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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 or ventilation load or airflow included.

Solution 1: Run the DM HVAC->Building Definition->Project Info command. Uncheck the Use Actual Supplied CFM in Ventilation 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 theĀ Use Actual Supplied CFM in Ventilation 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 either have to turn it off or insert diffusers to solve the problem.

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