Managing the cooling system in a modular datacentre

If the advantages and benefits of a modular datacentre are quite obvious in the context of its construction, the specific cooling requirements for a datacentre are such that this issue quickly becomes central to the building concept. Air conditioning, natural ventilation, free cooling … the solutions are numerous but how do you choose the best cooling system for a modular datacentre?
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Managing the cooling system in a modular datacentre

Installing an air conditioning system

To ensure the correct cooling of the server equipment, an air conditioning system can be used that comprises cooling down the hot air produced by the equipment and passing this through a cooling mechanism. This mechanism is made up of a series of plates or tubes which contain a liquid refrigerant. This type of cooling system is the most commonly used and is the safest way to cool server rooms. As in the case of a refrigerator, the liquid refrigerant is cooled by means of a compressor. In simplest terms the hot air generated in the server rooms is blown through transfer plates in such a way that when the air exits it is already cooled. Then the cooled air, sometimes also mixed, to a greater or lesser extent, with natural air, is recirculated within the server room.

The aims in using air conditioning

In order to improve the efficiency of the cooling system, it is necessary to analyse and optimise the course followed by the liquid coolant within the system. Instead of cooling the entire room, it is possible to cool down the servers more precisely by passing fresh air through the server racks. This provides a more focused cooling of the processors. In the construction of a modular datacentre, one of the key objectives is to devise a system of heat removal and cooling that keeps the costs low, that is relatively easy to maintain and where the module can be easily integrated into the central server room.

Hot aisle – cold aisle” cooling systems

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“Hot aisle – cold aisle” cooling system diagram
New cooling systems called “hot aisle – cold aisle” have been developed. The principle is simple: server rooms are arranged in such a way that the computer equipment is positioned between two aisles: a cold aisle and hot aisle. A device is used to push cold air from the cold aisle towards the servers and to evacuate the hot air into the hot aisle, which is then released to outside of the building. The efficiency of this type of system depends on the type of servers and their layout in the room but there can be a significant impact on the working conditions when the servers need maintenance and on the efficiency of the overall system depending on whether the hot or cold aisle is contained.

Best use of natural ventilation

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Bringing in cold air
Outside air sometimes can be cold enough to be used to replace the hot air generated by the server rooms. Ideally, it is used simply to let the natural air circulate around the servers. In this case, the humidity levels must be controlled within the buildings so that the computer equipment in the server rooms is not damaged. Apart from the economical aspect of this solution, it also helps in managing the environmental impact of the datacentre, which are usually large consumers of energy. It is also possible to reuse the heat that is generated: either in heating the offices of the datacentre or even other nearby facilities.

Efficiency of cooling systems

The impact of the cooling services in a datacentre cannot be underestimated due to fluctuating energy costs and by working alongside engineers different solutions can be regularly assessed. Some elements completely change the visible architecture, such as ground heat rejection, urban cooling systems or heat evacuation chimneys. Other more technical elements affect the internal arrangement, such as whether to use direct or indirect air, chilled water or more elaborate refrigerants. For small scale operations, a simple DX AC unit may be sufficient where as in larger operations the more efficient solution may depend on whether the CRAC units (Computer Room Air Conditioning unit) provide in-row cooling or operate through the wall.

Datacentres throughout Europe

The use of natural ventilation in cooling systems is of great interest to manufacturers and operators of datacentres. Recent studies show plans to locate datacentres in more northern regions to make the most of this natural cooling of air. In Europe, datacentres can take advantage of natural ventilation for at least half of the year. The main disadvantage is the management of ventilation during the summer months when the outside air temperature is not cool enough. In this case an emergency cooling system is required, meaning that there has to be two cooling systems incorporated into the design, increasing the construction costs without necessarily increasing the effectiveness of the system itself.
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‘Free-cooling’ system
Reid Brewin Architects is one of the leading architectural practices in France recognised for its experience in the design and construction of data centres, including modular data centres. The firm has worked on many projects throughout Europe and the Middle East, notably in France for Global Switch, Equinix, Digital Realty, Telecity, Sodearif and Bouygues Energy Services.