CA2422932A1 - Improvement to a hot water heater - Google Patents
Improvement to a hot water heater Download PDFInfo
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- CA2422932A1 CA2422932A1 CA 2422932 CA2422932A CA2422932A1 CA 2422932 A1 CA2422932 A1 CA 2422932A1 CA 2422932 CA2422932 CA 2422932 CA 2422932 A CA2422932 A CA 2422932A CA 2422932 A1 CA2422932 A1 CA 2422932A1
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Abstract
A safety and energy saving improvement to a hot water heater whereby water can be heated to a high temperature (scalding hot) required for sanitizing and energy storage, but then is is internally cooled to a lower, non-scalding temperature before it leaves the heater. This is accomplished by means of a low-cost internal heat exchanger. In its simplest form, the internal heat exchanger is a vertically oriented tube structure one end of which is open to the hottest water at the top of the tank and the other end of which exits the tank. By sending the hottest water downwards through this tube, the hot water passes through the cooler layers of water in the tank and so gives up heat energy resulting in a lower water exit temperature. To maximize heat transfer where high storage temperature is preferred, the heat exchanger includes a larger outer sleeve which surrounds the vertical tube structure and into which sleeve the cold feed water is made to flow through the annular space therebetween. Also disclosed are means to automatically move the sleeve and/or deflect the cold water flow path to automatically vary heat transfer in response to the seasonal change of temperature of the cold feed water.
Description
SPECIFICATIONS
BACKGROUND OF THE INVENTION
It is well known that deadly Legionella and other bacteria can breed in the lower temperature regions of hot water heaters, particularly the storage tank type of water heater. To kill these pathogens a relatively high storage temperature is required. This high temperature, while sanitizing the water, also makes it scalding hot. Children, the aged and the disabled are all susceptible to such scalding. It is estimated that in the U.S.A. some 4,000 children alone are scalded in this way each year.
SUMMARY OF THE INVENTION
Four facts about water and water heaters: One, is that the temperature of cold water cycles with the seasonal change in ground temperature, warmest in autumn, coldest at springtime. For example, at about the latitude of the U.S.A. and Canada border, the cold water can be 35°F
( 1.6°C) in March and 50°F ( 10°C) in October. Two, cold water is more dense, or heavier per unit volume, than warmer water. Three, is that in a hot water tank, the water is constantly in motion: either rising (made lighter) from being heated , or sinking (made heavier) from natural cooling. The water thus forms into temperature dependent layers in a phenomena known as stacking. Four, the higher the hot water storage temperature the more hot water is available for use in washing, showers, laundry, etc.
Water heaters use energy (electric, gas, oiI) to heat cold feed water in response to a temperature demand set by a thermostat. In tank-type (also referred to as storage-type) water heaters, the hot water exits from the top of the tank where the hottest water (lightest layers) accumulates. The water temperature below this upper layer progressively becomes cooler with the bottom layer being the coldest (heaviest).
Typically, the entire building's plumbing system is under constant pressure from the pumped, cold, underground water supply which splits into two plumbing lines at the point of entry into the building, one line to all the cold water faucets, the second line to feed cold water to the hot water heater. When a hot water faucet is opened, the pressure in the plumbing system leading back to the hot water tank is lowered and so the higher pressure cold feed water enters the hot water tank forcing the upper layer of hottest water in the tank out of the opened faucet.
To provide sanitary water, the water must be heated to a temperature of about 140°F, 60°C a temperature at which pathogens such as Legionella bacteria cannot exist. As well, the higher the storage temperature in the tank, the more energy it contains and so the volume of usable hot water is increased (i.e., more hot showers). But, the higher the temperature, the more the danger of instantaneous scalding. For non-scalding (or slow-scalding) hot water, the temperature should be no higher than about 105-120°F, 45-48°C but at this low temperature the danger of pathogen growth becomes a serious concern, and, as well, the amount of available hot water is reduced.
The instant invention enables a hot water tank to heat and store the water at high temperature while delivering a lower temperature hot water to the faucet. It accomplishes this through the use of an internal heat exchanger to transfer heat from the high temperature hot water to the low temperature cold feed water.
In the design of the instant heat exchanger, the hot water from the hottest upper layer is directed down through one or more long tubes) (vertical or angled) which islare surrounded by an open-ended plastic sleeve through which the cold feed water is made to flow on its way towards the coldest lower layer at the bottom of the tank. The hot water thus transfers some of its excess heat (temperature) to the cold water which is thereby heated.
In one embodiment, the heat exchanger comprises a long vertical loop of pipe with the loop near the bottom of the tank. The open end of this looped pipe is upwards in the hottest water and the other end exits the tank and connects to the building's plumbing. A
cold feed water sleeve surrounding this loop directs the cold feed water to flow about this loop.
BACKGROUND OF THE INVENTION
It is well known that deadly Legionella and other bacteria can breed in the lower temperature regions of hot water heaters, particularly the storage tank type of water heater. To kill these pathogens a relatively high storage temperature is required. This high temperature, while sanitizing the water, also makes it scalding hot. Children, the aged and the disabled are all susceptible to such scalding. It is estimated that in the U.S.A. some 4,000 children alone are scalded in this way each year.
SUMMARY OF THE INVENTION
Four facts about water and water heaters: One, is that the temperature of cold water cycles with the seasonal change in ground temperature, warmest in autumn, coldest at springtime. For example, at about the latitude of the U.S.A. and Canada border, the cold water can be 35°F
( 1.6°C) in March and 50°F ( 10°C) in October. Two, cold water is more dense, or heavier per unit volume, than warmer water. Three, is that in a hot water tank, the water is constantly in motion: either rising (made lighter) from being heated , or sinking (made heavier) from natural cooling. The water thus forms into temperature dependent layers in a phenomena known as stacking. Four, the higher the hot water storage temperature the more hot water is available for use in washing, showers, laundry, etc.
Water heaters use energy (electric, gas, oiI) to heat cold feed water in response to a temperature demand set by a thermostat. In tank-type (also referred to as storage-type) water heaters, the hot water exits from the top of the tank where the hottest water (lightest layers) accumulates. The water temperature below this upper layer progressively becomes cooler with the bottom layer being the coldest (heaviest).
Typically, the entire building's plumbing system is under constant pressure from the pumped, cold, underground water supply which splits into two plumbing lines at the point of entry into the building, one line to all the cold water faucets, the second line to feed cold water to the hot water heater. When a hot water faucet is opened, the pressure in the plumbing system leading back to the hot water tank is lowered and so the higher pressure cold feed water enters the hot water tank forcing the upper layer of hottest water in the tank out of the opened faucet.
To provide sanitary water, the water must be heated to a temperature of about 140°F, 60°C a temperature at which pathogens such as Legionella bacteria cannot exist. As well, the higher the storage temperature in the tank, the more energy it contains and so the volume of usable hot water is increased (i.e., more hot showers). But, the higher the temperature, the more the danger of instantaneous scalding. For non-scalding (or slow-scalding) hot water, the temperature should be no higher than about 105-120°F, 45-48°C but at this low temperature the danger of pathogen growth becomes a serious concern, and, as well, the amount of available hot water is reduced.
The instant invention enables a hot water tank to heat and store the water at high temperature while delivering a lower temperature hot water to the faucet. It accomplishes this through the use of an internal heat exchanger to transfer heat from the high temperature hot water to the low temperature cold feed water.
In the design of the instant heat exchanger, the hot water from the hottest upper layer is directed down through one or more long tubes) (vertical or angled) which islare surrounded by an open-ended plastic sleeve through which the cold feed water is made to flow on its way towards the coldest lower layer at the bottom of the tank. The hot water thus transfers some of its excess heat (temperature) to the cold water which is thereby heated.
In one embodiment, the heat exchanger comprises a long vertical loop of pipe with the loop near the bottom of the tank. The open end of this looped pipe is upwards in the hottest water and the other end exits the tank and connects to the building's plumbing. A
cold feed water sleeve surrounding this loop directs the cold feed water to flow about this loop.
In another embodiment, the hot water outlet is located near the bottom of the tack and is connected to a pipe that curves up to near the tank top where its end is open.
The too-hot water enters at the top and descends through cooler layers to the outlet. In yet another embodiment the hot water outlet is wrapped around the tank to be cooled through the tank wall. In further embodiment, the hot water is passes through a platform plate on which the tank sits.
A further refinement of the instant invention to help ensure commercial success, overcomes a considerable difficulty relating to the fact, that, as the temperature of the cold feed water changes with season, so does the temperature of the delivered hot water, which is undesirable.
To achieve an automatic thermostatic control of delivered hot water temperature of, say, 120°F (48°C), the heat exchanger should be designed to accomplish the required amount of heat transfer with the warmest cold feed water as typically occurs in the autumn.
This, in turn, requires that the tube and sleeve be optimally arranged (i.e., a concentric arrangement) in order to maximize exposure of surface of the hot water down tubes) to the cold water flow, and thereby ensure that the desired temperature lowering is achieved. Then, the design requires that the tube exposure be reduced as the cold water gets colder (i.e., a non-concentric arrangement).
This movement into and out of concentricity, may be accomplished by using well known thermostatic devices, such as shape memory alloy or bimetal spring(s), positioned between the sleeve and exposed to either the cold water or the delivered water, or both.
US patent 4,283,006 to Fedewitz discloses a device with shape memory alloy springs to effect a deflection of a fluid in a flue or chimney. The same principle may by used in the instant invention.
The common automobile cooling system thermostat develops linear movement from temperature change to push open a valve. That well understood technology can be used to effect a cold water redirection and consequent change in heat transfer rate between the cold water and the hot water.
The movement of the sleeve to effect a change to the rate of heat transfer, may also be accomplished in a more economical manner by having the entire heat exchanger angled. This will allow the outer plastic sleeve it to move radially (relative to the central hot water down tube) in reaction to the change of weight of the the cold feed water flowing through it. That is, as the cold water becomes heavier, from seasonal temperature change, the sleeve will move radially by force of gravity and thereby 'sink' out of concentricity reducing heat transfer, and, when lighter the sleeve will 'float' into concentricity increasing heat transfer.
Another method of achieving automatic sleeve positioning is to use the increased thrust of heavier cold water against an angled surface to move the sleeve.
Yet another way of reducing cooling from colder feed water is to deflect some of the cold water flowing about the hot water tube using a thermostatic material that opens about the tube in response to lower delivered hot water temperature.
An exterior thermostatic mixing valve between the cooled hot water and the too-hot water may be used to automatically adjust outlet temperature from the tank.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross section of a tank heater showing the arrangement and location of the internal heat exchanger which comprises a sleeve surrounding a hot water down tube or duct and the cold feed water flow and where the hot water outlet is located at the bottom;
Fgure 2 shows the same heat exchanger embodiment of Figure 1 in greater detail as to the method of assembly where a bolted plate carries the down tube and cold feed water inlet and the sleeve such that the entire one piece heat exchanger unit can be inserted from the top, and where a similar plate connection at the bottom carnes the outlet;
Figure 3 shows a cutaway view of another embodiment comprising a long vertical loop that carries too-hot water down through the cooler regions;
Figure 3b shows the same embodiment with a cold water sleeve;
Figure 4 shows another embodiment where directed cold feed water flows by capillary action down the hot water duct and where the duct extends through the bottom of the tank and out the extended rim of the tank;
Figure 5 shows the simplest embodiment with the least amount of change to the standard tank;
Figure 6 shows a concentric tube heat exchanger;
Figure 7 shows the same heat exchanger with cold feed water directed at the outer tube;
Figure 8 shows the same embodiment with the cold feed water being constrained by an enclosing sleeve;
Figure 9 top view of the same embodiment showing relationship of tubes and actuator;
Figure 10 is a top view of another embodiment where the cold feed water tube is clamped against the hot water duct to effect heat transfer between fluids;
Figure 11 is another embodiment where the hot water outlet is directed downwards external to the tank and in thermal contact with the tank's metal wall;
Figure 12 is another embodiment where the hot water outlet is wrapped around the tank to effect the desired heat transfer;
Figure 13 is another embodiment where the cool tank bottom rests on a heat transfer platen such that the hot water gives up heat to the cool platen;
Figure 14 is the same embodiment where the platen is shaped to provide greater thermal contact with the bottom of the tank.
Figure 1S shows the embodiment of Figure 1 with the addition of a thermostatic deflector to direct cold water flow to or away from the hot water tube in accordance to the cold water temperature;
Figure 16 is an enlarged view of the same embodiment showing only the deflector section.
Fgure 17 is an angled embodiment with escape openings on sleeve for cold water as it becomes progressively heated in its downwards travel Figure 18 the same embodiment including a positioning spring and an angled thrust surface to generate an automatically changing force to effect sleeve movement in accordance with cold water density;
Figure 19 shows the vector resultant force diagram of that embodiment when the cold feed water is at greatest density and thrust at its maximum;
Figure 20 shows the same diagram at lowest density and resulting thrust at its minimum.
DETAILED DESCRIPTION
In a hot water tank, the contained water is constantly in motion, either rising up from being heated whereafter it settles in layers or strata in upper regions, or, sinking from being cooled whereafter it descends to settle in layers or strata in lower regions. Fresh cold feed water creates the bottornmost layer or strata. Thus, from top to bottom in the tank, the water forms strata or layers of higher and lower temperatures respectively. This layering is a hot water tank is referred to as stacking and is due to the changes in density of water with temperature.
The present invention directs hot water drawn from in the hot, uppermost regions of the tank, downwards through a heat exchanger tube and therefore through cooler lower layers of water, to cool the hot water.
In Fig 1 is shown a storage tank hot water heater A, with outlet 6 for fully hot water and inlet for cold feedwater both at the top. Pressurized cold feed water 4 enters inlet 5. Normally, cold water 4 flows through a full length internal cold water delivery tube 9 which directs the cold feed water to the bottom of the heater as shown in Fig 3. In the instant invention internal cold water delivery tube 9 is preferably shortened so that the cold water can be used in heat exchanger 1.
According to the present invention, sanitized hot water 7 from the top of the tank is made to flow downwards through heat exchanger 1 to be cooled. Heat exchanger 1 may be a single hot water down tube la as shown in Figures 4, 5, 11, 12 or it may comprise multiple components including up tube lc, sleeve Ib, clamps 9b, platen 1e as shown in Figures 1, 2, 3, 6, 7, 8, 13, 14, and may also comprise multiple hot water down tubes la (not shown).
In Figure 1 one embodiment has heat exchanger 1 with outer sleeve 1b enclosing hot water down tube la. Cold water 4 enters inlet S and cold water down tube 9 which has just enough length to enter top end of sleeve 1b. Cold water 4 flows freely and directly against and about the exterior of hot water down tube la and cools the hot water 7 by heat transfer.
Cooled hot water exits the tank at outlet 6a for delivery to faucets. Hot water down tube la, sleeve 1b, and cold water down tube 9, may be fluted, dimpled, finned, coiled, squared, or otherwise adapted for increased surface area and/or turbulence to thereby increase the rate of heat transfer. Such adaptations may also include multiple tubes of smaller diameter which would greatly increase surface area and reduce flow rate in each tube, both of which increase the rate of heat transfer.
Such multiple tubes would all be spaced apart and open at the top and manifolded together at the bottom. Plastic material may be used for hot water down tube la if sufficient surface area is exposed to cold feed water 4 to effect sufficient temperature drop.
Fig 2 shows the heat exchanger 1 of Fig 1 enlarged and with construction details. The top of the tank 32 (only a section is shown) has a access hole 26 of sufficient diameter to receive heat exchanger 1 (and outlet 6a if a high temperature delivery is contemplated), both of which are pre-attached to plate 21a which is larger than hole 26 and which is secured to tank top 32 using gasket 20 and bolts 22. Hot water down tube 1 bends near it's lower end and has plate 21 attached to it. Plate 21 bolts to tank side 31 with gasket 20 and bolts 22 to cover hole 27 in Iower side portion 31 of tank A (only a section is shown). In this way the entire heat exchanger 1 along with inlet 5 and outlets 6, 6a, and plates 21, 21a can be prebuilt and then lowered into tank A through hole 26 such that outlet 6a passes through lower hole 27 after which both plates 21a and 21 may be bolted in place completing the assembly. Hot water 7 can flow through outlet 6 as fully hot water 7b or at outlet 6a as cooled hot water 7a.
In Figs l, 3b, opening if in down tube 1 (on the top side if tube 1 is angled) allows cold water 4 that is being progressively heated (and therefore made lighter) as it descends down tube L, to escape by flowing through opening if into the tank's main water body at any vertical strata consistent with its temperature/density. Opening if may take the form of multiple holes or a gap or slit in the down tube 1.
In Fig 3 heat exchanger 1 comprises a looped pipe with up leg la and down leg lc. Hot water 7 enters the down leg 1 a at the top and descends through the cooler regions and then up again through up loop lc to exit as cooled hot water 7a at outlet 6a.
Insulating cover 15 prevents the hot upper layers from reheating the cooled hot water. Such a loop with up leg la and down leg lc may be enclosed in a sleeve 1b shown in Figs. 3b such that cold feed water is directed against the loop. Such a sleeve may also have opening if to allow heated cold feed water 4a to escape at appropriate thermal stack positions.
Also shown in Fig 3 is an external thermostatic valve 10, with bimetal or shape-memory alloy actuating elements, which may be used on all embodiments between the outlets 6, 6a and/or between cold feed water inlet 5 and either hot water outlet 6, 6a to fine tune the outlet temperature of cooled hot water 7a.
Fig 4 shows another embodiment of the internal heat exchanger 1 where the cold feed water 4 is directed by angled cold water tube 9 to flow 4a against and along the outer wall of hot water down tube la. Tank bottom 30 is raised to permit outlet 7a to be as low as possible. This arrangement will allow the heat exchanger 1 to be inserted from the bottom.
Fig 5 shows the same embodiment but with exchanger 1 exiting above tank bottom 30. In this embodiment the tube la would be curved to allow fitting into the tank from the side outlet 6a. A sleeve (not shown) can be adapted to direct cold feed water 4 onto curved down tube la.
Figures 6, 7, 8 show heat exchanger 1 being two concentric tubes la, lc where the hot water 7 enters the top of outer tube la and descends to be cooled then ascends through inner tube lc to exit as cooled hot water 7a. As in Fig. 1, an insulation sleeve (not shown) on the upper portion of inner tube 17 can prevent reheating the cooled water. Figure 7 shows how the same embodiment can have cold feed water 4 directed at exterior of exchanger 1 by feed tube 9.
Heated feed water 4a sloughs off the tube at the bottom. Figure 8 shows the same embodiment further incorporating a sleeve 1b to hold cold feed water 4 in better thermal contact with tube la.
Funnel mouth 1d may be used to provide a swirling downward flow for better heat transfer.
Figs 8 and 9 show spacers 13 made of memory-shape alloy spring or bimetal material to provide temperature related movement of the outer tube concentric or offset from heat exchanger la, lc such that heat transfer can be reduced when cold feed water 4 is colder in the spring season. Figure ZO shows another embodiment where the cold feed tube 9 and the hot water down tube la are simply bound together tightly with clamping means 9b to provide heat transfer. Figures 1 l, 12, 13, 14 show external embodiments of heat exchanger 1. In Figure 11 hot water down tube la is in straight thermal contact with the wall of the tank A. In Figure 12 the hot water down tube la is wrapped around the exterior wall of tank A. In Figure 13 tank A
sits on a flat platen 1e that has the hot water down tube la as an internal passage. In Figure 14 the same embodiment has the upper surface of platen 1e made convex for better thermal contact with the concave tank bottom.
One difficulty with cooling the too hot water lies in the fact that the temperature of the cold feed water varies with latitude and with season. For example ground temperature (and therefore cold water temperature) at around the 46th parallel can be as cold as 35°F in spring (1.6°C) while in fall, the same ground has a temperature of 45°F
(7.2°C). This means that the cooling of the hot water will be affected, being cooled more at northern latitudes and in the spring and less at southerly latitudes in the autumn. Thus the temperature of the delivered hot water 7a would also vary from, say, 120°F (48.8°C) to 130 °F
(54.4°C).
To overcome this obstacle, the heat exchanger 1 embodiment shown in Figs 1 and 2 may be angled from the vertical as shown by the embodiment shown in Fig 17, 18 and arranged to enable the outer tube 1b to move. The movement of tube 1b is controlled by the cold feed water temperature. Since cold water is more dense, it is heavier. Therefore the outer tube 1b will respond to the added weight and move away from inner tube la. This will enable some room for the mixture of cold- and warmed feed water to stratify, whereby at least some of the colder feed water flows adjacent the tube 1b wall out of contact with down tube la, thus reduce heat transfer and net cooling. Another way in which such automatic cooling compensation may be achieved is by use of a inner thrust surface 100 on outer sleeve 1b. Since cold water is heavier, the net force exerted by cold feed water 4 impinging against angled thrust surface 100 is greater than when the cold feed water 4 is warmer (southerly latitudes and autumn season). This will move the outer sleeve 1b away from down tube 1a and reduce cooling effect when water is coldest and, conversely, maximize cooling when cold feed water 4 is warmest. One or more spring element 101 may be used to bias the outer sleeve towards maximum cooling when the cold feed water 4 is warmest. Such spring elements may be of shape-memory alloy or bimetal so as to change the spacing between tube la and sleeve 1b in response to temperature change of the cold water 4 and/or of the temperature of the delivered water 7a. Also by choosing a plastic material for outer sleeve 1b that is more buoyant, and by using standoffs 101a (Fig 18), the outer sleeve 1b may be ideally positioned for maximum cooling under the warmest cold water conditions. Then when the cold feed water 4 is colder, the outer sleeve 1b will automatically move so as to reduce cooling thus maintaining a near constant temperature of delivered water 7a.
Figs 19, 24 shows the vector forces of angled heat exchanger 1 of Fig 18. In Fig 19 longer line 103 at the angle of the outer sleeve 1b represents the flow of colder feed water when it is heavier while in Fig 20 shorter line 103 represents the flow of the warmer feed water when it is lighter. When cold water (Fig 19) occupies the interior of outer tube 1b the gravitational pull 104 produces a usable side force represented by the horizontal line 105. The effect of this side force 105 is to move outer sleeve 1b a distance proportional to the weight of the cold water. As the cold water 4 becomes warmer, the side force is reduced (Fig 20) and therefore the outer sleeve 1b is moved less increasing cooling of the hot water flowing in down tube la.
This same automatic moving of outer sleeve 1b may be accomplished using angled thrust surface 100 where the heavier water creates maximum force to move outer sleeve 1b the maximum distance to reduce heat transfer to the minimum.
Opening if along outer sleeve 1b serves to allow cold feed water, heated from its cooling of hot water in down tube la, to escape into the proper layer of the stack, so as to not upset the stacking order in the tank.
Fig 15 and 16 show the same embodiment as Fig 1 with the addition of a temperature sensitive deflector 9a installed at the outlet of internal cold water delivery tube 9. Such a deflector could be adapted to other embodiments shown in Figs 2, 3, 3b, 4, 5, 6, 7, 8. The deflector responds to cold water temperature, moving to first limit 9c (dotted line) to deflect the flow 4b (dotted arrow) towards the hot water down tube la thereby providing maximum cooling when the cold feed water temperature is warmest as in the autumn. When the cold water gets to its coldest in springtime, deflector 9a straightens and moves towards second limit 9b to direct the cold feed water in a more vertical path 4c thereby reducing the cooling effect on the hot water. By this means the delivered hot water 7a can be held to within acceptable tolerances as the cold water temperature varies through the year.
A variation of temperature sensitive deflector 9a may be used to deflect flow from a single cold water source 9 into one or or more separate down tubes 1b (not shown).
Such a variation could be used on the embodiments shown in Figs 1, 12, 13, and 14 which use external heat exchanger 1, la.
While the above disclosure refers mainly to tank-type water heaters, it is clear that the same means can be applied for cooling too hot water in instantaneous or on-demand type water heaters, to achieve the same safety benefits.
The too-hot water enters at the top and descends through cooler layers to the outlet. In yet another embodiment the hot water outlet is wrapped around the tank to be cooled through the tank wall. In further embodiment, the hot water is passes through a platform plate on which the tank sits.
A further refinement of the instant invention to help ensure commercial success, overcomes a considerable difficulty relating to the fact, that, as the temperature of the cold feed water changes with season, so does the temperature of the delivered hot water, which is undesirable.
To achieve an automatic thermostatic control of delivered hot water temperature of, say, 120°F (48°C), the heat exchanger should be designed to accomplish the required amount of heat transfer with the warmest cold feed water as typically occurs in the autumn.
This, in turn, requires that the tube and sleeve be optimally arranged (i.e., a concentric arrangement) in order to maximize exposure of surface of the hot water down tubes) to the cold water flow, and thereby ensure that the desired temperature lowering is achieved. Then, the design requires that the tube exposure be reduced as the cold water gets colder (i.e., a non-concentric arrangement).
This movement into and out of concentricity, may be accomplished by using well known thermostatic devices, such as shape memory alloy or bimetal spring(s), positioned between the sleeve and exposed to either the cold water or the delivered water, or both.
US patent 4,283,006 to Fedewitz discloses a device with shape memory alloy springs to effect a deflection of a fluid in a flue or chimney. The same principle may by used in the instant invention.
The common automobile cooling system thermostat develops linear movement from temperature change to push open a valve. That well understood technology can be used to effect a cold water redirection and consequent change in heat transfer rate between the cold water and the hot water.
The movement of the sleeve to effect a change to the rate of heat transfer, may also be accomplished in a more economical manner by having the entire heat exchanger angled. This will allow the outer plastic sleeve it to move radially (relative to the central hot water down tube) in reaction to the change of weight of the the cold feed water flowing through it. That is, as the cold water becomes heavier, from seasonal temperature change, the sleeve will move radially by force of gravity and thereby 'sink' out of concentricity reducing heat transfer, and, when lighter the sleeve will 'float' into concentricity increasing heat transfer.
Another method of achieving automatic sleeve positioning is to use the increased thrust of heavier cold water against an angled surface to move the sleeve.
Yet another way of reducing cooling from colder feed water is to deflect some of the cold water flowing about the hot water tube using a thermostatic material that opens about the tube in response to lower delivered hot water temperature.
An exterior thermostatic mixing valve between the cooled hot water and the too-hot water may be used to automatically adjust outlet temperature from the tank.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross section of a tank heater showing the arrangement and location of the internal heat exchanger which comprises a sleeve surrounding a hot water down tube or duct and the cold feed water flow and where the hot water outlet is located at the bottom;
Fgure 2 shows the same heat exchanger embodiment of Figure 1 in greater detail as to the method of assembly where a bolted plate carries the down tube and cold feed water inlet and the sleeve such that the entire one piece heat exchanger unit can be inserted from the top, and where a similar plate connection at the bottom carnes the outlet;
Figure 3 shows a cutaway view of another embodiment comprising a long vertical loop that carries too-hot water down through the cooler regions;
Figure 3b shows the same embodiment with a cold water sleeve;
Figure 4 shows another embodiment where directed cold feed water flows by capillary action down the hot water duct and where the duct extends through the bottom of the tank and out the extended rim of the tank;
Figure 5 shows the simplest embodiment with the least amount of change to the standard tank;
Figure 6 shows a concentric tube heat exchanger;
Figure 7 shows the same heat exchanger with cold feed water directed at the outer tube;
Figure 8 shows the same embodiment with the cold feed water being constrained by an enclosing sleeve;
Figure 9 top view of the same embodiment showing relationship of tubes and actuator;
Figure 10 is a top view of another embodiment where the cold feed water tube is clamped against the hot water duct to effect heat transfer between fluids;
Figure 11 is another embodiment where the hot water outlet is directed downwards external to the tank and in thermal contact with the tank's metal wall;
Figure 12 is another embodiment where the hot water outlet is wrapped around the tank to effect the desired heat transfer;
Figure 13 is another embodiment where the cool tank bottom rests on a heat transfer platen such that the hot water gives up heat to the cool platen;
Figure 14 is the same embodiment where the platen is shaped to provide greater thermal contact with the bottom of the tank.
Figure 1S shows the embodiment of Figure 1 with the addition of a thermostatic deflector to direct cold water flow to or away from the hot water tube in accordance to the cold water temperature;
Figure 16 is an enlarged view of the same embodiment showing only the deflector section.
Fgure 17 is an angled embodiment with escape openings on sleeve for cold water as it becomes progressively heated in its downwards travel Figure 18 the same embodiment including a positioning spring and an angled thrust surface to generate an automatically changing force to effect sleeve movement in accordance with cold water density;
Figure 19 shows the vector resultant force diagram of that embodiment when the cold feed water is at greatest density and thrust at its maximum;
Figure 20 shows the same diagram at lowest density and resulting thrust at its minimum.
DETAILED DESCRIPTION
In a hot water tank, the contained water is constantly in motion, either rising up from being heated whereafter it settles in layers or strata in upper regions, or, sinking from being cooled whereafter it descends to settle in layers or strata in lower regions. Fresh cold feed water creates the bottornmost layer or strata. Thus, from top to bottom in the tank, the water forms strata or layers of higher and lower temperatures respectively. This layering is a hot water tank is referred to as stacking and is due to the changes in density of water with temperature.
The present invention directs hot water drawn from in the hot, uppermost regions of the tank, downwards through a heat exchanger tube and therefore through cooler lower layers of water, to cool the hot water.
In Fig 1 is shown a storage tank hot water heater A, with outlet 6 for fully hot water and inlet for cold feedwater both at the top. Pressurized cold feed water 4 enters inlet 5. Normally, cold water 4 flows through a full length internal cold water delivery tube 9 which directs the cold feed water to the bottom of the heater as shown in Fig 3. In the instant invention internal cold water delivery tube 9 is preferably shortened so that the cold water can be used in heat exchanger 1.
According to the present invention, sanitized hot water 7 from the top of the tank is made to flow downwards through heat exchanger 1 to be cooled. Heat exchanger 1 may be a single hot water down tube la as shown in Figures 4, 5, 11, 12 or it may comprise multiple components including up tube lc, sleeve Ib, clamps 9b, platen 1e as shown in Figures 1, 2, 3, 6, 7, 8, 13, 14, and may also comprise multiple hot water down tubes la (not shown).
In Figure 1 one embodiment has heat exchanger 1 with outer sleeve 1b enclosing hot water down tube la. Cold water 4 enters inlet S and cold water down tube 9 which has just enough length to enter top end of sleeve 1b. Cold water 4 flows freely and directly against and about the exterior of hot water down tube la and cools the hot water 7 by heat transfer.
Cooled hot water exits the tank at outlet 6a for delivery to faucets. Hot water down tube la, sleeve 1b, and cold water down tube 9, may be fluted, dimpled, finned, coiled, squared, or otherwise adapted for increased surface area and/or turbulence to thereby increase the rate of heat transfer. Such adaptations may also include multiple tubes of smaller diameter which would greatly increase surface area and reduce flow rate in each tube, both of which increase the rate of heat transfer.
Such multiple tubes would all be spaced apart and open at the top and manifolded together at the bottom. Plastic material may be used for hot water down tube la if sufficient surface area is exposed to cold feed water 4 to effect sufficient temperature drop.
Fig 2 shows the heat exchanger 1 of Fig 1 enlarged and with construction details. The top of the tank 32 (only a section is shown) has a access hole 26 of sufficient diameter to receive heat exchanger 1 (and outlet 6a if a high temperature delivery is contemplated), both of which are pre-attached to plate 21a which is larger than hole 26 and which is secured to tank top 32 using gasket 20 and bolts 22. Hot water down tube 1 bends near it's lower end and has plate 21 attached to it. Plate 21 bolts to tank side 31 with gasket 20 and bolts 22 to cover hole 27 in Iower side portion 31 of tank A (only a section is shown). In this way the entire heat exchanger 1 along with inlet 5 and outlets 6, 6a, and plates 21, 21a can be prebuilt and then lowered into tank A through hole 26 such that outlet 6a passes through lower hole 27 after which both plates 21a and 21 may be bolted in place completing the assembly. Hot water 7 can flow through outlet 6 as fully hot water 7b or at outlet 6a as cooled hot water 7a.
In Figs l, 3b, opening if in down tube 1 (on the top side if tube 1 is angled) allows cold water 4 that is being progressively heated (and therefore made lighter) as it descends down tube L, to escape by flowing through opening if into the tank's main water body at any vertical strata consistent with its temperature/density. Opening if may take the form of multiple holes or a gap or slit in the down tube 1.
In Fig 3 heat exchanger 1 comprises a looped pipe with up leg la and down leg lc. Hot water 7 enters the down leg 1 a at the top and descends through the cooler regions and then up again through up loop lc to exit as cooled hot water 7a at outlet 6a.
Insulating cover 15 prevents the hot upper layers from reheating the cooled hot water. Such a loop with up leg la and down leg lc may be enclosed in a sleeve 1b shown in Figs. 3b such that cold feed water is directed against the loop. Such a sleeve may also have opening if to allow heated cold feed water 4a to escape at appropriate thermal stack positions.
Also shown in Fig 3 is an external thermostatic valve 10, with bimetal or shape-memory alloy actuating elements, which may be used on all embodiments between the outlets 6, 6a and/or between cold feed water inlet 5 and either hot water outlet 6, 6a to fine tune the outlet temperature of cooled hot water 7a.
Fig 4 shows another embodiment of the internal heat exchanger 1 where the cold feed water 4 is directed by angled cold water tube 9 to flow 4a against and along the outer wall of hot water down tube la. Tank bottom 30 is raised to permit outlet 7a to be as low as possible. This arrangement will allow the heat exchanger 1 to be inserted from the bottom.
Fig 5 shows the same embodiment but with exchanger 1 exiting above tank bottom 30. In this embodiment the tube la would be curved to allow fitting into the tank from the side outlet 6a. A sleeve (not shown) can be adapted to direct cold feed water 4 onto curved down tube la.
Figures 6, 7, 8 show heat exchanger 1 being two concentric tubes la, lc where the hot water 7 enters the top of outer tube la and descends to be cooled then ascends through inner tube lc to exit as cooled hot water 7a. As in Fig. 1, an insulation sleeve (not shown) on the upper portion of inner tube 17 can prevent reheating the cooled water. Figure 7 shows how the same embodiment can have cold feed water 4 directed at exterior of exchanger 1 by feed tube 9.
Heated feed water 4a sloughs off the tube at the bottom. Figure 8 shows the same embodiment further incorporating a sleeve 1b to hold cold feed water 4 in better thermal contact with tube la.
Funnel mouth 1d may be used to provide a swirling downward flow for better heat transfer.
Figs 8 and 9 show spacers 13 made of memory-shape alloy spring or bimetal material to provide temperature related movement of the outer tube concentric or offset from heat exchanger la, lc such that heat transfer can be reduced when cold feed water 4 is colder in the spring season. Figure ZO shows another embodiment where the cold feed tube 9 and the hot water down tube la are simply bound together tightly with clamping means 9b to provide heat transfer. Figures 1 l, 12, 13, 14 show external embodiments of heat exchanger 1. In Figure 11 hot water down tube la is in straight thermal contact with the wall of the tank A. In Figure 12 the hot water down tube la is wrapped around the exterior wall of tank A. In Figure 13 tank A
sits on a flat platen 1e that has the hot water down tube la as an internal passage. In Figure 14 the same embodiment has the upper surface of platen 1e made convex for better thermal contact with the concave tank bottom.
One difficulty with cooling the too hot water lies in the fact that the temperature of the cold feed water varies with latitude and with season. For example ground temperature (and therefore cold water temperature) at around the 46th parallel can be as cold as 35°F in spring (1.6°C) while in fall, the same ground has a temperature of 45°F
(7.2°C). This means that the cooling of the hot water will be affected, being cooled more at northern latitudes and in the spring and less at southerly latitudes in the autumn. Thus the temperature of the delivered hot water 7a would also vary from, say, 120°F (48.8°C) to 130 °F
(54.4°C).
To overcome this obstacle, the heat exchanger 1 embodiment shown in Figs 1 and 2 may be angled from the vertical as shown by the embodiment shown in Fig 17, 18 and arranged to enable the outer tube 1b to move. The movement of tube 1b is controlled by the cold feed water temperature. Since cold water is more dense, it is heavier. Therefore the outer tube 1b will respond to the added weight and move away from inner tube la. This will enable some room for the mixture of cold- and warmed feed water to stratify, whereby at least some of the colder feed water flows adjacent the tube 1b wall out of contact with down tube la, thus reduce heat transfer and net cooling. Another way in which such automatic cooling compensation may be achieved is by use of a inner thrust surface 100 on outer sleeve 1b. Since cold water is heavier, the net force exerted by cold feed water 4 impinging against angled thrust surface 100 is greater than when the cold feed water 4 is warmer (southerly latitudes and autumn season). This will move the outer sleeve 1b away from down tube 1a and reduce cooling effect when water is coldest and, conversely, maximize cooling when cold feed water 4 is warmest. One or more spring element 101 may be used to bias the outer sleeve towards maximum cooling when the cold feed water 4 is warmest. Such spring elements may be of shape-memory alloy or bimetal so as to change the spacing between tube la and sleeve 1b in response to temperature change of the cold water 4 and/or of the temperature of the delivered water 7a. Also by choosing a plastic material for outer sleeve 1b that is more buoyant, and by using standoffs 101a (Fig 18), the outer sleeve 1b may be ideally positioned for maximum cooling under the warmest cold water conditions. Then when the cold feed water 4 is colder, the outer sleeve 1b will automatically move so as to reduce cooling thus maintaining a near constant temperature of delivered water 7a.
Figs 19, 24 shows the vector forces of angled heat exchanger 1 of Fig 18. In Fig 19 longer line 103 at the angle of the outer sleeve 1b represents the flow of colder feed water when it is heavier while in Fig 20 shorter line 103 represents the flow of the warmer feed water when it is lighter. When cold water (Fig 19) occupies the interior of outer tube 1b the gravitational pull 104 produces a usable side force represented by the horizontal line 105. The effect of this side force 105 is to move outer sleeve 1b a distance proportional to the weight of the cold water. As the cold water 4 becomes warmer, the side force is reduced (Fig 20) and therefore the outer sleeve 1b is moved less increasing cooling of the hot water flowing in down tube la.
This same automatic moving of outer sleeve 1b may be accomplished using angled thrust surface 100 where the heavier water creates maximum force to move outer sleeve 1b the maximum distance to reduce heat transfer to the minimum.
Opening if along outer sleeve 1b serves to allow cold feed water, heated from its cooling of hot water in down tube la, to escape into the proper layer of the stack, so as to not upset the stacking order in the tank.
Fig 15 and 16 show the same embodiment as Fig 1 with the addition of a temperature sensitive deflector 9a installed at the outlet of internal cold water delivery tube 9. Such a deflector could be adapted to other embodiments shown in Figs 2, 3, 3b, 4, 5, 6, 7, 8. The deflector responds to cold water temperature, moving to first limit 9c (dotted line) to deflect the flow 4b (dotted arrow) towards the hot water down tube la thereby providing maximum cooling when the cold feed water temperature is warmest as in the autumn. When the cold water gets to its coldest in springtime, deflector 9a straightens and moves towards second limit 9b to direct the cold feed water in a more vertical path 4c thereby reducing the cooling effect on the hot water. By this means the delivered hot water 7a can be held to within acceptable tolerances as the cold water temperature varies through the year.
A variation of temperature sensitive deflector 9a may be used to deflect flow from a single cold water source 9 into one or or more separate down tubes 1b (not shown).
Such a variation could be used on the embodiments shown in Figs 1, 12, 13, and 14 which use external heat exchanger 1, la.
While the above disclosure refers mainly to tank-type water heaters, it is clear that the same means can be applied for cooling too hot water in instantaneous or on-demand type water heaters, to achieve the same safety benefits.
Claims (12)
1. In a hot water heater having a reservoir, a cold water inlet, a hot water outlet and heating means, the improvement comprising a heat exchanger, said heat exchanger being arranged to exchange heat between water entering said cold water inlet and water exiting said hot water outlet.
2. The improvement of claim 1 wherein said heat exchanger comprises a first conduit arranged to receive hot water from an upper portion of said reservoir, and a second conduit extending from said cold water inlet, said first and second conduits being located proximate to each other such that hot water exiting through said first conduit will be cooled by cold water passing through said second conduit.
3. The improvement of claim 2 wherein said first and second conduits are concentric.
4. The improvement of claim 3 further including means to increase turbulent flow of a liquid within at least one of said first and second conduits.
5. The improvement of claim 3 wherein said first conduit is interior of said second conduit.
6. The improvement of claim 5 further including at least one opening in said second conduit to permit cold water flowing therethrough to enter said reservoir
7. The improvement of claim 1 wherein said heat exchanger comprises a first conduit arranged to receive hot water from an upper portion of said reservoir, said first conduit having a downwardly extending section extending proximate the bottom of said reservoir, and an upwardly extending section in fluid communication with said hot water outlet, said upwardly extending section being at least partially insulated.
8. The improvement of claim 7 further including a second conduit extending from said cold water inlet, said second conduit distributing cold water proximate lower portions of said downwardly and upwardly extending portions of said first conduit.
9. The improvement of claim 1 further including means to control the degree of heat exchange between cold water entering said cold water inlet and hot water exiting said hot water outlet.
10. The improvement of claim 2 wherein said heat exchanger includes means for controlling the heat exchange capability according to the temperature of cold water entering therein.
11. The improvement of claim 1 wherein said heat exchanger comprises a first conduit arranged to receive hot water from an upper portion of said reservoir, said first conduit extending exteriorly of said reservoir and being in contact with a portion thereof to cause said heat exchange.
12. A method for controlling the temperature of hot water exiting a hot water heater, the method comprising the step of removing hot water through a hot water conduit having an entry located proximate an upper portion of a hot water tank, and passing said hot water through a heat exchanger to cool said hot water and to heat cold water entering said hot water heater.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US40224302P | 2002-08-09 | 2002-08-09 | |
| US60/402,243 | 2002-08-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2422932A1 true CA2422932A1 (en) | 2004-02-09 |
Family
ID=31715814
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2422932 Abandoned CA2422932A1 (en) | 2002-08-09 | 2003-03-19 | Improvement to a hot water heater |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2422932A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107270529A (en) * | 2017-08-22 | 2017-10-20 | 吉林大学 | A kind of storage-type electric water heater attemperator |
| US10215445B1 (en) * | 2015-12-22 | 2019-02-26 | Bernard J Mottershead | Thermosiphon system for hot water heater |
| CN109425100A (en) * | 2017-08-25 | 2019-03-05 | 艾欧史密斯(中国)热水器有限公司 | Water heating mechanism |
-
2003
- 2003-03-19 CA CA 2422932 patent/CA2422932A1/en not_active Abandoned
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10215445B1 (en) * | 2015-12-22 | 2019-02-26 | Bernard J Mottershead | Thermosiphon system for hot water heater |
| US10794614B2 (en) | 2015-12-22 | 2020-10-06 | Bernard J. Mottershead | Thermosiphon system for hot water heater |
| CN107270529A (en) * | 2017-08-22 | 2017-10-20 | 吉林大学 | A kind of storage-type electric water heater attemperator |
| CN107270529B (en) * | 2017-08-22 | 2023-04-14 | 吉林大学 | Water storage type water heater heat preservation device |
| CN109425100A (en) * | 2017-08-25 | 2019-03-05 | 艾欧史密斯(中国)热水器有限公司 | Water heating mechanism |
| CN109425100B (en) * | 2017-08-25 | 2024-01-09 | 艾欧史密斯(中国)热水器有限公司 | Water heating mechanism |
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