Lift Performance Criteria

Different types of buildings require a different approach to assessing what might be termed their working populations. This is an estimate of the maximum number of persons normally present on each floor of the building. For offices this may be based on the Net Internal Area (NIA) and a population density. For hotels, the type of hotel and number of rooms. For residential blocks, the category of housing, number of apartments and number of bedrooms per apartment.

The biggest factor affecting the lift design for any building is the working population and therefore it cannot be overemphasised how important it is to seek specific guidance and direction from the client, developer or proposed tenant on this very important variable. As a “rule of thumb” one passenger lift will be required for every 250 to 300 office users.

OFFICES – MORNING ONE-WAY UP-PEAK TRAFFIC

The table below provides some guidance but these variables can change greatly depending on the geographic location of the building and the client’s intended use of the building.

OFFICE BUILDING TYPICAL POPULATION DENSITIES
BUILDING OCCUPANCY TYPE
DIVERSIFIED TENANCY MIXED TENANCY SINGLE TENANCY
14 m^2 NIA / person 12 m^2 NIA / person 10 m^2 NIA / person

The three tenancy types are defined below:

  • Diversified Tenancy – where no single tenant occupies more than a single floor and no more than 25% of the building tenants are engaged in the same type of business activity.
  • Mixed Tenancy – where a single tenant has multi-floor occupancy or multiple tenants with the same business activity.
  • Single Tenancy – where one tenant occupies 80% or more of the building.

Population density of 1 person per 12 m^2 Net Internal Area equivalent to 1 person per 10 m^2 Net Internal Area with a utilisation factor of 80%.

Having calculated the total population an absentee factor of 15 to 20% is normally applied to account for staff not present due to annual leave, sickness, external meetings etc. In addition, depending upon the design of the stairwells and their ease of access, a further discount for staff preferring to use stair access at the very lowest floors might be applicable. This will then enable a working population to be arrived at.

Having established the working population then the appropriate standard of lift performance can be selected based on the following criteria:

Average Interval (AI) or Average Waiting Time (AWT) is used to evaluate the quality of lift service during the 5-minute peak traffic period. The following chart indicates typical standards used to evaluate levels of service based on average waiting time or average interval:

OFFICE BUILDING AVERAGE INTERVAL PERFORMANCE STANDARDS (5-MINUTE, A.M., UP PEAK)
GRADE OF SERVICE AVERAGE INTERVAL(BY CALCULATION) AVERAGE WATING TIME(BY SIMULATION)
EXCELLENT ≤25 seconds ≤20 seconds
GOOD ≤30 seconds ≤25 seconds
FAIR ≤35 seconds ≤30 seconds
UNACCEPTABLE >35 seconds >30 seconds

According to British Council for Offices 2009 (BCO) and CIBSE Guide D Guidelines:

  • For lifts with conventional control             Average Interval             = 30 s or less
  • For lifts with destination control                Average Waiting Time    = 25 s or less

The latest British Council for Offices (BCO) “Guide to Specification 2014” continues to recommend an Average Waiting Time of less than 25s but also specifies using an 85% up, 10% down and 5% inter-floor traffic demand. This can be easily set, if desired, within the AdSimulo application.

Group Handling Capacity is used to evaluate the quantity of lift service during the 5-minute peak traffic period. This is the number of persons, or percentage of the zone population, that can be transported by the lifts in the same 5-minute peak traffic period used to measure Average Waiting Time. The following chart indicates typical standards used to evaluate levels of service based on group handling capacity:

OFFICE BUILDINGGROUP HANDLING CAPACITY PERFORMANCE STANDARDS
(5-MINUTE, A.M., UP PEAK) (PERCENTAGE OF ZONE POPULATION)
GRADE OF SERVICE BUILDING OCCUPANCY TYPE
DIVERSIFIED TENANCY MIXED  TENANCY SINGLE TENANCY
EXCELLENT OVER 14% OVER 15% OVER 16%
 GOOD 13 TO 14% 14 TO 15% 15 TO 16%
 FAIR 11 TO 12% 12 TO 13% 13 TO 14%
UNACCEPTABLE UNDER 11% UNDER 12% UNDER 13%

According to British Council for Offices 2009 (BCO) and CIBSE Guide D Guidelines:

  • Up-Peak Group Handling Capacity = 15% or more for single tenant building
  • Up-Peak Group Handling Capacity = 12% or more for mixed or diversified tenancy

For lunchtime two-way peak traffic the recommendations are as follows:

  • Average Waiting Time: 40 s or less
  • Group Handling Capacity: 12% or more

The latest British Council for Offices (BCO) “Guide to Specification 2014” now simply recommends an Up-Peak Group Handling Capacity of at least 12% and a lunchtime two-way peak traffic demand of 13% with a 45% up, 45% down and 10% inter-floor traffic demand. Again this can, if desired, easily be set within the Adsimulo application.

HOTELS – EVENING TWO-WAY PEAK TRAFFIC

Typical guidelines for hotel working populations and good lift performance can be summarised as follows. Note however most major hotel operators publish their own guidelines for both guest and service lift design requirements. As a “rule of thumb” one guest lift will be required for every 100 guest rooms.

HOTEL BUILDING PERFORMANCE STANDARDS (5-MINUTE, TWO-WAY PEAK TRAFFIC)
TYPE OF HOTEL POPULATION (PERSONS / ROOM) AVERAGE INTERVAL (SECS) GROUP HANDLING CAPACITY (% OF POPULATION)
COMMERCIAL 1.3-1.7 ≤40-45 seconds ≥10-12%
CONFERENCE 1.8-2.0 ≤40-50 seconds ≥10-12%
TOURIST 2.0-3.0 ≤40-50 seconds ≥10-12%

RESIDENTIAL APARTMENTS – EVENING TWO-WAY PEAK TRAFFIC

Typical guidelines for residential working populations and good lift traffic performance can be summarised as follows:

RESIDENTIAL APARTMENTS PERFORMANCE STANDARDS 5-MINUTE, TWO WAY PEAK
TYPE OF BUIDING AVERAGE INTERVAL (SECS) GROUP HANDLING CAPACITY (% OF POPULATION)
LUXURY APARTMENTS ≤45-50 ≥8%
NORMAL APARTMENTS ≤50-60 ≥6-8%
LOW INCOME APARTMENTS ≤50-70 ≥5-7%

The working population of the building can be estimated using the following guidelines:

APARTMENT TYPE OCCUPANCY FACTORS FOR RESIDENTIAL BUILDINGS
LUXURY NORMAL LOW INCOME
Studio 1.0 1.5 2.0
1 Bedroom 1.5 1.8 2.0
2 Bedroom 2.0 3.0 4.0
3 Bedroom 3.0 4.0 5.0

CAR PARK STRUCTURES – EVENING ONE-WAY PEAK TRAFFIC

Typical guidelines for the lift traffic design of a parking facility is to estimate the population of the car park based on the average number of persons arriving per vehicle and the number of parking spaces available on each floor. The “working population” figure might also allow for some car park users preferring to take the stairs so a discount of the population at the lowest floors of the car park structure might be appropriate. The peak period is usually considered to be the evening “down peak” when car park users arrive at the car park main floor and need to be distributed to the parking floors either above or below the main floor. “Good” lift traffic performance is indicated in the table below:

CAR PARK STRUCTURE PERFORMANCE STANDARDS
(5-MINUTE, ONE-WAY PEAK TRAFFIC)
TYPE OF BUILDING ARRIVALS
(PERSONS / VEHICLE)
AVERAGE INTERVAL
(SECS)
GROUP HANDLING CAPACITY
(% OF POPULATION)
OFFICE 1.2 – 1.5 ≤40-45 seconds 8 – 10%
FREE STANDING 2.0 – 2.5 ≤45-60 seconds 8 -10%

Other types of car park structure e.g. retail related will require analysis of the 2-way peak traffic.

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