How Low-E Insulation Works

 

Heat Transfer

Convection is a warm air current, you can see convective heat from a hairdryer or from the surface of a hot road.

Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance. For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids-but it can happen in fluids.
 

Radiant heat is electromagnetic waves which can pass through anything.

Types of heat transfer


 

R/U/E Values

Types of heat transfer

U-values are a measure of a materials ability to conduct heat. The thermal performance of windows and doors is commonly stated in U-values. U-value is equal to 1/R (R-value).

R-values are the inverse of U-values: the resistance to heat flow.Low-E insulation products do have an R-value but the reason they work so well is in the name.

E-values or the ‘E’ in Low-E stands for Emissivity. Emissivity is the ability of a surface to emit or transfer radiant energy through itself - everything has an E-value.


 

Why use Aluminium?

Aluminium works better than other materials because it reflects 97% of radiant heat that comes in contact with it. Most fibre glass materials will only reflect 10% to 15% of radiant heat. Aluminium has a zero rating for air tightness, this is very important in any building as heat loss and cold bridging is huge.

Everything has an emissivity value, your clothes, a table. For example cast iron has an Emissivity of .85 This mean that 85% of heat that comes in contact with its surface to pass through it, which is why we make radiators from cast iron.

Aluminium has a natural low emissivity value of .03. This means that aluminium will only allow 3% of radiant heat that comes in contact with its surface to pass through it, the rest will be reflected back to the source. You’ve all heard about Low-E glass in windows. They work by the same principle, they have a Low Emissivity Coating on them which reflects radiant heat back to the source.

Here are the Emissivity values of some typical building materials:

MaterialEmissivity
Asphalt .90-.98
Brick
.93
Concrete
.85-.95
Wood
 .95
Fiberglass / Cellulose
.80- 90
Pure Aluminium Foil
.03- .05

 

Low-E, because it is made from pure aluminium, has an e-value of 0.03 which means 3% of radiant energy that comes in contact with its surface will pass through it.  Or another way to look at it is that Low-E will reflect 97% of radiant energy that comes in contact with it.