Image accessed from: Çengel, Y. A., Boles, M. A., & Kanoğlu, M. (2020).
Thermodynamics an engineering approach [9th edition]. Singapore: McGraw-Hill.
By looking at the thermal conductivity chart, we
can determine what materials we should use as an insulator or a
heat conductor. If we want a good heat conductor for something
like a heat sink, we should use a metal like iron or aluminum
that will allow heat to move through it quickly. If we instead
want to insulate an area, we will need a poor thermal conductor
like urethane, air, or glass fiber.
There are many different types of conventional building insulators that are commonly used. Here is a list of some of them:
Fibrous materials:
-Fiberglass: molten glass is spun or blown into fibers or blankets for insulation. Their effectiveness can be modified by changing the density of the material.
-Mineral wool: can come in rock wool (made from natural components like basalt) or slag wool (components of waste material that form on molten metal) Is made similarly to fiberglass, and has similar properties as fiberglass.
-Cellulose: made from recycled paper products, often has borate and ammonium sulfate to increase fire and insect resistance. Doesn't require a moisture barrier. It can be easily installed into older buildings without insulation, or in new buildings. A little moisture can be added to sprayed cellulose insulation to activate the starches in the material and make stick to building's surfaces.
-Natural Fiber Insulation materials: includes cotton, sheep's wool, straw, and hemp. Most of these have similar conductivity as other fibrous insulation materials.
Plastic insulation
-Polystyrene insulation: takes the form of sheets or small beads. Generally sheets are used as the beads are light and hold a static charge really well, which makes them frustrating to work with.
-Polyurethane insulation: takes the form of liquid spray or foam boards. The spray tends to perform better than the boards because it molds itself to the surface its sprayed on and fills in small cracks. Polyurethane will have a low-conductivity gas within its cells such as air or CO2 to create additional barriers for heat penetration.
-Polyisocyanurate insulation: comes in liquid spray or foam boards. Has a similar composition to polyurethane, but has a different plastic for the foam components.
Other
-Cementitious foam insulation: is a cement-based foam composed of magnesium silicate or magnesium oxide. It has a similar thermal performance to polyurethane and is nontoxic and nonflammable.
It should be noted that most of these insulators are designed with pores that trap air or another low conductivity gas within the insulation. This allows a gas to be the primary or a secondary insulator these insulators, which can lower the cost and make these insulators even more effective. Some of these insulators, like fiberglass or mineral wool are entirely designed around trapping air to use as a primary insulator.
However, this note brings up the question, why even use an insulator at all? Wouldn't just sealing the air in the insulating layer without the insulating material lead to a pretty good insulator? This would be true if only conduction was the only factor in heat transfer, but other heat transfer mechanisms such as convection makes an insulating material besides a sealed gas necessary. How convection influences insulation will be talked about more in that section.
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There are many different types of conventional building insulators that are commonly used. Here is a list of some of them:
Fibrous materials:
-Fiberglass: molten glass is spun or blown into fibers or blankets for insulation. Their effectiveness can be modified by changing the density of the material.
-Mineral wool: can come in rock wool (made from natural components like basalt) or slag wool (components of waste material that form on molten metal) Is made similarly to fiberglass, and has similar properties as fiberglass.
-Cellulose: made from recycled paper products, often has borate and ammonium sulfate to increase fire and insect resistance. Doesn't require a moisture barrier. It can be easily installed into older buildings without insulation, or in new buildings. A little moisture can be added to sprayed cellulose insulation to activate the starches in the material and make stick to building's surfaces.
-Natural Fiber Insulation materials: includes cotton, sheep's wool, straw, and hemp. Most of these have similar conductivity as other fibrous insulation materials.
Plastic insulation
-Polystyrene insulation: takes the form of sheets or small beads. Generally sheets are used as the beads are light and hold a static charge really well, which makes them frustrating to work with.
-Polyurethane insulation: takes the form of liquid spray or foam boards. The spray tends to perform better than the boards because it molds itself to the surface its sprayed on and fills in small cracks. Polyurethane will have a low-conductivity gas within its cells such as air or CO2 to create additional barriers for heat penetration.
-Polyisocyanurate insulation: comes in liquid spray or foam boards. Has a similar composition to polyurethane, but has a different plastic for the foam components.
Other
-Cementitious foam insulation: is a cement-based foam composed of magnesium silicate or magnesium oxide. It has a similar thermal performance to polyurethane and is nontoxic and nonflammable.
It should be noted that most of these insulators are designed with pores that trap air or another low conductivity gas within the insulation. This allows a gas to be the primary or a secondary insulator these insulators, which can lower the cost and make these insulators even more effective. Some of these insulators, like fiberglass or mineral wool are entirely designed around trapping air to use as a primary insulator.
However, this note brings up the question, why even use an insulator at all? Wouldn't just sealing the air in the insulating layer without the insulating material lead to a pretty good insulator? This would be true if only conduction was the only factor in heat transfer, but other heat transfer mechanisms such as convection makes an insulating material besides a sealed gas necessary. How convection influences insulation will be talked about more in that section.
Back to home page