Climate protection needs energy efficient data centers - Stulz GmbH

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Temperature levels in both the cooling cycle and the environmentinto which the heat load is dissipated, as wellas the temperature difference between supply and returnpiping, are decisive factors for a cooling system’s energyefficiency. The higher level is dictated by the temperatureof the surrounding environment (ambient temperature),the lower level by the transfer temperature from the aircycle.The ambient temperature depends on the data center’sgeographical location as well as on the time of dayand season. And the installation location of the heatexchangers is another factor which shouldn’t be underrated.Direct sunlight should be avoided at all costs, asthis would impair the performance and efficiency of thecooling system.And so various energy-optimized control strategies forthis cycle present themselves.determined by the particular CPU and server models andso could not be standardized.Thirdly, as in the air cycle, power control can also be usedto regulate mass flow in the liquid cycle in such a waythat the optimal temperature spread is exploited.5.3.4 Dynamic power control andequipment maintenanceAbove and beyond the application of optimized componentsand systems, the dynamic control of thesesystems will improve energy efficiency even further.Whereas the operating conditions at the systems’ setpoint (max. heat load) are relatively constant, powercontrol techniques can change various parameters whenthe heat load drops.Firstly, if ambient temperatures are relatively low, acontrol system can be used to regulate the dischargeof waste heat to the environment. In this case, the heatmust be temporarily stored. As data centers produce largeamounts of heat which cannot be stored indefinitely, theprime option here is to utilize daily temperature fluctuations.The required buffer tank must be adequatelydimensioned so that it can store the waste heat duringthe day and dissipate it to the surrounding air at night.Secondly, the heat occurring in components can betapped at the highest possible temperature. The higherthe temperature tapped at the ICT equipment, the moreefficiently can the HVAC system, particularly free coolingcomponents, be operated. The optimum solution herewould be “chip cooling”, whereby the heat is removed bymeans of a liquid heat transfer agent at levels roughlyequivalent to the component operating temperatures.This type of chip cooling is already being used in certainspecial applications, but the technology has not yetbeen introduced on a wide scale. Before this can happen,servers will have to undergo considerable constructionalchanges. Furthermore, these solutions would be entirelyPower control can throttle back or shut down the HVACsystems to meet the prevailing total heat load.The following strategies can be particularly recommendedhere:• The volume of air in the air cycle can be minimizedusing speed-controlled fans. (CAUTION: Minimumpressure of 25Pa in the underfloor plenum must besustained!)• Subject to the prevailing operating conditions, thefeed temperature in the fluid cycle can be set as highas possible.• By using dynamic control to regulate the free coolingswitch point, it is possible to achieve longer periods ofcooling without the use of chiller compressors.This will optimize the main components of the HVACsystem’s energy consumption:• The operating energy required by the fans for air circulationis reduced.• The drive capacities of the chillers’ refrigerationunits drop because their efficiency increases as thedifference between outlet air temperature and feedtemperature decreases.18
Energy Efficiency in the Data Center•The periods during which active cooling can be repla-ced by free cooling are considerably lengthened.The routine maintenance of all equipment is anotherimportant practice for ensuring energy efficient datacenter operations, and something which is also requiredby law. Dirty filters in particular cause high energyconsumption by increasing the load on fans or on pumpsin the water cycle. Power control can only provide optimalutilization if the equipment is properly serviced andmaintained.• 5.4 Free cooling5.4.1 Free cooling as an approach toincreasing energy efficiencyFree cooling is particularly suitable for the air conditioningof data centers located in cold and temperate climates. Itis important to differentiate between direct free coolingand indirect free cooling. Air conditioning systems for freecooling have been built for over 30 years. In recent years,the design of the systems has been refined in line withtechnological progress (microprocessor control, speedcontrolledcomponents etc.) and this has opened up evengreater potential for energy savings.5.4.2 Direct free coolingIn addition to a cooling cycle, the air conditioners are alsoequipped with a system of dampers. The damper controlsystem allows outside air to enter the room and indoorair to be transferred back outside or can be switched toa recirculation mode, i.e. the air is circulated within theroom being cooled and is cooled via the cooling cycle.Fig. 10: Air conditioning units with direct free coolingThe type of air handling system used depends on externalclimatic conditions and the required room conditions.Here one has to differentiate between free cooling mode,mixed mode operation (free cooling with additional coolingprovided by the cooling cycle) and recirculation mode(cooling via cooling cycle alone).In direct free cooling, cold outside air is transportedinto the room. The heat load from the IT equipment istransferred to the air stream and this transports it out ofthe room. The air current is fed or circulated through anexternal air filter and a fan unit.This mode of operation offers considerable energysavingspotential in cold and temperate climates inparticular, thanks to annual temperature patterns. If outsideambient temperatures rise, the air handling controlsystem switches to mixed mode so that additional heatcan be removed via the cooling cycle.In mixed mode operation the cooling cycle is initially onlyoperational for short periods when outside temperaturesare low. When outside temperatures rise, the coolingcycle runs more frequently until the air handling controlsystem finally shuts off the intake of outside air entirelyby means of a system of dampers, and the air handlingunit continues in recirculation mode. At high outsideambient temperatures the cooling cycle alone is responsiblefor extracting the heat from the ICT equipment via the19
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Climate protection needs energy efficient data centers - Stulz GmbH

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