D.W. Yarbrough

Thermal resistance of wall cavities containing reflective insulation

The numerically computed heat transfer coefficients are less than the measured values and do not reduce the disagreement between predicted and measured R-values for reflective assemblies. The Nu calculated in this project were 9 to 27 percent less than those published previously for aspect ratios from 4 to 100, and include aspect ratios greater than previously considered. The introduction of a vertical temperature gradient on the cavity reduces the difference between predicted and measured heat transfer coefficients. The calculated Nu increased when a temperature gradient is specified for the vertical boundaries and this results in a decrease in the calculated R-value.

Operating temperatures of recessed fluorescent fixtures with thermal insulation

Tests were performed to determine steady state surface temperatures for recessed fluorescent fixtures operated with and without thermal insulation on the top side of the fixture and to identify potential problems associated with the installation of thermal insulation. In addition to measuring temperatures, means were sought by which the fixtures can be thermally insulated and operated without fire hazards or damage to the fixture. (MCW)

Effect of vibrations on the density of loose-fill insulations

Testing results of the three major loose-fill insulation products marketed in this country subjected to a variety of vibrations and impacts in a laboratory setting to determine the magnitude of the resultant density increases, are presented. Results show repeated drops of 19 mm (.75 inch) and 152 mm (6 inch) produced density increases of up to 75% for fiberglass, 45% for rock wool, and 27% for cellulosic materials. The three insulation products were also subjected to vibrations ranging from 0.1 mm (.004 inch) to 6.35 mm (.25 inch) to obtain ratios of final density over initial density. Under the test conditions studied it was observed that the lighter materials settled more percentagewise than the dense materials.

Operating temperatures for a convectively cooled recessed incandescent light fixture

Test results are given for the operation of a recessed incandescent light fixture intended for residential use. The fixture is labeled for use in direct contact with attic thermal insulation. Temperature control of the powered fixture is provided by convective heat transfer from the ceiling side of the fixture. The fixture was operated at power levels up to two times the rated power of 75 watts and under thermal insulations up to R-40. In all operating configurations tested the fixture surface in contact with attic insulation was found to be less than 175/sup 0/C. The observed surface temperatures are judged to be safe for operation in contact with loose-fill or batt-type insulations. It was observed that the power leads inside one fixture configuration are exposed to temperatures as high as 168/sup 0/C. The electrical insulation could, therefore, have a limited life. The properties of the internal fixture wiring were not, however, studied in detail.