Abstract: Efficient vertical mobility is a critical component of tall building development and construction. This paper investigates recent advances in elevator technology and examines their impact on tall building development. It maps out, organizes, and collates complex and scattered information on multiple aspects of elevator design, and presents them in an accessible and non-technical discourse. Importantly, the paper contextualizes recent technological innovations by examining their implementations in recent major projects including One World Trade Center in New York; Shanghai Tower in Shanghai; Burj Khalifa in Dubai; Kingdom Tower in Jeddah, Saudi Arabia; and the green retrofit project of the Empire State Building in New York. Further, the paper discusses future vertical transportation models including a vertical subway concept, a space lift, and electromagnetic levitation technology. As these new technological advancements in elevator design empower architects to create new forms and shapes of large-scale, mixed-use developments, this paper concludes by highlighting the need for interdisciplinary research in incorporating elevators in skyscrapers.

Keywords: energy saving; efficiency; speed; long distances; comfort; safety; security

1. Introduction

When people think about the development of cities, rarely do they contemplate the critical role of vertical transportation. Consider, however, that each day, more than 7 billion elevator journeys are taken in tall buildings all over the world [1,2]. Efficient vertical transportation has the ability to limit or expand

our ability to build taller and taller skyscrapers, and recent innovations in elevator design promise to significantly reduce energy consumption.

Antony Wood, 2014, a Professor of Architecture at the Illinois Institute of Technology (IIT) and the Executive Director of the Council On Tall Buildings and Urban Habitats (CTBUH), explains that advances in elevators over past 20 years are probably the greatest advances we have seen in tall buildings [1]. Indeed, the race to build ever taller skyscrapers has sparked fierce competition among lift manufacturers to build faster, more efficient, safer, more comfortable and more economical elevators. For example, elevators in the Kingdom Tower in Jeddah, Saudi Arabia, under construction, will reach a height record of 660 m (2165 feet); and elevators in CTF Finance Center in Guangzhou, China, under construction, will travel with a speed record of 20 m/s (66 feet per second).

Daniel Levinson Wilk, a Professor of History at the Fashion Institute of Technology in New York and a board member of the Elevator Museum in Queens, explains in an article, 2014, titled “How the Elevator Transformed America” that the elevator is responsible for shaping modern life in ways that most people simply don’t appreciate and that he would like people to be more conscious of the elevators in their lives [3]. Professor Wilk is particularly .

Similarly, Andreas Bernard’s research shows [4] how elevators have been responsible for reshaping modern cities by concentrating large masses of people and activities in smaller areas, creating vibrant communities. Spatially speaking, the elevator’s role has been no less profound than that of the automobile in transforming modern cities. While cars have facilitated horizontal spread of cities and regions, encouraging sprawl and suburbia, elevators have enabled concentrating a large number of people and human activities in a smaller footprint. New advances in elevator technologies are likely to reshape cities further by enabling even taller buildings .

In addition to highlighting the importance of elevators in the development of our cities, this paper aims to educate about the intersection of green technologies with energy efficient elevators. New innovations are leading to the introduction of energy efficient elevators that not only consume less energy, but also produce clean energy. In this regard, the paper advocates for investment in innovative research and development of “green” elevators. “Green” has become an emerging and dominant design philosophy. With so many building products being marketed with a “green” angle, this paper provides useful information to help in making “green” choices when it comes to incorporating elevators in skyscrapers [5–9]. Architects and architectural students may particularly find this aspect of the paper useful since it contains essential knowledge for incorporating elevators in tall buildings.

Third, this paper discusses the need for revisions to local building codes to allow and encourage adoption of “green” elevators. Restrictive building codes in some countries, including the United States, are often a barrier to employing innovative, emerging, elevator technologies. Governments should consider financial incentives, perhaps in the form of tax credits, for the incorporation of green elevators into future skyscrapers and the retrofitting of green elevators into older buildings. Authorities should also encourage projects to pursue an efficiency-rating system such as LEED, BREAM, and ENERGY STAR.

Tokyo, Japan; Hitachi, Tokyo, Japan; and ThyssenKrupp, Essen, Germany). These companies are producing and implementing premium elevators that enjoy improved controls, hardware, and other systems that not only use less energy but are also much more compact, efficient, and even generate electricity that a building can use. This study also builds on the work of many scholars who have been active in elevator design and technology research.

The paper follows a simple structure. First, it describes recent technological advancements in elevator design. Next, it furnishes five detailed case studies that illustrate incorporating state-of-the-art technologies in major skyscraper projects around the world including: One World Trade Center in New York; Shanghai Tower in Shanghai; Burj Khalifa in Dubai; Kingdom Tower in Jeddah, Saudi Arabia; and the green retrofit project of the Empire State Building in New York. Then, the paper discusses technologies that focus on the passenger experience, including speed, comfort, security, and entertainment. Finally, it addresses future research and development on elevator design.

2. Recent Technological Developments

Much of the “green” agenda focuses on reducing energy consumption. Buildings consume about 40% of the world’s energy, and elevators account for 2%–10% of a building’s energy consumption. During peak usage hours, elevators may utilize up to 40% of the building’s energy [19]. Glen Pederick, 2014, explains that everyday there are more than 7 billion elevator journeys taken in buildings all over the world; and as such, energy-saving elevators will reduce energy consumption significantly [20]. Fortunately, new technologies and best practices involving motors, regeneration converters, control software, optimization of counterweights and cabin lighting can yield significant savings [20,21]. New elevators provide efficiency gains of about 30–40 percent than buildings with older lifts [14]. Researcher Patrick Bass writes of recent examples of ThyssenKrupp technologies that provide energy savings of about 27% and space saving of about 30% [22]. Research on energy efficiency conducted by De Almeida and colleagues has indicated that “considerable technical efficiency potentials exist for elevators (more than 60%)” [23]. They write “By improving the energy efficiency in existing and new equipment, elevators and escalators can contribute to current energy and climate targets in Europe.” Quantitative studies on energy consumption of newer and older elevator technologies are now being conducted to assess the value of the new technologies. In this regards, ISO 25745-2:2015 standards are used to help to estimate energy consumption. These standards provide measured values and calculations on an annual basis for different types of elevators and present the data according to different energy classification systems for new, existing, and modernized elevators.

However, research by De Almeida et al. explains that lack of awareness of “green” elevator technologies has impeded the full implementation of these technologies. This paper serves to respond to this gap and educate architects and developers on how to harness the power of these new technologies. For simplicity, new elevator technologies are discussed within two categories: energy-efficient hardware (e.g., AC power, machine-room-less technology, regenerative drives, elevator ropes, TWIN systems, double deck elevators, and LED lighting); and energy-efficient software (e.g., destination dispatching systems, people flow solutions, and standby solutions). Other technologies related to elevators are discussed in the subsequent section. In order to provide development continuity, the discussion starts by

briefly mentioning earlier energy-efficient innovations and then moves quickly to the most recent ones .

Energy-Efficient Hardware

AC and DC Motors

One of the significant advances in elevator technology has been from the replacement of conventional brushed DC (direct current) motors with more efficient AC (alternating current) motors. Before the 1990s, elevator systems relied on DC motors because it was easier to control elevator acceleration, deceleration, and stopping with this form of power. As a result, AC power typically was restricted to freight elevators, where comfort and speed are not as critical as in passenger elevators. By the late 1990s, however, more elevators had moved to AC machines because motor controller technology had advanced enough so that it could regulate AC power, enabling smooth stopping, acceleration, and deceleration [9,12,24].

Geared and Gearless Motors

High-rise buildings typically employ geared or gearless traction elevators capable of high or variable speed operation. In geared machines, the electric traction motor drives a reduction gearbox whose output turns a sheave over which the rope passes between the car and the counterweights. In contrast, in gearless elevators, the drive sheave is directly connected to the motor, thereby eliminating gear-train energy losses. Therefore, a major advantage of gearless motors is they save about 25 percent more energy than geared motors. Gearless motors also run faster and enjoy greater longevity because they feature higher torque and run at lower RPMs. The major disadvantage of gearless elevators is cost; materials, installation, and maintenance are generally more expensive than geared elevators. In spite of the cost, more elevators today use AC, gearless motor machines because they are more efficient and last longer [12,25].

Machine-Room-Less (MRL) Technology

Introduced in the mid-1990s, machine-room-less (MRL) technology was one of the biggest advances in elevator design since they went electric a century before. Manufacturers redesigned the motors and all other equipment normally housed in a machine room to fit into the hoistway, eliminating the need to build a machine room. Earlier, elevator equipment was so massive that a dedicated machine room (about 8 feet tall or greater) was required, usually placed above the hoistway atop a building’s roof. The machine room was costly because it needed to support heavy machinery (Figure 1). Today, MRL elevators are increasingly common [14,26]. The MRL system becomes even more energy efficient when it is combined with regenerative drives [14,26].

Figure 1. Gearless Machine-Roomless Revolution. Note space saving factor as technology advances. This increases usable spaces, which is crucially important in skyscrapers. (Source: http://www.otisworldwide.com).

Regenerative Drives

Regenerative drives are another remarkable advancement in energy-efficient elevator technology, providing the ability to recycle energy rather than waste it as heat. They work by capturing and converting the energy used from braking to maintain the elevators speed. More specifically, traction elevators use a counterweight to balance the weight of the elevator car and passengers. The counterweight is sized in an optimal way, approximately to a car loaded to 40%–50% of capacity. Hypothetically, if the counterweight is too heavy or too light, then the elevator will overwork the motor and the braking system. Instead, a middle weight is effective at leveling energy use in both up and down directions. When the elevator car is loaded less or more than the 50 percent capacity (traveling up cars are light, or traveling down cars are heavy) the elevator applies brakes to maintain their rated speed. Braking is provided by allowing the AC motor to operate as a generator, converting mechanical energy to electrical energy which is dissipated as heat by special heat resistors. The regenerative drive captures that energy and channels it back to the building or the city power grid.

Hughes [27], explains that the regenerative drive can harness and save energy in multiple ways including:

When the elevator slows down, it applies brakes and energy is In a conventional elevator system, that energy is dissipated as heat through a heat resister. The regenerative drive harnesses that energy.
Whenever an empty or lightly loaded elevator goes up, the elevator applies brakes to maintain the rated speed. As is the case of slowing down, that energy is usually lost but the regenerative drive harnesses it. Further, when an empty or a lightly loaded elevator goes up, the motor spins but the elevator’s counterweight does most of the work. The regenerative drive harnesses that spinning energy by transforming mechanical power into electrical
When a heavy elevator goes down, it applies brakes to maintain the desired In a conventional

system, the energy created by the braking system is lost. The regenerative drive harnesses that

energy. Further, when a heavy elevator goes down, the motor spins but gravity does most of the work. The regenerative drive again harnesses that spinning energy by transforming mechanical power into electrical power.

There is an additional energy savings that results from eliminating the need to cool equipment

that gets exposed to excess heat generated by conventional motors.

By design, regenerative drives use less energy than non-regenerative drives because they are much smaller, compact, and more
When a heavily-loaded elevator goes down, it applies brakes to maintain the desired speed. In a conventional system, the energy created by the braking system is lost. The regenerative drive harnesses that energy. Further, when a heavily-loaded elevator goes down, the motor spins but gravity does most of the work. The regenerative drive again harnesses that spinning energy by transforming mechanical power into electrical
When an empty or lightly loaded elevator goes up, the elevator applies brakes to maintain the

rated speed. That energy is lost in conventional elevators but the regenerative drive harnesses it. Further, when an empty or a lightly loaded elevator goes up, the motor spins but the elevator’s counterweight does most of the work. The regenerative drive harnesses that spinning energy by transforming mechanical power into electrical power. (Source: http://www.otisworldwide.com).

Figure 2. The regenerative drive system.

Over time these small amounts of harnessed and saved power on a daily basis add up to significant energy savings. Generally, a regenerative drive can reduce energy consumption between 20% and 40%. The ultimate amount of energy savings depends on several variables including: length of trips, frequency and pattern of use, and age of equipment [28]. Overall, the longer the traveled distances and the greater the number of trips result in the greater generated energy (Figure 3).

Figure 3. A comparison of energy consumptions among different elevator systems. (Source: http://www.otisworldwide.com).

Elevator Rope

The elevator rope is an essential component of traction elevators because it connects the elevator engine with the cab, sheaves, and counterweight. Conventionally, ropes are made of steel, which is strong enough to hold cabins. However, in supertall and megatall buildings, as these ropes get longer, they get extremely heavy—the rope weight increases exponentially with height. In very tall buildings, ropes may stretch for too long, adding dozens of tons of additional weight that can result in the rope breaking or snapping. In very tall buildings, almost 70% of the elevator’s weight is attributed to the cable itself, and when the rope gets too long it cannot support its own weight.

Johannes de Jong, Head of Technology at KONE, 2014, explains that the total rope’s weight for an elevator with a rated load of 2000 kilograms at a travel distance of 500 m can be about 27,000 kg. This weight needs to be accelerated and decelerated, and starting currents and energy consumption grows fast with the increase in height ([29], p. 822). De Jong further explains that when a 50–70 ton rope moves just 21 passengers, the long-term financial and ecological values of these systems are questionable. Another significant problem with very long cables is that during strong winds, they over sway and vibrate like guitar strings.” Consequently, long cables cause damage to the shaft and to themselves. For example, in the former World Trade Center Twin Towers, the elevators’ cables swung back and forth in the building, and over the decades, their movements resulted in wearing deep holes in the shaft walls. In response to these problems, elevator companies have been working on improving cable capabilities.

For example, Schindler has invented the aramid fiber rope, which is stronger and lighter than the conventional steel rope. Similarly, Otis has designed compact Gen2 lifts that replace the steel rope with a band of ultra-thin cables encapsulated in a polyurethane sheath. According to Otis, the new belt system is stronger and enjoys greater longevity than their original steel cables (Figure 4). In the same manner, Mitsubishi has manufactured a stronger, denser rope that incorporates concentric-layered steel wire. These stronger and lighter ropes require less energy to move and transport elevator cabs, leading to significant power savings.

Figure 4. Diagram of OTIS GeN2 Lift. (Source: http://www.otisworldwide.com).

However, the most significant breakthrough came recently from KONE. The “UltraRope” is comprised of a carbon-fiber core and a unique high-friction coating, making it extremely light and enabling cars to travel up to 1000 m (3280 feet). This is double the current maximum distance of 500 m (1640 feet) that cars can travel. Johannes de Jong explains “At a travel of 500 m the weight of the UltraRope is only 10% of the weight of steel ropes. This means that rope weight of a 2000-kilogram elevator traveling 500 m is only about 2500 kilograms with UltraRope, compared with 27000 kilograms with ultra-high strength steel ropes. The 90% reduction in rope mass also reduces the total moving masses by no less than 45%” ([29], p. 822–823). Further, in the case of maintenance and repair, the lighter UltraRope would require much less time for replacement than regular ropes, reducing downtime considerably. This large decrease in weight also reduces the energy needed in the acceleration and deceleration phases, resulting in about 15% energy reduction. According to Antony Wood, in summary, once the rope weight is reduced, the whole elevator system becomes more efficient.

This technological advancement is, referred to by Johannes de Jong as “the biggest change in elevators since 1853.” These carbon-fiber ropes are exciting to architects and developers as they may pave the path for a new generation of ever-taller buildings, even making Frank Lloyd Wright’s one-mile tower (Illinois Tower) proposal technologically quite feasible [30–32]. This also implies that the 828 m (2728 feet) Burj Khalifa in Dubai, in which the longest elevator travels a distance of 504 m (1654 feet), will not remain the world’s tallest building for very long. Antony Wood explains:

“This is finally a breakthrough on one of the “holy grail” limiting factors of tall buildings—that is, the height to which a single elevator could operate before the weight of the steel rope becomes unsupportable over that height—so it is not an exaggeration to say that this is revolutionary. However, it is not just the enablement of greater height that is beneficial—the greater energy and material efficiencies are equally important”.

According to KONE, the UltraRope makes sense in buildings 200 m or taller. The UltraRope will be implemented in the one-kilometer Kingdom Tower in Jeddah, Saudi Arabia, under construction (See Case Studies Section).

The TWIN System

Germany-head quartered ThyssenKrupp, jointly with Eros Elevators & Escalators, has developed a TWIN-system for high-rise buildings. The advantage of the TWIN is that two cabs run independently in a single shaft. The system keeps a safe distance between the two elevators (upper and lower cabins) that are running on top of each other [33,34]. The TWIN system basically provides savings in space as it cuts the number of shafts needed by one-third, compared to conventional elevators. Glen Pederick explains that the overall floor area savings from installing two less elevator shafts and a smaller lobby on each floor of a 31-story building is more than 830 m², which is equivalent to an area of 20 hotel rooms.

In addition to freeing useful space, the TWIN system reduces required building materials for shafts, and hence reduces costs. There is also one control machine for both elevators in the same shaft, leading to additional savings on space and energy. Through a computerized system, it also optimizes the travel of both cabins in assigning the most efficient destinations for passengers, providing efficient service that minimizes wait time and provides fewer stops and empty trips. This leads to additional energy savings. TWIN cars can travel in the shaft up to 7 m/s (23 feet/s) and travel down about 4 m/s (13 feet/s). When the TWIN system is applied, it is often mixed with non-TWIN lifts. The latter serves passengers who want to travel directly, for example, from the lowest floor to the top floor and vice versa [34].

Double Deck Elevators

Double Deck elevators are two cabs tall, where one cab serves even-numbered floors and the other serves odd-numbered floors, resulting in reducing the total number of needed elevators. Johannes de Jong explains that “a 52-story office building, which earlier would have needed 24 single deck cars in three zones, can now be designed using only two zones with a total of only 13 Double Decker elevators, reducing the required core by no less than 11 hoistways” ([28], p.1). Double Deck elevators can reduce a building’s overall energy usage by reducing the number of stops and even the total number of elevators required when used with destination dispatch controls. As skyscrapers are getting higher, reducing the number of needed elevators becomes more important because they eat up valuable interior space on every floor [35]. This is more critical in upper floors where floor size gets smaller. In general, space-saving elevator design is important because in high-rises elevators occupy more space than any other services. Above 60 floors, arrangements of Double Deck elevators and sky lobbies could be useful. Also, Double Deck elevators are most useful for shuttle applications in very tall buildings. However, the Double Deck elevators also suffer from some operational challenges. For example, for local service,

Double Deck elevators must load and unload two decks simultaneously. In addition, Double Deck elevators require stairs or escalators in the main lobby so that passengers can move between the lower and upper level lobbies to get to their destination floor [36]. Consequently, Double Deck elevators became less popular because of passengers’ dissatisfaction with having to transfer levels at the main lobby and due to non-coincident stops. In response, Klan et al. [36], de Jong and Pederick indicate that when Double Deck elevators are combined with Destination Dispatching Systems (See Section 2.2.1), these problems are mitigated substantially. Knowing each passenger’s destination enables the system to allocate passengers to elevator decks and cars strategically, allowing passengers to catch their elevator service from either the upper or the lower lobby, improving the overall performance of the service and reducing non-coincident stops [35,37].

LED Lighting

Robert Boog explains that energy efficient LED cab lights within an elevator car and their adjustment to movement detectors are one of the main contributors toward efficient power consumption in a building. LEDs (light-emitting diodes) save substantial energy for they require less power than incandescent, halogen, and fluorescent lamps. LED also emits less heat, resulting in less energy needed to cool the cab. LED lighting is currently utilized in many new buildings. Additionally, building owners are replacing traditional elevator lighting systems with LED lighting [38].

Energy-Efficient Software

New elevator control software allows for the conducting of Elevator Traffic Analysis, which inform how an elevator’s cycle affects its energy use. By observing and studying the irregular nature of elevator operation, number of floors traveled, periods of peak load, and low-load and empty trips, researchers can create energy consumption models that help to develop efficient control strategies and make recommendations for best management.

Destination Dispatching Systems

In a conventional call system, the users push up and down buttons, and elevators answer the call. This system works fine in buildings that have low “vertical ridership” and do not experience “rush hour” traffic. In heavy traffic, lots of buttons are pushed that will result in lots of elevator stops, increasing travel and wait time. Johannes de Jong explains that in a high speed elevator, say with a speed of 6 m per second, each stop may require as much as.

To address this problem, elevator designers have invented the Destination Dispatching System (DDS). It was first introduced in the 1990s following the surge of increased microprocessor capacity during the 1980s. A DDS is an optimization technique used for multi-elevator installations, which groups passengers for the same destinations into the same elevators. In real-time, the system analyzes input data from passengers and efficiently groups their destinations, resulting in decreasing the number of stops in every elevator’s trip. Upon entering a destination by using keypads or touch screens on the Destination Operation Panel (DOP), usually placed strategically in the lobby, the system quickly signals and directs each passenger to the assigned elevator to board.

Figure 5. Conventional (top) versus destination dispatching system (bottom). In conventional systems, passengers press an up-or-down call button and wait. Then the crowd board the first arriving car, jostle to select their destination and stop at every floor selected. With the latter system, passengers input their destinations prior to entering the car using keypads or touch-screens strategically placed in the lobby. The system instantly directs each passenger to a car specifically assigned to his or her requested floor. Once in the elevator car, it automatically takes the passenger to the destination floor.

DDS Benefits

James Fortune explains that the DDS provides important benefits including decreasing energy consumption, reducing waiting time, and minimizing crowding and congestion in the building lobbies and hallways. DDS’ manufacturers claim that the average traveling time can be reduced by about 30 percent. Katherine Rosman indicates that the average wait time for the elevator in a typical 16-floor building with a dispatch system is 13 s, while the average wait time for the elevator in the same building with a conventional system is 138 s [37].

In addition to saving time, the system eases pedestrian traffic flow since each passenger heads directly to a specific elevator, eliminating the need to rush to every arriving elevator, a common behavior exhibited by passengers. The system also improves accessibility, as a mobility-impaired passenger can move to his or her designated car in advance. The DDS is mostly appreciated during elevators’ “rush hours”, usually experienced in the morning and lunchtime [18]. Due to increased efficiencies in handling a large number of people, DDS reduces the required number of elevators. It also decreases wear-and-tear factor because elevators make fewer stops [39,40].

DDS Implementations

The way of using the DDS could lead to different levels of energy saving. For example, if the system has a passenger wait, say, an extra 15 s to get in an elevator that is already in transit, rather than immediately sending another elevator, it should save energy without inordinately affecting passenger service. Some systems also reduce elevator speed during low traffic times by about ten percent. That also will save energy without substantially affecting the service [39]. Another management strategy is related to switching the DDS mode from single to multiple destinations for optimizing performance in rush hours. That is, the DDS can assign a single elevator that travels to a range of destinations such as floor seven through floor nine, while assigning another elevator to destinations that range from floor ten through floor twelve, for example.

The DDS can be implemented as “full configuration” or “hybrid configuration”. In the “full configuration” scenario, destination hall panels are installed on all floors. In contrast, in the “hybrid configuration” case, the destination hall panels are installed only on the busiest floors (mainly the ground or lobby floor), while the other floors have conventional up and down call buttons. This is particularly beneficial to improve traffic flow leaving from the busiest floors, and is especially useful in buildings with heavy up peak traffic [39].

One problem with dispatching systems is that they do not differentiate a group of passengers from a single passenger. This could potentially lead to an elevator stopping to pick up more passengers than the elevator actually has capacity for, creating delays for other passengers. This situation is handled by two solutions: providing a load vane sensor on the elevator or supplying a group function button on the keypad. The load vane tells the elevator controller that there is a high load in car and doesn’t stop at other floors until the load is low enough to pick up more passengers. The group function button asks for how many passengers are going to a floor, and then the system sends the correct number of elevators to that floor.

DDS and Security

In today’s world, ensuring security in skyscrapers is exceedingly important. In this regard, the DDS can function as a secondary ring of security for buildings. For example, the DDS can help restrict access to certain floors by employing electronic devices that carry personal information. When scanned upon entering a building, the keycard integrates with the elevator dispatch system and can be set to call elevators that go directly to the floor for which the cardholder has clearance. In the same manner, if a visitor or tenant enters a location that requires a security clearance, the kiosk will prompt the user for security approval. Identifying devices come in many forms including keycards, RFID cards, infrared beams, key fobs, badges, PIN codes, key tags, and even watches. The card reading system also solve the problem of having one person press the elevator button multiple times, making the system think that there are multiple people waiting for the elevator; and hence, it may allocate an empty car to serve a single person [39].

DDS and Other Applications

Some systems use the card reader to alert the elevator to special needs. For example, a passenger who has trouble walking could be assigned to a closer elevator, or the doors could be held open longer.

If someone uses a wheelchair, fewer people could be assigned to the elevator to be sure that there is enough space. If someone is blind, a recording could speak the elevator letter or number. An elevator system could even be integrated into a building’s heating and cooling system so the temperature could be adjusted when people arrive in the morning and leave in the evening. DDS can also play a role when construction or renovation work is being performed. Facility executives could set keycards to access only the floors under construction for any long-term contractors, while locking out access to floors of the rest of the building [26].

People Flow Solutions

Similar to the DDS, People Flow Solutions are designed to smooth people flow and manage demand on elevators but mainly in extreme cases. This is illustrated in the case of the Abraj Al Bait Hotel Complex in Makkah, Saudi Arabia. The complex comprises seven towers including the tallest, the Clock Royal Tower that reaches a height of 601 m (1972 feet) with 120 floors, and a 15-story podium. It is situated in close proximity to the Masjid Al Haram, the holiest mosque in the Islamic faith. The hotel’s visitors travel to the Masjid Al Haram five times a day to conduct congregational prayers. The daunting task is to enable 75,000 people residing in the building complex to join the five daily prayers in the Masjid Al Harm within 30 min or less, and then bring them back to the hotel in a similar period of time. This required a careful study to understand “people flow” and to provide optimal solutions. The study recommended the implementation of over 180 elevators and more than 100 escalators in the hotel complex; 94 elevators and 16 escalators in the Makkah Clock Royal Tower. The elevators include large shuttles that can hold 54 passengers each and take visitors up to the 15th level, one of the sky lobbies of the tower. KONE has implemented a special group control software with artificial intelligence capabilities to learn and track passengers’ traffic patterns in order to optimize people flow solution [41].

Standby Solutions

Standby solutions power down the elevator’s equipment when it is not in use, providing substantial energy savings, especially in buildings with periods of low elevator usage. In-cab sensors and software automatically switch to a “sleep mode,” turning off lights, fans, music, and video screens when unoccupied. Energy savings from standby solutions could vary between 25% and 80% of the overall consumption of the elevator, depending on multiple variables including the employed control system, lighting type, floor displays and operating consoles in each floor and inside the elevator cabin. For example, the lighting feature would greatly factor in the saving formula. Lighting inside the elevator cabin can be switched off 40 s after the weight sensor “feels” that there is no one inside. Thus, reducing standby power, which can be relatively inexpensive in many cases, can dramatically cut total energy use.

3. Case Studies

The following case studies illustrate the implementations of state-of-the-art elevator technologies in major skyscraper projects in various parts of the world including: One World Trade Center in New York; Shanghai Tower in Shanghai; Burj Khalifa in Dubai; Kingdom Tower in Jeddah, Saudi Arabia; and the Empire State Building in New York. These projects are of national and international significance so that their sponsors, developers, and owners worked hard to implement the most advanced technologies in these buildings, including elevator technologies. Each case study starts by providing an overview of the building. Then, it explains technologies related to elevators structured according different topics.

One World Trade Center, New York, USA

Height: 541 m, 1776 feet

Floors above ground: 104; below ground: 5 Architect: Skidmore, Owings & Merrill Completion: 2014

Building Overview

The tower is the centerpiece of the 16-acre site where the twin towers stood before the 9/11 tragic event. Shaped like an obelisk with chamfered corners, One World Trade Center is the tallest building in the Americas. Designed by Skidmore, Owings, and Merrill (SOM), the tower not only establishes new architectural and safety standards, but it also employs state-of-the-art environmental and green features including sophisticated elevator systems. The advanced life-safety systems exceed that required by the New York City Building Code. The skyscraper’s structure contains nearly 50,000 tons of steel and 180 thousand cubic yards of concrete, making the building strong enough to withstand explosions, storms, and earthquakes. Among the unique safety features are extra strong fireproofing and air-filtering systems for chemical and biological particles, as well as pressurized and extra-wide emergency stairs. These features, among many others; however, made the building the most expensive skyscraper in the world. According to the Emporis database, One World Trade Center’s costs reached US $3.9 billion. About 26,000 people have been involved in constructing the 104-story skyscraper [17,41].

Elevator Systems

One World Trade Center contains a total of 73 elevators and 11 escalators. Only ten elevators travel directly from the ground floor to the roof. The five service elevators can stop at every floor, while the elevators to the observation deck speed to the top without stopping. These express elevators are the fastest in the Western Hemisphere (they travel with a speed of 10.16 m/s or 2000 feet-per-minute) and have a capacity of 4000 pounds. As such, the 394 m or1293-foot trip to the observation deck, located on the 102nd floor, takes about 40 s. Tenants working higher than the 64th story take an express shuttle to the sky lobby on the 64th floor, where they transfer to “local” lifts that take them to upper floors (Figure 6).

Figure 6. One World Trade Center. It contains a total of 73 elevators; ten travel directly from the ground floor to the top. The design employs state-of-the-art technologies in almost every aspect of elevators including: high-speed double-deck elevators that run at a speed of

10.16 m/s, computerized roller guides, air pressure differential system, destination dispatching system, and entertaining electronic displays. However, note that elevators continue to take up considerable space of the floor plans. (Source: http://www.SOM.com).

Originally, the intended speed for elevators was 9.1 m per second, but it was increased to 10.16 m/s to accommodate the number of tourists who want to visit the One World Trade Center observation deck. The design team expected more than five million visitors a year to the observation deck (14,000 people a day) and 10,000 people working daily on the office floors [42]. One World Trade Center is expected to enjoy an annual “vertical ridership” of 3.5 million people in its elevators while traveling on 198 miles of steel cable [42]. Eight 2.3-ton electric motors installed on 1 WTC’s roof power the high-speed elevators. Each elevator operates using a pulley-like system that consists of a cab and counterweights connected by a cable. There are 66 other elevators in the building, 20 of which run at 9.14 m/s. Together, One WTC’s elevators use about 454,000 kg of counterweight to ascend and descend the building’s hoistways.

Computerized Roller Guides

An elevator needs more than just robust motors and powerful current to enable it to travel long distances at high speeds. Like bullet trains, fast-moving elevators also require exceedingly smooth rails and rail joints to move swiftly. To provide a smoother ride, train-rail segments have been increased in length to reduce the number of joints over which a train must travel. For alignment precision considerations, the vertical positioning of elevator rails; however, limits their length to about 4.9 m (16 feet), which means any skyscraper will surely require a great number of rail joints. Elevators must

also account for tiny changes in the distance between guide rails that occur because of changes in temperature (contraction and expansion), wind forces, and other conditions that cause skyscrapers to sway slightly throughout the course of a day and night. These factors prevent the achievement of a perfect plane for an elevator to travel in very tall buildings [42].

In response to this problem, ThyssenKrupp has devised for the One World Trade Center computerized roller guides that mitigate the impacts of the bumps in the guiderails by exerting forces in the opposite direction. Roller guides keep an elevator’s wheels, known as rollers, in contact with the guide rails as the car ascends and descends. The rollers used at One WTC are made of polyurethane so they can absorb slight imperfections in the rail joints and are controlled by a system that pushes and pulls against the rails to prevent any misalignments or imperfections from causing shake and rattle. In other words, these active roller guide systems function as intelligent shock absorbers that respond in real-time. They simulate the function of a driver who knows that there is a large pothole on the road and swerves a bit to avoid it. For example, if the pothole was on the right-hand side of the road, the driver turns slightly to the left, and vice versa. Consequently, the express elevators not only move fast (25% faster than the express elevators that served the former World Trade Center Twin Towers), but they are also motionless when compared to the former twin towers, and passengers experience no shake or rattle [42].

Air Pressure Differential

Air pressure differential is also a concern when designing and building high-speed elevator systems that travel long distances, such as the case in supertall and megatall skyscrapers. The first issue of air pressure is related to the elevators as they pass floors with great speed, resulting in air drag in the elevator shaft. Air-pressure effect is similar to that experienced in a subway: as a train pulls into the station, it pushes a wall of air in front of it. Similarly, when a typical 4500-kg car with a 7300-kg counterweight swiftly ascends or descends into the elevator shaft, it generates enormous air displacement. With an area of high pressure above the car and low pressure below it, the hoistway doors above the car get pushed into the hallway, and the hoistway doors below the car get sucked into the hoistway. In response to the problem, ThyssenKrupp attached wedge-shaped aluminum shrouds around the top and bottom of the cabs to make them more aerodynamic when they rush up and down the shafts. The resulting aerodynamic form of the cab reduces air resistance, minimizes air displacement, decreases door rattling, and reduces wind noise—the “whooshing” sound [42].

The second issue of air-pressure concerns passengers’ comfort and safety, particularly related to the “ear-popping” effect as the elevator travels with higher speeds. This phenomenon results from a swift and drastic change in air pressure as the elevator ascends and descends rapidly, although this problem is more pronounced in the descending order. To appreciate the dynamic situation resulting from swift descent, it is important to note that elevators in super and mega tall buildings descend faster than a descending commercial airplane. That is, the landing process of an airplane may take about 30 min, and this provides a plenty of time to adjust air pressure in the airplane. In contrast, elevators in very tall buildings might have just 30 s to adjust air pressure or to de-pressurize. This gives elevator’s passengers limited time to adjust and forms the essence of the problem. In response, ThyssenKrupp’s approach at One WTC was to pressurize cars (provide extra air pressure inside the cars) to compensate for pressure drops, then slowly releasing it to keep passengers’ ears from popping. Through extensive research,

ThyssenKrupp’s engineers have found the optimal speed for fans that control air pressure inside cars while elevators descend swiftly. In all cases, however, because of the air-pressure problem, elevators continue to descend not faster than 10 m per second (33 feet/s) [42].