Guide to Condensation Management for Thermoelectric Cooling

The difference between smooth operation and operational failure

Condensation is a natural part of the cooling process. As the air conditioner cools, it will begin to dry the air within the enclosure and the moisture in the air will condense within the air conditioner. It is important to fully understand condensation so it can be managed correctly. While it is a completely normal process, without proper management condensation can cause serious damage to housed equipment.

What is Condensation?

Condensation is the process of reducing a gas or vapor to a liquid. During this process, water vapor is released from the air in the form of small drops of water (condensate) on cold surfaces, which become wet. Condensation occurs when the temperature of a space drops below the dew point, determined by the relative humidity in the air. Because water needs something to condense on to, condensate will form on the coldest surface of a cooled space. During thermoelectric cooling, this is typically the heat sink fins on the cold-side or internal portion of a thermoelectric air conditioner. Factors affecting condensate formation are:

• Relative humidity: When the relative humidity is high, the dew point is much closer to the ambient temperature. In environments with high relative humidity, even a small drop in temperature can create condensate.
• Temperature drops: When the ambient temperature drops quickly, the dew point does not always follow. Quick drops in ambient temperature can change the point at which the condensate will form and therefore moisture will condense on cold surfaces.
• Improper sealing: In an enclosure that is not properly sealed from the ambient environment, new air is constantly being introduced to the cabinet. This new air brings the ambient relative humidity with it. The air conditioner cannot effectively dry the air with constant introduction of moisture.
• Frequent equipment access: Equipment that is regularly accessed by opening doors or panels will continually be exposed to the ambient air at large volumes. In humid areas this will repeatedly raise the humidity levels in the enclosure and cause a regular generation of condensate.

EIC recommends a number of management options to avoid these common pitfalls:

• Drip Pans: All of EIC’s air conditioners have integral or auxiliary condensate drip pan options. These pans are designed to collect the condensate as it naturally flows down the heat sinks without impeding the airflow. The liquid is then routed out of the pan through a brass sump fitting and into a PVC drain tube.
• Drains: In most applications, the tube is simply routed out of the enclosure and allowed to drip as needed. Once outside the enclosure, the drain line can be routed to a collection basin, building drain, or directed outside through an exterior wall.
• Wicking Material: Wicking material is a viable solution when looking to allow condensation to exit the enclosure while avoiding the possible collection of water on surfaces below the drain line. The wicking material is inserted in the end of the drain tube and slows the release of the condensation, allowing it to be evaporated into the ambient environment.
• Absorbent Materials: In applications that cannot have any drainage from the cabinet, absorbent material can be installed in the drip pan to absorb any moisture that might collect. This must be regularly monitored in order to ensure the material does not become saturated and leak into the enclosure.
• Evaporators: The drain line can be routed outside of the enclosure to an evaporator. This is simply a small collection basin with an integral heater to expedite the evaporation process.

In the case of Class 1, Div. 2 condensate management, many enclosures cannot have a free-flowing drain line to the exterior environment. This is due to purging of the enclosure or the presence of ignitable gases in the ambient air. EIC recommends using collection containers within the enclosure that need to be manually emptied once a certain level of condensation has built up. Alternatively, some applications are well suited for a simple looped drain. This loop will hold a certain amount of liquid at the base of the loop and only allow condensate to exit when it fills above the upper part of the loop (similar to a sink trap).