At a time when energy efficiency is of utmost importance, recent developments in motor technology have changed the playing field within cooling tower HVAC systems. This new technology -- a permanent magnet (PM), laminated frame, direct drive motor -- allows for the removal of all the mechanical components such as gearboxes, drive shafts, disc couplings, and existing motors. By removing these mechanical components, you also remove their mechanical energy losses, thereby decreasing overall system energy demands. Additionally, you achieve higher motor efficiency gains with the PM technology over standard induction motor efficiencies found in old systems.
The Baldor•Reliance RPM AC Cooling Tower Direct Drive motor is designed exclusively for the cooling tower industry. The motor combines the technologies of power-dense, laminated frame rpm ac motors with high performance, permanent magnet rotordesigns. Combining this motor with a Baldor cooling tower variable frequency drive results in a system that is quiet, energy efficient, and easy to maintain.
To fully appreciate the benefits of this technology, it's important to understand cooling tower application. There are typically two types of cooling towers: cross flow towers and counter flow towers. These are defined by the direction of air passed over the wastewater.
A cooling tower is a structure that extracts waste heat from a process and distributes it to the atmosphere. The most common method is to let heated water fall through a moving airstream created by a fan located at the top of the tower. This evaporation takes a large amount of heat from the process. The heated water is distributed over a fill material, which increases the surface area the water travels on and the cycle time within the tower. The water is cooled as it descends through the fill. The cooled water is then collected in a cold water basin below the fill, from which it is pumped back through the process to absorb more heat.
A cooling tower, like the one in this photo, is a structure that extracts waste heat from a process and distributes it to the atmosphere.
Commonly, the size of a tower is identified by the diameter of the fan. Fan sizes range from 6ft to 40ft, with the most common applications in the 10ft to 26ft range. The fan speed is typically limited by industry standards for stressing, which are typically rated as a max fan tip speed of 12,000ft per min. This max tip speed generates a fan speed in the range of 147rpm to 382rpm. The most common solution for driving the fan in current cooling tower designs utilizes a standard National Electrical Manufacturers Association induction motor, driveshaft, disc couplings, and gearbox arrangement.
Cooling tower applications follow fan affinity laws, which state that horsepower (hp) varies by the cube of the fan speed. To put this in perspective, if we had an application requiring a 40hp load at full speed, but were able to reduce the speed 50 percent due to lower heat load requirements, the application need would only be 5hp, or only 12.5 percent of rated full load requirements. This reflects a great reduction of energy consumption.
The use of variable frequency drives (VFDs) on new construction has become much more commonplace in recent years due to the energy savings associated with these fan affinity laws. Additionally, most upgraded or refurbished towers are also being equipped with VFDs. These drives have the advantage of a soft mechanical start, which means there is no large starting current draw, plus they enable the fan to run at any desired speed, from zero to the maximum design speed for the application. The energy savings realized by using a VFD are well recognized and documented, and in case study evaluations can be shown to achieve 37 percent to 47 percent in energy saving as compared to applications without VFDs.
A minor point to start - I think you have the first and last pictures in the article switched.
I enjoyed the article but had to stop and think a bit (not a bad thing, by the way!). I was somewhat misled in my first reading by the early discussion of VFD and missed (a bit) the primary point of the author's presentation - the use of low speed motors (i.e. PM motors in this case) permits a greatly simplified mechanical system (i.e. no gear boxes, right angle drives, etc). Add that new simplicity (and I love simplicity!!) to a variable speed drive and you get some very compelling results.
Thanks for clarifying your point, Kevin. Engineering choices are certainly more complex than they used to be before green was a big concern. OTOH, there were always tradeoffs involved, and now another set of variables has been added to the mix. I think your point is well taken: instead of a different material for making magnets, an alternate to magnets altogether may be a better overall choice.
The point I was trying to make was a little different - that there are ways of designing motors to have similar functionality to those described without resorting to permanent magnets or using exotic materials at all. While using high energy magnets makes acheiving high efficiency "easier", that may not be the most responsible decision. In this case, there are motors from a different division of the same company that prove this point: http://www.abb.com/product/us/9AAC171953.aspx
NOTE: I have no affiliation whatsoever with any motor company - I'm just pointing out that today's engineering choices need to include "environmental responsibility" as well as the other dimensions of design.
Just as it is "easier" to get high performance from a heat pump system using freon, but environmental stewardship has forced the industry to change to other refrigerants.
Of course, another equally valid design choice would be to develop or use magnets that have similar high performance that don't use these kind of materials. I don't think this magnet technology exists yet. Neodymium magnets have appropriate uses where there is no other way to make the product small enough, but his this case I believe that using them in a large stationary motor application is probably not the best choice.
The IEEE article posted by Kevin points out that "rare earths" are a misnomer as they are in fact very common in the earths crust. In China the extraction process uses old technology. Should the Chinese withhold these elements, a free market would rapidly develop new and clean methods to supply them. In a controlled economy no incentives to cleanup the environment exist. Add the profit motive and new methods or alternative materials will rapidly be invented. China is discovering this idea and moves toward a free market while we in the US move toward a government controlled market. They will no doubt pass us economicly should these trends continue.
From the materials perspective, as well as the green perspective, the rare earth issue is an important point, Rob. What are the alternative materials for creating magnets with similar functionality?
Speaking of "tree hugging", although the efficiency benefits of variable-speed drive and simpler mechanics are clearly good, and are to be applauded - there is a darker side to the technology choices described. The high tech Neodymium magnets used in this motor are made from relatively rare materials which are nearly 100% mined in China due to the bad environmental impact from mining them. see: http://spectrum.ieee.org/tech-talk/green-tech/conservation/update-china-and-rare-earth-minerals
While these high energy magnets are sometimes the only realistic choice where small product size is paramount (such as audio earbuds) - the large mass of magnets used in these big motors are a questionable choice. Most hybrid cars are currently using similar motors, causing great shortages of these rare materials, and creating an unstable situation with reliance on China's supply of them.
As proven in some EV's - with good engineering you can still acheive high efficiency and power density, and be much more environmentally responsible by designing systems that use variable-speed induction motors (like the GM EV1 car) or variable-reluctance type motors. These motor types require more sophisticated drive electronics, but use only conventional silicon iron and copper in their motors, and no permenant magnets.
Engineers have a big challenge these days to design products that are efficient and cost effective, but also environmentally responsible as well.
This is another good example of energy savings via variable speed drives (VFDs). VFDs are showing up all over the plant. The big driver is energy savings.
I'd add another factor to the drive for energy efficiency--increasing environmental regulations. In some areas, that's another impetus for pursuing energy saving initiatives and technology.
Energy saving in all forms was big in 2011 and will be an industry focus in 2012. This includes all forms -- whether via permanent magnets and reduced parts counts, energy efficient motors, and energy harvesting. It's also interesting to note that what was previously regarded as something of a tree-hugging arena is now taken seriously well beyond the early adopters. Why? Three letters: ROI.
I would think the elimination of all of those mechanical parts mentioned would have a huge impact on reducing maintenance costs. Afterall, if cooling towers are like appliances, maintenance crews likely log hours fixing faulty gearboxes and drive shafts. I'm curious if other companies are offering similar permanent magnet technology (or other technologies) that could be leveraged for the same drive cooling tower applications with similar lower maintenance properties. That would seem like a big advantage.
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