Standard Practice for Determination of Thermal Resistance of Attic Insulation Systems Under Simulated Winter Conditions

Importancia y uso:

4.1 The thermal resistance of a ceiling system is used to characterize its steady-state thermal performance.

4.2 The thermal resistance of insulation is related to the density and thickness of the insulation. Test data on thermal resistance are obtained at a thickness and density representative of the end use applications. In addition, the thermal resistance of the insulation system will be different from that of the thermal insulation alone because of the system construction and materials.

4.3 This practice is needed because the in-service thermal resistance of some permeable attic insulations under winter conditions is different, lower or higher R, than that measured at or close to simulated room temperature conditions utilizing small-scale tests in which the insulation is sandwiched between two isothermal impermeable plates that have a temperature difference (ΔT) of 20 to 30°C [36 to 54°F]. When such insulation is installed in an attic, on top of a ceiling composed of normal building materials such as gypsum board or plywood, with an open top surface exposed to the attic air space, the thermal resistance under winter conditions with heat flow up and large temperature differences is significantly less because of additional heat transfer by natural convection. Fig. 1 illustrates the difference between results from small scale tests and tests under the conditions of this practice. See Ref (1-12) for discussions of this phenomenon.3

FIG. 1 Schematic of Thermal Resistance for a Permeable Attic Insulation Under Simulated Winter Conditions (Heat Flow Up)

Note 1: A constant hot-side temperature (T, hot) is used for both tests and the temperature difference increases as the cold side temperature (T, cold) is decreased. See 5.1.6 for requirements on size of air space.

4.4 In normal use, the thickness of insulation products ranges from 75 mm [3 in.] to 500 mm [20 in.]. Installed densities will depend upon the product type, the installed thickness, the installation equipment used, the installation technique, and the geometry of the insulated space.

4.5 The onset of natural convection under winter conditions is a function of specimen thickness for some materials. For purposes of this practice, the tests shall be carried out at thicknesses at which the product is used.

4.6 Since this practice simulates winter conditions, the heat flow direction shall be vertically upwards.

4.7 Specimens shall be prepared in a manner consistent with the intended installation procedure. Products for pneumatic installation shall be pneumatically-applied (blown), and products for pour-in-place installation shall be poured into place. See 5.2.

Subcomité:

C16.30

Volúmen:

04.06

Número ICS:

91.120.10 (Thermal insulation of buildings)

Palabras clave:

attic insulation; convection; thermal resistance; winter conditions;