www . refrigerationandaircon . co . za RACA Journal I July 2023 43
Support
• Granular insulation is composed of small nodules that contain voids or hollow spaces . It is not considered to be true cellular material since gas can be transferred between the individual spaces .
• Flexible / reflective foils are also known as radiant barriers . These are laminated foils or ‘ bubble ’ foils .
Porosity If the material is to be used in – or potentially will be in contact with – water , one must consider the porosity of the materials . Closed pore materials , such as polystyrene will be virtually impervious to water , while open pore materials will absorb water .
Insulation is produced in a variety of forms suitable for specific functions and applications . The combinations and type of insulation determines the proper method of insulation . The forms most widely used are :
• Rigid board comes in blocks , sheets or pre-formed shapes . Fibrous , cellular and granular insulations are produced in these forms .
• Blankets : fibrous insulations are produced in this form .
• Cement ( insulating and finishing ) can be produced from fibrous and granular insulation . They may be of the hydraulic air-setting or air-drying types .
• Foam materials , preformed pipe insulation , sheets .
TEMPERATURE What are the actual service temperatures ? There are a number of dimensions to temperature considerations :
• At very low temperatures insulation material becomes brittle and may crumble .
• At high temperatures the material may char , will soften , sinter , and finally melt .
• In some cases chemical reactions may occur , creating a fire hazard if exothermic .
• If the material is to be used under intermittent conditions , it must be able to withstand the thermal cycling – in terms of thermal expansion and elasticity .
How do you select the correct product for your application ? As outlined before , one must look at this as holistically as possible .
THERMAL CONSIDERATIONS When comparing the thermal performance of insulation materials , a few factors must be considered :
• Thermal conductivity changes as temperature changes . Thus , when comparing thermal results , one must take note of the temperature at which the product was tested .
• Thermal conductivity is different for different densities of product . Thus , the thermal test results must be for that particular product and specific product density .
Thermal Resistance ( R-value ) is the thickness of the product ( m ) divided by the thermal conductivity ( k-value ). The higher the R-value , the better the thermal performance of the product . Once you have decided on the thermal performance required , you can calculate the needed R-value . The R-value of insulation products can be compared directly ( at the same temperature ). Economics and other factors can then be used in the decisionmaking process .
One can achieve the correct R-value by thickness or density of product . A 10 % increase in thickness gives a 10 % increase in thermal resistance . Sometimes there are limitations on thickness due to space considerations .
Mechanical strength Is the material going to be exposed to possible mechanical damage in application or in use ? Must the product be rigid or flexible ? Is a high compressive strength needed ? ACRA ’ s practical area .
© Eamonn Ryan | RACA Journal
Fire Insulation materials must have the fire properties that comply with the fire regulations applicable to the area where they are being installed . The following properties must be considered : fire resistance ( where applicable ); flame spread ; smoke generated ; generation of toxic fumes ; and the potential dripping hazard .
Chemical considerations In general , materials that are acidic ( pH less than 7 ) should not be used in alkaline environments , and materials that are basic ( alkaline , pH above 7 ) should not come into contact with acidic materials or metals such as aluminium . Solvent resistance must also be considered .
Hygroscope If water vapour pressure inside the insulation is lower than that of the surrounding air , the material will attract water vapour ,
www . refrigerationandaircon . co . za RACA Journal I July 2023 43