Data Center Tour: Free-cooling

Good day, habrauser! We continue the series of articles and videos on the
Russian Intel Data Center and today we are considering a
free cooling system or free-cooling.

The entire cooling system of the data center consists of 2 circuits: internal and external.
The internal ones include chiller, pumping stations and precision air conditioners.
The principle of operation of the internal circuit is as follows: cold water (its temperature
is 7-8 degrees) from the chiller via pumping stations to
precision air conditioners, which cool the air directly in the
data center. The heat removed from the data center is fed back through the pumping stations to
chiller in the form of water heated to 13-14 degrees. There, this water is cooled again and the cycle
repeats again.

Since the chiller itself is a very heat-intensive device, it is
necessary to have an external circuit for cooling it, which includes heat exchangers
located directly on the street. Each heat exchanger in itself is a
rather complex device, but it practically does not require
electricity to operate , which is fundamentally different from the chiller. It is not just a
coil (as it may seem from the video), there are still a lot of levers, valves, etc.
With their help, the flow is regulated depending on the temperature on the street and inside
data center. So this is a fairly “smart” device. It is also worth noting that the
coolant in the external circuit through which heat is exchanged between the
chiller and the street is glycol (since in winter the water in it would simply freeze
).

For a complete understanding of the entire free-cooling system, it is worth remembering that there are
two free cooling technologies (we spoke about this in the very first review
devoted to the data center) - direct and indirect. Recall that with direct cooling, the
air from the street is chased directly to cool the servers. With indirect
free-cooling, the system includes the same chillers that we talked about above.

The implementation of the direct free-cooling system is justified only in rare cases.
So, for example, in the state of New Mexico in the USA, an experiment was conducted - there they built a
data center for about 900 servers and cooled them simply with air from the street. The air there is
quite dry, it is a desert. With the management of air humidity, to prevent
corrosion of the metal in the refrigerated equipment, there were no special problems. In the same
places as England or St. Petersburg, for example,
it is practically impossible to use direct free-cooling technology , because there the
elements of the data center equipment will very quickly fail.

On the whole, for the Central European climate, as, for example, in Germany or in
France, where it is too warm in summer and too cold in winter, it is necessary to
use devices that will bring the temperature of the supplied air to a
range acceptable for the data center. Not to mention Russia, where the temperature difference
during the year reaches 80 degrees and the dependence on such devices is even higher. Obviously,
when 30 degrees or more comes from the street in the summer, you need to cool the
air further . Likewise, it is not good when the air comes in too cold in winter. Therefore, it is
almost impossible to do without a chiller in the summer, and often in the winter (because no one
in their right mind will supply air cooled to -30 degrees into a room with
servers). At least 3-5 months a year, a chiller is simply necessary, and therefore, the
indirect free-cooling system justifies itself in most cases.

To summarize the general system for implementing free-cooling. Chillers that cool water
in the warm season, are switched off at a fairly low temperature and instead
heat exchangers are used in the system, in which heat from the internal
circuit is transferred to the external. This whole system works automatically. The chiller
switches itself on when the current conditions require it. In addition, there is a
supply of water (in large barrels) and when its temperature exceeds a predetermined limit, the
chiller is automatically turned on and begins to cool this water. When will be reached
a sufficient level of its temperature, the chiller will automatically turn off. It is
this water that enters the precision air conditioners. As a rule,
it is not required to manually intervene in the process of starting the chiller, except, of course, in situations where it does not
start automatically due to any emergency situations.
In general, when implementing free cooling in the cold season, the data center cooling system is
somewhat more complicated, but the savings on electricity justify these costs. The approximate
payback period in our Russian climate (of course, it depends on the weather, how
cold and long winters will be, etc.) is on average 2.5 years.

Ask a question to Leonid Shishlov here .