Hey Habr! A couple of weeks ago it was a hot day, which we discussed in the "smoking room" of the working chat. In just a few minutes, the conversation about the weather turned into a conversation about cooling systems for data centers. For techies, especially Selectel employees, this is not surprising, we talk about such topics all the time.
During the discussion, we decided to publish an article about cooling systems in Selectel data centers. Today's article is about freecooling, a technology used in two of our data centers. Under the cut - a detailed story about our solutions and their features. Technical details were shared by Leonid Lupandin, Head of the Air Conditioning and Ventilation Systems Service Department, and Nikolay Rubanov, Senior Technical Writer.
Cooling systems at Selectel
Here is a brief description of the cooling systems we use in all our facilities. We will move on to freecooling in the next section. We have in Moscow, St. Petersburg and the Leningrad region. The weather conditions in these regions are different, so we use different cooling systems. By the way, in the Moscow data center, it was often a joke that those responsible for cooling were specialists with the surnames Kholodilin and Moroz. It happened by accident, but still ...
Here is a list of DCs with the cooling system used:
- Berzarina - freecooling.
- Flower 1 — freon, classic industrial air conditioners for data centers.
- Flower 2 - chillers.
- Dubrovka 1 - chillers.
- Dubrovka 2 — freon, classic industrial air conditioners for data centers.
- Dubrovka 3 - freecooling.
In our data centers, we strive to maintain the air temperature at the lower limit of the recommended range. It's 23°C.
About freecooling
in two data centers, Dubrovka 3 и Berzarina, we installed freecooling systems, and different ones.
Freecooling system in DC Berzarina
The basic principle of freecooling systems is the rejection of heat exchangers, so that the cooling of computing equipment occurs due to blowing with the help of street air. It is cleaned with filters, after which it enters the machine room. In autumn and winter, cold air must be “diluted” with warm air so that the temperature of the air blown over the equipment does not change. In summer in Moscow and St. Petersburg additional cooling is required.
Adjustable air dampers
Why freecooling? Yes, because it is an efficient technology for cooling equipment. Free-cooling systems are generally cheaper to operate than classic air-conditioned refrigeration systems. Another plus of freecooling is that cooling systems do not have such a strong negative impact on the environment as air conditioners with freon.
Scheme of direct free-cooling with aftercooling without raised floor
An important point: free-cooling is used in our data centers along with after-cooling systems. In winter, there are no problems with the intake of external cold air - it is cool outside the window, sometimes even very much, so additional cooling systems are not needed. But in summer the temperature rises. If we were using pure freecooling, the temperature inside would be around 27°C. Recall that the temperature standard for Selectel is 23°C.
In the Leningrad region, the long-term average daily temperature, even in July, is around 20°C. And everything would be fine, but some days it is very hot. In 2010, the region recorded a temperature record of +37.8°C. Given this circumstance, it is impossible to fully count on freecooling - one hot day a year is more than enough for the temperature to go beyond the standard.
Since St. Petersburg and Moscow are megacities with polluted air, we use triple air purification when taking it from the street - filters of G4, G5 and G7 standards. Each subsequent one filters out the dust of ever smaller fractions, so that we have clean atmospheric air at the exit.
Air filters
Dubrovka 3 and Berzarina - freecooling, but different
For a number of reasons, we use different freecooling systems in these data centers.
Dubrovka 3
The first DC with free-cooling was Dubrovka 3. It uses direct free-cooling, supplemented by ABHM, an absorption refrigeration machine that runs on natural gas. The machine is used as an additional cooling in case of summer heat.
Data center cooling according to the free-cooling scheme with a raised floor
This hybrid solution made it possible to achieve a PUE of ~1.25.
Why ABHM? This is an effective system where water is used instead of freon. ABCM has a minimal impact on the environment.
As an energy source, the ABCM machine uses natural gas, which is supplied to it by a pipeline. In winter, when the machine is not needed, the gas can be burned to heat the supercooled outside air. It's much cheaper than using electricity.
View of ABHM
The idea to use ABCM as an aftercooling system belongs to one of our employees, an engineer who saw a similar solution and suggested using it in Selectel. We made a model, tested it, got an excellent result and decided to scale it.
The machine was built for about a year and a half, along with the ventilation system and the data center itself. In 2013, it was put into operation. There are practically no problems with it, but for work you need to undergo additional training. One of the features of ABHM is that the machine maintains a pressure difference inside and outside the DC room. This is necessary in order for hot air to escape through the valve system.
Due to the pressure difference, there is practically no dust in the air, since it simply flies out, even if it appears. Excess pressure pushes particles out.
System maintenance costs may be slightly higher than with conventional refrigeration. But ABKhM allows you to save money by reducing the consumption of electricity for heating the air and its aftercooling.
Berzarina
Scheme of the movement of air flow inside the server room
Freecooling with an adiabatic aftercooling system is used here. It is used in summer when the air becomes too warm, with temperatures above 23°C. In Moscow, this happens often. The principle of operation of the adiabatic system is the cooling of air as it passes through filters with liquid. Imagine a wet rag, from which water evaporates, cooling the fabric and the surrounding air layer. This is how an adiabatic cooling system works in a data center. On the path of the air flow, tiny drops of water are sprayed, which reduces the air temperature.
Working principle of adiabatic cooling
They decided to use freecooling here, because the data center is located on the top floor of the building. This means that the heated air thrown out to the outside immediately goes up, and does not suppress other systems, as it could happen if the DC was located on the lower floors. Thanks to this, the PUE indicator is ~1.20
When this floor was vacated, we were delighted, because we got the opportunity to design whatever we want. The main task was to create a DC with an efficient and inexpensive cooling system.
The advantage of adiabatic cooling is the simplicity of the system itself. It is simpler than air-conditioned systems and even simpler than ABCM, and allows you to save energy, the cost of which is minimal. However, it needs to be carefully controlled so that it does not turn out like Facebook did in 2012. Then, due to problems with setting the work parameters in the data center, a real cloud formed and it began to rain. .
Control panels
The system has been operating for only the second year, during which time we have identified a number of small problems that we are fixing with the designers. But this is not scary, because in our time it is important to constantly be in search of something new, not forgetting to check existing solutions.
We are constantly looking for opportunities to apply new technologies. One of them is equipment that works normally at temperatures above 23 °. Perhaps we will talk about this in one of the future articles, when the project reaches the final stage.
If you want to know more about other cooling systems in our DCs, then with all information.
Ask questions in the comments, we will try to answer everything we can.
Source: habr.com