The Effect of Air Flow on Measured Heat Transport through Wall Cavity Insulation

The methods commonly used for determining the thermal resistance of insulations in wall cavities do not include the effect of air movement through the insulation. Contributions to the total building heating or cooling load include the change in enthalpy of air moving through an insulation and the heat flux through the insulation due to the imposed thermal gradient. The two effects are not independent since the air movement affects the temperature distribution in the insulation. A heat-flow-meter apparatus meeting the requirements of the Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus ASTM C 518 has been configured to allow uniform air flow across thermal test specimens. The air flow is parallel to the heat flow direction. Air is introduced into the specimen chamber of the heat-flow-meter apparatus from an external source. The heat-flow-meter with controlled air flow has been used to determine total heat-flow rates as a function of air-flow rate, air-flow direction, and temperature for commonly used wall cavity insulation.