Failure to Correct for Thermal Shift Increases Operating Cost and Burn Potential

Thermal shift is a fairly new concept to the industrial insulation industry, but it has the potential to be an enormous pitfall if systems aren’t designed to account for it. While traditional insulations like calcium silicate, expanded perlite, mineral wool, and microporous blankets do not experience thermal shift, recent studies have discovered that it does affect some newer insulations, like silica aerogel.

So – what is thermal shift? Thermal shift is the permanent change in an insulation material’s thermal conductivity due to prolonged exposure to high temperatures (>300°F).

This can throw a wrench into the standard design method for specifying insulation systems. When designing a system for a specific temperature range, the designer or specifier  is aiming to accomplish many goals, which includes: 1) reduce energy consumption (and with it reduce operating cost) and 2) maintain safe-to-touch insulation surface temperatures. Generally, the system designer will choose an insulation product based on personal experience with the product and specification information provided by the product manufacturer.

These manufacturer-supplied specifications often refer to ASTM standard specifications that are in place to ensure that insulation products are consistent and will perform as expected – or, in the case of thermal shift, that the surface temperatures will be at or below the maximum allowable heat loss and surface temperature targets. While traditional insulations consistently meet their ASTM standard specifications, science has recently discovered that silica aerogel does not; it experiences thermal shift.

Initially, silica aerogel insulations meet the requirements of their respective ASTM standard specifications; however, after several hours of exposure to temperatures above 300°F, the material’s thermal performance begins to decrease. Exposure to higher temperatures causes the silica aerogel to fracture, resulting in a permanent reduction in thermal performance, or thermal shift. Simply put, the insulation no longer meets its ASTM standard specification.

Fortunately, silica aerogel insulation materials do not experience an indefinite decline in thermal performance. Despite the fractured silica aerogel, there are other components in the insulation material that still maintain their insulating values. The thermal performance will degrade to a certain point before stabilizing with a new thermal conductivity rating and safe-to-touch temperature. As a result, the new temperatures are consistent enough to enable a system design that can correct for thermal shift.

Computer programs, such as NAIMA’s 3E Plus software, can use the values of the compromised silica aerogel material to determine the correct thickness for flat and pipe applications rather than the ASTM or product data sheet values.  In many cases, adding an additional layer of silica aerogel insulation or using a hybrid insulation option is enough to offset the thermal shift of the innermost layer.

For example, the chart below demonstrates the degraded thermal performance of the compromised silica aerogel material, and the necessary thickness it would take to compensate for the decrease in performance.

Notice that the chart also indicates separate insulation thicknesses for flat surfaces (ASTM C518) and round pipes (ASTM C335). The different equipment geometries require different installation methods and, as a result, have different heat transfer properties. Therefore, in addition to accounting for thermal shift, designers and specifiers also need to ensure that they are using the data that is appropriate for the specific geometries of their system.

Many variables influence your system design, but when achieving maximum performance and safe-to-touch temperatures are a high priority, it’s crucial to evaluate more data than the information gathered from laboratory settings on the manufacturers’ data sheet, it should also account for real-world conditions that can affect the efficiency and safety of the entire operation.