Heat + Humidity = Hazard
Hot spots are areas inside the electronic enclosure that are not involved in natural convection. Formed mainly around the top of the electronic enclosure, hot spots occur due to undercuts or installations that prevent an exchange of air. A rise in ambient temperature can intensify the severity of hot spots.
In addition, external heat sources located near the enclosure can cause problems inside the enclosure. An open area, large orifices or a missing enclosure panel can produce avenues for external heat, dust and humidity to enter an enclosure. External heat sources also can magnify internal temperature.
If the temperature in the area surrounding the component rises to its maximum operating temperature, critical point is reached. If a component inside an enclosure reaches critical point, the only recourse is to open the enclosure. This is only a short-term solution. Active cooling via a closed-loop air conditioner, however, can prevent this type of crisis.
Humidity Inside the EnclosureHumidity is another enemy of electronic equipment. As the humidity levels inside an enclosure increase, the life expectancy of the components inside the enclosure decreases (figure 3). An air conditioner reduces the humidity level by converting the warm air inside the enclosure into cold air. This encourages the accumulation of condensation inside the air conditioner and dehumidifies the air inside the electronic enclosure.
At the beginning of the cooling process, the air conditioner produces a relatively high amount of condensation, which is collected and burned off into the atmosphere or released through a condensate drain line. Condensate must be extracted from the unit or it may cause damage to the electronic equipment. After a few hours of operation, the humidity inside the electronic enclosure adjusts to a constant level, lower than that outside the electronic enclosure.
Operational IssuesAn electronic enclosure air conditioner incorporates two airflow circuits: internal and external. The internal circuit cools the inside of the electronic enclosure. (figure 5). Thermal energy is extracted from the air inside the electronic enclosure by the coolant in the refrigerant circuit. With the aid of the condenser, the coolant transports the thermal energy into the external airflow circuit, where the coolant is cooled to release the thermal energy.
Correctly sizing an air conditioner requires precise information about the installed power components' heat dissipation, how the components are mounted and the type of enclosure to be used. Finally, the ambient conditions, including the dust or emission content in the ambient air, relative humidity level and known fluctuations in ambient temperatures, should be described.