Look beyond ‘R values’ when measuring thermal protection, urges TP3 Global
A supplier of thermal pallet cover solutions, TP3 Global, has advised specifiers in the pharmaceutical supply chain to ‘look beyond R values’ when specifying thermal protection solutions.
“R value is the common measure of performance assessment being requested by customers deploying thermal protection solutions, however it should be considered as only part of the story,” said Kevin Valentine, Chief Technical Officer at TP3 Global. “The R value is a measure of a material’s ability to resist heat transfer by conduction, with the higher the number equating to more protection. There are a number of risks with just using R values, including problems of confusing imperial units with International Standard of Units (SI) and also with the different test methods being used.”
As there has been a continued increase in the availability of temperature-controlled distribution lanes within the global pharmaceutical supply chain there has been a corresponding rise in the amount of thermal protection solutions. One such solution, thermal covers, are considered to be a cost-effective option to many, however, Valentine stated that as these are designed to protect against three sources of heat exchange, radiation, convection and conduction, R values, which only measure the latter, should be backed up with other criteria.
“R values do not take into consideration the importance of both convection and radiation, which specifically relates to potential breaks within controlled distribution lanes,” he emphasized. “Exposure to direct sunlight is a major source of radiated heat transfer and is a threat within any break in a controlled lane. It is not uncommon for the temperature in direct sunlight to be 15–20oC hotter than the ambient temperature within the shade. A break in a controlled lane on a warm summer’s day could see a pallet exposed to direct sunlight temperatures of 50–60oC, even in temperate regions. A thermal cover’s ability to reflect radiated heat is of major importance, as is its potential to emit heat, known as the emissivity value.”
Furthermore, testing conditions can influence ultimate R values. “A material tested with a 25mm air gap between its surface layers and the testing device will show a higher R value in comparison to a material with no air gaps,” Valentine continued. “Thermal conductivity of materials can also change at different temperatures. The R value of a material can differ by as much as 10% when tested at hot (above 25oC) or cold (below zero) temperatures. It is very important for specifiers to understand which method of test has been used.
“I would urge specifiers to look beyond R values during performance assessment. It is important to fully understand the limits of R values, the performance data being used and its origins, as part of the performance assessment and implementation of thermal protection products. This will help reduce risk and improve quality, whilst also reducing costs within the distribution of temperature sensitive pharmaceutical products,” he concluded.