Retrotec FanTestic (ATTMA) - Manual (Page 32)

rev-2014-10-27
Page 32 of 58
©Retrotec Inc. 2011-2014
4.4.2.2 Uncertainty
This shows the % uncertainty for each of the results.
4.4.2.3 Air permeability at 50 Pa
This is the measured flow result for this data set divided by the above grade building envelope surface
area.
It is a useful method of adjusting (or normalizing) the leakage rate by the amount of envelope surface
through which air leakage can occur. This is the average air flow that would occur through one square
meter of envelope at a 50 Pascal pressure.
Experience has shown that for buildings with a flow/surface area result of 1.0 or higher, very large cost-
effective reductions in infiltration can often be achieved using door fan guided infiltration sealing and
insulation techniques. In the 0.5 to 1.0 range, it is often more difficult to achieve economical
improvements in airtightness.
If you did not enter an Envelope Area value in the building dimensions section, permeability will not be
calculated.
4.4.2.4 Equivalent leakage area at 50
This is the area of “holes” left in the building.
It is an aerodynamic equivalent area based on a sharp edged orifice, so it should be taken as an
approximate value.
4.4.2.5 Air changes at 50 Pa
The air change rate, also known as Air Changes per Hour (often ACH50 or n
50
) is another commonly used
measure of building air tightness. ACH50 is the number of complete air changes that will occur in one
hour when a 50 Pascal pressure is applied across the building envelope.
ACH at 50 Pa is a useful method of adjusting (or normalizing) the leakage rate by the size (volume) of the
building. If the building volume is not entered in the building dimensions section, “Air change rate” will
not be calculated.
ACH at 50 Pa = (m 3 /h) / building volume in cubic metres
4.5 View Graph of data in the Data set
Data in the set can be viewed on graphs – click on “Show Graphs”. The graph will open in its own
window, and allow users the resize as necessary.