Climate protection needs energy efficient data centers - Stulz GmbH

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circulating air stream. In this mode the system also hasthe highest energy consumption.Direct free cooling is particularly suited for applicationin smaller facilities such as telecom containers/shelters.In view of the fact that larger scale facilities with greaterheat loads require proportionately larger volumes ofoutside air to be transported into the room through thebuilding envelope, and that room humidity has to becontrolled within narrow tolerances in data center air conditioning,direct free cooling is not normally an option forsuch installations.in the energy consumption of the air conditioning system.If outside air temperatures rise, the cooling cycle has to berun more frequently. Depending on the system’s design,it automatically shuts down the free cooling function athigh outside temperatures and cooling is then providedexclusively via the cooling cycle. This mode of operation isonly necessary when outside temperatures are high andthen it requires the highest energy input.The design and construction of indirect free cooling systemsvaries, sometimes considerably. The systems can becategorized in three basic groups:In addition, when operating a system with direct free cooling,the air filters require particular attention. The highvolumes of outside air shorten filter lifetimes drastically,especially in locations with high dust levels. They alsoreduce the efficiency of the air conditioning system andincrease operating costs.5.4.3 Indirect free cooling•••air conditioning units with integrated free coolingfunction and recooling unit (small and mid-sizerooms),water cooled units with central chilled water generationand integrated free cooling function in thechillers (mid-size and large rooms),water cooled units with central chilled water generationand external free cooling function via recoolingunit (large rooms).With indirect free cooling, unlike the direct version,outside air is not used directly to cool the ICT equipment.All the indirect free cooling systems outlined below workon the principle that, in free cooling mode, a water/glycolsolution is cooled by the outside air without using acooling cycle and can then be used to cool the circulatingair stream inside the facility. The interpolated water/glycol solution functions as the coolant and is circulatedthrough a piping system by pumps.5.4.4 Other energy-saving options: freecooling system designThe system design must be geared to the annual temperaturepattern of the particular location. All the systemcomponents must be carefully configured so that thesystem can provide the greatest possible energy savingsonce in operation.Indirect free cooling offers major energy-savings potentialfor data center air conditioning. Although the additionalcomponents required for indirect free cooling incur higherinvestment costs for the air conditioning system, thisadditional outlay is compensated in the medium term bydramatically reduced operating costs.The savings opportunities offered by indirect free coolingare particularly attractive in cold and temperate climates.Low outside air temperatures make it possible to reducechiller operation time which, in turn, leads to a reductionTo achieve this it is important to consider both room temperatureand room humidity to ensure that the system asa whole can make optimal use of free cooling.Room temperatureWithin a conceptual design framework, room temperatureis a crucial factor influencing both the configurationof the system and energy efficiency. Higher room temperaturescan be maintained over longer operating periodsby indirect free cooling, without the need for additionalrefrigeration, thus contributing directly to energy savings.20
Energy Efficiency in the Data CenterRoom humidityLike room temperature, room humidity also has aneffect on energy efficiency. Low relative humidity incombination with a higher room temperature will allowair conditioning units to be run more efficiently. Whenoperated under these conditions, the air conditioningunits are able to provide sensitive cooling, i.e. there is nodehumidification.Excessive relative room humidity combined with a lowerroom temperature will automatically cause the airconditioning units to produce latent cooling which willinevitably cause dehumidification of the air stream. Extrapower is then required to replenish humidity by meansof a humidifier to ensure that it does not sink belowacceptable levels.Scalable coolingModern air conditioning systems should also be able toreact flexibly to partial load conditions within the facilityand provide demand oriented cooling using the lowestpossible energy input. This can be effected by raising thechilled water temperature, as this will maximise the freecooling operating period still further. Scalability is particularlyrelevant when a facility is being upgraded in phasesor where there are fluctuating heat loads.An economic feasibility study must be carried out todetermine which system is the most suitable. The installationsituation, loads and acoustic conditions must alsobe taken into account here, so that a viable solution iseventually arrived at.• 5.5 Chilled water temperatureIn large-scale data centers around 90 per cent of thethermal energy is transported in a water/glycol solution(brine). In free cooling systems, brine as a heat transfermedium has a great advantage over direct evaporationsystems. When ambient outside air temperatures are lowenough, the cold air can be utilized to cool the data centerdirectly.To fully exploit this effect and reduce the proportion oflatent cooling to as near zero as possible, the temperatureof the brine in the air conditioning units must be ashigh as possible, approx. 12°C supply temperature andapprox. 18° return temperature. Higher temperaturesare even more advantageous from an energy efficiencyperspective.The average room air temperature in data centerscorresponds directly with the brine supply temperature.Experience has shown that the energy consumption of anair conditioning system can be reduced by about 15% atan average room temperature of 26°C as opposed to 22°C.The higher temperature of the room air permits higherchilled water supply temperatures, thus increasing thenumber of free cooling operating hours considerably andsubstantially raising performance levels (EER).• 5.6 The different types of cooling unitSuitable hardware is required before the above-mentionedcooling strategies can be put into practice. There area wide range of manufacturers on the market offeringair conditioning units of all shapes and sizes. To enablethe right choice to be made from an energy point of view,there now follows an examination of a wide variety ofdifferent systems.The types of unit available can basically be divided intocomfort and precision air conditioners. In both cases it ispossible to use chilled water (CW) and cooling agents (DX= direct expansion) as mediums for removing the thermalenergy extracted from the room air. In addition there arealso the water-cooled racks and several special, manufacturer-specificsolutions.1. The comfort devices include fan-coil-units (= fanconvectors) which have an air-water heat exchangerwith integrated blower, and the split unit air conditionerswhich use a cooling medium and are morecommonly used in smaller spaces. But these types ofunit have several disadvantages which make themunsuitable for application in computer rooms: The21
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Climate protection needs energy efficient data centers - Stulz GmbH

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