STULZ UK’s Johnathan Attwood warns that environmental regulation is increasing the cost of conventional cooling approaches widely used by the data centre sector. How can operators reduce their OPEX and improve their green credentials?
There is a need for increased education in the data centre sector on the different cooling options available and their implications for operating expenditure (OPEX), energy efficiency, and environmental impact. Many data centre operators are familiar with Direct Expansion (DX) systems or chilled water type systems, but there is a need for greater awareness of new approaches that can help data centres deliver on long-term sustainability goals.
Cooling technology is advancing at a pace with the emergence of new technologies such as hybrid cooling, which has the potential to significantly reduce energy consumption and the environmental impact of data centres. With cooling accounting for up to 40 percent of the energy used in data centres, and one of the biggest outlays for operators, there is a need to understand the hidden costs associated with the various technologies and how they compare.
During the past 15-20 years, DX has become the dominant cooling solution and, until recently, this was driven by the fact that it was considered cheap and simple to install. DX units offer a number of benefits, such as good levels of cooling, coupled with a low footprint. As these systems are based on indirect cooling, there is also no danger of introducing contaminants from outside into the data centre.
However, DX systems are less desirable from an energy efficiency perspective as well as their dramatic instability, in terms of refrigerant pricing, meaning that these units are no longer the low-cost option that they once were.
Chilled water cooling
Chilled water systems have also come to the fore in recent years, as the capacities in data centres have steadily increased. However, hybrid solutions offer the advantage of having a lower refrigerant charge per unit – despite the fact that these operate using a similar process to a chiller. Some of the largest hybrid solutions, for example, use 7.6kg of refrigerant per circuit (with a twin circuit).
An equivalent, conventional chiller system will use around 40 percent more refrigerant on a 1:1 basis. On large systems it is also important to note that, if a chiller fails, there is a greater risk of losing a significant amount of refrigerant. With a hybrid unit, the capacity is spread over multiple units, but the risk of losing large quantities of refrigerant is significantly reduced.
Hybrid cooling combines the reliability and control of a DX system, with the energy saving benefits of a free cooling system. In warmer months, when the external ambient temperature is above 20°C, hybrid systems can operates as a water-cooled DX system, where the refrigeration compressor rejects heat into the water circuit via a plate heat exchange (PHX) condenser. The water is pumped to an air blast cooler where it is cooled, and the heat rejected into the air.
In cooler months, below 20°C external ambient temperature, some systems cab automatically switches to a partial free cooling mode. In this mode, the water is directed through both proportionally controlled valves and enables proportional free cooling and water-cooled DX cooling to work together, with the dry cooler fans being used to cool the water to the desired level to achieve the required cooling capacity.