[EnergyPlus_Support] odd autosizing results

["Ian Doebber" <idoebber@xxxxxx>]

I have some odd results using the HVAC autosizing feature for a furnace and central air conditioner system for my residence and am curious how Energy Plus is handling this situation.  I am autosizing everything I can for both heating and cooling but specifying a flow/system of 700 cfm.  The zone sizing output spreadsheet shows that I need 11,925 W heating and 4,049 W cooling.  Yet the EIO file shows that I need 7,542 W heating with 1100 cfm and 4,802 W cooling with 590 cfm.  First question is that my EIO file shows that I need lower heating (7,542 W < 11,925 W) since it calculated it with a higher flow rate (1100 cfm > 700 cfm) and similarly a higher cooling (4,802 W > 4,409 W) since it calculated it with a lower flow rate (590 cfm < 700 cfm.  Is this correct.

My second question concerns how then Energy Plus sizes my equipment.  The EIO file states that with a 700 cfm flow rate, I will have 9,629 W heating and 6,040 W cooling.  This doesn't make sense.  My heating capacity then does not meet my maximum zone load of 11,925 W and cooling capacity then is too big for my maximum zone load of 4,049 W.  Where is Energy Plus calculating my equipment capacities from.

Thanks
Ian Doebber
Mechanical Engineering Graduate Student
Virginia Tech

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