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[EnergyPlus_Support] comparison of displacement ventilation with mixing ventilation

Hello,
  I am a new EnergyPlus user looking to use the UCSD displacement
ventilation model to compare the energy use to a space served by DV to
the energy use of a comparable space served by an overhead mixing
ventilation system.

One thing has me puzzled.  I am using Version 1.2.2 build 030.  If I
take the DisplacementVent_1ZoneOffice.idf input file, and simply
change the Room Air Modeling type to "Mixing", changing no other
parameters, and re-run the simulation, the zone load changes from
80416W in the DV case to 70221 in the mixing case.

Now, of course the SAT and possibly other parameters would be
different in the mixing case, but shouldn't the design load be the same?

DV Case: (From eio file) 

! <Zone Sizing Information>, Zone Name, Load Type, DesLoad {W}, Calc
Des Air Flow Rate {m3/s}, UserDes Air Flow Rate {m3/s}, Design Day
Name, Time of Peak, Temperature at Peak {C}, Humidity Ratio at Peak
{kgWater/kgAir}
 Zone Sizing, ZONE1, Cooling,   80416.    ,   6.4152    ,   8.3398   
, SAN_FRANCISCO_CA_USA COOLING .4% CONDITIONS DB=>MWB, 17:15:00,  
31.215    ,  0.93169E-02


Mixing Case: 

! <Zone Sizing Information>, Zone Name, Load Type, DesLoad {W}, Calc
Des Air Flow Rate {m3/s}, UserDes Air Flow Rate {m3/s}, Design Day
Name, Time of Peak, Temperature at Peak {C}, Humidity Ratio at Peak
{kgWater/kgAir}
 Zone Sizing, ZONE1, Cooling,   70221.    ,   8.9721    ,   11.664   
, SAN_FRANCISCO_CA_USA COOLING .4% CONDITIONS DB=>MWB, 17:15:00,  
31.215    ,  0.93169E-02


I don't see why the design cooling load should be significantly
different, if the room thermostat setpoint, building envelope and
internal loads don't change.  If the room is a normal ceiling height,
the average room temperature in a space with DV won't be significantly
different than the room temperature in the mixing case.  I am a new
user so maybe I am missing something obvious.

Thanks, John




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