Site analysis
Applied to any tracer gas measurement technique where tracer gas concentrations
and air exchange rates are determined directly at the measurement building.
Smoke leak visualization
A method of detecting leaks in the building fabric by pressurizing the building
and using smoke to trace the paths followed by the leaking air.
Specific airflow rate (or air change rate)
The ratio of the volumetric rate at which air enters (or leaves) an enclosed space
divided by the volume of that space. Its inverse is the nominal time co nstant.
Specific leakage area
Equivalent leakage area expressed per unit floor area.
Stack effect
Pressure differential across a building envelope caused by differences in the
density of the air due to an indoor– outdoor temperature difference.
Step injection technique
Tracer gas measurement technique in which the tracer is injected at constant
rate, starting from a given time.
Supply ventilation
A system in which air is supplied to a space(s) so creating an internal positive
pressure. Air leaves the building through adventitious or purpose-provided
openings.
Tachometer
Instrument for measuring velocity or speed of rotation, used to evaluate the
speed of fans, this in turn is used to calibrate the fan in terms of airflow.
Often used in blower doors.
Thermography
The process of converting the heat emitted from an object into visible pictures.
Used to indicate and represent the temperature distribution over part of a
building envelope.
Tracer gas
A gas used at low concentration, together with an analyser, to determine airflow
rates or other related quantities.
Tracer gas analyser
Any instrument used to evaluate the concentration of tracer gas in a sample of
air.
Tracer gas injection
Any process by which tracer gas is released into a space.
Tracer gas sampling
Any process by which tracer gas or air containing tracer gas is sampled for
analysis.
184 Ventilation and Airflow in Buildings
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