Humidity vs cooling?

im planning my next “server room” build. what i have so far is under the bed, 28" height, 54" wide, and 62" long, with insulation those dimensions will be less. 7 systems and 6 ups, pulling roughly 4000W of power, * i don’t have all the systems yet so i don’t know what the true power draw will be. network, cabling management, . . . . . is taken care of. SO now im stuck on “cooling”, i have 2 options.

1: make it a closed system. mount a blog cooled radiator, blog cooler outside with the cold water piped to a radiator under the bed, with fans cycling the air. with the radiator being the coldest part under the bed, it should grab 99% of any humidity/condensation, which will be piped back out side. MY ISSUE, if i have to open it up to do maintenance, the humidity of the room will flood in and may cause condensation on the computer systems. i guess the humidity difference between the room and under bed could be upwards of 60%

2: make an open system. starting with a filter to an inline dehumidifier and a high CFM fan. while routing the air duct around insulation to help damping the sound. finally exhausting but into the room. MY ISSUE, i’ll have to run that inline dehumidifier 24/7, and my HVAC system will have to run harder to keep up.

thoughts? other cons im missing? any other designs that would be better? Thanks before hand for reading this far.

Honestly both options seem like they will cause headaches. If you already have an HVAC system in the building then it would be easiest to leverage that as long as it isn’t already pushed to the limit. I did something similar once where I installed a larger duct and added a return to a room to keep it cool with all of the computers running.

For #1 I’m going to assume you conflated swamp-bog-blog, because no reasonable searches came up for ‘blog cooler’. Those only work well in really low humidity environments, so if you could have “upwards of 60%” humidity difference from an ideal box to the normal room humidity then that says a few things:

  • As mentioned, it would be a nightmare if you had to do maintenance or had some sort of failure where humid air pours in to a system below the dew point
  • This air at no less than 60% humidity will not cool very well with a swamp cooler, which negates the ‘below dew point’ aspect, but won’t cool the servers box off sufficiently
  • Even if it was dry enough to be effective, it would constantly use a lot of water to cool off a few thousand watts of gear
  • Constantly having to tend to refilling the swamp cooler
  • I live at the beach in Florida and the humidity is around that point outside. If the room is in a house with HVAC and doesn’t regularly see windows left open for hours or the system shut off indefinitely then humidity shouldn’t be quite that high indoors

More info would be needed about the environment of this server box under a bed. Not to mention the poor soul who has to sleep on this beast.

My experience with #2 is that using a dehumidifier in an air conditioned space is a massive waste of electricity (money). If you need humidity control above what your system currently gives while only heating/cooling then I believe they have thermostats that can cycle the system to keep both temperature and humidity in check. I have heard several people mention it recently but I haven’t seen it first hand.

An existing HVAC system should be able to easily deal with the load of a few extra servers. In many instances I see issues with airflow caused by too narrow and long of ducting for a room, and no way for that air to return so it is forced to return under a door. The narrower that gap, the more air restriction and less airflow.

I would run the system full tilt with the door open and see if heat is an issue. They make duct booster fans which can help with a lack of air while the HVAC is running, but I would make certain it has a sizable duct running to the room and add extra insulation as needed first since those measures don’t use electricity and are unlikely to fail. The room may need its’ own return duct.

4kw of equipment, in a bedroom?


again im not 100% sure, because i don’t own all of them yet. 3 systems with duel 1200W PSU each, and 4 computers with 1 700W PSU each, so roughly 4000W. im basing that off of the power supplies, not the gear that will be in them.

  • i live in middle of nowhere Virginia, roughly 40 to 100% depending on the day.

i will be sleeping on the bed. and there will be about a foot of insulation between the top of the servers and the bottom of bed.

i know a dehumidifier is a massive waste of electricity, that is my main issue with that option.

having them under a bed poses problems for efficient air circulation within the confines of the space and will also pose some problems maintaining them.
Its far better to place them in a closet or a dedicated enclosure designed for servers.
insufficient volume of space within any enclosure poses massive problem for humidity control as it is harder to remove heat from ( a small space will heat up rapidly and catastrophically if an exhaust fan fails)
typically a dust proof server cabinet has a 120mm filtered intake fan (located near the bottom of the cabinet and 1 120 mm exhaust located near the top ( this can be ducted outside or anywhere you want it))
Desiccant bags can help a lot. This site specializes in them .

this will be a 20 ft by 8 ft by 8ft shipping container micro home, under the bed is all i have.
and you clearly miss the “inline dehumidifier and a high CFM fan”, a 120mm fan is 70.5 CFM and im talking about a 460CFM fan. a fan blowing in and a fan blowing out. by my math the volume of this “enclosure” will be about 8 cubic feet, thats 57.5 times per MINUTE the “dirty/warm” air will be replaced.

As a human you want to maintain somewhere around 50% relative humidity, for your own health and comfort.

4kw is somewhere around 13k BTU. You could use a relatively simple and cheap (few hundred $) split system heatpump/ac to move that kind of heat outside. Only, it would cost you around 1kw -1.5kw of power to move it outside in the summer heat. You’d get dehumidification for free (not good if you go too far, but whatever, it’s easy to monitor).

Now, if you want to save power, you could theoretically do what hyperscale datacenters do… or at least maybe do something based on the same principle - setup cooling such that you can use the natural temperature differentials to your advantage and you don’t have to waste a lot of energy moving refrigerant around. In your case water cool as much as possible and connect to radiators outside. Theoretically you could go as high as keeping 80C in a loop, as it’s likely never more than 45C outside that means you don’t need a lot of refrigerant flow or lots of fan throughput. But you do need to be careful how you pick the cooling components for those temperatures.

Also, there’s going to be some heat you can’t capture in a loop like that, you can move extra heat by using a standard / smaller ac.

your in a bit of a quandry here as @risk suggested a small heat pump may help.
as he said going too far is going to produce a severe static environment.

If you are going to chill cool the cabinet you will always have some condensation problems. But your air movement should be enough to dramatically reduce that.
desiccant filtering can help remove some of the moisture from intake fans but you will not get rid of all of it.

one other thing do not use ionizer type air cleaners in any computer room or cabinet.
Ionized air transmits a static charge magnitudes above what dry air can do

im planing to set the inline dehumidifier between 40-60%. for me and the system i figured 24,000btu ac/heater, im sure i wont need the heater side. and 4kw is just a guess based on the PSUs im sure the running systems will be less then that.
so your saying some kind of geothermal cooling loop to help in the summer months.

Mini split

Anything else is just overcomplicating it.



You might as well just rig a dehumidifier to the HVAC intake inside the house and make a Rasberry pi thermostat and program it to run the fan if x humidity and shut off at x humidity unless HVAC is already running…

If that doesn’t work you might as well get one of those wall mount AC like a Samsung or LG. Then route the cold air threw a dehumidifier. On the opposite side of the room install a fan to vent the heat and to the outside and configure it to come on if its to hot or humid… And close off the HVAC vent to the room.

Basic but space saving and automatic once you get it tuned.


oh a “Ductless Mini Split Air Conditioner”, Adubs only used 2/5 of the name,so i wasn’t sure what he meant.

I used to run about a quarter rack in an enclosed space with active ducts and various other rigged environmental solutions similar to what you’re planning. I have since moved it to colocation at a datacenter an hour away. The entire cost of the colo is about what I was paying in extra electricity, not to mention the material costs of the ducts, beefy A/C, in-line fans, etc.

Idk what your reasons are for wanting to keep your servers in that close of proximity to you, but if you expect it to be cheaper than renting datacenter space, that might not be the case.

i live in the middle of no where VA, im sure the closest data center would be 3+ hours away

i’m a single guy, and at work most of the time, so i don’t see myself “using” a full 1 to 4 bedroom house. So build a 20 ft shipping container micro home, buy a house with the right property line, partition it so i can move said micro home to the back part of the property, and rent the house out.


doing something like that you have the rental home for the income providing your renters are good at keeping up payments It wouldn’t cost too much to build a small room on your container home to house your servers
an 8 by 8 shed can be well insulated and sealed fairly easy and would be a lot easier to maintain a controlled environment in.

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