Constant concentration technique
A method of measuring ventilation rate whereby an automated sy stem injects
tracer gas at the rate required to maintain the concentration of tracer gas at a
fixed, predetermined level. The ventilation rate is proportional to the rate at
which the tracer gas must be injected.
Constant injection rate technique
A method of measuring ventilation rate whereby tracer is emitted continuously
at a uniform rate. The equilibrium concentration of tracer gas in air is
measured.
Contaminant
An unwanted airborne constituent that may reduce the acceptability of the air
quality.
Contaminant removal effectiveness
See ventilation efficiency.
Continuity equation (or mass balance)
Mathematical expression relating to the conservation of matter, an example of
which is the equation equating the flow of tracer gas into a space with the flow of
tracer gas out of a space. this particular equation is the basis for evaluating air
exchange rates from tracer gas measurement.
Damper
Adjustable plate in a duct for controlling the flow rate.
Decay rate technique
A method for measuring ventilation rate whereby a quantity of tracer gas is
released and the decrease in concentration measured as a function of time.
Deduction method
Multi-fan testin g method in which the pressure differential between two zones of
a building is changed step by step in order to obtain the leakage characteristics of
building elements in these zones.
Density
Ratio of the mass of a quantity of matter to its volume.
Depressurization
Term used to describe fan pressurization when a static under-pressure is
created within the building.
Differential pressure
See pressure differential.
Discharge coefficient
A dimensionless coefficient relating the mean flow rate through an opening to
an area and the corresponding pressure difference across the opening.
Displacement flow (or piston flow)
With this type of flow, incoming outdoor air displaces internal air without mixing.
Glossary 177
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