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How To Know When To Change Your Air Conditioning
Filters
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Although we don't usually realize it,
we can actually reduce the running cost of a building by removing
the dust from the atmosphere. The furniture, walls and fittings are
preserved longer. It also improves the health of the occupants.
Removing dust is usually done by installing filters in the incoming
air stream or the circulating air stream. In air-conditioning
systems, these filters are installed at the air handling units or
AHU's.
How do we know when to replace the filters?
As more and more dust accumulates at the filters, the differential
pressures between the inlet and the outlet will increase. By
measuring the differential pressures, we will have a very good
indication of how much the filter has been choked by dusts. Persons
maintaining the air-conditioning plant should know at what
differential a filter should be replaced. Some of the dust particles
are so minute, that they cannot be seen by the naked eye. In all
appearances, the filter looks as good as new.
These are some factors to consider when determining when to change
the filter:
Mechanical strength of the filter
The final pressure of a filter is usually stated in the product.
That is the strength of the filtration medium. However, other
factors need to be considered - the strength of the filter walls,
frames and holders if not adequately designed can result in the
sagging of the filter housing that will result in leaks.
Changes in efficiency of the filter
This is particularly important in low efficiency filters. Their
efficiencies can be radically impaired as a result of high final
pressure losses. Particles that have been collected by the filter
can become detached and accompany the air stream. Fibrous particles
are less likely to become detached compared to granular particles.
Because of this, higher final pressure drops are permissible for the
former, although this should not exceed about 200 Pa in a
pre-filter.
With granular particles, the final pressure loss should not be
allowed to exceed 100 to 150 Pa.
Fine filters and HEPA filters are less sensitive to changes in
quality. In principle, they can be allowed to have a final pressure
loss up to the limit of their mechanical strength.
Permissible Air flow variations in the system
In this case, the flow pattern is more important than the particles
carried along the air stream. The permissible final pressure loss
here will depend on the total pressure and characteristics of the
fan and any other control facilities.
The filter will affect the air flow as a result of dust
accumulation. The filter has to be changed when the velocity of the
air in a laminar flow installation cannot be maintained or has
fallen below the required specifications.
Bacteriological reasons
Sometimes, the filters are replaced at regular intervals instead of
pre-defined pressure loss indications. This is to prevent
accumulation of bacteria and other microorganisms.
Suitable time window periods
Filters are often changed to coincide with pre-planned plant
shutdown periods. In these cases, production disturbances are
minimized. For example they can be arranged to be changed during
holidays.
Economic considerations
In terms of operating costs, there is an optimum final pressure
point to balance. By having longer intervals between filter
replacements, we do achieve lower filter replacement costs. On the
other hand, this will increase the operating energy costs due to
inefficiency.
Many years of working experience in Marine, Facilities, Construction has given the author material for writing e-books and articles related to engineering, and management. Subscribe to facworld ezine More information at Marine Engineer and M & E Engineer
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