solashared hot water system

Current situation and problems of solar shared hot water system

The large-scale solar shared hot water system was originally the earliest developed and most widely used solar hot water device in China. The so-called common system generally refers to the heat collection area greater than 10m2; The daily water output of the system exceeds 800L, and the system serves multiple people and households with more than one family. In fact, in the early 1970s, at the initial stage of China’s (provincial) solar heat utilization technology, according to the objective conditions and national (provincial) conditions of that year, it was also an inevitable choice to develop a shared hot water system. Therefore, the shared hot water system has become a complete set of systems widely developed and used throughout China long before the emergence of domestic solar water heaters in China. Until now, the shared hot water system still accounts for a considerable proportion in China’s solar hot water projects. In terms of development trend, according to the “12th Five Year Plan for renewable energy” issued by the national development and Reform Commission, China will build more than 100000 solar shared hot water systems in schools, hospitals, nursing homes and other public places during the 12th Five Year Plan period; Moreover, in the future urban high-rise buildings, it is also necessary to equip a large number of solar thermal utilization systems that provide domestic hot water to the residents of the whole building. Therefore, we have listed the technical quality problems of large-scale solar shared hot water system for discussion, not only because the system is larger and the technology involved is more complex than that of ordinary household solar water heaters, so it is more representative, but also, from the perspective of development, if we can find a new way to solve the problems scientifically according to the common technical quality problems of shared hot water system, It will greatly promote the technological progress and application scope of China’s collective hot water system and high-rise building solar hot water system projects.

The early solar energy centralized shared hot water systems installed in China (province) are almost all systems that operate in a natural circulation mode; The most common and common problems of this large natural circulation system are unreasonable system design, irregular pipeline layout and unscientific combination of collector arrays, which ultimately lead to low operation efficiency of the whole hot water system. In the built shared hot water system, the most prominent and widespread problem is that the high-level thermal insulation circulating water tank is rarely considered, and the landscape coordination and system safety of the installed building are rarely considered. In addition, no matter how large the heat collecting area and the capacity of the water tank are, a set of hot water devices invariably adopt the practice of connecting a piece of super large flat plate or vacuum tube array to form a natural circulation system. As a result, it is a strange phenomenon that tens of tons of high-level large water tanks and hundreds of square meters of heat collectors (or thousands of vacuum tubes) are connected in parallel (Series) to form a group of super large-scale “natural circulation system”. This installation method of hot water system not only exposes the defects of the manufacturer in the basic theory of hot water system design, but also artificially engages in large illegal buildings on the roof of the building, creating potential safety hazards. Due to the unscientific design of system engineering, the circulation of hot water system is not smooth to varying degrees, the efficiency of light and heat conversion is low, and the heat loss of pipeline is serious; The local flow of the system is uneven, which leads to the frequent occurrence of “thermal block” pipe air resistance “or” thermal short circuit “. Moreover, it has seriously weakened the ability of the hot water system to resist freezing, strong winds, earthquakes and other natural disasters.

In the design and installation of circulating pipe network of large-scale solar collective shared hot water system, several scientific principles for optimizing pipeline layout must be carefully implemented and observed:

(1) Equal process principle: in the whole solar hot water system, for any collector, the absolute value of the sum of the length of the circulating pipe under the cold water and the length of the circulating pipe on the hot water should be equal.

(2) “One short and three major” principle: in the hot water system, the hot water upper circulating pipe “has the shortest pipe length, the largest pipe diameter, the largest turning radius and the largest climbing angle”.

(3) “Straight and slow” principle: the cold water circulating pipe of the hot water system should “turn wide without edges and corners” and “cross in a straight line”.

In addition, it must be clear that the larger the shared hot water system is, the better; Generally speaking, if the total heat collection area of the hot water system exceeds 40m2-50m2, it must be considered to “break it into parts” and decompose it into several groups of small systems. Because the temperature difference circulating heat transfer power of the natural circulation system comes from the temperature difference thermosyphon pressure head generated by the hot water system; If the circulating pipeline of the hot water system is too large, the circulating resistance of the internal pipeline will inevitably be large, which is easy to cause poor heat exchange of the whole system, uneven local heating and the formation of thermal short circuit, pipeline circulating gas resistance and other system heat loss phenomena. Only after the super large hot water system is divided into several groups of “natural circulation constant temperature drainage (make-up) water system” combined in parallel or in series can it be possible to share the thermal insulation water storage tank with large tonnage and realize low-level concealed installation; Thus, it is possible to improve the light heat conversion efficiency of the whole hot water system, the available hot water output and the safety factor of the system.

It is reasonable to say that in China’s solar thermal utilization, the shared hot water system with a long history of development and successful experience should not have made the above general common sense mistakes again, but why do similar problems happen occasionally? In the final analysis, it shows that in our industry, a considerable number of small, medium-sized and micro enterprises have neglected the system engineering design of shared hot water system for a long time in dealing with large-scale solar hot water projects, and the construction personnel lack the learning and training of safety knowledge such as building environmental protection, building load, system wind and earthquake resistance. In addition, there is a long-term lack of mandatory installation standards for building integration: a professional system engineering design and installation construction team has not been formed in the industrial structure, which is the fundamental reason for the technical quality problems of the shared hot water system, which cannot be improved and solved for a long time.

Technically speaking, only after the solar energy thermal utilization system fundamentally solves the “collection and storage separation” and “building integration” installation, intelligently controls the operation, and realizes the Informatization Transformation of solar energy products, or the solar energy equipment is integrated into the technical connotation of informatization, can it be possible to improve the scientific and technological content of solar energy products and develop the technology and products of solar energy thermal utilization projects that can meet various installation conditions and use requirements. It can be said that, The integration of solar thermal utilization system into information control technology is not only the necessity of contemporary solar energy technology progress, but also an inevitable trend of new technology development that needs special attention in China’s solar energy industry.

On the basis of large-scale solar shared hot water system, after the introduction of information control technology, a new generation of high-tech series products can be developed, and can be effectively promoted and applied to other fields of solar thermal utilization in industrial and agricultural production. It should be said that Yunnan’s technological development work in this field is also relatively early, but so far in the actual promotion and application, the achievements have been very limited. The reasons are: on the one hand, Yunnan solar energy has not made enough efforts in the technological innovation of high-performance flat plate collectors for a long time, and there are few varieties of basic component series products, and the scope of application is not extensive. In general, Yunnan lags behind in the development, promotion and application of solar energy information control technology and controller series products. On the other hand, the weak technical force in the development and design of solar energy system engineering in Yunnan is also one of the main reasons that restrict the slow development of large-scale solar thermal utilization systems in industrial and agricultural production in the province.

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