MULTI®

New era of elevators to revolutionize high-rise and mid-rise constructions

A new era of vertical (and horizontal) transportation will reduce the elevator footprint in buildings while liberating architects to construct more creatively, higher and more user-friendly. Multiple cabins in a single shaft mean passengers would never have to wait more than 15-30 seconds for a lift.

For people living in the countryside, elevators are a fun novelty, especially when they have an interesting design or a glass floor. For people living and working in cities, however, they can be stressful. When you push the button, it can take a long time for the elevator to arrive, and often there’s a line of people waiting ahead of you.

That’s just one of the more obvious reasons why architects and engineers have long been trying to reimagine the elevator. How can space be saved, speed increased, new paths be taken and, also, waiting times decreased? A whole new era of elevators is about to begin that will allow all of this and more.

MULTI®

Trends

As cities grow, so do buildings

What are the current challenges of urbanization that elevators need to solve? When we understand this, it becomes clear why the new MULTI® concept in development at thyssenkrupp is so revolutionary.

Cities need to expand without sacrificing their open spaces and parks, which are essential for urban quality of life. In many cases, taller buildings are a solution that provide more living and working space, without increasing the ground area needed for construction.

Elevators have made it possible for buildings to reach new heights. However, the taller the building, the more shafts and, hence, more space you need for conventional elevators. In addition, the people who use elevators frequently have to put up with long waiting times. These two disadvantages make the upper floors less attractive for living and working, despite the perk of a great view.

Conventional elevators, current state-of-the-art elevators and MULTI® in comparison. Notice how the new approach takes up even less space and moves more people than the current state of the art.

History

No time to wait

Elevators certainly save time when compared to stairs, but there is still much room for improvement. In 2010, students at Columbia University found that if you add up all the time New York City’s office workers spend waiting for elevators within a single year, their accumulated waiting time amounts to 16.6 years, as compared to only 5.9 years they actually spend travelling in the elevators.

Clearly, the best way to save people’s valuable time is to find a solution that cuts waiting times rather than only speeding up the elevators.

The long way up

Elevators have come a long way. The first building with an elevator was the Equitable Life Building in New York City, completed in 1870. Though it was only 40 meters high, it was the world’s tallest building for almost 15 years. If we compare that with the record-shattering 828-meter Burj Khalifa in Dubai, we can safely say that elevators have made the impossible possible, but they remain limited: single carriages moving up, down and back again.

Why do elevators only have to go up and down? Some experts believe the invention of elevators that can travel in curves, horizontally and in continuous loops would be the greatest achievement of the elevator industry. Elevator concepts that approach this ultimate goal have existed for over a hundred years.

Daniel E. Condon submitted a patent for his “spiral elevator” in 1903. Condon’s elevator winds up and down the exterior of an observation tower in a continuous loop. As it was more interesting as a one-off attraction, Condon submitted another patent in 1904 that focused on buildings. Though the idea would have taken up too much floor space, it did contain an interesting idea: multiple cars on a continuous loop.

Looping, multi-carriage elevators have a long history

From paternoster to TWIN®

Paternoster elevators were a further development of the loop idea, in which multiple carriages indeed move up and down in a continuous circuit. Because of this, passengers never have to wait for more than a few seconds. The constant cycle of the paternoster means that passengers have to hop on and off moving carriages that don’t have doors, posing significant safety risks for the elderly and disabled. Though several examples of these lift systems still exist, they are no longer built.

The TWIN® elevator system (a thyssenkrupp invention) saw the first successful reintroduction of multiple carriages. As a result, TWIN® has already achieved significant space savings and person-moving capacity with two independent carriages in one shaft. Buildings such as the St. Botolph Building in London and the CMA Tower in Riad, Saudi Arabia, benefit from having fewer shafts. The technology is already capable of doing more with less. But what if it were possible to put even more cabins in a shaft?

Vision

The vision of MULTI®

Markus Jetter, Head of Research at thyssenkrupp Elevator, has been working with forward-thinking technologies for over two decades. He and his colleagues have pooled their expertise from a host of previous projects to create what was once considered unattainable: multiple elevator carriages traveling safely in a continuous loop. They call it MULTI®.

“Safety” is a key word here, Jetter emphasizes. Unlike the paternoster, MULTI® elevators will stop to let people on and off and, of course, will have doors. In essence, the people who use MULTI® will not see any visual difference to normal elevators. What they will notice, however, is that the elevator doors open every 15 to 30 seconds.

“One of the key innovations of the system is that we’ve completely done away with the cables.” Despite his knack for complex engineering, Markus Jetter knows how to explain the concept in simple terms. It’s like a circular train system on a vertical plane.

MULTI® Simulation

“Basically, you have to imagine a metro, like the Circle Line in London, and put it on the wall. The trains, then, become carriages travelling on vertical tracks in the elevator shafts.”

Markus Jetter - Head of Research, thyssenkrupp Elevator

Opening doors to new possibilities – in all directions

Many different technologies had to come together to make the MULTI® system feasible. First of all, it was clear that conventional wheels on tracks wouldn’t work. Luckily, the engineers were able to draw on their experience with magnetic linear propulsion which they gained from working on the Transrapid train project. High-tech mechanical brakes ensure the system is safe, efficient and flexible.

Advancements in lightweight design make it possible to reduce carriage weight by up to 50%. The consolidation of multiple carriages into fewer shafts will also make it possible to reduce the elevator footprint in buildings by up to 50%. And increase passenger throughput by at least 50%, as well.

In addition, expertise derived from TWIN® has pushed functional safety and technical controlling to new levels of sophistication. An innovative track changing system also allows for the horizontal connection of two shafts on the top and bottom to create a continuous loop – where cabins go up one shaft and down another.

These innovations open the door to many new possibilities, as well, giving architects new design options, empowering them to create innovative new buildings and let their creativity soar.

As cities grow, so do buildings

“Buildings are becoming like vertical cities, and they need a flexible transport system similar to a metro. Speed alone does not solve the challenges posed by tall buildings.”

Markus Jetter - Head of Research, thyssenkrupp Elevator

Efficiency and flexibility trump speed

Due to the constraints of passenger comfort, elevators can only travel so fast. As a result, quicker speeds only provide a marginal improvement in handling capacity. With the added limitation of having only one cabin per shaft, traditional elevators take up more and more space as buildings increase in height.

With MULTI® carriages capable of picking people up every 15-30 seconds, waiting times are brought to a minimum and handling capacity soars. Like a metro system, MULTI® can take the bulk of passengers to transfer stations every 50 meters or so where passengers can change to TWIN® or conventional elevators that cover shorter distances, like moving from the subway to a bus, so to speak.

The future of MULTI®

Will the concept also meet future demands on energy efficiency? As mentioned, the MULTI® concept can reduce the elevator footprint by up to 50%. These space savings can be used to reduce the overall size and external surface area of buildings which in turn reduces total energy needs.

Another possible development could involve the implementation of an energy recovery system that converts the kinetic energy of descending carriages into electrical power for the upward trip.

The first step, however, is to get a full-sized working prototype. Construction is currently underway to build such a prototype, to be completed within the next two years at the new “elevator test tower” in Rottweil. This will serve as the basis for inspection and certification, thus opening the door to real-world applications.