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[EnergyPlus_Support] e+ calculation of AHU minimum damper position in multizone system with VAV termi



Dear Group,
How does e+ calculate the minimum ODA damper position for a multizone VAV system during autosizing?

I have the following scenario. Big zone requires lots of air (say 30000 m3/h) for heating, but zero ODA. Small zone requires no air for heating because it has a radiator, but requires 80 m3/h min ODA. They are served by a common AHU.

If the AHU sets damper position as 80/(80+30000)=0.0026, then the small zone will require more air to get the minODA, i.e. 80/0.0026=30080 m3/h.
This would set the total demand for the AHU = 30080+30000. This obviously is unacceptable.

Does it then open the ODA damper such as to minimize the total m3/h? It may end up with the damper at 50% so that the small zone now receives 160m3/h and the total AHU is 30160. But this would mean the big zone is eating energy as it gets 30000m3/h with 50% ODA fraction...lots of ODA.

Any ideas?

Jean

PS. this example has been exagerated to show the principle



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