Design and Construction of a Guarded Hot Box Facility for Evaluating the Thermal Performance of Building Wall Materials

The focus of this study was to design and build a guarded hot box to test the R-Value of building materials. The Riverside Energy Efficiency Laboratory is looking to expand their testing capabilities by including this service. Eventually, the laboratory will become energy star certified.

A guarded hot box facility consists of two boxes maintained at specific temperatures and a guard box around each one that is maintained at the same temperature as the box it surrounds. The ASTM C1363 standard was used as guide for the construction and testing of sample specimen. This standard called for an air velocity profile uniform within 10 percent of the average. Velocity tests were performed with various different configurations to give a uniform velocity. Although the velocity did not meet standards, the configuration chosen included a piece of 1/4" pegboard placed 2" away from the top and the bottom of the inner box.

By using the known overall heat added and removed from the system, as well as all the heat losses the heat transferred through the specimen and its R-Value can be calculated. The uncertainty of the R-Value and the accuracy of the testing facility gave conflicting results. Future experiments will use improved testing methods that include differential thermocouples to obtain better uncertainty for the R-Value calculations.