Should the inlet air temperature and humidity of the air conditioning box be designed to be outdoor or return air?

The design air inlet state of the air conditioning box should be based on the air state that actually enters the equipment or processing unit at the selected calculation boundary. A new air unit usually starts from the outdoor design conditions, the return air unit adopts the return air condition, and the mixed air unit adopts the mixing state confirmed by the design; it cannot be unified to only take the outdoor or room set values.

The unit entrance and coil entrance must be marked separately.

If a fan, preheater or other unit is located in front of the coil, the air condition may have changed before entering the coil. The selection diagram should clearly indicate the status point numbers and indicate which operating mode each status belongs to. Before determining the ideal room return air value, it is also necessary to confirm whether there is additional heat or fresh air coming in on the return air path.

The fresh air inlet must use local project design meteorological conditions and clear pressure benchmarks; the return air inlet must adopt the representative state formed by the service area and return air path; after mixing or pretreatment, the state must be given according to the actual process, and preprocessing cannot be skipped. The three types of entrances correspond to different system forms and cannot be mixed. How to determine the proportion of new return air to the air-conditioning box based on project requirements, please refer toHow is the proportion of new return air to the air-conditioning box determined by project requirements?。

The new fan unit starts from outdoor design conditions

The air processed by the fresh air unit all comes from the outdoors. The design air inlet state should adopt the design meteorological parameters of the project location, including the design dry bulb temperature, wet bulb temperature or moisture content in summer and winter. Meteorological conditions in different regions vary greatly, and data from other projects cannot be directly applied.

The outdoor design conditions should also indicate the standards and guarantee rates adopted. When the fresh air chemical filter section is arranged in front of the surface cooler, it faces uncooled outdoor air. Please refer toHow to judge whether the MAU chemical filtration section is arranged before or after the surface cooler? . Under outdoor low temperature conditions in winter, preheating and antifreeze requirements need to be checked together. Please refer toWhat problems do air conditioning box preheating, heating and reheating solve respectively?。

The return air unit adopts the return air representative status

The air processed by the return air unit comes from the service area, and the designed air inlet state should adopt the representative state formed by the return air path. The return air temperature and humidity are affected by the room load, air flow organization and personnel activities, and cannot simply take the room set value. If there is fan temperature rise, pipe heat dissipation or fresh air infiltration on the way back to the air, the status will also change.

How the circulating air handling unit bears the indoor load can be referred toWhat indoor loads should the circulating air handling unit be selected based on? . Whether the return air measurement points can represent all service areas, please refer toCan the air conditioning box return air measurement points represent all service areas? . The return air status value should be based on representative measurement points or design calculations.

The mixed air unit adopts the confirmed mixing state

The mixed air unit handles fresh air and return air at the same time, and the inlet air state is the state after the new return air is mixed. The mixing state should be calculated by weighting the moisture content and enthalpy based on the dry air mass flow rate of the two air streams. The relative humidity percentage cannot be directly averaged. When the length of the mixing section is insufficient, the actual state at the coil inlet may deviate from the theoretical mixing value.

How to calculate the temperature and humidity of mixed air, please refer toHow should the temperature and humidity of the mixed air in the air conditioning box be calculated? . How long is the mixing section required? Please refer toHow long is the air mixing distance required in the mixing section of the air conditioning box? . The opening of the fresh air valve and return air valve cannot directly represent the ratio. Please refer toCan the opening of the fresh air valve and return air valve directly represent the air mixing ratio?。

The most adverse working conditions do not necessarily come from the same day

The maximum cooling load in summer, maximum dehumidification demand and low temperature conditions in winter may be controlled by different working conditions. They should be calibrated individually rather than using one set of air inlet parameters to cover the entire year. The calculation data should retain the status source and mode to facilitate review when the design changes.

The air supply volume is determined based on the number of air changes or the cooling and heating load. Please refer toIs the air supply volume of the air conditioning box determined based on the number of air changes or the cooling and heating load? . How to select the type of surface cooler according to the air inlet and outlet conditions, please refer toHow to select the type of air conditioner cooler according to the air inlet and outlet conditions? . The air inlet status under different working conditions corresponds to different coil and fan configurations.

Status points should be marked on the system diagram

Mark the status points such as air inlet, after mixing, after coiling, and air supply on the system diagram, and indicate the temperature, moisture content and corresponding operating mode of each point. In this way, the designer, equipment side and debugging side can use the same set of status data. If the status points are not marked, it is easy to select the fan according to one working condition and calculate the coil according to another working condition.

What project information should be prepared before selecting the air-conditioning box? Please refer toWhat project information should be prepared before selecting an air-conditioning box? . How to determine the sequence of functional sections of the air-conditioning box, please refer toOn what basis should the sequence of functional sections of the air conditioning box be determined? . The selection data is complete only when the status points correspond to the positions of the functional segments.

Aili industrial supporting equipment

When providing air inlet conditions to Aili Industrial, status points can be marked on the system diagram to facilitate consistent input for coils, fans, and control configurations. Aili's industrial manufacturing end covers the independent research and development and production of motors and fans, control systems, sheet metal, air filters and complete machine assembly. The air inlet status, functional section configuration and coil selection can be corresponded in the same set of supporting materials; non-standard working conditions can be adjusted according to the project meteorological conditions and operation mode.

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 solutions. The specific air inlet conditions, 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 debugging and performance test results.

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

Related questions and answers

Can the designed air inlet status of the return air unit be directly taken from the room set value?
Not recommended. The return air condition is affected by the room load, airflow organization and return air path. Representative return air conditions or design calculations should be used.

Is it enough for the mixed air unit to only provide two states: outdoor and indoor?
not enough. It is also necessary to give the proportion of new return air, calculate the state after mixing, and check the length of the mixing section and the uniformity of air flow.

Can Aili Industrial help confirm the design air inlet status?
The status points and equipment configuration can be checked based on the system form, meteorological conditions and operating modes. The specific values ​​must be confirmed by the system design.

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. How to select the type of air conditioner cooler according to the air inlet and outlet conditions?

4. What project information should be prepared before selecting an air-conditioning box?

Key points for selection and acceptance inspection