SINGLE FLOOR TRANSIT TIME t

The parameter tv requires the interfloor distance (df) and the rated speed (v) to be known. 5.7.1 Interfloor Distance

This is the time that a car takes to travel past two adjacent floors at rated speed and is defined by Definition 4.21 as the average interfloor distance divided by the rated speed.

The average interfloor distance df is normally determined as the total travel to the highest served floor divided by the number of possible stopping floors above the main terminal. Domestic dwellings average about 3.0 m per floor and commercial buildings range from 3.0 m to 3.3 m for older buildings to 3.6 m to 4.2 m (or greater) for modern buildings. In the latter case the increased floor to floor distance is required to

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accommodate other services (eg: air conditioning, electrical supplies) and various modern technological services (eg: computer networks, telecommunications).

Commercial buildings often introduce a mixed floor pitch for a number of reasons:

■ Some floors have increased heights, such as lobby/main terminal floors, service floors, special floors (eg: those containing a restaurant, lecture room, conference room, VIP suite, etc.).

■ Some floors are sometimes unavailable for alighting during periods of the day, such as the first floor (and sometimes the second floor) above the main terminal, service floors, security floors, etc.

It is recommended that an average floor height be assumed, and the irregularities be dealt with separately, as discussed in Chapter 7.

Where a lift is serving a set of floors or zone in a building, which are not adjacent to the main terminal, an extra time to make the jump to or from the express zone must be added to Equation (4.11), ie: 2te, where te is the time the lift takes to travel (without stopping) from the main terminal to the express zone terminal.

(5.22) The long “flight time” te can be found using the equations in Appendix 1.

5.7.2 Rated Speed

The value of the rated speed (v) is usually supplied by the lift maker, who will select it to meet various engineering requirements (i.e. gearing, drive controllers, product line considerations, etc.) and traffic purposes. For instance, goods lifts are generally slower than passenger lifts. Speed, however, is not a dominant factor in Equation (4.11), as illustrated by Example 6.1. It does become significant if the served floors are in an upper zone, where a higher speed will permit the unserved zone to be more rapidly traversed. If a value for v is not provided it must be chosen by the traffic designer.

The appropriate value for rated speed could be that recommended in the British, European and

International Standard Codes of Practice, taken together with experienced judgement. In general, the higher the building rise the faster the rated speed used. Often in a zoned building the rise from an express zone terminal may be small eg: 10 floors, but the express jump from the lower terminal to the express zone terminal may be large. It is this express jump, which largely determines the rated speed, that allows journey times to be kept at reasonable values.

Fire codes can determine a minimum value by requiring that it shall be possible to travel to the highest floor in the building from the fire control entrance level in (say) 60 s. Clearly this is not possible in very tall buildings and special arrangements must be made in these circumstances.

BS 5655: Part 6:1990 recommends rated speeds in relation to total travel according to building usage. This can be translated into the time to travel at rated speed (without allowance for acceleration,

deceleration or levelling) between the highest and lowest floors (the terminal floors), as shown in Table 5.2. This time is sometimes called the nominal travel time.

ISO 4190–6 recommends a maximum (theoretical) time of transit of between 20 s and 40 s to travel, at the rated speed, a distance equal to the total travel of the lift. The time is graded according to the likely interval at the main floor.

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There is no theoretical upper limit to lift rated speed and it does not, for example, affect passenger comfort. However, it is limited by practical factors, such as the maximum sheave diameter, rope bending radius, rope wear, safety (eg: overtravel), etc.

Table 5.2 Total time required to travel between terminal floors in different types of building

Building type Transit time (s)

Offices - large 17–20 - small 20 Hotels - large 17–20 - small 20 Hospitals 24

Nursing and residential homes 24

Residential buildings 20–30

Factories and warehouses 24–40

Shops 24–40

Table 5.3 provides guidance on the selection of the speed of a lift based on the premise that the total time to travel the distance between terminal floors at rated speed should take between 20 s and 30 s. In the table the single floor flight times assume a 3.3 m interfloor distance and are slightly larger than theoretically derived values to allow for the doors to be locked and proved, the brake to lift and other start-up delays. The range of values given for acceleration is typical of those found on installed

installations. Some installations nowadays limit the acceleration to about 1.2 m/s2 in order to provide a good ride quality. This will increase the single floor flight time and the eventual handling capacity. Table 5.3 Typic cal lift dynamics

Lift travel (m) Rated speed (m/s) Acceleration (m/s2) Single floor flight time (s)

<20 <1.00 0.4 10.0 20 1.00 0.4–0.7 7.0 32 1.60 0.7–0.8 6.0 50 2.50 0.8–0.9 5.5 63 3.15 1.0 5.0 100 5.00 1.2–1.5 4.5 120 6.00 1.5 4.3 >120 >6.00 1.5 4.3

The figures given in Table 5.3 apply principally to commercial buildings; speeds in residential and

institutional buildings may be subject to other design regulations, and similar height and similar function buildings can be installed with a wide range of equipment, eg: old persons’ homes compared to prestige flats.

5.7.3 Example 5.3

Two tenders have been received for the provision of a lift system of 10 person rated car capacity in a 15-storey office block having an interfloor height of 3.3 m. Assume a passenger transfer time of 1.2 s. Compare the two tenders. Table 5.4 gives the received tender information and Table 5.5 gives data deduced from the given data.

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Table 5.4 Tender information

Parameter Tender A Tender B

Rated speed (m/s) 1.6 2.5

Door opening time (s) 1.0 3.0

Door closing time (s) 3.0 3.5

Flight time (s) 6.0 5.5

Table 5.5 Deduced data for Example 5.3

Parameter Tender A Tender B Deduced from

Average number passengers (P) 8.0 8.0 CC=10 Average highest floor (H) 13.8 13.8 Table 5.1 Average number of stops (S) 6.4 6.4 Table 5.1 Single floor transit time (tv) (s) 2.06 1.32 Definition 4.21 Stopping time (ts) (s) 7.94 10.68 Definition 4.22 Passenger transfer time (tp) (s) 1.2 1.2 Design brief Performance time (T) (s) 10.0 12.0 Definition 4.23 Calculation of the round trip time for Tender A is as follows:

Calculation of the round trip time for Tender B is as follows:

Although the speed was different between Tender A and Tender B, other changes altered the values obtained from each of the component parts of the round trip time equation. The result was very similar traffic handling systems.