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Scientific Basics of an Insulator- Wenatchee and Chelan Home Inspections

By
Home Inspector with NCW Home Inspections, LLC

Scientific Basics of an Insulator- Wenatchee and Chelan Home Inspections

The basic principle of any insulator is its ability to limit the transfer of heat energy.

Heat is the energy exchange between two thermodynamic systems which differ in temperature. Like the Sun to the earth or your bare body to snow. The transfer of thermal energy will always go from the system of higher temperature to the colder system. When the two systems have reached a thermodynamic equilibrium (same temperature) they will cease to exchange thermal energy.

                                                              Three Modes of Heat transfer

Heat moves by three basic ways: conduction, convection, and radiation. The first two mechanisms need an intervening medium to work and this is where insulation plays its major role. Insulators can be any material or means by which any or all of the three heat transfer mechanisms can be interrupted.

 

 

Conduction

Conduction

Heat energy is stored in molecules as vibrations. The more the molecules vibrate the higher temperature. In some materials, it is easy for one molecule to make its neighbors start to vibrate. The neighbor molecule then makes more molecules vibrate. Before long all the molecules are vibrating (is a party!). Now the whole object has a higher temperature. This is heat conduction. Metals are very good at this as well as many liquids.  

 

 

 

 

convection

Convection

Convection is the movement of molecules within fluids (i.e. liquids, gases) and rheids (a solid material that deforms by viscous flow like lava).

For convection, warmed atoms and/or molecules which are free to move about like those in a gas or liquid circulate through the medium in a rather predictable route. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids

 

 

Radiation

Radiation

In radiation is heat energy that is transmitted via electromagnetic waves. The radioactive process requires no medium. In other words, radiation (for example, light and heat) can move through empty space (like between my ears ;  ). 

 

 

 

 

 

 

How Insulators Work

For conduction the best insulator is a vacuum, completely empty space. If there are no molecules, there can be no vibrations. A very good insulator is air. Gasses such as air do no transfer heat very well because the molecules are so far apart from each other.

With convection heat we want to use a poor heat conductor with as many dead air spaces we can create. Things like cellulose, fiberglass and foam board insulation work well because they interfere with the convective flow essential to that mechanism. The tiny air (or gas) filled spaces in the insulator limit heat flow because they greatly extend the time necessary for convective and conductive flow to occur.

For heat to move through these materials each cell, which there are millions, must relay the heat across it. The longer it takes, the slower the heat flow.

In the case of radiation we want heat radiation to be bounced off a substance rather than being absorbed by it. This is how a thermos bottle works or those shiny emergency heat blankets work. The shiny mirrored surface reflects heat (electromagnetic waves) back toward the source. Hot things in a thermos stay hot because heat is reflected back toward the hot contents and cool things stay cool because the heat from the outside is reflected away from the contents.

 

NCW Home Inspections, LLC  is located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Orville, Cle Elum, East Wenatchee, Quincy and many more...                             

NCW Home Inspections LLC-509-670-9572

Comments (4)

James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

I guess no one but me found this interesting enough to comment :) I learned a new term rheids, never heard that one before. I am familiar with these principals because of infrared camera training. This was very well written btw. You explain everything very well.

Jul 03, 2011 12:15 PM
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC

Jim,

Welcome to my geekdom ;) Yeah I was wondering if this would be interesting to many.

I love the whole science behind buildings and how the interact with our environment.

Jul 03, 2011 02:28 PM
Anonymous
Hollis

This is a good article Donald--well thought out and well composed.  I especially appreciate the graphics.  They really help make the points.

Jul 08, 2011 06:53 AM
#3
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC

Hollis,

Thank you. Good discussion going on in linkedin. Thanks

Jul 08, 2011 10:34 AM