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atwhaley / cfast

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Lower height of detector produces faster detection time #115

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
What steps will reproduce the problem?
1. Setup compartment of 16.2m x 12.6m x 3.5m
2. Add Med growth t2 fire in centre of compartment
3. Add heat/smoke alarm
4. Locate alarm 5.1m away from fire radially
5. Run simulation and note detector activation time 
6. Lower the height of the detector by 0.5m
7. Run simulation and note decreased detector activation

What is the expected output? What do you see instead?
The expected output should be an increased detection time for a lower detector 
height but the opposite occurs.  

What version of the product are you using? On what operating system?
I'm using CFAST 6.2.1 on Windows 8

Please provide any additional information below.
Can someone let me know if this is a bug or not or something inherent in the 
way the calculations are done?

Original issue reported on code.google.com by fok.laur...@gmail.com on 11 Jun 2014 at 1:27

GoogleCodeExporter commented 9 years ago 
What's your initial height for the detector?  Depending on the relative 
position of the fire and detector, I can see this happening since the detector 
is just doing a heat transfer calculation from all elements of the surroundings 
to the detector.  If the relative contribution to the heating of the detector 
by fire radiation goes up, the detection time can be expected to decrease.  If, 
on the other hand, the detector is located in the ceiling jet initially and 
then lowered out of the ceiling jet while not coming that much closer to the 
fire, the detection time should increase since the convective contribution to 
detector heating would go down.

I suspect this is an artifact of how CFAST does the heating calculation for 
this test case.  If you have an input file, we can examine it further.

Original comment by cfastdev@gmail.com on 25 Jun 2014 at 7:27

GoogleCodeExporter commented 9 years ago 
What's your initial height for the detector?  Depending on the relative 
position of the fire and detector, I can see this happening since the detector 
is just doing a heat transfer calculation from all elements of the surroundings 
to the detector.  If the relative contribution to the heating of the detector 
by fire radiation goes up, the detection time can be expected to decrease.  If, 
on the other hand, the detector is located in the ceiling jet initially and 
then lowered out of the ceiling jet while not coming that much closer to the 
fire, the detection time should increase since the convective contribution to 
detector heating would go down.

I suspect this is an artifact of how CFAST does the heating calculation for 
this test case.  If you have an input file, we can examine it further.

Original comment by cfastdev@gmail.com on 25 Jun 2014 at 7:30

GoogleCodeExporter commented 9 years ago 
With no response for six months, we'll close this for now.  You can post a new 
issue if you have additional information.

Original comment by cfastdev@gmail.com on 30 Dec 2014 at 3:21