significant improvement in cooling efficiency. More recently, a new cooling


technology has emerged which is set to significantly disrupt the traditional methods of cooling, both financially and environmentally: evaporative cooling. It’s also sometimes referred to as adiabatic cooling or CREC (computer room eco cooling). As with all good ideas, nature has


been using this very process for millions of years already. It works on the basic principle that


when water evaporates it draws energy and heat away with it. Just in the same way that people (and all mammals) naturally sweat during the summer to cool themselves down, this technology draws warm ambient air through a wetted filter or fine mist, which in turn causes some of the water to evaporate and cool the ambient air. Try licking the back of your hand


and then blowing on it – that cold tingle you feel is evaporative cooling. In comparison to traditional


compressor-based air conditioning units, evaporative chillers use up to 90% less power. This allows efficient data centres to achieve a PUE of 1.1, an efficiency figure previously impossible with traditional cooling methods. Today, big companies such as


Facebook and Google have built new data centres that work exclusively on evaporative cooling.


What about all the water? On a very hot day in the UK, a typical evaporative cooler will use an estimated 100 litres of water per hour. That sounds like a lot, but to put this in perspective, taking a bath or a power shower uses around 80 litres and washing your car with a hosepipe takes between 400-480 litres. To minimise water wastage further,


some evaporative chillers will do clever things such as recirculate a reservoir of water so that water which does not evaporate can be reused. Waste water – defined as water that


has been recirculated for a while - can even be drained and used as ‘grey water’ in things such as toilets. On a like-for-like basis, even taking


into account the carbon cost of water production, evaporative cooling is still significantly more efficient than traditional cooling systems.


Some more cool tips Even though evaporative units can be retro-fitted into legacy data centres and comms rooms, the capital expenditure can be quite high, especially if you’ve got a traditional system which is less than 6 -7 years old. While the biggest energy consuming component of a refrigerant-based CRAC unit is the compressors - which usually cannot be improved upon without great expense - the second most power hungry part is usually the CRAC fans themselves, which circulate the air around the data centre real estate. Traditionally, and certainly on older


CRACs, these fans work at just one speed, regardless of the level of cooling required. Not only does the CRAC fan work at 100% speed regardless of the heat load - thus drawing the maximum amount of power all the time - it also generates heat itself, and needs to be cooled. This particular issue can be solved


relatively cheaply by installing variable speed fans. This may seem simple enough to


do, but qualified AC engineers are still required, as the control system of the CRAC needs to be updated to control the speed in relation the amount of cooling required. Other cheaper quick wins include


methods of reducing cold air leakage. If you open your fridge at home, the compressor keeping the food cool has to work extra hard as all the cold air is spilling out into the warmer ambient air of the kitchen. The same is true of cold air in a cold


aisle and any gaps that lead into the hot aisle. If the cold air isn’t being directed through hardware, it is being wasted. Brush grommets, which insulate


the hole in which power and data cables enter a rack, are one good way of reducing leakage, as are blanking plates, which can be fitted above and below servers to help prevent air seeping out.


Keeping the PUE levels down


Some bright ideas Not many people know that you can buy LED tube lighting that - with a minor modification - will fit into the old- style fluorescent light fittings. The light quality is excellent and


even though per unit they’re more expensive in the short run, they use half the amount of electricity to run and generate half the amount of heat, meaning less work for your CRACs. Combined with PIR-activated


lighting, these two changes alone can both reduce your carbon footprint and provide you with a return on investment in less than two years. In summary, if you’re building a


data centre from scratch it’s essential to plan for the most efficient cooling system you can but if you’re renovating a legacy data centre you need to work harder to assess the latest green cooling technologies and what your budget can stretch to.


Jack Bedell-Pearce is Managing


Director of the independent, eco- friendly colocation and connectivity supplier, 4D Data Centres. With a PUE of 1.14, it is one of the greenest data centres on the planet.


www.4d-dc.com


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