Calibrated Hot Box: An Effective Means for Measuring Thermal Conductance in Large Wall Sections

A large calibrated hot box apparatus, utilizing highly thermal resistant walls, has been constructed to permit fast and accurate thermal conductance measurements for large vertical sections. The test wall section, nominally 9 by 14 ft (2.7 by 4.2 m), is placed between two chambers maintained at different temperatures. The net heat flow through the test wall is the algebraic sum of the measured input electrical energy and the chamber wall heat transfer which is measured using a heat meter technique. With the use of high thermal resistance walls, the correction for chamber heat flow is generally less than 1 percent. Other data required for the final calculations are obtained using an automatic data monitoring and recording system. Data analysis and report preparation are performed using a computerized program written especially for the equipment.

These, and additional design features, permit a wide variation in mean temperature capability (0 to 100° F), air infiltration measurement capability (0 to 54 standard cubic feet per minute (scfm) at up to 10 in. H₂° ΔP), and efficient usage of manpower by automating control, data taking, and analysis (test frequency of three per week for a manpower requirement of 1 to 2 h per day, excluding specimen construction).

Close agreement was found between the expected and measured thermal results, using calibration specimens measured in the ASTM Test for Thermal Conductivity of Materials by Means of the Guarded Hot Plate (C 177-63). Data in support of the basic conclusions of the paper are presented with the addition of suggestions for including the calibrated hot box as a useful ASTM test standard.