Vertical Transportation Design and Traffic Calculations – Part Seven



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 10-20% to account for:

  • Persons working at home,
  • Persons away on holiday,
  • Persons away sick,
  • Persons away on company business,
  • Vacant posts,
  • Persons who arrive before or after the peak hour of incoming traffic,
  • Hot desking.


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.

Table-1 gives guidance of probable peak arrival rates of many building types.


Building type
Arrival rate (%)
Interval (s)
Hotel
10-15
30-50
Flats
5-7
40-90
Hospital
8-10
30-50
School
15-25
30-50
Office( multiple tenancy)


Regular
11-15
25-30
prestige
15-17
20-25
Office( single tenancy)


Regular
15
25-30
prestige
15-17
20-25

Table-1: Percentage arrival rates and up-peak intervals


 The up peak intervals will vary from building to another due to effects such as:

  • The type of building occupancy (different business interests or single tenant)
  • The starting regime (unified or flexi-time)
  • The location of bulk transit facilities such as buses and trains (distant alighting places will result in a spread of arrivals owing to different pedestrian walking speeds).


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:
  1. The car opens its doors at the main terminal floor
  2. Passengers board the car;
  3. The doors close.
  4. The car then runs to the first stopping floor going through periods of acceleration, travelling at rated speed, deceleration and leveling. (Travel at rated speed may not occur if the inter-floor distance is too small.)
  5. At the first stopping floor, the doors open and one or more passengers alight;
  6. The doors close. This sequence continues until the highest stopping floor is reached.
  7. In the highest stopping floor, after the doors have closed, the car is considered to make an express run to the main terminal, thus completing the round trip. 


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:

  • A round trip time should not usually exceed two to three minutes (except in very tall buildings) as the majority of this time can represent the journey time for some passengers with destinations on the top floors of a building, which is undesirable.


Therefore a round trip consists of a number of elements as follows:

First: elevator standing times:

  1. Passenger loading time tt,
  2. Passenger unloading time tu,
  3. Door closing and opening times tc and to.


Second: elevator running times:

  1. Inter-floor jump time (for a single floor assuming rated speed reached) tf(1),
  2. Time to travel in the upward direction at rated speed for jumps greater than a single floor ta,
  3. Time to travel from the highest floor to the main terminal te.


The following Table-2 gives full definitions of the elevator‘s round trip time parameters

Time period
Symbol
Description
Passenger
loading time
tt
The average time for a single passenger to enter a car (boarding time, entry time).
Passenger
unloading time
tu
The average time for a single passenger to leave a car (alighting time, exit time).
Passenger
transfer time
tp
The average time for a single passenger to enter or leave a car, ie: tp=tt+tu/2
Door closing
time
tc
A period of time measured from the instant that the car doors start toclose until the doors are locked.
Door opening
time
to
A period of time measured from the instant that the car doors start toopen until they are open 800 mm.
Door operating
time
td
The sum of the door opening and closing times, ie: td=tc+to
Car call dwell
time
tcd
The period of time that the car doors remain open at a stop in response to a car call, provided no passengers cross the threshold.
Landing call
dwell time
tld
The period of time that the car doors remain open at a stop in response to a landing call, provided no passengers cross the threshold.
Single floor flight
time
tf(1)
The period of time measured from the instant that the car doors are locked until the lift is level at the next adjacent floor.
Multi-floor flight
time for a jump
of n floors
tf(n)
The period of time measured from the instant that the car doors are locked until the lift is level at the nth adjacent floor.
Upward multi-floor jump time
ta
Time to travel in the upward direction at rated speed for jumps greater than a single floor.
Express return time
te
Time to travel from the highest floor to the main terminal.
Single floor
transit time
tv
The period of time for a lift to travel past two adjacent floors at rated speed, ie: tv=df/v where df is the interfloor distance and v is the rated speed.
Stopping time
ts
A composite time associated with each stop, ie: ts=tf(1)+tc+t0−tv
Performance
time
T
The period of time between the instant the car doors start to close and the instant that the car doors are open 800 mm at the next adjacent floor.
Cycle time
tcyc
The period of time between the instant the car doors begin to close until the instant that the car doors begin to close again at the next adjacent floor provided no passengers have crossed the threshold.

Table-2

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 tt + P tu) + (S+1)(tc+to) + (S+1) tf(1) + (H-S) tv + (H-1) tv

So,
RTT = 2Htv + (S+1)ts + 2Ptp

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:

  1. The average number of passengers (P) carried,
  2. The average highest floor reached (H),
  3. The average number of stops made (s),
  4. Single floor transit time (tv) which depends on Interfloor distance (df) and Rated speed (v),
  5. Time consumed when stopping (ts) which depends on Single floor flight time (tf1) and Door closing time (tc) and door opening time (to)
  6. Passenger transfer time (tp)


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)

  • 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



8.2 The Average Highest Floor Reached (H)

The Average Highest Floor Reached H can be determined from the following equation:



Where:


  • N is the number of floors above the main terminal
  • P is the number of passengers carried.

Also, Table-3 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.



Table-3: 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, Table-3 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:

  1. Interfloor distance (df),
  2. Rated speed (v).


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.

building
The interfloor distance (df)
Domestic dwellings
around 3.0m per floor
commercial buildings
from 3.3 m to 3.6 m upwards

Important Notes:

Commercial buildings often introduce a mixed floor pitch for a number of reasons, e.g:
  1. Some floors have increased heights, such as lobby/main terminal floors, service floors, special floors (restaurant, lecture, conference, VIP suites, etc)
  2. Some floors which are sometimes not available for alighting during periods of the day such as the first (and sometimes the second) floor(s) above the MT, service floors, security floors.
  3. It is recommended that an average floor height be assumed and that any irregularities be dealt with separately.


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 tv + (S+1)ts + 2P tp + 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:

  • For instance, goods lifts are generally slower than passenger lifts.
  • Speed, however, is not a dominant factor in the RTT equation; it does become significant, if the served floors are in an upper zone, where a higher speed will permit the ‘un-served zone to be rapidly traversed.
  • Where no value for rated speed is available it must be chosen by the traffic designer.
  • The BS 5588 fire code determines a minimum value of rated speed as it indicates that the speed of a firefighting lift shall be sufficient to enable it to run the full travel of the building in less than 60 s. This is clearly not possible in very tall buildings where special arrangements must be made.
  • For major buildings and for groups of lifts there is no simple relationship between the rated speed and the building height. Section 4 of BS 5655: Part 6 recommends rated speeds in relation to total travel according to building usage. These speeds can be translated into a nominal travel time to travel at rated speed (without allowance for acceleration/deceleration/leveling) between the highest and lowest floors (the terminal floors), as shown in Table-3.



Building type
Transit time (s)
Offices and hotels:

- Large
17-20
- Small
20
Hospitals, nursing/residential homes
24
Residential buildings
20-30
Factories and warehouses, shops
24—40

Table-3: Total time required to travel between terminal floors in different building types

  • ISO 4190/6 also recommends a maximum (theoretical) time of between 20 s and 40 s to travel at rated speed a distance equal to the total travel of the lift. The time is graded according to the likely interval at the main floor.
  • There is no theoretical upper limit to lift rated speed (it does not, for example, affect passenger comfort) but it is limited by practical factors such as maximum sheave diameter, rope bending radius (fatigue), rope wear, safety aspects (e.g. overtravels), etc.


Guidance for the selection of the speed of a lift based:

  • Table-4 gives guidance for the selection of the speed of a lift based on the premise that the total time to travel the distance between terminal floors at rated speed should only take between 20 s and 30 s.
  • In this table, the single floor flight times assume a 3.3 m interfloor distance and are slightly larger than theoretically derived values to allow for brake lift times and other start-up delays.
  • In the past, the numerical value for maximum jerk was twice the numerical value of acceleration (i.e. rated acceleration reached in 0.5 s), but nowadays, in order to achieve a soft ride, jerk is never more than 1.5 times the numerical value for acceleration with an upper limit of 2.2 m/s3.



Lift travel
(m)
Rated speed
(m/s)
Acceleration
(m/s2)
Single floor flight time
(s)
<20
<1.00
0.4
10.0
20
1.00
0.4-O.7
7.0
32
1.60
0.7-0.8
6.0
50
2.50
0.8-0.9
5.5
63
3.00
1.0
5.0
100
5.00
1.2
4,5
120
6,00
1.2
4.5
>120
>6.00
1.2
4.5
Table-4: 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) + 2Ptp

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:

  1. Single floor flight time (tf(1)),
  2. Door closing time (tc),
  3. Door opening time (to).


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:

  1. The rated speed,
  2. The acceleration
  3. The jerk.


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.

Table-4 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 start-up 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. Door width,
  2. Door type
  3. Door weight.



1- Effect of door width:

Narrow doors of 0.8 m width
They are fitted to cars of rated capacities up to 12 persons and wider doors thereafter.
Wider doors of 1.3 m width
They are fitted on goods lifts and hospital lifts.

2- Effect of door opening:

Side opening doors

They have to open the whole width of the doorway, which will take more time.
center opening doors
Faster door operation is achieved and the symmetrical reaction against the car frame will reduce car sway.

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:

  • BS EN 81 requires the maximum energy to be limited to 10 joules, provided the safety edge is operative.
  • If the safety edge is inoperative then the energy value must not exceed 4 joules.
  • The maximum values of energy acquisition limit the maximum values of door speed, when closing as follows:


Door weight Kg
maximum speed m/s
150 kg
0.23 m/s
500 kg
0.13 m/s


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.

Table-5 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 Table-6, for a wider selection of door operators.


Door
type
Closing and opening times (s) for stated door width (m)
Closing
Opening (normal)
Opening (advanced)
0.8
1.1
0.8
1.1
0.8
1.1
Side
3.0
4.0
2.5
3.0
1.0
1.5
Center
2.0
3.0
2.0
2.5
0.5
0.8

Table-5: Typical door dosing and opening times


Operator
Door
type
Opening
size(mm)*
Opening
time(s)
Closing
time(s)
Low speed
Two-speed
800
4.8
4.8
900
5.1
5.1
Center opening
800
4.1
4.1
900
4.7
4.7
Medium speed
Two-speed
800
2.9
3.3
900
3.1
3.5
1000
3.3
3.7
1100
3.5
4.2
Center opening
800
2.3
2.5
900
2.4
2.6
1000
2.5
2.7
1100
2.7
3.3
High speed
Two-speed
800
1.8
2.8
900
1.9
3.4
1000
2.0
3.6
1100
2.2
3.4
Center opening
800
1.5
2.0
900
1.6
2.2
1000
1.7
2.5
1100
1.8
2.9
*Door height taken as 2100 mm in all cases
Table-6: 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:

  1. The shape of the car,
  2. The size of car entrance
  3. The type of car entrance,
  4. The type of the building (e.g. commercial, institutional, residential)
  5. The type of passenger (age, gender, agility, purpose).


The following is given as a general guide for the passenger transfer time (tp):

  • If the car door width is 1.0 m or less assumes passengers enter or exit in single file.
  • For door widths of 1.0 m and above assume the first six passengers enter or exit in single file and the remainder in double file.
  • Consider 1.2 s to be the average passenger transfer time (entry or exit).
  • For situations where passengers have no reason to rush or are elderly, increase the transfer times up to about 2 s.
  • ISO 4190/6 considers a passenger transfer time of 1.75 s as suitable for residential buildings.


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.
Vertical Transportation Design and Traffic Calculations – Part One
The Concept of Traffic Planning,
The (4) Methods of Traffic Design Calculations,
Principles of Interior Building Circulation:
A- Efficiency of Interior Circulation
Vertical Transportation Design and Traffic Calculations – Part Two
B- Human Factors
Vertical Transportation Design and Traffic Calculations–Part Three
C- Circulation and Handling Capacity Factors:
Corridor handling capacity,
Portal handling capacity,
Stairway handling capacity,
Escalator handling capacity,
Vertical Transportation Design and Traffic Calculations – Part Four
Passenger Conveyors (Moving Walkways and Ramps) handling capacity,
Lifts Handling Capacity.
D- Location And Arrangement Of Transportation Facilities
Vertical Transportation Design and Traffic Calculations – Part Five
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),
Vertical Transportation Design and Traffic Calculations – Part Six







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