Question

Dave mc  |   Jul 21 2008  3:44AM GMT

Split systems are fully acceptable and are available up to about 100kw.
The only disadvantages are that when the outside temperature goes above 35degC the efficiency drops as the temperature difference across the condenser coil drops and the heat transfer is reduced. Thus on hotter days the efficiency drops and higher power usage is required when compared to a condenser water system or chilled water system that uses a cooling tower to reject the heat.
I don’t recommend a window types as they are not designed for this purpose and always have a percentage of fresh air intake and along with the poor filters allow dirt to pass into the computer environment. The air distribution is also ineffective and would only be acceptable in a very small server room with only a couple of servers ( low capacity)
If a larger computer centre is proposed a central plant using chilled water is more efficient compared to using a lot of split systems (one lot of inefficiency compared to a lot of single inefficiency’s)
In relation to Humidity the article above id a good one but to add a couple of points from my 25 years in operating data centres.
You can easily allow the humidity wander between 20 to 80% provided you can prevent quick swings of temperature and control the static.
If a any static computer room floor that is correctly earthed is fitted then the static cant build up. (the racks must also be correctly earthed) if you cant prevent the static build-up then the static should not be allowed to go below the 35% mark (thus the goal of 40%)
In relation to the high humidity you should not allow the humidity to go above the 80% jus tin case the temperature with in the room does drop to quickly and thus allowing the moisture to condense out, gut as noted in the article if the room is at 80% then as the air passes thought he server it rises and makes the relative humidity in the server drop and the moisture is unlikely to drop out. Simple rule is not to allow the temperature in the computer room drop to quickly.

Hope this helps and not makes it as clear as mud, let me know if you need more info.

Bobkberg  |   Jul 21 2008  3:40PM GMT

Previous posters have made some excellent points. The mention of efficiency triggered a thought on my part, although it is somewhat peripheral to the issue.
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I cannot count the number of installations - especially smaller to midsize ones where the roof-top unit is sitting in full sunlight.
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If you want more efficiency, do NOT add heat to your air conditioning system, put a shading structure over the rooftop unit. It will also lower your electric bill relative to cooling obtained.
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More related to the topic is not only avoiding window-style air conditioners (for the dirt they allow in) but to keep the air in the data center as dust free as possible.

Dust buildup acts as an insulating blanket which will accelerate the aging of your equipment. Higher humidity levels will also “help” to make the dust stick “better”.

Bob