Data Room Cooling - High Ceiling

[new2hvac]

I'm looking at a cooling application in a computer room. The equipment, lights, people, etc amount to about a 40-ton load.

This room is about 6000 SF and does not have a raised floor. The room is currently being cooled by the building system which is ducted above the false ceiling...about 15' above the floor.

How can I design this system to ensure there is enough air flow to reach the equipment on the floor? I've heard I should double the typical CFM/SF (4 CFM/SF around the exterior walls and 2 CFM/SF in the interior). Would this work? Is there a more "proveable" method? Are there certain types of diffusers that would work better than others?

 

[KenRad]

new2hvac,

I’m no expert in the design of computer room HVAC, but I can tell you what my experience has been in dealing with these rooms and the folks who own them.

First off, it is very unlikely that you will be able to satisfy both room occupants and the MIS folks who specify that the room be maintained at near Arctic conditions, unless of course they are one in the same. In this case, the information specialists will gladly break out their fur-lined parkas, knowing that their precious servers are enjoying a comfortable existence. There is no low end to the temperature specs for these rooms.

Your question implies that the cooling equipment is existing. If it is not too late, you might want to consider building some redundancy into your equipment arrangement. If you only have one air handler or rooftop unit serving this space, how are you going to repair or maintain it, and still keep all that computer equipment from certain meltdown? One of our computer rooms has enough 5-ton Liebert packaged units to survive a SCUD missile hit without losing adequate cooling capacity.

On the subject of air distribution -- think wind tunnels. If they haven’t done it already, it is only a matter of time before they stuff 12,000 ft2 worth of electronics into your 6,000 ft2 room, creating hot spots due to lack of air movement. The more violent you make the air patterns, the more likely the conditioned air will find its way where it needs to go. Again, computer department occupants will be thrilled.

Another must for air distribution is flexibility. If you’ve been paying attention to the computer room over a period of months, you’ve noticed that these people have a habit of re-arranging things about as often as Intel comes up with a new processor. If you’ve achieved some semblance of balance with the air distribution, it will soon be destroyed. I use ball-and-socket type diffusers with adjustable deflection and rotation, and leave the settings to whoever is doing the re-arranging. A company called Air Concepts makes these (

http://www.airconceptsinc.com).

---KenRad

 

[mdonner]

I suggest to use return air hoods over hot spots (equipment), with diffusers over the isles.

 

[stevenw]

Welcome to the world of the computer room.
Yes they keep it cold in the room.
Ask they for a wish list.
Most operators have seen several computer room and can tell you what they liked.
Run your ducts down the isles.
Give them high throw, 4 way adjustable grilles w/ balance dampers at least every 8 feet, provide lots of return grilles.
Be prepaired to loop the duct so you can back feed an area if needed.
Provide motorized dampers on the back-up unit so you don't spin the fan backwards while it sits.
Remember the cost of the hvac is small compaired to the cost of their down time.
We spec a couple warehouse fans w/ wheels to sit in the corner as stand by.
If the hvac goes down at least they can use the fans to blow air on the hot spots.
Good Luck.

 

[glfrank]

I've done computer rooms before and I generally agree with the comments already made. Also, consider the following:

1. I assume your talking about rack mount servers and drive arrays.
2. Since your supplying air from above it's critical to get the cool air to the right side of the boxes and the hot out of the space. I recommend you push for a back to back and front to front arrangement of the racks. If you let the IT guys install the equipment the way they want, they might arrange the rachs front to back, front to back. It sounds logical but it's not. The rack mount equipment I'm familar with draws cooling air in the front and discharges hot air out the back. If they arrange the racks front to back, front to back the heat from one row will be drawn into the next.
3. With the racks front to front and back to back you can supply air from the ceiling where the racks are front to front, and retun air at the ceiling where the racks are back to back.
4. I think it took less then 30 minutes for our data center to overheat the first time we lost cooling. Make sure you have the ability to prop the doors open and have some box or pedestal type fans around just in case.
5. Back-up HVAC ... we built our data center with a primary system using chilled water and a back-up using DX that was fed by an emergency generator. Start-up of the DX was supposed to be automatic, but there were occasions when the primary unit would go down and the back-up failed. Our systems are mission critical, so we now have a 3rd unit as a back-up to the back-up. The back-up and 2nd back-up start up based on temperature rise in the space.
6. Someone above commented that IT gous will put 12,000 SF of gear in a 6,000 SF room ... I agree. We started out with racks about 5' tall, we now have racks 7' tall. It's also true they change and move stuff around, although in our data center the racks are fixed ... they add or remove equipment from the racks.
7. We built an office inside the data center, separate from the control room, which was to be used by the operations guys. We came back a few months after the center was opened and they had moved an AS400 into a 12'x12' room and were complaining that it was overheating. The room was in the back corner of the data center and had glass from 4'up to the ceiling height. We had to remove the glass to allow air from the data center floor space to circulate into this room.

What ever you design, think flexibility. Once you build it and IT starts up you can't go back and shut down to make changes! Hope this helps, good luck.

 

[lilliput1]

You may be able to do overhead distribution now while your load is still fairly light at 150 SF/ton. However 80 to 50 SF/ton are typical design values for computer rooms. You should convince your company to go with at least 24" to 30" high raised floor now while loads are still manageable. Raised floor will allow use of downflow computer room AC units which are more flexible & reliable than overhead central air distribution systems. It also allows easier wiring of components. The transition can be staged in portions so the operation of the computer room can be maintained with minimal downtime.
Problem with overhead distribution is how to get cold air down near the floor where the rack ventilation air intakes are located, without interfering with the hot air coming off the top of the racks. You can blow towards the walls & use Coanda effect to get the air down along the walls. At the middle portions you can drop round ducts to the floor & terminate them with 360° perforated duct diffusers made by United. You need balancing damper in the duct drop. Using the 360°perforated diffuser allows you to distribute more air with less blow than supply air registers.

 

[bagph2]

My sad experience with data room:

The supplier gave the PABX and computer load but neglected to say that the UPS will be housed in the same room.

The fire protection installed a FM200 fire suppressant without consulting HVAC so our ceiling diffusers did not come with automatic dampers to isolate the data room in case FM200 is released.