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BSEE
DATA CENTRES & CABLE MANAGEMENT When big is best for keeping data centres cool
Steve Simmonds, special projects engineer with Spirotech, discusses why the chemical compound glycol is among the ‘coolest’ solutions for keeping temperatures under control in data centres, and the equipment needed to achieve it
O
ur growing reliance on digital forms of communication, accelerated by the pandemic, mean that data centres have never been as
important as they are today. A hotbed of activity running 24 hours a day, hot is what they cannot afford to be, as this could result in disastrous downtime.
Data centres have become a cornerstone of Great Britain plc, enabling not only an obsession with TikTok, Instagram and other virtual platforms, but also helping major financial institutions, retailers, telecoms companies and public bodies to function.
Globally they consume 3% of the world’s electricity, and industry forecasts suggest this is going to treble.
Precision cooling is vital for the optimum performance of data centre hardware such as servers, storage, networking and communications systems.
An array of heat removal systems means there is plenty of choice, some using air as the coolant, others utilising water, some deploying a refrigerant, and some glycol.
Fundamentally, all capture the heat generated by the IT equipment inside the building and transfer it through the piped coolant to a form of heat exchanger, which releases it to the outside environment.
Where glycol is used the system fluid is a mixture of ethylene or propylene glycol and water, the former lowering the latter’s freezing point from 0°C to around -50°C, depending on the concentration used.
For glycol-chilled systems the chiller is located on the inside of the building, while the collected heat is released via a dry cooler positioned on the data centre’s exterior.
The dry cooler works through fans driving outdoor air through the glycol-filled coil in the heat exchanger, releasing the unwanted warmth to the atmosphere.
Selfcontained system
Glycol based systems are necessarily self- contained, or closed, as this antifreeze type fluid is toxic and cannot be allowed to enter the public realm because of the risk to health. As a consequence, they are factory tested and sealed prior to installation.
Despite this, losses are almost unavoidable and, in any case, the fluid will expand and contract as the temperature fluctuates, and any deficits will need to be made up.
Because of glycol’s toxicity, a simple refill of fresh water is not possible. Instead the losses have to be mitigated by drawing from a ready-mixed solution held in a glycol storage tank. The storage tanks are by necessity large, needing to compensate for the size of the data centre and that the ‘topping up’ cannot come from an external source.
Spirotech, which offers tanks up to 1,000 litres in capacity, is one of the few system fluid conditioning specialists to have the capability to manufacture and supply them to these large sizes. If additional capacity is needed, they can be installed in series to store more. Filling of pre-mixed fluid can be either a standalone, self-sensing system, or can be controlled by the pressurisation system. In both cases the storage tank has a level alarm that will alert the user if more fluid is required, and ultimately shutdown refill if there is insufficient fluid.
This ensures correct management of the exact quantity of fluid required to be fed to the ‘live’ pressurised side.
Another scenario is having a system designed that ensures a full redundancy package. This is
14 BUILDING SERVICES & ENVIRONMENTAL ENGINEER MARCH 2022
so that if one unit fails, whether that is a pressure maintenance unit or an expansion vessel, then there is always a back-up, which is generally a must for these critical systems.
There are many different levels of redundancy, which vary depending on the application, but which can be covered by working in close consultation with the specifier or end-user.
Advantages over air
One advantage a glycol-based cooling method has over an alternative air cooled system is that the entire refrigeration cycle is contained within Computer Room Air Conditioner, or CRAC, units. This takes up less space.
The CRAC units are positioned around the edges of the IT room and deliver cold air through the void beneath a raised floor. Another advantage is that the pipes transporting the glycol can be extended for longer distances and can service several CRAC units from just one dry cooler and pump package.
In colder locations, a further benefit is that the glycol in the dry cooler can become so cold the refrigerant cycle can be turned off and an economiser mode engaged, providing ‘free’ cooling and thereby reducing operating costs. Like all cooling and heating systems, it is not just a case of setting them up and letting them run. They need continual monitoring, adjustment and maintenance if they are to continue to operate with maximum efficiency. Gases in the system fluid will need to be removed to prevent destructive contamination that will lead to dirt and corrosion caused by oxygen reacting with the system materials. Although the majority of air present when the system is initially filled will mostly be removed through automatic vents and deaerators, this is not always completely successful and some residual gas will remain.
Alongside oxygen, nitrogen present can form ‘air cushions’, or ‘dry’ pockets, that will cause pumps to be noisy and have to work harder, increasing energy consumption. Consequently, these microbubbles and dissolved gases will need to be expelled using powerful vacuum degassers, which will remove more than 99% of the unwanted gases.
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