Thermal Insulation

 

INSULATION TESTING

 

Insulation Testing

Most countries (including the United States) have laws requiring that commercially available insulation materials be tested and rated by an accepted methodology. In the United States these standards are set by the American Society for Testing and Materials (ASTM).  The "correct" test for an insulation depends on the type of insulation material and the application. To provide useful and meaningful test results, the ASTM describes many different test "standards", each designed to scientifically duplicate heat-flow characteristics encountered in a particular environment.  Commonly specification designations include C177, C201, C236, C335, C518, C745, C976, C1114 and others. Within each of these specifications exists the possibility to further refine certain parameters to more closely match the requirements of individual applications. Each test (if properly conducted) gives accurate results for the conditions it is designed to mimic.  However, it should be recognized that the thermal performance of a single insulation product will vary dramatically in different tests. Therefore,  no single test method will properly describe the performance of an insulation material under all conditions. It is up to the engineer and/or their insulation consultant to identify the appropriate test methods for any given application.

For those interested in obtaining greater detail on individual test specifications, they can be ordered directly from ASTM at http//www.astm.org.

Bogus Tests or Advertising Hype?

For the design engineer, trying to understand insulation testing can be both time consuming and frustrating. Even with sufficient technical expertise, there is often no assurance that the insulation purchased will really match the specifications published by the manufacturer. Depending of the type of insulation, variations in the production process alone can change the actual value for a given sample by 30% or more from the publish data. To make matters worse, many of the insulation manufacturers do not possess the equipment and personnel needed to maintain a continuous quality assurance program to catch such production deviations.

Further complicating the issue is the growing frequency with which manufacturers intentionally use improper (although otherwise legitimate) test methods to gain an artificially high performance rating (i.e. "R" value). While such tactics greatly overrate the performance of the product in its intended (and most common) applications, the practice remains entirely legal since the manufacturer can provide calibrated test data to document their claims. 

Perhaps the clearest example of this is the addition of an aluminum (or similar) "radiant heat barrier" foil to the surface of an insulation material. As explained in the section on radiant heat (see Heat Movement - Conduction, Convection and Radiation), this increasingly common and widely misunderstood practice permits the manufacturer to legitimately "document" virtually any "R" value desired by simply varying the ratio of radiant to conductive heat used in the test. While the test data is real enough, the problem occurs when the product is advertised for use in applications which bear little resemblance to the test conditions.  They fail to point out that in most applications, where the foil facing is pressed against another material, no benefit is gained by using such foils.

Poor Enforcement

Responsibility for the enforcement of the insulation standard test laws lies with the U.S. Federal Trade Commission.  To date, there has never been a federal action taken by the FTC against an insulation manufacturer for providing misleading "R" values. As a result, many don't bother to test their material at all preferring instead to simply make a "guesstimate" which, as you might imagine, may be more than a little optimistic. 

Politically inclined individuals might want to add their voice to those of us who would like to see better enforcement by contacting the Federal Trade Commission directly at  http://www.ftc.gov/.

Glacier Bay's Own Insulation Testing Program

As engineers working with thermal insulations as well as heating and cooling system designs, it is imperative that the Glacier Bay engineering staff know the true effective thermal conductivity of a wide range of insulation products.  To gain this information Glacier Bay maintains a database of insulations tested "in house" on our own ASTM C-518 test equipment.  For the convenience of our website visitors, we publish a portion of this database in Insulation Test Results Table.

Engineers using the information contained in this table are reminded that the ASTM C-518 test method and the temperatures used in this testing are applicable for general use in refrigerating, freezing and air conditioning applications in which conduction is the primary means of heat movement.  This may, or may not be indicative of the conditions in your application.

 

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