Retrotec USACE - Manual (Page 449)

GL1
GLOSSARY
ACH @ 50 Pa. ACH @ 50 Pa is cfm 50 × 60 minutes/hour, divided by the
house volume. It is also referred to as “air changes at 50 Pa” or “ACH
50.”
air barrier. The air barrier defi nes the surface that separates the inside air
from the outside air. Generally, this should be an inner barrier such as
sheet rock, which prevents air from moving through the insulation. The
air barrier should be in contact with the insulation. The air barrier should
not be outside the insulation.
air leakage. Pertains to how leaky an enclosure may be. See airtightness.
airtightness. Pertains to how free air leakage may be in an enclosure. In actual
fact, measurements can only be made of air leakage rates, not airtightness
itself, so one could think of these terms as being opposites. In spite of the
confusion, the terms are used interchangeably.
average bias pressure. A series of 12 test pressure points that are averaged
to produce a single value.
background pressure. See bias pressure.
baseline pressure. A method of reading or determining the background or
bias pressure by having a digital gauge accumulate readings over an ad-
justable time period.
bias pressure. The pressure that exists when the enclosure has been prepared
for the test, but before the fan pressurization system is activated. There
is always some bias pressure due to stack, wind, fl ues, and active HVAC
systems. There are two components of bias pressure. A fi xed static offset
(usually due to stack or HVAC) and a fl uctuating pressure (usually due
to wind or elevator operation). In ASTM bias pressures are called “zero
fl ow pressures” for the pressure measured with zero fl ow going through
the door fan.
blower door. Commonly used term for a door fan, a calibrated fan capable
of measuring airfl ow. The door fan is temporarily mounted in a doorway,
hence the name. Door fans do not use blowers. A blower more accurately
describes an air-moving device of the squirrel cage variety; hence the
adjective “blower” does not normally apply to most door fans, which do
not use blowers.
building automation system (BAS). Similar to the building management
system (BMS) and energy management system (EMS). A digital control
system that is used to monitor and possibly control the function, opera-