The high-rise nature of the Middle East's construction boom makes lifts a principal feature of MEP design. James Fullerton, MEP quantity surveyor for DG Jones International outlines recent developments in the technology.
The high-rise nature of the Middle East’s construction boom makes lifts a principal feature of MEP design. James Fullerton, MEP quantity surveyor for DG Jones International outlines recent developments in the technology.
Elevators in their numerous forms have existed for many years now. Brunelleschi’s elevators were created during one of the most creative periods in the history of mankind, but it wasn’t until Elisha Graves Otis in 1954 created the first safe elevator that the city was born and without this Dubai would look remarkably different.
Planning for vertical transportation is a key engineering design issue and certain decisions need to be addressed in the early design process. The main design considerations for choosing either electric traction drive or hydraulic for a particular project are the number of floors, the height of the building, the number of people to be transported, desired passenger waiting times and frequency of use.
The costs of different solutions can vary widely and it is important to strike a balance between capital cost; maintenance; the value of floor area to be occupied by the lift shafts and lobbies; and performance criteria.
The most significant development in the recent history of elevators has been the introduction of Motor Room Less (MRL) lifts. These have been increasing their share of new installations in lieu of the more traditional solution of using a motor room.
Hydraulic lifts are another option, but their application is limited to low-rise, low usage installations, however the flexibility in the location of the motor room is one advantage of these products.
The Code of Practice followed in the UAE is BS EN 81 Parts 1, 2, 3, 72 and 80. The ASME A17.1 code does not specifically address MRL design.
The main solutions Motor Room or MRL installations are electric traction lifts that provide high performance without the need for frequent maintenance such as lubrication and adjustments.
The principle of these lifts is that traction steel ropes attached to a sheave powered by an electric motor lower and raise the elevator car rather than it being pushed from underneath. In gearless elevators the motor turns the sheave directly; in geared elevators, the motor turns a gear train that rotates the sheave.
Most MRL solutions are based on gearless technology. Traditionally in motor room configurations the sheave, motor and control system are all housed in a machine room above the elevator shaft. MRL installations are proving extremely popular in Europe where space, cost-effectiveness and environmental considerations are high priority design issues in new construction developments.
Nevertheless, MRL solutions are becoming more frequently adopted as their benefits are becoming more apparent.
First invented by Kone in 1996 (called EcoDisc), MRL lifts are arranged with the drive motor mounted within the shaft and controls housed in a compact panel adjacent to a door housing, thereby removing the need for a machine room.
This was made possible by the development and application of permanent magnet (PM) system technology in the lift motor that reduces the size of the motor by up to four times. For example, a 6.5kW motor used in a MRL configuration can perform the same task as a conventional 16.8kW traction machine; there is an even greater difference when compared to hydraulic systems. Smaller motors also use less energy.
Most manufacturers can now supply MRL solutions, each with their own adaptations. Mitsubishi has recently incorporated several new features into its motors. Technical developments such as increasing the density of the armature winding in the PM and applying their own proprietary joint-lapped core, further reduced the lift motor dimensions while improving its power output. To date the focus from all manufacturers has been on maximising the power output of the motor while reducing its physical size.
Even though the machinery for MRL is installed in the lift shaft it should be noted that all machinery spaces are subject to the same basic requirements regarding accessibility, lighting, ventilation, protection against environmental influences and strength, that apply to machine rooms. This also applies to access requirements for maintenance and inspection of components if deemed to be of particular importance.
MRL solutions range up to 30 floors and can reach up to speeds of 2.5m/s. For projects with exacting performance criteria in terms of travel height and velocity, there is no alternative to having a machine room, which may be arranged above, below or, in exceptional cases, to one side of the lift shaft.
Since the application of MRL technology is relatively new and due to the very fact that each of the major manufacturers provides propriety products, maintenance needs careful consideration. Therefore when evaluating the technical aspects the end-user or building owner should be aware of the potential pitfalls of being trapped into a high cost maintenance contract and left with no alternative.
In traction sheave lifts the counterweight is generally dimensioned on the weight of the car and half the payload. This is the energy corresponding to the weight of the car saved both when the car is traveling full and empty.
However on empty down trips, which is common on residential elevators, the hoisting system requires its maximum power as it has to be able to lift the net difference between the counterweight and the unloaded car.
New developments by certain manufacturers have eliminated the need for a counterweight and elevators using this technology can have cars up to a third larger than traditional elevators designed in the same lift shaft. For example a passenger car with a capacity of six people could be increased to nine people.
Again the primary function and area of innovation is the motor and the implementation of a flexible roping arrangement using high-tensile-strength ropes. The main applications for counterweight installations other than new build properties are value engineering exercises and refurbishment schemes.
Several factors combine to influence the cost of a lift installation, including the requirement for and location of the motor room; intelligent car group control; number of floors; passenger capacity, finishes and facilities.
MRL installations are generally cheaper to install, give greater architectural flexibility and increased lettable space. Presently the speed and number of floors limit their installation, but as technology develops so too will the amount of projects using MRL elevators.