Pressure spikes and oscillations using HVAC and ZONEs (FDS 6.7.5)

[Tom Miles]

Hi all,

I was hoping to see if anyone could potentially help with a problem that I'm having relating to pressure spikes and oscillations in my model which utilisies HVAC and ZONEs.

Description of model and analysis

The model is a relatively simple geometry; a rectangular fire compartment off a T-shaped lobby which in turn leads to a stair enclosure (see attached image). There is a mechanical smoke ventilation system in the lobby, comprised of a mechanical extract and a natural inlet. There is additional ventilation in the fire compartment to provide a source of oxygen to the fire. The aim is to prevent smoke ingress into the stair in both the means of escape and fire-fighting phases (represented in the model as the lobby and stair doors opening and closing at different times with the fire at different HRRs).

Description of problem

I have made each of the mechanical extract, natural inlet and fire inlet HVAC systems, with each room being a different ZONE. I find that the model works as expected until the lobby door closes (at 180 s), at which point there appears to be a sudden fluctuation in pressure and general flow pattern in the fire compartment (at which point is now a sealed compartment again). This leads to a pressure oscillation in the fire compartment (circa +500 to -300 Pa) which does not resolve until the lobby door reopens later on.

For the period where the lobby door is closed but the stair door is still open (180-185 s), the pressure in the lobby remains stable as expected. However, when the stair door shuts at 185 s, this then leads to a sudden surge of air being forced through the natural inlet into the lobby, which unsurprisingly leads to an even larger pressure oscillation than that seen in the fire compartment.

Interestingly, the pressure DEVC readings are sampled at 1 s intervals (same as the SLCF readings), yet the extreme pressure oscillation only seems to be picked up when viewing the SLCFs and not the DEVCs.

A few things to note

1. An AOV (i.e. natural inlet vent) is provided at the head of the stair, which is a physical HOLE leading to OPEN vents above. I assume this explains why the pressure in the lobby is stable while the stair door is opened.
2. I have tried altering PRESSURE_RELAX_TIME up to 5 seconds, but see no appreciable difference in results.
3. I have tried altering the length, losses and area of the HVAC DUCTs, but to no particular avail.
4. Each final NODE in each HVAC system goes to ambient.
5. The attached image shows a scenario where I put two fire vents in the model to see if that might help dampen the pressure oscillation in the fire compartment - no appreciable difference in results.
6. The primary reason for using the HVAC methodology on this project was to utilise the MAX_FLOW parameter of the extract fan, as that would obviously alter the extract flow rate automatically following the simple quadratic fan curve, rather than specifying a pre-determined extract flow RAMP. On future project's I'll likely move away from HVAC and specify the RAMP myself, but I'm stuck on this project as it is only one aspect of a wider project which all utilises HVAC.

My thought process

1. Seeing as the extract vent appears to work as intended, I assume that the problem is with the HVAC inlet vents in the lobby and fire compartment?
2. My first thought was to try and run a model which just uses OPEN vents instead of HVAC vents for the natural inlets, but my understanding is that ZONEs are not compatible with OPEN vents - is that correct? If so, if I was to use OPEN vents and remove the ZONEs, would that also then mean that I would no longer be able to use the HVAC extract (and therefore the MAX_FLOW parameter) either? I also assume that OPEN vents have an advantage of bi-directional flow across the vent, as opposed to the single-direction flow in HVAC ducts, which may help alleviate certain pressure oscillations?
3. Would changing the AOV at the head of the stair to another natural HVAC inlet system potentially help with the stability of resealing each ZONE when the respective doors close?

Any help would be greatly appreciated! Happy to provide more information if required.

Cheers,

Tom

[dr_jfloyd]

Can you attach a copy of your input?

[Tom Miles]

Hi Jason,

It would take me a little while to tidy up the full input file, but the input pertaining to the HVAC systems and ZONEs is below. Note this is for the latest scenario that I modelled with 2 no. fire vents and minimum friction to the ducts. Please do let me know if you need anything more.

&ZONE ID='lobby', XB=9.7,12.2,9.4,17.5,0.0,3.0/

&ZONE ID='fire compartment', XB=10.0,22.4,19.6,25.0,0.0,4.5/

&ZONE ID='stair', XB=12.2,15.1,11.0,15.4,-3.0,4.3/

&VENT ID='fire supply air vent_01', SURF_ID='HVAC', XB=22.4,22.4,19.5,21.5,0.1,0.8/

&HVAC ID='Node08', TYPE_ID='NODE', DUCT_ID='Duct', VENT_ID='fire supply air vent_01'/

&HVAC ID='Node09', TYPE_ID='NODE', DUCT_ID='Duct', AMBIENT=.TRUE., XYZ=28.0,19.270702,2.25/

&HVAC ID='Duct', TYPE_ID='DUCT', AREA=1.4, PERIMETER=5.4, LOSS=1.0,1.0, NODE_ID='Node08','Node09', ROUGHNESS=0.0, LENGTH=6.009257/

&VENT ID='fire supply air vent_02', SURF_ID='HVAC', XB=17.4,19.4,25.3,25.3,0.1,0.8/ 

&HVAC ID='Node06', TYPE_ID='NODE', DUCT_ID='Duct04', VENT_ID='fire supply air vent_02'/

&HVAC ID='Node07', TYPE_ID='NODE', DUCT_ID='Duct04', AMBIENT=.TRUE., XYZ=19.629298,31.0,2.25/

&HVAC ID='Duct04', TYPE_ID='DUCT', AREA=1.4, PERIMETER=5.4, LOSS=1.0,1.0, NODE_ID='Node06','Node07', ROUGHNESS=0.0, LENGTH=6.102555/

&VENT ID='VT_MainExtract_Corridor', SURF_ID='HVAC', XB=12.1,12.1,9.6,10.2,1.8,2.8, COLOR='BLUE'/

&HVAC ID='Node_MainExtract_Corridor', TYPE_ID='NODE', DUCT_ID='Duct_MainExtract_Damper', VENT_ID='VT_MainExtract_Corridor'/

&HVAC ID='Node_MainExtract_Internal', TYPE_ID='NODE', DUCT_ID='Duct_MainExtract_Damper','Duct_MainExtract_Fan', XYZ=17.6,10.2,3.0/

&HVAC ID='Node_MainExtract_Ambient', TYPE_ID='NODE', DUCT_ID='Duct_MainExtract_Fan', AMBIENT=.TRUE., XYZ=22.6,10.2,3.0/

&HVAC ID='Duct_MainExtract_Damper', TYPE_ID='DUCT', AREA=1.2, PERIMETER=3.4, DAMPER=.TRUE., LOSS=1.0,1.0, NODE_ID='Node_MainExtract_Corridor','Node_MainExtract_Internal', ROUGHNESS=0.0, LENGTH=5.552477, DEVC_ID='TIMER->OUT'/

&HVAC ID='Duct_MainExtract_Fan', TYPE_ID='DUCT', AREA=0.6, PERIMETER=3.4, FAN_ID='Fan_MainExtract01', LOSS=1.0,1.0, NODE_ID='Node_MainExtract_Internal','Node_MainExtract_Ambient', ROUGHNESS=0.0, LENGTH=5.0, DEVC_ID='TIMER->OUT'/

 

&VENT ID='Natural_Vent', SURF_ID='HVAC', XB=13.0,13.7,18.0,18.0,1.8,2.8/ 

&HVAC ID='Node_Natural_Ext', TYPE_ID='NODE', DUCT_ID='Duct_Natural_Inlet', AMBIENT=.TRUE., XYZ=17.0,21.0,5.5/

&HVAC ID='Duct_Natural_Inlet', TYPE_ID='DUCT', AREA=0.65, PERIMETER=3.6, DAMPER=.TRUE., LOSS=1.0,1.0, NODE_ID='Node_Natural_Int','Node_Natural_Ext', ROUGHNESS=0.0, LENGTH=5.706356, DEVC_ID='TIMER->OUT'/

&HVAC ID='Node_Natural_Int', TYPE_ID='NODE', DUCT_ID='Duct_Natural_Inlet', VENT_ID='Natural_Vent'/

&HVAC ID='Fan_MainExtract01', TYPE_ID='FAN', TAU_FAN=-10.0, MAX_FLOW=8.0, MAX_PRESSURE=50.0/

Thanks,

Tom

[Kevin McGrattan]

It is very difficult to diagnose the problem without a running case. Verifying the workings of the HVAC system in the absence of fire is a key part of your analysis. 

[Tom Miles]

Hi Kevin,

I'm having trouble trying to attach the FDS file to this message so will try again shortly in a future message. I have a model up and running with no fire, and will report back any findings.

Thanks,

Tom

[Tom Miles]

No luck trying to attach the FDS file so please find text input below - sorry for the inconvenience!

&HEAD CHID='HVAC_problem_model', TITLE='HVAC_problem_model'/

&TIME T_END=900.0/

&DUMP DT_DEVC=1.0, DT_HRR=1.0, DT_RESTART=300.0, DT_SLCF=1.0/

&PRES PRESSURE_RELAX_TIME=3.0/

&MESH ID='fire_compartment1', IJK=81,90,45, XB=6.8,14.9,16.6,25.6,0.0,4.5/

&MESH ID='Stair', IJK=32,73,124, XB=12.1,15.3,9.3,16.6,-6.0,6.4/

&MESH ID='fire_compartment2', IJK=81,63,45, XB=14.9,23.0,19.3,25.6,0.0,4.5/

&MESH ID='FF_lobby', IJK=24,72,30, XB=9.7,12.1,9.4,16.6,0.0,3.0/

&ZONE ID='lobby', XB=9.7,12.2,9.4,17.5,0.0,3.0/

&ZONE ID='fire compartment', XB=10.0,22.4,19.6,25.0,0.0,4.5/

&ZONE ID='stair', XB=12.2,15.1,11.0,15.4,-3.0,4.3/

&SPEC ID='WATER VAPOR'/

&PART ID='water_drops',

      SPEC_ID='WATER VAPOR',

      DIAMETER=2000.0,

      QUANTITIES='PARTICLE DIAMETER',

      SAMPLING_FACTOR=1/

&REAC ID='POLYURETHANE',

      FYI='NFPA Babrauskas',

      FUEL='REAC_FUEL',

      C=6.3,

      H=7.1,

      O=2.1,

      N=1.0,

      SOOT_YIELD=0.1/

&RAMP ID='room door timer_RAMP', T=59.75, F=-1.0/

&RAMP ID='room door timer_RAMP', T=60.25, F=1.0/

&RAMP ID='room door timer_RAMP', T=179.75, F=1.0/

&RAMP ID='room door timer_RAMP', T=180.25, F=-1.0/

&RAMP ID='room door timer_RAMP', T=459.75, F=-1.0/

&RAMP ID='room door timer_RAMP', T=460.25, F=1.0/

&CTRL ID='invert', FUNCTION_TYPE='ALL', LATCH=.FALSE., INITIAL_STATE=.TRUE., INPUT_ID='room door timer'/

&CTRL ID='room door timer', FUNCTION_TYPE='CUSTOM', RAMP_ID='room door timer_RAMP', LATCH=.FALSE., INPUT_ID='TIME'/

&DEVC ID='TIME', QUANTITY='TIME', XYZ=11.0,13.0,1.0/

&RAMP ID='stair door LH timer_RAMP', T=64.75, F=-1.0/

&RAMP ID='stair door LH timer_RAMP', T=65.25, F=1.0/

&RAMP ID='stair door LH timer_RAMP', T=184.75, F=1.0/

&RAMP ID='stair door LH timer_RAMP', T=185.25, F=-1.0/

&RAMP ID='stair door LH timer_RAMP', T=399.75, F=-1.0/

&RAMP ID='stair door LH timer_RAMP', T=400.25, F=1.0/

&CTRL ID='Stair door LH timer', FUNCTION_TYPE='ALL', LATCH=.FALSE., INITIAL_STATE=.TRUE., INPUT_ID='stair door timer LH'/

&CTRL ID='stair door timer LH', FUNCTION_TYPE='CUSTOM', RAMP_ID='stair door LH timer_RAMP', LATCH=.FALSE., INPUT_ID='TIME'/

&DEVC ID='TIME', QUANTITY='TIME', XYZ=11.0,13.0,1.0/

&RAMP ID='stair door RH timer_RAMP', T=64.75, F=-1.0/

&RAMP ID='stair door RH timer_RAMP', T=65.25, F=1.0/

&RAMP ID='stair door RH timer_RAMP', T=184.75, F=1.0/

&RAMP ID='stair door RH timer_RAMP', T=185.25, F=-1.0/

&CTRL ID='Stair door RH timer', FUNCTION_TYPE='ALL', LATCH=.FALSE., INITIAL_STATE=.TRUE., INPUT_ID='stair door timer RH'/

&CTRL ID='stair door timer RH', FUNCTION_TYPE='CUSTOM', RAMP_ID='stair door RH timer_RAMP', LATCH=.FALSE., INPUT_ID='TIME'/

&DEVC ID='TIME', QUANTITY='TIME', XYZ=11.0,13.0,1.0/

&CTRL ID='invert4', FUNCTION_TYPE='ALL', LATCH=.FALSE., INITIAL_STATE=.TRUE., INPUT_ID='TIMER->OUT2->OUT->OUT->OUT->OUT->OUT->OUT'/

&DEVC ID='TIMER->OUT2->OUT->OUT->OUT->OUT->OUT->OUT', QUANTITY='TIME', XYZ=11.0,13.0,1.0, SETPOINT=60.0/

&PROP ID='Sprinkler',

      QUANTITY='SPRINKLER LINK TEMPERATURE',

      ACTIVATION_TEMPERATURE=68.0,

      RTI=185.0,

      C_FACTOR=0.7,

      PART_ID='water_drops',

      FLOW_RATE=42.0,

      PARTICLE_VELOCITY=0.0,

      DROPLET_VELOCITY=5./

&DEVC ID='fire vent_01 duct flow', QUANTITY='DUCT VOLUME FLOW', DUCT_ID='Duct'/

&DEVC ID='extract duct flow', QUANTITY='DUCT VOLUME FLOW', DUCT_ID='Duct_MainExtract_Fan'/

&DEVC ID='inlet duct flow', QUANTITY='DUCT VOLUME FLOW', DUCT_ID='Duct_Natural_Inlet'/

&DEVC ID='fire vent_02 duct flow', QUANTITY='DUCT VOLUME FLOW', DUCT_ID='Duct04'/

&DEVC ID='inlet duct vel', QUANTITY='DUCT VELOCITY', DUCT_ID='Duct_Natural_Inlet'/

&DEVC ID='fire vent_02 vel', QUANTITY='DUCT VELOCITY', DUCT_ID='Duct04'/

&DEVC ID='fire vent_01 vel', QUANTITY='DUCT VELOCITY', DUCT_ID='Duct'/

&DEVC ID='extract duct vel', QUANTITY='DUCT VELOCITY', DUCT_ID='Duct_MainExtract_Fan'/

&DEVC ID='inside door temp', QUANTITY='TEMPERATURE', XYZ=11.0,18.8,2.0/

&DEVC ID='outside door temp', QUANTITY='TEMPERATURE', XYZ=11.0,17.8,2.0/

&DEVC ID='outside stair temp', QUANTITY='TEMPERATURE', XYZ=11.7,11.0,2.0/

&DEVC ID='inside stair temp', QUANTITY='TEMPERATURE', XYZ=12.7,11.0,2.0/

&DEVC ID='centre room temp', QUANTITY='TEMPERATURE', XYZ=14.9,21.2,2.0/

&DEVC ID='inside door vis', QUANTITY='VISIBILITY', XYZ=11.0,18.8,2.0/

&DEVC ID='outside door vis', QUANTITY='VISIBILITY', XYZ=11.0,17.8,2.0/

&DEVC ID='outside stair vis', QUANTITY='VISIBILITY', XYZ=11.7,11.0,2.0/

&DEVC ID='inside stair vis', QUANTITY='VISIBILITY', XYZ=12.7,11.0,2.0/

&DEVC ID='centre room vis', QUANTITY='VISIBILITY', XYZ=14.9,21.2,2.0/

&DEVC ID='inside door pres', QUANTITY='PRESSURE', XYZ=11.0,18.8,2.0/

&DEVC ID='outside door pres', QUANTITY='PRESSURE', XYZ=11.0,17.8,2.0/

&DEVC ID='outside stair pres', QUANTITY='PRESSURE', XYZ=11.7,11.0,2.0/

&DEVC ID='inside stair pres', QUANTITY='PRESSURE', XYZ=12.7,11.0,2.0/

&DEVC ID='centre room pres', QUANTITY='PRESSURE', XYZ=14.9,21.2,2.0/

&DEVC ID='stair door flow', QUANTITY='VOLUME FLOW', XB=12.1,12.1,10.4,11.3,0.0,2.1/

&DEVC ID='lobby door flow', QUANTITY='VOLUME FLOW', XB=10.5,11.6,18.2,18.2,0.0,2.1/

&DEVC ID='Sprinkler_NF1', PROP_ID='Sprinkler', XYZ=20.0,24.5,4.4/

&DEVC ID='Sprinkler_NF2', PROP_ID='Sprinkler', XYZ=20.0,20.0,4.4/

&DEVC ID='Sprinkler_NF3', PROP_ID='Sprinkler', XYZ=12.0,24.5,4.4/

&DEVC ID='Sprinkler_NF4', PROP_ID='Sprinkler', XYZ=12.0,20.0,4.4/

&DEVC ID='Lobby pres 2m', QUANTITY='PRESSURE', XYZ=11.2,15.0,2.0/

&DEVC ID='Lobby temp 2m', QUANTITY='TEMPERATURE', XYZ=11.2,15.0,2.0/

&DEVC ID='Lobby vis 2m', QUANTITY='VISIBILITY', XYZ=11.2,15.0,2.0/

&DEVC ID='Lobby pres 1p5m', QUANTITY='PRESSURE', XYZ=11.2,15.0,1.5/

&DEVC ID='Lobby temp 1p5m', QUANTITY='TEMPERATURE', XYZ=11.2,15.0,1.5/

&DEVC ID='Lobby vis 1p5m', QUANTITY='VISIBILITY', XYZ=11.2,15.0,1.5/

&DEVC ID='TIMER->OUT', QUANTITY='TIME', XYZ=6.8,16.6,0.0, SETPOINT=60.0/

&MATL ID='GYPSUM',

      SPECIFIC_HEAT_RAMP='GYPSUM_SPECIFIC_HEAT_RAMP',

      CONDUCTIVITY_RAMP='GYPSUM_CONDUCTIVITY_RAMP',

      DENSITY=780.0,

      EMISSIVITY=0.7/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=0.0, F=0.25/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=70.0, F=0.25/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=80.0, F=0.23/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=100.0, F=0.19/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=110.0, F=0.17/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=111.0, F=0.17/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=125.0, F=0.14/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=130.0, F=0.13/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=140.0, F=0.13/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=141.0, F=0.13/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=220.0, F=0.13/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=221.0, F=0.13/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=300.0, F=0.13/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=540.0, F=0.15/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=600.0, F=0.16/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=650.0, F=0.17/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=800.0, F=0.18/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=1000.0, F=0.35/

&RAMP ID='GYPSUM_CONDUCTIVITY_RAMP', T=1001.0, F=0.78/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=0.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=70.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=80.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=100.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=110.0, F=52.45/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=111.0, F=18.12/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=125.0, F=9.54/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=130.0, F=6.67/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=140.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=141.0, F=3.08/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=220.0, F=3.08/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=221.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=300.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=540.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=600.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=650.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=800.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=1000.0, F=0.95/

&RAMP ID='GYPSUM_SPECIFIC_HEAT_RAMP', T=1001.0, F=0.95/

&MATL ID='GLASS01',

      FYI='Quintiere, Fire Behavior',

      SPECIFIC_HEAT=0.84,

      CONDUCTIVITY=0.76,

      DENSITY=2700.0/

&MATL ID='CONCRETE',

      FYI='Medium weight concrete, http://people.bath.ac.uk/absmaw/BEnv1/properties.pdf',

      SPECIFIC_HEAT=1.0,

      CONDUCTIVITY=0.51,

      DENSITY=1400.0/

&SURF ID='PLASTERBOARD',

      FYI='Properties From X',

      COLOR='SANDY BROWN',

      DEFAULT=.TRUE.,

      MATL_ID(1,1)='GYPSUM',

      MATL_MASS_FRACTION(1,1)=1.0,

      THICKNESS(1)=0.025/

&SURF ID='GLASS',

      RGB=176,224,230,

      TRANSPARENCY=0.2,

      MATL_ID(1,1)='GLASS01',

      MATL_MASS_FRACTION(1,1)=1.0,

      THICKNESS(1)=0.01/

&SURF ID='CONCRETE',

      COLOR='GRAY',

      MATL_ID(1,1)='CONCRETE',

      MATL_MASS_FRACTION(1,1)=1.0,

      THICKNESS(1)=0.012/

&SURF ID='BURNER01',

      RGB=255,50,46,

      HRRPUA=125.0,

      RAMP_Q='BURNER01_RAMP_Q',

      TMP_FRONT=600.0/

&RAMP ID='BURNER01_RAMP_Q', T=0.0, F=0.0/

&RAMP ID='BURNER01_RAMP_Q', T=5.0, F=6.0E-4/

&RAMP ID='BURNER01_RAMP_Q', T=10.0, F=2.4E-3/

&RAMP ID='BURNER01_RAMP_Q', T=15.0, F=5.4E-3/

&RAMP ID='BURNER01_RAMP_Q', T=20.0, F=9.6E-3/

&RAMP ID='BURNER01_RAMP_Q', T=25.0, F=0.015/

&RAMP ID='BURNER01_RAMP_Q', T=30.0, F=0.0216/

&RAMP ID='BURNER01_RAMP_Q', T=35.0, F=0.0294/

&RAMP ID='BURNER01_RAMP_Q', T=40.0, F=0.0384/

&RAMP ID='BURNER01_RAMP_Q', T=45.0, F=0.0486/

&RAMP ID='BURNER01_RAMP_Q', T=50.0, F=0.06/

&RAMP ID='BURNER01_RAMP_Q', T=55.0, F=0.0726/

&RAMP ID='BURNER01_RAMP_Q', T=60.0, F=0.0864/

&RAMP ID='BURNER01_RAMP_Q', T=65.0, F=0.1014/

&RAMP ID='BURNER01_RAMP_Q', T=70.0, F=0.1176/

&RAMP ID='BURNER01_RAMP_Q', T=75.0, F=0.135/

&RAMP ID='BURNER01_RAMP_Q', T=80.0, F=0.1536/

&RAMP ID='BURNER01_RAMP_Q', T=85.0, F=0.1734/

&RAMP ID='BURNER01_RAMP_Q', T=90.0, F=0.1944/

&RAMP ID='BURNER01_RAMP_Q', T=95.0, F=0.2166/

&RAMP ID='BURNER01_RAMP_Q', T=100.0, F=0.24/

&RAMP ID='BURNER01_RAMP_Q', T=105.0, F=0.2646/

&RAMP ID='BURNER01_RAMP_Q', T=110.0, F=0.2904/

&RAMP ID='BURNER01_RAMP_Q', T=115.0, F=0.3174/

&RAMP ID='BURNER01_RAMP_Q', T=120.0, F=0.3456/

&RAMP ID='BURNER01_RAMP_Q', T=125.0, F=0.375/

&RAMP ID='BURNER01_RAMP_Q', T=130.0, F=0.4056/

&RAMP ID='BURNER01_RAMP_Q', T=135.0, F=0.4374/

&RAMP ID='BURNER01_RAMP_Q', T=140.0, F=0.4704/

&RAMP ID='BURNER01_RAMP_Q', T=145.0, F=0.5046/

&RAMP ID='BURNER01_RAMP_Q', T=150.0, F=0.54/

&RAMP ID='BURNER01_RAMP_Q', T=155.0, F=0.5766/

&RAMP ID='BURNER01_RAMP_Q', T=160.0, F=0.6144/

&RAMP ID='BURNER01_RAMP_Q', T=165.0, F=0.6534/

&RAMP ID='BURNER01_RAMP_Q', T=170.0, F=0.6936/

&RAMP ID='BURNER01_RAMP_Q', T=175.0, F=0.735/

&RAMP ID='BURNER01_RAMP_Q', T=180.0, F=0.7776/

&RAMP ID='BURNER01_RAMP_Q', T=185.0, F=0.8214/

&RAMP ID='BURNER01_RAMP_Q', T=190.0, F=0.8664/

&RAMP ID='BURNER01_RAMP_Q', T=195.0, F=0.9126/

&RAMP ID='BURNER01_RAMP_Q', T=200.0, F=0.96/

&RAMP ID='BURNER01_RAMP_Q', T=205.0, F=1.0086/

&RAMP ID='BURNER01_RAMP_Q', T=210.0, F=1.0584/

&RAMP ID='BURNER01_RAMP_Q', T=215.0, F=1.1094/

&RAMP ID='BURNER01_RAMP_Q', T=220.0, F=1.1616/

&RAMP ID='BURNER01_RAMP_Q', T=225.0, F=1.215/

&RAMP ID='BURNER01_RAMP_Q', T=230.0, F=1.2696/

&RAMP ID='BURNER01_RAMP_Q', T=235.0, F=1.4646/

&RAMP ID='BURNER01_RAMP_Q', T=240.0, F=1.6596/

&RAMP ID='BURNER01_RAMP_Q', T=245.0, F=1.8546/

&RAMP ID='BURNER01_RAMP_Q', T=250.0, F=2.0496/

&RAMP ID='BURNER01_RAMP_Q', T=255.0, F=2.2446/

&RAMP ID='BURNER01_RAMP_Q', T=260.0, F=2.4396/

&RAMP ID='BURNER01_RAMP_Q', T=265.0, F=2.6346/

&RAMP ID='BURNER01_RAMP_Q', T=270.0, F=2.8296/

&RAMP ID='BURNER01_RAMP_Q', T=275.0, F=3.0246/

&RAMP ID='BURNER01_RAMP_Q', T=280.0, F=3.2196/

&RAMP ID='BURNER01_RAMP_Q', T=285.0, F=3.4146/

&RAMP ID='BURNER01_RAMP_Q', T=290.0, F=3.6096/

&RAMP ID='BURNER01_RAMP_Q', T=295.0, F=3.8046/

&RAMP ID='BURNER01_RAMP_Q', T=300.0, F=4.0/

&RAMP ID='BURNER01_RAMP_Q', T=1500.0, F=4.0/

&OBST ID='rh fire room wall', XB=22.4,23.0,19.3,25.3,0.0,4.5, COLOR='CYAN', SURF_ID='GLASS'/ 

&OBST ID='lift lower block', XB=9.7,10.2,9.3,10.4,0.0,3.0, SURF_ID='PLASTERBOARD'/ 

&OBST ID='lift mid block', XB=9.7,10.2,11.3,12.6,0.0,3.0, SURF_ID='PLASTERBOARD'/ 

&OBST ID='lift top block', XB=9.7,10.2,13.5,16.6,0.0,3.0, SURF_ID='PLASTERBOARD'/ 

&OBST ID='Stair top wall block', XB=12.5,15.3,15.6,16.6,-6.0,4.6, SURF_ID='PLASTERBOARD'/ 

&OBST ID='Stair RH wall', XB=14.9,15.3,9.3,16.6,-6.0,4.6, RGB=240,240,240, TRANSPARENCY=0.094118, SURF_ID='PLASTERBOARD'/ 

&OBST ID='Stair lower wall', XB=12.5,14.9,9.3,10.5,-6.0,4.6, RGB=240,240,240, TRANSPARENCY=0.094118, SURF_ID='PLASTERBOARD'/ 

&OBST ID='landing 0', XB=12.5,14.9,10.5,12.1,-0.3,0.0, SURF_ID='CONCRETE'/ 

&OBST ID='landing -1', XB=12.5,14.9,10.5,12.1,-3.3,-3.0, SURF_ID='CONCRETE'/ 

&OBST ID='mid-landing -1', XB=12.5,14.9,14.6,15.6,-1.8,-1.5, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 01', XB=12.5,13.6,12.1,12.6,-3.0,-2.8, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 02', XB=12.5,13.6,12.5,13.0,-2.8,-2.6, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 03', XB=12.5,13.6,12.9,13.5,-2.6,-2.4, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 04', XB=12.5,13.6,13.4,13.9,-2.4,-2.2, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 05', XB=12.5,13.6,13.8,14.2,-2.2,-2.0, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 06', XB=12.5,13.6,14.1,14.6,-2.0,-1.8, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 07', XB=12.5,13.6,14.5,14.9,-1.8,-1.6, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 08', XB=13.8,14.9,12.1,12.6,-0.3,-0.1, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 09', XB=13.8,14.9,12.5,13.0,-0.5,-0.3, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 10', XB=13.8,14.9,12.9,13.5,-0.7,-0.5, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 11', XB=13.8,14.9,13.4,13.9,-0.9,-0.7, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 12', XB=13.8,14.9,13.8,14.2,-1.1,-0.9, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 13', XB=13.8,14.9,14.1,14.6,-1.3,-1.1, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 14', XB=13.8,14.9,14.5,14.9,-1.5,-1.3, SURF_ID='CONCRETE'/ 

&OBST ID='Fire bed obstruction', XB=16.4,18.4,20.0,22.0,0.0,0.2, SURF_IDS='BURNER01','INERT','INERT'/ 

&OBST ID='Obstruction', XB=12.6,14.9,18.0,18.9,0.0,4.5, SURF_ID='PLASTERBOARD'/ 

&OBST ID='Obstruction', XB=6.8,14.9,16.6,18.4,3.0,4.5, RGB=240,240,240, TRANSPARENCY=0.117647, SURF_ID='PLASTERBOARD'/ 

&OBST ID='fire room door', XB=10.5,11.6,18.2,18.4,2.1,3.0, SURF_ID='PLASTERBOARD'/ 

&OBST ID='fire room door', XB=11.9,12.6,18.0,18.4,0.0,3.0, SURF_ID='PLASTERBOARD'/ 

&OBST ID='fire room door', XB=6.8,10.3,18.0,18.4,0.0,3.0, SURF_ID='PLASTERBOARD'/ 

&OBST ID='fire room door', XB=10.5,11.6,18.2,18.4,0.0,2.1, RGB=207,47,61, SURF_ID='PLASTERBOARD', CTRL_ID='invert'/ 

&OBST ID='fire room door', XB=10.3,10.5,18.2,18.4,0.0,3.0, SURF_ID='PLASTERBOARD'/ 

&OBST ID='fire room door', XB=11.6,11.9,18.2,18.4,0.0,3.0, SURF_ID='PLASTERBOARD'/ 

&OBST ID='WC filler block', XB=6.8,10.0,18.4,25.6,0.0,4.5, SURF_ID='PLASTERBOARD'/ 

&OBST ID='top fire room wall', XB=10.0,23.0,25.3,25.6,0.0,4.5, COLOR='CYAN', SURF_ID='GLASS'/ 

&OBST ID='stair door LH', XB=12.1,12.5,10.8,11.3,1.526557E-15,2.1, RGB=213,25,14, SURF_ID='PLASTERBOARD', CTRL_ID='Stair door LH timer'/ 

&OBST ID='stair enclosure walls', XB=12.1,12.5,10.4,11.3,-6.0,1.526557E-15, SURF_ID='PLASTERBOARD'/ 

&OBST ID='stair enclosure walls', XB=12.1,12.5,11.3,16.6,-6.0,4.6, SURF_ID='PLASTERBOARD'/ 

&OBST ID='stair enclosure walls', XB=12.1,12.5,9.3,10.4,-6.0,4.6, SURF_ID='PLASTERBOARD'/ 

&OBST ID='stair enclosure walls', XB=12.1,12.5,10.4,11.3,2.1,4.6, SURF_ID='PLASTERBOARD'/ 

&OBST ID='stair door RH', XB=12.1,12.5,10.4,10.8,1.526557E-15,2.1, RGB=213,25,14, SURF_ID='PLASTERBOARD', CTRL_ID='Stair door RH timer'/ 

&OBST ID='stair AOV', XB=13.0,14.0,12.0,13.0,4.5,4.7, RGB=240,24,7, SURF_ID='CONCRETE', CTRL_ID='invert4'/ 

&OBST ID='stair ceiling', XB=12.5,13.0,12.0,13.0,4.5,4.7, SURF_ID='CONCRETE'/ 

&OBST ID='stair ceiling', XB=12.5,14.9,10.5,12.0,4.5,4.7, SURF_ID='CONCRETE'/ 

&OBST ID='stair ceiling', XB=12.5,14.9,13.0,15.6,4.5,4.7, SURF_ID='CONCRETE'/ 

&OBST ID='stair ceiling', XB=14.0,14.9,12.0,13.0,4.5,4.7, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 01', XB=12.5,13.6,12.1,12.6,-6.0,-5.8, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 02', XB=12.5,13.6,12.5,13.0,-5.8,-5.6, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 03', XB=12.5,13.6,12.9,13.5,-5.6,-5.4, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 04', XB=12.5,13.6,13.4,13.9,-5.4,-5.2, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 05', XB=12.5,13.6,13.8,14.2,-5.2,-5.0, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 06', XB=12.5,13.6,14.1,14.6,-5.0,-4.8, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 07', XB=12.5,13.6,14.5,14.9,-4.8,-4.6, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 08', XB=13.8,14.9,12.1,12.6,-3.3,-3.1, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 09', XB=13.8,14.9,12.5,13.0,-3.5,-3.3, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 10', XB=13.8,14.9,12.9,13.5,-3.7,-3.5, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 11', XB=13.8,14.9,13.4,13.9,-3.9,-3.7, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 12', XB=13.8,14.9,13.8,14.2,-4.1,-3.9, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 13', XB=13.8,14.9,14.1,14.6,-4.3,-4.1, SURF_ID='CONCRETE'/ 

&OBST ID='Stair 14', XB=13.8,14.9,14.5,14.9,-4.5,-4.3, SURF_ID='CONCRETE'/ 

&OBST ID='mid-landing -1', XB=12.5,14.9,14.6,15.6,-4.8,-4.5, SURF_ID='CONCRETE'/ 

&VENT ID='fire supply air vent_01', SURF_ID='HVAC', XB=22.4,22.4,19.5,21.5,0.1,0.8/ 

&VENT ID='fire supply air vent_02', SURF_ID='HVAC', XB=17.4,19.4,25.3,25.3,0.1,0.8/ 

&VENT ID='Mesh Vent: Stair [XMAX]', SURF_ID='OPEN', XB=15.3,15.3,9.3,16.6,4.6,6.4/ 

&VENT ID='Mesh Vent: Stair [XMIN]', SURF_ID='OPEN', XB=12.1,12.1,9.4,16.6,4.6,6.4/ 

&VENT ID='Mesh Vent: Stair [XMIN]', SURF_ID='OPEN', XB=12.1,12.1,9.3,9.4,4.6,6.4/ 

&VENT ID='Mesh Vent: Stair [YMAX]', SURF_ID='OPEN', XB=12.1,15.3,16.6,16.6,4.6,6.4/ 

&VENT ID='Mesh Vent: Stair [YMIN]', SURF_ID='OPEN', XB=12.1,15.3,9.3,9.3,4.6,6.4/ 

&VENT ID='Mesh Vent: Stair [ZMAX]', SURF_ID='OPEN', XB=12.1,15.3,9.3,16.6,6.4,6.4/ 

&VENT ID='Vent #1', SURF_ID='OPEN', XB=12.1,15.3,9.3,16.6,6.4,6.4/ 

&VENT ID='VT_MainExtract_Corridor', SURF_ID='HVAC', XB=12.1,12.1,9.6,10.2,1.8,2.8, COLOR='BLUE'/ 

&VENT ID='Natural_Vent', SURF_ID='HVAC', XB=13.0,13.7,18.0,18.0,1.8,2.8/ 

&HVAC ID='Node08', TYPE_ID='NODE', DUCT_ID='Duct', VENT_ID='fire supply air vent_01'/

&HVAC ID='Node09', TYPE_ID='NODE', DUCT_ID='Duct', AMBIENT=.TRUE., XYZ=28.0,19.270702,2.25/

&HVAC ID='Duct', TYPE_ID='DUCT', AREA=1.4, PERIMETER=5.4, LOSS=1.0,1.0, NODE_ID='Node08','Node09', ROUGHNESS=0.0, LENGTH=6.009257/

&HVAC ID='Node06', TYPE_ID='NODE', DUCT_ID='Duct04', VENT_ID='fire supply air vent_02'/

&HVAC ID='Node07', TYPE_ID='NODE', DUCT_ID='Duct04', AMBIENT=.TRUE., XYZ=19.629298,31.0,2.25/

&HVAC ID='Duct04', TYPE_ID='DUCT', AREA=1.4, PERIMETER=5.4, LOSS=1.0,1.0, NODE_ID='Node06','Node07', ROUGHNESS=0.0, LENGTH=6.102555/

&HVAC ID='Node_MainExtract_Corridor', TYPE_ID='NODE', DUCT_ID='Duct_MainExtract_Damper', VENT_ID='VT_MainExtract_Corridor'/

&HVAC ID='Node_MainExtract_Internal', TYPE_ID='NODE', DUCT_ID='Duct_MainExtract_Damper','Duct_MainExtract_Fan', XYZ=17.6,10.2,3.0/

&HVAC ID='Node_MainExtract_Ambient', TYPE_ID='NODE', DUCT_ID='Duct_MainExtract_Fan', AMBIENT=.TRUE., XYZ=22.6,10.2,3.0/

&HVAC ID='Duct_MainExtract_Damper', TYPE_ID='DUCT', AREA=1.2, PERIMETER=3.4, DAMPER=.TRUE., LOSS=1.0,1.0, NODE_ID='Node_MainExtract_Corridor','Node_MainExtract_Internal', ROUGHNESS=0.0, LENGTH=5.552477, DEVC_ID='TIMER->OUT'/

&HVAC ID='Duct_MainExtract_Fan', TYPE_ID='DUCT', AREA=0.6, PERIMETER=3.4, FAN_ID='Fan_MainExtract01', LOSS=1.0,1.0, NODE_ID='Node_MainExtract_Internal','Node_MainExtract_Ambient', ROUGHNESS=0.0, LENGTH=5.0, DEVC_ID='TIMER->OUT'/

&HVAC ID='Node_Natural_Ext', TYPE_ID='NODE', DUCT_ID='Duct_Natural_Inlet', AMBIENT=.TRUE., XYZ=17.0,21.0,5.5/

&HVAC ID='Duct_Natural_Inlet', TYPE_ID='DUCT', AREA=0.65, PERIMETER=3.6, DAMPER=.TRUE., LOSS=1.0,1.0, NODE_ID='Node_Natural_Int','Node_Natural_Ext', ROUGHNESS=0.0, LENGTH=5.706356, DEVC_ID='TIMER->OUT'/

&HVAC ID='Node_Natural_Int', TYPE_ID='NODE', DUCT_ID='Duct_Natural_Inlet', VENT_ID='Natural_Vent'/

&HVAC ID='Fan_MainExtract01', TYPE_ID='FAN', TAU_FAN=-10.0, MAX_FLOW=8.0, MAX_PRESSURE=50.0/

&SLCF QUANTITY='TEMPERATURE', PBX=17.0/

&SLCF QUANTITY='TEMPERATURE', PBZ=1.5/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBZ=1.5/

&SLCF QUANTITY='VISIBILITY', PBZ=1.5/

&SLCF QUANTITY='TEMPERATURE', PBZ=2.0/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBZ=2.0/

&SLCF QUANTITY='VISIBILITY', PBZ=2.0/

&SLCF QUANTITY='PRESSURE', PBZ=1.5/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBY=11.0/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBX=11.0/

&SLCF QUANTITY='PRESSURE', PBX=11.0/

&SLCF QUANTITY='VISIBILITY', PBX=11.0/

&SLCF QUANTITY='TEMPERATURE', PBX=13.4/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBX=13.4/

&SLCF QUANTITY='VISIBILITY', PBX=13.4/

&SLCF QUANTITY='TEMPERATURE', PBZ=3.0/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBZ=3.0/

&SLCF QUANTITY='VISIBILITY', PBZ=3.0/

&SLCF QUANTITY='TEMPERATURE', PBZ=3.5/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBZ=3.5/

&SLCF QUANTITY='VISIBILITY', PBZ=3.5/

&SLCF QUANTITY='TEMPERATURE', PBZ=4.0/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBZ=4.0/

&SLCF QUANTITY='VISIBILITY', PBZ=4.0/

&SLCF QUANTITY='PRESSURE', PBZ=2.0/

&SLCF QUANTITY='PRESSURE', PBZ=2.5/

&SLCF QUANTITY='PRESSURE', PBZ=3.0/

&SLCF QUANTITY='PRESSURE', PBZ=3.5/

&SLCF QUANTITY='PRESSURE', PBZ=4.0/

&SLCF QUANTITY='TEMPERATURE', PBY=24.0/

&SLCF QUANTITY='TEMPERATURE', PBY=18.0/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBY=18.0/

&SLCF QUANTITY='PRESSURE', PBY=11.0/

&SLCF QUANTITY='TEMPERATURE', PBY=11.0/

&SLCF QUANTITY='VISIBILITY', PBY=11.0/

&SLCF QUANTITY='TEMPERATURE', PBZ=0.5/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBZ=0.5/

&SLCF QUANTITY='VISIBILITY', PBZ=0.5/

&SLCF QUANTITY='PRESSURE', PBZ=0.5/

&SLCF QUANTITY='PRESSURE', PBY=21.0/

&SLCF QUANTITY='TEMPERATURE', PBY=21.0/

&SLCF QUANTITY='VISIBILITY', PBY=21.0/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBY=21.0/

&SLCF QUANTITY='PRESSURE ZONE', PBZ=0.5/

&SLCF QUANTITY='PRESSURE', PBY=10.0/

&SLCF QUANTITY='TEMPERATURE', PBY=10.0/

&SLCF QUANTITY='VISIBILITY', PBY=10.0/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBY=10.0/

&TAIL /

[Randy McDermott]

Tom,

Out of curiosity, can you attach the file if you change the extension to ".txt" ?  I thought this was only a GitHub thing, but maybe Google has adopted this convention now as well.

--
You received this message because you are subscribed to the Google Groups "FDS and Smokeview Discussions" group.
To unsubscribe from this group and stop receiving emails from it, send an email to fds-smv+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/fds-smv/1cfb6117-dbc5-42a7-9676-12e8d59b7d8an%40googlegroups.com.

[Tom Miles]

Hi Randy,

Yes that seems to work, see attached...

[Randy McDermott]

Thanks!  Now we just need to get the word out... I'll add this to the welcome message.

To view this discussion on the web visit https://groups.google.com/d/msgid/fds-smv/40bdad3b-927e-49fc-87d8-97505044655dn%40googlegroups.com.

[dr_jfloyd]

I'll run your file. A few comments just looking at it:

In the fire room your two natural air vents are both at the floor. HVAC only flows one direction at a time and both these vents will see more or less the same pressure based on the ZONE pressure and their elevation. The fire room oscillation may due to interactions between the vent flow and the fire size.  Vents flow in and you mix fuel and air better and the fire size increases temporarily. This increases the pressure and stops / slows the vent flow. Now fuel and air doesn't mix as quickly and the fire size drops. This drops the pressure and starts/increases the vent flow.

Your fuel has a molecular weight of over 100 g/mol.  We note in the User's Guide that high molecular weight fuels and the assumption of gamma=1.4 for undefined species do not play well together.  Suggest normalizing the fuel chemistry to a lower MW.

You have no leakage in your pressure zones. Any small velocity error at the walls or changes in internal temperature will cause pressure changes that have no where to go if all HVAC vents are closed. This might be a contributing factor.

[Tom Miles]

Thank you Jason, your comments are very helpful. A few thoughts of my own:

1. Your point about the natural air vents at floor level makes complete sense. The reason they are modelled this way is basically just a strategic move in order to retain as much heat and smoke in the model as possible without having to open a window at a higher level. Does this effectively mean that this low-level HVAC vent methodology might always be a problem unless the fire compartment contains other openings / leakage paths?
2. Going back to an earlier point in my initial message, if I was to replace natural HVAC vents with simple OPEN vents, I would have to remove ZONEs as well. Would this mean that I could no longer use the HVAC extract (with MAX_FLOW) too? If I could still use the HVAC extract, that would be the main thing for now as I would be content with OPEN vents acting as natural inlets.
3.  Regarding your final point, I can see how that relates to the fire compartment when the door shuts (where the only HVAC vents are the low-level inlets and I suppose it ties into your first point too). When it comes to the lobby, there is an extract and an inlet, so no HVAC vents are closed per se. Does this point relate to the lobby? Note similar pressure oscillations and spikes are seen in both the fire compartment and lobby, despite the differing HVAC configurations.
4. FYI @Kevin, I ran the model without a fire and the same pressure problems occur, indicating that it's my HVAC setup that's the problem.

Cheers,

Tom

[dr_jfloyd]

I think having two large vents like that at the floor is not helping. You can only get flow in one direction with HVAC and these vents will likely be both flowing in or out at the same time. If all you care about is getting the correct total HRR and smoke production you could set SUPPRESSION=.FALSE. so you can use all the air in the fire room plus air in the hallway when the door is open. That alone might get you to the point where you can sustain the fire without needing large vents (though you would need to add leakage to the fire room). As it is now those large vents are having going to a significant impact on the pressurization of the fire room by the fire that would not reflect a real building. 

HVAC will still run with OPEN vents; however, since the room background pressure will no longer change the pressure in the room will close ambient at the exhaust location and you are just going to wind up getting close to the max flow.

I ran a case last night where I changed your fire vents into two 4 m x 0.2 m vents one at the floor and one at the ceiling. I got rid of the PRESSURE_RELAX_TIME. The fire room no longer saw large pressure swings and oscillations in the hallway dropped to quite a bit. Your exhaust fan is 8 m3/s.  You have ~100 m3 of air volume in the hallway between the fire room and the stair. This is 250 air changes per hour which is a lot of flow for such a small volume. Is this a realistic flow for such a small space? Over the area of the stair door, the pressure drop your system is going to impose is going to add a lot to the force needed to open the exit stair door.

[Tom Miles]

Thank you once again Jason for taking the time to look at this in detail.

Please note that the two inlet vents in the fire compartment isn't my typical methodology, this was just one scenario I considered in an attempt to reduce the pressure oscillation in the fire compartment (the oscillation was already occuring with just one vent, which in itself was smaller than either of the two in the scenario you've seen).

Thanks for clarifying re. using HVAC extract with OPEN vents. The reason why the MAX_FLOW is so high is because this is the top storey of a tall building which has varying floor configurations below, some of which need extract rates close to the maximum stated (it is the same extract shaft serving all floors). In turn, this is why I specified MAX_PRESSURE=50, as that would (hopefully!) limit pressure differentials to within tenable limits for escaping occupants. In reality, for this floor I only expected to see the fan achieve 3-4 m3/s, which is what my results are showing. Therefore, removing ZONEs and using OPEN vents doesn't seem to be an option at the moment if I'm aiming to be consistent across all models for this particular building. It appears that given all this, I will have to persevere with ZONEs for now and try to resolve the issue behind the pressure oscillations.

Out of curiosity, you said that the pressure oscillations in the lobby reduced quite a bit in your model - do you have a rough number that you could put on that? I assume from your wording that it helped but didn't solve the issue to the extent of being able to class the problem as solved?

Cheers,

Tom

[dr_jfloyd]

< 40 Pa

Do dampers only open on the floor with a fire? I'm not sure what your exact objective is, but if you are trying to prove to an AHJ that this is a valid system design to keep smoke clear AND avoid high door opening forces, then you should try to accurately model both the fan and the duct losses rather than just assuming values for LOSS, MAX_FLOW, and MAX_PRESSURE. For example your supply duct loss is 1; however, in reality this would be a louvered opening through a wall into a tee connecting to the supply shaft that then goes out the roof where it likely has some kind of elbow or something to turn the flow sideways to limit water entrance. 

[Tom Miles]

Thanks. Yes, dampers only open on the fire floor.

Our intention isn't to validate the detailed elements of the smoke control design (e.g. duct lengths, losses, area etc.), rather the strategic performance criteria required for the system to keep the stair clear of smoke. We use MAX_PRESSURE in the hope that when it comes to reviewing the model results, the model hasn't failed the pressure tenability criterion (< 50 Pa). Thus, in effect the extract rate we obtain from the model results is more important than the MAX_FLOW, as we're not realistically expecting 8m3/s to be reached (especially on this floor!). It's just that all models for the floors below are run using a MAX_FLOW of 8m3/s, some get close to achieving it whilst others don't, so we're just trying to be as consistent as possible. I understand from a brief discussion with you previously that if you're using HVAC with all ducts/nodes leading to ambient and have no interest in validating the smoke control design beyond the damper on the wall, there's little benefit to actually using HVAC at all (i.e. you might as well specify your extract rates explicitly at the damper rather than relying on MAX_FLOW and MAX_PRESSURE to work it out for you) - I'll heed this advice on future projects!

[Tom Miles]

Hi Jason,

Just to update you - I've run a couple of models with two smaller 0.6m2 inlet vents/ducts at high and low levels (have staggered them in one scenario and have them directly aligned in another). I've also tried with PRESSURE_RELAX_TIME reset to default as you did. Interestingly, the pressure oscillations occur much sooner (at ~ 25 seconds), so this is even before the doors open. I'm intrigued to find out why we're seeing such different results...

[dr_jfloyd]

I took your case and did the following:

-added leakage to the three rooms (made three copies of the PLASTERBOARD SURF to set LEAK_PATH with). I'd did this doing a rough calculation the room surface areas and adding 1E-4 m2/m2 of leakage to the floor in each room.

-normalized the fire chemistry by dividing C,H,O,N by 10 to avoid a high molecular weight

-removed the air vents from the fire room

-set SUPPRESSION=.FALSE.

The case is attached. Note I didn't keep your outputs; I simplified them down for the purpose of just looking at the HVAC behavior. I ran it out for 600 s and it is very well behaved now using the current release of FDS.