Is the air supply volume of the air conditioning box determined based on the number of air changes or the cooling and heating load?

The air supply volume of the air conditioning box cannot be determined solely by the number of air changes or only by the heating and cooling loads. The room airflow and cleanliness requirements, sensible heat and humidity load, and ventilation and air supply conditions should be checked separately, and then the design will confirm which one forms the control requirement and verify whether the air supply status is achievable.

Why do different constraints give different air volumes?

The number of air changes reflects the volume cycle requirements, and the load law depends on the temperature or enthalpy difference of the air delivery. In areas where the equipment generates a lot of heat, even if the number of air changes is sufficient, the temperature treatment may still be insufficient; another type of clean area may still need to maintain a high circulation volume when the temperature load is not large. Therefore, a single experience multiple cannot be used universally.

Circulation and coverage need to check the service volume, air flow organization and process cleanliness conditions; heat and moisture load need to check the load, allowed air supply status and actual processing capacity; fresh air supplementary air needs to independently calculate personnel fresh air, exhaust air supplement and air volume balance. The three constraints each answer different questions and cannot be substituted for each other. How to distribute the room load to the units, please refer toWhat indoor loads should the circulating air handling unit be selected based on?。

The number of air changes controls the airflow organization

The number of air changes is usually used to ensure adequate air circulation in the room to maintain air flow organization, temperature and humidity uniformity and cleanliness. For clean rooms or pollution control areas, even if the heat load is not large, a certain number of air changes are needed to dilute pollutants, maintain pressure differences and ensure air flow coverage. When the number of air exchanges is insufficient, local retention, uneven temperature and humidity, or substandard cleanliness may occur.

The number of air changes is related to the room volume, air supply method and air flow organization. For the same number of air changes, the actual effects of different air supply arrangements may be different. For the specific basis of clean room air supply volume, please refer toHow does the fresh air task of the clean room MAU correspond to the process exhaust air? Explanation on the division of labor between circulation and air supply.

The hot and cold load tube is treated with temperature and humidity

The air supply volume is determined according to the cooling and heating load, which is based on the room's sensible heat, latent heat load and allowable air supply temperature difference or enthalpy difference. In areas where equipment generates a lot of heat, people are densely packed, or process moisture is obvious, the load method is often the control condition. However, the air volume given by the load method still needs to be checked to see if the air supply status is achievable, including whether the coil can handle the target temperature and moisture content and whether the fan can provide the corresponding pressure.

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 difference between dehumidification capacity and cooling capacity can be referred toHow to calculate the dehumidification capacity of air conditioning box from the difference in air moisture content? . If the supply air temperature difference given by the load calculation is too large, the actual capacity of the coil and air supply outlet may not match.

Fresh air and exhaust air form the third type of constraints

Fresh air volume, exhaust air volume and make-up air volume constitute another set of constraints for air volume balance. Fresh air for personnel, supplementary process exhaust air, pressure difference maintenance and leakage will all affect the air supply volume. For the relationship between fresh air volume and total air supply volume, please refer toHow to calculate the fresh air volume and total air supply volume of the air conditioning box separately? ;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?。

In areas with a large exhaust air volume, the makeup air volume may become a control condition for the air supply volume. If the calculation is based only on the number of air changes or cooling load, the demand for supplementary air may be ignored, resulting in insufficient pressure difference in the room or failure to discharge air properly.

After the air volume is determined, the performance chain must be closed

After the air supply volume is selected in the design, it is necessary to continue to check the coil, filter section, fan pressure and terminal distribution. Increased air volume does not automatically mean better cooling. If the cooling source or processing unit is not matched, the air condition may deviate from the target. Project records should document the control conditions rather than just the final numbers.

The air volume and resistance of the filter section, the pressure budget of the fan and the air volume distribution of the end air outlet must be checked simultaneously. Please refer toWhat functional segments should be included in the internal resistance of the air conditioning box? andHow is the total pressure of the air conditioning box fan determined by the internal resistance and external demand? . When the air volume units are inconsistent, you can refer toHow to convert the air volume unit of air conditioning box in m³/h, L/s and CFM?。

Aili industrial supporting equipment

Aili Industrial can match the complete machine according to the air volume and status confirmed by the design. The fan, motor and filter are checked under the same working condition; the parts involving the room load need to be connected with the system design data. 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. Air volume, resistance and operating points can be confirmed in the same package; non-standard air volume can be adjusted according to project conditions.

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; multiple equipment linkage can understandMatching method of FFU computer group control system ; terminal particle filtering can be combinedHEPA/ULPA filter confirmation; when it comes to gaseous pollution control, you can communicate separatelyChemical filter solutions. The specific air volume, 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.

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Related questions and answers

Is it okay to determine the air supply volume based only on the number of air changes?
not enough. The number of air changes ensures circulation and airflow organization, but areas with large heat and moisture loads may still need to be calibrated according to load, and the supplementary air requirements must also be checked separately.

Is it okay to determine the air supply volume based only on heating and cooling loads?
Not enough either. The load method gives the air volume required for temperature and humidity treatment. It is also necessary to check the cleaning requirements, air flow organization and supplementary air conditions.

Can Aili Industrial help check the air supply volume?
The air volume, pressure and air condition confirmed by the design can be combined to match the complete machine. The specific air volume basis needs to be confirmed by the system design.

Related articles

1. How to calculate the fresh air volume and total air supply volume of the air conditioning box separately?

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

3. What functional segments should be included in the internal resistance of the air conditioning box?

4. How is the total pressure of the air conditioning box fan determined by the internal resistance and external demand?

Key points for selection and acceptance inspection