The Array Diffuser (Distance/Angle) command is used to array devices on the drawing in a straight line from the first diffuser in a set direction with a set distance between each diffuser.
Use this command instead of the standard CAD ARRAY command.
To array a diffuser using the distance/angle method, go to
Ribbon: DM HVAC->Diffusers-> 
Array Diffuser (Distance/Angle)
Pulldown Menu: DM HVAC->Modify Diffusers->Array Diffuser (Distance/Angle)
You will be prompted to select the diffusers to array.
Select diffusers to array:
You will then be prompted to set an offset distance and angle. The distance between each diffuser in the array is based upon the distance from the specified point to the first diffuser.
Offset distance and angle:
You will then be prompted to specify the number of diffusers in the array, including the selected diffuser.
Number of diffusers in array (including selected diffuser):
The diffusers in the array will be generated in the direction of the specified point from the selected diffuser.