Full Description

In a previous paper, it was shown that sound power level for a variable air volume (VAV) terminal device (box) could be related to mass flow rate and upstream static pressure. The fitted equation allows sound power to be calculated with satisfactory accuracy .for intermediate flow rates and pressures not actually tested.

The purpose of this paper is to develop a reliable technique for predicting box performance for intermediate sizes while performing a minimum of tests to obtain data. Testing of every box size in a series over its complete range of operating parameters is a very expensive process. It would be expected that the prediction technique could be used only for geometrically similar boxes, a supposition not visually apparent but determinable only after a sufficient number of tests were performed over the complete range of box sizes, flow rates and pressure drops.

To determine if this could be accomplished, a series of tests were performed in an ADC-certified laboratory. The box series was a round inlet-round outlet box with the same diameter on each. The only box function was to control the volume rate of flow.

Tests were run on nine sizes, represented by the diameter of the inlet, 4, 5, 6, 7, 8, 10, 12, 14, and 16 in. (102, 127, 152, 178, 203, 254, 305, 356, and 406 mm); eight static pressures, 0.5, 1, 1.5, 2, 2.5, 3, 4, and 6 in. of water (0.13, 0.25, 0.38, 0.50, 0.63, 0.75, 1.00, and 1.49 kPa); and four: flow rates, which of course varied with box size. Sound data were taken in bands 2-7, which resulted in 288 separate tests with 1728 sound data points.

Citation: ASHRAE Transactions, 1983, vol. 89, pt. 1B, Atlantic City, NJ