One of Dyplast's efforts over the past years has been to advocate for clarity and full disclosure of technical and empirical information - - not only in Dyplast literature but also in literature generally within the public domain. Dyplast's recent Technical Bulletins, Qwik Guides, and Articles (e.g. LNG Industry Magazine) set good examples.
Thus we feel we must comment on a Technical Paper presented at the recent IIAR Conference in Orlando titled: "Hygrothermal Analyses of Ammonia Refrigeration Pipe Insulation Systems" which contains misinformation. The Paper represents that it used computer modeling to predict moisture content that would accumulate in various insulation materials on ammonia refrigeration pipe over long periods, up to 10 years. Pipe insulation scenarios with and without vapor retarders were modeled.
In general, we offer that readers should always be cautious when evaluating conclusions from computer modeling software that are contrary to empirical evidence and logical thought processes.
Dyplast's most pertinent comments include:
Point #1: The Paper states it used 1.8 lb/ft3 polyisocyanurate (PIR) as its test specimen; to our knowledge this density of PIR is very rarely, if ever, used in ammonia refrigeration pipe applications. More commonly it is 2.0 or 2.5.
Point #2: The Paper predicts that over ten years, without a vapor retarder, the moisture content of the PIR insulant would be about 90% by volume. First of all, ammonia refrigeration systems present challenging problems, and the installation guidelines for virtually ALL insulants require a vapor retarder - - and more often a vapor barrier. Yet even without a vapor retarder, the claim of 90% moisture by volume lacks credibility. 90% by volume is over 3000% by weight, meaning the 1.8 lb/ft3 insulant would weight 56 lb/ft3. To our knowledge, a moisture content at this absurd level has never been recorded, and frankly appears impossible.
Point #3: The Paper indicates a thermal conductivity of 0.187 Btu.in/hr.ft2°F at 10°C was utilized in the calculations, which does not even meet ASTM C591 Standards (≤ 0.18), and thus could not be used on an ammonia refrigeration system. The k-factors of ISO-C1/2.0 and 2.5 meet ASTM C591 requirements.
Point #4: The Paper does not explain how the computer model works or to what extent the outputs have been validated against real-life scenarios. Dyplast may address this in a future Technical Bulletin.
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