COLD INTO THE


Data centres can waste a lot of energy through overcooling. Sophia Flucker and Robert Tozer describe how ‘air performance metrics’ can help increase effi ciency


D


ata centre energy consumption has grown signifi cantly in recent years, much of it being used in cooling systems.


By understanding air management performance and applying air fl ow metrics, energy use can be signifi cantly reduced. There is also scope for preventing ‘overcooling’. ‘Air management performance’ describes


how effectively conditioned air is employed to cool IT equipment in a data centre. By understanding this, ineffi cient operation can be identifi ed, quantifi ed and targeted. Data halls are typically arranged with


cabinet rows placed front-to-front (cold aisle) and back-to-back (hot aisle). Vented fl oor tiles or fl oor grilles are placed in the cold aisle to deliver cold air to the front intake of the cabinets and IT equipment; hot exhaust air is rejected into the hot aisle. Some of the air supplied by the cooling


The costs from overcooling often do not impact on the IT department budget, so the incentive to operate with better energy effi ciency is not there


38 CIBSE Journal April 2012


unit reaches the IT equipment, while some bypasses it (that is, returns to the cooling unit without passing through the IT equipment, providing no useful cooling). Where bypass (BP) is high, this prevents the full capacity of the cooling units from being realised – the air available to cool the IT equipment may be insuffi cient for the load (see Figures 1a and 1b). Sources of bypass fl ow include:


● Floor grilles in the wrong place i.e. in the hot aisle, not in the cold aisle;


Data halls are typically arranged with cabinet rows placed front-to- front (cold aisle) and back-to-back (hot aisle)


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