Does adding a chemical filter to an old air conditioning system require a fan replacement?

Direct answer: not necessarily. However, 'no need to change' must be based on evidence and cannot be judged based on feelings.

After adding a chemical filter section to the old air conditioning system, the system resistance increased. At the same fan speed, the air volume may decrease. How much the air volume decreases depends on the new resistance and fan margin. If the margin is enough, adjusting the gear or damper can restore it; if the margin is not enough, the fan or system configuration may need to be adjusted.

The key to judging whether to replace the fan is to obtain several data: the original fan curve, the actual air volume of the original system, the resistance of the new filter section, and the target air volume. Only when these data are put together can a conclusion be drawn.

Get actual operating data

The first step in transformation evaluation is to clarify the true status of the original system.

Fan parameters. Record the fan model, rated air volume, rated static pressure, speed range and motor power. If there is a fan performance curve, use it directly; if not, you can obtain it from the original equipment manufacturer, or calculate it based on actual measured data.

Current operating point. Record the actual air volume, pressure difference in each section, fan gear or frequency before modification. The design parameters and the actual status after many years of operation may be different, and field data should prevail. For specific pressure difference records, please refer to Discussion of what items should be checked during daily inspection of chemical filters .

System resistance constitutes. The resistance of the initial effect, medium effect, high efficiency, surface cooler, heater, air duct and valve is recorded separately. After adding a new chemical filtration section, the total resistance is the sum of all sections. For specific accounting methods, please refer to Discussion of how much the added resistance of the chemical filter will increase the fan's electricity consumption .

These data are the basis for subsequent judgments. Without any one item, the assessment is incomplete.

Evaluate available headroom

With the data, fan margins can be assessed.

How much new resistance is there? Ask the chemical filter supplier for initial resistance and final resistance data at the target air volume. Note: The resistance of the chemical filtration section may change with operation time, and both the initial resistance and the final resistance must be considered.

How does the fan operating point change? Add the new resistance to the total system resistance and compare it with the fan curve to find the new operating point. If the air volume at the new working point is still within the acceptable range, it means that the original fan still has margin. For specific curve reading methods, please refer to Discussion on whether the chemical filter air volume should be selected based on the total air volume of the system or the air volume of a single unit .

The final resistance conditions must also be checked. When the filter material reaches the end of its life, the resistance will increase. If calculated based on initial resistance only, the air volume may be available in the early stage but may not be sufficient in the later stage. For specific life assessment, please refer to Discussion of how long chemical filters last .

How much air volume is allowed to drop. If the end is a clean room, the decrease in air volume will affect the number of air changes and air flow organization. The allowable decrease depends on the cleanliness requirements and system margin. You can't just look at 'it's enough if it can be transferred'.

Speed ​​range and motor load

If the calculation finds that the original fan can be compensated by speed regulation, other boundaries must be checked.

Speed ​​range. What is the allowable speed range of fans and motors? How far is the current operating gear from the upper limit? If it is already close to the upper limit, continuing to increase the speed may exceed the allowable range.

Motor load. As the speed increases, the current and power will change. It is necessary to confirm whether the rated power of the motor is sufficient and whether there is any risk of overheating. For specific verification methods, please refer to Discussion on how to check the original motor load when rebuilding a chemical filter .

Noise and vibration. Increased rotational speed may increase noise and vibration. If there are noise requirements in the vicinity of the air conditioning system, or the equipment is sensitive to vibration, the impact will need to be assessed.

control conditions. If the fan is regulated by a frequency converter or control system, verify that the controller can support the new operating point. The group control system may need to be recalibrated.

Compare overall renovation plans

If the original fan margin is insufficient, there is more than one way to replace the fan.

Increase filter area. Choose a chemical filtration section with a larger effective area to achieve lower resistance under the same air volume. This method does not require replacing the fan, but you need to confirm whether the installation space allows it.

Optimize air ducts. Check existing air ducts to see if there are spaces where resistance can be reduced, such as cleaning out dust accumulation, reducing elbows, or adjusting valves. Such changes often do not require replacement parts. Please refer to the specific location assessment Discussion of what conditions should be evaluated first before adding a chemical filter to an existing clean room .

Adjust the fan. If the first two methods are not satisfactory, consider replacing the fan. When replacing the fan, pay attention to the working point, motor power, control method and installation interface of the new fan, and make sure they match the original system.

Reevaluate goals. If system conditions dictate that air volume cannot be restored, you can evaluate whether the target area or air volume requirements can be adjusted. This needs to be confirmed with the craftsman.

Each option must verify the gas treatment goals and air volume, and the established protection requirements cannot be reduced in order to retain the fans.

Actual verification after transformation

The calculation is only a prediction, and actual measurement is required after the transformation is completed.

Air volume measurement. Measure the actual air volume under stable working conditions and compare it with the design value. If it is low, check whether it is the fan working point, filter section resistance or air duct problem. For specific methods, please refer to whether chemical filtration modification requires re-doing the air volume balance . Discuss

Outlet concentration detection. Detect the target gas outlet concentration according to project requirements to confirm that the chemical filtration section meets the treatment objectives. For specific sampling methods, please refer to Discussion of sampling points for chemical filter performance verification .

Record operating data. The air volume, pressure difference, fan gear and outlet concentration after modification should be recorded and archived as a basis for subsequent maintenance.

Project judgment example

An old air conditioning system plans to add a chemical filtration section. The calculation found that the new initial resistance was about 80 Pa and the final resistance was about 150 Pa. The working point of the original fan at the current gear still has about 15% margin from the lower limit of air volume.

After the transformation, the original air volume can be maintained by raising the fan by one gear under the initial resistance condition. When running close to the final resistance, the fan needs to be increased by one gear. The current is still within the allowable range and the noise change is acceptable. The original fan has not been replaced.

Another project calculation found that the original fan margin was less than 5%, and the air volume would drop significantly after adding a new filter section. After evaluation, a chemical filtration section with a larger effective area was selected to reduce the resistance by about 30%. With a small speed adjustment, the air volume requirements were met, and the fan was not replaced.

These two cases illustrate that whether to replace the fan depends on the accounting results, not experience. involving When selecting chemical filter product series , it is recommended to provide the original fan curve, system data and target air volume to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s transformation package

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide chemical filter product series and supporting air supply equipment. For old system renovation projects, the original fan parameters, system resistance, target air volume and installation space can be combined to assist in checking the configuration of the chemical filtration section and the fan working point.

Related products:Chemical filter product series、MAU box chemical filter、FFU comes with chemical filter . Providing original system data and modification requirements when inquiring will help confirm the appropriate solution. The specific selection is subject to the technical documents and test results confirmed by the project.