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Elevators, Control Systems and Energy
We tend to diminish or take for granted the influence elevators have
had on the building industry over the last 150 years. Try imagining the
skylines of New York, Hong Kong, London or Dubai without the use of
elevators and instead having just 3 or 4 story buildings everywhere.
You can’t fathom it because without elevators they wouldn’t be the same
cities. Elevators today are a staple of any multi-story building,
taking on important roles beyond people moving and becoming an integral
part of life safety and yes, even energy management. What follows is an
overview of how elevators are controlled, managed and integrated and
their role in building energy management.
It all starts with the passenger interacting with the elevator. Traditionally this has meant the passenger initiating a “hall call”, pressing the up or down button to indicate which direction they want to go and then once inside the car, initiating a “car call” as to the floor they choose.
The latest passenger control strategy is called “destination control” and operates differently. Passengers instead identify the floor they need to go to in the hall rather than in the car and the control system directs the passenger to a particular cab. The destination controls provide more efficient and optimal use of the elevators especially during peak times by minimizing the number of elevator trips, increasing car availability, reducing waiting time and improving traffic flow. We’re so accustomed to “traditional controls” that it’s common for someone using destination control for the first time to become a little confused and flummoxed by the lack of floor buttons within the car.
Beyond the passenger interaction are a series of sensors, controllers, sequences of operation and real-time calculations or algorithms that balance passenger demand and car availability. Elevator sensors provide data on car positions, car moving direction, loads, door status, hall calls, car calls, pending up hall and down hall calls, number of runs per car, alarms, etc. The elevator controllers are typically Programmable Logic Controllers (PLC) that may be configured for a single car, multiple cars or sized by the number of stops and including interfaces for monitoring, voice synthesizers, etc. The controller may also have a function enabling the testing the systems without shutdown of the elevator.
Usually controllers are interconnected with a serial network such as RS-485. Because PLCs are used in variety of industries (industrial, processes, vehicles, etc.) a wide variety of communications protocols are used, most of which are not familiar names in the building system industry. One would expect something like Modbus to be used but that’s not always the case. What you find in many of the microprocessors in the PLC is the use of protocols that came out of automation in other industries. Interestingly however, ASHRAE’s Standing Standard Project Committee SSPC 135 has a working group addressing elevators and vertical transport and is developing extensions to allow the monitoring of elevator systems using the BACnet protocol. Obviously the use of BACnet by elevator control systems would facilitate their integration with other BACnet-based building systems.
Integration to other building systems
Elevators are an essential component of the life safety system for buildings and are integrated with the fire alarm system. For decades, when a fire system alarmed it would signal the elevator control system to initiate “elevator recall” to return cars to the lowest floor and hold the doors open for both occupant safety and to provide elevators for emergency responders. Historically building occupants have been instructed during a fire to use stairs, to avoid elevators during an alarm.
The 911 attacks on the World Trade Center in New York triggered a reconsidering of evacuation methods for high-rise buildings, where elevators would no longer be reserved for emergency responders but also be used for evacuation purposes. It was the investigation of the World Trade Center lead by NIST Building and Fire Research Laboratory and their recommendations that became the basis of changes in code (http://wtc.nist.gov/reports_october05.htm). By using the elevators, it was estimated that all occupants in any building of any height could be evacuated in less than one hour. Using the elevators for evacuation in high-rise buildings understandably require a different set of control procedures and different elevator characteristics. In 2009 both the International Building Code and NFPA 5000: Building Construction and Safety Code incorporated requirements for elevators to be used during fires for evacuations including designated Fire Service elevators mandated for buildings over 120 feet high.
The new codes also require a Fire Command Center to monitor in real time temperature and smoke in elevator lobbies and the machine room, as well as hall calls, location of the car in hoistway, travel direction, etc. NEMA SB 20 lays out the “Fire Service Annunciator and Interface” which covers the design, operation and arrangement of equipment intended to display data and status of building systems to provide certain control functions including that of the elevator. Finally, no longer can the integration of the fire alarm system and the elevator be accomplished using “dry contacts”. It now has to use a communication protocol, regardless if it’s an open industry standard or a proprietary communications protocol.
Most of the relevant data from the controllers is related to car activity: the car position, direction, car load and door status. From that data a management system consisting of a workstation and manufacturer’s software application can then create metrics for a group or particular car such as total number of door openings, number of runs per car or call, up and down hall calls, etc. Some of the key performance indicators that facility managers would look for may include passenger “wait times during peak time’ or “time for a car to go from bottom to the top floor”. These metrics may indicate inadequate controls, misconfiguration or even equipment malfunction.
Many elevator manufacturers can now provide remote monitoring of the equipment through Software as a Service (SaaS). The monitoring looks for malfunctions or abnormal operating parameters and either dispatches a technician or alerts the building owner. Some manufacturers provide customer dashboards accessible via a web browser and provide owners with information such as performance summaries and maintenance histories. This may work well for building owners who may not have that specialized expertise on staff.
Clients with a portfolio of buildings equipped with elevators from different manufacturers or with different ages of systems from the same manufacturer will require enterprise management. The enterprise management of elevators needs a network touching each building, interfaces into the elevator controllers or the management systems, middleware or gateways to normalize and standardize different communications protocols and data formats, development of a universal naming convention for elevator equipment and data tags, and finally, a set of applications to manage and analyze the data. The benefits of an enterprise system are (a) the capability to monitor different makes of elevators and multiple buildings, (b) a common database, (C) a common user interface for facility engineers, and (d) common metrics for evaluating elevator performance. From a service and maintenance aspect the enterprise system also allows for alarms and faults to be prioritized rather than responded to in a first-come, first-served basis.
On the initial industry push for building energy conversation and sustainability, elevators were pretty much disregarded. Elevators were ignored by LEED; even elevator manufacturers were spouting that elevators could contribute to LEED by using renewable woods and low-emitting materials in their cars rather than anything dealing with energy. Generally elevator energy consumption is about 5-10% of the building’s total consumption, modest compared to HVAC and lighting system but still significant. The energy consumption of an elevator varies depending on the number of floors, load capacity and the type of motor or drive. Assuming an eight hour day, 5 to 30 floors and loads of 2,500 to 4,000 lbs., the average energy consumption will range between 30 to 169 kWh per day. Here are a few energy management aspects of elevators:
The lesson here is to not to overlook the role of elevators in life
safety and energy management and instead to exploit their functions and
characteristics to improve building performance. For more information,
write us at email@example.com.
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