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How do I calculate the moisture load for my battery dry room application?

When considering the moisture load for battery dry rooms, it can be split into two categories:

  1. The internal load
  2. The infiltration load

While any source of moisture should be limited to a bare minimum it will not be possible to eliminate completely due to the below.

The internal load

The internal source of moisture should be limited as much as possible in dry room applications. Therefore, the only source of moisture in such dry rooms is typically personnel who need to access the room during operation. The maximum number of people expected to occupy the room at once normally dictates the internal moisture load of the design condition.

Cotes calculates the internal moisture load per person as 120g/h.

The infiltration load

To reduce infiltration of moisture into the dry room, there should be kept a positive pressure compared to the surrounding environment. With the slight over-pressure in place, it can be ensured that internal humidity levels are not disturbed by leaks. However positive pressure will result in air loss.

The lost air must be fed into the dry room via the dehumidifier. The required amount of air is taken from outdoors at much higher humidity and thus, introduces a great humidity load on the drying system.

The tighter the room is, the less air will be required to hold a positive pressure and thus less air will need to be dehumidified. 

Furthermore, any intended air extraction from the room will add another requirement for fresh air resulting in larger and more costly dehumidifiers and an increase in energy consumption.

The consequence of fresh air requirements is highest in times of high external humidity levels.


In summary, to calculate the moisture load, the following is required:

  • The number of workers to occupy the room at the same time.
  • External design conditions.
  • The volume of air required to hold positive pressure (room tightness).
  • The air required for extraction.