Myths about "condensate water" in HVAC construction. Know more

2024-09-29

Condensation water refers to the water condensed from the water vapor in the room air due to the low surface temperature of the heat exchanger of the indoor unit of the air conditioner. It flows out from the water collection tray under the evaporator of the indoor unit and is discharged through the condensation pipe. Let's understand the misunderstandings of "condensation water".

I. Theoretical cause analysis of condensation water generation
When outdoor air exchanges heat with the surface cooler of the air conditioning main unit and absorbs heat, because the wall temperature of the surface cooler is lower than the dew point temperature of outdoor air, the water vapor contained in outdoor air precipitates and dew forms on the wall of the surface cooler. When the dew drop increases to a certain extent, it will slide down to the condensation water tray below the surface cooler, thus forming condensation water.

II. Practical cause analysis of condensation water generation
The fundamental reason for air condensation is that when the indoor air temperature drops below its dew point temperature, condensation will occur. In actual air conditioning projects, there are many reasons for the occurrence of condensation phenomena, mainly as follows:

Unreasonable design of the fresh air and exhaust system
Due to the unreasonable setting of the fresh air and exhaust system within the air conditioning area, excessive negative pressure is generated, causing unorganized outdoor air to enter the room, thereby increasing the humidity of the air and its condensation dew point. The surface temperature of the air outlet is lower than the dew point temperature of the unorganized air that has just infiltrated the room, resulting in condensation at the air outlet.
Insulation materials do not meet requirements
In air conditioning projects, insulation is a very crucial link. The quality of insulation effect will directly affect the loss of air conditioning cooling capacity and indoor air conditioning effect, and increase the operating cost of air conditioning. More seriously, if the thermal conductivity of the insulation layer exceeds the standard, the thickness is insufficient, or the insulation layer falls off, and the material properties and thickness do not meet the design requirements, condensation phenomena will occur.
Large temperature difference air supply
In order to reduce engineering cost, low-temperature air supply technology is blindly adopted to reduce the air supply volume, thereby reducing the fan power and duct size. However, due to the extremely low temperature of the cold air delivered by the air supply outlet, the water vapor in the air quickly condenses near the air supply outlet due to low temperature, forming condensation water.
Relatively high humidity
Due to poor air distribution or forced use of humidifiers, the relative humidity of the air in the area of the air conditioning air outlet is relatively high, and the dew point temperature rises, making it extremely easy to generate condensation water.
The air conditioning terminal exchanges heat with indoor air to cool and dehumidify the air. Because the wall temperature of the air conditioning terminal is lower than the dew point temperature of indoor air, the water vapor contained in indoor air will precipitate and dew forms on the wall of the air conditioning terminal. When the dew drop increases to a certain extent, it will slide down to the condensation water tray below the air conditioning terminal, thus forming condensation water.

III. Methods to prevent condensation water generation
Based on the analysis of the causes of condensation in air conditioning systems and aiming at the influencing factors that cause condensation, the following several effective prevention methods are summarized:

Reasonably design the fresh air and exhaust system
Adopt measures such as reducing exhaust air volume and increasing supply air volume to ensure a certain positive pressure value indoors and prevent condensation water from being generated due to the infiltration of hot and humid air. When the air conditioning system is running, doors and windows should be closed to prevent hot and humid air from entering and causing condensation at air outlets and other places. Since the air conditioner itself has dehumidification ability, as the air conditioner operates, the indoor air humidity will gradually decrease and condensation will gradually reduce.
Correct selection and reasonable calculation of insulation materials
There are a wide variety of insulation materials with different insulation properties, and there is a wide range of choices. Therefore, the parameters such as unit weight, thickness, and heat transfer coefficient of the insulation materials for air conditioning water pipes and air ducts must meet the design requirements. The thickness of the insulation layer should also be calculated according to the principle of preventing condensation, and not estimated blindly. Preventing condensation means that the surface temperature of the insulated pipeline and equipment should be greater than the dew point temperature of the air outside the insulation layer to ensure that condensation does not occur most of the time.
Reduce the air supply temperature difference
Increase the air supply volume to increase the air supply temperature and reduce the air supply temperature difference to prevent condensation. The air supply temperature should meet the design requirements to prevent the occurrence of condensation phenomena caused by low-temperature air supply. Generally, it can be solved by adjusting the flow rate of chilled water (i.e.
, reducing the flow rate of chilled water), increasing the air supply temperature or increasing the air supply speed.
Reduce indoor relative humidity
The optimal indoor relative humidity should be 49% - 51%. Dehumidifiers and other tools can be used to dehumidify and reduce indoor relative humidity. Under the condition that it does not affect indoor hygiene requirements (such as dust and debris, etc.), the ratio of fresh air return can be changed. Reducing the ratio of fresh air return and increasing the dehumidification capacity can make the supply air state point meet the dehumidification requirements.
Use materials with lower thermal conductivity to make air vents
Thermal conductivity refers to the heat transferred through a 1-square-meter area in 1 hour when the temperature difference between the two surfaces of a 1-meter-thick material is ≤1°C under stable heat transfer conditions. For example, if a wooden air outlet is used, the general outlet condensation is due to excessive indoor humidity, and the air temperature can be increased.
If it is a louvered air outlet, the angle of the blades can be adjusted to make the outlet turbulent. Or a thin PE insulation board can be installed on the side of the existing central air conditioning outlet, or the air output can be increased.

IV. Design of air conditioning condensation water discharge
For central air conditioning projects such as hotels with multiple functions and strong comprehensiveness, there are generally three ways to discharge condensation water:

Set up a separate pipeline system for condensation water discharge and discharge it into the designated drainage ditch. This method is not affected by other factors and is conducive to the discharge of condensation water, but there should be enough space at the installation site and the installation location must be guaranteed. If conditions permit, this discharge method should be given priority.
Set up pipelines for condensation water discharge on each floor, and after aggregation, connect them into the sewage drainage main pipe on a certain floor of the building. In order to ensure that the horizontal pipe of the sewage drainage main pipe on the floor does not condense, an appropriate thickness of insulation layer should be added outside the horizontal main pipe.
Connect it to the nearby drainage pipe nearby at the installation location of each terminal. This method is simple and convenient, but the condensation problem that may be caused outside the drainage pipe due to condensation water discharge must be considered.
After the installation of the drainage pipe on the floor is completed, a water filling test should be carried out to check whether the drainage slope is sufficient and whether the drainage is unobstructed. If any problem is found, it should be rectified in time.