Published Date 23/11/17 08:00
Carel’s recent participation at “Data Center World” (DCW) Asia in Singapore was a great opportunity to meet some of the industry’s leading players in the southeast Asian area, addressing issues relating to data centre cooling in this region specifically and throughout Asia in general. This part of the world is experiencing strong economic growth, and with this comes a considerable increase in demand for IT infrastructure, which nowadays represents an essential support for the growth of all types of business. In this highly dynamic environment there are numerous innovations and, like elsewhere in the world, there is a tendency to use cloud computing services, or “COLO” (common location, facilities hosting third-party servers). In principle this can bring considerable optimisation, as it makes it possible to use data centres located in parts of the world with more favourable climatic conditions and thus exploit free cooling, with significant energy savings.
Nonetheless, it is not always possible for two reasons, one relating to the ability of the network to carry data from a remote location (which may become a bottleneck), the other involving more the physical control of accessibility to the data, especially when sensitive.
Such issues are particularly evident in critical applications, for example data centres for financial institutions that perform short latency transactions and handle highly valuable information, i.e. “virtual money”.
For these reasons, the whole region, and particularly Singapore, a very important financial centre, expects to see the construction of numerous new data centres.
Climate conditions, however, are not conducive to the use of energy-saving techniques such as free cooling and direct evaporative cooling, which are widely used in many modern data centres around the world.
The figure illustrates the temperature and humidity conditions in Singapore on an hourly basis throughout the day, and on an annual basis, taken from historical data collected by ASHRAE; it is clear that, even assuming a data centre with “cold aisle-hot aisle” architecture and a server air intake temperature of 25°C and exhaust temperature of 37°C, fresh outside air cannot be introduced to obtain adequate cooling. Indeed, the possibility to exploit free cooling is not only limited by the temperature, which in any case never falls below 23°C (on its own making free cooling potentially usable), but also by the relative humidity, which in this case is often higher than 80%, giving local outside conditions that are defined as “Admissible” and not “Recommended” by the ASHRAE TC 9.9 “Thermal Guidelines” on the design of data centres.
One very popular way today to reduce energy consumption in data centres, where outside air cannot be introduced, is indirect evaporative cooling: this technique exploits the well-known effect of lowering the temperature through the evaporation of water in a secondary or auxiliary air stream, which then cools the primary air flow via a heat exchanger. In this way, the air inside the server rooms is recirculated and no additional moisture is added, while there is no limitation on the humidity of the secondary air stream, which can even reach saturation, thus maximising the effect.
Even so, however, the specific temperature and humidity conditions are such that the evaporative effect cannot provide all the required cooling capacity on its own, not even considering new types of heat exchangers with wetted surfaces to increasing the cooling effect. There is no doubt though that this technology is effectively an applicable option in these regions.
Another interesting opportunity comes from the new technologies associated with variable-speed compressors equipped with BLDC motors. As can be seen from the figure, and as is widely known, these motors are very efficient, featuring less losses from friction and magnetisation current than conventional motors: these advantages are especially significant at part loads, i.e. in conditions where the compressor can operate at speeds below the maximum.
It would therefore be possible to evaluate the use of units featuring IEC and at the same time a refrigerating circuit with BLDC compressors; indirect evaporative cooling could thus provide a reduction in load in order to reduce the cooling capacity delivered, at the same time increasing the efficiency of the compressor that operates at lower speed.
In the case of Singapore, with the configuration and temperatures described above, the secondary air could reach 28°C, meaning that even with a medium-efficiency heat exchanger load can be reduced by 40%, with a simultaneous 50% increase in refrigerant circuit efficiency.
Obviously, an accurate assessment must take into account the total cost of ownership (TCO), however, these quick simulations, even when rounding down the results, show a potential that deserves close examination by the industry as a whole to evaluate this solution.
DCW Singapore 2017 PRESENTATION
Humidity Control + Energy Saving: is there a solution?