WO2008027041A1

WO2008027041A1 - Multisection water storage tank with thermal stratification for thermal energy utilization systems

Info

Publication number: WO2008027041A1
Application number: PCT/US2006/033902
Authority: WO
Inventors: Yuanguang Li; Yu J. Chen; Yuhui Kuang
Original assignee: United Technologies Corporation
Priority date: 2006-08-30
Filing date: 2006-08-30
Publication date: 2008-03-06

Abstract

A hot water storage tank of a solar energy utilization system has its interior horizontally partitioned into a series of tank sections by thermally insulated vertical baffles. The lower end of each tank section is connected to the upper end of the next tank section in the series. Water inside the tank is thermally stratified both horizontally from one section to the next and also vertically within each section of the tank. As a result, energy loses within in tank are significantly reduced.

Description

MULTISECTION WATER STORAGE TANK WITH THERMAL STRATIFICATION FOR THERMAL ENERGY UTILIZATION SYSTEMS

BACKGROUND OF THE INVENTION

The present invention relates to- thermal energy utilization systems. In particular, the present invention relates to a hot water storage tank for storing thermal energy for subsequent use.

Systems have been developed to utilize thermal energy produced by solar energy systems or industrial waste heat recovery systems to heat and cool buildings, and to provide hot water. These systems use a liquid, such as water, for absorbing, transporting and storing thermal energy. The water is stored in a hot water storage tank, and is circulated from the tank to a heating device (such as a solar collector or liquid/air heat exchanger of an industrial waste heat recovery system), where it is heated, and then back to the tank. When thermal energy is needed for heating or cooling, hot water is drawn from the tank and circulated through a load, such as a heat exchanger of a room heating system, a water heater system, or an absorption chiller. The water, after passing through the load and having transferred thermal energy, is then returned to the bottom of the hot water storage tank.

' Thermal stratification within the hot water storage tank is an important factor in efficient operation. The hottest water is delivered to the top end of the tank from the heating device, and water delivered to the load is also drawn from the top end of the tank so that the highest temperature water is applied to the load. Water received back from the

; load has transferred thermal energy and thus is at a lower temperature. That cooler water is delivered to the bottom end of the hot water storage tank. Water being delivered to the heating device for heating is drawn from the bottom end of the hot water storage tank.

Thermal stratification enables the system to have quick start up

) functionality, and it also allows the stored thermal energy to be maintained at a higher energy grade level. An effective design to achieve thermal stratification is to use a tall hot water storage tank with horizontal baffles to partition the water storage space into several vertically stacked sections. The baffles diminish the water mixing in the vertical direction. This allows the water at the top of the tank to remain at the highest temperature, and for water at the bottom of the tank to remain a lower temperature.

For most commercial buildings, however, the hot water storage tank must be installed in the basement. As a result, there generally is a limit on the allowable height of the water tank. Large water tanks required for commercial buildings generally have a large horizontal cross-sectional area and a limited height. Mixing between hot and cold layers of water tends to be high, and thermal stratification is poor. There is a need for an improved hot water storage tank for use in a solar energy utilization system that is consistent with the space constraints required in commercial buildings, but provides improved thermal stratification. BRIEF SUMMARY OF THE INVENTION

A hot water storage tank for use in a thermal energy utilization system has a tank body with an interior that is partitioned into a series of side-by-side tank sections. A channel connects the lower end of each tank section to an upper end of the next tank section in the series. The tank has a first inlet and a first outlet and an upper end of the first tank section in the series, and has a second inlet and a second outlet at the lower end of a final tank section in the series. Water is circulated from the second outlet, through a heating device* and back to the first inlet. Water is also circulated from the first outlet, through a load, and back to the second inlet.

The tank sections are thermally insulated to allow thermal stratification in a vertical direction in each tank section. The tank is also thermally stratified in a horizontal direction, with a highest water temperature within the first tank section, and a lowest average water temperature within the final tank section. The thermal stratification of water within the tank both horizontally from one section to another and vertically within each section reduces energy loses while allowing a lower height of the tank. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a thermal energy utilization system including a hot water storage tank partitioned to provide horizontal and vertical thermal stratification.

FIG. 2 is a cross-sectional view of the hot water storage tank partitioned to provide a series of tank sections.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of thermal energy utilization system 10, which includes solar hot water storage tank 12, heating device 14, load 16, pumps 1& and 20, and first and second circulation loops 22 and 24. Hot water storage tank 12 is an insulated tank which is internally partitioned to form a series of interconnected tank sections 12A, 12B....12N. Each tank section is relatively tall with respect to its horizontal cross-section, so that thermal stratification of water within each tank section can occur. The lower end of each section is connected to the upper end of the next tank section in the series.

Different sections of water tank 12 can be considered to be separate smaller water tanks. The water temperature of the upper region of first tank section 12A will be the highest water temperature within tank 12. Through thermal stratification, water at the lower end of section 12A will be at a lower temperature than water at the upper end. Similarly, water at the upper end of second section 12B will have a higher temperature than water at the lower end of tank section 12B. The temperature at the lower end of final tank section 12N will have the lowest temperature within tank 12.

Since water flows from the lower end of each section to the upper end of the following section in the series, the average temperature of each tank section will be higher than that of the next section in the series. As a result, water within tank 12 is thermally stratified both horizontally from one section to the next and also vertically within each section.

Tank 12, heating device 14, and pump 18 are connected in first circulation loop 22. Water from the lower end of final tank section 12N is circulated by pump 18 through heating device 14, and back to the upper end of first tank section 12A. Heating device 14 may be a solar collector, a liquid/air heater exchanger, or other device for recovering or generating thermal energy and transferring the thermal energy to the circulating water. Heating device 14 heats the water as it is circulated, so that the cooler water withdrawn from section 12N is replaced by higher temperature water delivered to first section 12A.

Hot water storage tank 12, load 16, and pump 20 are connected in second circulation loop 24. Hot water is withdrawn from the upper end of first tank section 12A and pumped through load 16 where thermal energy is extracted from the water. Water is then returned to the lower end of final tank section 12N. Load 16 may be a heat exchanger used to heat air, water, or other fluids to provide heating, cooling or other functions using the thermal energy extracted from the water circulating in second loop 24.

FIG. 2 shows a cross-sectibn of tank 12, which includes tank body 30 which is horizontally partitioned by pairs of thermally insulated, vertically mounted baffle plates 32, 34 to create a series of separate tank sections 12A, 12B...12N. Each pair of baffle plates 32, 34 defines a water flow channel 36, which interconnects the lower end of a channel to the upper end of the next channel in the series.

Tank 12 includes first and second inlets 38 and 40, and first and second outlets 42 and 44. First inlet 38 and second outlet 44 are connected to the upper end of first tank section 12A. Second inlet 40 and first outlet 42 are connected to the lower end of final tank section 12N.

Water that has been heated by solar collector 14 is introduced into tank 12 through first inlet 38. The region of highest water temperature within tank 12 will be at the upper end of first tank section 12A where both first inlet 38 and second outlet 44 are located. Water is withdrawn from tank 12 through second outlet 44, and circulated to load 16 through second loop 24.

Baffles 32 and 34 provide thermal isolation between adjacent tank sections, and also limit the intermixing of water from one section to the next. Within each tank section, vertical thermal stratification can occur, so that the highest temperature water within each tank section is at the top, and the lowest temperature water is at the bottom of that tank section. Flow of water from each tank section to the next is limited to the passageway provided by water flow channel 36. As a result, water flowing through tank 12 from section 12A to section 12N will travel in a serpentine path from the lower most part of each tank section to the upper most region of the next tank section in the series. As a result, thermal stratification occurs horizontally from section-to-section, with first section 12A having the highest average water temperature, and section 12N having the lowest average water temperature.

The region of lowest temperature water within tank 12 will be located at the lower end of tank section 12N. Second inlet 40 and first outlet 42 are located at the lower end of tank section 12N. Water that is to be heated by heating device 14 is withdrawn through first outlet 42. It is pumped by pump 18 through heating device14 and delivered back to first inlet 38. Water that has been used by load 16 has a reduced temperature because thermal energy has been removed by load 16. The water from load 16 is returned to tank 12 through second inlet 40.

The horizontal partitioning of tank 12 with vertical baffles to create a series of side-by-side tank sections 12A-12N results in thermal stratification of the water within the tank both horizontally from one section to the next, and also vertically within each tank section. As a result, significant thermal stratification can be achieved, and energy loses reduced, without the need for an extremely tall water tank. This provides more energy efficient water storage for those installations (such as in the basement of commercial buildings) where the height of the storage tank is limited.

The number of tank sections 12A-12N will depend on size constraints of tank 12 and the desired thermal gradient from the highest water temperature to the lowest water temperature within the system. Generally, more tank sections will allow a greater thermal gradient to exist within tank 12.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

CLAIMS:

1. A hot water storage tank comprising: a tank body having an interior partitioned into a series of tank sections by thermally insulated baffles; a channel connecting a lower end of each tank section to an upper end of a next tank section in the series; a first inlet at an upper end of a first tank section in the series for receiving water from a heating device; a first outlet at the lower end of a last tank section for delivering water to the heating device; a second inlet at the lower end of a last tank section in the series for receiving water from a load; and a second outlet at the upper end of the first tank section for delivering water to the load.

2. The hot water storage tank of claim 1 , wherein the channel extends between a closely spaced pair of the thermally insulated baffles.

3. The hot water storage tank of claim 2, wherein a first thermally insulated baffle of the closely spaced pair extends downward from a top inner wall of the tank body, and wherein a second thermally insulated baffle of the closely spaced pair extends upward from a bottom inner wall of the tank body.

4. A hot water storage tank comprising: a tank body having an interior horizontally partitioned to form a plurality of thermally insulated, interconnected tank sections so that water within the tank body is thermally stratified vertically within the tank sections and thermally stratified horizontally among the tank sections; a first inlet at a first tank section of the plurality for receiving heated water; and a first outlet at a last tank section of the plurality for delivering water to be heated.

5. The hot water heater of claim 4 and further comprising: a second outlet at the first tank station from which water is withdrawn; and a second inlet at the last tank station through which water is returned.

6. The hot water storage tank of claim 4 and further comprising: a pair of vertically mounted thermally insulating baffles between each pair of adjacent tank sections.

7. The hot water storage tank of claim 6, wherein the pair of vertically mounted thermally insulating baffles comprises: a first baffle extending downward from a top inner wall of the tank body; and a second baffle extending upward from a bottom inner wall of the tank body.

8. The hot water storage tank of claim 7, wherein the first baffle has a bottom end spaced from the bottom inner wall of the tank body, and wherein the second baffle has a top end spaced from the top inner wall of the tank body.

9. The hot water storage tank of claim 8 and further comprising: a channel extending between the first and second baffles for providing a water passage from a bottom portion of one tank section to a top portion of an adjacent tank section.

10. A thermal energy utilization system comprising: a heating device for transferring thermal energy to water; a load for extracting thermal energy from water; and a hot water storage tank connected in a first circulation loop with the heating device and connected in a second circulation loop with the load, the hot water storage tank being horizontally partitioned to form a plurality of interconnected storage tank sections configured to provide thermal stratification vertically within each tank section and horizontally among tank sections.

11. The thermal energy utilization system of claim 10, wherein the first circulation loop is connected to an upper end of a first tank section and to a lower end of a last tank section of the plurality of tank sections.

12. The thermal energy utilization system of claim 11 and further comprising: a first pump connected in the first circulation loop for circulating water from the lower end of the last tank section through the heating device to the upper end of the first tank section.

13. The thermal energy utilization system of claim 12, wherein the second circulation loop is connected to the upper end of the first tank section and to the lower end of the last tank section.

14. The thermal energy utilization system of claim 13 and further comprising: a second pump connected in the second circulation loop for circulating water from the upper end of the first tank section through the load to the lower end of the last tank section.

15. The thermal energy utilization system of claim 14, wherein the hot water storage tank comprises: a pair of vertically mounted thermally insulating baffles between each pair of adjacent tank sections.

16. The thermal energy utilization system of claim 15, wherein the pair of vertically mounted thermally insulating baffles comprises: a first baffle extending downward from a top inner wall of the tank; and a second baffle extending upward from a bottom inner wall of the tank.

17. The thermal energy utilization system of claim 16, wherein the first baffle has a bottom end spaced from the bottom inner wall of the tank, and wherein the second baffle has a top end spaced from the top inner wall of the tank.

18. The thermal energy utilization system of claim 17 and further comprising: a channel extending between the first and second baffles for providing a water passage from a bottom portion of one tank section to a top portion of an adjacent tank section.

19. The thermal energy utilization system of claim 10, wherein the heating device comprises a solar collector.

20. The thermal energy utilization system of claim 10, wherein the heating device comprises a heat exchanger.