CASE STUDY DETAILS:
Whenever an elevator up
grade is considered, it is usually done out of need to improve reliability and service. While proper elevator maintenance should address this issue, at times, building owners and managers believe that it’s in their best interest to upgrade the elevating device.
There are varying degrees of upgrades that can be performed, from simple retrofit of elevator cabs, door operators, door locks, steppers, valves, and fixtures to a full modernization of controllers and drive systems. In this case study, the upgrade was motivated by a lease renewal and slight tenant discomfort with frequent elevator problems
Although a cab and fixture upgrade was performed two years earlier, the improved aesthetics did little to improve the reliability and perception of the elevator equipment. The building owner was motivated to fully upgrade the elevator in order to secure the conditional lease agreement, which required an elevator control upgrade.
Elevator companies provide standard modernization packages designed to deliver a reasonable upgrade in the most cost effective way. While no person knowledgeable about cars or computers would buy a standard off the shelf package and would rather customize them, most property managers and owners buy standard packages designed by elevator companies if they are cost effective. After a barrage of proposals from five different elevator contractors and questions about the relevancy of each component and a huge pricing discrepancy between the five contractors, the owner opted for the services of an elevator consultant.
There were two major issues facing the building owner here: the first was obviously the pricing difference between the various elevator contractors and the second was making sense out of what all these components meant and whether they were needed or not.
SORTING THROUGH UPGRADE OPTIONS
After inspecting the elevator system and reviewing in detail what was needed, the consultant suggested a cost competitive alternative with better equipment. In essence, one contractor proposed upgrading the elevator components from relay logic to microprocessor based. Choosing this contractor would have been, in the consultant’s opinion, money wasted. Two other contractors provided a reasonable solution and package, but not a great one for a class B building.
While these contractors opted for maintaining the DC motor, the consultant proposed replacing it with an AC motor. Although no one quoted a closed loop variable voltage variable frequency drive (VVVF), the cost/benefit of a closed loop system outweighs the slight additional cost. Nor was a load weighing device included initially, but was added at the consultant’s request.
A digital position encoder is essential for accuracy and only one contractor proposed such a device, while the non-proprietary electronic controller was not proposed by any of the contractors. Two contractors recommended an integrated bidding based dispatcher, while others were satisfied with a simple and independent dispatching system.
Closed loop door operators were not proposed by any of the bidders until they were requested. Whisperflex™ compensating chain was also suggested because of the condition of the existing chain. Rope gripper, additional noise filtering and new car fixtures were added as well. Although, the fixtures were modernized few years earlier, upgrade proposals did not take into consideration a future modernization.
The following is a list of items which were recommended by the consultant and ensuing benefits to the client:
RECOMMENDED EQUIPMENT
Closed loop VVVF
An open loop system does not take advantage of the readily available technology and systems which tell the elevator controls what the elevator motor and cab are doing. Therefore, the elevator drive would design an acceleration and speed profile pattern but does not know exactly what the motor or the cab is doing. Hence the drive cannot adjust for all the variables like temperatures, slip, over voltage and wear. What does that mean? Closed loop systems mean more accurate stopping and ride comfort all the time. Also, the cost benefit of such system is very attractive.
Noise filtering
VVVF drive and motors generate noise back into the building. The generators are cleaner than the VVVF drives because they are regenerating power through the AC end of the system. Therefore the generator mimics the power created by the utility company. However, drives do not have this ability and create electrical noise or harmonics. If the three phase power is not part of the building feed and is completely independent, then this may not be of great concern and the standard filtering of the power may be sufficient. However, if the building is reusing the power and it is equipped with sensitive electronic systems like computer servers (in this case) or medical devices, then filtering is critical.
Dispatcher
Dispatching strategies are important to the elevator controls because the assignment of elevator calls and reducing wait times are functions of the dispatcher. There are various dispatching strategies utilized by the elevator dispatcher like sophisticated fuzzy logic systems and neural logic. The more elevators you have in a bank the more relevant dispatching becomes.
Closed loop door operator
The door operator is critical to the elevator door system and performance time. Closed loop operators are now very common and reliable. Although not all are created equal, they are still much better than the open loop system because the closed loop operator can control the closing pressure to compensate for building stacking effect and dirt in the sill.
Compensation upgrade
Although the chain compensation is working properly and upgrading to another type of compensation does not improve the performance of the elevator, the existing chain compensation was worn and noisy. Since chain compensation is never replaced by elevator contractors due to noise alone, upgrading makes sense. Newer compensation chains are coated in a rubber jacket which eliminates the noise completely.
Load weighing
Load weighing technology is old but very important. Load weighing provides your elevators with the ability to pre-torque the motor so that passengers do not feel the rollback (especially on gearless elevators). It also gives the controller information about the available capacity in the elevator. Therefore, a full elevator does not stop on every floor so that waiting passengers can say “that’s OK; we’ll take the next car”. This delay and inconvenience are not needed or appreciated. They also reduce system efficiency and prolong tenant overall destination time.
Upgrading the elevator system can include many considerations that the building owner or manager should be aware of. Asking questions about the system you are buying can be fun and informative. The key is not to rush into the upgrade because, once you buy a system, you want to be able to live with it for at least 25 years without the need to upgrade unless of course you want to.
Ray Eleid, P.Eng. is Director of Strategic Development with Solucore Inc.
Published in Published in Canadian Property Management Magazine Apr 2003
