What impact does the coil head-on wind speed have on heat exchange and water entrainment in the air conditioning box?

The wind speed facing the coil is calculated based on the volume flow rate through the coil and its effective windward area, which will affect heat transfer, air resistance and the risk of water droplets carrying under wet conditions. The same upper limit value cannot be applied to all air conditioning boxes without departing from the coil structure, fin status and drainage conditions.

First confirm the size of the area and air volume

Calculating the unit's overall width and height may overestimate the actual effective area; using outdoor standard air volume instead of the actual volumetric flow rate at the coil position may also produce deviations. When selecting, the air condition and effective cross-section should be explained, and the cross-section distribution should be checked to see if it is even, because when the average wind speed is appropriate, it may still be locally high.

The effective area should cover the actual windward side of the coil and the range blocked by the structure; in wet conditions, attention should be paid to the condensation volume, fins, water film, drainage and drip-carrying characteristics; supporting effects include air resistance, fan power and necessary water-blocking measures. The three conditions correspond to different design links, and you cannot just give one wind speed number. 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?。

Effect of head-on wind speed on heat transfer

The head-on wind speed affects the contact time between the air and the coil surface and the heat transfer coefficient. When the wind speed increases, the heat transfer coefficient usually increases, but the contact time shortens and the air side resistance increases. When the wind speed decreases, the contact time increases, but the heat transfer per unit area may decrease, and the coil area utilization efficiency decreases. Design wind speed requires a balance between heat transfer capacity and resistance.

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? . 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? . After the wind speed changes, the air outlet status and dehumidification capacity of the coil may also change.

Risk of water entrainment in wet conditions

Under wet conditions, a water film forms on the coil surface, and the air flow may carry water droplets away from the coil. When the head-on wind speed is too high, the risk of water droplets being carried increases, which may cause moisture in downstream components, reduced filter performance, or water accumulation in the box. The risk of water carrying is also related to the fin form, water film thickness, drainage method and water retaining structure. You cannot just look at one wind speed value.

For the functions of water baffles and water removal structures, please refer toHow to combine the slope of the water pan of the air-conditioning box with the layout of the drain outlet? . For the relationship between dehumidification capacity and cooling capacity, please refer toHow to calculate the dehumidification capacity of air conditioning box from the difference in air moisture content? . The airflow state behind the coil under wet conditions will also affect subsequent filters or chemical filtration sections. Please refer toHow to judge whether the MAU chemical filtration section is arranged before or after the surface cooler?。

Uneven cross-sectional wind speed distribution will amplify local risks

The average head-on wind speed is appropriate, but it does not mean that the wind speed is uniform throughout the cross-section. Uneven distribution of airflow at the coil inlet, reduced diameter of the box, partial blockage of the filter, or biased flow at the fan outlet may cause the local wind speed to be higher than the average. Local high wind speed areas are more likely to carry water, while local low wind speed areas may have insufficient heat exchange.

The length of the mixing section and airflow organization will affect the cross-sectional uniformity, please refer toHow long is the air mixing distance required in the mixing section of the air conditioning box? . The filter section is arranged before and after the fan, which will also change the air flow state at the coil inlet. Please refer toWhat needs to be considered when arranging the filter section before and after the fan?。

When water leakage occurs, you cannot just add a water baffle

Coil cleaning, pan drainage, local airflow and actual air volume need to be checked at the same time. Adding a water baffle will change the resistance and cleaning conditions and cannot replace the correction of front-end problems. If dust accumulates on the coil surface or the fins fall down, the water film may be unevenly distributed, increasing the risk of local water entrainment.

Changes in fan air volume will also affect the oncoming wind speed, please refer toIf the total air volume of the air conditioning box is insufficient, should I check and measure it first or should I increase the speed first? . For water system flow and temperature difference changes, please refer toWhat water parameters should be confirmed before connecting the air conditioning box to the cold water system?。

The project should check the allowable range according to the selected coil management data

Different coil structures, fin spacing and drainage designs have different allowable wind speeds. The project should check the allowable range based on the selected coil data and wet working conditions, and observe the actual condensate discharge during commissioning. Wind speed can be used as a screening condition in the design stage, and ultimately it still needs to be confirmed based on coil performance and on-site performance.

For condition checks before starting the machine for the first time, please refer toWhat conditions need to be checked before the air conditioner 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?。

Aili industrial supporting equipment

Aili Industrial can jointly check the air flow conditions based on the coil section, fan and box, and provide actual working conditions to help implement the heat exchange and drainage requirements together. Aili Industrial Manufacturing covers the independent research and development and production of motors and fans, control systems, sheet metal, air filters and complete machine assembly. The coil section, box structure and water retaining and drainage design can be matched in the same package; non-standard coils and boxes can be adjusted according to on-site air volume 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 head-on wind speed, heat transfer effect and delivery scope still need to be verified based on the corresponding coil 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

The higher the head wind speed, the better the heat transfer?
Not exactly. When the wind speed increases, the heat transfer coefficient increases, but the contact time shortens, the resistance increases, and the risk of water entrainment also increases under wet conditions, which requires a comprehensive balance.

The average wind speed is appropriate, why is it still carrying water?
When the cross-sectional wind speed distribution is uneven, local high wind speed areas may contain water. Air flow organization, filter blockage and fan outlet deviation should be checked.

Can Aili Industrial help check the wind speed facing the coil?
The air flow conditions can be checked based on the coil data, air volume and box structure. The specific wind speed range needs to be confirmed based on the selected coil and on-site working conditions.

Related articles

1. Will the greater the number of coil rows in an air-conditioning box, the greater the cooling capacity?

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

3. How to combine the slope of the water pan of the air-conditioning box with the layout of the drain outlet?

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

Key points for selection and acceptance inspection