Monday 28 November 2011

Cooling in a damp climate

On the other hand you have the problem of cooling such a concentrated hotspot.  And air conditioning is not of the most stable devices.  Your indoor environment is sensitive to the smallest bit of sunlight and the outdoor units are very vulnerable all together. It ends up spending a lot of time de-icing so see to that your runoff is adequate.  Can be a problem when your fire extinguishing system needs a completely sealed room.  And your insurance, for it to be pressure tested.
A cool but humid climate is not always the best for a datacenter.  Yes you need to run your airconditioning slightly less but you get a lot more de-icing issues.  One of the reasons reverse cycle airconditioning for home heating never gained popularity in Ireland.  Compared to colder but much drier climates like Scandinavia.  If you have a weather station with a separate outdoor unit you will know what I mean.  They spend a lot of the time showing a humidity error because of very high values.  

Underfloor cooling was meant for network racks where the passage through the rack is unobstructed due to the shortness of the equipment.  Full length servers make blockages for the flow of the air through the rack so it’s better to give it cold air at the front and remove the hot air from the back of the rack.  This way you create cold hallways in front of racks and hot hallways behind racks.  If you have several rows of racks this do require that every second is turned the opposite way, avoiding that one servers hot exhaust becomes another’s cooling air intake.
A downside of hot and cold aisles is that where you are most likely to work, at the front where the console is, is also the place where there is a constant cold draft.  You could alternatively place the consoles at the back. It eases the cabling. These days it’s more normal to remote control the whole room so there is little need for direct human access.  And you could also increase the general temperature of the room slightly. Rather than set it at 19c you could experiment with 22c.

Few will run their cooling via the ups due to the large power demands and the resulting shortening of ups running period at time of grid failure.  If your computer room has generator backup, you will need to restart your cooling with the generator.  Lack of cooling will make your equipments internal fans increase in speed as room temperature goes up, eventually overloading fuses and cables. 
You can temporarily rectify the situation by pumping cold air in from the outside or redistributing the air already in the room better by a dedicated fan and an extendable tunnel, easily and cheaply bought from a hardware store like MachineMart.  
Due to the vulnerable nature of airconditioning you will need to overdimension.  You should have at least enough that 1/3 of the cooling capacity can be offline for maintenance and you are still able to keep the temeperature within range. 
It can sometimes be difficult to spot a failing airconditioning.  Simple filter or other error messages on the control panel is mostly self explaining, but sometimes you have a rise in temperature without any message.  Check the exhaust for that it’s actually cold.  Sometimes they keep on running but just blow out thes same air at the same temperature as it went in.  Specially if the outdoor part of the unit has failed.

I will again point out the importance of an environment monitor. They are relatively cheap for what they protect and the same one that monitors your power can also monitor the room temperature.  Place sensors in several different positions since it’s highly unlikely to be a uniform temperature in the whole room.  And single failures can result in hotspots.

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