WO2010075031A2

WO2010075031A2 - Pressurized solar water heater

Info

Publication number: WO2010075031A2
Application number: PCT/US2009/067876
Authority: WO
Inventors: Kaiping Ao
Original assignee: A.O. Smith Corporation
Priority date: 2008-12-16
Filing date: 2009-12-14
Publication date: 2010-07-01
Also published as: CN101435632A; CN101435632B; WO2010075031A3

Abstract

A pressurized solar water heater. The water heater includes a water storage tank and a solar heat collection device. The solar heat collection device includes a lateral heat collector and longitudinal header. One end of the heat collector is connected with the header, forming a first heat exchange circulating loop; the header is installed at an angle to vertical and has a U-shaped heat exchange tube with two branch lines inside. The U-shaped heat exchange tube is also at an angle to vertical along with the header, and the two branch lines are at a high position and a low position respectively. The two branch lines extend upward and are connected with corresponding circulation connections of the water storage tank, forming a second heat exchange circulating loop.

Description

PRESSURIZED SOLAR WATER HEATER

RELATED APPLICATION

[0001] The present patent application claims the benefit of prior filed co-pending Chinese Patent Application No. 200810243590.5, filed on December 16, 2008; the entire content of which is hereby incorporated by reference.

FIELD OF INVENTION

[0002] This invention relates to a type of solar water heater, in particular to a pressurized solar water heater, which belongs to the field of solar energy application technology.

BACKGROUND

[0003] As determined by the applicant, there are main two kinds of existing solar water heaters, non-pressurized solar water heaters and pressurized solar water heaters. The storage tank of a non-pressurized solar water heater is directly connected with a solar heat collector, so users use the hot water heated directly by solar energy with no intermediate heat exchange link. Because the storage tank is non-pressurized, insufficient water impact force can be a shortcoming in service. In addition, because antifreeze can't be added to the water, an outside water pipe, connected with the solar heat collector, may freeze in cold weather.

[0004] The storage tank of a pressurized solar water heater is connected to a cyclical heat-absorption coupling of a solar heat collector by a heat exchange device. Because the storage tank is not directly connected to the solar heat collector, it may have internal pressure, enabling a powerful water output. Additionally, antifreeze can be added to the cyclical heat- transfer medium in the solar heater to avoid freezing.

[0005] Chinese Patent Application No. 01216199.3 discloses a kind of vacuum solar heat collector, which includes a plurality of all-glass vacuum solar heat collectors, a manifold, a bracket and a reflector. The manifold is connected to the all-glass vacuum solar heat collector. A heat exchange pipe is positioned inside the liner of the manifold, and the two ends of the heat exchange pipe protrude through side of the liner, and are connected with the storage tank through the connecting pipe. An obvious shortcoming of such structure is that the heat exchange pipe protrudes through the side of the manifold liner, resulting in a heat exchange area that is small and provides low heat efficiency. What's more, the structure is loose and the shape is complicated, making manufacture and installation very difficult.

[0006] In addition, Chinese Patent Application No. 01216418.6 discloses a pressurized solar heat collector having a vacuum solar heat collecting tube. The vacuum solar heat collecting tube includes an all-glass vacuum heat collecting tube, a reflector, a manifold, a bracket, a water inlet, and a water outlet. The water inlet and the water outlet are set in the liner of the manifold. A plurality of U-shaped pressurized heat exchange tubes are installed inside the storage tank of the manifold, and all the places where the U-shaped pressurized heat exchange tubes pass through the manifold are sealed. By means of the U-shaped tubes, this product overcomes the shortcomings of aforesaid patent application - the small heat exchange area, the loose structure and the complicated shape. However, another problem appears: because the left and right pipes of the U-shaped pressurized heat exchange tube are symmetrically arranged and because the inlet and outlet are at the same level, it is not possible to form a thermosyphon using a temperature differential at the water inlet and outlet. Therefore, it is very difficult to start natural circulation of the water. Accordingly, the heat efficiency is quite low.

SUMMARY

[0007] The invention produces a kind of pressurized solar water heater which can avoid aforesaid shortcomings and problems, and which has larger heat exchange area, and higher heat exchange efficiency. At the same time, a compact structure and a regular shape, make it easy to manufacture and install.

[0008] A pressurized solar water heater includes a water storage tank and a solar heat collection device. The solar heat collection device has a lateral heat collector and a longitudinal header. One end of the heat collector is connected with the header, forming a first heat exchange circulating loop. The header is installed at an angle to vertical, and includes a U-shaped heat exchange tube having two branch lines inside. The U-shaped heat exchange tube is, together with the header, also at an angle to vertical, resulting in the two branch lines having a high position and a low position respectively. The two branch lines extend upward and are connected with circulation connections of the water storage tank, forming a second heat exchange circulating loop. [0009] Because the U-shaped heat exchange tube of this invention is installed at an angle to vertical, and the branch lines are at high and low positions, a temperature differential is produced, forming a second heat exchange circulating loop. In addition to the excellent heat exchange performance, this invention also provides a compact structure and regular shape, making it easy to manufacture and install.

[0010] In theory, the angle between the U-shaped heat exchange tube and vertical may be 1 -90° where the U-shaped heat exchange tube meets the header. However, experiments indicate that the angle between the U-shaped heat exchange tube and vertical of 5 -35° is preferable. Further the invention can include a casing added in the heat collectors to reduce the volume inside the vacuum heat collector, further improving heat exchange efficiency and shortening the time needed to start the first heat exchange circulating loop.

[0011] In brief, the invention solves a technical problem by scientific and rational pipeline arrangement, resulting in an economic, practical, and efficient heat exchange means for a pressurized solar water heater with natural circulation. Experiment proves that the heat exchange efficiency is higher, the heat emission is lower, and the daily heat gain per unit area is 20%-30% higher than common pressurized solar water heaters.

[0012] In one embodiment, the invention provides a pressurized solar water heater, having a water storage tank and a solar heat collection device. The storage tank includes a first circulation connection and a second circulation connection. The solar heat collection device includes a lateral heat collector and a header. The header is positioned at an angle to vertical, and includes a U-shaped heat exchange tube having a first branch line and a second branch line. The first branch line is positioned above the second branch line. The first and second branch lines extend upward and connect to the first and second circulation connections. A first end of the lateral heat collector is connected with the header and forms a first heat exchange circulating loop, and the first and second branch lines form a second heat exchange circulating loop.

[0013] In another embodiment, the invention provides a water heater having a tank and a solar heat exchanger. The tank includes a cold water inlet, a hot water outlet, a circulation loop outlet, and a circulation loop inlet. The cold water inlet supplies water to the tank under pressure. The solar heat exchanger is positioned at an angle to vertical, and includes a header, and a U-shaped tube positioned in the header. The U-shaped tube includes a first branch line and a second branch line. The first branch line is positioned above the second branch line and is connected to the first circulation loop inlet. The second branch line is connected to the first circulation loop outlet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Fig. 1 is a schematic diagram of an embodiment of the invention.

[0015] Fig. 2 is the side view of the embodiment shown in Fig. 1.

[0016] Fig. 3 is a plan view of the embodiment shown in Figure 1.

[0017] Fig. 4 is a cut-away view of a portion of a header and branch lines to show how the thermosyphon starts a second heat exchange circulating loop.

DETAILED DESCRIPTION

[0018] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0019] Figs. 1-3 show a construction of a pressurized solar water heater 100. The water heater 100 includes a water storage tank 105 and a solar heat collecting device 110. A shell 115 of the tank 105 includes a transverse cylinder container 120 having a thermal insulator 125. A hot water outlet 130 is connected at the top of the container 120 and a cold water inlet 135 is connected at the bottom of the container 120. Tap water is provided under pressure to the cold water inlet 135. The water heater 100 also includes a circulation inlet sleeve 140 (or hot water inlet) and a circulation outlet sleeve 145 (or cold water outlet) which form a solar circulating loop at the bottom of the container 120.

[0020] The solar heat collecting device 110 is a wall-hung solar heat collector suitable to be installed outside a building, and includes a set of lower transverse (horizontal or lateral) casing vacuum heat collecting tubes 150, an upper (at the top) vacuum heat collecting tube 155, and a longitudinal (semi-vertical) header. The casing vacuum heat collecting tube 150 includes a vacuum heat collecting tube and a casing. The casing reduces the volume of the vacuum heat collecting tube and enhances heat exchange efficiency, shortening the time needed to start a first heat exchange circulating loop. Approximately half of the upper vacuum heat collecting tube is filled with a heat exchange fluid, while the other half is reserved for expansion. The header is composed of a header shell 160 and an inner pipe 165 inside the header. First ends of the casing vacuum heat collecting tubes 150 and the vacuum heat collecting tube 155 are plugged into and supported by a vertical end bracket 170. Second ends of the casing vacuum heat collecting tubes 150 and the vacuum heat collecting tube 155 are plugged into the header shell 160, and connected with the inner pipe 165 of the header, forming the first heat exchange circulating loop. The header is installed at an angle α to vertical, and includes a U-shaped stainless steel corrugated heat exchange tube 175 (e.g., a metal corrugated heat exchange tube, a metal serpentine heat exchange tube, a metal straight heat exchange tube or a metal fin type heat exchange tube) having a first branch line and a second branch line inside. The U-shaped stainless steel corrugated heat exchange tube 175 is, together with the header, also at the angle α to vertical, resulting in the first branch line being positioned above the second branch line. The two branch lines extend upward, and pass through circulation loops 180 and 185. The branch lines are connected with corresponding circulation connections of the water storage tank-circulation inlet sleeve 140 and circulation outlet sleeve 145 respectively, forming a second heat exchange circulating loop.

[0021] Arranging the U-shaped heat exchanger at the same angle α of installation as the header, combined with height difference between the heat circulating tube inside the heat storage tank, enables the system to produce a natural temperature differential. This provides a small primary starting power, allowing the heat exchange circulation loop to achieve a natural convective heat exchange (refer to Figure 4).

[0022] During operation, solar energy is absorbed by the vacuum heat collecting tubes and is accumulated in the inner pipe 165 of the header by a thermosyphon function of a heat exchange fluid inside the tubes (i.e., the first heat exchange circulation loop). When the heat exchange fluid of the heat collecting device expands due to heating, it enters the upper vacuum heat collecting tube 155 where half of the tube is empty and causes the vacuum heat collecting tubes to carry heat into the inner pipe 165 of the header by thermosyphon circulation. Heat is then transferred to the pressurized water circulating inside the tube by the stainless steel corrugated heat exchange tube 175 inside the inner pipe 165 of the header through surface heat exchange. The pressurized circulating water in the U-shaped stainless steel corrugated heat exchange tube 175 produces thermosyphon convection due to a temperature differential, and carries heat to the upper portion of the water storage tank. Experiments prove that the hot water gain per unit area of the heat collector of this construction is 20%-30% higher than the existing solar water heaters. Table 1 below shows test data comparing a water heater incorporating the invention and an existing wall-hung solar water heater.

Table 1

[0023] A steam refill port 180, open to air, on the top of the inner pipe of the header 165 prevents pressure build up, due to thermal expansion, of the heat exchange fluid in the vacuum heat collecting tube, and makes refilling of the liquid convenient.

[0024] Arranging the U-shaped heat exchanger inside the heat collector header simplifies the structure while not reducing the water storage volume of the water storage tank. The U- shaped structure puts all the metal heat exchangers inside the header resulting in no unnecessary circulating lines outside of the header. This effectively increases the heat exchange area, and also reduces heat emission of the system. In addition, the structure is aesthetically pleasing, and freezing, and the resulting cracking, of the heat exchanger is prevented.

[0025] Because the heat exchange fluid, in the heat collecting device, expands when heated, the common solution is to add an expansion tank in the heat collecting device. However, the top vacuum heat collecting tube, in addition to performing heat collection, allows for expansion of the heat exchange fluid. Further, about a 100mm long section of the top vacuum heat collecting tube has a film coating shading technology allowing the liquid level of the heat exchange fluid inside the header and vacuum heat collecting tube to be clearly observed during fluid refilling. During installation, only half of the top vacuum heat collecting tube is filled with fluid and the other half is reserved for expansion, reducing cost, and effectively avoiding energy loss due to fluid expansion. [0026] Thus, the invention provides, among other things, a pressurized solar water heater. Various features and advantages of the invention are set forth in the following claims.

Claims

CLAIMSWhat is claimed is:

1. A pressurized solar water heater, comprising: a water storage tank having a first circulation connection and a second circulation connection; and a solar heat collection device having a lateral heat collector, a header, positioned at an angle to vertical, including a U-shaped heat exchange tube having a first branch line and a second branch line, the first branch line positioned above the second branch line, the first branch line extends upward and connects to the first circulation connection and the second branch line extends upward and connects to the second circulation connection, a first end of the lateral heat collector connects with the header forming a first heat exchange circulating loop; wherein the first and second branch lines form a second heat exchange circulating loop.

2. The pressurized solar water heater according to claim 1 , wherein the lateral heat collector includes a casing.

3. The pressurized solar water heater according to claim 2, wherein the lateral heat collector includes a plurality of lower lateral heat collectors including a vacuum heat collecting tube and the casing, and an upper vacuum heat collecting tube, wherein half of the upper vacuum heat collecting tube is filled with a heat exchange fluid.

4. The pressurized solar water heater according to claim 3, wherein the header includes a header shell having an inner pipe and a vertical end bracket, a first end of each casing vacuum heat collecting tube and a first end of the upper vacuum heat collecting tube connected to and supported by the vertical end bracket, and a second end of each casing vacuum heat collecting tube and a second end of the upper vacuum heat collecting tube connected to the inner pipe, forming the first heat exchange circulating loop.

5. The pressurized solar water heater according to claim 4, wherein the inner pipe includes an open to the air steam refill port positioned near a top of the inner pipe.

6. The pressurized solar water heater according to claim 5, wherein an angle between the stated U-shaped heat exchange tube and vertical is about 5-35°.

7. The pressurized solar water heater according to Claim 6, wherein the U- shaped heat exchange tube includes a metal corrugated heat exchange tube.

8. A water heater, comprising: a tank including a cold water inlet, the cold water inlet supplying water to the tank under pressure, a hot water outlet, a circulation loop outlet, and a circulation loop inlet; and a solar heat exchanger positioned at an angle to vertical, the solar heat exchanger including a header, a U-shaped tube positioned in the header and including a first branch line and a second branch line, the first branch line positioned above the second branch line and connected to the circulation loop inlet, and the second branch line connected to the circulation loop outlet.

9. The water heater of claim 8, further comprising an upper lateral heat collector connected to the header.

10. The water heater of claim 9, further comprising a plurality of lower lateral heat collectors connected to the header and positioned below the upper lateral heat collector.

11. The water heater of claim 10, wherein the lateral heat collectors include a heat collecting tube and a casing.

12. The water heater of claim 9, wherein a heat exchange fluid fills less than 100% of the upper lateral heat collector.

13. The water heater of claim 9, wherein the heat exchange fluid fills about 50% of the upper lateral heat collector.

14. The water heater of claim 8, further comprising a heat exchange fluid refill port positioned near the top of the header.

15. The water heater of claim 8, wherein the solar heat exchanger is positioned at an angle of 5-35° to vertical.

16. The water heater of claim 8, wherein the first branch line and the second branch line are positioned at an angle of 5-35° to vertical.

17. The water heater of claim 10, further comprising a inner pipe positioned in the header, the heat collecting tubes connected to the inner pipe, the inner pipe and heat collecting tubes forming a second circulation loop.

18. The water heater of claim 8, wherein the cold water inlet is positioned in a lower portion of the tank, the hot water outlet is positioned in an upper portion of the tank, the circulation loop outlet is positioned lower in the tank than the cold water inlet, and the circulation loop inlet is positioned in the tank at a level between the cold water inlet and the hot water outlet.