How To Know When To Change Your Air Conditioning Filters
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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