Prevention And Control of Condensate Overflow in Fan Coil Units

The overflow of condensate from fan coil units is a common malfunction of centralized air conditioning systems in summer, which often occurs in hot and humid weather and can cause unnecessary damage to air-conditioned rooms. 

For example, in the following situations:

a) The water stains on the ceiling panel damage the indoor building decoration, and the maintenance workload of the fixed ceiling will be greater.

b) If the overflow of condensate is not detected in a timely manner, it will damage office appliances.

c) Special rooms that require 24-hour air conditioning, unmanned electrical equipment rooms, etc., usually cannot utilize the fan coil system or VAV system in the office area. The air conditioning system is often configured separately, and the overflow of fan coil condensate can cause greater economic losses to these rooms.

The overflow of condensate from the fan coil unit is caused by the blockage of the condensate water pipeline connected to the condensate tray of the fan coil unit. Due to the operation of the fan coil unit under wet conditions in summer, the dust and fine fibers on the surface of the heat exchange coil unit will be washed down by the condensate water and deposited in the condensate water tray, leading to bacterial growth and the generation of gel like dirt, gradually blocking the condensate water pipe. There are several reasons for the overflow of condensate water from fan coil units, including equipment manufacturing, engineering design, construction, and operation management.

The condensate generated during the operation of fan coil units, integral air conditioners, and combination air conditioning units must be promptly drained. The design of the condensate discharge pipeline should pay attention to the following matters:

Horizontal pipelines should maintain a slope of no less than one thousandth along the direction of water flow; And no water accumulation is allowed.

When the condensate tray is located in the negative pressure section of the unit, a water seal must be installed at the outlet of the condensate tray, and the height of the water seal should be about 50% higher than the negative pressure (equivalent to water column temperature) at the condensate tray. The outlet of the water seal should be connected to the atmosphere.

In order to prevent condensation on the surface of the condensate pipeline, anti condensation verification must be carried out.

The top of the condensate riser should be designed with a breathable pipe leading to the atmosphere.

When designing and arranging condensate water pipelines, the possibility of regular flushing must be carefully considered, and necessary facilities should be designed and arranged.

The nominal diameter DN (mm) of the condensate water pipe should be determined based on the calculation of the flow rate through the condensate water.

In general, about 0.4kg of condensate is generated every 1kW of cooling load per hour; In situations with high latent heat load, approximately 0.8kg of condensate is generated every 1 kW of cooling load and 1 hour of cooling load.

During the construction of the air conditioning system, insufficient installation of the inclination angle of the condensate tray of the fan coil unit, long condensate pipeline with few supports, and insufficient slope during the construction of the condensate pipeline cannot guarantee the stiffness of the pipeline can all cause poor condensate discharge during system operation. In addition, the absence of a cleaning port during the construction of the condensate pipe may result in the inability to clean the condensate main pipe during use.

Failure to regularly clean all fan coil units and condensate water pipelines by operation and maintenance personnel can also cause condensate water to overflow from the fan coil units. In theory, the condensate tray of fan coil units should be cleaned once a year before use in summer, and then cleaned again after running for 2-3 months. Many large office buildings have air conditioning systems that operate from March to December, while electrical equipment rooms provide cooling throughout the year. As a result, the condensate pipe of the fan coil unit needs to be cleaned 3-4 times a year to avoid blockage.