Abstract: An apparatus for attenuating sound in a HVAC system has an inlet mouth aria a tube downstream of the inlet mouth. In the improvement, the inlet mouth defines a surface of revolution formed by rotating a segment of an ellipse about the long axis aria at a fixed distance therefrom. The new apparatus has an air flow transition chamber which permits air flow to "normalize" after air enters the apparatus at its inlet end but before such air enters the inlet mouth. The apparatus also has a baffle between the entry portion and the apparatus outlet end and positioned to occlude the enclosed cavity between the interior tube and the outer housing. The apparatus thereby more effectively attenuates sound in the third octave band. Optionally, the apparatus (either alone or in combination with a VAV terminal unit) has exterior insulation for preventing moisture condensation and further reducing objectionable sound.

Abstract: The disclosure involves a variable air volume (VAV) terminal unit having an inlet collar, a box-like compartment connected to the collar and an insulation layer on the exterior surface of the compartment. The compartment is made of non-fibrous, rigid sheet-like material and an air stream flows through the compartment in contact with the sheet-like material and along a path spaced from the insulation layer. A method for making the variable air volume terminal unit involves steps including forming a plurality of flat, panel-like insulating components and securing a separate component to each of at least two compartment surfaces.