Simultaneously cooling and humidifying in winter?

Question

I have a couple racks of server equipment that generate a fair amount of heat, so I basically need cooling year-round. I'm in a building that has 2-pipe HVAC, i.e. central A/C during the summer and heating during the winter. The temperature is comfortable during "A/C season", with it on HIGH 24/7, but has been uncomfortable during heating season.

I turned the convector completely off when they switched to heat in the building, but that wasn't sufficient, it would get up to 80 degrees just due to the ambient heat of the building at large, and even blowing cold air in from outside when it was cooler wasn't sufficient, particularly on warmer days. So I ended up getting a portable A/C unit for the space, and it actually worked very well, even though it was only a single-hose unit. When it was cold enough outside (under 60 degrees), rather than running the A/C, I would just leave some ducting coming out of the (horizontal) window in place to bring some of the cooler air inside.

A little bit later on, I noticed I was getting shocked a lot with static electricity - surprise, the humidity was very low. I've been taking some measurements and it gets as low as 20% RH. I got a humidifier which has been able to help a little bit, but this is the conundrum that I run into:

• If I leave the window completely closed, it gets far too hot inside. No matter how cold it is outside (even below freezing), eventually I will need to turn on the A/C or open the window
• Any time the A/C runs, it automatically dehumidifies. This is fine in the summer, but counterproductive in the winter, when the humidity is already low. In fact, the few times I've run it most recently, no condensate even drained out of it, so I think the humidity was too low for it to dehumidify anything.
• Opening the window (or running the A/C) will bring the humidity down, when it's already too low inside. For example, I just opened the window an hour ago this morning, and the temperature has dropped from 73 F to 65 F, but the humidity has also dropped from 25% RH to 20% RH, bad to worse. And the past few days I've run a humidifier, it hasn't seemed to be able to successfully get the humidity above 25% (maybe because the outside air was cooler/drier?). I would like to be able to maintain it in the 30-40% range, since somewhere around 30-35% I stop getting shocked.

Is there a good way that to simultaneously keep the temperature low, while maintaining a comfortable humidity? I realize that normally these are opposite goals. These seem to be in constant tension with each other, since bringing cold air in from outside will make the air drier, and running the A/C will actively dehumidify the air. I imagine if I had the window constantly open (or A/C running), and enough humidifiers running at the same time, I could probably maintain a desired humidity, but that seems far from ideal. (For example, I imagine I could fill the humidifiers up, run them, and then potentially drain the same water as A/C condensate, which seems silly.)

Is there a way I can effectively keep the space cool (60-65 F) while preventing the humidity from dropping too low (~35%)? I should mention, the space in question is just one, large space (with a window), and that is the space I am trying to cool/humidify.

Requirements/considerations:

• The equipment generating the heat cannot be moved/altered
• No (permanent) modifications can be made to the building
• I can open the window (or close it)
• I can obtain and run equipment (e.g. portable A/C, portable humidifier, etc.)
• I don't have any preference between opening the window or running the A/C (besides the window can only be opened if below, say, 55 F, to be able to cool effectively). I would be fine with running the A/C even in cold or freezing temperatures, if that was somehow more optimal for sustaining humidity levels.
• Efficiency and electricity usage are not considerations (aside from not tripping a breaker)
• This is only for "heating" season (e.g. winter). In the summer, the central A/C is sufficient.

Answer 1

You need a separate humidifier - or perhaps a "swamp (evaporative) cooler".

The nature of AC, or bringing in cold outside air and heating it, is that it results in low humidity, because the AC coils get cold enough to condense water from the air inside, or the outside air simply can't hold much water if cold; Warmer air can hold much more water. So with a certain amount of water in the air, even if it's 100% humidity outside, the warmed air is lower % humidity because it can hold more water than the cold outside air does.

A "Swamp cooler" cools low-humidity air by blowing it trhough a damp pad - the evaporation both cools and humidifies the air. In your setup, that would go on the hot-air output of the rack equipment before it made it to the rest of the house.

For instance, when running from outside, you'd go outside air to rack intake to rack output to swamp cooler.

A humidifier simply runs room air through a damp pad to humidify it, and would probably best be placed away from the rack equipment and AC.

Answer 2

Some other things that might help:

1. Vent your A/C to the rest of the building rather than the outside.
2. Draw the air for the A/C from the rest of the building.
3. Weatherstrip the top and sides of the door from the server room to the rest of the building.

Drawing cold, dry air from outside is going to reduce the humidity more than if you get more humid air from inside. It requires more work from the A/C since the inside is warmer, but that's well within the capability of an A/C. They normally move heat out of the cold inside and into the warm outside. That's how they work all summer.

If you move the heat out of the server room and into the rest of the building, it reduces the heating needs of the rest of the building. The way that you have it now, you're increasing the heating needs of the rest of the building. You're venting heat out of the server room to the outside. Some of the air that replaces the vented air will be heated air from inside.

The weatherstripping would encourage the air draw to be from the cooler air near the floor.

A bigger project might be to add a high air return from the server room to the central system with a multi-zone system that would allow cooling on one zone while another is calling for heating. The server room would be its own zone and receive cooling year round.

Another option is to put in a ductless mini-split to cool the server room that exhausts its heat internally. Preheat water to the boiler. Or preheat air to the furnace. The ideal would be to tie into a centralized heat pump that can vent outside if there's too much heat or keep the heat inside when it's cooler.