Temperature chaining can mean temperature, thermal or energy chaining or cascading. Temperature chaining has been introduced as a new concept at Datacentre Transformation in Manchester by the company Asperitas as part of a vision on a Datacentre of the Future. It is a method of transforming electrical consumption in datacentres into usable heat. The concept is based on creating high temperature differences in a water based cooling circuit in a datacentre. The premise is that every system in a datacentre can be equipped with a shared water infrastructure which is divided into multiple stages with different temperatures. The different temperatures are achieved by setting up different liquid cooling technologies with different temperature tolerances in a serial cooling setup as opposed to a single parallel circuit. This creates high temperature differences with a low water volume. This results in a datacentre environment which is capable of supplying constant temperature water to a re-user, thus transforming the facility from an electrical energy consumer into a thermal energy producer.
History Temperature or energy chaining is applied in heating systems where hydraulic designs allow for return loops and serial heaters. The temperature chaining principle is also used in refrigeration systems which adopt cascading circuits. The Amsterdam Economic Board has presented the 4th generation of district heating networks which will adopt thermal cascading to increase flexibility and to make the district networks future proof. Within datacentres, the traditional approach towards the critical IT load is cooling. Temperature chaining works on the basic premise that the IT is a heating source. To harvest this heat, liquid cooling is used, which allows the application of hydraulic heating designs to the datacentre.
Liquid cooling infrastructure in datacentres Introducing water into the datacentre whitespace is most beneficial within a purpose-built set-up. This means that the focus for the design of the datacentre must be on absorbing all the thermal energy with water. This calls for a hybrid environment in which different liquid based technologies are co-existing to allow for the full range of datacentre and platform services, regardless of the type of datacentre. The adoption of liquid cooled IT in datacentres allows for more effective utilisation or reduction of the datacentre footprint. This means that an existing facility can be better utilised to allow for more IT. The higher heat capacity of liquids allows for more dense IT environments and higher IT capacity. With most liquid technologies, the IT itself becomes more efficient. This is caused by the reduced or eliminated dependence on air handling within the IT chassis. Individual components are cooled more effectively and can therefore be used with higher amounts of energy and closer to each other. When liquid penetrates the IT space, internal fans are reduced or completely eliminated which saves energy. This also reduces the emergency power requirements within the facility.
Liquid datacentre technologies Liquid cooling technologies can be roughly divided into four different categories: cooling at the room, rack or chip level and immersion. Computer Room Air Conditioning or Air Handlers (CRAC/CRAH) can be water cooled. Indirect Liquid cooling (ILC) involves water cooled racks with (active) rear door or in-row heat exchangers which are water cooled. The advantage of the active rear doors is that all the heat from air cooled IT is immediately absorbed by the water circuit when it leaves the rack which eliminates the need for CRACs, also in partial ILC implementations. This makes cooling systems very efficient, and supports limited efficiency on the IT itself by assisting ventilation. Direct Liquid Cooling (DLC) effectively cools parts of the IT with purpose built coolers which combine cold plates and pumps that are mounted directly onto the chips instead of a traditional heat sink. This generates energy efficiency on the IT side due to the reduced amount of fan energy. Although the water circuit captures all of the heat from the largest heat sources inside the chassis, this approach may still require CRAC units or combinations with ILC for rejection of thermal energy from the rest of the IT components. Total Liquid Cooling (TLC) completely immerses the IT components in liquid. There is hardly any energy loss and IT equipment is made very energy efficient, eliminating kinetic energy (fans) from being used by the IT. Since water conducts electricity, an intermediate dielectric substance is required which requires forced or convective transfer of heat. This dielectric can be oil or chemically based. The infrastructure and power advantages are maximised with this approach and the energy footprint is fully optimised. Since there is no such thing as one solution for all, any platform should be designed with the optimal technology for its different elements. Therefore, each part of a platform should be set up with a mix of optimised technologies. For example, storage environments are least suitable to be cooled directly by liquid due to the low energy production and the common dependency on moving parts. These can be set up in water cooled racks. High volumes of servers which require the least maintenance can best be positioned in a Total Liquid Cooling environment. Varying specialised server systems which require constant physical access are best situated in Direct Liquid Cooled environments. A prerequisite for each technology before it can be applied in a temperature chaining scenario is a level of control (by PLC) over its own cooling infrastructure and compatibility in the sense of fittings and liquid compatibility.
Temperature chaining
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