Modelling Internal Door Leakage of Hot Combustion Products

[MScFire Student]

2 cases:

• Door closed                            - Leakage around edges = 0.0084m2, as per Klote & Milke: Principles of Smoke Management: Table 6.2.
• Door Partial Opened by 20% - Leakage = 0.378m2, as per calculation.

 

Setup both cases using FDS 6.2: 9.3.2: Localized Leakage approach by designating two &VENT, one for each side of the door, connected via &HVAC with TYPE_ID='LEAK' using AREA= 0.0084m2 and 0.378m2 respectively.

 

Question:

• For the partial open door you want to retain all the properties of the hot combustion products rushing through the 20% opening, therefore you should set LEAK_ENTHALPY=.TRUE. on the HVAC input?
• For the door edge leaks should you leave LEAK_ENTHALPY at default .FALSE. or set it to .TRUE. as well?

Anybody got any comments or suggestions?

[dr_jfloyd]

If you wish to preserve the enthalpy of the gas flowing through the leak, then yes you should set LEAK_ENTHALPY=.TRUE.

For a partially open door, little enthalpy from the gas flowing out will transfer to the door edge and door jamb. For a closed door, most of the leakage is probably from the bottom edge as the other edges have the door jamb to seal against and the bottom is either open or has a sweep attached to it. There will also be more heat loss as the pathlength around the door edge will be large in comparison to the width of the leak (0.0084 m^2 is about a 1 mm gap around the edge of the door vs. about 35 mm for a typical door thickness). 

[MScFire Student]

Thanks dr_jfoyd, that's kinda what I thought.

Quick question re setting up the leak. The SURF_ID has to be set for each VENT but it can't be 'HVAC', so what do you set it to?

Do you set it to the same SURF_ID as the original door?

[dr_jfloyd]

That is probably the most appropriate thing to do. For example, say you have a 10 cm grid and a 2 cm wide opening for the cracked door. In this case the majority of the wall surface area at the crack actually is the door.

[lvp]

Hi dr_jfoyd, MScFire Student

I did try to model a simple small leakage using localized leakages approach as described in FDS 6 user guide 9.3.2 page 108 but:

   *   it seems no smoke through the leakage as seen in smoke view

   *   when I set LEAK_ENTHALPY=.TRUE. to the HVAC input, the FDS did not run and have an Error: "Problem with HVAC line..."

Is there any problem with my input file? Your comment is much appreciated. I have attached the simple input file for your review.

Thanks in advanced.

Tun

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[dr_jfloyd]

Running your case as is gives the following error using FDS 6.2:

ERROR: Leakage path must have VENT2_ID defined. Ductnode ID: null (CHID: HVAC2)

If I fix that error and LEAK_ENTHALPY=.TRUE., your case runs fine.  Make sure you are running the latest version of FDS, the custom leakage inputs were a feature added to FDS 6.2.