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R Values and U Values
Current techniques for controlling heat loss involve using materials and surfaces that provide a high resistance (R value) to conducted heat or cold. Some commonly used materials include fibre insulation, rigid foam sheets, injected foams, composite quilts and thermal blocks of various kinds. In order to calculate a structures U value, the rate at which it will lose heat. Thermal conductivity of materials is measured in (W/m²k), preceded by R for Resistance in (m²K/W). All the K values for the various materials and surfaces specified are added together and the U value determined by making the calculation. This method of calculating heat loss has become standard practice because virtually all materials used in the construction of ceilings, walls and floors are designed to slow the escape of conducted heat. These calculations are usually achieved by a U -Value Calculator. Apollo currently uses the BuildDesk U3.4 and BRE U -Value calculator.
The Apollo heat reflective barrier system does not rely on the U value of a structure in order to control heat escape. Instead it reflects heat as electro-magnetic energy similar in principal to a “silvered” vacuum flask. The Apollo heat reflective membrane, is a tough flexible barrier that reflects 95% of radiant heat. It is a tear resistant, non-tarnish building material that has proved its worth throughout the world.
With joins sealed using Apollo heat reflective tape, it prevents air infiltration and leakage through roofs, ceilings, walls and floors providing an excellent vapour barrier for these structures. Used in floor constructions, it can also restrict the ingress of methane and carbon dioxide from landfill and the movement of airborne radon from the sub-soil into the building.
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| Emissivity
Emissivity is a measure of the amount of heat a surface can either absorb or emit. For instance, an emissivity value of 1 .0 represents a perfect absorber of infrared energy. ... Typical building materials have an emissivity value of between 0.85 and 0.95, thus absorb the majority of the energy, resulting in high fuel bills for either heating or air conditioning.
Apollo’s Thermo-Foil®ES HRM, for example, has an emissivity of only 0.046, so 96.7% of radiant heat is reflected back. Please see our individual product documentation for specific specifications. Apollo’s membranes effectively block the passage of infrared energy through structures, where as all soft insulation absorbs hot or cold energy and emits it back into the structure when the environmental internal or external conditions change.
There is confusion in the building industry when it comes to quantify performance of other systems such as radiant barriers with the use of R-values or 'equivalent R-values' for products which have entirely different systems of inhibiting heat transfer. According to current standards, R-values are most reliably stated for bulk insulation materials.
The tests and procedures to evaluate bulk insulators are not applicable to radiant barriers. Although radiant barriers have high reflectivity (and low emissivity) over a range of electromagnetic spectra (including visible and UV light), its thermal advantages are mainly related to its emissivity in the infra-red range. Emissivity values are the appropriate metric for radiant barriers. Their effectiveness when employed to resist solar radiation is established, even though R-value do not adequately describe them.
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