When selecting the air handling units, firstly, the air volume, air pressure, cold heat, outlet noise and air filtration requirements of the air handling unit are determined according to the load calculation results of the central air-conditioning system. However, due to various reasons such as design or manufacture, we often find that there are some problems in the selected aair handling unit, such as insufficient air cooling, insufficient cooling capacity, condensation on the outer surface of the unit, overflow of condensate pan, and water behind the surface cooler section. Therefore, this requires us to strictly control the quality when selecting equipment, so as to prevent problems before they happen. My own experience has the following points:

1. Unit body insulation; To prevent condensation on the casing, the national standard stipulates that the thermal resistance of the insulation layer of the casing should not be less than 0.68m-2/kW, and cold bridges should be prevented at the joints of various sections of the casing. At present, PEF or polyurethane foam is widely used as thermal insulation materials.
2. Wind speed on the windward side: At present, in order to reduce the size of products, some manufacturers often make the wind speed on the windward side of air handling units larger, which results in water behind the cold section of the air handling units; If the design of water baffle is unreasonable, the problem will be more serious. Therefore, we should control the windward wind speed of the surface cooler at 2 ~ 2.5m/s when selecting models.
3. Air leakage index: According to the national standard, when the static pressure in the combined air handling unit is 700Pa, the air leakage rate in the machine shall not exceed 3%. In actual use, we found that the air leakage rate of air handling unit on site was as high as 10%.
After analysis, this is mainly caused by the following reasons. (1) the sealing material performance is not good. (2) The structural design of the unit is unreasonable; (3) The installation quality on site is poor; (4) The rigidity of the air handling unit with large air volume is poor, and it is easy to deform when starting and stopping operation.
4. Insufficient cooling and heat: The design and selection of surface coolers of domestic manufacturers are based on the empirical formula of small sample test results, which has certain errors in itself
5. Overflow of condensate tray: This problem is the most common phenomenon in the use of air handling unit at present, and the user’s reaction is also the strongest.
The reasons for this problem are as follows: (1) The windward wind speed is too high. (2) The surface cooler is in the negative pressure section, and no water seal is set when the unit leaves the factory. (3) The length and depth of condensate tray are not enough. As for the problem of excessive wind speed on windward side, we should negotiate with the manufacturer to determine the height of water seal and the length and depth of condensate tray when ordering.