Filters protect both the air handling unit and building occupants. Proper maintenance ensures they do their job effectively without wasting energy or causing problems.
Why Filter Maintenance Matters
Air Quality
Filters remove particles from supply air – dust, pollen, pollution, and microorganisms. Dirty or failed filters compromise air quality, affecting occupant health and comfort.
Equipment Protection
Filters protect coils, fans, and other components from dirt accumulation. Clogged coils reduce efficiency. Dirty fans become unbalanced. Contamination causes premature failure.
Energy Consumption
As filters load with dirt, pressure drop increases. Fans work harder to maintain airflow, consuming more energy. Severely blocked filters can double fan energy consumption.
System Balance
Extremely dirty filters restrict airflow, affecting system balance and potentially causing comfort problems in served spaces.
When to Change Filters
Pressure Monitoring
The most reliable approach. Measure pressure drop across filters and change when it reaches the manufacturer’s recommended final pressure drop. Many AHUs include differential pressure gauges or sensors.
Time-Based Replacement
Where pressure monitoring isn’t available, time-based replacement provides a fallback:
- Pre-filters: typically 1-3 months
- Main filters: typically 6-12 months
- HEPA filters: typically 12-24 months
These are guidelines only. Actual life depends on pollution levels, operating hours, and filter capacity.
Visual Inspection
Regular inspection identifies obvious problems – damage, bypass, or unusual contamination. Visual inspection supplements but doesn’t replace pressure monitoring.
Choosing Replacement Filters
Match the Original Specification
Filters are specified for a reason. Changing to different grades affects air quality and system performance. If you want to change specification, consider the implications carefully.
Filter Classifications
Filters are classified by efficiency:
- ISO Coarse (formerly G grades) – pre-filters catching large particles
- ISO ePM10, ePM2.5, ePM1 – fine filters rated by particle size captured
- HEPA/ULPA – high-efficiency filters for critical applications
Genuine vs Compatible
Original equipment filters guarantee fit and performance. Compatible alternatives can work well but quality varies. Ensure any alternative meets the same specifications.
Filter Changing Procedure
Safety First
Isolate the fan before accessing filter sections. Dirty filters may contain biological material – appropriate PPE protects maintenance staff.
Bag Dirty Filters
Contain dirty filters immediately on removal to prevent releasing captured particles back into the air or plant room.
Check Housing
Inspect filter frames and seals. Bypassing around poorly sealed filters defeats their purpose. Replace damaged seals.
Install Correctly
Ensure filters seat properly with no gaps. Observe airflow direction markings. Filters installed backwards have much lower efficiency.
Record Keeping
Log filter changes with dates and pressure readings. This data helps optimise replacement intervals.
Pre-Filter Strategy
Two-stage filtration using coarse pre-filters ahead of main filters extends main filter life. Pre-filters catch large particles cheaply, protecting more expensive fine filters.
Pre-filters need more frequent replacement but cost less per change. The economics usually favour two-stage approaches.
Upgrading Filtration
If air quality requirements change, filter upgrades may be possible:
Check Fan Capacity
Higher-grade filters have higher pressure drops. Verify the fan can handle increased resistance without unacceptable airflow reduction.
Consider Filter Housing
Better filters may be deeper, requiring housing modifications.
Assess Need Properly
Higher filtration isn’t always better. Match filtration to actual requirements rather than over-specifying.
Our Support
i-Flow can advise on filter specifications for our equipment and supply replacement filters. Contact us for filter enquiries.
