Insulation. Thermal insulation is a materials that blocks or slows the flow of heat through the...

Insulation

Insulation

• Thermal insulation is a materials that blocks or slows the flow of heat through the building envelope.

• Vital to most green building designs because it allows spaces to retain what heat they have and avoid gaining excess heat from outside

Insulation

• Insulation is primarily designed to prevent heat transfer from conduction and radiation

• Resistance to conduction is measured by the R-value (higher thermal resistance = higher R-value)

• Resistance to radiative heat transfer is measured by emissivity (high resistance = low emissivity and high reflectance)

Insulation

• Conduction is the dominant factor when materials are touching each other

• When there is an air gap between materials radiation becomes important

• Convection usually becomes an issue when significant air pockets are involved

2-categories

• Fibrous or cellular products – resist conduction and can be inorganic (glass, rock wool, slag wool, perlite, vermiculite) or organic (cotton, synthetic fibers, cork, foamed rubber, polystyrene)

• Metallic or metalized organic reflective membranes – block radiation heat transfer and must face open air space to work

Insulation

Insulation

• Because R-values are 1/conductance (U)– Doubling the thickness of insulation will not cut

heat loss in half– Exponential decay of heat flow

Low-Emissivity Insulation (Radiation)

• Radiative heat transfer may be important to avoid– Attics or warehouses where the sun heats the

building’s skin excessively• Thin sheet of reflective material can make as

much diff as adding many inches of conventional insulation

• Usually called radiant barriers

Radiant Barriers

• Have low emissivity (.1 or less) • Have high reflectance (.9 or more)• Shiny reflective or white materials• Only reduce radiative heat transfer

Convection and Insulation

• Convection through fluids (air) can also transfer heat

• Unwanted convection through the building envelope can cause unwanted heat gains or losses through infiltration

• Suppressing convection often makes insulation effective

Convection and Insulation

• Convection within the building envelope hurts insulation as well

• Still air is an excellent insulator, often used in insulation by small pockets of air

• Foam insulation is better than batt insulation because there is less convection of air within the foam

Insulation

• Fibrous or cellular products prevent conduction by keeping air still

• Batt insulation traps air in a mat made from a low conductivity solid, glass or organic fiber

• Open cell foam traps tiny bubbles of air or other gas in a poor conductor, however gas can still migrate

• Closed cell foam, gas cannot travel from cell to cell

Insulation Materials

• Typically comes in 5 different forms– Batting– Blown-in– Loose-fill– Rigid foam board– Reflective films

Batting/Blankets

Blown-in/Loose-fill

Foamed in Place

Rigid Board

Reflective

Working Together

• Diff forms can be used together• Usually higher density insulation should not

be placed over top of lower density material that is easily compressed

• Hot air rises by convection, so it generally pools at the underside of surfaces and conducts heat upwards into those materials

• Radiant barriers are more effective at preventing heat from flowing downward through a space than up

Movable Insulation