How to decrease humidity level in a server room
Solution 1:
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humidity level inside the room is far from the ideal.
That depends.
"Ideal" usually means 0%, as no water based corrosion will be possible at all. Of-the-shelf servers, switches and equipment usually does operate at ~65% relative humidity without any problem, when the temperature is high enough to prevent condesing.
From the HPE ProLiant Guides:
[...] Operating relative humidity: 8% to 90% (non-condensing)
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I heard that using a dehumidifier can cause static charge buildup in the room.
This is somewhat true; the static charge buildup is not directly caused by the dehumidifier, but by dry air (and moving parts inside your servers). It is very common in plastic industries, for example, to prevent electrostatic discharge with high humidity.
Constant air humidity can decisively contain static electricity environment. Above an air humidity of approx. 55%, the conductivity of the air is sufficient to discharge the electrical charge into the atmosphere - without causing any damage.
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What are my options to solve this issue?
From your drawing, I conclude that your server room has about 20m³. To get that ~60% humidity out of the air, you can use electrical dehumidifiers or a chemical one. While the chemical one is usually good for one or two drying-sessions (around 3$ for ~500ml, good for 20m³), for long-term usage I would go for the electrical one. It's cheap, around 100$, and you can just get one from your local hardware store. Most "at home" devices are made for ~100m³ and will fill your needs (close the doors, windows and ceiling fans).
My personal opinion is, just leave it. A humidity level of 50-80% is very common in server rooms (of this size) and most of the usual equipment does not have any problem with it. Just keep a close eye on the temperature; you want to prevent condensing at all cost.
Solution 2:
I heard that using a dehumidifier can cause static charge buildup in the room.
Then the server room was designed by an idiot. ANY server room I have seen in the last 30 years had the racks and (this, automatically) all relevant equipment grounded. Once grounded, and buildup charge is automatically discharged to the ground.
Also, dehumidifiers can cause charge mostly because dry air supports build up charge. Given that your server room is more like a humidor that is sort of a wanted state, you know.
How the heck do you end up with a wet server room to start with? With no window open, all entries normally closed and air conditioning running I would seriously investigate where the water is coming rooom. Unless the door is open all the time OR totally unsuitable for a server room - the humidity inside should slowly go down.
Solution 3:
You need to add heat to the server room. Enough heat to make the A/C work harder to maintain your set temperature, but not so much heat that the temperature rises above the desired range.
A well-designed HVAC system for a server room will include an air cooling device, a separate air heating device, a temperature sensor and a humidity sensor. If the air cooling device and air heating device are within the same air duct, the air cooling device MUST come first. During times of high humidity, the A/C will cool the air below the desired temperature and remove a lot of humidity, then the heater will boost the air temperature up to the desired temperature, resulting in much dryer air than an A/C alone can give you.
If you are using a mini-split HVAC and using the "Dry" mode, this simply reduces the fan speed to improve dehumidification. Ultimately, it will not give you the dry air that you desire. A standard mini-split is the wrong equipment for this room.
Try a one-day experiment: forget about "Dry" mode. Use "Cool". Set your air conditioner for the desired temperature, then plug in the biggest electric heater that you can safely run in the server room. Monitor the temperature and humidity. You will be pleasantly surprised. I predict that you will see a dramatic drop in humidity within the first 1-2 hours with no change of temperature.
The permanent solution is to hire an HVAC contractor that knows how to control temperature AND humidity, and this will involve both heating and cooling at the same time when it is hot and humid.