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Missing Roof Load

Monday, January 18th, 2010

If you run an HVAC building load calculation and your roof load is 0, check to see if you have a plenum return defined. If you do, the roof load is included in the “Plenum” category in the system load. The roof load is not included in the room load at all. Whether you have a plenum return is specified by the zone that the room is in.

To check this, use the Edit Rooms command.

Ribbon: DM HVAC->Rooms and Walls->  Edit Rooms

Pulldown Menu: DM HVAC->Building Definition->Rooms->Edit Rooms

Select the room with 0 roof load. Beside the Zone field, press the Edit button to open the Zones dialog box. The Plenum setting is in the bottom-left of the dialog box. If it is disabled, use the Next, Previous, and Find buttons to look at other zones above the initial zone until you find the zone where Plenum Return is enabled.

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