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  #1  
Old 03-30-2010, 10:17 PM
PeterC PeterC is offline
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Default Rack Cooling

Due to our limited space we are having some heat issues behind three racks where the heat aisle faces some comm racks. I know if was a bad design but we had constraints and the engineer convinced me it should not be a problem. While the comm racks are only at 80 degrees F I would prefer to drop that down to 75.

I was wondering if there are some good products to vent the exhaust heat through the top of the rack. We currently have APC Netshelter SX 42U 600mm wide x 1070mm Deep racks. We are thinking about covering up the rear doors and exhausting the heat out the top rear into the ceiling plenum (AC return air). I have seen some "chimney" products but they seem expensive for a sheet metal box.

Any links you can suggest?
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Old 03-31-2010, 09:08 AM
raid raid is offline
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Quote:
Originally Posted by PeterC View Post
Due to our limited space we are having some heat issues behind three racks where the heat aisle faces some comm racks. I know if was a bad design but we had constraints and the engineer convinced me it should not be a problem. While the comm racks are only at 80 degrees F I would prefer to drop that down to 75.

I was wondering if there are some good products to vent the exhaust heat through the top of the rack. We currently have APC Netshelter SX 42U 600mm wide x 1070mm Deep racks. We are thinking about covering up the rear doors and exhausting the heat out the top rear into the ceiling plenum (AC return air). I have seen some "chimney" products but they seem expensive for a sheet metal box.

Any links you can suggest?
Just a few questions to help me understand what solution is best for you.

Can you provide a rack layout in plan view with the distances between the racks?
Are the commís racks in open frame or standard racks?
I assume that the APC racks are your server racks and are not used in the commís racks?
What is in the commís racks, are they Cisco side cooled or a mixture of air flows?
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Old 04-04-2010, 07:43 AM
anil.chandaliya anil.chandaliya is offline
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Hi Peter,

Instaed of venting the exhuast heat from top of the rack, you can think of having hot aisle containment.
This would be easy to deply and maintain as compare to venting exhuast air. Additionally, this would provide better separation of hot air from your common racks.
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Old 04-07-2010, 07:36 PM
PeterC PeterC is offline
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Sorry guys... I took a few days off.

Based on the room layout, square footage, and weight load restrictions we did not have many options on rack placement. So hot aisle containment is preferred but not possible.

Cold aisle is five feet and then the hot aisle in question is just over four feet between the back of the server racks and the front of the comm racks. Comm racks are two - two post 84inch tall open frame comm racks with 6 inch cable management on either side and between the comm racks. We have blanking plates on all racks. with a few "U" of exceptions on the comm racks.

The comm racks are populated with Cisco switches/routers, media converters (external fiber connections), Sensaphone, sound masking gear, and various patch panels... so it is a mixture of air flows.

I zipped up a layout of the area in question. hope this helps.
Attached Files
File Type: zip hotissue.zip (39.1 KB, 435 views)
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  #5  
Old 04-07-2010, 11:56 PM
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KenB KenB is offline
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Chimneys wil be a big help, even if you don't go all the way up to an above-ceiling return. Just getting the hot air up higher will help stratify the hot and cold air layers. Make sure the baffle is easy to swing out of the way for accessing the rear of the servers. I'm not familiar with any add-on suppliers (and I'd be leery of those that didn't extend your rack depth at least 8 in.), but the Chatsworth and Wright Line cabinets with integral chimneys I've seen work very well. Maybe a local sheet metal guy could retrofit your existing cabinets based on these designs.

Ken

Last edited by KenB; 04-08-2010 at 02:26 PM.
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Old 04-08-2010, 01:03 AM
raid raid is offline
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As you have an overhead hot air return plenum, you should use it wherever possible. The APC ducted rear door, while not cheap, does work very well. This is not just a passive system like some; fans are used to force the hot air out of the rack. You need to check to see if you have sufficient UPS power in each rack to run the fans.

The big problem with these doors is the ďDoor Swing and Door ClearanceĒ you can have problems with clearance from the next suite also in the same suite where non APC racks are installed, so check this carefully.

I cannot recommend the rear passive ducted system (Chatsworth), as it only works if all of the equipment in the rack is the same make and model. This system relies on the air pressure generated by the IT equipment fans to force the hot air out of the rack, via the duct (this is an enclosed system not like a normal vented rear door). If you install a mix of equipment in these racks you can get equipment overheating. An example; blade servers will generate very high air pressures and a 1RU server or switch generates very little. What will happen is the small fan in the 1RU device is totally overwhelmed by the pressure in the rack and the hot air is forced back through the device.

All the other solutions I can think of are either very expensive (active rear door cooling) or will be difficult to add to your existing APC racks.

Sorry I canít think of any other alternatives.
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Old 04-08-2010, 09:01 PM
PeterC PeterC is offline
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Thanks for the info it is greatly appreciated. We did look at those APC doors but as you mentioned they are very expensive. They also add 10 to 12 inches of depth.

We are currently testing out building some ducting with fans to help draw out heat from the top rear of the rack. We purchased two 215 cfm fans for the test... little cardboard, duct tape, etc and we should be able to see if it will work. If it does work we will get a contractor to build it in sheet metal. I am sure that it will be much cheaper.
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Old 04-09-2010, 06:19 AM
raid raid is offline
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Something to watch out for is that you donít make the fans to weak or even to powerful. As you realize if they are to weak you donít get all the hot air into the overhead air plenum. If you make them to powerful you can draw in a lot of cold air as well, this will reduce the efficiency of your AC system. Also you can disrupt the air flow into the overhead air plenum, this may unbalance the air flow from some of the other return air vents. Once you get the unit installed use an anemometer, before and after installation, just to make sure there are no air flow problems around the room.

I would recommend using variable speed fans, they are more expensive but the ability to adjust them as required make it worth the extra cost.

PS: Please donít think that Iím being negative, itís just that I have worked on these systems before and the solution is never a simple as we first believe, or as Homer would say DOH!
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Old 04-09-2010, 03:03 PM
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KenB KenB is offline
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Agreed about too little fan capacity. A good rule of thumb is that 150 cfm of air is required to cool a 1kW load. My suggestion is to leave an open-topped chimney -- the server fans will move enough air -- just give them enough chimney volume to avoid pressure buildup and have a curved deflector (like a turning vane) at the bottom.


Ken
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Old 04-09-2010, 03:14 PM
PeterC PeterC is offline
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Thanks again Raid!

We don't have anything to measure air flow (other than our hand or a piece of paper). We have been focusing on temperature readings within the rack and room. With our mock up the temp at the bottom of the rack goes up two degrees and down several degrees toward the top of the rack (this is measured inside the rear of the rack). The big difference is temp drop at the front of the comm racks which is the ultimate goal.

We are only planning to apply this to two racks so I don't think that it is drastic enough to throw off the whole room; however we will watch the return draw from the other side of the room. We can move return air grates around and are procuring some backer rod to seal off the return air ducts in the lights.

Thank you for the continued feed back
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