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Cooling Architectures in IT Data Centres

on365 know that next generation data centres demand next generation cooling strategies as incumbent room cooling mechanisms were never intended to cope with the increase in heat generation. Cooling systems that are inefficient, unpredictable and low in power leverage only the same effect on the hardware it is supposed to protect. on365 can help design and implement row-oriented and rack-oriented cooling architectures to address these issues and are confident that these methods will emerge as the preferred solution for high demand data centre environments.

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Electrical power used by today's IT devices nearly all ends up as waste heat that is expelled by method of air cooling fans. With ever increasing numbers of devices in data centres the flow of hot air increases and together represent the total waste heat output of the data centre, waste heat that must be removed. on365 find that pre-planning to combat this complex flow of waste heat is most successful when it includes either row or rack based air conditioning.

Traditionally one or more room based air conditioners dealt with this hot air whilst at the same time replenishing with cold air pushed into the data center. Power is the major obstacle and this method of cooling is only effective when the total power required to cool the room is just a fraction of the overall power consumed by all devices. Newer rack or row configurations help with better predictability, higher density, greater efficiency and a number of other benefits.  

Any air conditioning unit within a data centre has two core functions, namely to provide bulk cooling capacity and to provide distributed cooling to IT loads. The various methods used to meet these requirements are the same at the room, row or rack level, the only difference being the way they physically distribute the cool air in the second of these functions.
 
Room Row Rack
A summary of the basic operating principles of each method are provided in the following sections:

Room-oriented architecture
In room-oriented architecture the cooling devices are deployed to address the room temperature and work together to combat high total heat load in the room. Typical room architecture includes multiple air conditioning units with either direct uninhibited access to vents and grilles or partially covered by raised flooring or overhead plenum configurations

Row-oriented architecture

In a row-oriented architecture the cooling units are associated directly with rows of IT devices and are usually designed into the infrastructure from inception. Greater predictability, more accurate and shorter airflow paths plus higher overall densities are the primary advantage of row over room architecture.

Rack-oriented architecture

In rack-oriented architectures the cooling device is designed into the rack itself and directs even shorter airflow in exactly defined paths that are immune to changes in room climate and physical constraints. The highest power density and maximum capacity for the cooling device is achieved in this configuration.

Mixed architecture

There are no rules to prevent a data center from deploying some or all of the above architectures.

Summary and analysis

on365
have reviewed and analysed vendor comparison tables that suggest the following conclusions:

  • The modular rack-oriented architecture is the most flexible, fast to implement, and achieves extreme density, but at the cost of additional hardware.
  • Room-oriented architecture gives great cost and simplicity advantages however is inflexible, difficult to implement, and gives sub-standard performance at higher density.
  • The modular row-oriented architecture provides many of the flexibility, speed, and density advantages of the rack-oriented approach, but with a cost similar to the room-oriented architecture.

There are a number of practical issues that require additional explanation and discussion regarding the merits of either architecture.

Capacity usage
Most users naturally assume that if they have 500 kW of cooling units installed, they can install and cool 500 kW of IT loads. This is simply not the case.

Humidification
Often the function of maintaining humidity, to reduce the risk of damaging static discharge, is integrated into the computer room air conditioning unit. In architectures that may increase the number of air conditioning units, a natural question is whether the number of humidification devices must also increase.

Efficient power
With increasing rates on electricity and the increase in power density in modern computer rooms the costs of cooling implementation are becoming more than just a fraction of the overall. The effect of power density on running costs needs to be carefully considered in the planning phase.

Latent heat from piping near IT equipment
Research shows that users are very concerned with water or refrigerant piping co-located with IT equipment.

Location
The location of an air conditioning unit can have a dramatic effect on the system performance.

Redundancy
Redundancy is necessary in cooling systems to permit maintenance of live systems and to ensure the survival of the datacentre mission if an air conditioning device fails.

Conclusion

The conventional legacy approach to data centre cooling using room-oriented architecture has technical and practical limitations in next generation data centres. The need of next generation data centres to adapt to changing requirements, to reliably support high and variable power density, and to reduce electrical power consumption and other operating costs have directly led to the development of row and rack-oriented cooling architectures. These two architectures are more successful at addressing these needs, particularly at operating densities of 3 kW per rack or greater.

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