Experimental study on the thermal conductivity and moisture ingress in closed-cell mechanical pipe insulation systems at below ambient conditions (ASHRAE RP-1646)

Abstract

Mechanical pipe insulation systems are commonly used around chilled water pipes to reduce heat gain from the ambient. Often water vapor condensate accumulated inside the pipe insulation and it might lead to a degradation of the insulation thermal conductivity. There are not any standardize test methods for characterizing this phenomena and literature showed that the values of the thermal conductivity of pipe insulation systems are different from flat slabs due to the radial configuration and the presence of split joints. This article first introduces work on the improvement of a novel test apparatus for measuring pipe insulation thermal conductivity at below ambient temperature. Then, measured from the improved experimental devices, new experimental findings on the thermal conductivity of three closed-cell pipe insulation systems, that is, cellular glass, elastomeric rubber and PIR, are presented. The first two of these insulation materials were tested without a sheet or film vapor retarder whereas the third was tested with a sealed polyvinylidene chloride plastic film vapor retarder. Data showed that these closed-cell pipe insulation systems were resistant to the moisture ingress, and the thermal conductivity slightly increased with the moisture content. The impacts of joint sealant and vapor jacket were key factors to the system moisture ingress and should be carefully considered during system design and installation. The results in this article showed the importance of including appropriate insulation thickness safety margins due to the presence of insulation joints and the possible joint sealant in order to achieve condensation control.