Originally posted 2009-08-25 11:01:11. Republished by Blog Post Promoter

Insulation – How It Works

Heat – Definition

Heat is a form of energy that occurs in two completely different ways. The first form of heat occurs in any material substance whether a solid, gas or liquid. The random vibration of atoms and molecules that make up the structure of the material. The higher the vibration the higher the energy, so temperature is used to measure the heat energy.

The second form of heat energy is electromagnetic energy, which travels in empty space. Heat radiation is the same as light, X-rays and radio waves. The energy originates from the vibration of the electric charges in matter. So any material that absorbs the electromagnetic energy has an increase in temperature. Most heat energy is beyond the visible spectrum and is known as infrared. I use a thermal imaging camera to find causes of heat loss and missing insulation.

Insulation

The purpose on insulation is to keep heat from moving and escaping. Heat moves through three methods: conduction, radiation and mass transfer. The fourth mode, convection, is driven by the other three.

Most heat loss through a buildings insulation occurs through conduction. Conductive heat transfer occurs as molecules and atoms collide with each other exchanging kinetic energy. Conduction occurs only between items of matter. Heat cannot move across a vacuum by conduction. Thermos bottles are a great example of a vacuum preventing loss of heat by conduction.

Insulation minimizes the amount of matter through which heat can move. Although not a vacuum this works on similar principles. Gas has a much lower density than solids, so insulation works by eliminating as much solid material as possible and replacing it with gas, the surrounding air. Porous insulation holds the air in place by using small quantities of solid material as a matrix to hold the air still. The air sticks to the insulation so that the air is held stationary. The solid material is spread to ensure that each air molecule is close to a solid for an attachment point.

Most of the heat conduction is through the trapped air, much less is through the solid material. Even so the heat conduction is significant and manufactures try to make the solid insulation as thin as possible. Fiberglass batts are designed to align fibers perpendicular to the heat flow, so that heat is not travelling along fibers.

Manufactures of foam insulation are faced with eventual loss of gases which are diffused through foam over time. As yet no solution has been found for this action.

Blocking Heat Radiation

Opaque reflects heat energy or is absorbed by object. Absorbed radiation increases the temperature of the object which is then transferred by conduction. Insulation blocks convection transfer which indirectly blocks heat radiation.

Heat Loss by Mass Transfer

Air and water are two materials used in mass transfer of heat or cooling. Air can also move large amounts of heat through the building envelope. A leaky building envelope can account for greater energy loss than conduction or convection. Air leakage in buildings is driven by wind, chimney effect and un-balanced operation of fans. This can be reduced by ensuring vapour barrier is sealed throughout.

Convection and Heat Loss

Heat and cold air will rise and fall when temperature is changed by either being warmed or cooled by conduction. This rising and falling of air is a huge cause of energy loss. Insulation prevents air movement by restricting air movement. The importance of proper installation and filling of cavities will directly affect the performance of material.