Adiabatic data center cooling

    Up to 35-40% of all energy consumed by the data center is spent on cooling server racks and engineering systems. The adiabatic principle of cooling the data center can significantly reduce power consumption compared to traditional systems. An economical way to cool the data center will be implemented at the DataPro data center in Moscow.

    Weather in the data center

    In recent years, the density of equipment in data centers has increased significantly, and with it the cost of power has also increased. In Russian commercial data centers, one rack consumes on average from 3 to 10 kW - about the same amount of heat has to be removed from it. At the same time, the most significant “contribution” to the overall landscape of energy consumption is made by cooling systems: their share reaches 35-40%.

    In an effort to optimize the traditional scheme, specialists tried to remove heat by using more efficient refrigerants and by choosing the optimal parameters of the system. But these were half measures that did not allow to achieve significant savings.

    The most energy-intensive part in the traditional cooling scheme is a compressor and condensing units. The abandonment of these components in combination with the use of cold outside air (freecooling - the so-called scientific use of free cooling) was the first revolutionary step towards an optimized, low-cost cooling system in terms of energy resources. This approach has been adopted by many data centers around the world. The principle of freecooling is now widely used in many data centers in Russia, mainly in those regions where the temperature has been kept low for many months. Obviously, the use of such technology is quite justified in Murmansk or Norilsk. But is it possible to build an energy-efficient data center in a hot climate? For Russian data centers, this question is also not idle,

    Hot cooling

    Data center "Mercury" eBay

    paradoxically, but around the world there are many examples of the location of data centers in a hot climate - in conditions much more extreme than in Russia. For example, the Mercury data center was built by eBay in the American city of Phoenix, Arizona in a hot desert, where the thermometer reaches 50 degrees C in the summer, and this is important for the eBay business such as continuity and reaction time of the application at the request of users around the world - every second a huge volume of transactions with a total amount of about 2 thousand dollars is concluded on the portal of this company. That is, the reliability of all data center systems is in the first place in the list of priorities. It would seem that to cool such a data center it would be more reasonable to place it in the northern latitudes.

    And yet, eBay built its data center in Arizona, and it didn’t burn out. It would seem that the use of external air was out of the question. But, having analyzed all the possibilities to reduce energy consumption, eBay experts came to the conclusion that it is freecooling that will best provide the required efficiency of the new data center in the desert. The secret is that in combination with freecooling, adiabatic hydration was applied at this facility.

    Wind was blowing from sea

    It has long been noticed that the air coming from the sea is cooler than the steppe wind blowing in the direction of the water area. In ancient Rome, the houses were cooled in this way: under the open windows there was a pool with a fountain: passing above the water, the air was cooled as a result of its evaporation.

    Wet cooling towers are also based on this principle, which is one of the oldest cooling methods that is actively used in production. The principle of operation of these systems is based on cooling water by a stream of air blown through its surface.
    A more advanced version of this process is used in adiabatic air cooling systems.

    Issue economy

    Adiabatic cooling of the data center is an inexpensive and reliable system in which there are no complex units and no redundancy of nodes is required. To implement adiabatic humidification, practically no energy is required - only water is consumed. Thus, the cost of chilled air is low, which, if used correctly, can significantly increase the energy efficiency of air conditioning systems.

    In general, the equipment of modern data centers tolerates a higher temperature and an increase in air humidity. The acceptable limits are those recommended by ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers). The first edition of these recommendations, published in 2004, set an upper limit of 25 degrees Celsius with a humidity of 40%, and in the second (2008) - 27 degrees with a humidity of 60%. In the recommendations of 2011, two new classes of equipment for data centers appeared - A3 and A4 with a temperature range of up to 40 and 45 degrees. Although such “hot” cooling is not yet widespread, innovation lovers are actively starting to use it. This allows you to significantly expand the geography of the use of "green" cooling.

    Adiabatic cooling is not always required, only in the hottest months. In the cold season, cooling is done using external air. Not so long ago, adiabatic cooling systems were mainly used in regions with a dry and hot climate. But recent developments by manufacturers of HVAC equipment have shown great potential for using adiabatic cooling systems in temperate European regions.

    “It should be noted that neither the initial temperature of the water, nor the air temperature practically affect the process, unlike humidity,” explains Mikhail Balkarov, technical expert at Emerson Network Power. - So if the data center is in the desert, but at the same time has a source of water, a completely effective system is obtained. But if it rains at an air temperature of plus 25 degrees Celsius, then, alas, no cooling can be removed from the system, because during rain the humidity of the outside air is close to 100%.

    Michael notes that it is necessary to take into account local moisture anomalies that occur near large bodies of water. In addition, in Russian regions with variable weather, you may have to have two systems at the same time - traditional and alternative, which will significantly increase the size of capital investments and can nullify all attempts to save.

    The disadvantage of the adiabatic cooling method is also an increase in air humidity. Concerns may arise that humidity will become a threat to sensitive electronic equipment in the data center. One example of such an incident is discussed below (see the Facebook in the Rain section).

    Among other shortcomings of the adiabatic cooling system, the expert notes the consumption of water and the need to prepare this water. “Water is wasted on the order of 2 l / h per 1 kW / h at peak consumption and about 0.3 l / h on average during the warm season,” says Balkarov. “This is notable money, and when considering the costs of cleaning, it's even more noticeable.”

    Water needs to be cleaned, emphasizes Mikhail Balkarov, because upon evaporation all minerals are in the air in the form of fine dust. “And if for cooling towers this is a fairly cheap process associated with rough cleaning - cleaning is mainly provided to prevent scale, then nozzles in the adiabatic system require microfilters and osmotic filtration,” the expert explains. So, not only the cost of the system, but also the operating costs are increasing. ”

    When using adiabatic cooling, it should be remembered that the issues of water supply, sanitation and water treatment, which, in turn, will flow into problems of architecture and building structures, will have to be addressed. Do not forget about the cost of water. While its price is not comparable to the cost of electricity, but it is constantly growing.

    WUE ratio

    The use of adiabatic cooling systems reduces PUE and energy consumption, but water consumption can be very high. Therefore, the Green Grid organization in March 2011 introduced another parameter characterizing the useful water consumption in the data center - the water utilization coefficient WUE (Water Usage Effectiveness). The coefficient is calculated by the formula:

    WUE = annual water consumption / power of IT equipment.

    The unit of measurement of WUE is l / kW / h.

    Facebook was the first data center operator to openly share the WUE value. In the data center located in the city of Primeville in the second half of 2011, this parameter was 0.22 l / kW * h.

    In general, the use of adiabatic cooling allows achieving high energy efficiency of the data center: PUE coefficient can reach 1.043, due to the fact that auxiliary equipment, including the cooling system, consumes only about 4% of the data center energy even in summer, and even less in winter (in winter PUE period is about 1.018). The efficiency of condensing systems based on chillers or DX-conditioners is much lower, for them PUE = 1.3 - an excellent result.

    The Mercury data center mentioned at the beginning of the article, with an area of ​​12,600 square meters and a capacity of 4 MW, has been operating for more than a year. Using freecooling in conjunction with adiabatic evaporative cooling in this data center has proven effective.

    Facebook data centers

    Facebook adiabatic cooling system

    Another striking example of the use of new cooling technologies is Facebook data centers. Facebook built its first own data center in the American town of Prienville, in 2010. A year later, a second, duplicate data center was built in Forest City, North Carolina. The energy efficiency factors (PUE) of these sites are: 1.07 for Data Center in Primeville and 1.09 for Data Center in Forest City. This was achieved only by reducing losses in the transmission and conversion of electricity, as well as higher working air temperatures inside the data center (+35 ° C is allowed in racks in a cold corridor).

    In the data centers, a traditional cooling system is installed, but it is used only in emergency cases. The main air conditioning system is direct freecooling with several air treatment chambers through which the outside air passes.

    Initially, air from the outside is taken in by air intakes on the second tier and enters the preparation chamber, where it is filtered and mixed with hot air. Further, air passes through the refrigeration panels. They are a humidification chamber with a large number of pipes spraying distilled water with nozzles under high pressure, thereby increasing humidity and lowering the temperature of the purged air. To fine moisture could not conduct electricity, use distilled water. Further on the air path are membrane filters that separate large particles of moisture. Then the air is sent by powerful fans to the engine room. Waste water is collected in a special tank and treated.

    Facebook in the rain

    Once inside a cooled room in Facebook’s data center in Prienville, a cloud of moisture formed, which literally covered the server rooms along with their (sorry for the pun) cloud computing.

    In 2001, this data center faced a problem in the operation of the control system, due to which the temperature of the air used to cool the servers reached more than 26 degrees Celsius, and humidity - over 95%. As a result, condensate began to accumulate and a rain cloud formed, filling all the space with computing equipment. It was impossible to believe what was happening. Calls began to colleagues to the center of the escalation of problems, but they could not understand for a long time, what kind of rain cloud are we talking about? It was easier to convince them that the apple trees bloomed on Mars than in the fairy tale about rain.

    To save electricity, Facebook used outdoor air to cool its data center instead of a traditional system. But after the control system failed, the recirculation of heated air with a low level of moisture through the cooling system based on a water evaporator began.

    This led to the fact that the air was very moist and a cloud formed, which did a lot of trouble. Some servers are completely out of order: those specialists who were in the data center could observe how the servers spark and agonize. Worse than anything and it was impossible to imagine. However, the incident did not happen again: Facebook experts carefully insulated the contacts in the places where the servers are connected to power sources, protecting them from moisture.

    And what about Russia?

    Adiabatic cooling systems in Russia are not very popular yet, but experts believe that in the coming years, data center designers will be increasingly interested in them. The reason for this is Federal Law FZ-261, which sets a strict framework for energy consumption and requires an increase in energy efficiency by 40% by 2020. The only possible scenario that will satisfy such requirements is a switch to freecooling combined with adiabatic cooling. And the first examples of such implementations are already there. In particular, this cooling principle will be used in the new DataPro data center in Moscow under construction.

    The design of this site involves the use of a cost-effective solution for providing the necessary climatic conditions - the modular EcoBreeze system manufactured by Schneider Electric. DataPro plans to implement the largest installation of this system in Europe in its own mega-data center in Moscow at Aviamotornaya Street, an object with an installed capacity of 20 MW. The EcoBreeze system is built using the principle of wet cooling towers (a variation of adiabatic cooling technology) combined with freecooling, which are discussed in this article. In Moscow, where high electricity tariffs are set, the use of this system will allow significant savings in operating costs in the data center.

    “Technical solutions using adiabatic cooling cannot be called innovative, since they are successfully used in many data centers abroad,” explains Alexey Soldatov. - But the use of this principle in Russian data centers is a rare phenomenon. The EcoBreeze installation at our Moscow site is one of the first deployments. ”

    But at another facility, in the DataPro company data center in Tver, the traditional principle of using freon routes is used to cool server rooms and electrical equipment, which is due to low capital costs and low electricity tariffs.

    At the Tver facility, another variation of the adiabatic principle is applied - isothermal humidification to maintain the required humidity level in server rooms, which we will discuss in our next article.

    Principle of operation
    Mikhail Balkarov. Excerpt from the book “Server and Data Center Cooling. Bases.”, 2011. The

    principle of operation of the adiabatic cooling system is to spray water in the form of tiny droplets that are injected into hot air. (The water should be cleaned of all kinds of impurities.) Water evaporated in the air can cool it to a temperature close to the temperature of a wet thermometer.

    Strictly theoretically, the cooling limit in this process is noticeably lower and is equal to the dew point temperature. To realize this possibility, it is enough to cool part of the initial air to the temperature of the wet thermometer by evaporation of water, and then use it to cool the remainder without moistening. Further, the cold air is also humidified, acquiring a lower temperature. The process can be repeated again with part of the air, reaching a temperature close to the dew point. The only obvious technical difficulty in achieving the lowest possible temperature is a several-fold increase in the required volumes of supplied air and the area of ​​the heat exchanger.

    Such systems are either made according to the principle of wet cooling towers, that is, they use a large surface of the plates covered with a thin film of water, or they spray water under pressure of several hundred atmospheres, through micron nozzles, with very small drops directly into the air ducts.

    Then, either a temperature exchange occurs with what needs to be cooled, or moist air is directly used to cool the equipment. Water consumption is about 2 Kg per 1 kW / h of heat removed. Since most of the water evaporates, the requirements for its chemical composition increase accordingly, which requires the use of ion-exchange filters or reverse osmosis filters.

    When using nozzles, strict requirements are imposed on mechanical impurities; installation of microfilters after a high-pressure pump is required. These complications are associated with the fact that, starting with a certain droplet size, the evaporation process is very fast, and due to this, the size of the irrigation chamber is significantly reduced.

    The use of nozzles of a larger diameter, medium and low pressure, is easier in terms of the operation of nozzles and the water treatment process. But at the same time, part of the water does not participate in the process and merges (the drops do not have time to evaporate completely), in addition, the dimensions of the humidification chambers become comparable with the rest of the system.

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