<\/span><\/h2>\nDew point occurs when the temperature difference between the low-temperature material surface and the higher-temperature space reaches the dew point, which is determined based on the parameters on the humid air graph.<\/span><\/p>\nWhat is the phenomenon of vent dew?<\/span><\/em><\/figcaption><\/figure>\nIn the field of air conditioning and ventilation, the problem of fogging and how to fix it is always the most shared and interested topic. Dew condensation not only causes unsightly but also affects the architecture of the building such as water seepage, rotting the decorative plaster ceiling, shorting electrical equipment and damaging the interior below.<\/span><\/p>\n<\/span>Causes of vent dew<\/span><\/span><\/h2>\nThe typical environment of Vietnam is tropical climate: hot and humid, temperature fluctuations during the day can be very large. At the location of low-temperature air-conditioning vents, when exposed to humid air in the room, if the temperature is lower than the dew point temperature, the humid air will turn into dew and cause dew condensation at the vents. This phenomenon often occurs with the first operation of the ventilation system, or when the weather changes.<\/span><\/p>\nThere are also the following basic reasons:<\/span><\/p>\n<\/span>1. Due to indoor unit<\/span><\/strong><\/span><\/h3>\n\nThrottle valve is broken, or clogged<\/span><\/li>\nThe indoor unit fan is weak, not enough air flow<\/span><\/li>\nCondensate pump weak, or damaged<\/span><\/li>\nHeat exchanger indoor unit, dust return filter mesh<\/span><\/li>\n<\/ul>\n<\/span>2. Due to construction techniques<\/span><\/strong><\/span><\/h3>\nInsulation is not properly applied, the door box is not insulated, the thickness of the layer is not correct<\/span><\/p>\nThe cold air duct is open, the flexible duct is torn or bent, causing the air flow to decrease<\/span><\/p>\nToo long hard and soft wind pipes create too much resistance, making the wind speed out at the door weak<\/span><\/p>\nThe condensate line does not ensure the slope, the condensate does not drain properly, overflows the trough, returns to the coil and is blown down the vent.<\/span><\/p>\nIn indoor units with high pressure head and fan capacity, more condensate traps should be arranged<\/span><\/p>\n<\/span>3. By design<\/span><\/strong><\/span><\/h3>\nCalculation of the flow distribution on the pipeline, the outlet at the vent positions of the AHU, FCU is not accurate<\/span><\/p>\nThe main air duct, branch pipe, flexible pipe to the air outlet are arranged too far, the indoor unit pressure head is not enough<\/span><\/p>\nThe arrangement of the number of air vents is not suitable in terms of quantity and location. Avoid placing air vents in high temperature areas: near glass doors, avoid hot air circulation: atrium locations, main doors often come in and out…<\/span><\/p>\nThe calculation and design of the ducts are not suitable: size, length, branching… leading to too high or too low wind speed.<\/span><\/p>\nNormally, we calculate the wind speed in the pipeline as follows:<\/span><\/p>\n\nMain pipeline wind speed is: 11m\/s<\/span><\/li>\nThe return pipe wind speed is: 6m\/s<\/span><\/li>\nThe wind speed at the louver, the wind mouth is: 2.5m\/s<\/span><\/li>\nIn flexible ductwork is: 3.5m\/s<\/span><\/li>\n<\/ul>\nThe selection of cooling capacity is lacking, the outlet temperature at the vent is usually from 10\u00b0C to 15\u00b0C because there is not enough cooling capacity for the room space, so the temperature difference at the surface of the louver and the surrounding air is very big<\/span><\/p>\n<\/span>4. Improper arrangement of cold air outlet<\/span><\/strong><\/span><\/h3>\nWhen designing, it is necessary to arrange the air vent to avoid placing too close to the glass door or the glass wall that is directly exposed to the sun outside, which will cause a temperature difference that is easy to dew on the glass wall and the wind mouth.<\/span><\/p>\n<\/span>5. Due to technical insuring of cold air duct insulation<\/span><\/strong><\/span><\/h3>\n– When constructing duct insulation, cold air outlet should be carefully calculated to avoid dew condensation. Technical characteristics of the insulation layer should be checked such as thickness, density,\u00a0 <\/span>and thermal conductivity coefficient of materials<\/span><\/em> .<\/span><\/p>\n– It should be noted that outdoor and indoor installation spaces in air-conditioned spaces will have different insulation thicknesses.<\/span><\/p>\n<\/span>6. Design without cooling load<\/span><\/strong><\/span><\/h3>\n– Lack of cooling load is one of the frequent causes of dew at the mouth of the wind.<\/span><\/p>\n– The air outlet temperature is usually from 10 \u00b0C to 14 \u00b0C, so after using the air conditioner, the room temperature does not decrease, there will be a phenomenon of dew at the mouth, to overcome it is necessary to determine the air-conditioning space, calculate suitable load, for special spaces, not based on experience, but must calculate the design by specialized software to calculate the design.<\/span><\/p>\n– Design of water trap at indoor units with large fan head is not technical, leading to condensate being sucked into the unit.<\/span><\/p>\n<\/span>How to fix the phenomenon of vent dew.<\/span><\/span><\/h2>\nHow to fix the phenomenon of vent dew.<\/span><\/em><\/figcaption><\/figure>\nIt must be affirmed that it is impossible to completely solve the problem of dew. However, solutions can be used to limit the accumulation of dew at the mouth of the wind. That solution depends on the use of the project and investment costs.<\/span><\/p>\nAs mentioned in the basic causes above, we have 3 main methods to deal with the root:<\/span><\/p>\n<\/span>1. Increase the air outlet surface temperature<\/span><\/b><\/span><\/h3>\nFor some designs, there is a small resistance at the vent surface to warm the surface above the dew point of the air state in the conditioned space.<\/span><\/p>\n<\/span>2. Isolate the surface causing dew<\/span><\/b><\/span><\/h3>\nThis is the treatment method commonly used by operational engineers. By increasing the wind velocity at the vent, we can drive away the surrounding moist air layers and limit their contact with the vent surface.<\/span><\/p>\nHowever, this method can only be used in a very small number of cases. Because the increased wind speed at the mouth will cause noise and when the ambient humidity is too high, this is not effective and can also cause additional energy consumption in the fan. \u261e Fix dew in the mouth of the wind.<\/span><\/p>\n<\/span>3. Use dehumidification processes<\/span><\/b><\/span><\/h3>\nThe dehumidifier can be used directly or the dehumidifier (the dehumidifier can be used separately or in the same room as the air conditioner).<\/span><\/p>\n<\/span>4. Design Solution<\/span><\/strong><\/span><\/h3>\n– For constructions, it is absolutely required not to drop water on objects inside. The system of ducts and louvers must be designed to go underground. The direction of blowing for diffusion as well as heat recovery is upward or horizontal. The fresh air duct system must undergo dehumidification treatment. The calculation of wind speed in the ductwork, at the supply and return air intakes must also be calculated and adjusted accordingly.<\/span><\/p>\n– With works with lower requirements. It is possible to arrange ventilation systems, air vents on the ceiling and downwards. With this system, it will help reduce investment costs to match the budget.<\/span><\/p>\n