Attention to Detail - The Basics of Green IT
April 18th, 2008 | by Steve O'Donnell |Data Centre Basics
There are some basics that just need to be done to keep a data centre efficient and as green as possible. Maintaining the floor is often a task that is left too late. Gaps and unnecessary holes in the floor are bad news and lead to the mixing of hot and cold air which drops efficiency, keep the floor maintained, replace tiles with holes, close open vents in the wrong place. Better still take out excess vented tiles and replace them with plain tiles. Even closed vented tiles leak air.
Blockages to airflow under the floor reduce airflow efficiency and can cause hotspots in the data centre halls. Keep extra rolls of cable and other junk either in a store cupboard or at worst above floor level. Blockages can divert airflow away from key areas.
Ignore areas of the data centre that are hot - actually this can be a good thing - provided that these are not located in front of cabinets. Hot spots in front of cabinets are bad as this means that the equipment will be drawing in hot air, reducing the cooling efficiency. Hot spots in front of cabinets generally means that the rack layout is poor with cabinet backs facing cabinet fronts. Resist the temptation to place open tiles in hot aisles, the “advice” that this lift the hot air up so that it extracts efficiently is utter nonsense and should be ignored. Hot aisles are designed to be hot and are less efficient if they have open tiles in them. Don’t worry about the humans, they can survive high exhaust temperatures for long periods.
Poor airflow from open tiles can be caused by a number of problems. Too many open tiles reducing the plenum pressure overall, blocked underflow caused by overflowing cable trays or stored junk. Badly maintained refrigeration units or blocked filters can reduce airflow as well reducing plenum pressure.
If designing a new hall, keep the cable trays above ground, it can make a huge difference and is much easier to manage. The photograph below is from the iNet Data Centre in Milan and shows a great arrangement.
If you really need to have high density equipment in a hall exhaust the air from that equipment straight out to the atmosphere, bringing in fresh air to replace. An example is shown below.
Maintaining strong separation between hot and cold aisles is particularly important and I have written on this extensively. However blocking off open gaps in cabinets is key as is fitting empty (and fully blanked) cabinets into gaps or alternatively filling full length curtains in gaps.
You should test the soundness of your floor by pressure testing and checking that all cableways that lead between halls are properly blocked off. This is important for a number of reasons, it reduces cold air leakage, slows the spread of fire and smoke within the facility and discourages rodent entry. Cold air leakage from below the floor can make a significant difference to data centre energy efficiency. Cable entry points into cabinets need to be closed off as well, as this can offer an alternative air flow route from cold to hot avoiding the equipment we need to cool. Fit raised floor grommets or bean bags around the holes to close off excess airflow. A good example can be found at KoldLok and Flowlogix Air Stops
An alternative approach that some data centre operators are beginning to look at is one begun by a small start up company AdaptivCool who have a very comprehensive solution that just squeezes the last joule of energy out of your existing refrigeration plant. Ideal if you just have to get that bit extra cooling power and can’t increase the CRAC density.
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