lift design

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DESIGN OF LIFT

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For design of lifts factors to be considered are –

1. Population or no. of people who require lift service.

2. Handling capacity or maximum flow rate required by the people.

3. Interval or quality of service required.

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1.Population : Population is calculated based on occupancy type of the building

Type Occupancy area/per person

Residential 12.5

Educational 4

Institutional 15

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Assembly hall with(a)Dance floor(b)Dinning

0.61.5

Business 10

Mercantile (a)With basement(b)With shops on

uppers

36

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Industrial 10

Storage 30

Hazardous 10

Above area per person is gross area of the floor in square meters. In case of office building 75% of the inherent occupancy is expected to arrive in time (period of ½ hr. before opening time which peak traffic period also).

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Floating population may also be there to counterfeit the effect of late coming persons. 100% population as calculated from floor occupancy basis to be adopted as total population to be served, during peak hours.

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2.Quantity of Service :

The quantity of service is a measure of the passenger handling capacity of a vertical transport system. It is measured in terms of the total number of passengers handled during each five minutes peak period of the day.

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3.Quality of Service :

The quality of service on the other hand is generally measured by the passenger waiting time of the various floors. Quality of service or Acceptable interval:

20 to 25 seconds

Excellent

30 to 35 seconds

Good

35 to 40 seconds

Fair

40 to 45 seconds

Poor

Over 45 seconds

Unsatisfactory

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Handling Capacity & RTT :

The handling capacity is calculated by the formula:

H = (300 x Q x 100)/T x P

Where

H = Handling capacity as the percentage of the peak population handled during 5 min.

Q = Average number of passengers carried in a car

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T = waiting interval, and

P = Total population to be handled during peak morning period. (It is related to the area by a particular bank of lifts)

The value of ‘Q’ depends on the dimensions of the car. It may be noted that the capacity loaded always to its maximum capacity during each trip and, therefore, for calculate the value of ‘Q’ is taken as 80% of the maximum carry capacity of the car.

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The waiting interval is calculated by the formula :

T = RTT/N

Where,

T = waiting interval

N = number of lifts, and

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RTT = round trip time, that is, the average time required by each lift in taking one full load of passengers from ground floor, discharging them in various upper floors and coming back to ground floor for taking fresh passengers for the next trip.

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RTT is the sum of the time required in the following process :

a)Entry of the passengers on the ground floor,

b)Exit of the passengers on each floor of discharge,

c) Door closing time before each floor of discharge,

d)Door opening time on each discharging operation,

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e)Acceleration periods,

f) Stopping and leveling periods,

g)Period of full rated speeds between stops going up, and

h)Period of full rated speeds between stops going down.

It is observed that the handling capacity is inversely proportional to the waiting time which in turn is proportional to RTT.

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The round trip time can be decreased not only by increasing the speed of the lift but also by improving the design of the equipment related to opening and closing of the landing and car doors, acceleration, deceleration, levelling and passenger movement.

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a)The most important factor in shortening the time consumed between the entry and the exit of the passengers to the lift car is the correct design of the door and the proper car width, for comfortable entry and exit for passengers, it has been found that most suitable door width is 1000 mm and that of car width is 2000.

b)The utilization of centre opening doors also favors the door opening and closing time periods.

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Capacity :

Minimum size of car recommended for a single purpose building is one suitable duty load of 884 Kg. For large building car 2040 Kg. according to requirement.

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Layout :

The width of car is determined by the width of entrance, and the depth of car is regulated by loading per sq.mtr. Permissible. Centre opening door are the most practicable and most efficiency entrance with for passenger lifts.

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Speed :

It is dependent upon quality of service required and the quality of service desired. Therefore, no set formulae for indicating the speed can be given.

Recommended Speeds :

The following are general guidelines :

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Office Building Passenger Lifts

Sl. No.

No. of Floors Recommended Speed

1. 4 to 5 floors 1 MPS

2. 6 to 12 floors 1.5 MPS

3. Above 12 floors Above 1.5 MPS

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Residential Building Passenger Lifts

Sl. No.


1. 4 to 8 floors 1 MPS


3. Above 12 floors Above 1.5 MPS

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Hospital Lifts (Bed cum Passenger Lifts)

Sl. No.


1. Upto 4 floors 0.5 MPS


3. Above 8 floors 1 MPS

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Goods Lifts

Sl. No.


1. Upto 6 floors 0.5 MPS

2. Above 6 floors 0.75 MPS

Note:

(1) For passenger cum gods lifts speed shall be followed as that of passenger lifts.

(2) Actual speed shall be worked out on the basis of traffic analysis.

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Calculation of R.T.T.

The most probable number of floors on which lift may have to be stopped is given by statistical formula:

Sn = n [ 1-(n-1)/n)Np]

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Where

Np= Total number of passengers entering the car at ground floor (Entrance Lobby) during peak period which is equal to car capacity.

n = Total number of floors served above ground floor.

Sn = Most probable number of stops.

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No. of upper floors served

Number of Passenger/Trip (Car Capacity)

10 12 14 16 18 20

18 8 9 10 11 12 13

16 8 9 10 10 11 12

14 7 8 9 9 10 11

12 7 8 9 9 10 10

10 6 7 8 8 9 9

8 6 6 7 7 8 8

6 5 5 6 6 7 7

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Now,

R.T.T. = Entrance lobby time + Sn x floor serving time + Return trip time (D-2d)/Vc.

Where, Sn = Probable number of stops

D = Total Lift travel in one direction (m)

d = Distance travelled during acceleration or deceleration (m)

Vc = Contract speed of elevator in m/s also.

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D = ½ ft2

Where,

f = acceleration in m/sec2

t = Time for acceleration

= 2 seconds for lifts upto 2.5 m/s.

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(a)Entrance Lobby Time : This consists of door opening, car loading, door closing time and acceleration at entrance lobby generally ground floor plus retardation time (while returning from top).

(b)Floor serving time: This consists of door opening time, transfer (loading or unloading time), door closing time, acceleration and de-acceleration (retardation) time.

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(c)Loading/ Unloading time: Practically observed loading and unloading time for lifts of different capacity are given below:

No. of Passenge

rs

Entrance lobby Loading

time in second

Transfer time i.e. loading and

unloading time at upper floors

8 7 1

13 12 1.25

16 14 1.5

20 17 1.6

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Actually average time required for entrance of each passenger in car depends upon total number of persons entering the car and already available in car. It may be one second per person when car is partially loaded and 0.75 second when it is completely empty. Time for emptying car is less and equal to 0.75 second for single person but there is a tendency that all persons vacate the car simultaneously after opening if the doors.

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(d)Door Opening and closing time: Door closing time is more as compared to door opening time. This is due to fact that when all persons have entered in the car, it takes time for people to select and press the push button for summoning the lift to various destinations.

Total time for door opening and closing operation can be taken as given below:

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Type of Door operation Capacity

8 13 16 20(a) Power operated single

slide(b) Power operated double

slide(c) Power operated centre

Opening(d) Collapsible with attendant

(e) Collapsible without attendant

3.8 3.8 - -

3.2 3.2 - -

2.8 2.8 3.2 3.2

2.5 2.5 3 3

4 4 - -

Door closing and opening time, at entrance floor shall be one second more than all above.

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(e)Distance travelled by lift during acceleration or retardation is assumed to be equal. This can be calculated by using formula.

d = ut + ½ ft2

Where U is initial speed = 0, f is acceleration or retardation rate and t is the time elapsed. It is assumed that during each cycle, lifts acceleration and retardation time is about 2 second.

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Rate of acceleration will vary with type of as given below:

Lifts speed m/s Rate of acceleration

m/sec2

1 0.50

1.5 0.75

2.5 1.00

More than 2.4 to 8

2.50

More than 8 and floors more than

50

4.00