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have cut many new vents in hoistways as part of our modernization projects, and it is often necessary to add a duct from the hoistway to an exterior wall or roof vent -- with a rated enclosure. It is common to find venting from the hoistway up through the machine room floor and then to the outside, a no-no under current codes. Sometimes one can reuse one or both openings for the required vent and cooling openings.
Note that the latest UBC omits the exception that permits the damper on new construction, allowing it only in existing buildings. We have not had enough experience with the new language to know how Authorities Having Jurisdiction (AHJ's) will interpret that for modernizations. In a high-rise building, of course, the AHJ can, and often does, require addition of hoistway pressurization as a condition of modernization of the elevator.
Electrically, codes now require two fused disconnects in the machine room to serve each elevator, one for three-phase power and one for 110 V single-phase for car lights and outlets. Most projects require adding or upgrading one or both. AHJ's also want some little things, such as good machine room and pit lighting, and GFI outlets in both places.
In Washington state, codes require two forms of communication with the elevator car, a telephone, preferably hands-free, for use by trapped occupants, and an intercom that communicates with the fire control station. Usually the elevator contractor handles the intercom all the way, but includes the telephone only from the car to the machine room.
Another common retrofit is adding the interconnections between fire sprinklers and elevators to shut off elevator power before sprinkler heads in the machine room or hoistway top can release water.
Warning! The methods required by Seattle differ radically from the rest of the state.
c) Architectural and Structural
Architecture associated with elevators can include fun stuff, like custom interiors and selecting hall fixtures to match period decor. Adding stone flooring or other weighty materials to an elevator that didn't have them can cause technical problems -- be careful -- but usually the environment is benign. Often, the issue is that the elevator equipment is not properly separated from the surrounding
non-elevator uses. In these cases, it is frequently simplest just to build a stud & gypboard
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rated wall around it and make a proper machine room.
Structural is usually concerned with seismic bracing of car and counterweight rails, and with tying machine beams to the building structure.
HARMONIC DISTORTION; RESONANCE
The biggest drawback of most of the current generation solid-state elevator controllers is that they feed back lots of harmonic currents into the
building's electrical system. What is a harmonic current? You buy electricity at a frequency of 60 hertz, 60 cycles per second. A harmonic is a current and voltage oscillating at frequencies that are an odd multiple of 60. The usual "bad guys" are the low ones, the third through the ninth or the fifteenth, depending upon the type of device. This means they have frequencies of 3 x 60 or 180 hertz, 5 x 60 or 300 hertz, and so on.
Why are they bad? For one thing, they waste energy. They can also cause trouble in electrical equipment, like overheating. One client had to spend a lot of money to reduce harmonics in his building because a tenant's CAD monitors were burning out from excess harmonics in the building's electrical system.
Other equipment also produces harmonics -- PC's, printers, copiers, lighting ballasts -- and they add up within the electrical distribution system. Because elevator motors are big loads, their power supplies and controllers can contribute a lot of harmonics.
In a related concern, we recently encountered a building that has capacitors in the electrical system to correct power factor, a situation becoming more common as electric utilities charge higher and higher rates for low power factor. Analysis of the system revealed that there would be strong resonance between the preferred elevator drive and the natural frequency of the building electrical system "tuned" by the inclusion of capacitors, causing real headaches, probably to the point of the building being inoperable with the elevators and the capacitors on line together.
This whole field of harmonics and resonance in building electrical systems is becoming very important, and we will treat it in more depth in a future issue of WLEetter.
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