Lifts & Vertical Transport Lab
Run an up-peak traffic analysis for a lift group: round trip time, interval, five minute handling capacity and average waiting time against targets for offices, apartments, hotels and hospitals. Then the electrical side: motor size, supply current, group diversity and what goes on the standby generator with firefighting and evacuation lifts.
How to use: enter the floors, population and the lift group. Defaults load for the building type. Tap i for help.
1. Inputs
2. Lift group
Lobby plan with the shafts, a 3D group with moving cars and the cars over time in up-peak.
3. Checks
4. Traffic analysis (CIBSE Guide D up-peak)
5. Electrical loads
6. How it works
Up-peak analysis
The morning up-peak is the classic design case for offices: everyone arrives at the main lobby and goes up. CIBSE Guide D works out how many stops a car makes (S) and how high it goes (H) for an average load of 80% of the car capacity, then the round trip time from travel, stopping, door and passenger transfer times.
Interval and handling capacity
Interval is the round trip time divided by the number of lifts: the average time between car departures from the lobby. Handling capacity is how many people the group moves in five minutes, as a share of the population. Offices aim for about 25 to 30 s interval and 12 to 15% handling capacity, apartments 45 to 90 s and 5 to 8%.
Electrical design
A traction lift motor lifts the car load minus the counterweight balance. Variable voltage variable frequency drives keep the starting current low and can feed energy back on regenerative drives. Groups never all start at once, so a diversity factor applies to the feeder. On mains failure, lifts return one at a time on the standby generator, while firefighting (BS EN 81-72) and evacuation lifts (BS EN 81-76) stay powered from secure supplies.
Concept traffic study to CIBSE Guide D up-peak formulas. Use a lift consultant or the maker's simulation (lunch peak, two way traffic, destination control) for the final selection.