2For design of lifts factors to beconsidered are –1. Population or no. of people whorequire lift service.2. Handling capacity or maximum flowrate required by the people.3. Interval or quality of service required.
31. Population : Population is calculatedbased on occupancy type of thebuildingType Occupancyarea/per personResidential 12.5Educational 4Institutional 15
4Assembly hall with(a)Dance floor(b)Dinning0.61.5Business 10Mercantile(a)With basement(b)With shops onuppers36
5Industrial 10Storage 30Hazardous 10Above area per person is grossarea of the floor in square meters. Incase of office building 75% of theinherent occupancy is expected toarrive in time (period of ½ hr. beforeopening time which peak traffic periodalso).
6Floating population may also bethere to counterfeit the effect of latecoming persons. 100% population ascalculated from floor occupancy basis tobe adopted as total population to beserved, during peak hours.
72. Quantity of Service :The quantity of service is a measureof the passenger handling capacity ofa vertical transport system. It ismeasured in terms of the total numberof passengers handled during eachfive minutes peak period of the day.
83. Quality of Service :The quality of service on the otherhand is generally measured by thepassenger waiting time of the variousfloors. Quality of service or Acceptableinterval:20 to 25secondsExcellent30 to 35secondsGood35 to 40secondsFair
9Handling Capacity & RTT :The handling capacity is calculated bythe formula:H = (300 x Q x 100)/T x PWhereH = Handling capacity as the percentage ofthe peak population handled during 5min.Q = Average number of passengers carried
10T = waiting interval, andP = Total population to be handled duringpeak morning period. (It is related tothe area by a particular bank of lifts)The value of ‘Q’ depends on thedimensions of the car. It may be noted thatthe capacity loaded always to its maximumcapacity during each trip and, therefore,for calculate the value of ‘Q’ is taken as80% of the maximum carry capacity of thecar.
11The waiting interval is calculated bythe formula :T = RTT/NWhere,T = waiting intervalN = number of lifts, and
12RTT = round trip time, that is, theaverage time required by each lift intaking one full load of passengers fromground floor, discharging them invarious upper floors and coming backto ground floor for taking freshpassengers for the next trip.
13RTT is the sum of the time required in thefollowing process :a) Entry of the passengers on the groundfloor,b) Exit of the passengers on each floor ofdischarge,c) Door closing time before each floor ofdischarge,d) Door opening time on each dischargingoperation,
14e) Acceleration periods,f) Stopping and leveling periods,g) Period of full rated speeds betweenstops going up, andh) Period of full rated speeds betweenstops going down.It is observed that the handling capacity isinversely proportional to the waitingtime which in turn is proportional toRTT.
15The round trip time can be decreasednot only by increasing the speed of thelift but also by improving the design ofthe equipment related to opening andclosing of the landing and car doors,acceleration, deceleration, levelling andpassenger movement.
16a) The most important factor in shorteningthe time consumed between the entryand the exit of the passengers to the liftcar is the correct design of the door andthe proper car width, for comfortableentry and exit for passengers, it hasbeen found that most suitable doorwidth is 1000 mm and that of car widthis 2000.b) The utilization of centre opening doorsalso favors the door opening andclosing time periods.
17Capacity :Minimum size of car recommendedfor a single purpose building is onesuitable duty load of 884 Kg. For largebuilding car 2040 Kg. according torequirement.
18Layout :The width of car is determined bythe width of entrance, and the depth ofcar is regulated by loading per sq.mtr.Permissible. Centre opening door arethe most practicable and mostefficiency entrance with for passengerlifts.
19Speed :It is dependent upon quality ofservice required and the quality of servicedesired. Therefore, no set formulae forindicating the speed can be given.Recommended Speeds :The following are general guidelines :
20Office Building Passenger LiftsSl.No.No. of Floors RecommendedSpeed1. 4 to 5 floors 1 MPS2. 6 to 12 floors 1.5 MPS3. Above 12 floors Above 1.5 MPS
21Residential Building Passenger LiftsSl.No.No. of Floors RecommendedSpeed1. 4 to 8 floors 1 MPS2. 8 to 12 floors 1.5 MPS3. Above 12 floors Above 1.5 MPS
22Hospital Lifts (Bed cum Passenger Lifts)Sl.No.No. of Floors RecommendedSpeed1. Upto 4 floors 0.5 MPS2. 5 to 8 floors 0.75 MPS3. Above 8 floors 1 MPS
23Goods LiftsSl.No.No. of Floors RecommendedSpeed1. Upto 6 floors 0.5 MPS2. Above 6 floors 0.75 MPSNote:(1) For passenger cum gods lifts speed shall befollowed as that of passenger lifts.(2) Actual speed shall be worked out on thebasis of traffic analysis.
24Calculation of R.T.T.The most probable number of floors onwhich lift may have to be stopped is givenby statistical formula:Sn = n [ 1-(n-1)/n)Np]
25WhereNp= Total number of passengers enteringthe car at ground floor (Entrance Lobby)during peak period which is equal to carcapacity.n = Total number of floors servedabove ground floor.Sn = Most probable number of stops.
27Now,R.T.T. = Entrance lobby time + Sn x floorserving time + Return trip time (D-2d)/Vc.Where, Sn = Probable number of stopsD = Total Lift travel in one direction (m)d = Distance travelled during accelerationor deceleration (m)Vc = Contract speed of elevator in m/salso.
28D = ½ ft2Where,f = acceleration in m/sec2t = Time for acceleration= 2 seconds for lifts upto 2.5 m/s.
29(a)Entrance Lobby Time : This consists ofdoor opening, car loading, door closingtime and acceleration at entrance lobbygenerally ground floor plus retardationtime (while returning from top).(b)Floor serving time: This consists ofdoor opening time, transfer (loading orunloading time), door closing time,acceleration and de-acceleration(retardation) time.
30(c)Loading/ Unloading time: Practicallyobserved loading and unloading timefor lifts of different capacity are givenbelow:No. ofPassengersEntrance lobbyLoading time insecondTransfer time i.e.loading andunloading time atupper floors8 7 113 12 1.2516 14 1.520 17 1.6
31Actually average time required forentrance of each passenger in cardepends upon total number of personsentering the car and already available incar. It may be one second per personwhen car is partially loaded and 0.75second when it is completely empty.Time for emptying car is less and equalto 0.75 second for single person butthere is a tendency that all personsvacate the car simultaneously afteropening if the doors.
32(d)Door Opening and closing time: Doorclosing time is more as compared todoor opening time. This is due to factthat when all persons have entered inthe car, it takes time for people toselect and press the push button forsummoning the lift to variousdestinations.Total time for door opening and closingoperation can be taken as given below:
33Type of Door operation Capacity8 13 16 20(a) Power operated single slide(b) Power operated double slide(c) Power operated centreOpening(d) Collapsible with attendant(e) Collapsible without attendant3.8 3.8 - -3.2 3.2 - -2.8 2.8 3.2 3.22.5 2.5 3 34 4 - -Door closing and opening time, atentrance floor shall be one second more thanall above.
34(e)Distance travelled by lift duringacceleration or retardation is assumedto be equal. This can be calculated byusing formula.d = ut + ½ ft2Where U is initial speed = 0, f isacceleration or retardation rate and t isthe time elapsed. It is assumed thatduring each cycle, lifts acceleration andretardation time is about 2 second.
35Rate of acceleration will vary with type ofas given below:Lifts speed m/s Rate ofacceleration m/sec21 0.501.5 0.752.5 1.00More than 2.4 to 8 2.50More than 8 andfloors more than 504.00