Insulation - How it Works
Insulation normally works on the principle of trapping air in a material. By doing this, thermal conductivity through the material is reduced and as a consequence, heat loss from a building is also drastically cut down
Using Air As a Low Thermal Conductivity Material
Insulation is a material with a low thermal conductivity or high thermal resistance. Basically this means that the material is used as a blocking device to prevent heat passing from one region to another. In the case of a house, it prevents heat leaking from inside the house to the outside.
Insulation relies on the principle of trapping air in a foam or mesh of fibers. Since air is a good insulator, this reduces the heat transfer through the material. It is important that the air is trapped in pockets or cells. If the air is simply held in a bag or between two sheets of material as in the case of double glazing, the effect of the insulation is not as great as air currents carry some heat through the trapped air.
What is Insulation Used For?
Insulation has many uses.
- Its used in the walls and lofts of homes to prevent heat loss to the outside air
- Pipes are insulated to prevent them freezing
- Double or triple glazing relies on trapping a layer of insulating air between sheets of glass. The air in the intervening space reduces conduction of heat from the inner pane to the outer pane of glass and loss of that heat to the outside air
- Insulation is used to lag boilers and the hot water pipes of central heating systems in order to maximize the heat flowing to radiators. Insulation is also important around steam pipes in power stations as vast amounts of heat would be lost from the steam which could have a much higher temperature than 100 C or 212 F when under pressure. Asbestos was once used for lagging pipes and boilers in ships, trains, heating systems etc. It had the advantage of being a good insulator when formed into boards, ropes or lagging and also was heat resistant since it was of mineral origin. Its use has been more or less discontinued due to the hazardous affect of asbestos fibers which cause a chronic lung disease called asbestosis.
- The walls of fridges and freezers are hollow when manufactured and are then insulated with an expanding foam. This reduces the flow of heat from the ambient air into the fridge cavity. Cooler boxes are also insulated in a similar way.
- Handles of saucepans, frying pans and other cooking utensils are made from wood, Bakelite or other plastic which acts as a thermal insulator to prevent you burning your hand.
- The wings and fuselage of the space shuttle and other spacecraft needed to be insulated to prevent the delicate skin from being melted due to friction with the air during re-entry through Earth's atmosphere. In the case of the space shuttle, light weight insulating and heat resistant foam tiles were used and these were bonded to the body of the shuttle.
Insulation is Used in the Loft and Walls of Your Home
Insulation in the home takes several forms. In the loft/attic space, the space between the floor joists is commonly insulated with between 4 to 8 inches of fiber glass, rock wool, sheep's wool or shredded paper impregnated with a fire retardant chemical. More up to date building regulations recommend a greater thickness of material. The space between the roof rafters can also be insulated either with the materials mentioned above, or a foam can be sprayed onto the inner surface of the roof.
Walls are also insulated. Commonly, expanded polystyrene or other foam sheeting materials are used to insulate walls both inside and outside. Building codes must be followed to ensure that the material is not exposed to flame in the event of a fire.
Attic and wall insulation
Attic and wall insulation
Wall insulation, cooler boxes, flasks for keeping hot or cool, coffee cups
Used as insulation in fridges and freezers
Formerly used for insulating boilers and lagging pipes
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