--- title: "Number of lifts for office building" subject: "Industrial Power Distribution and Illumination" chapter: 5 key: "semester_6/industrial_power_distribution_and_illumination:lift-number-office-building" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/lift-number-office-building site: BCT Engineering --- # Number of lifts for office building Industrial Power Distribution and Illumination · Chapter 5: Electrification of Industrial Building - Asked in: 2073 Magh, 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/lift-number-office-building - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-5 ## Question Calculate the number of lift require to empty a office building having following details: | S.N | Description | Quantity | |---|---|---| | 1 | Number of floor | 20 | | 2 | Total rental area above ground floor (m²) | 20000 | | 3 | Estimate rental area per person (m²) | 10 | | 4 | Time required empty to building (minute) | 60 | | 5 | Average floor height of building (m) | 3.5 | | 6 | Lift capacity number of person in each car | 10 | | 7 | Speed of lift (meter/minute) | 135 | | 8 | Estimated stop | 1 stop each 10 m | | 9 | Time required at the ground floor for synchronizing | 30 Sec | | 10 | Time required above ground floor at each stop | 10 Sec | ## Short answer Population 2000. Round trip time 162.22 s, one lift handles 221.92 persons/h. Required lifts = 2000/221.92 ≈ 9.01. Install 10 lifts, each 10-person, speed 135 m/min. ## Answer The number of lifts is found from the population to be moved, the time allowed, and the round trip time of one car. **Interpretation**: travel height is taken as 20 floors × 3.5 m = 70 m; one stop every 10 m on a trip; lift speed 135 m/min both ways. #### Step 1: population ```text Persons = rental area / area per person = 20000 / 10 = 2000 persons ``` #### Step 2: round trip time (RTT) of one car ```text Travel height H = 20 × 3.5 = 70 m Running time (up + down) = 2 × 70 / 135 min = 1.037 min = 62.22 s Number of stops = 70 / 10 = 7 stops Stop time = 7 × 10 s = 70 s Ground floor time = 30 s RTT = 62.22 + 70 + 30 = 162.22 s ``` #### Step 3: handling capacity of one lift ```text Trips per hour = 3600 / 162.22 = 22.19 trips Persons per hour = 22.19 × 10 = 221.92 persons ``` #### Step 4: number of lifts ```text Persons to move in 60 min = 2000 N = 2000 / 221.92 = 9.01 → round up ``` **Answer: 10 lifts** (each 10-person, 135 m/min) are needed to empty the building in 60 minutes. | Quantity | Value | |---|---| | Population | 2000 persons | | Round trip time | 162.22 s | | Capacity per lift | 221.92 persons/h | | Lifts required | 9.01 → 10 | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How is the population to be moved found? A. Rental area / area per person = 20000 / 10 = 2000 B. Number of floors x lift capacity C. Rental area x area per person D. Floors x 10 persons Answer: A. Population equals rental area divided by area per person. (Key point: Population) 2. Which components make up the round trip time? A. Only travel up B. Running time up and down, stop time for all stops, and ground floor time C. Door time only D. Waiting interval only Answer: B. RTT = 2H/v + (stops x 10 s) + 30 s = 62.22 + 70 + 30 = 162.22 s. (Key point: Round trip time) 3. How many stops are taken for 70 m height with one stop per 10 m? A. 20 B. 10 C. 3.5 D. 7 Answer: D. 70 / 10 = 7 stops, each 10 s, giving 70 s. (Key point: Stops) 4. One lift handles 221.92 persons/h. How many lifts empty 2000 persons in 60 min? A. 9.01 rounded up to 10 B. 9.01 rounded down to 9 C. 20 D. 5 Answer: A. 2000/221.92 = 9.01, and fractional lifts are rounded up, so 10. 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