As the cost of power is one of fundamental elements of data centres’ operational costs, and a significant proportion of this cost is formed by power consumed for the operation of a cooling system, new solutions that could provide data centre cooling capabilities with less power consumption and hence lower costs is always a topical issue.
Another reason that makes us think about this matter is the increasingly growing computing capacities that are stored in these data centres which accordingly require higher cooling energy to ensure the best possible climatic conditions for technologies that are processing these data.
The third reason requiring constant addressing regarding efficient cooling options is climate change. Although these changes are not rapid, there is a constant trend for the average outdoor air temperature to go up year on year. This means that the necessary cooling capacities also increase.
In order to provide a more efficient cooling process, one of trends is the use of natural resources and processes with as little use of additional power as possible. In this blog article, we are going to touch upon two trends:
so-called free cooling solutions that provide the use of outdoor air or water from a nearby water-source for the cooling process, and
adiabatic cooling facilities provided by temperature changes when a substance changes its state of aggregation (evaporation process), also often known as evaporative cooling.
With good reason, naturally available resources and processes are considered as cooling efficiency enhancing options/solutions. Their use is attractive because in appropriate conditions they provide a chance to reduce the use of necessary energy, which is produced via the consumption of non-renewable resources, as well as to reduce CO2 emissions from energy production.
The free cooling idea is based on the use of natural resources (outdoor air or water from a nearby water source) in the cooling process. During certain periods (season/time of day) or in climatic zones where the temperature of the aforementioned natural resources is suitable for these purposes, the free cooling solution can be very effective.
With the free cooling approach for data centre cooling, when the outdoor temperature is sufficiently low, outdoor air is either directly pumped into the data centre, allowing the air to cool the data centre, or the air is delivered to a cooling system for cooling circulating fluid when it flows back with the heat collected from the rooms of the data centre.
When using a nearby water source, the cooling is provided by the circulation of water through the cooling infrastructure of the data centre and its return back to the water source. It happens differently from the usual closed-loop cooling solution which provides the continuous circulation of cooling fluid through closed-loop cooling and traditional air-conditioning systems.
In both of the above cases, the operation of industrial (conventional) cooling equipment is significantly more intense during periods when the temperature of these natural resources is unsuitable for cooling purposes.
Such solutions can provide significant power resource savings, as during the time when the use of free cooling is possible, the consumption of electrical power will be significantly lower than in cooling with only conventional cooling equipment.
Another no less beneficial effect provided by the aforementioned solution is the lifespan prolongation of the conventional cooling equipment by reducing the load. It also automatically means lower repair costs and operating costs associated with maintenance of the equipment.
However, one should keep in mind that the free cooling solution is not completely free of charge. For example, compressors are required to carry out outdoor air delivery to the data centre and the circulation; filters are needed to purify the outside air used for cooling and so on. Free-cooling options are often unavailable 24/7 all year round. One must consider the periods when the temperature of the required natural resources is unsuitable for the use of such solutions.
Adiabatic or evaporative cooling is based on a different solution. In this case, cooling is carried out by using the change of the water’s physical state – evaporation, resulting in a reduced temperature. In nature this phenomenon can be observed during hot weather near waterfalls where the air is naturally cooler and water droplets evaporate.
This solution, unlike the previous one, is effective in conditions when the outside air temperature reaches about 25°C, which is already high enough to ensure the evaporation of fine water droplets (mist). In order to use this process for cooling, technological equipment providing the development of fine water mist (spray) is used before cooling equipment collectors. Evaporation of the water mist leads to lowering the temperature of the cooling air which is inflowing to the cooling equipment, which in turn requires less energy for cooling equipment to ensure the optimum temperature in the data centre.
This solution is most effective in climatic zones with a relatively long hot season (e.g. Italy, Spain) and without high relative air humidity, which can severely limit the evaporation process.
Within the industry, the given solutions for cooling efficiency advancement are often referred to as economisers.
However, one should remember that when choosing one of these solutions for data centre cooling, detailed calculations are required to estimate the actual energy efficiency as accurately as possible, and then the system should also be assessed from the perspective of stable long-term operational continuity, which is critical for a data centre.