Selection of collector and system structure

Selection of collector and system structure

The choice of collector is closely related to the system engineering structure and system scale. In the Chinese solar market, solar collectors with large output, stable quality and relatively popular use mainly include three categories: copper-aluminum composite tube-plate flat-plate collectors, all-glass vacuum tube collectors and vacuum heat tube collectors. Solar collector. In developed countries in Europe and the United States, mainstream solar products have been stable on the mainstream product of high-quality flat panel collectors. According to the relevant unit’s sample survey report on the global solar energy production and application in the first five years of the 21st century (before 2005), it reflects: the product structure of 433 solar water heater manufacturers in 21 countries with better solar energy applications in the world (including China) : The production of flat panels accounted for 92.61% of the total number of enterprises, the production of vacuum tubes accounted for 2.77%, and the production of simple water heaters accounted for 4.62%. Product market sales: flat panels accounted for 94.88%, vacuum tubes accounted for 2.46%. By 2010 and beyond, the production and sales of flat panels still occupies the mainstream position including European and American countries, while all-glass vacuum tubes are almost exclusively concentrated in China for production and sales. The upper and lower sides of the collector frame, all around, four corners, water leakage, air leakage and heat leakage and other stubborn diseases. The flat panel has the advantages of separation of collection and storage, easy to organically integrate with the facade of the building, and anchor installation. Starting from the engineering design of large-scale shared solar water heating system, we still believe that the choice of heat collectors should be preferred. The new type of high-quality flat plate is suitable because in large-scale systems, vacuum tube collectors can generally only be installed with vertical headers and horizontally inserted glass vacuum tubes to achieve the installation of large systems. This kind of system completely solves the single-hole blind tube in the vacuum tube. Before circulatory obstacles, the heat collection components of large-scale natural circulation systems or forced circulation systems were selected. From theory to practice, there are still many uncertain factors that violate scientific principles, so a cautious attitude should be taken.

Selection of collector and system structure
System heat collector

The determination of the heating area (AC) of the system collector is an important part of the engineering design of the solar energy system. Since the heat collection area is directly proportional to the average daily water consumption (QW) and the produced water temperature (tm), it is proportional to the annual average solar irradiance (JT) and collector efficiency (ηcd) and the system heat loss rate (ηL). Inversely. Therefore, generally we can use the formula to calculate the area required to install the system:
Where Cw is the specific heat of water at constant pressure (kJ/kg·℃)

The product water temperature (tm) is equal to the difference between the operation termination temperature (tend) and the initial water temperature (t0).
f is the solar insolation rate (%)

In fact, as long as we know the average daily water production per m² collector formally tested by the quality supervision department and the daily hot water consumption required by the system, we can simply calculate the heat collection area of ​​the collector configured for the system. For example: It is known that the system’s integrated tube-plate flat-plate collector can produce 80L~100L of hot water above 45℃ per m² per m²: the daily average hot water consumption of the newly built solar hot water system is 1500L, and the need to install this type can be roughly estimated. Area parameters of solar collectors:
1500÷80=18.75 (m²); 1500÷100=15 (m²)

Then according to the local solar sunshine stability rate and the user’s actual hot water consumption, the average value is taken after a comprehensive balance: 16.8 (m²) ≈ 8 (blocks), and the heat collection area of ​​the system and the amount of flat plate collectors can be roughly calculated .

In addition, the factors that affect the water production of the system are not only the sunshine rate, but also have a lot to do with the design of the system structure. Generally speaking, the thermal efficiency of the forced circulation system is higher than that of the natural circulation. In the natural circulation system, the hot water output of the constant temperature supplementary water system is higher than that of a simple natural circulation system. The selection of collectors and the connection method between collectors are also closely related to the selection of the circulation method of the hot water system.

Selection of collector and system structure
Solar water heating system

For the shared solar hot water system of multi-storey buildings, it is generally not advisable to choose a natural circulation system with high-rise large-tonnage thermal insulation circulating water tanks from the perspective of building integration and system safety considerations. Because the higher the floor, the more users, and the larger the area of ​​the heat-collecting array, the water tank will inevitably be larger, and the position must also be more demanding. The potential safety hazards cannot be underestimated. What’s more, the natural circulation system with collector area of ​​more than 30m², the circulation pipe network is too long, too many bends, the water resistance, air resistance and heat loss of the pipelines along the way can also not be ignored. Therefore, we recommend that the thermal insulation hot water storage tank with a total hot water output of 3.0t or more can be configured with a low-level thermal insulation water tank. The system should be replaced with a small-capacity high-level thermal insulation circulating water tank and still operate in a natural circulation heat exchange mode. However, the system should be transformed into a natural circulation constant temperature discharge method or a natural circulation constant temperature replenishment method to build the system, because such a system is more convenient to install, the safety is significantly improved, and the operating efficiency of the system can also be greater.

If the user masters the new technology and new products of the flat-plate natural circulation system integrated tube-plate solar collector-water heater, only a few pieces of it need to be introduced, and it can be transformed into a direct-flow system with a natural circulation constant temperature and water supplement on the basis of the direct-flow system. System way to run. The biggest advantage of this system is that it can automatically grasp the temperature dynamics of the hot water body in the heat collecting plate core at any time, and make real-time adjustments to the water flow through the automatic control system, so as to ensure the efficient operation of the system. Generally speaking, the thermal efficiency of this direct-flow-natural circulation constant temperature water supplement system is much higher than that of all shared hot water systems including forced circulation, and its hot water output can reach more than 150% of the traditional natural circulation system. Moreover, the thermal insulation hot water storage tank can be separated for collection and storage, placed in a low position, cold and hot water are not mixed, and the available hot water output can be greatly increased; the system has a series of special valves that are difficult to achieve in traditional systems, such as valve opening and hot water supply. Function. If this system can be equipped with a dual-function simple photovoltaic constant temperature water release (or water replenishment) secondary cycle intelligent controller, or a small capacity air source heat pump system as an auxiliary energy system, the system can be transformed into a higher Advanced solar thermal energy utilization system with full-automatic heating 24 hours a day, with a higher standard of solar thermal conversion efficiency.