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The paper describes a procedure for measurement of steady-state heat transfer through the walls of air duct systems under actual operating conditions and configuration. The procedure uses two independent measurement techniques. A calibrated hot box is the primary measurement technique and an airstream temperature-drop measurement provides a secondary technique.
The calibrated hot box is a heavily insulated box which is sealed around a duct conveying cold air. A temperature controller and electric resistance heaters maintain the box temperature as close as possible to ambient temperature. Thus, the laboratory space acts as a guard for the box. The energy input to the box is measured with a watt-hour meter. The total energy input, corrected for the heat transfer through the box wall, represents the heat transfer through the test system.
The temperature-drop technique uses thermocouples to measure the temperature difference betweeen two stations in the test duct and orifice plates to measure airflow. The heat transfer from this technique is compared with calibrated hot-box measurements.
An automatic data collection system is used so that tests can be conducted over a long period of time to assure steady-state conditions and to determine reproducibility.
Verification of the calibrated hot-box technique is achieved by testing a specially constructed section of duct whose heat transfer can be readily calculated. Experimental and calculated data are presented for this duct section.
air ducts, calibrated hot box, heat transfer, thermal transmission, thermal conductivity
Senior engineer, Owens/Corning Fiberglas Corp., Granville, Ohio