Cannot reach 50 pa factors for houses – Retrotec Residential Pressure & Air Leakage User Manual
Page 65
Page 65 of 75
If the “n” value on the gauge is set to 0.60 and the building n is different, a small error, as shown in Table 22 will
result if the
[@ Pressure]
function is used at the Achieved Pressure to estimate a result at 50 Pa.
Table 22: Errors in Estimated Flow at 50 Pa if gauge "n" = 0.60 differs from actual n
Actual Flow Exponent (n) of Enclosure
0.50
0.55
0.60
0.65
0.70
0.75
Achieved
Pressure (Pa)
10
-14.9%
-7.7%
0.0%
8.4%
17.5%
27.3%
15
-11.3%
-5.8%
0.0%
6.2%
12.8%
19.8%
20
-8.8%
-4.5%
0.0%
4.7%
9.6%
14.7%
25
-6.7%
-3.4%
0.0%
3.5%
7.2%
11.0%
30
-5.0%
-2.5%
0.0%
2.6%
5.2%
8.0%
35
-3.5%
-1.8%
0.0%
1.8%
3.6%
5.5%
40
-2.2%
-1.1%
0.0%
1.1%
2.3%
3.4%
45
-1.0%
-0.5%
0.0%
0.5%
1.1%
1.6%
50
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
55
1.0%
0.5%
0.0%
-0.5%
-0.9%
-1.4%
60
1.8%
0.9%
0.0%
-0.9%
-1.8%
-2.7%
65
2.7%
1.3%
0.0%
-1.3%
-2.6%
-3.9%
70
3.4%
1.7%
0.0%
-1.7%
-3.3%
-4.9%
Achieved pressure is the actual maximum pressure achieved in the enclosure during the test.
Error = (
Pressure of Interest
Achieved Pressure
)
(Actual n−Assumed n)
In the tables, the Pressure of Interest is 50Pa, and Assumed n is 0.65 or 0.60
The actual flow exponent n for an enclosure can be calculated by measuring enclosure leakage at multiple
pressure differences, from 10 to 50 Pa, and determining the slope of the line on the graph of pressure versus
flow which will be linear if graphed on a log-log scale, and the slope will be n.
Cannot Reach 50 Pa Factors for houses
If you have a situation where you cannot reach the required 50 Pa during the test, there is a way to estimate the
flow at that pressure based on the measured pressure and flow you did achieve. This is the procedure the gauge
uses for extrapolating the flow at the required pressure when you use the
[@ Pressure]
key. The following
equation describes the relationship between the flow at the required pressure of 50 Pa and the actual measured
flow at the measured pressure:
Flow at 50 Pa = (Flow at measured pressure) ∗ (
50 Pa
measured pressure
)
n