DCN August 2017 - Page 27

Cooling Figure 1: Direct free cooling. inlet temperature and server exit temperature are well known to have a significant effect on the efficiency of any cooling system and the higher the former, the more efficient a cooling system can become. Although the concept behind free cooling is relatively straightforward, there are a number of ways to go about achieving it. Direct free cooling metric – the closer it is to 1.0 then the better the facility is doing in managing its use of non-computing energy – and free cooling can help lower this figure. So what do we mean by the term free cooling? Gartner defines it as ‘any technique used to reduce the energy consumed by cooling systems or the time that the cooling units run by using the outside temperature of air or water to cool the data centre or other facilities’. Free cooling helps save energy and for most of the time UK ambient air temperature is colder than that required in the data centre – so a simple ventilation system can maintain compliant conditions. Figure 2: Indirect free cooling with air/air plate heat exchanger. With direct free cooling, filtered outside air is fed directly into the data centre if the CRAC system determines that it is at the right temperature. This means that the compressors do not have to operate as often, saving electrical energy. However, in urban areas air quality might not be good enough and is often full of particles, which can be very hostile to modern IT equipment. Therefore, Temperature gauge Before looking at free cooling in greater depth, it is worth noting that there are various measurable temperatures present in a data centre including supply air, return air, room air, cold aisle, and server inlet and exit temperatures. Server August 2017 | 27