Lifts are expensive items for any office building, costing upwards of £100,000 each to install. Yet the standard calculations used by engineers to decide how many lifts a building will need, together with their size and speed, are unreliable and outdated, according to research released by Stanhope this week.
The developer and project manager says this leads to over-specification and waste of resources.
The research is the latest in a series of 'position papers' issued by Stanhope on the technical specification of office buildings, designed to raise standards across the industry.
'We've got all these standards that bear no relevance to real life,' claims Ron German, Stanhope director. The company is calling for standards that recognise how the use of office space has changed since the 1970s and are also free of jargon, so that agents and occupiers can understand them.
The most influential factor in designing a lift service is 'peak handling capacity'. The standard practice is to ensure that the lifts are large enough, fast enough and plentiful enough to transport 15% of a building's total population from the lobby to their floors within five minutes. This figure is based on what is believed to be peak demand, occurring in the morning as everyone arrives for work.
Trickle, not a flood
Yet Stanhope's research found that this standard is a dramatic over-estimation of real need. It studied the flow of people arriving for work at eight office buildings in London and found that employees trickle in far more slowly than is being allowed for, with no more than 6.1% of the total arriving within the same five-minute period.
Stanhope repeated the exercise at lunchtime, to test the theory that demand will reach higher peaks than in the morning as people leave for appointments, shopping and leisure. This time the maximum percentage of building occupants travelling either in or out within the same five minutes reached almost 7%, higher than at the start of the day but still much lower than the 15% typically allowed for when lifts are specified.
Stanhope's explanation is that the existing standards date from the 1970s when office workers lived by a stricter nine-to-five routine and spent more time at their desks. Today, the population of a building at any one time is much more fluid.
The developer is also critical of many of the other assumptions that go into specifying lifts. For example, it believes that occupation density, or the number of people assumed to occupy a building, is often overestimated. Occupation density will determine the anticipated volume of passenger traffic. Yet Stanhope points out that the three existing standards, produced by British Standards, the Chartered Institute of Building Services Engineers (CIBSE) and the British Council for Offices (BCO) are all at odds with each other. British Standards suggests occupancy of one person per 10 sq m; the CIBSE recommends a range of between 8-20 sq m per person and the BCO recommends 14 sq m per person. Stanhope agrees with the BCO.
Stanhope also argues that calculations in 'waiting time' for a lift are often linked inappropriately with 'interval time', which is the time taken for a lift to complete a cycle from ground floor to the top and back. Waiting times are reckoned at 70%-80% of interval time, but Stanhope says this is an unreliable way of working.
In addition, Stanhope says the standard calculations ignore recent changes in lift-call technology. The latest computer control systems are designed to minimise the time between a user calling a lift and arriving at their chosen floor by referring to the other calls made, instead of minimising the time between a call and the lift's arrival. 'Such advances are serving to make existing standards even less relevant,' says the report.
'We have proved that the standards by which most lift services are designed don't work,' adds German. 'But we haven't yet done the work to establish what the appropriate standards are.'
German suggests that the British Council for Offices could work with technical institutions such as the Chartered Institute of Building Services Engineers (CIBSE) to come up with the standards.
Richard Kauntze, chief executive at the BCO, says: 'We welcome the report and would want to respond to it. This is exactly the kind of challenge that the BCO is well-placed to respond to.'
Copies of the report, Lift Performance and Specification, are available free from Stanhope on 020 7170 1700.