"Finer Points of Building Information Modeling" (May 2011, http://bit.ly/BIM0511) is a very good article. The concerns and suggestions mentioned are extremely important in the application of HVAC modeling. We are a design/build mechanical contractor, and generic models are close to useless for our purposes; we always require actual models. "Or equal" models might work for a consulting engineer, but not for us. Thank you for printing this informative article.
Hans Knape, PE
St. Louis, Mo.
"Climate Change of a Different Kind" (Weil I'm Thinking of It ..., April 2011, http://bit.ly/Weil_0411) only serves to perpetuate short-term thinking that is very dangerous to the long-term viability of the HVAC industry. A real "climate change" would be when folks quit turning to the federal tax code to incentivize customers to do what already is in their best interests to do. Everyone has to contribute to the deficit/debt-reduction effort, and that includes businesses that have come to rely on tax credits and taxpayer subsidies (a.k.a. "federal spending") to jump-start their businesses.
Protecting federal incentive programs may be great membership relations in the short term, but if the deficit and debt are not brought under control, there will be no business and no national trade associations, interest rates will skyrocket, financing will disappear, many people will go out of business—particularly small businesses—and jobs will be lost. Sure, "The idea is to help … industry create an environment in which building energy use, comfort, and safety are optimized," but isn't that the building owner's primary objective and responsibility anyway? Isn't the best incentive one based in profits and the free market, rather than taxpayer-subsidized tax credits and other subsidies?
The day of the Federal Trough is over—or at least it should be—and real "climate change" will implant itself in Washington, D.C., only when everyone understands, accepts, and insists on the greater good that results from a balanced federal budget and a shrinking national debt—equitably achieved through shared sacrifice.
The HVAC industry's responsibility is to make its customers aware of what's available to cost-effectively meet their energy and comfort needs in the safest, cleanest, and most efficient manner possible and to illustrate to those customers why it's in their best financial interests to do what they need to do. This industry has a story to tell and viable technologies to market. It shouldn't need a taxpayer-funded "assist" to get that point across, only a focused, dynamic, and informed sales force.
W. Randall Rawson
President/Chief Executive Officer
American Boiler Manufacturers Association
Interesting article ("Investigation Into the Failure of Chilled-Water-Pipe Insulation," March 2011, http://bit.ly/Lotz_0311). Humidity conditions are tropical in some mainland U.S. locations and arid/semi-arid in others. The author mentioned outdated insulation specifications being one of the problems he sees in his forensic services. The business of architecture and engineering services reaches nationwide for many firms. Dryer climates can allow the design of buildings with economies that wetter climates cannot. The transfer of successful, attractive, and economical designs into unsuitable climate zones has been a problem for decades.
Often, a plan review by a local engineering firm or consultant is a very small price to pay for risk reduction and quality control. Copying and pasting can be a time-saver that ends up being a serious problem.
Kansas City, Mo.
A discussion of flexible ductwork ("Predicting the Performance of Flexible-Duct Systems," December 2010, http://bit.ly/Allen_1210) is not complete without reviewing the sound-attenuation benefits of using flex duct. Properly designed and installed flexible duct can make the difference between a noisy, unacceptable HVAC system and a quiet system.
For commercial work, 8 to 12 ft of flex size at less than 600 fpm typically is used to connect diffusers and grilles to duct submains and branches. The flex pressure loss is minimal: 0.02 in. for 10 ft straight, even if we double the "0.1"/100 ft" sizing.
The acoustical benefits of elbows made of flex are 10 or even hundreds of times greater than those of hard radius elbows.
Grady C. Burch, PE
exp Services Inc.
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