Claims:
1. A hybrid storage water heater, comprising of:
a first water tank (inner tank) 3 with rubber partition completely surrounded by a second water tank (external tank) 2 in thermal communication with each other and connected such as to permit a thermal circulation of water between them;
a first electric heating element 7 disposed inside the said first tank 3 and a second electric heating element 6 disposed inside the said second tank 2 with different heating capacity assembeled over a base plate 5, each individually controlled by a separate thermostatic device responsive to the temperature of water in the said tanks;
a first, second and third heat transfer and circulation conduits (8,4,9) in fluid flow communication with each other, provided at a lower end of the second tank (external tank) 2 , upper portion and lower end of the first tank (inner tank) 3, respectively, wherein said cold water inlet 8 being connected to said first heat transfer and circulation conduit; an intermediate water inlet in communication with said second heat transfer and circulation conduit 4 provided over the upper portion of the said first tank 3 for flow of water from second tank 2 to first tank 3; and a hot water outlet 9 being connected to the third heat transfer and circulation conduit located at a lower end of the of said first tank 3.

2. The hybrid storage water heater as claimed in claim 1, wherein said first tank 3 is located within said second tank 2.

3. The hybrid storage water heater as claimed in claim 2 wherein said tanks (3,2) are coaxially located one within the other.

4. The hybrid storage water heater as claimed in claim 3 wherein said cold water inlet 8 and heated water outlet 9 are located at a lower portion of the second tank 2 and first tank 3 respectively and the intermediate water inlet 4 is located at a upper portion of the first tank 3.

5. The hybrid storage water heater as claimed in claim 1 wherein said first and said second heat transfer circulation conduits are composed of high heat conductivity metal pipes.

6. The hybrid storage water heater as claimed in claim 1 wherein said thermostatic devices are preset to operate at different temperatures.

7. The hybrid storage water heater as claimed in claim 1 wherein the second tank 2 is provided with anti corrosive coating.

8. The hybrid storage water heater as claimed in claim 1 wherein the heating element 7 disposed inside the first tank 3 is of high power capacity configured for rapid heating than of the heating element 6 disposed inside the second tank 2 configured for slow heating.

9. The hybrid storage water heater as claimed in claim 1 wherein the said water heater is configured for three different modes namely QUICK, ECO AND TURBO based on switching preference of the two heating elements.

10. The hybrid storage water heater as claimed in claim 1 wherein the said heater further includes at least one controller coupled with plurality of sensors configured for controlling the temperature of water separately at said individual tanks in real time.

, Description:
Field of the Invention
The present invention relates to hybrid storage water heaters. More particularly, the present invention relates to storage water heaters having at least two tanks preferably one inside the other with different volume operably connected for continuous supply and efficient water heating.

Description of the Related Art
A variety of water heaters are available, including storage water heaters, demand water heaters, heat pump water heaters, tankless coil water heaters, indirect water heaters, and solar water heaters. One of the most popular water heater designs is the storage tank water heater. The storage tank water heater stores heated water in a tank. The heated water is provided through an outlet from the tank, and is replaced by unheated water through an inlet to the tank. A control device, typically comprising a thermostat, monitors the water temperature in the tank and activates a heating device to heat the stored water when the stored water falls below a certain temperature.

Current water heaters are of below and as shown in Fig 1 are of three types
1. A simple immersion heating rod, which can be immersed in a water container
This being in open, does not have any safety mechanisms available to the user and therefore rarely used now a days.
2. Instant water heater with a small storage capacity of 1,2 or 3 Liters
This type is with higher capacity heating element like 3000 Watts and has the limitation of storage capacity. When heater is switched on, water in the small tank gets heated up rapidly. Hot water from instant heaters needs to be mixed with cold water to get a comfortable water temperature suitable for taking bath. If the water outlet is kept open heating will be slow. Therefore a trial and error mixing, checking of water temperature cycle is to be followed by the user. Safety protections like over temperature cut off is provided by almost all makers today. But time required to get sufficient amount of hot water is more and requires the user’s attention and intervention.
3. Storage water heaters of capacity 10/20/30 /50 or more Liters.
This is commonly used today. Generally are with lower capacity heating element like 1500-2000 Watts. Electrical, mechanical and thermal protection is provided to this type of heaters. Heater needs to be switched on for a long time to get sufficient hot water to take bath is a disadvantage.

Conventional storage water heater uses a tubular heating element to heat water in a tank. Water which is heated inside the tank stores heat energy absorbed from the heating element. As soon as the water reaches a comfortable set temperature, a thermostat switches off the heating element.

The water in the storage tank water heater cools from the drawing of heated water from the tank, which causes unheated water to flow into the tank, or from standby heat loss, which is caused by natural radiation heat loss. One way to minimize standby heat loss is by installing a water heater with a smaller storage tank. How small the water heater can be depends on the number of individuals to be served. For example, in a household of up to three individuals, a 50 L storage tank water heater is commonly recommended; in a household of more than three and up to seven individuals, an 80 L storage tank is commonly recommended.

When the user starts drawing hot water from the tank, fresh water is drawn from outside hence outflowing hot water is replaced by inflowing cold water. This will reduce the temperature of water in the tank below the set temperature and thermostat switches on the heater. Water in tank can not be maintained at a comfortable temperature when the heat carried away by the outflowing water is higher than the heat supplied by heating element, which results into limited water availability with the right temperature. If the quantity of hot water required is high, energy required by the heating element also increases.

In a prior art document, a Tiwanese Patent TW M478120U, titled “Improvement of Electric Water Heater” discloses a water heater in which hot water moves upwardly and cool water downwardly. This ensures a good mix of the hot and cold water, so that the eater body has generally uniform temperature. However, the water heater can only operate for a short intermittent periods of time, as the electric heater used cannot work continuously.

To solve this problem, a watertank is proposed which has a heating furnace core that is immersed in water inside the tank. The heating furnace core is able to contain a small sample of water in the tank. A tubular electric heating element is disposed within the heating furnace to heat up small sample of water in a relative short time. Steam pressure builds up in the tank which propels the hot water into an outlet in the base of the tank. However, hot water in the tank tends to rise while cool water sinks. Therefore, a layer of hot water is formed at the top of the tank which does not mix with cooler water at the bottom of the tank. As the outlet is in the base of the tank, this causes the water leaving the outlet to be cooler water, and the hotter water remains at the top of the tank. As a result, the temperature of the water expelled from the tank is not always hot enough.

Chinese Patent CN02149630.7 (WO2004/055447) titled “Environment –protectional instataneous water heating storage type electric water heater”, proposes a water storage tank containing a radiation heat collector. A water inlet tube and directs cool water into the radiation heat collector. The radiation heat collector comprises a hot water direct injecting tube, which, in turn, comprises a hot water injecting nozzle for dispensing hot water. In operation, water at the top of the water storage tank is drawn and mixed with hot water inside the collector by venturi principle (page 6, lines 5-18). Hot water dispensed from from the radiation heat collector is replaced by inflowing cool water. Therefore, the volume of water inside the radiation heat collector is constant. Consequently, the Venturi principle is not effective. In a direct injection circualating water storage” mode (page 6, line 19 to page 7, line 3), hot water inside the radiation het collector directly spurts to the top of the water storage tank. This keeps hot water at the top of the tank and does not encourage mixing of the water in the storage tank.

Chinese patent no 700034549 entitled “Storage Type Water Heater’’ (henceforth referred to as STWH) proposes a heating chamber containing a heating element, placed within a water storage tank towards the bottom. Inlets and outlets are structured in such a way that water circulates inside the tank and gets heated when hot water is not drawn from the outlet. However, when water is drawn, circulation is limited to the heating chamber with little or no role for the water tank.

Effectively, the heating chamber acts as an instant water heater. The only benefit of this configuration is in the situation where hot water is not drawn continuously. Depletion of stored heated water in smaller capacity storage tank water heaters is a common problem in a household demanding more than the recommend capacity of the water heater. For example, a 40 L water heater may adequately supply a household of two individuals with heated water; however, if the household infrequently requires a heightened demand, such as in the case of accommodating guests for several days, the same 40 L water heater may not be able to adequately supply the household with heated water. Purchasing a larger water heater for the household may be wasteful, however, as the heightened demand occurs only infrequently, and the larger capacity water heater has a greater standby heat loss. Likewise, connecting another separate water heater in series with the original 40 gallon water heater will also result in additional standby heat loss.

There exists a second category of electrical water heaters, namely the so-called instant- or flow-heaters, which comprise a small vessel installed at the immediate vicinity of the hot water tap and which are adapted to be actuated by the consumption of water through the tap. Closing the tap automatically deactivates the heating element. These devices require a relatively high power heating element (of about 5 KW) in order to instantly raise the temperature of the water flowing therethrough. Besides the high rated electrical element (which frequently requires a special electrical installation), there is another disadvantage, namely, that there is no possibility to mix the instantly heated water with the cold mains water supply in order to regulate the temperature of the consumed water.

Still another deficiency of the flow heaters resides in that the heating element is usually built-in within the device and therefore not easily replaced in case of its burning up or other failure.

Object of invention
It is the general object of the present invention to overcome the disadvantages of the above-mentioned conventional storage as well as flow domestic water heaters.
It is an object of the invention to provide a relatively small and therefore more aesthetic and space-saving hybrid storage water heater, which will function both as a storage water heater and as a flow water heater using the existing installation of the conventional large and cumbersome domestic storage heater, and which is readily replaceable for such storage heaters.

Another object of this invention is to achieve continuous flow of hot water.

Another object of this invention is a Water heater which consumes minimum electric power.

Another object of this invention is to achieve flexibility in operation & able to supply quantity of hot water depending on the user requirement.

Another object of this invention is to operate the heater at different modes such as Quick (Instant), Eco (Storage) and Turbo (Hybrid) from the same water heater for the convenience of different type of needs of the users.

SUMMARY of the invention
Herein disclosed is a hybrid storage water heater for providing heated water to one or more users including a first tank (inner tank) enclosed inside a second tank (outer tank) and a mode selection device that is operable to switch between a plurality of modes. The first tank is for storing water in a turbo heated state and for providing water in the heated state during the said modes. The second tank is for storing water in an unheated state. During the selected modes, storing water in a heated state at a particular temperature and for providing water in the heated state in a particular mode.

According to the invention there is provided an electric water heater, particularly for domestic use, having a cold water inlet and a heated water outlet, comprising: first and second water heating tanks wherein the first tank is completely surrounded by the second tank i.e. one inside the other and in thermal communication with each other such as to permit a thermal circulation of water between them; and at least one first electric heating element provided within the first tank and another second heating heating element provided within the second tank, each individually controlled by a separate thermostatic device responsive to a preset temperature in each of the said tanks. The water heater further includes first, second and third heat transfer and circulation conduits in fluid-flow communication with each other, provided at a lower portion of the second tank as inlet and lower and upper portion of the first tank, respectively, said cold water inlet being connected to said first circulation conduit at second tank; another intermediate inlet in communication with a second conduit provided within said first tank for supplying water flowing through said second circulation conduit to said first tank; and a water outlet through a third conduit located at a lower portion of said first tank and connected to said heated water outlet.

According to a preferred embodiment of the invention the said first and second tanks are cylindrical, coaxially located one within the other, and said cold water inlet is located at a lower portion of the second tank and heated water outlet is located at the upper portion of the first tank, the intermediate water inlet is located at a upper portion of the first tank, in fluid connection from upper portion of the second tank.

According to an exemplary embodiment, the shape and configuration of the herein discussed hybrid storage water heater can be designed to have an aesthetic look and to accommodate all the technical features like inlet outlet heating elements insulation etc, discussed in detail here under. Further the heat transfer circulation conduits are composed of high heat conductivity metal pipes.

The said separate thermostatic devices are preset to operate at different temperatures, advantageously and further connected with microcontroller pre-programmed for three different modes and can be controlled from remote location, respectively.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 is a pictorial view of different water heaters available in market as prior art;
FIG. 2(a) is a schematic view of a hybrid storage water heater including a first tank positioned inside a second tank, wherein both tanks are heated by electric heating elements;
FIG. 2(b) is a pictorial view of a hybrid storage water heater including a first tank positioned inside a second tank, wherein both tanks are heated by electric heating elements;
FIG. 3 (a) is a schematic view of water flow diagram of the hybrid storage water heater in accordance with the present invention;
FIG. 3(b) is a block diagram of the hybrid storage water heater in accordance with the present invention;
FIG. 3(c) is a flow diagram of the working of the hybrid storage water heater in accordance with the present invention;
FIG. 4 is a block diagram illustrating different modes of heating of the hybrid storage water heater in accordance with the present invention;
Fig 5 is a graphical representation of the test results of the hybrid storage water heater in accordance with the present invention;
FIG. 6 is a block diagram of hybrid storage water heater system including a remotely located mode selection device operable to receive manual selection data and selection data over a network.

DETAILED DESCRIPTION
Hybrid Storage water heater as disclosed herein has an external water tank with suitable anti corrosion coating with water inlet and outlet provided at bottom. There is provided an inner mini tank with suitable capacity heating element and temperature sensing device for required thermal protection. Heating element of suitable lower power capacity is provided in the external tank along with temperature sensing device for protection. Also disclosed is a method is capable of providing water at right temperature quickly and continuously to the user.

Fig. 2 is a schematic and pictorial view and of a first embodiment of a multi-tank water heater. The storage water heater includes a first tank (inner water tank) with rubber partition 3 which is completely surrounded by a second tank 2 (external water tank )which is provided with outer core insulator shell i.e body shell 1 providing a insulated covering for a tank 2 having a first inlet 8. Both the tanks posses separate heating elements viz 6 and 7 assembled over a base plate of heating elements 5. The only one hot water outlet pipe conduit is connected from the first tank 9. The inlet conduit of the first tank with rubber partition 4 is in thermal communication with the second tank from the upper corner such that the water is filled in the first tank 3 after filling of the water in the second tank 2. In order to have an efficient and continuous flow of water the first tank 3 is preferably disposed near the top inner portion of the second tank 2. The outlet conduit 9 and the inlet conduit 8 are connected with first tank 3 and second tank 2 separately. Heated water is drawn from the outlet conduit 9, which causes water to enter the top of the inlet conduit 4 of the first tank 3 from the inlet conduit 8 of the second tank 2.

As shown in Fig 3, the water flow according to an embodiment of the present invention having a cold water / room temperature inlet 8 and a heated water outlet 9 through second and first tanks respectively which are in thermal communication with each other such as to permit a thermal circulation of water between them. Each of the said first and second tanks are provided with separate heating elements preferably of different power ratings and at least one first electric heating element provided within the first tank and another second heating heating element provided within the second tank, each individually controlled by a separate thermostatic device responsive to the temperature of water in each of the said tanks. Since the arrangement of the said tanks are made one inside the other, there are possible first, second and third heat transfer and circulation conduits in fluid-flow communication with each other. The first heat exchanging and circulation is provided at a lower portion of the second tank when the heating element 6 is activated. The second heat transfer and circulation is provided at the inlet 4 of the first tank which is at upper portion of the both first and second tank. The third heat transfer and circulation is provided inside the first tank when the heating element 7 is activated.

Therefore the storage water heater with a hybrid heating disclosed herein provides the user with hot water at comfortable water temperature for bathing. User’s intervention in temperature monitoring and mixing of hot water with cold water is not required as this heater provides temperature comfortable for bathing. Heater is also capable of providing hot water continuously at the right temperature from the time the heater is switched on. Hot water flow of min. 3 L/Min is sufficient for the user for his /her needs. Waiting time to get hot water with right temperature is reduced to 3 minutes.

There is no danger of extra hot water falling accidentally on the body as in case of instant water heater or cold water falling on the body as in case of storage water heater.

In an embodiment the storage water heater disclosed has an second tank 2 (external water tank) is provided with suitable anti corrosion coating with water inlet conduit 8 provided at bottom. Heating element 6 of suitable lower power capacity is provided in the second tank 2(external tank) along with temperature sensing device (not shown) for protection. Mechanical Safety valve (not shown) is provided along with the water pipe. There is also provided a first tank 3 (inner tank) with suitable capacity heating element preferably greater (double) than the capacity of heating element connected with the second tank 2 (External tank) and another temperature sensing device (not shown) for thermal protection. The first tank 3 (Inner tank) is enclosed in an insulating material like rubber padding which prevents the heat flow from inner to outer tank through the body of first tank to second tank.

The rating capacity of heating elements will vary depending on the tank capacity and water flow requirement.

The first tank 3 (Inner tank) and heating element 7 provides rapid heating. The second tank 2 (external tank) and heating element 6 provides mass heating. There is a heat flow from the rapid heating region to the rest of the tank. Rapid heating region, slow heating region and continuous water flow in and out together does the hot and cold water mixing within the tank. Temperature sensors provided in the second tank 2 (external tank) controls the max temperature in the whole tank. Even if the water is not drawn, temperature remains constant and heater is cut off.
This method is capable of providing water at right temperature quickly and continuously to the user. When inner water heater 7 is energized, user can get quick supply of hot water. This provides the user with convenience of instant supply. When the external heater 6 is energized it provides the user with the convenience of large amount of water as in a storage water heater. If the user chooses to get a continuous water supply of large quantity, both the modes can be activated.

Hence three modes of selection is available to the user, which can be provided by switching ON/OFF the pair of heating elements provided inside the different tanks at different times as shown in Fig 3 namely:
1. Quick (Instant)
2. Eco (Storage) and
3. Turbo (Hybrid)

Process Flow for said water heater as shown in Fig 3(c):
Step 1: Cold or room temperature Water from continuous feed pipe will enter in water inlet pipe (8)
Step 2: Water is entered in External Tank (2 heating tank) through water inlet pipe (8)
Step 3: If the heating element (6) is turned ‘on’, then water in External Tank 2 (2 heating tank) will be heated by heating element (6)
Step 4: Water now enters in inlet of rubber partition (4). This acts as a outlet for tank (2 heating tank)
Step 5: Water is entered in Inner tank (3 Rubber Partition) through inlet of rubber partition (4).
Step 6: If the heating element (7) is turned ‘on’, then water in Inner Tank (3 Rubber Partition) will be heated by heating element (7)
Step 7: Hot water now enters in Oulet Pipe (9). This acts as an outlet for Inner Tank (3 Rubber Partition) as well as oulet (Delivery) of the Water Heater Unit.
Step 8: The water from oulet pipe is a Hot water delivery by Water heater Unit.
This hot water is then routed to faucets or showers or mixer or as per need of the customer for bathing water.
The heat loss from Outer Tank to the external surrounding is prevented / minimised with help of provision of thermally insulating foam material in between the Outer tank and the exterior body of the water heater unit. To avoid any gaps and air blocks in this foam insulation and to improve the effectiveness of the thermal insulation, this foam is in-situ injected in-between the Outer tank and the exterior body.

Hybrid water heater will therfore consume less power compared to the cited water heaters as evident from the graphical representation shown in Fig 6. Moreover current prior art solutions cannot provide quick and continuous hot water supply to the user.

Current user requirements:
1. User requirements vary depending on the number of people in the household, geometric location, occupation and time constraints of each individual.
i) A nuclear family which has max four members – require less hot water but in a short period. Require at least 30 L of hot water every 15-30 min.
ii) All working family who has morning time constraints – Needs water in short period 25-35 L every 10-15 min
iii) A big family where number of people are more who require higher amount of hot water per family at least every 30 min – 1 hour interval
iv) Geometric location where ambient temperature is drastically different – getting hot water to full fill above needs is a challenge for all groups

In an embodiment, a first controller is coupled to a sensor to monitor the water temperature in the first tank. A second controller is coupled to a sensor to monitor the water temperature in the second tank. The first controller and second controller are configured to deactivate the first and second electric heating element if the temperature of the water in the first tank reaches a certain high reference temperature in real time and remotely.

In another embodiment, there is provided a microcontroller which is programmed to operate the hybrid storage in accordance with the three modes preferably Quick (Instant), Eco (Storage) and Turbo (Hybrid). Further , the high reference temperature can be set to prevent any accidents. The microcontroller can also be controlled from a remote location using IOT. A person skilled in the art will be able to appreciate the various technical features described herein and workout the same without any diffficulty.

The first and second controllers may be combined in one unit and further connected with a display. Thus, a single controller can be connected to the sensors and provide switching to both the heating elements. The single controller thereby controls the heating of both the first and second tanks in the different modes accordingly as discussed above. Likewise, the switching device can be combined with the single controller, thus placing all electronics, control circuitry and valves in a single control device.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.