CN210463621U

CN210463621U - Solar reflecting plate capable of preventing overheating in summer

Info

Publication number: CN210463621U
Application number: CN201921062930.4U
Authority: CN
Inventors: 杨旭东; 陈肖萌; 郭放
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2019-07-09
Filing date: 2019-07-09
Publication date: 2020-05-05
Anticipated expiration: 2029-07-09

Abstract

The utility model provides a can prevent overheated solar energy reflecting plate in summer, belong to solar energy and utilize technical field, the solar energy reflecting plate is installed between two adjacent vacuum tubes of horizontal vacuum tube solar collector, and the sectional shape of this solar energy reflecting plate is gradually extension D 'E' that a section circular arc DE corresponds on the heat absorption pipe; the included angle between the point D and the vertical plane and the line corresponding to the circle center of the heat absorption pipe is 40-60 degrees, and the included angle between the point E and the vertical plane and the line corresponding to the circle center of the heat absorption pipe is 100-140 degrees; the distance from the point D to the point D 'is 10-30 mm, and the distance from the point E to the point E' is 60-100 mm. The utility model discloses utilize summer solar altitude angle height, the phenomenon that winter solar altitude angle is low, spotlight when realizing winter solar low angle of incidence through reflection design, the optical effect who shelters from during summer solar altitude angle of incidence to reduce the overheated risk in summer when improving solar collector efficiency in winter.

Description

Solar reflecting plate capable of preventing overheating in summer

Technical Field

The utility model belongs to the technical field of solar energy utilizes, in particular to can prevent overheated solar reflecting plate in summer.

Background

Solar energy is used as a clean energy source for a large amount of winter heating and domestic hot water in cold and severe regions. As a solar energy collecting device, compared with the traditional flat plate collector, the vacuum tube collector has better heat insulation performance and is widely used along with the reduction of the production cost.

At present, vacuum tube solar heating mainly faces two difficulties: 1) when solar radiation is weak in winter, the building heat supply requirement is large, and a lower solar energy guarantee rate can be caused in a limited heat collection area or an area with insufficient solar energy resources; 2) when solar radiation is strong in summer, heat is not needed for a building, so that a vacuum tube heat collector is overheated, the service life of the heat collector is shortened, and the vacuum tube can be broken under extreme conditions.

At present, the vacuum tube heat collector is combined with a reflecting plate, and the reflecting plate improves the overall energy efficiency of the vacuum tube heat collector by increasing the solar radiation receiving area and adopting a reflection and light condensation mode. The existing reflecting plate can be divided into a static type and a light following type, and the static reflecting plate can meet corresponding requirements due to the fact that the low-temperature heat collector requires a low water outlet temperature (40-120 ℃); the light-following type reflector is generally used for medium and high temperature heat collectors. According to the shape classification of the static reflecting plate, the common static reflecting plate of the vacuum tube heat collector can be divided into a plane reflecting plate, a parabolic reflecting plate and a composite parabolic reflecting plate; the parabolic and compound parabolic reflectors reflect and focus the incident light rays onto the vacuum tube at different angles by using non-imaging optics.

The existing reflecting plate only considers the increase of the energy efficiency of the vacuum tube heat collector singly, although the heating effect in winter can be improved, the solar reflecting plate can cause more serious summer overheating, and the solar reflecting plate capable of improving the energy efficiency in winter and preventing the summer overheating is urgently needed.

SUMMERY OF THE UTILITY MODEL

The utility model aims at overcoming prior art's weak point, provide one kind and can improve the efficiency in winter and can prevent the overheated solar energy reflecting plate in summer simultaneously. The utility model discloses utilize summer solar altitude angle height, the phenomenon that winter solar altitude angle is low, spotlight when realizing winter solar low incidence angle through reflection design, the optical effect who shelters from during summer solar altitude angle to make this solar reflecting plate can reduce the overheated risk in summer when improving solar collector efficiency in winter.

In order to achieve the above purpose, the utility model adopts the following technical scheme:

the utility model provides a solar energy reflecting plate capable of preventing summer overheating, which is arranged between two adjacent vacuum tubes of a horizontal vacuum tube solar heat collector, wherein each vacuum tube consists of a heat absorbing tube and a glass outer tube, and the sections of the heat absorbing tube and the glass outer tube are both circular; the solar heat collector is characterized in that the cross section of the solar reflecting plate is in the shape of an involute corresponding to a section of circular arc DE on the heat absorbing pipe and is marked as a curve D 'E'; wherein, the included angle between the point D and the vertical plane and the connecting line corresponding to the circle center of the heat absorbing pipe is 40-60 degrees, and the included angle between the point E and the vertical plane and the connecting line corresponding to the circle center of the heat absorbing pipe is 100-140 degrees; the distance from the point D to the corresponding involute end point D 'is 10-30 mm, and the distance from the point E to the corresponding involute end point E' is 60-100 mm.

Furthermore, the radius of the heat absorption pipes is 30-50 mm, and the distance between the heat absorption pipes is 80-120 mm.

Further, the installation angle of the solar heat collector is 10-15 degrees higher than the local latitude.

Further, the solar reflecting plate is a metal plate with the reflectivity higher than 0.8.

The utility model has the characteristics and beneficial effects that the utility model utilizes the principle of curve involute, any point on the reflecting plate, and the incident angle is the solar altitude angle α of 12 points when the sun is true within 0-1 month after the heating season is over₂The reflected light ray of the point is tangent to the outer wall of the heat absorption tube, and according to the edge light ray theorem, the incident angle is less than or equal to α₂The light can be condensed on the heat absorption pipe, the light with higher incidence angle is reflected to the sky, thereby achieving the effect of heating in winter, and when the incidence angle α is not less than the solar altitude α of 12 o' clock when the sun is true at the end of the heating season₁When the heat absorption tube is used, the reflecting plate above the heat absorption tube partially shields the heat absorption tube, so that the heat reduction effect in summer is achieved.

Drawings

Fig. 1 is a schematic view of an overall structure of a solar reflecting plate and a solar collector according to an embodiment of the present invention.

Fig. 2 and 3 are schematic diagrams of the working principle of the present invention.

Fig. 4 (a) - (d) are graphs showing the numerical simulation results of the reflection and shielding effect of the present invention varying with the incident angle of light.

Fig. 5 is a graph of solar altitude versus collector optical efficiency for the numerical simulation results shown in fig. 4.

Detailed Description

The technical scheme of the present invention is further described in detail with reference to the accompanying drawings and embodiments:

the utility model provides a can prevent overheated solar energy reflecting plate in summer mainly is to being used for building heating and domestic hot water etc. to the vacuum tube solar collector's that hot water demand scope is 40-120 ℃ reflecting plate, see figure 1, solar collector orientation is south just, and the vacuum tube thing transversely is certain inclination and arranges and place, and every vacuum tube below has a slice reflecting plate 3, and each reflecting plate 3 all fixes on the support of the solar collector left and right sides (this support is in the figure meaning). The reflection plate is made of a metal plate having a reflectance higher than 0.8 (a polished aluminum plate is used in the present embodiment). Each vacuum tube is respectively composed of a heat absorption tube 1 and a glass outer tube 2, and the sections of the heat absorption tube 1 and the glass outer tube 2 are both circular. The section shape of the reflecting plate 3 is an evolute corresponding to a section of circular arc DE on the heat absorbing pipe 1 and is marked as a curve D 'E'; wherein, the included angle between the connecting line of the point D and the circle center of the corresponding heat absorbing pipe and the vertical plane is 40-60 degrees, and the included angle between the connecting line of the point E and the circle center of the corresponding heat absorbing pipe and the vertical plane is 100-140 degrees; the distance from the point D to the corresponding involute end point D 'is 10-30 mm, and the distance from the point E to the corresponding involute end point E' is 60-100 mm.

The working principle of the solar reflecting plate is shown in fig. 2 and 3, solar radiation received by a single vacuum tube is affected by the upper reflecting plate and the lower reflecting plate 3 together, wherein heat increase in winter is realized by the reflecting plate below the single vacuum tube, heat reduction in summer is realized by the reflecting plate above the single vacuum tube, and the annual operation effect of the solar heat collector is changed along with the change of an included angle α between incident light and a horizontal plane.

The section shape of the solar reflecting plate provided by the embodiment of the utility model is an involute corresponding to a section of circular arc DE on the heat absorbing pipe 1, and is marked as a curve D 'E'; the curve D 'E' is determined according to the following steps:

1) setting the parameter of the solar altitude α at the time of the heating season ending day and the real solar time 12 o' clock₁The solar altitude angle α of 12 o' clock of the real sun of the day in 0-1 month after the heating season₂The solar altitude α at the 12 o' clock of the real sun in summer solstice₃(ii) a The center of any heat absorbing pipe 1 of the solar heat collector is O, the center of the heat absorbing pipe 1 below the heat absorbing pipe is M, and the center distance between the two is L_cThe radius of the outer wall of each heat absorption pipe 1 is r_iThe installation angle of the solar heat collector is β;

wherein the radius r of the heat absorbing pipe 1_iThe thickness of the reflecting plate is 30-50 mm, the distance between the heat absorbing pipes 1 is 80-120 mm, the installation angle β of the solar heat collector is preferably 10-15 degrees higher than the local latitude, and the optical efficiency of the reflecting plate is the maximum in the inclination angle interval.

2) And establishing a rectangular coordinate system by using the point O, and determining the coordinate of the lower endpoint E' of the solar reflecting plate 3 according to the following formula:

passing through the E' point to be taken as a tangent line of the outer wall of the upper heat absorption tube 1 to obtain a tangent pointE point, two points are at a distance L_EE′；

3) Let the equation for curve D 'E' be:

x＝r_i·sin(ω)-ρ(ω)·cos(ω)

y＝-r_i·cos(ω)-ρ(ω)·sin(ω)

in the formula:

omega is a polar angle which rotates anticlockwise by taking an O point as a circle center and a negative semi-axis of a y axis as an initial point, and omega is₀≤ω≤ω_m，ω₀、ω_mAre polar angles of point D, E, respectively, and ω₀＝α₂；ω_mThe determination of (2) is as follows: the passing point E' is taken as the tangent of the heat absorption tube 1, the corresponding tangent point is E, and the included angle between the connecting line of the point E and the circle center O and the negative axis of the y axis is omega_m；

L_DD′Is the length of the straight line segment DD', L_DD′＝ρ(ω₀)＝0.5L_EE′(1+cos(ω_m-ω₀))-0.5r_i·(ω_m-ω₀+sin(ω_m-ω₀))，L_EE′Is the length of straight line segment EE';

the coordinates of the end point D' on the solar reflection plate 3 are:

D′(x)＝r_i·sin(ω₀)-ρ(ω₀)·cos(ω₀)

D′(y)＝-r_i·cos(ω₀)-ρ(ω₀)·sin(ω₀)。

the section shape of the reflecting plate of the utility model is according to the involute principle of the base circle of the heat absorbing pipe, the normal line of any point on the curve bisects the incident angle equally and is α₂The light ray is tangent to the point to the base circle, point E is the upper end point of the heat absorbing tube where the reflected light ray can reach, and the incident angle is α₂The lower tangent point D of the heat absorption tube and the light ray is the lower end point which can be reached by the reflected light ray, and the curve of the reflecting plate D 'E' can be regarded as a smooth curve formed by points corresponding to the tangent line from the point D to the point E on the heat absorption tube.

The working principle of each reflecting plate can be divided into winter heat increasing and summer heat reducing for explanation:

1. the heat increase in winter is realized by a reflecting plate below a single vacuum tube, and the curvature design principle of any point on the reflecting plate is that when the reflecting plate forms an included angle of α with the horizontal plane₂When the light ray is incident to the point, the reflected light ray is tangent to the heat absorbing tube, and according to the edge light ray theorem, when the incident angle of the light ray is α - α₂When the light is incident on the reflecting plate, the light can be condensed on the heat absorbing pipe, and when the incident angle α is more than or equal to α₂At this time, the light is reflected back to the sky.

2. Summer heat reduction is realized by a reflecting plate above a single vacuum tube when the incident light angle α is more than α₁When the vacuum tube is in use, the reflecting plate above the vacuum tube can shield the vacuum tube partially, passes through the end point E' of the upper reflecting plate and has a horizontal included angle of α₁Is tangent to the heat absorption tube and has a horizontal included angle of α₂The incident light passes through the center of the heat absorption tube, the incident angle α is not more than α₁When the incident angle α is more than α₁When the incident angle α is α, the partial absorption area of the heat absorption tube is blocked by the upper reflecting plate₂The effective absorption area of the absorber tube was reduced to 50%.

The rule that the annual operation effect changes with the incident light angle α is as follows:

finally, the following table parameters are given as examples (where r₀The radius of the outer wall of the outer glass tube), it is right to verify the effect of the utility model. The model is put into Trace Pro optical analysis software for numerical simulation, and during simulation, the reflecting plate is set to be an ideal mirror surface (the reflectivity is 1.0), and the heat absorption tube is set to be an ideal absorber (the absorptivity is 1.0).

Letter identification	Unit of	Value taking
			α₁	°	40
α₂	°	55
			α₃	°	73
β	°	50
			L_c	mm	100
r_i	mm	23.5
			r_o	mm	29

The light effect of each incident angle is shown in fig. 4, in the graph (a) to (d), the light incident angle α is 30 °, 55 °, 65 ° and 85 ° respectively, the reflected light generated by the reflecting plate is shown in the graph, as can be seen from the graph, when α ° is less than or equal to 40 °, the light incident on the reflecting plate is condensed on the heat absorbing pipe, when 40 < α ° is less than or equal to 55 °, the reflected light is continuously condensed, part of the area of the heat absorbing pipe is blocked, when α > 55 °, the reflected light is reflected to the sky, and the effective heat absorbing area of the heat absorbing pipe is continuously reduced.

Further, the effective lighting area of the single vacuum tube heat collector is defined as A_etcAnd the effective daylighting area is A after the reflection plate is added_reflectIF (a) is defined as the ratio of change in the lighting area after the reflector is added_reflect-A_etc)/A_etcWhen the length of the vacuum tube is 1800mm, the trend that the effective daylighting area of the vacuum tube changes along with the incident angle α is shown in fig. 5, it can be seen that when the incident angle α is not more than 55 degrees, the effective daylighting area of a single vacuum tube provided with the reflecting plate of the embodiment is larger than the effective daylighting area of a single vacuum tube not provided with the reflecting plate of the embodiment, so that the effect of increasing heat in winter is achieved, and when the incident angle α is more than 55 degrees, the effective daylighting area of a single vacuum tube provided with the reflecting plate of the embodiment is smaller than the effective daylighting area of a single vacuum tube not provided with the reflecting plate of.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. A solar energy reflecting plate capable of preventing overheating in summer is arranged between two adjacent vacuum tubes of a horizontal vacuum tube solar heat collector, each vacuum tube consists of a heat absorption tube and a glass outer tube, and the sections of the heat absorption tube and the glass outer tube are circular; the solar heat collector is characterized in that the cross section of the solar reflecting plate is in the shape of an involute corresponding to a section of circular arc DE on the heat absorbing pipe and is marked as a curve D 'E'; wherein, the included angle between the point D and the vertical plane and the connecting line corresponding to the circle center of the heat absorbing pipe is 40-60 degrees, and the included angle between the point E and the vertical plane and the connecting line corresponding to the circle center of the heat absorbing pipe is 100-140 degrees; the distance from the point D to the corresponding involute end point D 'is 10-30 mm, and the distance from the point E to the corresponding involute end point E' is 60-100 mm.

2. The solar reflecting panel according to claim 1, wherein the radius of the heat absorbing pipes is 30 to 50mm, and the pitch of the heat absorbing pipes is 80 to 120 mm.

3. The solar reflecting panel according to claim 1, wherein the installation angle of the solar collector is 10-15 ° higher than the local latitude.

4. The solar reflector panel of claim 1, wherein the solar reflector panel is a metal panel having a reflectivity greater than 0.8.