Understanding the Challenges in Vertical Transportation
The continuous pattern of rural-to-urban migration suggests that the global population’s urban residency is anticipated to exceed 50% at an increasingly rapid rate. Consequently, urbanization has led to a surge in the construction of multi-story commercial and residential buildings. The transportation needs of individuals within these vertical habitats cannot be adequately met by the mere provision of stairs, and elevators have become an indispensable component of low and high-rise buildings.
Elevators can consume 2% to 10% of a building’s total energy demand, with energy consumption increasing to 40% during peak hours of utilization. This energy usage is not only during operation, but also in standby mode. Additionally, the lighting and ventilation systems of an elevator system consume a considerable amount of energy.
The industry faces two key challenges:
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Vertical Traffic Bottleneck: Large-scale buildings are particularly susceptible to vertical traffic bottlenecks during peak hours, due to the restricted physical capacity of the elevators combined with the temporary traffic increase. This contributes to long waits, unhappiness, and irritation among passengers.
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High Energy Consumption: Instabilities in speed, deviations from optimum engine power and speed, and forced braking all contribute to increased energy losses in the lift system. Additionally, passenger traffic is a determining factor in energy usage, with elevators in commercial buildings consuming considerably higher energy than those in residential buildings.
Methodology Used in the Study to Optimize Elevator Energy Consumption
To address these challenges, this case study action research explores the potential for energy savings in the elevator system of a contemporary high-rise office building, while maintaining industry-standard service levels. The methodology involved the following steps:
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Optimizing Elevator System Performance: The researchers employed traffic simulation to determine the optimal number of elevators, their capacity, and speeds necessary to maintain industry-standard service levels for the given population.
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Enhancing Elevator Management System: The researchers introduced a suitable elevator management system using traffic simulation to improve the performance of the elevator system.
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Evaluating Energy Consumption: The researchers conducted an energy simulation in conjunction with traffic simulation to assess the energy consumption of the elevator system.
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Implementing Green Measures: The researchers implemented green measures, primarily through the introduction of a regenerative system, to effectively reduce the electrical energy consumption of the elevator system.
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Assessing Energy Performance: The energy simulation was repeated to evaluate the energy performance of the elevator system and determine the annual energy savings resulting from the integration of green elements.
Details of the Case Study Building
The proposed office space development project is located in the central business district of Colombo, Sri Lanka. The building consists of 32 floors and 4 basements, with a total height of 157.1 m and around 43,500 m2 of floor space. The objective of the development is to provide rentable office space to business entities.
The building has two types of typical office floors, with net internal areas of 819 m2 and 791 m2, respectively. The population of the building was estimated based on the net rentable area of each floor, using the CIBSE and ISO standards for office occupancy.
Data Collection
The data required for the investigation of the elevator performance was gathered from the developer and the building design team. This included information such as:
- Building design and layout
- Number of floors and their intended usage
- Population of the building based on occupancy standards
- Passenger arrival patterns and traffic flow
- Elevator specifications, including number, capacity, and speed
Optimizing Elevator System Performance
The initial architectural design proposed six passenger elevators and two service elevators for the building. However, the traffic simulation results showed that the number of elevators in the system was insufficient, and the performance of the system was far below the industry standards.
To improve the performance, the design team took several steps:
- Increasing the Number of Elevators: The number of passenger elevators in the middle core was increased from 6 to 8.
- Introducing Zoning: The building was divided into zones, with some elevators serving specific floor ranges.
- Adjusting Elevator Speeds: The speeds of the elevators were increased from 3 m/s to 4 m/s.
Even after these changes, the performance did not reach a satisfactory level in terms of average waiting time (AWT), average time to destination (ATTD), and five-minute handling capacity (HC5).
Enhancing Elevator Management System
To further improve the performance of the elevator system, the design team introduced a destination management system (DMS) and compared it to the conventional Quardlex Operation system.
The implementation of DMS significantly enhanced the efficiency of the elevator system, reducing the need for elevators by 20% to 25%. This was achieved by optimizing elevator travel, reducing unnecessary trips and idle times.
The results showed that DMS improved the HC5 from 7.9% to 12%, and the ATTD from 129 s to 117 s, compared to the conventional system.
Implementing Green Measures
To optimize the energy consumption of the elevator system, the design team implemented several strategies:
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Efficient Mechanical Components: The team selected gearless AC motors with permanent-magnet synchronous motors (PMSM) and variable-voltage variable-frequency (VVVF) inverters, which can save up to 30% in energy consumption compared to conventional systems.
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Lightweight Materials: The team specified lightweight cabin materials, ropes, and finishing materials to minimize the overall elevator load and reduce energy consumption.
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Standby Mode: The team implemented measures to either shut down or place the electronic devices in standby mode to minimize energy consumption during idle periods.
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Regenerative System: The most significant energy-saving measure was the integration of a regenerative system into the elevator system. This allows the elevator motor to act as a generator during braking, capturing and reusing the energy that would otherwise be dissipated as heat.
Assessing Energy Performance
The energy simulation, integrated with the traffic simulation, was used to calculate the overall energy consumption and regeneration of the elevator system. The results showed that the incorporation of the regenerative system, along with the implementation of efficient mechanical components and the DMS, led to a 36% reduction in the energy consumption of the main passenger elevator group.
Additionally, the two-car group and the service elevator group achieved energy savings of 39% and 40%, respectively, through the integration of the regenerative system.
Conclusion
The findings of this case study demonstrate the significant potential for energy savings in elevator systems while maintaining industry-standard service levels. By implementing a holistic approach that includes optimizing the elevator system, enhancing the management system, and integrating green measures, the researchers were able to achieve a 36% reduction in the energy consumption of the elevator system.
The strategies employed, such as the use of efficient mechanical components, lightweight materials, standby modes, and the integration of a regenerative system, not only contribute to energy savings but also align with the broader goals of sustainable building design. These findings provide valuable insights for building designers, owners, and policymakers in establishing benchmarks for reducing energy consumption in elevator systems.
The success of this case study highlights the importance of balancing energy efficiency with service quality, and the potential for elevator systems to play a crucial role in the transition towards more sustainable and energy-efficient commercial buildings.
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