I have another question about whether people have gotten wind speed to
have an effect on crack infiltration.
Below is an hourly report for a few hours of January 1st. I have a
building set up with each space's infiltration based on the crack
method, with an infiltration schedule of all 1.0s. Exterior walls are
set up with crack coefficients pretty high (leaky building) - the
coefficient is about 7.5, which corresponds to a 0.6" crack around the
entire perimeter of the wall (it's a leaky corrugated metal wall
construction).
This report is for a typical west (270) facing wall, about 45 feet by 8
ft tall. 70 feet below the neutral level. As expected, there is CFM
infiltration, which is great. The CFM values decrease as you go up the
building (12-story), which is perfect. Means the whole crack method vs
neutral height is working. However, there appears to be NO impact of
the infiltration based on wind speed. The CFM for this given wall is
entirely dependent on the OA DB temp, and does not change at all with
wind speed. See below. Highlighted areas show similar temp hours but
with varying wind speed. CFM for this 1st floor exterior wall doesn't
change at all with differing wind speeds.
I thought that the crack method was supposed to alter CFM based on wind
speed, but NOT alter based on difference in indoor and outdoor temp.
What am I doing wrong here? For a leaky building, wind speed SHOULD
have a greater impact on CFM than stack effect.
Var 4
Var 17
Var 19
Var 3
Var 4
Var 7
OA DB
Wind Spd
Wind direction
Outside air film U-value
Pressure diff due to wind velocity & stack effect
Crack method air flow for wall (cfm)
19
6
270
1.81016
0.109004
703.896
19
6
270
1.80501
0.109004
703.896
19
8
270
2.10433
0.109004
703.896
19
4
270
1.50129
0.109004
703.896
18
5
315
1.66397
0.111218
711.009
16
3
248
1.37812
0.115674
725.112
12
0
0
1.13297
0.1247
752.869
9
4
248
1.53612
0.13157
773.33
9
0
0
1.10755
0.13157
773.33
12
0
0
1.10909
0.1247
752.869
18
3
180
1.35996
0.111218
711.009
21
10
180
2.40378
0.104603
689.541
21
3
180
1.34907
0.104603
689.541
James Hansen, PE, LEED AP
