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9.6.2 Cabin air filter performances
Filter performance is defined according to the following
parameters :
g
Efficiency & dust holding capacity
The efficiency is the ratio of particles that are trap-
ped by the filtration process.
The efficiency is specified for a defined particle size.
In practice, a cabin filter must be capable of trap-
ping 100% of particles measuring 10µm in diameter
and between 10% and 30% of particles measuring
0.25µm in diameter.
The dust holding capacity is the quantity of solid
particles a filter can retain before a defined flow
resistance is reached, that is to say before the filter
is to be changed.
g
Pressure drop
The difference in flow resistance upstream and
downstream of the filter, is related to the air flow
resistance created by the filter; it is also known as
“head loss”.
The head loss depends on the filter soiling. The
filter must produce the lowest possible head loss
to optimise the air conditioning system perfor-
mances.
g
Gas absorption level
This feature is applicable to active carbon filters (CA
and PCA), it reflects the amount of gas that is ab-
sorbed by the filter media.
The cabin air filter design is a trade-off between the
pressure drop and the dust holding capacity, this to
assure the appropriate air flow in the cabin as well as
an efficient filtration process.
The service life of a filter corresponds to the maximum
amount of particles before clogging occurs.
The service life varies according to the use conditions
(surrounding pollution, frequent use of the A/C sys-
tem…)
9. The Heating
Ventilation and
Air Conditioning
unit (HVAC)
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