To determine whether a folded frame combined filter needs to be replaced, a comprehensive judgment should be made based on multiple factors such as the attenuation of its filtration performance, changes in resistance, appearance condition, and usage environment, to avoid premature replacement causing waste, or late replacement affecting system operation. The following are the specific judgment methods and indicators:
I. Core judgment Index: Resistance (pressure difference) reaches the upper limit
The air resistance (pressure difference) of the filter is the most direct indicator to determine whether it is clogged and is also the most commonly used basis for replacement in the industry.
Principle: The resistance of a new filter is relatively low (referred to as “initial resistance”). As the filtered dust accumulates continuously, the pores of the filter material are blocked, and the resistance when air passes through gradually increases (referred to as “final resistance”). When the resistance reaches the “final resistance” specified by the manufacturer, it indicates that the filter material is saturated and must be replaced.
Operation method
Install differential pressure gauges (such as U-tube differential pressure gauges or electronic differential pressure transmitters) before and after the filter to monitor resistance changes in real time.
Record the “initial resistance” of the filter (the resistance when newly installed, usually 5-20Pa, depending on the model).
When the resistance rises to the “final resistance” (generally 2 to 3 times the initial resistance, for example, the initial resistance is 10Pa and the final resistance is about 20 to 30Pa, please refer to the product manual for details), it needs to be replaced.
Note: If a differential pressure gauge is not installed, it can be indirectly judged by the decrease in the air volume of the ventilation system (such as a significant weakening of the wind force at the outlet) – excessive resistance will lead to insufficient air volume, affecting the normal operation of the ventilation or air conditioning system.
2. Visual inspection: The filter material is contaminated or damaged
By observing the appearance of the filter with the naked eye, one can quickly determine whether it needs to be replaced urgently.
Severe dust accumulation on the surface of the filter material: If the surface of the filter material (such as non-woven fabric, glass fiber) is covered with dust, blackened or lumped, and still cannot be cleaned after being blown with compressed air (folded frame filters are usually disposable and cannot be cleaned), it indicates that the dust holding capacity has reached the upper limit, and the filtration efficiency has dropped significantly.
Filter material damage or deformation
If the filter material is torn or has holes (which may be caused by improper installation, air flow impact, or foreign object puncture), unfiltered air will directly penetrate it, losing its filtering function. It must be replaced immediately.
The collapse of the folded frame structure and the deformation of the protective net cause the filter material to wrinkle or stack, reducing the filtration area and requiring replacement.
Edge seal failure: Gaps appear at the sealing area between the outer frame and the filter material (such as glue peeling off or aging of the sealing strip), which can cause “bypass” (air flowing through the gaps without filtration). At this point, even if the filter material is not saturated, it needs to be replaced to ensure the filtration effect.
Iii. Estimation based on the usage environment and cycle
If there is a lack of monitoring equipment, a rough judgment can be made based on the pollution level of the usage environment and the replacement cycle based on experience, but adjustments should be made in light of the actual situation
In severely polluted environments, such as ventilation systems near industrial zones and construction sites, or workshops with a lot of dust (such as woodworking and foundry workshops), the dust accumulation rate of filters is fast, and the replacement cycle is usually 1 to 3 months.
For ordinary environments, such as central air conditioning systems in office buildings, shopping malls, and other public places, the pollution is relatively light, and the replacement cycle is generally 3 to 6 months.
Pre-filtration in clean environments, such as the primary filtration in clean rooms (used to protect medium and high-efficiency filters), as the upstream air has already undergone certain treatment, the replacement cycle can be extended to 6-12 months, but it needs to be confirmed in conjunction with differential pressure monitoring.
Note: The cycle is for reference only. In case of sudden environmental pollution (such as sandstorms, dust leakage in workshops), it is necessary to inspect and replace in advance.
Iv. Auxiliary Judgment: Abnormal system operation
When abnormalities occur in the filtration system or associated equipment, it may be an indirect signal of filter failure:
Downstream equipment contamination: If the pleated frame filter is used as a pre-filter, and the medium/high-efficiency filters downstream of it get clogged prematurely or the dust accumulation rate on the equipment surface increases (such as dust accumulation in air conditioning ducts or excessive dust in clean rooms), it may be that the pleated frame filter has failed and is not effectively intercepting coarse particles.
Rising energy consumption: The fans in the ventilation system consume more electricity to overcome high resistance. If the electricity bill increases significantly and other faults are ruled out, it may be that the resistance of the filter is too high, and it needs to be replaced to reduce energy consumption.
Summary: Change the priority of judgment
First choice: The pressure difference reaches the final resistance (the most scientific and accurate, suitable for scenarios with monitoring equipment);
Second choice: Obvious contamination or damage in appearance (intuitive judgment, applicable to all scenarios, especially in cases where urgent replacement is required);
Reference: Environmental and cycle estimation (as an auxiliary, it needs to be verified in combination with the first two items).
Timely replacement of failed folding frame combined filters can prevent a decline in ventilation efficiency, an increase in energy consumption, damage to downstream equipment, or deterioration of indoor air quality, while ensuring the economy and stability of the filtration system.