Standard Test Method for THERMAL CONDUCTANCE AND TRANSMITTANCE OF BUILT-UP SECTIONS BY MEANS OF THE GUARDED HOT BOX.

Purpose: To determine the overall coefficient of heat transfer commonly referred to as the U factor.

General Information: This test method is designed primarily for heterogeneous panels found in the construciton fo walls, roofs, and floors of buildings. Air is moving across the system surfaces to simulate actual service conditions. This air flow is an integral part of the overall U factor and is included in overall U calculations.

Method: A reasonably representative panel must be constructed to fit the guarded hot box.

The term "guarded hot box" consists of a metering box, guard box, and a cold box. See the figure above.

Thermocouples, connected in series, are used to measure surface and air temperatures. The power supply to the apparatus should be free from any other drains on the system so that metering of electrical input is constant and accurate. Heating and cooling units and circulating fans must be capable of operating continuously for a minimum of 8 hours.

Adjust test conditions of temperature and orientation to simulate circumstnaces of use. Maintain test conditions until constant temperature and heat flow readings are reached. Continue the testing for at least eight hours in order to obtain two sets of readings, each a minimal four hour period.

Typical U Factor Value: .06 Btu/Hr, SF, degree F is representative of an energy-saving design for roofs of metal buildings.

This test procedure is not a usual quality control procedure due to it's relatively high cost.