Subject: Effect of Water/Ice/Moisture on Insulation Value

Open cell or fibrous materials tend to perform worse in-service when comparing water absorption, water vapor permeability and wicking than do closed-cell materials. The amount of closed cell structure compared to open cell structure may be to some degree an indicator of the performance of the material, however closed cell materials may still have high permeance so comparison of all specific physical properties is important.

Refrigerant systems, chilled water systems and HVAC systems are often insulated to conserve energy and prevent surface condensation or "sweating". When an open-cell material is used on these systems and the vapor retarder system fails, water vapor may move into the insulation, condense and eventually saturate the insulation material. This may lead to partial or complete insulation system failure.

The problem becomes more severe as the system temperatures move lower and when the system operates continuously in the cold mode. The driving forces are greater on these systems and water vapor will condense and freeze on or within the insulation.

Again, as more water vapor in absorbed, the thermal conductivity of the insulation material moves higher which leads to lower surface temperatures. The K-Value of Ice is 15.4. Water is 4.15. Compare this to the K-Value of Polyisocyanurate of .19, Extruded Polystyrene at .288 or Cellular Glass at .292. Ludwig Adams of E.I. DuPont in a report states that through their testing it was found that "4% moisture in an insulation material reduced the insulation value by 70%".

Lower surface temperatures of the pipe insulation lead to more condensation which may eventually lead to insulation system freeze-up, frost-ups and "popping off" of the insulation material due to ice formation. Considering that refrigeration systems may operate at temperatures of -70°F or colder, the problem may be severe. These problems may not only lead to insulation failures but may also lead to a complete failure of the entire insulation system.

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