How to calculate efficiency of flat plate solar collector

In recent years, due to the large-scale use of fossil fuels in different countries, the earth's climate has become unstable, natural disasters have occurred frequently, and human living environment has been greatly threatened. At this time, renewable energy such as solar energy will become the main body of development and utilization. The advantages of abundant solar energy resources, huge energy, clean and pollution-free are recognized, and the collector as the core component of solar thermal utilization is the key link for the development and utilization of solar energy. To date, different types of collectors have emerged, so the efficiency of the flat plate solar collector needs to be measured.

List：

• The significance of calculating efficiency of flat plate solar collector

• The main method for calculating the efficiency of solar collectors

• The pros and cons of various methods

The significance of calculating efficiency of flat plate solar collector

The most important indicator for evaluating the performance of a flat plate solar collector is the thermal efficiency of the flat plate solar collector itself. Accurate measurement of the efficiency of flat plate solar collector is an effective way to effectively use solar energy to achieve energy conservation in buildings.

The main method for calculating the efficiency of solar collectors

The light-transmissive insulation material is made of tempered glass and PC sunlight board, and the heat exchange method uses a serpentine single-layer passage and a serpentine double-layer passage. 4 collector plates are named as “transparent insulation material-heat transfer fluid passage”: type I (tempered glass - serpentine single-layer passage), type II (tempered glass - serpentine double-layer passage), type III ( PC Sunshine Board - Serpentine Single Layer Pathway, Type IV (PC Sunshine Board - Serpentine Double Layer Pathway). The heat absorbing core of each type of heat collecting plate adopts aluminum plate of 1000mm×2000mm×1mm, and the surface is sprayed with primer and then sprayed with black lacquer; the serpentine passage adopts 1 mm aluminum strip, and the surface is sprayed with primer and then sprayed with black lacquer; The bottom insulation is made of 50 mm benzene board; the frame is made of 30 mm wooden frame with black lacquer finish.

Using contrast method, PC solar panel and tempered glass, single layer and double layer channel as contrast factors, summed up four groups of contrast experiments, that is, type I is compared with type II, type III, type IV, then type II and III. Comparison of type and type IV, then comparing type III with type IV, and finally selecting the best type. To ensure the comparability, only one factor is different for each type of contrast, or the light-transmitting insulation material is different or the heat carrier fluid path is different, because I There are two different conditions for type IV, type II and type III, but there is no comparison, so there are only 4 comparison methods left.

The two heat collecting plates are placed side by side to ensure that the ambient temperature, the solar radiation angle and the surface wind speed of the two heat collecting plates are the same at the time of testing. And share a forced draft fan for forced ventilation. Since the cross-sectional area of the air flow passages in the heat collecting plate is the same, the air flow rates in the two heat collecting plates are the same. The temperature of the air outlet of the collector plate and the ambient temperature were recorded by a temperature recorder, and the wind speed of the air inlet was tested by an anemometer. According to the formulas (1) and (2), the mass flow rate and heat collection of the heat collecting plate can be calculated, and the efficiency of the heat collecting plate can be calculated according to the heat collecting efficiency formula (3) of the collecting plate.

m = cFρ(1)

Q = mCp(tp-ta) (2)

η = Q Qs (3)

Where: m is the mass flow rate of the collector plate; Q is the heat supply of the collector plate; v is the average flow velocity of the collector plate; F is the effective cross-sectional area of the collector plate; ρis the air density; Cp is the constant pressure of the air Specific heat; tp is the outlet air temperature of the collector plate; ta is the inlet air temperature of the collector plate; Qs is the amount of heat received by the collector plate. It can be known from equations (1), (2), and (3) that the same solar radiation is received, and the heat output from the collector plate is only related to the temperature of the air outlet. The higher the outlet temperature, the more heat is output, and the heat collecting efficiency is higher. Therefore, comparing the temperature of the two sets of hot plate outlets, the heat collecting effect of different structural collector plates can be determined.

The pros and cons of various methods

Advantage

In this way, the effects of different factors can be reduced. Under the same environmental factors, the flat plate solar collector efficiency measurement has a variety of comparisons, the measured data is more realistic.

Disadvantages

Weather instability has a large impact on the measurement of data. When the measured time is in winter, the heat of the sun is very low and it is not possible to clearly measure the correct flat plate solar collector efficiency. Although the summer sun is very good, it is inevitable to encounter windy, rainy, cloudy weather, which has a great impact on the final flat plate solar collector efficiency.

Through the experiments of the methods in the article, the measurement of the efficiency of the flat plate solar collector can be satisfied. The person in need can select the best performance to meet the needs through the resulting efficiency data.

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