The HVAC Factor: Insulation For Chilled Water Piping

The HVAC Factor: Insulation For Chilled Water Piping


Engineers have noticed that moisture failures and severe mold issues are most frequently seen in the hot humid areas of the United States. However, studies show that there are many expensive moisture/insulation failure/mold/rot/corrosion issues in New England and in the Midwest.

A recent series of tests have been conducted on various chilled water pipe insulations in-situ to determine the relative efficiency of the various products. The three tests sites were commercial operating facilities in South Texas, South Florida, and Houston, Texas. The insulations were installed by mechanical insulation contractor employees. All of the insulations were installed using procedures specified by the design engineer and using the factory furnished vapor barrier jacket.

The cellular glass insulation in the test was installed in 1980. All of the other insulations were installed after 2000. The ASJs (All Service Jackets) on the glass fiber, phenolic, and polyurethane pipe insulation were covered with mold indicating the insulation surface temperature was below the ambient dew point as a result of the water in the insulation. Only the cellular glass insulation did not absorb condensation and hence did not result in thermal degradation. Only the cellular glass pipe insulation facer was pristine even after 25 years in service.

Chilled Water  Piping Heat Gain Chart
Table 1 shown at above is the central piece of this research. The various insulations (three of the four) gained moisture from the ambient air, reducing the thermal value of the pipe insulation. The phenolic insulation gained from 400% to 1000% moisture reducing the insulation’s effectiveness. The polyurethane insulation gained 1000% and up in heat transfer. The glass fiber insulation gained from 400% to almost 700%. The cellular glass remained the same with no moisture/thermal gain.

This test data shows that heat transfer through the pipe insulation into the chilled water system has increased by 400% in the glass fiber insulation. For the polyurethane, the heat transfer has increased almost 300%. Under these circumstances the system owner will be paying more to run the chiller system. This test data was on piping at the South Texas test site.

The test data shown in this article is probably typical for buildings in the U.S. Gulf Coast and Florida where the temperature and humidity are higher than in most of the U.S. In a previous paper (ASHRAE Journal April 1989) I defined “hot humid climates” as areas listed in the ASHRAE 1% standard design criteria of 90°F dry bulb with 76°F or higher wet bulb. In the U.S., this includes the Gulf Coast, Florida, and coastal areas from Washington, DC south to Florida. Three of the four insulations tested lost thermal value over time due to condensation in the insulation.

Read the whole study at

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