Size isn't everything...
One key piece of information you're missing is the power consumption of all the equipment in the room.
Reg reader "PG" has mailed looking for advice on "a suitable air conditioning unit for a small office/data centre." PG says the facility has "no windows, only a door to the outside world" and is approximately "6m (l) x 3m (w) & 2.8m (h)." "It's over 33c in here today and a few of the non-critical servers have shut down (rack …
Unfortunately, there isn't. There are entirely too many variables in the question ""I have a single-car sized garage in an undisclosed location, with unknown insulation, unknown available power, and hardware consuming an unknown amount of power, that I need to turn into conditioned space; can you help?" ...
Suggestion: Call out three local HVAC companies, and get three estimates. Make sure each company knows you are talking to two other companies. Do not name drop between companies! This probably your best option from a cost/benefit perspective.
Or, if you want to wing it, head to your local large "home center" and ask their "expert" for advice on this kind of installation in your area. Then take the recommended kit back to the shop, install it & keep your fingers crossed.
"windowless room" suggests that it's deep in a building. Are there ducts, or can you drill through to the outside? Without an external heat exchanger, you won't achieve very much.
As an aside, to Jake, I'd call an air conditioning company to avoid having embarassing conversations with High Voltage or High Vacuum engineers. The FLA "HVAC" is Highly Ambiguous.
... I rather suspect that in this conversation, there is absolutely zero ambiguity whatsoever when one uses the term "HVAC".
I have been putting in servers since the Glass House days, and have never had anyone ask why I needed high vacuum or high voltage AC to keep the hardware cool when I bring up newly required HVAC needs.
The second thing is to put a big ventilator or two in the open door and blow out the heat. Perhaps you can survive until the aircon people arrive.
Oh, and better get someone to install it for you. The pipes between the heat exchange unit and the AC are not trivial to install.