DEGREE PROJECT, IN COMPUTER SCIENCE , FIRST LEVEL STOCKHOLM, SWEDEN 2015 The Efficiency of Double-Decked Elevators A COMPARISON BETWEEN SINGLE-DECKED AND DOUBLE-DECKED ELEVATORS IN A SKYSCRAPER ENVIRONMENT WILLIAM SCHRÖDER AND JACK SHABO KTH ROYAL INSTITUTE OF TECHNOLOGY CSC SCHOOL The Efficiency of Double-Decked Elevators A comparison between single-decked and double-decked elevators in a skyscraper environment Jack Shabo, William Schröder Degree Project in Computer Science, First Cycle - DD143X School of computer science and communications Royal Institute of Technology Supervisor: Vahid Mosavat Examinator: Örjan Ekeberg Abstract The purpose of this study was to investigate the efficiency of double-decked elevators in a skyscraper environment. This was done by simulating elevator activity using different elevator types and elevator control algorithms. The results gained from the simulation suggested that double-decked elevators always provide better performance over using regular single-decked elevators. Some control algorithms proved to have up to ten times better efficiency compared to others using double-decked elevators. Sammanfattning Syftet med denna rapport var att undersöka hur effektiva dubbeldäckade hissar är i skyskrapsmiljö. Detta gjordes med att genomföra en simulation över olika hisstyper och kontrollalgoritmer. Resultatet från simulationen indikerar att dubbeldäckade hissar alltid ger bättre prestanda jämfört med vanliga enkeldäck- ade hissar. Vissa kontrollalgoritmer visade sig vara upp till 10 gånger så effek- tivare än andra med dubbeldäckade hissar. Contents 1 Introduction 1 2 Terminology 2 3 Background 3 3.1 Environments, Elevators and Efficiency . 3 3.1.1 Low to High Rise Buildings . 3 3.1.2 Skyscrapers . 3 3.1.3 Measuring Elevator Efficiency . 5 3.1.4 Passenger Traffic and Time . 6 3.2 Classical Control Algorithms . 6 3.2.1 Single Automatic Control . 6 3.2.2 Collective Control . 7 3.2.3 Zone Control . 7 3.3 Advanced Control Algorithms . 7 3.3.1 Search Control . 8 3.3.2 Destination Dispatch . 8 3.3.3 Double-decked Control . 9 4 Problem Definition 11 4.1 Problem Statement . 11 4.2 Purpose . 11 5 Method 12 5.1 Traffic Generator . 12 5.1.1 Interfloor Traffic . 13 5.1.2 Up-peak Traffic . 13 5.1.3 Down-peak Traffic . 13 5.1.4 Lunch time Traffic . 13 5.2 Elevator Implementations . 14 5.3 Simulating the Control Algorithms . 14 5.3.1 Local Elevators . 14 5.3.2 Shuttle Elevators . 15 5.4 System Specifications . 15 5.5 Simplifications . 16 5.6 Assumptions . 16 5.7 Validity through Testing . 17 6 Results 18 6.1 Single Automatic . 18 6.2 Single Automatic Zone . 19 6.3 Single Automatic Search . 20 6.4 Selective Collective . 21 6.5 Selective Collective Zone . 22 6.6 Selective Collective Search . 23 6.7 Diagrams . 24 7 Discussion 27 7.1 Interpretations . 27 7.2 Error Sources . 29 7.3 Applications . 30 8 Conclusion 31 References 32 1 Introduction Effective elevator control is far more sophisticated than serving one passenger at a time. Instead, programmers face the challenge of assigning multiple pas- sengers to elevators within certain time constraints. In fact, when assigning n passengers to elevators in the general case, there are n! potential pick-up or- ders. Furthermore, if all possible pick-up orders are allowed and considered by a scheduler, the corresponding problem of planning an optimal route has proven to be NP hard[1]. In order to cope with this problem, there are multiple heuristic and ap- proximate elevator control strategies each performing differently according to a variety of parameters. Using the most efficient strategies, or more precisely con- trol algorithms, is vital to impressive buildings. One such example would be the tallest building in the world: Burj Khalifa [2] which has 57 elevators, 167 floors and hundreds of thousands of visitors per year[3]. However, not only the control algorithms constitute a varying factor in the problem of time optimization; an elevator consisting of several elevator cars stacked upon each other serve as an alternative to the single-decked version. The skyscraper Burj Khalifa [2], as well as other buildings of the same scale, use such varying elevators. Thus with respect to the plethora of control algorithms the issue is raised of whether or not more complex elevator types provide better time efficiency for buildings of high altitude. 1 2 Terminology Pick-up The state in which a passenger embarks on an elevator. Drop-off The state in which a passenger disembarks from an elevator. Control algorithm An algorithm allocating elevators in response to passen- ger calls, including the order in which pick-up and drop-off occur. Elevator car A metallic box in which passengers ride the elevator. An eleva- tor consist of one or more of these boxes. Single-decked An elevator consisting of one elevator car. Double-decked An elevator consisting of two elevator cars stacked upon each other. Sky lobby A secondary lobby higher up in a building. Shuttle elevator An elevator which only travel between lobbies, including sky lobbies. Local elevator An elevator that travel between a certain amount of floors, including only one lobby/sky lobby. Waiting time The time a passenger has to wait before embarking on an elevator. Travel time The time a passenger remains within an elevator before disem- barking. 2 3 Background This section will go over the necessary background information needed to under- stand the remaining parts of the report. First, there will be an introduction of different buildings and the elevator systems used in these. Thereafter, different control algorithms for different types of buildings will be introduced. Finally, the control algorithms used in double-decked elevators will be presented. 3.1 Environments, Elevators and Efficiency Different buildings require different types of elevator systems. A regular suburb residential building of a few floors (typically no more than 20) tend to be served by one or in some cases two elevators. At the same time there are buildings such as Burj Khalifa which have over 50 operating elevators. Obviously, these vastly different buildings require some sort of categorization in consideration to the elevator systems involved. 3.1.1 Low to High Rise Buildings To begin with, consider regular buildings having less than 20 floors, a category which represents the majority of buildings. The buildings of this category tends to be referred to as low-, medium and high rise buildings depending on the amount of floors involved. Generally, they have a need for an elevator but tends not to have more than one or two shafts. Due to the simplicity of these systems they do not present a particularly challenging problem to operate [4]. 3.1.2 Skyscrapers In contrast, when buildings reach extreme heights problems with time con- straints arise due to the long travel distance of the elevators. This category of buildings, named more commonly as very tall buildings or skyscrapers [4], calls for a more efficient solution. While more shafts and efficient control algorithms could improve the situation, only a certain amount of space in the buildings can be assigned to elevator shafts. For this reason, there are solutions that improve the efficiency of each shaft by allowing multiple elevators to operate in each shaft. The obvious problem with this would be that the elevators are in the way of each other. Today there are two different solutions to prevent this from occurring. To begin with, there are double-decked elevators which solves the issue by simply attaching two elevator cars together so that two floors, one directly above the other, can be served simultaneously [6], see Image 3.1. This strategy can clearly increase performance since one shaft can serve two calls at the same time. Consider for example two different groups of people making calls on two adjacent lower floors. A double-decked elevator would allow both these groups to embark on the two different elevator cars before traveling towards their destination floors. While it is true that passengers of one of the elevator cars might have to wait for passengers boarding the other elevator car, such 3 delay is negligible compared to the time it takes for a regular elevator to ascend with one group of passengers and descend back again to pick up the next. Image 3.1: Double-decked elevators [7] Although double-decked elevators can as much as double the elevator per- formance, passengers traveling to high numbered floors are still likely to have to stop on a number of intermediate floors to let other passengers on and off. To truly deal with this problem, having sky lobbies allow passengers to travel with shuttle elevators directly to special floors, the sky lobbies, from which pas- sengers then switch elevator and use a local elevator to get to their respective final destination floor [10]. As an example, Image 3.2 shows a schematic figure of a sky lobby implementation. In this, each sky lobby serve all floors from the sky lobby floor up to the floor below the next sky lobby using local elevators. Consequently, the local elevators for the different sky lobbies can share shafts since each sky lobby as well as the main lobby only serve a separate range of floors. Each such interval can be treated as a separate sub-building which can be operated as its own high-rise building. Therefore it can be concluded that as the number of floors grows the amount of local elevator shafts does not need to be increased, although extra shafts for shuttle elevators provides extra service to the different sky lobbies. 4 Image 3.2: A schematic overview of the sky lobbies in the old World Trade Center buildings [9] Moreover, there is nothing that prevents double-decked elevators from being used in conjunction with sky lobbies.