Retrotec DM-2 - Manual (Page 63)

Page 63 of 72
©Retrotec Inc. 2012
Appendix C: Errors occur in estimated flow if gauge and
actual “n” don’t match
If a gauge has the extrapolation or flow exponent “n” set to an assumed value but the actual exponent
(a true measured exponent value for the building) differs, the flow values estimated by the gauge
when using the @ Pressure feature will be off by an error amount. The tables below show the percent
error that can result from entering an incorrect exponent value in the gauge and using the [@
Pressure] function.
If the “n” value on the gauge is set to 0.65 and the actual enclosure n is different, a small error, as
shown in Table 15 will result if the [@ Pressure] function is used at the Achieved Pressure to estimate
result at 50 Pa.
Table 15: Errors in Estimated Flow at 50 Pa if gauge "n"= 0.65 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 -21.4% -14.9% -7.7% 0.0% 8.4% 17.5%
15 -16.5% -11.3% -5.8% 0.0% 6.2% 12.8%
20 -12.8% -8.8% -4.5% 0.0% 4.7% 9.6%
25 -9.9% -6.7% -3.4% 0.0% 3.5% 7.2%
30 -7.4% -5.0% -2.5% 0.0% 2.6% 5.2%
35 -5.2% -3.5% -1.8% 0.0% 1.8% 3.6%
40 -3.3% -2.2% -1.1% 0.0% 1.1% 2.3%
45 -1.6% -1.0% -0.5% 0.0% 0.5% 1.1%
50 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
55 1.4% 1.0% 0.5% 0.0% -0.5% -0.9%
60 2.8% 1.8% 0.9% 0.0% -0.9% -1.8%
65 4.0% 2.7% 1.3% 0.0% -1.3% -2.6%
70 5.2% 3.4% 1.7% 0.0% -1.7% -3.3%
If the “n” value on the gauge is set to 0.60 and the enclosure n is different, an error, as shown in Table
16 will result if the [@ Pressure] function is used at the Achieved Pressure to estimate result at 50 Pa.
Table 16: 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%