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From a scientific point of view, the formulae used to calculate heat
transfer by conduction and radiation are as follows:
For conduction: q" = (T OUTSIDE - T SURFACE/ΣR)
For radiation: q" = εσ(T4 SURFACE - T4
SURROUNDINGS),
Where,
ΣR = sum or total of thermal resistances
ε = surface thermal emissivity
σ = 5.67 x 10-8 (Stefan-Boltzmann constant)
An effective conductive heat barrier (insulating against heat transfer
by conduction) reduces the heat transfer by conduction by providing
thermal resistance (R-value). This is where mass insulation such as
fiberglass wool. polystyrene, etc. come into play. The main drawback
to conductive insulation relates to thickness. The thicker the
better. A secondary but equally important drawback of mass insulation
is its degradation and consequent loss of R-value with again or with
water (vapor or liquid form) absorption.)
An effective radiant heat barrier (protecting against heat transfer
by radiation) will stop the heat from entering the building and
avoid the problem of managing heat once it has entered the building.
This is where ASTEC plays a major role: it prevents up to 85% of the
heat transfer by solar radiation and it very effectively manages
the balance (15%) of the absorbed heat by re-radiating out of the
receiving surface (i.e. roof, wall, etc.) with its high emissivity.
An effective radiant heat barrier does not depend on thickness or
even R-value; it depends on high solar reflectivity and high thermal
emissivity.
Therefore, the radiant heat barrier (i.e.: ASTEC) prevents the
problem from occurring while the conductive heat barrier attempts
to manage it once it has occurred.
Some applications require a conductive heat barrier only, some
projects require a radiant heat barrier only, and others combine
both types of heat barriers.
