CAN Newsletter magazine
Hydraulic drive technology in elevator construction comes into play when large forces or architecturally sophisticated solutions are required. Hydraulics now takes a step forward - elevator technology is becoming smart and networked.
Tony Aschwanden, Head of Product and Application - Elevator at Bucher Hydraulics in Neuheim, Switzerland, explained: "Freight elevators with high loads are the domain of hydraulic elevators. Equipped with one or more cylinders, they can lift loads of more than 40 tons over 25 meters and higher". A clear benefit of hydraulics: the forces can be transferred directly via the building foundation, whereas in the case of traction elevators they usually make their way into the building structure via the shaft head.
But these powerhouses can also look elegant: another area of application is architectural elevators featuring large areas of glass, but with no sign of suspension ropes, which would have a negative visual impact and be distracting. A central cylinder, often a telescopic design below the car, slim and shining, appears delicate and aesthetic. Modern designs even work without any lateral car guidance at all, for example with round glass cars. This allows elevator doors to be installed in any direction. The hydraulics themselves also keep a low profile: the power unit and other equipment fit in a wall cabinet or in the shaft.
There are about five million elevators in the EU. They use about 18 terawatt hours of electricity per year, about 0,7 percent of the total electricity demand. That's why within the foreseeable future, elevators are to become subject to the EU Ecodesign Directive. A pilot study has already been completed under the leadership of the Fraunhofer Institute for Systems and Innovation Research (ISI). In terms of energy efficiency, however, hydraulic elevators have already been heading in the right direction for quite a long time. In fact, looking at their whole service life, they are usually superior to traction elevators, according to a study by the Spanish technology center Instituto Tecnológico de Aragón (Itainnova). The Swiss Federal Office of Energy, in its study "Electricity Consumption and Savings Potentials in Elevators," also attests that typical hydraulic elevators in apartment buildings have lower maintenance costs than traction elevators.
A major factor in saving energy: the use of frequency inverters. Without a frequency inverter the pump's drive motor runs at full speed right from the start. The travel curve - i.e. acceleration, full speed, and deceleration – is controlled by a valve. The surplus oil is fed back to the tank in an energy wasteful manner, causing it to heat up unnecessarily. As a result, an oil cooler may even become necessary.
Frequency inverters, on the other hand, control the motor from as low as zero speed. As a result, only as much oil is pumped as is needed for the ideal travel curves. "With 30 to 40 percent energy savings, the extra cost of the frequency inverter pays for itself, especially in frequently used elevators," reasoned Aschwanden.
But there's more. One example: the use of supercapacitors, or supercaps for short. They can be charged and discharged much faster than rechargeable batteries. In addition, they withstand far more charging cycles. Among other applications, they became known for storing electrical energy in Kers, - the Kinetic Energy Recovery System - used in Formula 1 racing cars, and for regenerative braking in buses and trains.
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