Cooling |
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A number of challenges complicate the task of operating an efficient cooling infrastructure . Cooling system capacity is nearly always oversized owing to availability requirements , a fact made worse because data centres often operate at less than 50 per cent load . Furthermore , the amount of equipment in a data centre , and its layout , changes , forcing changes to the cooling operation as a consequence .
Cooling systems are typically assembled using equipment from different vendors , with consequent challenges of compatibility and coordination between them .
The bigger picture
An effective control system should enable management to consider the overall effect of adjustments to one part of the cooling infrastructure on the installation as a whole . That in turn means that manual adjustments made to individual elements should be superseded by automatic controls as far as possible .
An effective control system should shift between different operation modes like mechanical , partial economiser and full economiser mode automatically , based on outdoor air temperatures and IT load to optimise energy savings . It should also co-ordinate the operations of indoor cooling devices to prevent demand fighting between the CRAHs . IT space humidity should be centrally controlled by maintaining dew point temperatures at the IT intakes , which is more cost effective than maintaining relative humidity at the return of the cooling units .
Levels of control
Device level control involves the control of individual units such as chillers . Such controls are
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‘ An effective control system should shift between different operation modes to optimise energy savings .’ |
usually built into the equipment by vendors themselves . Device level controls typically do not cater for communication with other devices ; rather their purpose is to ensure predictability of operation and reliability of the devices . They also act as the foundation for higher level control plans .
Device level controls require less experience of data centre operators who typically adjust set points to the prevailing environmental requirements . They entail no extra capital cost because they are built into the equipment by its vendors . Nevertheless , they can achieve significant energy savings through the use of fans , compressors and pumps which can be adjusted according to IT load . Device level control on its own should typically only be used for a small IT room with only one cooling unit , for example split air cooled DX .
Group level control , the next level up , refers to the co-ordination of several units of the same type of device , namely CRAHs typically from the same infrastructure vendor and controlled by the same control algorithm .
This allows some resolution of demand fighting and permits greater co-ordination between different units . It can be particularly effective in the case of failure of a single unit because redundant units can be held in standby mode and activated automatically when required . The main limitation of group level control is that it can only control similar devices , and typically only from the same vendor .
System-level control , the next level up , co-ordinates the operation of different cooling subsystems within a data centre , for example a pump and a CRAH . System level control can also co-ordinate the operation between packaged chillers outdoors and the indoor air handlers to minimise energy use .
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Benefits of this level are that it can look at , say , a chilled water system holistically and take note of the dynamics to minimise total cooling energy consumption . IT can also move between different modes of operation without human intervention .
Again though , the limitation is that such control systems typically work best with equipment from the same vendor and so for a more holistic control system for a large data centre , it is necessary to consider the highest level of control system : Facility level control .
The highest level
Facility level control integrates all functions of a building into a common network that manages everything in the building from heating , ventilation , air conditioners and lighting systems to the security , emergency power and fire-protection systems . It provides the most comprehensive picture and therefore enables the most co-ordinated and efficient cooling strategy involving all of a data centre ’ s operations .
The benefits of facility level control over the other levels are that it can monitor the status and performance of both power and cooling systems from the utility connection right down to the IT servers . It can analyse the dependencies and interconnected nature of infrastructure components and communicate effectively with data centre operators . It can also share information with other infrastructure management systems , sending and receiving status and alarm information between electrical power monitoring systems ( EPMS ) and data centre infrastructure management ( DCIM ) systems .
For larger data centres , facility level control is advisable as a means of ensuring efficient operation , reducing power consumption and reaching and maintaining a low power usage effectiveness rating .
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August 2017 | 23 |