Stratification tube

Abstract

A water heating system includes at least one heating unit; a tank including an upper dome, a lower dome, and a sidewall connecting the upper dome to the lower dome, the upper dome, the lower dome, and the sidewall defining a tank volume; and a heating loop fluidly connecting the tank to the at least one heating unit. The tank includes a stratification tube connected thereto.

Description

STRATIFICATION TUBEBACKGROUND

[0001] The present disclosure relates to water heaters, and more particularly to heat pump water heaters, and even more particularly to large commercial heat pump water heating systems.

[0002] In some examples of water heating systems, water is removed from a water heater tank, heated, and re-introduced into the tank. However, re-introducing water into the tank can cause undesirable mixing of already-heated water within the tank. This can leave the tank unable to properly satisfy a demand for heated water.

[0003] Accordingly, a need exists for a way to re-introduce the heated water into the tank that reduces or eliminates this undesirable mixing.SUMMARY

[0004] A water heating system according to the present disclosure provides advantageous solutions to these and other known problems in the art. The water heating system, in one independent aspect, includes: at least one heating unit; a tank including an upper dome, a lower dome, and a sidewall connecting the upper dome to the lower dome, the upper dome, the lower dome, and the sidewall defining a tank volume; and a heating loop fluidly connecting the tank to the at least one heating unit. The tank further includes: a cold water inlet configured to supply unheated water to the tank; a hot water outlet configured to deliver heated water from the tank; a supply port configured to supply water from the tank to the at least one heating unit via the heating loop; and a return port in the sidewall configured to deliver heated water back into the tank via the heating loop. The return port is connected to a stratification tube extending into the tank volume. The stratification tube includes a first end connected to the return port, a body extending along a longitudinal axis, and a second end opposite of the first end. The second end is capped, and the body includes a plurality of apertures configured to flow the heated water from the return port, through the body, and into the tank volume. The second end of the stratification tube extends across the tank volume such that the second end is closer to the sidewall than to the return port.

[0005] In another aspect, which may be combined with any preceding aspect, the body of the stratification tube includes a first portion, a second portion, and a third portion. The first portionextends along the longitudinal axis from the first end and the second portion extends along the longitudinal axis from the first portion such that the first portion is connected to the second portion. The third portion extends along the longitudinal axis from the second portion such that the third portion is connected to the second portion. The first portion includes the plurality of apertures. The second portion is substantially absent any apertures. The third portion includes at least one aperture.

[0006] In another aspect, which may be combined with any preceding aspect, the plurality of apertures are arranged in one or more rows extending along the longitudinal axis.

[0007] In another aspect, which may be combined with any preceding aspect, the upper dome is located above the lower dome with respect to gravity, and the plurality of apertures in the first portion and the at least one aperture in the third portion face the lower dome.

[0008] In another aspect, which may be combined with any preceding aspect, substantially none of the plurality of apertures face the upper dome.

[0009] In another aspect, which may be combined with any preceding aspect, the second portion includes three or less apertures arranged adjacent to the second end of the stratification tube.

[0010] In another aspect, which may be combined with any preceding aspect, the third portion includes three or less apertures, and the three or less apertures face the lower dome.

[0011] In another aspect, which may be combined with any preceding aspect, the stratification tube extends along the longitudinal axis, from the return port, across at least 90% of a diameter of the tank volume.

[0012] In another aspect, which may be combined with any preceding aspect, the first portion extends along the longitudinal axis, from the return port, across at least 50% of the diameter of the tank volume.

[0013] In another aspect, which may be combined with any preceding aspect, the stratification tube is at least one selected from the group consisting of polypropylene, polyethylene, and polyvinyl chloride.

[0014] In another independent aspect, a system configured to heat water includes: a tank having a tank volume, and a stratification tube attached to a sidewall of the tank. The stratification tube is configured to return water heated by a heating unit back into the tank volume. The stratification tube includes a first end configured to receive the heated water, a body extending along a longitudinal axis, and a second end opposite of the first end. The second end is capped, and the body includes a plurality of apertures configured to flow the heated water from the first end, through the body, and into the tank volume.

[0015] In another aspect, which may be combined with any preceding aspect, the body of the stratification tube includes a first portion, a second portion, and a third portion. The first portion extends along the longitudinal axis from the first end and the second portion extends along the longitudinal axis from the first portion such that the first portion is connected to the second portion, The third portion extends along the longitudinal axis from the second portion such that the third portion is connected to the second portion. The first portion includes the plurality of apertures, the second portion is substantially absent any apertures, and the third portion includes at least one aperture.

[0016] In another aspect, which may be combined with any preceding aspect, the plurality of apertures are arranged in one or more rows extending along the longitudinal axis.

[0017] In another aspect, which may be combined with any preceding aspect, as installed into a water tank, the body of the stratification tube includes an upper side with respect to gravity and a lower side with respect to gravity, and the lower side of the first portion includes the plurality of apertures.

[0018] In another aspect, which may be combined with any preceding aspect, the upper side of the first portion and the upper side of the second portion are substantially devoid of apertures.

[0019] In another aspect, which may be combined with any preceding aspect, the third portion includes three or less apertures.

[0020] In another aspect, which may be combined with any preceding aspect, the tank is generally cylindrical and includes a longitudinal axis extending along a centerline of the generallycylindrical tank. The longitudinal axis of the stratification tube is generally perpendicular to the longitudinal axis of the tank.

[0021] In another aspect, which may be combined with any preceding aspect, the body is cylindrical and, along the longitudinal axis, has length to diameter ratio between 16: 1 and 24: 1.

[0022] In another aspect, which may be combined with any preceding aspect, a ratio of a diameter of the stratification tube to a diameter of an aperture of the plurality of apertures is between 6: 1 and 10: 1.

[0023] In another aspect, which may be combined with any preceding aspect, the first portion, along the longitudinal axis, is between 50% and 60% of an entire length of the stratification tube along the longitudinal axis.

[0024] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Fig. 1 illustrates a water heating system according to an embodiment of the invention.

[0026] Fig. 2 illustrates a stratification tube for use with the water heating system of Fig. 1.

[0027] Fig. 3 is a section view of a tank of the water heating system shown in Fig. 1.

[0028] Fig. 4 is a section view of the stratification tube shown in Fig. 2.

[0029] Fig. 5 illustrates the tank of the water heating system of Fig. 1.

[0030] Fig. 6 illustrates a chart showing a change in water temperature versus time in the water heating system of Fig. 1 when no stratification tube is installed in the tank.

[0031] Fig. 7 illustrates a chart showing a change in water temperature versus time in the water heating system of Fig. 1 when a stratification tube is installed in the tank.DETAILED DESCRIPTION

[0032] 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.

[0033] Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, it includes at least the degree of error associated with the measurement of the particular quantity). The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4”. The term “about” may refer to plus or minus 10% of the indicated number. For example, “about 10%” may indicate a range of 9% to 11%, and “about 1%” may mean from 0.9-1.1. Other meanings of “about” may be apparent from the context, such as rounding off, so, for example “about 1” may also mean from 0.5 to 1.4.

[0034] Fig. 1 illustrates a water heating system 10, which in the illustrated embodiment is a heat pump water heating system. The water heating system 10 includes heating units 15 and a tank 20. The heating units 15 are connected to the tank 20 by a heating loop 25, which fluidly connects a tank volume 30 of the tank 20 to each heating unit 15. In the embodiment shown in Fig. 1, there are three heating units 15, although other numbers of heating units 15 are contemplated, such as one, two, or five. Further, in the embodiment shown in Fig. 1, the heating units 15 are connected to the tank 20 in parallel, however, in some embodiments the heating units 15 are connected to the tank 20 in series. In operation of the water heating system 10, water 35 is removed from the tank volume 30 by the heating loop 25 via a respective pump 70, heated by the heating units 15, and returned to the tank volume 30. In other embodiments, only a single pump 70 is used and valves can be used to determine flow to the heating units 15.

[0035] Heat pump water heating systems such as the water heating system 10 operate as either a single-pass system or a multi-pass system. In both types of systems, water 35 to be heated is circulated through the heating units 15 via the respective pump 70. The heating units 15 includea condenser 40, and high-pressure, high -temperature vapor refrigerant is simultaneously circulated through the condenser 40. In the condenser 40, heat is transferred from the refrigerant to the water 35, thereby cooling and condensing the refrigerant while simultaneously heating the water 35. The heating units 15 accomplish this by passing the refrigerant in a refrigerant loop 45 from the condenser 40, through a compressor 50, then through an evaporator 55, and then by an expansion valve 60. A fan 65 passes air over the evaporator 55 to help heat refrigerant in the evaporator 55. While the heating units 15 illustrated herein are air-sourced heating units 15 that use a vapor compression system to extract thermal energy from ambient air and direct that thermal energy into the water 35, in other embodiments different heating units 15 are used, such as water-sourced heat pumps, combustion systems, and electric resistance systems, among others.

[0036] In a multi-pass water heating system 10, the water 35 is typically circulated through the condenser 40 at a constant and relatively high flow rate, such that the temperature of the water 35 is incrementally increased with each pass through the condenser 40. In contrast, in a singlepass water heating system 10, the flow rate of the water 35 is regulated such that the temperature of the water 35 exiting the condenser 40 is at a desired setpoint. This heated water 35 is then ready to be delivered for a use at that setpoint, or can be stored within the tank 20 at the desired setpoint for later use. Generally speaking, single pass water heating systems 10 provide a higher overall system efficiency than do multi-pass systems. However, they require a more complicated control system in order to precisely regulate the water flow rate in order to heat the water 35 to the desired setpoint. Since multi-pass systems operate with a fixed water flow rate, the control system can be much simpler. For these reasons, large (e.g., 750 or 1000 or 2500 liter storage volume) commercial heat pump water heating systems 10 often use such a multi-pass approach.

[0037] Problems can arise in multi-pass water heating systems 10 when the water 35 is reintroduced into the tank from the heating loop 25 in a not fully heated state (i.e., at a temperature below the desired setpoint). Preferably, the tank 20 of water 35 is in a thermally stratified state, with water 35 that has been heated to the desired setpoint temperature being maintained near an upper dome 75 of the tank 20 where the water 45 can be drawn off via a hot water outlet 80 to satisfy a demand for heated water 35. The water 35 that has not yet been fully heated remains near a lower dome 85 of the tank 20. Undesirable mixing of the incoming heated water 35 from the heating loop 25 and the water 35 already in the tank volume 30 that has been heated to the desiredsetpoint temperature will destroy the stratification, leaving the tank 20 unable to adequately satisfy a demand for heated water 35 because the water 35 near the upper dome 75 will not be at the desired setpoint temperature.

[0038] With continued reference to Fig. 1, the tank 20 includes a supply port 87 and a return port 90 that are fluidly connected to the heating loop 25. The supply port 87 supplies relatively cooler water 35 to the heating loop 25 and the return port 90 returns heated water 35 from the heating loop 25 to the tank volume 30. Because density of the water 35 decreases as temperature of the water 35 increases, the water 35 within the tank volume 30 will become stratified as the water 35 is heated. For this reason, it is preferable to have the supply port 87 lower in the tank 20 with respect to a direction of gravity 95 than the return port 90. Preferably, both the supply port 87 and the return port 90 are located in a bottom half of the tank 20 with respect to the direction of gravity 95. The tank 20 also includes a cold water inlet 100 located near the lower dome 85, which is opposite from the upper dome 75. Preferably, the cold water inlet 100 is located below the supply port 87 and the return port 90 with respect to the direction of gravity 95. In some alternate embodiments, the cold water inlet 100 can extend through the upper dome 75 and can continue through the tank volume 30 to deliver the cold water to near the lower dome 85. The upper dome 75 and the lower dome 85 are connected by a sidewall 105, in which the supply port 87 and the return port 90 are located. Together, the upper dome 75, lower dome 85, and sidewall 105 result in a generally cylindrical tank 20 with a centerline 110.

[0039] When operational, the lower dome 85 is lower than the upper dome 75 with respect to the direction of gravity 95, such that the centerline 110 is parallel to the direction of gravity 95. This is preferable because unheated water 35 is supplied to the tank 20 at, or near to, the lowest point in the tank 20 (i.e., the lower dome 85) via the cold water inlet 100, and heated water 35 is removed from the tank at, or near to, the highest point in the tank 20 (i.e., upper dome 75) via the hot water outlet 80. The location of the cold water inlet 100 and the hot water outlet 80 thus prevent mixing of water as best as possible, and limit disruption of the stratification of the heated water 35 within the tank volume 30.

[0040] As briefly described above, mixing of water 35 in the tank 20 can result in undesirable effects to the performance of the water heating system 10 by disrupting the water 35 stratificationwithin the tank 20. Fig. 6 illustrates this phenomenon. More specifically, Fig. 6 illustrates the undesirable mixing that can occur within water heating storage tank 20 during a heating event, as predicted using computational fluid dynamics simulation. Referring to Fig. 5, which is a more detailed illustration of the tank 20, at a start of the heating event (at time=0), a top half 115 of the tank 20 is filled with water 35 that has been previously heated to a desired setpoint temperature of 60°C, and a bottom half 120 of the tank 20 is filled with water 35 at an unheated temperature of 18°C. The water 35 temperature at each of six evenly spaced locations TC1-TC6 in the tank 20 is shown in Fig. 6. As shown in Fig. 5, the tank volume 30 is divided into 6 about equal, vertically arranged fluid volumes, with one of the locations TC1-TC6 tracking the fluid temperature at each fluid volume midpoint. Fig. 6 illustrates the change in temperature that is expected to occur over time at each of the six locations TC1-TC6 during the heating event. In Fig. 6, the heating event is more precisely water 35 being drawn from the tank 20 through the heating loop 25 supply port 87 at a flow rate of 216.5 L / min and returned to the tank 20 through the heating loop 25 return port 90 with a 5.5 degree temperature rise, equivalent to a heating rate of ~83kW. The heating event begins at Time=0.

[0041] As shown in Fig. 6, the water 35 returning to the tank 20 from the heating loop 25 rapidly will mix with the heated water 35 in the top of the tank 20, such that after about 1.5 minutes all but the top sixth of the tank (i.e., TCI) will be mixed, and after about three minutes the entire tank volume will be mixed to a uniform temperature of about 40°C. The entire tank volume 30 will then be slowly heated to the 60°C setpoint temperature over the following about eighteen minutes. During that time, water 35 provided from the tank in response to a demand for hot water 35 would be below the setpoint temperature, which is undesirable.

[0042] To address this issue by limiting undesirable mixing that can occur, a stratification tube 125 is connected to the return port 90 and extends into the tank volume 30. Referring again to Fig. 1, the stratification tube 125 is connected to the return port 90 such that heated water 35 from the heating loop 25 passes through the stratification tube 125 after passing through the return port 90 but before being released into the tank volume 30. The stratification tube includes a body 140 with a first end 130 and a second end 135. The body 140 is generally cylindrical and includes a longitudinal axis 145 extending along the centerline of the generally cylindrical body 140. The first end 130 is connected to the return port 90, and the second end 135 is capped such that heatedwater 35 cannot escape the stratification tube 125 along the longitudinal axis 145. Preferably, the stratification tube 125 extends from the return port 90 and across the tank volume 30 such that the second end 135 is closer to the sidewall 105 than to the return port 90. Even more preferably, the stratification tube 125 extends from the return port 90 across at least 90% of a diameter 150 of the tank volume 30.

[0043] Fig. 2 illustrates a more detailed view of the stratification tube illustrated in Fig. 1. The stratification tube 125 extends along the longitudinal axis 145 from the first end 130 to the second end 135. The first end 130 is threaded to facilitate attachment to the return port 90. The body 140 is divided into three portions, a first portion 155, a second portion 160, and a third portion 165. The first portion 155 extends along the longitudinal axis 145 from the first end 130 and the second portion 160 extends along the longitudinal axis 145 from the first portion 155 such that the first portion 155 is connected to the second portion 160. The third portion 165 extends along the longitudinal axis 145 from the second portion 160 such that the third portion 165 is connected to the second portion 160. The first portion 155 includes a plurality of apertures 170. The plurality of apertures 170 shown in Fig. 2 are arranged in rows extending along the longitudinal axis 145 of the stratification tube 125, although other embodiments are contemplated. The second portion 160 is absent, or is substantially absent, from any apertures. The third portion 165 includes at least one aperture 175, and more preferably, three apertures 175. In some embodiments, the third portion 165 includes one or two apertures 175. The third portion 165 is preferably less than 10%, and preferably less than 5%, of a length 180 (shown in Fig. 3) of the body 140 of the stratification tube 125. The third portion 165 connects the second portion 160 to the second end 135, and thus the apertures 175 are adjacent to the second end 135.

[0044] Fig. 3 illustrates a section view of the tank 20 taken along line A- A in Fig. 1. The view in Fig. 3 is from the lower dome 85 of the tank 20 looking upward relative to the direction of gravity 95. Fig. 3 better illustrates how the length 180 of the body 140 of the stratification tube 125 extends across the diameter 150 of the tank volume 30, and illustrates the length 180 of the body 140 extending at least 90%, from the return port 90, across the diameter 150 of the tank volume 30. It has also been found to be particularly advantageous to have the first portion 155 extend, from the return port 90, across at least 50% the diameter 150 of the tank volume 30. Even more particularly, it has been found to be particularly advantageous to have the first portion 155extend, from the return port 90, across between 50% and 60% of the diameter 150 of the tank volume 30.

[0045] Fig. 3 also illustrates the length of the portions of the body 140. More particularly, Fig. 3 illustrates a length 185 of the first portion 155, a length 190 of the second portion 160, and a length 195 of the third portion 165. The lengths 185, 190, 195 add to the length 180 of the stratification tube 125. Fig. 3 also illustrates the relative orientation of the plurality of apertures 170 and the apertures 175 in the stratification tube 125. Fig. 3 is a view from the lower dome 85, and the apertures 170, 175 are visible from the lower dome 85. Thus, the plurality of apertures 170 and the apertures 175 face the lower dome 85 and expel heated water 35 downward relative to the direction of gravity. 95. This orientation of the plurality of apertures 170 and the apertures 175, and more broadly the stratification tube 125, reduces undesirable mixing of heated water 35 within the tank volume 30. In preferred embodiments, none of the plurality of apertures 170 and the apertures 175, or substantially none of the plurality of apertures 170 and the apertures 175, face the upper dome 75 (i.e., upwards relative to the direction of gravity 95).

[0046] Fig. 4 illustrates a section view of the stratification tube 125 taken along B-B in Fig. 2. The section is taken along the longitudinal axis 145 of the stratification tube 125. To further illustrate the orientation of the plurality of apertures 170 relative to the direction of gravity 95, an upper side 200 with respect to the direction of gravity 95 and a lower side 205 with respect to the direction of gravity 95 are shown in Fig. 4. Notably, all the plurality of apertures 170 are formed on the lower side 205 (i.e., the lower half) of the stratification tube 125. Fig. 4 likewise illustrates a diameter 210 of the stratification tube 125 and a diameter 215 of one of the plurality of apertures 170.

[0047] Through testing the inventors have found that the specific dimension ranges of the stratification tube 125 disclosed herein particularly and most effectively limit the undesirable mixing of heated water 35 introduced into the tank 20 via the return port 90. The length 180 to diameter 210 ratio of the stratification tube 125 is about 20:1, and is preferably in the range of about 16: 1 to about 24: 1. A ratio of the stratification tube 125 diameter 210 to the diameter 215 of the plurality of apertures 170 and the apertures 175 is in the range of about 6: 1 to about 10: 1. The stratification tube 125 can be manufactured from materials including, but not limited to,polypropylene (PPH, PPR, etc ), polyethylene (PE, PEX, HDPE), and polyvinyl chloride (PVC, CPVC, PVC-C).

[0048] Fig. 7 illustrates data from the same simulated heating event used to create the plot in Fig. 6, with an identical water heating system 10, but with the stratification tube 125 installed. In sharp contrast to the results without the stratification tube 125, when the stratification tube 125 is installed the previously heated water 35 in the top about 1 / 3 of the tank 20 (i.e., the two fluid volumes associated with TCI and TC2) for about 11 minutes after the heating event is expected to experience virtually no mixing with the unheated water 35 lower in the tank 20. The top about 1 / 3 of the tank 20 is expected to remain at the initial, heated temperature for about 17 minutes. At 17 minutes of elapsed time, the mix temperature (i.e., the average of the temperatures TC1-TC6) of the tank 20 will already have been raised to a temperature of about 55°C, or within 5 degrees of the setpoint temperature of 60°C. As a result, with the stratification tube 125 installed a draw of hot water 35 from the tank 20 during a heating event can be accommodated without substantial deviation from the desired water 35 temperature, thus providing a more consistent heated water 35 temperature at the hot water outlet 80.

[0049] Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.

Claims

CLAIMSWhat is claimed is:

1. A water heating system comprising: at least one heating unit; a tank including an upper dome, a lower dome, and a sidewall connecting the upper dome to the lower dome, the upper dome, the lower dome, and the sidewall defining a tank volume; and a heating loop fluidly connecting the tank to the at least one heating unit, wherein the tank further includes: a cold water inlet configured to supply unheated water to the tank, a hot water outlet configured to deliver heated water from the tank, a supply port configured to supply water from the tank to the at least one heating unit via the heating loop, and a return port in the sidewall configured to deliver heated water back into the tank via the heating loop, and wherein the return port is connected to a stratification tube extending into the tank volume, the stratification tube comprising: a first end connected to the return port, a body extending along a longitudinal axis, and a second end opposite of the first end, wherein the second end is capped, wherein the body includes a plurality of apertures configured to flow the heated water from the return port, through the body, and into the tank volume, and wherein the second end of the stratification tube extends across the tank volume such that the second end is closer to the sidewall than to the return port.

2. The water heating system of claim 1, wherein the body of the stratification tube includes a first portion, a second portion, and a third portion, wherein the first portion extends along the longitudinal axis from the first end and the second portion extends along the longitudinal axis from the first portion such that the first portion is connected to the second portion, wherein the third portion extends along the longitudinal axis from the second portion such that the third portion is connected to the second portion, wherein the first portion includes the plurality of apertures, wherein the second portion is substantially absent any apertures, and wherein the third portion includes at least one aperture.

3. The water heating system of claim 2, wherein the plurality of apertures are arranged in one or more rows extending along the longitudinal axis.

4. The water heating system of claim 3, wherein the upper dome is located above the lower dome with respect to gravity, and wherein the plurality of apertures in the first portion and the at least one aperture in the third portion face the lower dome.

5. The water heating system of claim 4, wherein substantially none of the plurality of apertures face the upper dome.

6. The water heating system of claim 2, wherein the second portion includes three or less apertures arranged adjacent to the second end of the stratification tube.

7. The water heating system of claim 4, wherein the third portion includes three or less apertures, and wherein the three or less apertures face the lower dome.

8. The water heating system of claim 2, wherein the stratification tube extends along the longitudinal axis, from the return port, across at least 90% of a diameter of the tank volume.

9. The water heating system of claim 8, wherein the first portion extends along the longitudinal axis, from the return port, across at least 50% of the diameter of the tank volume.

10. The water heating system of claim 1, wherein the stratification tube is at least one selected from the group consisting of polypropylene, polyethylene, and polyvinyl chloride.

11. A system configured to heat water, the system including: a tank having a tank volume, and a stratification tube attached to a sidewall of the tank, wherein the stratification tube is configured to return water heated by a heating unit back into the tank volume, the stratification tube comprising: a first end configured to receive the heated water, a body extending along a longitudinal axis, and a second end opposite of the first end, wherein the second end is capped, and wherein the body includes a plurality of apertures configured to flow the heated water from the first end, through the body, and into the tank volume.

12. The system of claim 11, wherein the body of the stratification tube includes a first portion, a second portion, and a third portion, the first portion extends along the longitudinal axis from the first end and the second portion extends along the longitudinal axis from the first portion such that the first portion is connected to the second portion, wherein the third portion extends along the longitudinal axis from the second portion such that the third portion is connected to the second portion, wherein the first portion includes the plurality of apertures, wherein the second portion is substantially absent any apertures, and wherein the third portion includes at least one aperture.

13. The system of claim 12, wherein the plurality of apertures are arranged in one or more rows extending along the longitudinal axis.

14. The system of claim 13, wherein, as installed into a water tank, the body of the stratification tube includes an upper side with respect to gravity and a lower side with respect to gravity, and wherein the lower side of the first portion includes the plurality of apertures.

15. The system of claim 14, wherein the upper side of the first portion and the upper side of the second portion are substantially devoid of apertures.

16. The system of claim 15, wherein the third portion includes three or less apertures.

17. The system of claim 14, wherein the tank is generally cylindrical and includes a longitudinal axis extending along a centerline of the generally cylindrical tank, and wherein the longitudinal axis of the stratification tube is generally perpendicular to the longitudinal axis of the tank.

18. The system of claim 11, wherein the body is cylindrical and, along the longitudinal axis, has length to diameter ratio between 16: 1 and 24: 1.

19. The system of claim 11, wherein a ratio of a diameter of the stratification tube to a diameter of an aperture of the plurality of apertures is between 6: 1 and 10: 1.

20. The system of claim 12, wherein the first portion, along the longitudinal axis, is between 50% and 60% of an entire length of the stratification tube along the longitudinal axis.

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