Why does the data center still have doubts about the application of cold storage?
The characteristics of the data center determine its need for uninterrupted operation. To achieve this, stable and continuous cooling is one of the basic conditions. However, cooling requires electric energy to operate. In case of power failure, it takes time for diesel generator and other standby power supplies to start up to stable power supply, and it also takes time for the chiller to recover after power recovery, which will lead to insufficient cooling, affecting the operation of the server, and even downtime in serious cases.
Therefore, the data center should be equipped with a standby cold source or emergency cold source to ensure uninterrupted cooling. Cold storage is one of the important ways for the data center to carry out redundant emergency cooling. At present, it is gradually developing, and the discussion about its application advantages and hidden dangers is also increasing.
Cold storage can be used for emergency and peak shaving
From the principle, cold storage is a kind of cold source storage mode using natural cold sources. It uses the day night alternate cold and heat changes to cool through the night excess valley power, and stores the cold source in the form of low-temperature water. At present, there are three types of cold storage: water storage, ice storage and phase change material storage. Among them, water thermal storage is a widely used thermal storage mode in China, which has rich experience in design and operation. In recent years, its application in data centers has gradually increased; With the maturity of technology and products, ice storage has also become a feasible solution for data center cold storage. At present, there are also relevant attempts.
For cold storage, China has also put forward corresponding specifications. According to the Code for Design of Data Centers (GB 50174-2017) (hereinafter referred to as the Code), Class A data centers using chilled water air conditioning systems should be equipped with cold storage facilities, and the cold storage time should meet the operating requirements of electronic information equipment.
The specification clause description also describes the emergency cooling supply scenario of cold storage in detail : 1. When two power supplies are switched, the chiller needs to be restarted, and the cold source of the air conditioner is provided by the cold storage device; 2. When the power supply is interrupted, the electronic information equipment is powered by the uninterruptible power supply system equipment, and the cold source of the air conditioner is also provided by the cold storage device.
Therefore, the time for cold storage device to supply cold energy shall not be less than the power supply time of UPS equipment. The cold storage capacity provided by the cold storage device includes the cold storage capacity in the cold storage tank and related pipelines, and the cold storage capacity in the main engine room.
standard It is shown that when the diesel generator is used as the backup power supply, the minimum backup time of the battery of the uninterruptible power supply system in the Class A data center is 15 minutes. That is to say, the time for cold storage device to supply cold energy is at least 15 minutes.
Figure: Intercept and organize from 《 GB 50174-2017 Code for Design of Data Center 》
The original purpose of cold storage is to provide continuous cooling. However, considering the current status of data center cooling and the redundancy of chillers, Cold storage can also play a regulating role in energy reserves, and cut peak and fill valley. The cold energy stored in the cold storage station can be released during the daytime peak for the use of the data center, helping the data center to obtain the benefit of the difference between peak and valley electricity prices and reduce the cost of electricity charges.
At present, there are data centers to practice and obtain good benefits. At the 16th annual ceremony of China's IDC industry (IDCC2021), representatives of the participating enterprises said that the capacity configuration of the cold storage tank designed by the enterprise for a data center in Beijing was more than 6 times that of the conventional cold storage design of the general data center, which mainly stored cold in the trough phase, and discharged cold in the daytime peak phase, ensuring the long-term buffer of refrigeration continuity, making continuous refrigeration more redundant, Reduce the operation and maintenance cost by more than 1 million yuan every year.
Problems encountered in the development of cold storage
Cold storage is the use of natural cold sources. It can provide emergency cold sources, cut peak and fill valley, which is of great significance to the cost reduction and efficiency increase of the data center. However, there are two sides to it. In practical applications, cold storage also faces many "problems".
PUE may rise
PUE is an important indicator to measure the energy efficiency level of the data center. Reducing PUE has become an important goal in the construction and operation of the data center. However, cooling storage may cause an increase in PUE value. This is mainly because cold storage requires energy supply to maintain the cold storage state, which will increase the power consumption outside of IT equipment, resulting in an increase in PUE.
In terms of water storage and ice storage, many data centers currently use medium temperature water for cooling in water storage, which has high efficiency, but low cold storage density. Therefore, it occupies a large space. In order to save space, in addition to reserving space in the design, and making use of fire prevention pools and some unimportant spaces, Water cooling storage also increases the temperature difference of cooling storage by reducing the temperature of cooling storage, which may lead to the decrease of the efficiency of the host and the increase of the power consumption of cooling storage. If PUE is calculated normally, it will play a negative role.
Although the space occupation of ice storage is small, its storage temperature is low. Data shows that its ice making temperature is generally - 4 to - 8 ℃, far lower than the storage temperature of 4 ℃ for water storage. If you want to maintain this temperature, it will also produce more energy consumption, which will also affect PUE.
This has caused the data center to have more concerns about the arrangement of cold storage equipment, which has formed a certain barrier for the development of cold storage equipment.
A certain probability brings security problems
Security is the foundation of the data center, and the addition of cold storage equipment itself may bring new security risks.
On the one hand, the installation of equipment may increase the probability of safety failures. In particular, the cold storage tank has a large volume, complex equipment and great difficulty in installation. Its construction may cause safety accidents, such as the settlement accident of the cold storage tank, and because the settlement of the cold storage tank and the main building is different, the pipeline connecting the cold storage tank and the system is cut off, resulting in engineering accidents, etc; On the one hand, the use of equipment may also bring about safety problems. The duration and stability of the cold storage can provide a cold source need to be determined in combination with the situation of the data center, which will lead to differences in the design and layout of the cold storage equipment, as well as different requirements for the design of the internal water distributor. Affected by these factors, once the cooling time of the cold storage tank does not meet the actual needs, In the process of use, it may affect the security of the data center.
Great impact on the overall layout
The data center is a whole. The cold storage equipment occupies a large space and interacts with the data center. Its construction has a great impact on the overall layout.
For example, when planning the cold storage equipment, not only its own operation, maintenance, commissioning and overhaul should be considered, but also the possible impact of operation, maintenance and overhaul on the operation of the data center should be evaluated. Hidden dangers and problems should be found in time to ensure the installation and normal operation of the system; For another example, during the construction of water cooling storage, the peak shifting and valley filling water cooling storage can be combined with emergency cooling supply, as well as with the emergency pool and fire pool of cooling water. At this time, the water cooling storage scheme should fully consider the possible impact of various functional pools, so that the pool will not have negative effects on other pool functions during its application.
The cold storage equipment has a great impact on the planning and construction of the data center, which means that the data center needs to invest more in operation and is more difficult to build, which affects the application of the cold storage equipment to a certain extent.
Solution and development direction
From the perspective of cold storage function, it can ensure the normal operation of the data center, make full use of natural cold sources, reduce the operating cost of the data center, and has its own necessity in the data center. However, if you want to complete a wider range of promotion and application, you need to solve the above problems. In combination with relevant practice and exploration, the following schemes and directions are mainly included at present:
Comprehensive calculation PUE
PUE plays an important role in the process of energy efficiency water balance in the data center. If you want to play the role of cool storage in cooling and avoid the negative impact of cool storage on PUE, you need to fully consider the cooling effect of cool storage, consider its role in cost reduction and efficiency increase, and calculate PUE as a variable with flexibility.
At present, some places have explored this issue. For example, the Guidelines for the Construction of Shanghai Data Center (2021 Edition) proposes to comprehensively consider the role of several technologies in improving the energy efficiency of the data center itself and the city as a whole, and encourage the effective application of technologies. The comprehensive PUE index is calculated on the basis of the benchmark PUE index, and the comprehensive PUE index is taken as the constraint condition of the guideline for each data center.
comprehensive The calculation formula of PUE is: PUE comprehensive =PUE benchmark —∑ γ i
γ Staggered peak cold storage factor To measure the degree to which the evaluated data center reduces the peak power load by adopting the cold storage technology. According to the proportion of the annual cumulative total cooling discharge to the total cooling consumption, different peak shift storage factors can be determined:
Promote the development of cold storage technology
Technology is the source power to promote industry progress and improve the application range of products. The safety problems faced by cold storage and the impact on the overall construction can be alleviated or even solved through technology.
Based on the current reality, the progress of cold storage technology is mainly divided into two aspects. On the one hand, it is the improvement of intelligent technology. Whether it is peak shaving or valley filling, the control of cold storage temperature needs to be combined with the status of the data center. Only high intelligent means can further achieve the accuracy of control and coordination on the existing basis, and improve the efficiency of energy use; On the other hand, the technology based on cold storage needs continuous progress, and the related exploration is also increasing at present. For example, the development of dynamic ice storage system, in which the ice slurry system, due to its high efficiency, small size, extremely low failure rate, has significantly better performance than the ice making sliding unit and supercooled water ice making system, has become one of the optional technologies of the ice storage system in the data center.
Fully integrated with power storage
Data center power storage refers to the storage of new energy to supply power to the data center. Combining it with cold storage means that new energy power generation is used for cold storage.
Cold storage has the feature of using electric energy in the valley at night, and new energy storage also needs time to complete charging. The combination of the two can fully combine this feature to achieve further utilization of time and energy efficiency. For example, solar energy can be used to store energy in the daytime and supply power for cold storage at night through photovoltaic equipment.
At the same time, through the integration of power storage and cold storage, on the basis of the original provision of emergency cooling, peak shaving and valley filling, further improve the use of new energy, and promote energy conservation and carbon reduction in the data center. At the current stage, it also provides new ideas for the development of new energy consumption and power storage.
Linkage with multi industry cold source supply
With the approaching of the "double carbon" goal, the use of energy is becoming more adequate and interconnected, and data infrastructure is expected to form linkages with many livelihood industries.
As an industry closely related to energy, the data center not only needs large-scale cold storage, but also generates a large amount of heat energy, which makes it a foundation for becoming a super energy complex. By developing cold energy and waste heat, it can supply energy for multiple industries, form an energy interaction and linkage development of multiple industries and scenarios, and turn high load energy into high energy supply.
In terms of cold storage, in theory, the data center can combine a variety of scenarios, such as near ski resorts, large-scale cold chain logistics, etc., to form an energy use ecosystem with high energy efficiency and low carbon emissions by providing continuous cold sources. Of course, there are many preconditions for forming this scenario, including stable cold storage, sufficient cold sources, and economic benefits. At present, the conditions in this regard are relatively lacking.
To sum up, as an emergency cold source, cold storage is an important choice for the data center to realize uninterrupted cooling supply, and peak shaving and valley filling can be carried out, but its negative impact on PUE, existing safety hazards, and high construction difficulty cannot be ignored. If the data center wants to make good use of cold storage, it needs to explore in many aspects, such as the choice of water and ice storage, For example, the timely adjustment of PUE calculation considerations and methods, such as the development of technology and security, still has a long way to go.
