How to consider the incorporation of MAU fresh air into the air inlet status of the circulating unit?

The inlet status of the circulation unit should be determined based on its actual return air and MAU supply air access locations. If the fresh air is mixed upstream of the circulation unit, the coil inlet air is not the return air of a single room; if the fresh air bypasses the unit and is connected at the back end, its status cannot be directly counted as the unit inlet.

First confirm where the MAU air supply is connected.

Mark the MAU air outlet interface, circulation unit return air outlet and circulation unit coil on the same air flow diagram to clarify each air branch. Connected to the upstream of the circulation unit, connected to the downstream of the circulation unit, or connected to the middle section of the air supply pipe, the three methods correspond to different inlet states of the unit. Before the location is confirmed, room return air parameters or outdoor parameters cannot be directly applied.

If the MAU air supply is connected upstream of the circulation unit, the inlet of the circulation unit is a mixture of return air and MAU supply air; if the MAU air supply is connected downstream of the circulation unit, the circulation unit inlet is usually determined according to the return air path, and the mixed supply air state needs to be calculated separately. Regarding how to determine the proportion of new return air, please refer toHow is the proportion of new return air to the air-conditioning box determined by project requirements?。

The mixing state should be calculated according to the dry air mass flow rate

When the MAU supply air and the circulation unit return air are mixed upstream, the inlet state should be weighted according to the dry air mass flow rate of the two air streams to the moisture content and enthalpy, and then the temperature and relative humidity are calculated from the mixing state. The relative humidity percentages of the two air streams cannot be directly averaged, nor can the room return air temperature be used instead of the coil inlet temperature.

For specific calculation methods of mixed air state, please refer toHow should the temperature and humidity of the mixed air in the air conditioning box be calculated? . If the length of the mixing section is insufficient or the air flow is stratified, the theoretical mixing state may deviate from the actual state of the coil inlet. Please refer toHow long is the air mixing distance required in the mixing section of the air conditioning box?。

Don’t re-count loads already handled by the MAU

When selecting a circulation unit, it is easy to include the heat and moisture load already borne by the MAU into the circulation unit again. If the MAU has treated the fresh air to a lower moisture content, the circulation unit coil inlet status should be determined based on the mixing status of the treated fresh air and return air, rather than recalculating based on the outdoor fresh air status. Conversely, if only the ideal return air is taken and the MAU supply air incorporated upstream is ignored, the inlet load of the circulating unit may also be underestimated.

What indoor loads should the circulating unit bear, please refer toWhat indoor loads should the circulating air handling unit be selected based on? . For the corresponding relationship between MAU fresh air tasks and process exhaust, please refer toHow does the fresh air task of the clean room MAU correspond to the process exhaust? . Load distribution and air paths should be consistent.

Temperature rise of air ducts, fans and air leakage will change the inlet status

When the MAU air supply passes through the air duct and reaches the entrance of the circulation unit, it may be affected by the heat dissipation of the air duct, the temperature rise of the fan, and air leakage. For long-distance air ducts, non-insulated air ducts, or air ducts passing through high-temperature areas, the supply air temperature may deviate from the MAU air outlet parameters. Air duct leakage will change the air supply volume and also affect the mixing ratio.

The design data should indicate whether the MAU air outlet state and the circulation unit inlet state are at the same point. If different, the temperature rise, air leakage and air volume changes along the way should be given. The pressure caliber should also be consistent, please refer toWhat is the difference between static pressure, total pressure and static pressure outside the air conditioner box? . Changes in system resistance may change the actual air supply volume, please refer toWhat functional segments should be included in the internal resistance of the air conditioning box?。

Control and measurement points should correspond to the actual mixing path

If MAU is mixed upstream of the circulation unit, the temperature and humidity measuring point at the entrance of the circulation unit should be able to reflect the state of the mixed air. The measuring point location should avoid the single airflow concentration area, and if necessary, set up a representative measuring point after the mixing section. The control logic should clarify how the circulation unit responds when the MAU air supply volume changes to avoid fluctuations caused by simultaneous adjustments on both sides.

For control point table and signal definition, please refer toWhat point tables need to be provided before the air-conditioning box is connected to the building automation system? . Whether the return air measurement point can represent the service area, please refer toCan the air conditioning box return air measurement points represent all service areas? . How to position the supply air temperature sensor to avoid local airflow, please refer toHow should the air supply temperature sensor of the air conditioning box avoid the influence of local airflow?。

If the operating mode changes, the entry status must be rechecked.

The mixing ratio and inlet status may change during normal production, on duty, when the MAU is partially shut down, or when the circulation unit reduces air volume. The design stage is only calculated based on one working condition, and the coil inlet status may deviate during operation. The operating mode table should list the MAU air supply volume, circulation unit return air volume and mixing ratio under each state, and describe the control strategy.

For condition checks before starting the machine for the first time, please refer toWhat conditions need to be checked before the air-conditioning box is turned on for the first time? . How to change the debugging sequence from stand-alone to system linkage, please refer toHow to change the debugging sequence of air conditioning box from stand-alone unit to system linkage? . During commissioning, the inlet status of the MAU and circulating unit when operating jointly should be verified.

Aili industrial supporting equipment

Aili Industrial can collaboratively check the matching parameters of the MAU, circulation unit and FFU; it is recommended to submit a system diagram with the location of fresh air access, rather than just giving each equipment independent air volume. Aili's industrial manufacturing end covers independent R&D and production of motors and fans, control systems, sheet metal, air filters and complete machine assembly. The interfaces and operating points of MAU, circulation units and terminal air supply equipment can be matched in the same package; non-standard air ducts can be adjusted according to the on-site access location.

Product form can be viewedAir handling unit andFan box page; clean air supply package can be combinedFFU fan filter unit andEFU equipment end fan filter unit verification; terminal particle filtration can be combinedHEPA/ULPA filter confirmation; when it comes to gaseous pollution control, you can communicate separatelyChemical filter solution; multiple devices can be linked together to understandFFU computer group control system . Supporting method of The specific entrance status, equipment performance and delivery scope still need to be verified based on the corresponding configuration data and on-site working conditions. The actual effect is subject to on-site air volume balance and performance test results.

Submit project parameters:https://ailigy.com/contactus.html

Related questions and answers

The MAU supply air is connected upstream of the circulation unit. Can the entrance be counted as room return air?
cannot. The calculation should be based on the mixing state of return air and MAU supply air, otherwise the influence of temperature, humidity and air volume of MAU supply air will be ignored.

MAU has already processed fresh air, does the circulating unit still have to bear the fresh air load?
There is usually no need to repeat loads already handled by the MAU, but the circulation unit inlet conditions and coil tasks should be checked against the actual mixing status.

Can Aili Industrial help check the mixing status of MAU and circulation unit?
The mixing status and interface can be checked based on the system diagram, access location and air volume of each device. The specific plan needs to be confirmed according to the project conditions.

Related articles

1. How is the proportion of new return air to the air-conditioning box determined by project requirements?

2. How should the temperature and humidity of the mixed air in the air conditioning box be calculated?

3. What indoor loads should the circulating air handling unit be selected based on?

4. How does the fresh air task of the clean room MAU correspond to the process exhaust?

Key points for selection and acceptance inspection