Can the air conditioning box return air measurement points represent all service areas?

The air conditioning box return air measurement point usually reflects the mixed air collected at that location and cannot automatically represent all service areas. The return air volume, temperature, humidity, and load of each zone are different. Even if the total return air reading reaches the set value, there may still be local areas that deviate from the target, which needs to be judged based on the control zone.

Chasing from zone readings to return air mixing ratio

Areas of large return air volumes will have a greater impact on the mix readings, and areas of small air volumes but significant load changes may be masked by the average. Air leakage from the return air duct, mixing in non-production areas, or the proximity of the probe to a single branch will also affect the representativeness. The return air source and airflow path should be checked first before deciding on the main control basis.

Source verification should cover the return air proportion of each area and whether there is additional mixing; target verification should determine whether the regional requirements are consistent and whether independent adjustment is needed; trend verification should observe the relationship between the regional and total return air readings when the load changes. The three items correspond to different problems, and all areas cannot be judged by just one return air measurement point. How to calculate the temperature and humidity of the mixed air in the air conditioning box, please refer toHow should the temperature and humidity of the mixed air in the air conditioning box be calculated?。

The return air measuring point reflects the average state after mixing

A single return air measuring point is usually installed in the return air duct or mixing section and measures the state of the air passing through that location. If the return air from multiple areas is mixed in a duct or ceiling, the measurement point reading is closer to the mixed average than the true state of a certain area. Areas with large return air volumes will have a greater impact on the mix readings, and areas with low return air volumes may be averaged out.

Whether the return air measurement points can represent the service area depends on whether the return air is fully mixed, whether the location of the measurement points is reasonable, and whether the loads in each area are close. The more even the mix and the more consistent the loading, the better the representation of a single point; conversely, a single point may mask local problems.

When the regional load difference is large, a single point is prone to distortion.

When there are equipment-intensive areas, personnel changing areas, or different process areas in the service area, the temperature and humidity loads in each area may vary greatly. Equipment-dense areas generate a lot of heat and the return air temperature may be high; people-dense areas have a large humidity load; areas close to exterior walls are affected by the building envelope. If these areas share an air conditioning box and a return air measurement point, normal average readings do not mean that each area meets the requirements.

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? . The panel shows how the air-conditioning box in the workshop copes with large-area air supply zones. Please refer toHow does the panel display air-conditioning box in the workshop deal with large-area air supply zones? . Zoning control can effectively improve regional representation.

Return air paths and air leakage will affect measuring point readings

Before reaching the measurement point, the return air may pass through the ceiling, mezzanine or duct, and may be affected by heat dissipation, air leakage or fresh air infiltration along the way. Air leakage from the return air duct will change the air volume, temperature and humidity, and the measurement point readings may deviate from the actual return air condition. Local heat sources or cold surfaces in the return air path may also cause the measuring point to shift.

For the relationship between return air valve opening and actual return air volume, please refer toCan the opening of the fresh air valve and return air valve directly represent the air mixing ratio? . Mixing section length and air flow uniformity, please refer toHow long is the air mixing distance required in the mixing section of the air conditioning box?。

When is it necessary to supplement regional monitoring?

For areas with large load differences or independent process targets, the design can evaluate the zoning measurement points and corresponding adjustment plans. The addition of new sensors does not automatically solve the control contradiction. It is also necessary to clarify how different regional requirements participate in control. If there is only a single centralized unit, the common air conditions and local compensation methods it can provide must be stated.

Regional measuring points should avoid local airflow and heat sources, and the installation location should represent the typical conditions of the area. For sensor installation and calibration requirements, please refer toHow to determine the installation and calibration requirements for air conditioning box temperature and humidity sensors? . 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?。

Control logic should reflect partitioning requirements

If the requirements of each area are different, controlling the entire unit by just one return air measurement point may not be able to satisfy all areas at the same time. The control logic can take into account weighting of zoned measuring points, maximum/minimum value selection or independent regulating valves. Specific strategies should be determined based on regional importance, load variation range, and control accuracy requirements.

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? . During debugging, the response relationship between the return air measuring point and the regional measuring point should be verified when the load changes in different areas. Please refer toHow to change the debugging sequence of air conditioning box from stand-alone unit to system linkage?。

Aili industrial supporting equipment

Aili Industrial can check the point interface based on the control zone and return air data. The project team provides regional trends, which helps determine whether a single return air measurement point is suitable as a control basis. 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. Return air measurement points, control logic and box interfaces can be matched in the same package; non-standard configurations can adjust the measurement points and valve solutions according to zone control requirements.

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 measuring point layout, control strategy 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 regional monitoring results.

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

Related questions and answers

Can one return air measurement point represent all areas served by the entire air conditioning box?
uncertain. The return air measurement points reflect the average state after mixing, and local deviations may be masked when regional load differences are large.

What should we do if the regional load difference is large?
The design can evaluate the zoning measuring points, independent regulating valves or zoning unit plans to clarify how the needs of each area participate in the control.

Can Aili Industrial help check the return air measurement point plan?
The measurement point layout and interfaces can be checked based on the control zone, return air path and regional requirements. The specific plan needs to be confirmed based on on-site conditions.

Related articles

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

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

3. How does the panel display air-conditioning box in the workshop deal with large-area air supply zones?

4. How to determine the installation and calibration requirements for air conditioning box temperature and humidity sensors?

Key points for selection and acceptance inspection