Emergency Power Back-Up Systems (UPS) for Elevators
There was a time when people would have to endure climbing several flights of stairs just to get to the floor they need to go to. Then elevators and lifts came to be and the world was never the same again.
Today, elevators play a vital role in daily living. In fact, most governing bodies in cities already require an elevator in buildings for the convenience of the public. With the need for elevators and particularly the increase in multi-level buildings there has emerged the requirement for emergency power to ensure that elevators continue to function properly even when there is an outage so as to ensure public safety.
Traction Elevators V Hydraulic Elevators
Traction Elevators
To understand the most basic mechanism of a traction elevator, think about how a pulley functions.
The elevator cab in a traction elevator is lifted with cables, using weights to counterbalance the weight of the cab with the riders just like in a simple pulley system. The weight of the cab is usually balanced by a counterweight that equals the mass of the cab plus an additional 45% to 50% of the rated load. However, the ropes which lift the traction elevators pass over a wheel attached to an electric motor above the elevator shaft. The traction elevator uses less energy than the hydraulic elevators because the motor is only used to overcome friction – there is no lifting involved because of the counterweight system.
Hydraulic Elevator
The hydraulic elevator uses a pump system to push a cylinder of fluid on a piston, lifting the cab. The energy used to lift the elevator never is recovered on the trip going down and is completely lost. This loss of energy is due to the fact that the hydraulic elevator does not have a counterweight system.
Because of issues with rusting, the fluid now used in the pump system in modern elevators is oil as opposed to water. However, the oil may cause major safety issues if there are any leaks in the system.
One advantage of the hydraulic elevators is that it can be installed in a simpler building structure than that of the traction elevator. The cylinder used to move the elevators up and down is supported by the soil beneath the building rather than the building itself which is required by the traction elevator. But weighing both the advantages and disadvantages of these two systems, most new elevators are traction elevators and only a minority are hydraulic elevators.
What are the standby power requirements of elevators?
With more and more elevators being used by the public each day, building codes require at least 90 minutes of full load backup power for elevators in high-rise buildings to ensure the safety of passengers in the event of a utility power failure. Buildings that don’t comply with this requirement may fail a building inspection and be denied a permit to operate.
A standby generator used to be the choice for backup power in elevators. But due to new air quality control regulations and the heavy maintenance requirements of a standby generator, the use of Uninterruptible Power Supply (UPS) has become increasingly popular.
What are the factors to consider when choosing backup power for an elevator?
A few but extremely important factors need to be considered when using a UPS system as the backup power source for an elevator.
- The following is a critical point to consider. There can be no back-feed electricity from the elevator. In order to reduce the energy required to run an elevator, some elevator manufacturers promote an “energy-saving” regenerative systems to their elevator installations. However, this type of regenerative system cannot be used with a UPS because it back feeds power to the UPS rather than to the main electrical panel and causes damage to the UPS. If there is regenerative power the UPS will not function and will go into a short circuit protection mode and shut down every time the elevator regenerates power
- There will need to provide supporting documentation by the engineer /contractor that demonstrates that the UPS will support the elevator, its accessories, and exhaust fans for at least 90 minutes under maximum load conditions.
- The building code now requires a notification system be in a place that alerts the responsible parties that the elevator is on backup power when utility power is lost
- The UPS/battery backup system load capacity must not only be sized to handle the normal operating current but also the inrush/peak current of the elevator and any attached device (such as fans). Therefore, it is imperative that the UPS be sized sufficiently above the peak/inrush current to allow for the proper heat dissipation encountered with continuous use.
- Some cities, such as found in the San Francisco Bay Area, require that any battery backup systems having batteries containing 50 or more gallons of electrolyte fluids be contained in a separate fire-rated room. The fact is that most if not all UPS equipment that can support elevators for at least 90 minutes will either be at this threshold or exceed it.
- It is very common that the UPS equipment provided to back up an elevator will require a custom configuration built to the unique, specific elevator load requirement. This means that although the system will be built to ANSI/UL certification standards, there will need to be a field inspection certification
Staco Energy (www.stacoenergy.com) has been providing UPS equipment for a wide array of markets including the industrial, commercial, educational, medical and data center markets. They have expertise in building UPS to the requirements for backing up elevators. Any questions? Call us at Peninsula Technical Sales where we have deep technical knowledge on UPS and other power condition equipment: Phone: 408-650-3636; E-mail: sales@pentech.com; web site: www.pentech.com
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