Submarine ventilation

Diesel-powered submarines are forced to resurface regularly to get a fresh supply of oxygen and to dispose the waste gases they produce onboard. The humidity levels might reach high values during air intake or stealth mode. Therefore; generally DX coils and jet fans are used for space ventilation, whereas medium temperature chillers are used for electronic systems cooling.

Humidity 

The reason behind using DX coil systems is to reduce air temperatures to eliminate humidity in the air. Also during stealth mode the HVAC system for space ventilation might be paused for certain periods which also creates high humidity inside the ship. Thus, DX coils remove the humidity much faster.

Solutions for nuclear submarines

Nuclear submarines are generally much bigger in size and therefore one DX system might not be enough. There are generally two types of solutions:

1. Having two independent identical systems on either side of the ship’s center line, working in conjunction with the direct-expansion coolers.
    
2. Having a chilled water unit with low temperature (e.g. 7-12ºC) water trace in order to handle the humidity problem. However, the problem with this solution is that condensation forms on the electronics. In general, new ships adopt medium temperature chillers for weapon management systems, which have a trace of 18-24 ºC.