Retrotec USACE - Manual (Page 325)

Appendix F F31
TABLE F5. DEVIATIONS FROM THE ASTM E 779-03 STANDARD
ASTM E 779-03 U.S. Army CE Protocol Reason for change
6.2.2
“accuracy of +/- 5% of measured
pressure.” The gage must have an accuracy of ± 1 %
or 0.5 Pa, whichever is greater and must
have had its calibration checked against a
NIST traceable standard within 2 years. Modern gauges are typically much more
accurate than the analog gauges that
ASTM was written to accommodate and
there is every reason to take advantage of
the increased accuracy.
8.4
“If the product of the absolute value
of the indoor/outdoor air temperature
difference multiplied by the building
height, gives a result greater than 200 m
o C (1180 ft °F), do not perform the test,
because the pressure difference induced
by the stack effect is too large to allow
accurate interpretation of the results.”
The protocol allows for a wider range
of heights and temperatures by limiting
bias pressure to 30% of the lowest test
pressure when testing both ways and
10% when testing one way. The ASTM requirement of 200 m o C
(1180 ft °F) would only permit four-story
buildings 14.6 m (48 ft) high to be tested
when the indoor/outdoor temperature
difference was less than 13.6
o C (25 °F),
which would be impractical. The Protocol
is both more stringent and more fl exible
due to the higher minimum test pressures
that tolerate higher bias pressures. The
ASTM requirement of 200 m
o C (1180
ft °F) produces a stack of about 4.2 Pa,
which is 42% of the lowest 10 Pa test
point whereas the Protocol permits a
maximum bias pressure (wind and stack)
of 30% of the lowest test pressure when
testing both ways and 10% when testing
one way. This results in a maximum
allowable bias pressure of 7.5 to 15 Pa
and 5 Pa for the Protocol.
8.5
“Preferred test conditions are wind speed
of 0 to 2 m/s [0 to 4 mph] and an outside
temperature from 5 to 35° C. [41 to
95° F.].” Preferred test condition superseded by
requirement to keep bias pressure within
limits. The ASTM preference of wind speeds less
than 4 mph and outside temperature
range from 5 to 35° C. [41 to 95° F]
would mean that the rescheduling of test
would be required in about 50% of all
cases. This is impractical and the more
robust procedure in the protocol takes
care of wind and temperature differences
by accurately measuring bias pressures
over a period of time and then requiring
that the air leakage measurements are
made over the same time period.
8.10
“…. Pressure difference shall be from 10
to 60 Pa…at least fi ve data points…” “Adjust the door fan speed to establish
a series of 12 equally spaced Building
Pressure Test Points where each Test Point
is an accumulation of at least 10 readings
taken over a time period that is at least
double the time taken to collect Bias
Pressure Test Points” Because results are required at 75 Pa,
taking data up to and including this point
of interest vastly increases accuracy and
repeatability. The Protocol is far more
stringent than ASTM yet with modern
equipment takes less effort than the old
manual way of taking readings.
8.13
“For each test, collect data for both
pressurization and de-pressurization.” Testing in both directions is preferred.
Testing from +/– 75 Pa to +/– 50 Pa is
acceptable because buildings tend to leak
slightly more under positive pressure. Testing in both directions results in
simpler and more repeatable tests.
Tests with trailer mounted fans or the
building’s HVAC systems may only be
possible in one direction and the protocol
allows for then to be used.