In most cases, the lower the wind speed, the better the effect of the filter. 　　
The diffusion of small particle size dust (Brownian motion) is obvious. The wind speed is low, the air flow stays in the filter material for a long time, and the dust has more chance to impact the obstacles, so the filtration efficiency is high. Experience shows that for high efficiency filter, the wind speed decreases by half, the dust transmittance will be reduced by nearly one order of magnitude (efficiency value increases by 9), wind speed doubles, and transmittance will increase by an order of magnitude (efficiency reduction of one 9). 　　
Similar to the effect of diffusion, when the filter material is electrostatic (electret material), the longer the dust stays in the filter material, the more likely it will be adsorbed by the material. With the change of wind speed, the filtration efficiency of electrostatic material will change significantly. If you know that there is static electricity on the material, the air flow through each filter should be reduced as much as possible when designing the air conditioning system. 　　
According to the traditional theory, when the wind speed is reduced, the probability of dust and fiber collision will be reduced, and the filtration efficiency will be reduced. But in practice, this effect is not obvious, because the wind speed is smaller, the rebound force of the fiber to the dust is also smaller, and the dust is easier to be stuck. 　　
The higher the wind speed, the greater the resistance. If the service life of the filter is based on the final resistance, and the wind speed is high, the service life of the filter will be short. It is difficult for ordinary users to observe the effect of wind speed on filtration efficiency, but it is much easier to observe the effect of wind speed on resistance. 　　
For the high efficiency filter, the velocity of air flow through the filter material is generally in the range of 0.01 ~ 0.04 M / S. in this range, the resistance of the filter is directly proportional to the filtered air volume. For example, the initial resistance of a 484 × 484 × 220mm high efficiency filter is 250pa under the rated air volume of 1000m3 / h. If the actual air volume in use is 500m3 / h, its initial resistance can be reduced to 125pa. 　　
For the general ventilation filter in the air conditioning box, the speed of air flow through the filter material is in the range of 0.13 ~ 1.0m/s, the resistance is no longer a linear relationship with the air volume, but an upward arc. If the air volume increases by 30%, the resistance may increase by 50%. If the filter resistance is a very important parameter for you, you need to ask for the resistance curve from the filter supplier.