Causes and Preventive Measures for Air Conditioner Condensate Water

I. Overview of Condensate Formation
Condensate water originates from the cooling process of the indoor unit of an air conditioner. When the surface temperature of the heat exchanger drops below the dew point temperature of the indoor air, water vapor in the air condenses on the surface, forming liquid water. This condensate then flows from the drip tray beneath the evaporator and is discharged through the condensate drain pipe.
Theoretical cause: During heat exchange with outdoor air, the surface temperature of the cooling coil on the air conditioning host unit falls below the dew point temperature of the outdoor air. At this point, water vapor contained in the outdoor air condenses into droplets on the coil surface. Once these droplets accumulate to a certain volume, they drip down into the condensate drip tray beneath the cooling coil, ultimately forming condensate water.
Practical causes:

Improper design of the fresh/exhaust air system: An improperly configured fresh and exhaust air system in the conditioned space may create excessive negative pressure, allowing untreated outdoor air to infiltrate the room in an uncontrolled manner. This increases both air humidity and dew point temperature. When the surface temperature of the air outlet falls below the dew point temperature of this infiltrated air, condensation occurs at the air outlet.

Substandard insulation materials: The selection and installation of insulation materials are critical in air conditioning engineering. If the insulation material has an excessive thermal conductivity, insufficient thickness, has become detached, or fails to meet design specifications, it can lead to increased heat loss, reduced air conditioning performance, and severe condensation problems.

Large temperature differential supply air: To reduce costs, some air conditioning systems employ low-temperature supply air technology to decrease supply air volume and fan power. However, excessively low supply air temperatures can cause water vapor in the air to condense rapidly near the supply air outlet, forming condensate water.

High relative humidity: Poor airflow distribution or excessive humidification can increase the relative humidity in the vicinity of the air outlet, raising the dew point temperature and making condensation more likely.

Heat exchange process at the air conditioning terminal unit: When the terminal unit cools and dehumidifies the indoor air, its surface temperature falls below the dew point temperature of the indoor air, causing water vapor to condense into droplets on the surface. As these droplets accumulate, they drip into the condensate drip tray beneath the terminal unit, forming condensate water.

II. Strategies for Preventing Condensate Formation
Based on an in-depth understanding of the causes of condensation in air conditioning systems, the following effective preventive measures are proposed for each contributing factor:

Optimize the fresh/exhaust air system design: Adjust the fresh air ratio to maintain slight positive pressure indoors, preventing the infiltration of warm, moist air that leads to condensation. At the same time, ensure that doors and windows remain closed during air conditioning operation to block the entry of external warm, moist air. As the air conditioner runs, its inherent dehumidification capacity will gradually reduce indoor humidity, thereby decreasing condensate production.

Carefully select and precisely calculate insulation materials: Strictly select insulation materials that meet design requirements, ensuring that parameters such as density, thickness, and thermal conductivity comply with specifications. Calculate the insulation layer thickness precisely based on anti-condensation principles, ensuring that the surface temperature of pipes and equipment remains above the dew point temperature of the air surrounding the outer surface of the insulation, thereby minimizing the risk of condensation.

Reduce the supply air temperature differential: Increase the supply air volume, raise the supply air temperature, or increase the supply air velocity to ensure that the supply air temperature aligns with design requirements, preventing condensation caused by low-temperature supply air. This can typically be resolved by adjusting the chilled water flow rate or raising the supply air temperature.

Control indoor relative humidity: Maintain indoor relative humidity within the optimal range (approximately 49%–51%). This can be achieved by using a dehumidifier or, provided indoor hygiene conditions are met, by appropriately adjusting the fresh/return air ratio — reducing the fresh air volume while increasing the dehumidification capacity — to ensure that the supply air state point meets dehumidification requirements.

Use air outlet materials with low thermal conductivity: Selecting materials with low thermal conductivity for air outlets, such as wooden air outlets, can help reduce condensation at the outlet. When indoor humidity is excessively high, the air temperature can be appropriately raised.

Modify air outlet structure or add auxiliary measures: For louvered air outlets, adjusting the blade angle can increase turbulence at the outlet. Alternatively, adding thin PE insulation boards to the edges of existing central air conditioning outlets, or increasing the air discharge volume, can reduce the risk of condensation.

III. Condensate Drainage System Design
For central air conditioning projects in large-scale comprehensive buildings such as hotels, condensate drainage typically employs one of the following three methods:

Independent drainage system: A dedicated condensate drainage piping system is installed to discharge condensate directly into a designated drainage channel. This method facilitates efficient condensate drainage but requires sufficient on-site installation space and appropriate positioning. It is recommended as the preferred option when conditions permit.

Floor-level collection and drainage: Condensate drainage piping is installed separately on each floor and then consolidated into the main sewage drainage stack at a designated floor level. To prevent condensation on the horizontal main pipe, an insulation layer of appropriate thickness must be applied to its exterior.

Direct connection to nearby drain pipes: Each air conditioning terminal unit is connected to the nearest available drain pipe. This method is simple and convenient, but attention must be paid to the potential for condensation on the exterior wall of the drain pipe caused by condensate discharge. After installation on each floor, the drain pipes should undergo a water-fill test to verify that the drainage slope is adequate and that drainage flows freely. Any issues identified should be rectified promptly.