Rate of absolute humidity increase in space

[sider]

Hi all,

I could use some advice regarding the issue of increased humidity in the building.
I am currently on a project that is being built with a dew point of the outside air of 23.2°C (x=18g/kg). The space is cooled by the perimeter CRAC units which also have to cool and dehumidify outside air (only 1 does dehumidification). The new building in question is a data center with a raised floor and cold and hot aisles. A small part is the cold aisle (temperature of supply, the one where there is server intake, while the other area is the hot aisle (temperature of return).

After the dehumidification is done to the relative humidity of 60% for 22 °C (x=10g/kg), the absolute humidity decreases, but after the cycle starts, the humidity quickly rises, even though the building looks sealed quite well. The space volume is 500 m3.

There is no pressurization in place for the given space during the testing now, and although there is an opening of doors from time to time, from my point of view the humidity rises so fast.
So my question is, could somebody maybe help how could this happen?
I understand that without pressurization, there could be local spots of underpressure (on CRACs inlet), but is that sufficient to somehow pull the air from outside through some cracks?

 

[nuuvox000]

Yes, depending on where the returns and supply are located, it could be pulling in air at one point and pushing it out in other places. Is there any ventilation for the space? I believe there should be if the area is every occupied. This can be used to pressurize the space. What do the spaces look like around the server room? I was on a project once where they placed the server room next to a warehouse with evap coolers. Just imagine the humidity issues they would have with that setup.

 

[sider]

Yes, there is ventilation provided which is planned to supply fresh unconditioned air from the outside, which the units should dehumidify, but, with it on, humidity increases even faster.
The exhaust from the server room would transfer to another one, however, with the fan on, there is pressurization, but there is also additional latent load.
So even without ventilation on, and transfer dampers shut, there is ingress of humidity.

Spaces around the server room are conditioned (1 side), the other 3 sides are outer conditions with high humidity as mentioned.
I am puzzled how fast the absolute humidity rises once it is down.

 

[nuuvox000]

If it increases even faster with the ventilation unit, then I think your ventilation unit is not able to dehumidify the air; if it's important to maintain a relative humidity, you'll need a dehumidifier.

Why is there exhaust in the server room? What is it's purpose?