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No Outside Air in Building Load Calculations

Tuesday, November 19th, 2013

Problem: When you run your HVAC building load calculations, there is no outside air, ventilation load, or airflow included.

Solution 1: Run the Project Info command.

Ribbon: DM HVAC->Building Definition->  Project Info

Pulldown Menu: DM HVAC->Building Definition->Project Info

Uncheck the Use Actual Supplied Airflow in Ventilation and Psychrometric Calculations box.

This solution will use the calculated supply airflows for the ventilation calculation.

Solution 2: Insert supply diffusers with airflows in your rooms.

This solution will use the supply airflow from the diffusers that are inserted for the ventilation calculation.

Explanation: When the Use Actual Supplied Airflow in Ventilation and Psychrometric Calculations box is checked, the ventilation calculations use the airflow from the diffusers inserted on the drawing. If no diffusers are inserted, there is 0 supply airflow, and various calculations based upon a percentage of the supply airflow end up being 0 also.

The option is included for when you want to do your ventilation calculations based upon your actual design, rather than the calculated supply airflows for the project.

If you turn it on before diffusers are inserted, it doesn’t work. You have to either turn it off or insert diffusers to solve the problem.

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