The reality is, it’s more than likely you’re just someone looking to have a lift installed or simply found yourself wondering ‘how is lift capacity calculation decided’ as you travelled upwards towards your office in a lift one morning. Unless you design and manufacture lifts, it’s not common knowledge as to how we decided how many people can fit in a lift at one time.
In order to be able to calculate passenger lift capacity, there must first be a basic understanding of the lift traffic. The introduction of computerised traffic analysis started in the mid-1970s however began a new era in the sophistication and speed of analysing lift traffic performance. It also enabled much more complex variations in floor populations, entrance/exit locations, and control system types to be analysed quickly and accurately
Analysing lift traffic for planning and comparative purposes are based upon the performance of a lift system during a theoretical five-minute period in an existing building’s peak traffic. The performance of a lift service with this five-minute peak period has two distinct measures.
These measures are:
- Quality of service – This is often measured by the time between consecutive lifts arriving at the main lobby and known as Average Interval (AI) or by the Average Waiting Time (AWT) – both measured in seconds. If we divide the 5-minute (300 s) peak period by the Average Interval we get the number of car departures in the peak 5-minute period.
- Quantity of Service – measured by how many people can be moved in a given type of traffic in 5 minutes. If we multiply the number of car departures within 5 minute period by the number of passengers in the car we can calculate how many people have been moved. Known as the 5-minute Handling Capacity it is usually expressed as a percentage [%] of the population served by the given group of lifts.
These theoretical performance characteristics can then be compared to industry benchmarks.
These measures of performance will be directly influenced by a wide range of factors that need to additionally be taken into account;
- The working population of the building or part of the building is served by the group of lifts.
- The number of lifts (including their capacity, speed, and performance characteristics).
- The predominant traffic flow being simulated i.e. one way or two way.
- The lift control system utilised (conventional or destination).
- The number of floors served (including the total travel distance of the lifts).
- Where users enter and exit the building.
The outputs of traffic analysis will give an accurate indication of the quality and quantity of lift service provided i.e. what the waiting times are and what percentage of the building population can be transported by the lifts in a given time period.
It is important to remember that when you are having your Lift Capacity Calculation assessed that it is carried out by a LOLER compliant engineer to ensure that your lift is safe for all users.