HVAC modeling in FDS 6.7.5

[Jack]

Hi all,

I encountered problems in modeling the HVAC system in FDS 6.7.5. To focus on HVAC, I created a simple model including only basic obstructions and the HVAC settings, see attachment. An outlet duct with a fan and an inlet duct without the fan (open duct) are defined. Physically, the extraction should generate an under-pressure in the compartment and the flow rate in the inlet and outlet should more or less the same (because of no other openings except for leakage). These are confirmed in the simulation using FDS 6.5.3, see the attached plots. However, when switching to FDS 6.7.5 with the same input file, the above physical phenomena are not obtained, see the attached plots. What would be the problem? Do I miss some updates in FDS 6.7.5?

Thanks for any answers.

[Kevin]

I don't see an attachment.

[Jack]

Sorry, I cannot add any attachments or plots in the original post. So I give the input codes here:

&HEAD CHID='VENTILATION'/

&TIME T_END=100.0/

&MISC TMPA=27.9/

&MESH ID='MESH1',   IJK=64,54,44, XB=-0.05,1.55,-0.05,1.30,-0.05,1.05/

&ZONE ID='Zone01', XB=0.75,0.625,0.5, LEAK_AREA(0)=3.32E-6, LEAK_PRESSURE_EXPONENT(0)=1.0, LEAK_REFERENCE_PRESSURE(0)=50.0/

&DEVC ID='P_FL1', QUANTITY='PRESSURE', XYZ=0.375,0.312,0.1/

&DEVC ID='P_FL2', QUANTITY='PRESSURE', XYZ=0.375,0.312,0.9/

&DEVC ID='VolumeF_ADM', QUANTITY='DUCT VOLUME FLOW', DUCT_ID='ADM'/

&DEVC ID='VolumeF_EXT', QUANTITY='DUCT VOLUME FLOW', DUCT_ID='EXT'/

&DEVC ID='LEAKF01', QUANTITY='DUCT VOLUME FLOW', DUCT_ID='LEAK 0 1'/

&DEVC ID='LEAKV01', QUANTITY='DUCT VELOCITY', DUCT_ID='LEAK 0 1'/

&MATL ID='steel',

      SPECIFIC_HEAT=0.46,

      CONDUCTIVITY=45.0,

      DENSITY=7820.0/

&SURF ID='wall',

      LEAK_PATH=1,0,

      MATL_ID ='steel',

      THICKNESS =0.025,

      BACKING= 'EXPOSED'/

  

&OBST ID='ground',  XB=-0.05,1.55,-0.05,1.30,-0.05,0.00, SURF_ID='wall'/

&OBST ID='ceiling', XB=-0.05,1.55,-0.05,1.30, 1.00,1.05, SURF_ID='wall'/

&OBST ID='Front',   XB=-0.05,1.55,-0.05,0.00,-0.05,1.05, SURF_ID='wall'/

&OBST ID='Back',    XB=-0.05,1.55, 1.25,1.30,-0.05,1.05, SURF_ID='wall'/

&OBST ID='Left',    XB=-0.05,0.00,-0.05,1.30,-0.05,1.05, SURF_ID='wall'/

&OBST ID='Right',   XB= 1.50,1.55,-0.05,1.30,-0.05,1.05, SURF_ID='wall'/

&OBST ID='ADM', XB= 0.1,0.15,0.6,0.65,0.8,1.0, SURF_ID='INERT', THICKEN=.TRUE./

&VENT ID='ADM_vent', SURF_ID='HVAC', XB= 0.1,0.15,0.6,0.6,0.8,0.9, COLOR='BLUE'/

&HVAC TYPE_ID='DUCT', ID='ADM', NODE_ID='ADMnode_1','ADMnode_2', AREA=0.001, LOSS=3.28,3.28, LENGTH=32.4/

&HVAC TYPE_ID='NODE', ID='ADMnode_1', DUCT_ID='ADM', XYZ=11.5,10.0,0.0, AMBIENT=.TRUE./

&HVAC TYPE_ID='NODE', ID='ADMnode_2', DUCT_ID='ADM', VENT_ID='ADM_vent'/

&OBST ID='EXT', XB= 1.35,1.4,0.6,0.65,0.8,1.0, SURF_ID='INERT', THICKEN=.TRUE./

&VENT ID='EXT_vent', SURF_ID='HVAC', XB= 1.35,1.4,0.65,0.65,0.8,0.9, COLOR='RED'/

&HVAC TYPE_ID='DUCT', ID='EXT', NODE_ID='EXTnode_1','EXTnode_2', AREA=0.001, LOSS=4.95,4.95, LENGTH=32.4, FAN_ID='EXT_fan'/

&HVAC TYPE_ID='NODE', ID='EXTnode_1', DUCT_ID='EXT', VENT_ID='EXT_vent'/

&HVAC TYPE_ID='NODE', ID='EXTnode_2', DUCT_ID='EXT', XYZ=11.5,10.0,0.0, AMBIENT=.TRUE./

&HVAC TYPE_ID='FAN', ID='EXT_fan', MAX_FLOW=0.06646, MAX_PRESSURE=221.93/

&TAIL/

[Jack]

Hi Kevin,

After several trials, a solution was found: specify the pressure zone using the sextuplet XB instead of the single XYZ value. Combining with my previous post, there might be some problems in the zone definition in the current version.

[dr_jfloyd]

In the file you pasted above you are using XB on ZONE but only give three points. The way a namelist works is if you specify fewer points than an array holds and do not explicitly define which points you are providing the data is read starting with the first array location. So XB=a,b,c  means  x1=a, x2=b, y1=c and y2,z1,and z2 are the null values which puts them outside the domain.  If I change the XB to XYZ things seem to work fine.

[junyi li]

Thanks, Jason. This is indeed what I overlooked. The model works fine after the modification.

dr_jfloyd <drjf...@gmail.com> 于2021年3月4日周四 下午6:41写道：

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