Guide To Water/Liquid Cooling in Data Centres
Discover more about water/liquid cooling in the data centre
Why liquid or water cooling in data centres is an alternative to the traditional data centre air conditioning system.
Utilising liquid or water cooling in data centres through the use of water-cooled racks, is fast becoming an alternative method to the traditional data centre air conditioning system of CRAC units. As servers have got smaller in size, server densities within 19” server racks have increased resulting in racks with higher heat loads, this increase in data centre cooling demand makes cooling the servers efficiently more of a challenge.
Whilst air-conditioned data centres can cope with lower density racks, they may struggle with racks with a higher processing and power density, often requiring additional cooling from in-row / in-rack air handlers. This is because air is a gas and as such has a poor heat conductivity. Whereas water has between 50 and 1,000 times the capacity to remove heat. There is a perceived serious downside to water cooling in that water and electronics don’t mix well and the end result if they do could be catastrophic. However, the latest liquid / water cooled systems often use side or rear door heat exchangers that form their own self-contained system and offer leak protection to contain any leaks to the system itself; or in the case of some liquid cooling solutions use refrigerant liquids that turn to a gas if they leak. Data centre liquid / water cooling is also more energy efficient. A data centre air conditioning system such as CRAC units uses more than 40kW of power to cool a 100kW data centre load. Compare this to a water-cooled system, such as the USystems ColdLogik system, for the same heat load it uses about 4kW.
What liquid / water cooled server rack options are there?
When it comes to liquid or water-cooled server racks there are several options available on the market. Most cabinet manufacturers will offer a liquid or water-cooled option. EDP Europe offer three liquid / water cooled server rack options:
- ColdLogik – USystems ColdLogik is an advanced water-cooled server rack solution capable of cooling loads of up to 58kW per rack. The ColdLogik rear coolers are so effective that they allow the supply water temperatures to rise from the traditional 6°C for CRAC systems to between 14°C and 24°C, reducing chiller size and energy costs. ColdLogik rear door coolers have proven to be the ideal solution for data centre operators responsible for housing high density processing systems such as HPC clusters.
- Rittal – The Rittal Liquid Cooling Package is a range of in-row coolers that offer cooling output to up to 30kW. Each uses air to water heat exchangers to cool the hot exhaust air, while cold conditioned air is delivered laterally in front of the servers.
- PSH Liquid Cooled Rack Solution – The PSH liquid cooled rack solution is a retro-fitting solution to most 42U x 600mm wide racks. The solution uses a refrigerant liquid such as R134A or CO2, which is harmless to electrical equipment, meaning there is no requirement for a leak prevention system. If the system does develop a leak, the escaping liquid immediately turns into a non-flammable gas. The solution consists of an outdoor unit that contains the condenser, compressor and refrigerant reservoir and the indoor unit that fits to the rear of an existing 42U rack, with the two units joined by pipework. The indoor unit incorporates a cooling coil that has thermostatically controlled fans and is capable of handling capacities between 15kW and 30kW.
How does the ColdLogik water cooling system work?
At the centre of the ColdLogik water cooling system are the ColdLogik CL20 Rear Coolers a range of passive and active rear cooler doors that either come pre-installed to the rack or can be retro-fitted to existing racks via an interface frame or aisle cooler. The range enables cooling from 12kW to the 58kW delivered by the CL20 C14 Rear Cooler.
As the ColdLogik water cooling system can operate with higher water temperatures of between 14°C to 24°C the external cooling selection is less restrictive meaning that the rear coolers can be feed with water from other sources other than chillers, for example boreholes, rivers, lakes or sea water etc. Another benefit of the ColdLogik water cooling system is its patented Leak Prevention System (LPS) which, in the event of a pipework breach stops water from escaping. Not only that, but it allows the water cooling system to continue running unimpaired. The ColdLogik system works at its optimum energy performance when it is the sole cooling solution i.e. there is no additional air conditioning. All of the room’s cooling is provided by the Rear Coolers and managed by the ColdLogik Management System (CMS) and ColdLogik Room Management System (RMS) that constantly monitors the temperature and responds to the heat removal demands placed on the system to maintain the room’s ambient temperature.
How does the air heat exchange rear door affect server room cooling?
The ColdLogik Rear Cooler is a type of air heat exchange rear door, that controls the server room cooling process. Ambient air within the room is pulled into the cabinet and passes through the IT equipment. The resulting hot air produced by the IT equipment is exhausted directly on to the heat exchange rear door. Within the rear door is the water-cooled coil which removes the heat at source. The exiting air from the door provides the server room cooling and is returned into the room at a predetermined temperature. On active doors the fans are controlled by the CMS and will adjust in speed depending on the heat load so to maintain the ambient temperature.
Does a liquid cooled rack provide cooler server rack cooling?
A liquid cooled rack will provide greater server rack cooling than racks being cooled by traditional air conditioning. As previously mentioned air is a poor conductor of heat whilst liquid can dissipate much higher heat loads. As rack densities are increasing the need for better server rack cooling becomes more of a necessity. Liquid cooled racks such as ColdLogik can handle heat loads of up to 58kW, which is the equivalent of 29 electric fires!
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