DESC:Field of Invention
The present invention relates to an electric water heater, particularly a multimode water heater with atleast an Instant and Storage mode of operation.
Background of the Invention
The following background discussion includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Requirement of hot water is very common for daily household tasks. Water heaters or water geysers are common appliances useful for meeting hot water requirements in daily life. Although these appliances provide continuous supply of hot water but the bottleneck with existing geysers and water heaters is with their power consumption and time involved in heating sufficient amount of water in shorter duration.

The storage water heaters for residential purpose in India come in 6,10,15,25,35,50,70,100,140 and 200 litres capacity (capacities defined in IS 2082). Market study has shown that 15L and 25L capacity water heaters are most popular for residential use. Most water heaters use a 2kW or 3kW heating element to heat water since most houses in India are not equipped to handle electrical load of more than 4 to 5kW. The problem with water heaters of capacity 15L and more is that they take a significant amount of time to heat water from ambient temperature to 75ºC. Below table shows time required to heat water for different capacities:

In the above table, the time to heat water has been calculated using the formula:
E= Pt = mCp? T ........ Equation (1)
Where:
E = energy in kJ
P = Power of heating element in kW
t = time in seconds
m = mass in kg
Cp = specific Heat Capacity of water = 4.184 kJ/ºC/kg
?T = difference in initial and final temperature
assuming the initial water temperature to be 25ºC, final water temperature till thermostat cuts off the power supply is 75ºC and the heating element is positioned at the bottom of the water heater tank such that all the water inside the tank heats up uniformly.

The values in above table shows that for capacity of 15L tank, it takes 26.13 minutes with 2kW heating element and 17.42 minutes with 3kW heating element to heat the water. For higher capacities, the time to heat water is even higher. This means that a user of any product of 15L capacity or higher has to wait for long duration to get hot water from the water heater. This excessive waiting time for hot water is a problem for the user.

There are various water heaters available in the market. One type is tank-less water heaters. US9702585 discloses tank-less electric water heaters.

US 20170251528 discloses electric water heater in which electromagnetic pulse waves are used for heating. The device comprises a housing including an upper cover and a lower shell, and a metal guide tube and a magnetic coil both of which are mounted in the housing.

However, these water heaters suffer with a drawback that they don’t have any provision to provide hot water when needed with immediate effect or in very short time duration. The Instant water heaters that are available in the market, have small capacity tanks (1L to 3L) and can provide hot water very quickly but they cannot heat and store large quantity of water (15L or more). Thus, there is a need for a water heater that can provide both functionalities of storage as well as an instant water heater, and which is also energy efficient and economically viable.

Object(s) of the Invention
An object of the present invention is to provide a highly efficient multi-mode water heater with atleast “Instant” and “Storage” mode for heating water.
Yet another object of the present invention is to provide a highly efficient multi-mode water heater with a provision to heat quickly a small amount of water, when the user chooses to use Instant mode, to a temperature of approximately 75 degree Celsius irrespective of the total capacity of water heater.
Yet another object of the present invention is to provide a highly efficient multi-mode water heater which will be able to heat and provide minimum 5 liters of water at 72°C in less than 10 minutes for an inlet water temperature of 25°C.
Yet another object of the present invention is to provide an energy saving multi-mode water heater.
Yet another object of the present invention is to provide a highly efficient multi-mode water heater where 5 minutes of heating is sufficient to provide 25L of water above 400C for an inlet water temperature of 250C when withdrawn at 3 liters per minute (flow to be started after initial 5 minutes heating) while the water heater is kept in Instant mode.
Yet another object of the present invention is to provide a highly efficient multi-mode water heater with electronic controls that can keep the water inside the tank to a fixed pre-heated temperature when the ambient temperature decreases to low levels, so that the water heater can provide hot water quickly in the Instant mode.
Yet another object of the present invention is to provide a highly efficient multi-mode water heater with an electronic thermostat for the top heating element with very low differential i.e. very less difference between thermostat cut-off and cut-in temperatures (For example, cut-off temperature can be set at 750C and cut-in can be set at 740C so that the differential is just 10C) so that the top heating element has a very quick response to temperature change.
Yet another object of the present invention is to provide a cost effective multi-mode water heater.

Summary of the Invention
In an aspect of the Invention, there is provided a water heater with multiple modes of operation comprising:
a) an external body comprising a water storage tank encapsulated with a layer of heat insulating material;
b) said storage tank comprising:
i) atleast a top section (A1),
ii) atleast a bottom section (A2) comprising atleast a sacrificial anode protecting tank steel against corrosion (B), atleast an Inlet pipe providing cold water to the bottom part of the tank (C), atleast an Outlet pipe (D) with orifice (D1) for withdrawing hot water from the top of said storage tank (A)
iii) optionally a cylindrical shell (A3) connecting said top ellipsoidal head to bottom ellipsoidal head,

iv) Heating assembly comprising atleast 2 heating elements;

where atleast a bottom heating element (E) is installed near the inlet pipe at the location (E1) of bottom part of said storage tank (A) where the vertical distance between said location of bottom heating element (E1) and orifice (D1) of said outlet pipe (D) is defined as “m”;

wherein atleast one top heating element (F) is installed at the location (F1) of top section of said storage tank (A) where the vertical distance between said location of heating element (F1) and orifice (D1) of said outlet pipe (D) is defined as “n”;

wherein the location of bottom heating element and the top heating element varies with respect to the equation n < m/2;
and wherein n >50mm.

In another aspect of the Invention, there is provided a method of operating the water heater with multiple modes of operation comprising the steps of:
a) selecting the mode of operation from Instant or Storage mode through switch (K) where activating said switch (K) in Instant mode cuts-off power supply to the bottom heating element and supplies power to only the top heating element causing small quantity of water to be heated quickly for instant use;

b) activating switch (K) in Storage mode causes a top thermostat to divert power from the top heating element to bottom heating element, when the top thermostat senses a threshold temperature, for heating the complete volume of water for regular use.

Brief Description of the Drawings
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings in which:
Figure 1 (a) illustrates construction of water heater, according to an embodiment of the present invention
Figure 1 (b) illustrates prototype tank with 4 spuds for heating element where bottom most spud is for the regular heating element. The effect of position of top heating element was studied by assembling the heating element in the top 3 spuds. The ‘n’ values as shown in the figure are explained in the ‘detailed description’ section below.
Figure 2 illustrates (a) Front view of inside construction (b) Side view of Inside construction.
Figure 3 illustrates wiring diagram, according to an embodiment of the present invention.
Figure 4 illustrates flow chart for functioning of water heater. Here, TG represents temperature in °C as measured by thermal cut-out G, TH represents temperature in °C as measured by SPDT (Single Pole Double Throw) thermostat H and TJ represents Temperature in °C as measured by thermostat J.
The following figures (5 to 8) should be read in conjunction with the ‘Experiments and Results’ section to completely understand their context.
Figure 5 illustrates heating time graph representing water temperature (0C) at top of tank vs. time (minutes) for n=98mm and Instant mode
Figure 6 illustrates Hot Water Output graph representing outlet water temperature (0C ) vs. water volume (litres) for n=98mm and Instant mode
Figure 7 illustrates Continuous water flow graph representing bucket water temperature (0C ) vs. water volume (litres) for n=98mm and Instant mode
Figure 8 illustrates result of the effect of position of top heating element when assembled in the second from the top spud where figure 8(a) illustrates water temperature versus time graph and figure 8(b) illustrates outlet water temperature versus volume of water withdrawn. The results illustrated are for n=158mm and Instant mode
All temperature values shown in the graphs have been measured in degree Celsius.
Detailed Description of the Invention:
The present invention provides an electric water heater, particularly a multi-mode water heater with atleast an Instant and Storage mode and its method of operation.
The water heater is technically advantageous with the provision to heat only a small amount of water as desired by the user, to a temperature of approximately 750C irrespective of the total capacity of water heater.
An embodiment of this particular water heater which was used to do this study is shown in Figures 1 and 2. This embodiment shows a vertical water heater. This should not be taken to limit the scope of this study. Alternate embodiments, including but not limited to horizontal water heaters, can also be used to derive the claims mentioned in this study. In an embodiment of the horizontal water heaters, the top and the bottom section of the vertical water heaters will correspond to the left and right section of the horizontal water heaters respectively.

In an embodiment, the water heater with multiple mode of operation comprising:

a) an external body comprising a water storage tank encapsulated with a layer of heat insulating material;
b) said storage tank (A) comprising:
i) atleast a top section (A1),
ii) atleast a bottom section (A2) comprising atleast a sacrificial anode (B) protecting tank steel against corrosion , atleast an inlet pipe (C) providing cold water to the bottom part of the tank , atleast an outlet pipe (D) with orifice (D1) for withdrawing hot water from the top of said storage tank (A)
iii) optionally a cylindrical shell (A3) connecting said top ellipsoidal head to bottom ellipsoidal head, In absence of the cylindrical shell, the two heads can be welded together.

iv) Heating assembly comprising atleast 2 heating elements;

where atleast a bottom heating element (E) is installed near the inlet pipe at the location (E1) of bottom part of said storage tank (A) where the vertical distance between said location of bottom heating element (E1) and orifice (D1) of said outlet pipe (D) is defined as “m”;

wherein atleast one top heating element (F) is installed at the location (F1) of top section of said storage tank (A) where the vertical distance between said location of heating element (F1) and orifice (D1) of said outlet pipe (D) is defined as “n”;

wherein the location of bottom heating element and the top heating element varies with respect to the equation n < m/2;
and wherein n > 50mm.

In an embodiment, mode of operation comprises atleast an Instant/Immediate mode and a Storage/Regular mode.

In another embodiment, the water heater comprises atleast a mechanical or electronic switch for switching between said mode/s.

In another embodiment, the water heater comprises safety device for cutting off power supply to said heating elements in case the temperature of the water exceeds a threshold temperature 1.

In another embodiment, the safety device comprises atleast a thermostat, atleast a thermal cut-off.

In another embodiment, the insulating material comprises foam and like material.

In another embodiment, the external body and said tank are connected with respect to said inlet pipe (C) for the entry of cold water to the bottom part of said tank, an outlet pipe (D) for withdrawing hot water from the top of said tank (A).

In another embodiment, the water heater comprises a Ready mode for operation wherein said Ready mode switches ON and OFF said bottom heating element (E) as required to maintain the temperature of water inside the tank at constant 250C.

In an embodiment, the water heater comprises a steel tank of 25L capacity for storing water. For alternate embodiments, different capacities and different materials can be used for the construction of the tank. In this embodiment (illustrated in Figure 1), the tank comprises of atleast 3 parts i.e. top ellipsoidal head (A1), bottom ellipsoidal head (A2) and a cylindrical shell (A3). The bottom head comprises of atleast 3 spuds welded to it for assembly of:

1. atleast a sacrificial anode that protects tank steel against corrosion (B)
2. atleast an Inlet pipe that provides cold water to the bottom part of the tank (C)
3. atleast an Outlet pipe that is used to withdraw hot water from the top of the tank (D)

In this embodiment, the cylindrical shell (A3) comprises of atleast 2 spuds for assembly of the heating elements. One spud is located at the bottom part of the shell (A3). The heating element (E) is assembled in this spud sitting at the bottom part of the shell near the inlet pipe. In an alternate embodiment, the spud can also be located on the bottom head (A2).

In such embodiments, the vertical distance between the orifice (D1) of the outlet pipe (D) and the location (E1) where the bottom heating element (E) is assembled to the tank (A1 or A2 or A3) is defined as m. The vertical distance is with reference to the placement of the water heater when it is mounted in the same position as it is intended to be installed at the user’s place. The water heater, in order to provide best results, has the bottom heating element (E) placed as close as possible to the bottom of the tank for effective heating of water inside the tank. When water heats inside a tank, its density decreases and it rises to the top while cold water moves down. Therefore, if heating happens at the bottom of tank, it ensures that all water inside the tank gets heated.

The second spud is placed near the top of the tank and is welded to the shell (A3) in this embodiment. In another embodiment, it can also be welded to the top head (A1). This placement of the second heating element (F) provides enhanced technical effect as the heating element assembled to this spud is used for heating less than half the water that the tank can hold. The vertical distance between the orifice (D1) of the outlet pipe (D) and the location (F1) where the top heating element (F) is assembled to the tank (A1 or A2 or A3) is defined as n. The vertical distance is with reference to the placement of the water heater when it is mounted in the same position as it is intended to be installed in the customer place.

The distance n is most important for water heater to give efficient result in terms of obtaining small quantity of heated water in smaller duration. The distance n defines the functionality and the benefit of having the second top heating element (F). The condition for distance n, for efficient use of the second heating element (F), is defined as following:

n>50mm, however, ----- Equation (2)

In an embodiment, any alternate construction with m and n satisfying equation (2) can be used to get the benefits of using the top heating element to heat quickly a smaller amount of water as compared to heating the full tank using the bottom heating element. The heating elements for top and bottom can be designed in any power rating that meets the requirement of the end user.

In another embodiment, the construction/structure of the water heater is not limited to a specific construction. The water heater may have any possible construction/structure qualifying the requirement where n >50mm however should also qualify as

The specific value of “n” i.e. the distance between the top heating element and the orifice of the outlet pipe should not be less than 50 mm so that the top heating element is always submerged in water. If the position of “n” is lesser than 50 mm, it would pose a risk of ‘dry firing’. ‘Dry firing’ means that the heating element is powered ON while not being completely submerged in water. This is very risky as the high heat energy from the heating element can cause fire and severe damage to the water heater and its surroundings.

Working of Water Heater:
In an aspect of the Invention, there is provided a method of operation of the water heater.
In an embodiment, the method of operating the water heater with multiple modes of operation comprising the steps of:

a) selecting the mode of operation from Instant or Storage mode through switch (K) where activating said switch (K) in Instant mode cuts-off power supply to the bottom heating element and supplies power to only the top heating element causing small quantity of water to be heated quickly for instant use;

b) activating switch (K) in Storage mode causes a top thermostat to divert power from the top heating element to bottom heating element, when the top thermostat senses a threshold temperature, for heating the complete volume of water for regular use.

Figure 3 illustrates wiring diagram for the water heater, as one of the preferred embodiment of the present Invention. The thermal cutout (G) is a safety device that cuts off power supply to the heating elements if the temperature of water goes above 900C (or any other pre-fixed temperature). The SPDT (single pole double throw) thermostat (H) is used to divert power supply from top heating element (F) to bottom heating element (E) when SPDT thermostat (H) reads a temperature of 750C (or any other pre-fixed temperature).
The water heater comprises switch (K) that allows user to choose between 2 modes: Instant mode and Storage mode. In Storage mode, switch (K) allows power to be supplied to bottom heating element (E) when SPDT thermostat (H) diverts power from top heating element (F) to bottom heating element (E). In Instant mode, switch (K) does not allow power to be supplied to bottom heating element (E) in any condition. This means that when the end user chooses Instant mode, only top heating element (F) gets power supply. Thus, the water heater is capable of acting both as an instant and a storage water heater, depending on the position of switch (K). When user needs instant hot water, he/she will be able to choose Instant mode which will heat a small quantity of water very quickly while when user wants to use the product as a regular storage water heater, he/she will be able to choose Storage mode which will heat all the water in the tank i.e. make the product work like a regular storage water heater.

An embodiment of the water heater comprises Thermostat (J) which is used to cut-off power supply to the bottom heating element (E) when the temperature reaches a certain pre-specified value.
Figure 4 illustrates flowchart explaining the working of this product. The switch (K) dictates when the customer is using the product in Instant or Storage mode.
In an alternate embodiment, the SPDT thermostat can be replaced by a regular SPST (single pole single throw) thermostat (similar to thermostat J) and the switch (K) can be modified to be used as a switch to give electric power either to the top heating element (F) for Instant mode or bottom heating element (E) for Storage mode.
In another embodiment, the mechanical switch K can be replaced by an electronic control which can have an additional Ready mode for places where the ambient temperature goes very low.
In an embodiment, the Ready mode switches ON and OFF the bottom heating element (E) as required to maintain the temperature of water inside the tank at constant 250C. This will ensure that the user gets the benefit of Instant mode even in very low ambient temperature condition.

In another embodiment, the water heater employs electronic thermostats using thermistors to sense temperature and power circuit boards to control the heating elements. This can have the advantage of having very close cut-in (temperature at which the heating element switches on) and cut-off (temperature at which the heating element switches off) temperatures, especially for the top heating element. A temperature differential (between cut-in and cut-off) of 10C can provide quick response from the top heating element which is an added benefit for the user. With mechanical thermostats, it is difficult to achieve a temperature differential of less than 50C with good accuracy and repeatability.

The Invention is further described with the help of non-limiting examples:
In an embodiment, where m = 312 mm, using equation (2), the condition of n is < 156 mm. For n=156 mm, with only the top heating element (F) in ON condition, around half the water inside the tank will be heated and it will take half the time to heat water to a specific temperature compared to when the bottom heating element is switched ON. As the value of n decreases, the top heating element heats lesser amount of water and subsequently the time to heat water to a specific temperature will keep decreasing. This has been substantiated with experiments considering different values of n and the results have been discussed as henceforth.
In this embodiment, n = 98 mm has been used, keeping in mind the objective of hot water within 10 minutes and some manufacturing constraints.

In this embodiment, the heating elements of 3 kilowatt power rating were used in both top and bottom positions.
Following examples demonstrates the experiments conducted to verify the performance of this water heater.
Example 1:
This particular experiment was done to study the role of the position of the top heating element (F) in the water heater which in turn shows the significance of the value of n. Fig. 1 (b) shows 3 different positions for the top heating element (F) that were studied.

a.) As option 1, the top heating element (F) was installed in the top most spud. For this position, n= 98mm. The top heating element (F) was switched ON to heat water by selecting Instant mode using switch (K). The top heating element (F) was switched off as soon as the water temperature reached 75°C, as measured at the top (D1) of the outlet pipe (D). The temperature increase was measured and recorded. Results are shown in Fig. 5. It was observed that it took 8.5 minutes to heat water from 310C to 750C.
This experiment showed that with the top heating element of 3kW power rating and n = 98mm, it took 8.5 minutes to heat water from 31°C to 75°C (Fig. 5). This is a temperature increase of 44°C. For an inlet water temperature of 25°C, the time taken to reach 75°C can be calculated by the following formula:

:

This shows that for an inlet water temperature of 25°C and volume of 25 liters of water, the water heater when operating in Instant mode, can heat water to 75°C in less than 10 minutes.
Continuing the experiment after the water temperature reached 75°C as measured at (D1), water was withdrawn from the water heater through the outlet pipe (D) at a flow rate of 3 liters per minute (the water heater was kept in OFF condition during this). Simultaneously, cold water entered the water heater through the inlet pipe (C) at a temperature of 31°C at the same flow rate of 3 liters per minute. There was almost no mixing of the cold water from inlet with the hot water at the top of tank because the inlet (C) is located at the bottom of the tank and the flow rate was low. A total of 25 liters of water was withdrawn which is same as the volume of the tank. The temperature of water at the outlet pipe orifice (D1) was measured every one second during the flow and recorded simultaneously.

Fig. 6 shows the results of this experiment where it is evident that more than 5 liters of water was at a temperature higher than 70°C. It was calculated from data that the average temperature of first 5 liters of water that was withdrawn from the water heater was 74.46°C.

b.) As option 2, the top heating element (F) was now installed at spud 2 with n = 158mm. This value of n is very close to the critical value of n < 156mm as calculated from equation 2. Fig. 8(a) shows heating time and fig. 8(b) shows the hot water output. It was observed that the hot water output had increased but the time to heat water to 750C had also increased to more than 12 minutes. This proves that as the value of n increases, the top heating element (F) becomes less effective in providing hot water quickly. This is the basis of the definition of equation 2.

c.) Option 3 where n is equal to 185 mm, it can be easily inferred that it will take more time for heating water to 75°C as the amount of water that will be heated will increase further.

Inference: From these set of experiments, it can be inferred that it is essential to have a low value of n to get the benefit of quick hot water. With n=98mm, it is possible to heat small amount of water (approximately 5 liters) from 250C to 750C in less than 10 minutes.

Example 2:
This experiment was done with continuous flow of water to show the practical advantage of having the top heating element (F) with a low value of n. n= 98mm was used for this experiment.
The water heater was put in Instant mode and switched ON. The top heating element (F) got switched on and water was heated for 5 minutes and then water was withdrawn through outlet pipe (D) while the heating element (F) was kept switched ON. This allowed the cold water to get heated before being withdrawn from the tank. 50 litres of water was withdrawn and collected in a plastic bucket. This situation was made to replicate the normal water heater usage in an Indian household. The temperature of the water in the bucket was measured every one second throughout the flow time and recorded simultaneously. This experiment was repeated at different flow rates. The experiment was conducted at 3,4,5,6 and 7 litres per minute (LPM). The flow rates were manually set and therefore the actual flow rates were slightly different from the intended ones. Figure no. 7 illustrates flow rates and the final temperature of the water in the bucket which decreased as the flow rate was increased.

From the data of figure 7, the average temperature of first 25L of water withdrawn was calculated. At 3 litres per minute, the temperature of first 25L of water collected in the bucket was 490C. The inlet temperature was 310C. Since water heating is a linear function as seen from equation (1), the final temperature of 25L water in the bucket will be 430C if the inlet water temperature is 250C.

Inference: 5 minutes of heating was sufficient to provide 25L of water at 430C for an inlet water temperature of 250C when withdrawn at 3 litres per minute when the water heater was kept in Instant mode. This quantity of hot water is enough to fill a regular 25L bucket in a typical Indian bathroom which can be used for a quick bath. This shows the practical advantage of having a top heating element with low n value (n=98mm for this specific study) and using the water heater in Instant mode where only the top heating element (F) gets power supply.

All experiments in this study were done with mechanical controls (mechanical thermostats and mechanical switch (K)) to meet the objective of a cost-effective water heater. In alternate embodiments, electronic controls can be used to further improve upon the benefits illustrated in this study.

Example 3:
The water heater behaves as a conventional regular water heater when used in Storage mode. Thus, the energy consumed by the water heater used in Instant v/s Storage mode was compared.
The energy consumed for heating water from 25°C to 75°C under Instant mode (for n=98mm) can be calculated by the following formula:

Time = 9.66 minutes has been used from equation (3).

From equation 1 it is known that the energy required to heat full tank of 25L of water from 25°C to 75°C is 5230kJ, which illustrates that the water heater, with the top heating element at position with n=98mm, reduces energy consumption by more than 3 times (by reducing the amount of hot water that is heated).

Inference: From the above equation, it is evident that in Instant mode, the water heater uses 1737 kJ of energy while in Storage mode it uses 5230 kJ of energy so there is a huge energy benefit when the water heater is used in Instant mode. This save in energy is due to the lesser quantity of water being heated in Instant mode. So when the consumer wants only a small amount of hot water, he/she can use Instant mode and save energy instead of heating all the water in the tank, that would happen in a regular water heater or when this water heater is used in Storage mode.
,CLAIMS:We Claim:

1. A water heater with multiple modes of operation comprising:
a) an external body comprising a water storage tank encapsulated with a layer of heat insulating material;
b) said storage tank comprising:
i) atleast a top section (A1),
ii) atleast a bottom section (A2) comprising atleast a sacrificial anode protecting steel tank against corrosion (B), atleast an Inlet pipe providing cold water to the bottom part of the tank (C), atleast an Outlet pipe (D) with orifice (D1) for withdrawing hot water from the top of said storage tank (A)
iii) optionally a cylindrical shell (A3) connecting said top ellipsoidal head to bottom ellipsoidal head,

iv) Heating assembly comprising atleast 2 heating elements;

where atleast a bottom heating element (E) is installed near the inlet pipe at the location (E1) of bottom part of said storage tank (A) where the vertical distance between said location of bottom heating element (E1) and orifice (D1) of said outlet pipe (D) is defined as “m”;

wherein atleast one top heating element (F) is installed at the location (F1) of top section of said storage tank (A) where the vertical distance between said location of heating element (F1) and orifice (D1) of said outlet pipe (D) is defined as “n”;

wherein the location of bottom heating element and the top heating element varies with respect to the equation n < m/2;
and wherein n >50mm.
2. The water heater as claimed in claim 1, wherein said mode of operation comprises atleast an Instant/Immediate mode and a Storage/Regular mode.
3. The water heater as claimed in claim 1, comprises atleast a mechanical or electronic switch for switching between said mode/s.
4. The water heater as claimed in claim 1, comprises safety device for cutting off power supply to said heating elements in case the temperature of the water exceeds a threshold temperature.
5. The water heater as claimed in claim 4, wherein said safety device comprises atleast a thermostat, atleast a thermal cut-off.
6. The water heater as claimed in claim 1, wherein said insulating material comprises foam and like material.
7. The water heater as claimed in claim 1, wherein said external body and said tank are connected with respect to said inlet pipe (C) for the entry of cold water to the bottom part of said tank, an outlet pipe (D) for withdrawing hot water from the top of said tank (A).
8. The water heater as claimed in claim 1, comprising a Ready mode for operation wherein said Ready mode switches ON and OFF said bottom heating element (E) as required to maintain the temperature of water inside the tank at constant 250C.
9. A method of operating the water heater with multiple modes of operation comprising the steps of:

a) selecting the mode of operation from Instant or Storage mode through switch (K) where activating said switch (K) in Instant mode cuts-off power supply to the bottom heating element and supplies power to only the top heating element causing small quantity of water to be heated quickly for instant use;
b) activating switch (K) in Storage mode causes a top thermostat to divert power from the top heating element to bottom heating element, when the top thermostat senses a threshold temperature, for heating the complete volume of water for regular use.