Feasibility analysis of the overall system plan

Feasibility analysis of the overall system plan

After we get the design drawings of the building that needs to install the solar water heating project, we must first determine the geographic coordinates and orientation of the building, and calculate according to the solar altitude angle (α) during the main heating period of the solar water heater And set the best installation angle (β) of the collector. We know that the sun moves back and forth between the Tropic of Cancer (±23°27′) throughout the year, and the sun reaches the northernmost Tropic of Cancer on the summer solstice (June 21-22); the winter solstice (December 21-23) Day of the day) The sun returns to the southernmost Tropic of Capricorn; at the spring and autumn equinoxes, it is above the equator. In the area north of the tropic, the sun is in the sky above the south where the hour angle (ω=0) is zero every day at 12 noon local time. Therefore, the azimuth angle (γ) of the collector in the area north of the Tropic of Cancer in the northern hemisphere can meet the requirements only by placing it facing due south. However, in low latitudes within the range of the regression zone (±23°27′), the sun is basically in the south in winter and stays in the north in summer; the installation angle (β) and azimuth angle (γ) of the collector must be considered The real azimuth angle of the sun during the main use period of the water heater can reasonably determine the best system layout. As for the collector installation angle (β), if it is required that the local noon sunlight can irradiate the collector vertically, that is, when the azimuth angle of the collector γ=0; the solar hour angle ω=0; according to the discussion of the solar illumination angle , The formula for the angle of incidence of sunlight (θ) can be derived:


When: β = φ collector installation angle (β) is equal to the geographic latitude angle (φ), the above formula can be further simplified as:


Where: θ is the incident angle of sunlight to the collector; φ is the geographic latitude angle; α is the height angle of sunlight; δ is the angle between the sun’s rays and the earth’s equatorial plane, also known as the solar declination angle; β is the set Heater installation angle; ω is the solar hour angle.

For another extreme case, when the installation angle β=90°, that is, the collector needs to be wall-mounted vertically on the balcony guardrail, or when the window sill on the facade of the building is up and down or left and right, we can use the following formula to calculate the sunlight exposure Incident angle on the collector (θ):


After obtaining the sunlight incidence angle (θ), we should adjust the installation angle (β) of the collector appropriately from the scheme design to make it “close” as far as possible and satisfy: the sunlight incidence angle (θ) and the set angle Heater installation angle (β) complementary geometric conditions; namely: ∠θ+∠β≥90°

Feasibility analysis of the overall system plan
Figure 1 The geometric relationship between the incident angle on the inclined plane and the installation angle of the latitude angle

The flat-plate natural circulation system integrated solar collector-water heater developed by Kunming Nankai Energy Research Institute is a set of water heaters that realize the ultra-light, ultra-thin, natural circulation system integration of collection and storage. The heat preservation and hot water storage tanks are no longer restricted by the connecting pipes in the system circulation. Therefore, the installation angle facing the sun can be adjusted arbitrarily between 10° and 50°. When adjusting the installation angle, you only need to select at 12 noon local time and adjust the normal of the collector to when the orthographic sunlight projection is zero (ie: solar incidence angle θ=0: azimuth angle γ=0: solar hour angle ω=0) Simply lock and it can be done. However, for ordinary collectors and fixed-installed collector arrays for large systems, the situation is more complicated. It is a very important task to determine the installation angle of the collector as accurately as possible. Because it directly affects the heat collection efficiency of the entire system. Generally speaking, the emphasis is on water heaters that are used from the vernal equinox to the autumnal equinox, that is, the summer half of the year, because the average solar declination during this period is about 11°43′: δ=φ -β given in Figure 2 Take Kunming as an example, the geographic latitude angle of Kunming φ=25°01′; the average declination angle of the sun in the summer half year δ=11°43′; therefore:

The installation angle of the collector: β=25°01’-11°43’≈14°, which is closer to the conditions of use.

On the contrary, the system installation angle (β) used in the winter half year should be the local latitude angle minus the average declination angle of the winter half year (-11°43’);

The installation angle of the collector: β=25°01’-(-11°43’)=36° to meet the minimum requirements.

The situation is even more complicated for a system that is used in a balanced manner throughout the year. It is closely related to the annual distribution of rain, snow, haze, and freezing in the climate change of each installation site. It needs to be carefully analyzed and evaluated in all directions. Determine the specific installation method. Take Kunming as an example. In a normal year, Kunming enters the rainy season around May 18 each year until the rainy season ends in early and mid-November; the number of sunshine hours in the winter half of the year is relatively more. However, the strongest period of sunshine each year occurs during March to May of that year.

After actual measurement, analysis and comparison, relevant experts believe that it is safer to set the optimal installation angle at 27° for the solar hot water system in Kunming that is used evenly throughout the year.

There is a theory in the relevant special research report that “as long as winter can get the best results, other seasons will not be a problem.” To be sure, because the ambient temperature in summer is high, and the average temperature of cold water is also high, the optimal heat collection period of the solar collector should be selectively arranged in the winter with the worst sunshine. However, it should also be noted that in the northern hemisphere north of the Tropic of Cancer, if the collectors use the largest installation angle in winter, under the condition of limited roof installation space, the excessive installation angle increases the heat collection of the front and rear two rows. The distance between the collectors needs to be reserved for shading, which will inevitably reduce the total installation area of ​​the collector. In actual life, the annual peak water consumption of hot water generally occurs in summer and autumn. So we must discuss the relevant gains and losses dialectically. For the hot water system that is planned to be used throughout the year, the best installation angles are in different latitudes and should be processed according to different correction values. It must not be simplistically generalized.

It is necessary to pay special attention to the installation angle of the collectors during the winter solstice to calibrate the minimum installation row spacing (D) between collectors, so as to avoid the shadow of the front row and affect the effective lighting and heat collection area of ​​the rear collectors.


In the formula: H is the rear height of the collector;
Q is the solar altitude angle at noon on the winter solstice where the collector is installed.

In order to facilitate the designer to simplify the system design and calculation, we give the reference value of the D/H ratio for some latitudes during the period from 9 am to 3 pm during the winter solstice:

Geographic latitudeD/H ratio
30° 1.85
35° 2.31
40° 3.00
45° 4.19
Table 1 D/H reference values of collector installation angles in different geographic latitudes

On the roof plan of the building, the designer can start the layout of the solar hot water system collector array according to the determined main sunlight collection period (northern hemisphere positive south) orientation and the minimum separation distance of the collectors. And design the piping system diagram. In the meantime, it is necessary to simultaneously mark the surrounding parapet walls, elevator-like raised buildings, cold water storage tanks, building vents, cold and hot water pipe wells, and the avoidance of the load-bearing support tripods of the system’s heat preservation and hot water storage tanks. The location and the shadow occlusion range of related objects. Based on the principle of compactness and economy, the collector arrays are arranged neatly and orderly. Through the operations on the map, the area of ​​the collector and the production of hot water in the system can be preliminarily estimated with empirical data. Then compare it item by item with the hot water demand data provided by Party A; for the unsatisfied part, it is necessary to make further program adjustments and optimization design again. This is repeated several times to conduct an in-depth feasibility analysis of the design plan; finally, with sufficient calculation and actual measurement data, to clarify the scientificity, feasibility, innovation, necessity and superiority of the system design plan. At the same time, it is necessary to carefully evaluate the conclusive opinions obtained from qualitative and quantitative data analysis of objective economy and reliability after comparing with other parallel schemes. After the plan is basically finalized, the project budget data such as the system parts and components list, the material consumption list, the raw and auxiliary material purchase model and the component assembly quantity list should be sorted out, and the project budget estimate and the date and stage steps of the implementation of the contract should be reported. , And a pragmatic after-sales service commitment. Finally, the above concluding opinions are used to form a complete project feasibility analysis report or project proposal. Provided to Party A or the owner, through negotiation or an explanatory defense of the plan, and on the basis of the consensus of all parties, can the system engineering implementation contract be formally signed.