Fiberglass's Bad Rap
I was pleased to see the article about the successful use of internal duct liner to quiet the auditorium HVAC system at Houlton Jr/Sr High School ("With Polyimide-Foam Duct Liner, Air Is Felt, not Heard, in School Auditorium," Design Solutions, November 2010). Too often, designers feel the need to resort to the use of sound attenuators with high pressure drops that eat up expensive fan horsepower. The part of the article concerning air-quality concerns of traditional fiberglass liner, however, was disappointing.

For too long, the association of fiberglass with asbestos has been allowed to continue, much to the disadvantage of designers who want to provide a quiet HVAC system.

The question mark concerning the health aspects of fiberglass was removed in 2002, when the International Agency for Research on Cancer reviewed the health records of fiberglass-factory workers and concluded the workers were healthy. This opinion is shared by the National Science Foundation and the American Society of Heating, Refrigerating and Air-Conditioning Engineers, yet we have this idea the jury still is out.

Two remarks in the article stand out. First, the senior acoustic consultant for the Houlton project said, "There are certain kinds of projects—schools and hospitals, for example—where any kind of liner is prohibited, unless it is encapsulated." Hospital codes do have a high standard for "sensitive areas," such as operating rooms and recovery areas, but the standard for general and administrative areas is like that of any office building, for which there is no rule regarding the use of duct liner or board. In schools, there similarly are no limitations, although many school officials have directed their designers to avoid fibrous products because the 2002 information has yet to reach them. As a result, we have classrooms that exceed ANSI S12.60, American National Standard Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools, background-noise levels.

Also troubling are remarks by the president of the Houlton Community Arts Center Council, who said: "I was there when the demolition was started. ... The old fiberglass liner had completely collapsed down the length of the ducts. I saw all the dirt in it and how the batts were falling apart." Any duct—lined or unlined—will get dirty if filters are not changed, and any liner can get ripped apart if not installed properly. Allowing these remarks to stand without a fuller explanation might allow the reader to draw different conclusions.
Mike Bergen
Air Handling Services
Philadelphia, Pa.

Run-to-Failure Maintenance
Regarding "Running (Literally) to Failure" (Editor's Notes, September 2010): Formerly a manager of the HVAC department of a local school district, I have found the only "run-to-failure" programs that are cost-effective, balancing the financial and operational-efficiency/occupancy-comfort sides, are at fan levels of 300 cfm and below. Anything higher creates more disruption to learning and comfort than dollars saved and, thus, requires a preventive-maintenance schedule.

Even when we had larger manpower budgets, the sheer number of small fan units prohibited us from reaching all of them more frequently than once a year.
Larry Toddy, CEM
Tucson Unified School District No. 1
Tucson, Ariz
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Letters on HPAC Engineering editorial content and issues affecting the HVACR industry are welcome. Please address them to Scott Arnold, executive editor, at scott.arnold@penton.com.