Refrigeration coil for Server Room A/C

[hammerdog]

Hey all,

Sorry if this get long winded. More info is better than too little. I need some input on a little server room project. I am expanding my server room because it has just gotten TOO small. I have a typical IT department that feels the need to take up every last availble space in the rack with "another blade or switch" and if the room can fit two racks then let's stick another rack in the room....fill it with blades and switches...blah, blah. My air flow is now non-existing and my mini split is satifying the room temp of 68 but not neccessarily keeping the servers as cool during peak usage.

Original layout of the room is 6' x 10' x 8' high. I installed a 21,500 BTU mini split at 7' for the single 6' rack. Over the years an addional 6' rack and computer station was placed in the room. The existing mini split system still maintains the room temp but with the air flow pattern non-existing we've had to add box fans to create an adquate air pattern. Per HP, Dell, APC etc the total BTU output (once you add up their calculations) is 90,000 BTU!! There is no way my server room need or could handle an 8 ton unit.

Now, for the feedback.
I'm going to elongate the room and add a new primary cooling system but leave the existing mini split as my back-up or supplemental system. I feel that a walk-in type ceiling mounted fan coil would be best because they draw from the back and exhaust cool to the front. I can place it towards the rear of the racks (heat load) and exhaust cool air above the racks and cycle off the wall back into the servers. Since my new server room will basically be longer than wide I will be creating a cold front portion and a warm back portion. The air flow pattern is ideal. Since the walk-in fan coil is 3-4 times the CFM of my A/C fan coil I figure I can maintain or drop my BTU rating of the coil (compared to an A/C coil) and then size comdensor unit. My thought process was to basically to create an over capacity wine cooler.

Here is what I plan to mesh together; Tecumseh 1 hp R135A AJA4512 Condensing unit (interior-place in warehouse) with a Bohn 9000 BTU, 1300 CFM electric defrost (should never need). I'll use a pressure switch and TXV instead of a thermostat. So, what am I missing or over looking?

Rip away...

 

[willard3]

If you want to do this right, hire an Engineer.

 

[DRWeig]

Compared to the cost of your work, the cost of an engineer can be minimal.

I'll share similar experience. Note that I did hire an ME to help out, he spent 90 minutes at the room sketching out a budget-happy way to do it and left the details to me since it was such a small project. Being able to stand there in the actual room is lots better than trying to envision something over the internet in a forum.



Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[hammerdog]

Heck, always easier to pass things off to someone else. Too many company dynamics and politics to list as why I just need to take care of everything myself.

Ignore the room etc, what are the "issues" of using a refrigeration fan coil in an A/C application given Im using 134a? No one wants the wind tunnel effect for A/C so don't move enough air in my opinion for server room applications.

 

[willard3]

Also, read forum policies which begin as follows:

>>>These fora should not be used to bypass your own in-depth research on the issues that affect you, nor is it intended to be a substitute for appropriate professional assistance within your field or geographical region.

 

[DrRTU]

I have been doing D/B contracting for over 25 years. We have completed numerous designs of installation of customer supplies equipment or our used / salvaged data equipment for data rooms. First, do your math correctly on the room load. You state the RSG is 8 ton and the you are using a 21K total DFS split which at best 60% sensible. Adding 9K even at 90% SR does not seem correct. What happens to your machines & room during high power use? The use of a high temp condensing unit can make sound sense due to low ambient and robust components but the application will be odd due to elevated suction conditions. Stay away from a suspended exposed evap unit. Yes lower fan hp but moisture above a rack is bad. The parts you are quoting sounds like refrigeration guy has left over parts and your trying to make it work. Do the math on a used Liebert, second larger DFS or fan coil and ACC with head pressure controls &HGBP. If you build up a system, think about service when you are not around. Hot isle and cold isle is great. Don’t be concerned about too much air flow – its a data room. You don’t see wine coolers with 80F entering conditions. A turbo air ductless will give you better reliability than what you are trying to do.