Tracer Gas Testing
Tracer gas testing
potentially provides useful information on building and HVAC performance
in several ways.
and characterization of air movement pathways.
In this testing protocol, air sampling is first performed to assess
if there is any background levels of tracer gas, typically sulfur hexafluoride
(SF6). After documenting that no measurable quantities of tracer are
present, a tracer gas release is initiated. Then if tracer gas is detected,
it will be from this release, and a pathway between two or more locations
in a building can be determined. If the measured tracer gas concentration
builds rapidly to an equilibrium value after the release and drops rapidly
after the release is terminated, then the pathway is short and direct.
If however, the measured tracer persists, or even continues to increase,
after the release has been terminated, then the pathway involves an
intermediate significant volume that acts as a reservoir for this transfer
of Ventilation rate. In this determination, the building
is initially does with a quantity of tracer and allowed to become well
mixed. Sampling is then performed over time to document the rate at
which the tracer concentrations decreases or “decays”. The
ventilation rate, in air changes per hour, can then be determined from
this tracer decay rate. This determination is especially useful in buildings
that have been evacuated since the monitoring of peak carbon dioxide
(CO2) cannot be used to determine the ventilation rates.
Determination of Volumetric Flow.
In this determination a measured quantity is released into the air stream
to be measured. Downstream of this release location, sampling is performed.
A calculation is then performed to determine what volume the tracer
needed to be diluted into to yield the tracer measurement obtained.
In this determination it is the pathway of air movement from an external
release, such as from a stack, which is evaluated to assess whether
this discharge is re-entering the building.