Climate protection needs energy efficient data centers - Stulz GmbH

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2.3.volume of circulated air is very small, the chilled air isblown in from above, which is highly disadvantageousfrom a thermodynamic perspective, the split unitscause excessive dehumidification, the control systemsare only very basic and do not take room humidityinto account. What is more, the split units operateinefficiently as far as sensible cooling is concerned 8 .This means that they are neither energy efficient norsuitable for year-round operation.Precision air conditioners were originally developedfor use in computer rooms and can be divided intotwo groups, according to the air-flow routing: downflow(= air intake from the top, discharge throughthe base) and upflow (= air intake from bottom frontor rear, discharge through the top. These units havemicroprocessor controls which constantly monitorboth temperature and relative humidity and are programmedfor energy optimized operation. Precisionair conditioners deliver virtually 100 per cent sensiblecooling and efficiently apply the energy used forcooling production to reduceroom temperature levels.Another strategic point in the design of energy-efficientprecision air conditioners is the dimensioning ofthe heat exchanger surface area 9 . The greater this is,the lower the dehumidification capacity. This can bediscerned from the observation of a minimal differencebetween sensible and overall cooling performance.This difference, also known as latent cooling,extracts humidity from the return air and consumesenergy. However, as the relative humidity in datacenters needs to be kept within the tolerance limitsprescribed by the hardware manufacturers to avoidproblems with electrostatic charging, more energyhas to be expended to replenish the room air with theextracted humidity.The performance of computer hardware continuesto soar, whilst dimensions steadily decrease anddevelopments such as the (blade) server in particular,mean that today’s HVAC technology faces the additionalchallenge of dealing with heat loads of 30 kWand more per rack. The answer is a rack with a built-inair-water heat exchanger and load-dependent, speedcontrolled fans. This ensures adequate cooling for allthe computers in the rack and it also means that onlythe computers are cooled, not any other loads such astransmission, lighting etc.4. In addition to the standard cooling units alreadydescribed above, there are also some manufacturerspecificsolutions which cannot be elaborated uponhere (rack-mounted cooling modules which enhancecold-aisle cooling, for example). These solutionscertainly have their justifications when used in thespecific applications for which they were conceived,but a detailed examination of their energy efficiencycharacteristics is beyond the scope of this guide.• 5.7 Different cooling mediaThe cooling systems for IT environments can be differentiatedaccording to both the type of unit and the coolingmedium it employs. Every type of cooling is based on thephysical law which states that energy can never be destroyed,only transported. In computer environments air isused as a primary energy carrier because of its superiordistribution qualities. Water, however, can store heataround 3,500 times better than air can, and is thus thebetter choice of medium for transporting the extractedheat out of the room. Depending on the type of applicationand local conditions, it may be feasible to use coolingmedia other than water.Water as a cooling mediumWater lends itself to use as a cooling medium primarilyon account of its easy controllability, ready availability andvery moderate expense. In addition, at low outside temperaturesit is easy and cost-effective to run a water-basedcooling operation which exploits free cooling advantagesand reduces energy consumption.The disadvantages of water within the data center areno longer relevant thanks to the technological progressof the past decades:22
Energy Efficiency in the Data Center• Modern pump systems are infinitely adjustable,depending on the required volume of water and temperaturedifference and when the pumping capacity isthrottled back, energy consumption is automaticallyreduced as well.• Through the addition of an antifreeze agent (“glycol”),the freezing point can be lowered to far below 0°C.Nowadays, these agents are also corrosion inhibitors,which makes them doubly useful.• Today, compared with other cooling mediums, wateris much the safer coolant for data center application.This can be accredited to its leak detection potentialand/or the fact that the water system can be sealedagainst electrical systems through the use of conduitswith systematic drainage.Refrigerants as cooling mediaRefrigerants are often synthetically produced, chemicalsubstances or compounds. Their low boiling points aretaken advantage of in chillers. Of course, natural substancessuch as water 10 , ammonia or carbon dioxide are alsoused as refrigerants. Ammonia, in particular, is one of themost important refrigerants around, but safety requirementsdo not permit its use in data centers.The refrigerant market has undergone a major transformationover the past 10-15 years due to ecologicalfactors such as the destruction of the ozone layer and thegreenhouse effect through the emissions of syntheticsubstances. Air conditioning technology is therefore alsoattempting to reduce the amount of refrigerant used insystems to an absolute minimum or to switch to naturalrefrigerants. Here are the most common synthetic refrigerants,all of which belong to the group of alkyl halides:at present, the refrigerant R22 is still in use in manyinstallations. This substance can still be sold for service ormaintenance applications up to 31.12.2009, and followingthat, until 31.12.2014 servicing may still be carried out, butusing the recycled product only. However, it is foreseeablethat by 2010, the last systems using R22 will have to bedecommissioned or at least converted to a different refrigerantwith zero ozone depletion potential.R407C is the most widely used replacement productfor R22. It is a blend of three individual components: 23per cent R32 (difluoromethane CH2F2), 25 per cent R125(pentafluoroethane CHF2CF3), 52 per cent R134A (1,1,1,2tetrafluoroethane CH2FCF3). It is relatively easy to replaceR22 with R407C. R407C has zero ozone depleting potential,but it does have high global warming potential.The operational disadvantages of R407C prompted thechemical industry to develop a substitute in the formof R410A. This is also a mixture and consists of 50 percent R32 (difluoromethane CH2F2) and 50 per cent R125(pentafluorethane CHF2CF3). It is not possible to substituteit for R22 in existing installations however, as coolingcycle pressure levels for R407C are considerably higher.Its global warming potential is slightly lower than that ofR407C.The pure substance R134A is a well-known and widelyused refrigerant. However, as its volumetric coolingcapacity only amounts to approx. 50 – 70 per cent of thatof R22, depending on operating conditions, systems of acomparable size will be correspondingly less efficient. Theenvironmental impact in respect of greenhouse gas emissionsis slightly less than that of either R407C or R410A.Carbon dioxide as a cooling mediumAt this point we should like to briefly discuss the use ofcarbon dioxide (R744). Even if, initially, this should seemsomewhat unusual, carbon dioxide does, in fact, constitutean energy efficient alternative cooling medium.Compared to water, carbon dioxide has a far superiorstorage capacity, which means that pipe diameters can besmaller and less energy is required for the transportationof the medium from manufacturer to end-user.The present high investment costs are a disadvantage,which means the larger the installation capacity, themore economic the application.A further drawback to the use of carbon dioxide as acooling medium is the need for high operating pressure23
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Page 30 and 31: The requirements for the individual
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