What role does the supply air dew point play in the selection of fresh air air conditioning boxes?

The supply air dew point reflects the moisture level of the air and is an important indicator for judging the dehumidification depth of the fresh air air conditioning box. If the goal is to limit the amount of moisture introduced into the room, supply air dry-bulb temperature alone is often insufficient; reheating can change temperature and relative humidity but will not lower the dew point in the absence of humidification or condensation.

Deducing the desired state from the room moisture balance

Room moisture loss, personnel and fresh air exchange determine how much moisture needs to be removed or added. The design should first clarify how much latent heat the air conditioning box assumes in the system, and then give the corresponding supply air moisture content or dew point. For systems that centrally process fresh air, the target room temperature cannot be directly regarded as the coil outlet dew point.

The system division of labor should write down the latent heat tasks undertaken by the fresh air unit and circulation processing respectively; the equipment capacity should write down the achievable state under the actual cold source, coil and adjustment conditions; the room target should write down the allowable moisture level at the target temperature. The three items correspond to different design links, and you cannot just give one dew point number. How to calculate the dehumidification capacity of air conditioning box from the difference in air moisture content, please refer toHow to calculate the dehumidification capacity of air conditioning box from the difference in air moisture content?。

Dew point reflects moisture content better than dry bulb temperature

The dry bulb temperature only reflects the sensible heat state of the air and does not directly indicate how much moisture is contained in the air. Dew point is the temperature at which air cools to saturation and is directly related to moisture content. The same dry bulb temperature, different moisture content corresponds to different dew points; the same dew point, different dry bulb temperatures correspond to different relative humidity. When controlling room moisture, dew point is more meaningful than dry bulb temperature.

Why do you need to consider the temperature when selecting an air conditioning box based on relative humidity? Please refer toWhy does air conditioning box selection depend on relative humidity and temperature? . The relationship between supply air dew point and moisture content is also used in dehumidification calculations.

Reheating changes the temperature but does not lower the dew point

Reheating can increase the supply air temperature and lower the relative humidity, but without humidification or condensation, the moisture content and dew point of the air remain unchanged. If the coil outlet dew point does not drop to the target value, adjusting the supply air temperature by reheating will not solve the problem of excessive moisture. The function of reheating is to restore the supply air temperature, not to reduce the moisture content.

What problems do preheating, heating and reheating solve respectively? Please refer toWhat problems do air conditioning box preheating, heating and reheating solve respectively? . 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?。

How to write dew point requirements into the selection information

The corresponding air volume, inlet status, target dew point or moisture content and final air supply temperature should also be stated, and whether it is reheated after coiling should be noted. If the cold source temperature and heat transfer conditions cannot support the goals, the plan should be re-evaluated; low dry-bulb temperature or high relative humidity outlet air readings should not be directly regarded as evidence that a low dew point has been achieved.

The air conditioning box is designed to determine whether the inlet air temperature and humidity should be outdoor or return air. Please refer toShould the inlet air temperature and humidity of the air conditioning box be designed to be outdoor or return air? . How to confirm the cold water parameters, please refer toWhat water parameters should be confirmed before connecting the air conditioning box to the cold water system?。

Low dew point targets place greater demands on coils and cooling sources

The lower the target dew point, the lower the coil surface temperature needs to be and the higher the cold water temperature or cold source capacity requirement. Simply increasing the number of coil rows may not necessarily achieve a low dew point. The cold water temperature, water flow rate and heat exchange area must also be checked. If the cold source conditions are insufficient, the system plan should be re-evaluated instead of simply increasing the coil size.

For the relationship between coil row number and cooling capacity, please refer toWill the greater the number of coil rows in an air-conditioning box, the greater the cooling capacity? . For the relationship between coil water flow and design cooling capacity, please refer toHow does the water flow rate of the air conditioning box coil correspond to the designed cooling capacity?。

Aili industrial supporting equipment

Aili Industrial can check the dehumidification and reheat configuration based on the air inlet and outlet status of the complete set, and also explain the cold water conditions during consultation, which will help determine whether the goal can be achieved under actual working conditions. 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. Coils, reheating sections, sensors and control logic can be matched in the same package; non-standard dew point targets can be adjusted according to cold source conditions and on-site working 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; terminal particle filtration can be combinedHEPA/ULPA filter confirmation; when it comes to gaseous pollution control, you can communicate separatelyChemical filter solutions. The specific dew point target, coil configuration 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

Are supply air dew point and supply air temperature the same thing?
no. Temperature reflects the state of sensible heat, and dew point reflects moisture content. Reheating increases the temperature without lowering the dew point.

If only the supply air temperature target is given, can the selection of fresh air air-conditioning boxes be completed?
not enough. If the goal is to control moisture, the supply air moisture content or dew point also needs to be given, otherwise the dehumidification depth cannot be judged.

Can Aili Industrial help verify supply air dew point targets?
The coil and reheat configuration can be checked based on the air volume, inlet status and cold water conditions. The specific goals need to be confirmed based on the project conditions.

Related articles

1. How to calculate the dehumidification capacity of air conditioning box from the difference in air moisture content?

2. Why does air conditioning box selection depend on relative humidity and temperature?

3. What problems do air conditioning box preheating, heating and reheating solve respectively?

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

Key points for selection and acceptance inspection