This time the radiant heat from the candles flame transfers through the air and 97% of it reflects back towards the candle rather than your hand. To demonstrate how radiant barriers work, we can continue with the hand and candle example, with the addition of a piece of aluminum foil. However, if you were to touch the piece of aluminum, the full 200 oF would transfer to your hand via conduction. When you place your hand near the heated aluminum, only 3% or 6 oF of its radiant heat absorbs into your hand. This time, replace the candle with a piece of aluminum heated to 200 oF. Since emissivity is a little more intricate to understand, we will use another example similar to the hand and candle one used previously. Aluminum’s emissivity rating of 3% represents the aluminum’s ability to transfer heat in the form of radiation. The radiant heat reflected from aluminum will eventually absorb into some other non reflective object. This means that 97% of the radiant heat directed at a piece of aluminum reflects away from the aluminum. Aluminum typically has a reflectivity of 97% and an emissivity of 3%. Percentage values are used to represent a materials reflectivity and emissivity. Aluminum is a cost effective material that has high reflectivity as well as low emissivity. Perforated radiant barriers are usually made from aluminum. The radiant heat from the candles flame transfers through the air and your hand absorbs the heat. One prominent example of radiant heat transfer would be to place your hand near a lit candle. Radiant heat transfer, unlike conductive heat transfer, does not require direct contact for heat transfer to take place. If the waves reflect off an object, they will continue to travel until another object absorbs them. Other objects either absorb or reflect these radiant waves. Radiant heat primarily transfers by either electromagnetic, infrared or UV waves. Radiant heat transferĮverything with a temperature greater than 0 oK emits radiant heat. Radiant barriers reduce heat loss caused by convective looping and wind washing which insulation alone may be susceptible to. Placing perforated radiant barriers directly on top of attic insulation in mixed and cold climates improves the thermal performance of insulation.
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