheses

8.3 Average Number of Stops (S)
The Average Number of Stops S can be determined from the
following equation:
Also, Table3 in above gives values for S for a number of
standard car sizes and a typical range of floors above the main terminal With
P assumed to be 80% of rated capacity.

8.4 Single Floor Transit Time (tv)
Single Floor Transit Time (tv) depends on two variables:
8.4.1 The Interfloor Distance (df)
The Interfloor Distance (df) is the average interfloor distance
normally determined as the total travel divided by the number of possible
stopping floors above the MT.
Important Notes:
Commercial buildings often introduce a mixed floor pitch for a
number of reasons, e.g:
Where a lift is serving a set of floors or zone in a building,
which is not adjacent to the main terminal, an
extra time to make the jump to/from the express zone must be added to the
above RTT equation, i.e. 2 He tv, where He is the number of average height
floors passed through to reach the first served floor of the express zone. So,
the RTT Equation becomes:
RTT = 2H t_{v} + (S+1)t_{s}
+ 2P t_{p} + 2He tv
8.4.2 Rated speed (v)
The value of the rated speed (v) is usually supplied by the lift
maker, who will select it to meet various engineering requirements (gearing,
drive controllers, product line, etc) and traffic purposes.
Important rules for lifts’ rated speed:
Table3: Total time required to travel between terminal floors in different building types
Guidance for the selection of the speed of a lift based:
Table4: Typical lift dynamics

8.5 Time consumed when stopping (ts)
The stopping ts is an artificial time developed as a
mathematical simplification and cannot be measured directly. It can be
determined from the following equation:
ts = door operating time (td) + single floor
flight time (tf(1)) – single floor transit time (tv)
ts = td + tf(1)  tv
Another time, the performance time (T), can be more easily
measured and is very useful in determining the performance of a lift.
T = door operating time (td) + single floor
flight time (tf(1)) = td + tf(1)
This gives:
ts = T  tv
So, the RTT Equation can be modified to show the time parameters
in more detail by including the performance time T as follows:
RTT = 2H df/v + (S+1)(T – tv) + 2Pt_{p}
_{}
The performance time (T) has the most effect on the RTT. It is
easily measured as it is the time taken between the instant a stationary lift
starts to close its doors until the instant the doors are 800 mm open at the
next adjacent floor.
Therefore, the three components of cycle time (T) need to be
selected carefully to achieve the correct handling capacity for the lift
installation. These three components are:
8.5.1 Single floor flight time (tf(1))
The single floor flight time, tf(1), is the time taken from the
instant the car doors close until the car is level at the next adjacent
floor. It is dependent on:
Thus flight times can be obtained for any distance or number of
floors travelled.
Fortunately for designers of lift drives, there are limits on the maximum values that both acceleration and jerk can attain. These constraints are imposed by the physiology of the human body. Passengers are uncomfortable when subjected to values of acceleration greater than about one sixth of the acceleration due to gravity (that is about 1.5 m/s2). There is a similar constraint on the maximum value of jerk at about 2.2 m/s3. Table4 in above indicates the likely range of acceleration values and single floor flight times. The single floor flight times are slightly larger than a theoretical calculation would give, in order to allow for startup delays.
8.5.2 Door closing time (tc)
It is the time taken from the instant the car doors start to
close until they are locked up. It is dependent on:
1 Effect of door width:
2 Effect of door opening:
3 Effect of door weight:
The weight of the door is determined by many factors such as
fire resistance, height, width, configuration etc. Because a door is a moving
object it can gather considerable kinetic energy. To protect passengers from injury
the following rules are followed:
8.5.3 Door opening time (to)
It is the time from the instant that the doors start to open at
a landing, to the instant that the doors are open sufficiently wide (about
800 mm) to allow the movement of passengers, when exiting or boarding.
Door opening time is not subject to energy constraints and,
provided the trapping hazard between door panel and door architrave is
negligible, it can operate at any speed.
However, as the same door operator will be used for both
directions of movement, opening times will not be significantly faster.
Table5 gives representative values for the two door types, two
door sizes, and with and without advanced opening. A fuller range of door
times can be found in Table6, for a wider selection of door operators.
Table5: Typical door dosing and opening
times
*Door height taken as 2100 mm in all cases
Table6: Door operating times

8.6 Passenger transfer time (tp)
It is the time a single passenger takes to enter or leave a car.
This parameter is the vaguest of all the components of the RTT equation,
principally because it is dependent on human behavior. The passenger transfer
time can vary considerably and is affected by:
The following is given as a general guide for the passenger
transfer time (tp):

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


Traffic design calculations:
1 Calculation of the Number of Round Trips for a Single Car,
2 Estimation of Population,
3 Calculation of the Average Number of Passengers per Trip (P),
4 Calculation of the Uppeak Handling Capacity (UPPHC),
5 Calculation of the Waiting Interval (Passenger Waiting Time),
6 Calculation of The percentage population served (%POP),


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