Hello, Habr! A couple of weeks ago it turned out to be a hot day, which we discussed in the "smoking room" of the work 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 constantly talk about similar topics.
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. The technical details were shared by the head of the air conditioning and ventilation systems service department Leonid Lupandin and senior technical writer Nikolai Rubanov.
Cooling systems at Selectel
Here, briefly about which cooling systems we use in all our facilities. Let's move on to freecooling in the next section. We have several data centers 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, the reason for jokes was often that those responsible for cooling were specialists with the names Kholodilin and Moroz. It happened by chance, but still ...
Here is a list of DCs with the used cooling system:
- 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 keep air temperatures at the lower end of the ASHRAE recommended range. It is 23 ° C.
About freecooling
In two data centers, Dubrovka 3 and Berzarina , we have installed free cooling systems, and different ones.
The main 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 and then enters the machine room. In autumn and winter, cold air must be "diluted" with warm air so that the temperature of the air that blows over the equipment does not change. Additional cooling is required in Moscow and St. Petersburg in summer.
Dampers Why Free Cooling? Because it is an effective equipment cooling technology. Freecooling systems are generally cheaper to operate than conventional 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.
An important point: freecooling is used in our data centers together with aftercooling 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 air temperature rises. If we were to use pure freecooling, the temperature inside would be around 27 ° C. As a reminder, Selectel has a temperature standard of 23 ° C.
In the Leningrad Region, the long-term average daily temperature, even in July, is around 20 ° C. And all 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, one cannot fully rely on free cooling - 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 threefold air purification when taken from the street - filters of standards G4, G5 and G7. Each subsequent one filters out the dust of ever smaller fractions, so that at the outlet we have clean atmospheric air.
Dubrovka 3 and Berzarina - freecooling, but different
For a number of reasons, we use different free-cooling systems in these data centers.
Dubrovka 3
The first DC with freecooling was Dubrovka 3. Direct freecooling is used here, supplemented by ABHM, an absorption refrigeration machine that runs on natural gas. The machine is used as aftercooling in case of summer heat.
This hybrid solution allowed us to achieve PUE ~ 1.25.
Why ABHM? It is an efficient system that uses water instead of freon. ABHM has a minimal impact on the environment.
As a source of energy, the ABHM machine uses natural gas, which is supplied to it by a pipeline. In winter, when the car is not needed, the gas can be burned to heat the subcooled outside air. It is much cheaper than using electricity.
The idea to use ABCM as an aftercooling system belongs to one of our employees, an engineer, who saw a similar solution and proposed to apply it at Selectel. We made a model, tested it, got a great result and decided to scale it.
The car was under construction for about a year and a half, together with the ventilation system and the data center itself. In 2013, she was commissioned. There are practically no problems with it, but to work you need to undergo additional training. One of the features of the ABHM is that the machine maintains the pressure difference inside and outside the DC room. This is so that hot air can 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. Excessive pressure pushes particles out.
System maintenance costs are arguably slightly higher than conventional cooling. But ABHM allows you to save money by reducing the consumption of electricity for heating the air and its additional cooling.
Berzarin
Freecooling with an adiabatic aftercooling system is used here. It is used in summer when the air gets too warm, with temperatures above 23 ° C. This happens quite often in Moscow. The principle of operation of the adiabatic system is air cooling when passing through filters with liquid. Imagine a wet rag that evaporates the water, cooling the fabric and surrounding air. This is roughly how an adiabatic cooling system works in a data center. Tiny water droplets are sprayed along the path of the air flow, which reduces the air temperature.
Here we decided to use free- cooling , because the data center is located on the top floor of the building. This means that the heated air ejected outside immediately goes up, and does not suppress other systems, as it could happen if the DC is located on the lower floors. Thanks to this, PUE of ~ 1.20
When this floor was vacated, we were delighted, because we were able to design whatever we wanted. 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 systems with air conditioning and even simpler than ABHM, and allows you to save energy, the costs of which are minimal. However, it needs to be closely monitored to ensure that it doesn't work out like Facebook did in 2012. Then, due to problems with setting the operating parameters in the data center, a real cloud formed and it started to rain. This is not a joke .
The system has been in operation for only the second year, during which time we have identified a number of small problems that we are eliminating 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 the 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 a future article, when the project reaches its final stage.
If you want to know more about other cooling systems in our DC, then here is an article with all the information.
In the comments, ask questions, we will try to answer everything we can.