WO2020165458A1

WO2020165458A1 - Electric boiler, central heating system comprising an electric boiler, tap water heating system comprising an electric boiler and method for operating the same

Info

Publication number: WO2020165458A1
Application number: PCT/EP2020/054123
Authority: WO
Inventors: Stefan REIJMAN HINZE; Eelke SIJBRANDIJ
Original assignee: Boilersync B.V.
Priority date: 2019-02-15
Filing date: 2020-02-17
Publication date: 2020-08-20
Also published as: EP3924669A1; NL2022590B1

Abstract

Electric boiler (110) comprises a main cold water inlet (118), first and second vessels (111) for heating water, a controller, and a main hot water outlet (117). Each vessel (111) comprises a respective inlet (112) for receiving cold water from the main cold water inlet (118), a respective electric heating element (114) for heating the cold water, a respective outlet (116) for supplying hot water to the main hot water outlet (117) and a respective shut off (113) valve for controlling the flow through the first outlet. The electric boiler (110) is configured for receiving single phase electric power having a maximum power rating of 5000 W or less and to supply the electric power to the heating elements (114) of the vessels one at a time in order to heat the first vessel (111) and the second vessel sequentially.

Description

ELECTRIC BOILER, CENTRAL HEATING SYSTEM COMPRISING AN ELECTRIC BOILER, TAP WATER HEATING SYSTEM COMPRISING AN ELECTRIC BOILER

AND METHOD FOR OPERATING THE SAME

Technical field

[0001] The present invention generally relates to electric boilers in general and electric boilers for heating systems in particular. Furthermore, the present invention relates to a central heating system comprising such an electric boiler and to a tap water heating system comprising such an electric boiler. Furthermore, the invention relates to a method for operating such an electric boiler, such a central heating system and such a tap water heating system.

Background art

[0002] Conventional boilers for use in central heating systems or water heating systems typically use fossil fuels such as natural gas as a source of energy. These fossil fuels are combusted in the boiler to generate heat that can be used to warm up water contained in a vessel of the boiler.

[0003] In light of global warming and pollution the use of fossil fuels as a source of energy is being discouraged, while the use of electrical energy is being encouraged.

[0004] Conventional boilers may be replaced with variants running on electrical energy such as disclosed in US 20140202549A1 to meet with this change. However, for fast and convenient operation these typically require peak power which is more than a single phase (e.g. 16A/20A 230V AC 50Hz) circuit of the distribution board can provide. Therefore, it is mostly required to install an expensive three phase or a more powerful single phase connection for the boiler.

Object of the invention

[0005] It is an object of the present invention to provide an electric boiler that does not have one or preferably all of the disadvantages of known electric boiler systems in that it allows for fast and convenient operation, can be powered through a conventional single phase outlet and does not require structural changes in the buildings infrastructure for hot water and/or heating.

Summary of the invention

[0006] According to a first aspect of the invention there is provided an electric boiler as set out in the appended claims.

[0007] According to a second aspect of the invention there is provided a central heating system as set out in the appended claims. [0008] According to a third aspect of the invention there is provided a tap water heating system as set out in the appended claims.

[0009] According to a fourth aspect of the invention there is provided a method of operating a boiler, a central heating system or a tap water heating system as set out in the appended claims.

[0010] According to a fifth aspect of the invention there is provided a kit of parts for installing an electric boiler as described herein.

[0011] According to a sixth aspect of the invention there is provided a method for installing an electric boiler, or a use of the electric boiler, as set out in the appended claims.

[0012] The electric boiler comprises a main cold water inlet, a first and a second vessel arranged for heating water, a controller and a main hot water outlet. The first vessel comprises a first inlet arranged for receiving cold water from the main cold water inlet, a first electric heating element (e.g. electrical resistance) arranged for heating the cold water, a first outlet arranged for supplying hot (heated) water to the main hot water outlet and a first shut off valve arranged for controlling the flow through the first outlet. The second vessel comprises a second inlet arranged for receiving cold water from the main water inlet, a second electric heating element (e.g. electrical resistance) arranged for heating the cold water, a second outlet arranged for supplying hot (heated) water to the main hot water outlet and a second shut off valve arranged for controlling the flow through the second outlet. The controller is configured for controlling electric power delivery to the first electric heating element and the second electric heating element.

[0013] According to the invention, the electric boiler is configured for receiving single phase electric power having a maximum power rating of 5000 W or less. The controller is further configured to supply the electric power to the first electric heating element and to the second electric heating element one at a time in order to heat the first vessel and the second vessel sequentially. By way of example, when the first electric heating element is receiving electric power, the second heating element is not receiving electric power and only water in the first vessel is heated, and vice versa. Advantageously, the electric boiler comprises a single (i.e. only one) electric connection interface (e.g. a plug or electric terminals for connecting an electric cable) for connecting (all components of) the electric boiler to the electric grid (mains power supply). The electric connection interface is a single phase connection interface.

[0014] An electric boiler according to the invention comprising multiple vessels which are sequentially heated advantageously spreads out the electric power consumption for heating water to a certain temperature over a longer period of time. This enables powering the boiler through a conventional (single phase) domestic electrical outlet. In the meantime a reservoir of energy is created in the form of heated water that can be supplied by the electric boiler in a short amount of time. Such a boiler reduces the installation costs, while maintaining the fast and convenient operation of conventional boiler systems. Furthermore, spreading the reservoir volume over multiple smaller vessels shortens the time required to heat up water contained in a single vessel to an operational temperature, which further enhances the convenience.

[0015] In a preferred embodiment the controller of the electric boiler is further configured to control opening either one of the first shut off valve and the second shut off valve. This has the benefit that hot water from only one vessel is used at a time, which improves the speed of heating the vessels in light of the sequential operation of the heating elements. Typically, the shut off valves are motorized shut off valves.

[0016] Beneficially, the first vessel further comprises a first temperature sensor configured for determining a first water temperature of water contained in the first vessel, and wherein the controller is configured to switch the supply of power from the first heating element to the second heating element when the first water temperature reaches a predetermined threshold temperature. It is preferred that the predetermined threshold temperature is near the boiling point as this provides the highest level of capacity, without requiring additional components or reinforcements that would be required for higher temperatures. Typically, the threshold temperature lies between 60 and 100 degrees Celsius. Preferably, the threshold temperature is between 70°C and 99°C, or between 80°C and 96°C, and preferably between 90°C and 95°C.

[0017] Preferably, the second vessel further comprises a second temperature sensor configured for determining a second water temperature of water contained in the second vessel, and wherein the controller is configured to switch off the power supply when the first water temperature and the second water temperature both reach the predetermined threshold temperature.

[0018] The temperature sensor configured for determining the water temperature of water contained inside the vessel is preferably arranged at a side of the vessel opposite to the heating element. This ensures that the temperature that is sensed is in accordance with the temperature of the water contained in the vessel.

[0019] The vessel can have any shape, rectangular is preferred in light of its form factor, spherical is preferred in light of its uniformity of isolation and strength, and a vessel having a cylindrical shape offers the best balance between the two. Preferably, each vessel has a volume between 20 and 80 liters, more preferably between 30 and 60 liter, even more preferably between 40 and 50 liter. A vessel with such a volume offers good performance in terms of the heating time required to reach the threshold temperature.

[0020] The heating element is preferably arranged in the middle of one of the sidewalls of the vessel such as an endcap of a vessel having a cylindrical shape, because this offers the best heating performance. Even more preferably, the heating element is arranged in a central region just below the geometrical center of one of the sidewalls of the vessel, such as an endcap of a vessel having a cylindrical shape, such that more space is available above the heating element than below to allow hot water to rise more easily.

[0021] Beneficially, at least one and preferably each of the first vessel and the second vessel and more preferably any further vessel (e.g. a third vessel and/or a fourth vessel) comprises a permeable partitioning panel arranged inside the vessel for dividing a volume of the corresponding vessel in a first compartment and a second compartment. Preferably, such permeable partitioning panel is configured such that the first compartment comprises the corresponding inlet and the second compartment comprises the corresponding outlet. The benefit of providing such a permeable partitioning panel is that it allows the boiler to provide hot water for a prolonged period of time, because mixing of cold water entering a vessel with warm water already contained in the vessel is hindered or delayed. This allows a prolonged supply of hot water of a more uniform (and higher) temperature to the main hot water outlet. A permeable partitioning panel projects inside the vessel, such as a baffle, and may comprise a single aperture for instance provided in a central area of the panel. Preferably, a permeable partitioning panel comprises a plurality of apertures provided in diverse locations dispersed over the panel, such that it reduces turbulent mixing of cold water entering the vessel with the hot water contained in the vessel while minimizing the obstruction of the flow by the permeable partitioning panel. Such permeable partitioning panel for instance has an open area between 60% and 90% or preferably between 75% and 80%. Preferably, apertures of the plurality of apertures have a surface area of between 100mm² and 325mm². Such apertures may have a circular shape and are advantageously arranged to form a mesh. A practical embodiment of such a permeable partitioning panel comprises a perforated plate having a same geometry and surface area as a cross section of the vessel (e.g. orthogonal to a longitudinal axis of the vessel). The permeable partitioning panel can alternatively be a meshed gauze.

[0022] The first or second compartment may comprise a temperature sensor and/ora heating element. In a preferred embodiment, the temperature sensor is provided in the first compartment and the heating element is provided in the second compartment. Such an arrangement is typically suitable for a vessel comprising a permeable partitioning panel allowing heat exchange (e.g. convection) between the first and the second compartment. This may be the case for partitioning panels comprising a plurality of apertures dispersed over the panel, for instance a wire mesh or perforated plate suitable for reducing or preventing turbulent mixing of water from the first compartment and the second compartment.

[0023] Alternatively, the or in addition, an (additional) temperature sensor and possibly a (an additional) heating element may be provided in the first compartment. Such arrangement is typically suitable for a vessel comprising a permeable partitioning panel allowing low levels of heat exchange (e.g. convection, conduction, radiation) between the first and the second compartment. In such situations, this may improve heat exchange from the heating element to the cold water entering the vessel, since it increases a temperature difference between the heating element and the water contained in the first compartment.

[0024] A boiler according to the present invention is preferably configured for placement in a single room, such as a technical or utility room, of a building, such as a home. In a preferred embodiment the boiler comprises three, four or even more vessels, advantageously with a volume between 30 and 60 liter, and preferably between 40 and 50 liter in order to match the performance of conventional boilers. A boiler comprising four such vessels having a cylindrical shape with a diameter between 15 cm and 60 cm, preferably between 20 cm and 40 cm, or even more preferably between 25 and 35 cm, such as 30 cm for matching the form factor of conventional boilers.

[0025] In a preferred embodiment the main hot water outlet is configured for draining hot water from the first vessel and the second vessel and preferably any further vessel (e.g. a third vessel and/or a fourth vessel) provided in the boiler. Hot water can be drained from the plurality of vessels simultaneously, but is preferably drained sequentially to the main hot water outlet. To this end, the shut off valves of the plurality of vessels (first, second, etc.) are preferably controlled to open one at a time, e.g. when one of the shut off valves is open to drain hot water from the respective vessel, the shut off valves of the other vessels remain closed. Such drained water may then be supplied to the hot water infrastructure of the building such that it is delivered to hot water outlets provided in the building such as taps or showers. Preferably, the main hot water outlet comprises a single conduit such as a manifold fluidly connected to the first outlet and the second outlet at a first end and a tap, a heat exchanger or a central heating system at a second end. [0026] In a preferred embodiment the first vessel and the second vessel and preferably any further vessel (e.g. a third vessel and/or a fourth vessel) comprises fastening means for assembling the first vessel and the second vessel and preferably any further vessel (e.g. a third vessel and/or a fourth vessel) to form an array of vessels (e.g. in one or two directions). Advantageously, the fastening means comprise a frame configured for receiving the corresponding vessel and arranged for being fastened to a frame of another vessel.

[0027] Preferably, the vessel has a cylindrical shape and the fastening means comprises a frame configured for receiving the vessel and arranged for being fastened to another frame of another kit of parts. For instance, the frame comprises interlocking elements configured for interlocking with corresponding interlocking elements provided on the other frame. Preferably, the frame has a rectangular cuboid shape and for instance comprises movably or detachably arranged encaging means for encaging the vessel. In a beneficial embodiment, four edges of the frame correspond to a height of the vessel and eight edges of the frame correspond to the diameter of the vessel.

[0028] According to an aspect of the invention there is provided a kit of parts comprising an electric boiler according to the invention. The benefit of such kits of parts is that they enable assembling a hot water boiler in a modular fashion that can be precisely tailored to the specific needs for hot water and/or central heating and that it allows for installation of the boiler by one person.

[0029] Alternatively, the kit of parts is configured for assembling a boiler having a higher maximum power rating and for instance allowing for simultaneously heating a plurality of vessels. The kit of parts comprises a vessel configured for heating water and fastening means configured for assembling a plurality of vessels, for instance fastening means as described previously.

[0030] Preferably, the vessel has a cylindrical shape and the fastening means comprises a frame configured for receiving the vessel and arranged for being fastened to another frame of another kit of parts. For instance, the frame comprises interlocking elements configured for interlocking with corresponding interlocking elements provided on the other frame. Preferably, the frame has a rectangular cuboid shape and for instance comprises movably or detachably arranged encaging means for encaging the vessel. In a beneficial embodiment, four edges of the frame correspond to a height of the vessel and eight edges of the frame correspond to the diameter of the vessel.

[0031] Optionally, the kit of parts further comprises one or more of the following parts: a temperature sensor, a heating element and a controller. [0032] According to an aspect of the invention there is provided a method for installing an electric boiler as described in the present disclosure comprising the steps of providing a plurality of kits of parts as described herein and assembling the plurality of kits of parts, in particular such that the vessels are arranged in an array.

Brief description of the figures

[0033] The invention will now be explained in greater detail with reference to the figures in which equal or similar parts are indicated by the same reference signs and in which:

[0034] Figure 1 shows a schematic representation of a preferred embodiment of the boiler according to the invention.

[0035] Figure 2 shows a schematic representation of a preferred embodiment of the central heating system comprising the boiler according to the invention.

[0036] Figure 3 shows a schematic representation of a preferred embodiment of the tap water heating system comprising the boiler according to the invention.

[0037] Figure 4 shows a schematic representation of a preferred embodiment of a vessel of an electric boiler according to the invention.

[0038] Figure 5 shows a perspective view of an embodiment of a vessel of an electric boiler according to the invention.

[0039] Figure 6A and 6B show two perspective views of a vessel of an electric boiler according to the invention.

[0040] Figure 7 shows a perspective view of an embodiment of a plurality of vessels of an electric boiler according to the invention assembled in an array.

Description of embodiments

[0041] Referring to Fig. 1 , an example boiler 110 comprises four insulated vessels 111 arranged hydraulically in parallel that are each supplied with cold water through an inlet 112. Each of the vessels 111 can have a size of 40 liters, and more or less than four vessels can be provided in boiler 110, such as two, three, five or more. The inlets 112 of the vessels 111 are each connected to a main cold water inlet 118, e.g. through an inlet manifold. The vessels 111 have a cylindrical shape, e.g. with a diameter of 30 cm, even though other shapes are possible as well. Each of the vessels 111 comprise an electric heating element 114 advantageously arranged near a center of one of the sidewalls of the vessel 111 or near a center of one of the endcaps for a cylindrical vessel. The water contained within the vessels 111 is heated by means of sequentially operating the heating elements 114 in the four vessels 111. The heating element 114 of each vessel 111 has a maximum power rating of 5000 W or less, preferably between 3000 and 4500 W. A temperature sensor 115 is configured to sense the water temperature of the water contained in the vessels 111. Such a temperature sensor 115 may be arranged in a sidewall of the vessel or an endcap for a cylindrical vessel, for instance opposite to the heating element 114. The inlet 112 for the cold water may be arranged near the heating element 114, while the outlet 116 for hot water may be arranged near the temperature sensor 115. At the outlet 116 of each vessel 111 a motorized shut off valve 113 is arranged whose operation is controlled by a controller (not shown). These shut off valves 113 are in turn connected to a main hot water outlet 117, e.g. through an outlet manifold.

[0042] The boiler 110 may be used in a closed system configuration, for instance as a central heating boiler for providing hot water to a central heating system, for example comprising convectors or radiators. In such cases the return line of the central heating system is fluidly connected to the main cold water inlet 118 and the supply line of the central heating system is fluidly connected to the main hot water outlet 117.

[0043] In a preferred embodiment, referring to Fig. 2, the boiler 210 differs from the boiler 110 in that it further comprises a buffer tank 211 configured for providing a hot water buffer, comprising a buffer tank outlet 212 fluidly connected to the supply line 213 of a central heating system and a buffer tank inlet 214 fluidly connected to the return line 215 of the central heating system. Such a buffer tank 211 further comprises a heat exchanger 216 (e.g. helical coil) of which one end (inlet) is fluidly connected to the main hot water outlet 217 and another end (outlet) is fluidly connected to the main cold water inlet 218. The heat exchanger 216 being configured to heat the water contained in the buffer tank 211. A pump 219 can be fluidly coupled to the main cold water inlet 218 and/or main hot water outlet 217 for circulating hot water between the vessels 111 and the heat exchanger 216, e.g. in a closed circuit. A pump 220 can be fluidly coupled to return line 215 and/or supply line 213 configured to circulate the water through a radiator 221 of the central heating system. Optionally, the flow generated by the pump 219, 220 is controlled by the controller. The buffer tank 211 may further comprise a temperature sensor 222 arranged for sensing the temperature of the water contained in the buffer tank 211 , which can be used by the controller to control the pumps 219,220 arranged in the piping circuit of the boiler 210 and/or central heating system. Preferably, the controller is arranged for keeping the temperature of the water contained in the buffer tank 211 at a setpoint temperature suitable temperature for heating, e.g. between 60 and 90 degrees Celsius, or even more preferably between 70 and 80 degrees Celsius. The return Iine215, supply line 213, main cold water inlet 218 or main hot water outlet 217 may further comprise a fill / drain valve, a ball valve, a pressure relief valve, an expansion tank 223 and/or an (automatic) air vent 224. The central heating system may further comprise a thermostat arranged to control the flow of hot water through the return line 215 and supply line 213 for instance by operating the pump 220 through the controller. Alternatively or additionally, the radiator 221 may comprise a thermostatic valve arranged to control the flow of hot water through the radiator. Alternatively or additionally, the boiler 210 or the central heating system may comprise a means for determining an outside temperature to control a predetermined threshold temperature or setpoint temperature.

[0044] In addition, or alternatively, the boiler 310 may be used in an open system configuration, for instance as a hot water supply for a hot water outlet like a tap 311 as shown in Fig. 3. In such cases the main cold water inlet 318 is fluidly connected to the main water connection 313 supplying water with a pressure for instance 6 to 8 bar through an inlet combination 314 typically comprising a shut off valve, a check valve with overpressure discharge and an overpressure valve. Boiler 310 differs from boiler 110 in that the main cold water inlet 318 further comprises a shunt 315 fluidly connected to a first mixing valve inlet of a mixing valve 316, the mixing valve further comprising a second mixing valve inlet and a mixing valve outlet. The second mixing valve inlet is fluidly connected to the main hot water outlet 317 and the mixing valve outlet is fluidly connected to a hot water pipe network 312. Preferably, the mixing valve 316 is arranged to mix the water supplied by the shunt 315 and water supplied by the main hot water outlet 317 such that the mixing valve outlet provides water to the hot water pipe network 312 having a temperature between 40 and 80 degrees Celsius, preferably 50 and 70 degrees Celsius and even more preferably about 60 degrees Celsius. At the tap 311 the temperature can be lowered even further, by mixing the water from the hot water pipe network 312 with additional cold water supplied by the main water connection 313.

[0045] A preferred manner of operating an electric boiler 110, 210, 310 according to the invention is to heat the vessels 111 one at a time to a predetermined threshold temperature, to reach an operational state of a vessel 111. The vessels 111 having reached the operational state can subsequently be used for supplying hot water to the main hot water outlet 117, 217, 317 one at a time, or simultaneously.

[0046] Referring to Fig. 4, a permeable partitioning panel 425 may be provided in a vessel 411 dividing the vessel 411 in a first compartment 431 and a second compartment 432, such that one compartment, e.g. the first compartment 431 , comprises the inlet 412 of the vessel 411 and the other compartment, e.g. the second compartment 432, comprises the outlet 416 of the vessel 411. The partitioning panel 425 can be made of a perforated or meshed plate, comprising one or more through holes. Alternatively, the partitioning panel can be formed of one or more baffles projecting inside the vessel 411 , and which may or may not be arranged coplanar. The first compartment 431 or the second compartment 432 may comprise one or more apertures 427, 428 configured for receiving for instance a heating element 414 or a temperature sensor 415. In the shown embodiment a first end cap 433 of the vessel 411 comprises a first aperture 428 configured for receiving a temperature sensor 415 in the first compartment 431 and a second end cap 434 of the vessel 411 comprises a second aperture configured for receiving a heating element 414 in the second compartment 432.

[0047] Referring to Fig. 5-7, a vessel 411 comprising fastening means 426 configured for assembling a plurality of vessels 411 forming an array 430.

[0048] The fastening means 426 preferably comprises a frame 426 that has a rectangular cuboid shape and defines a volume configured for receiving the vessel 411. By way of example, the cuboid defined by the frame 426 can circumscribe the vessel 411. Frame 426 can comprise a framework of rods arranged at the edges of the cuboid shape. The frame 426 may comprise a first part 426A configured for receiving the vessel 411 and a second part 426B configured for engaging the first frame part 426A for encaging the vessel 411. The frame may further be equipped with co-operating interlocking elements 429A, 429B for interlocking multiple frames 426 comprising vessels 411 forming an array 430 for use in an electric boiler 110, 210, 310 according to the invention. Such interlocking elements may be configured as female parts 429A and male parts 429B provided on the frame 426.

Claims

1. Electric boiler (110, 210, 310) comprising:

a main cold water inlet (1 18, 218, 318),

a first vessel (11 1) arranged for heating water, a second vessel arranged for heating water,

a controller, and

a main hot water outlet (1 17, 217, 317),

wherein the first vessel (1 1 1) comprises a first inlet (112) arranged for receiving cold water from the main cold water inlet (1 18, 218, 318), a first electric heating element (114) arranged for heating the cold water, a first outlet (116) arranged for supplying hot water to the main hot water outlet (117, 217, 317) and a first shut off (1 13) valve arranged for controlling the flow through the first outlet,

wherein the second vessel comprises a second inlet arranged for receiving cold water from the main water inlet, a second electric heating element arranged for heating cold water, a second outlet arranged for supplying hot water to the main hot water outlet and a second shut off valve arranged for controlling the flow through the second outlet,

wherein the controller is configured for controlling electric power delivery to the first heating element (1 14) and the second heating element,

characterized in that the electric boiler (110, 210, 310) is configured for receiving single phase electric power having a maximum power rating of 5000 W or less, wherein the controller is configured to supply the electric power to the first heating element (1 14) and to the second heating element one at a time in order to heat the first vessel (1 11) and the second vessel sequentially.

2. Electric boiler (1 10, 210, 310) according to claim 1 , wherein the controller is further configured to control opening of the first shut off valve (1 13) and the second shut off valve one at a time.

3. Electric boiler (1 10, 210, 310) according to claim 1 or 2, wherein the first vessel (11 1) further comprises a first temperature sensor (1 15) configured for determining a first water temperature of water contained in the first vessel (111), and wherein the controller is configured to switch the supply of power from the first heating element (114) to the second heating element when the first water temperature reaches a predetermined threshold temperature.

4. Electric boiler (1 10, 210, 310) according to claim 3, wherein the controller is configured to maintain the shut off valve (1 13) of the respective vessel closed until the predetermined threshold temperature is reached.

5. Electric boiler (110, 210, 310) according to claim 3 or 4, wherein the threshold temperature lies between 60 and 100 degrees Celsius, preferably between 90 and 95 degrees Celsius

6. Electric boiler (110, 210, 310) according to any one of the preceding claims, wherein the first vessel (111) and the second vessel each have a volume between 20 and 80 liters, preferably between 30 and 60 liter, even more preferably between 40 and 50 liter.

7. Electric boiler (110, 210, 310) according to any one of the preceding claims, further comprising a third vessel arranged for heating water and a fourth vessel arranged for heating water,

wherein the third vessel comprises a third inlet arranged for receiving cold water from the main cold water inlet (118, 218, 318), a third electric heating element arranged for heating cold water, a third outlet arranged for supplying hot water to the main hot water (117, 217, 317) outlet and a third shut off valve arranged for controlling the flow through the third outlet,

wherein the fourth vessel comprises a fourth inlet arranged for receiving cold water from the main water inlet (118, 218, 318), a fourth electric heating element arranged for heating cold water, a fourth outlet arranged for supplying hot water to the main hot water outlet (117, 217, 317) and a fourth shut off valve arranged for controlling the flow through the fourth outlet,

wherein the controller is further configured for controlling electric power delivery to the third electric heating element and to the fourth electric heating element, and

wherein the controller is configured to supply the electric power to the first to fourth heating elements one at a time in order to heat each of the first to fourth vessels sequentially.

8. Electric boiler (210) according to any one of the previous claims, wherein at least one and preferably each one of the first and the second vessel, and optionally the third and the fourth vessel, comprises a permeable partitioning panel for dividing a volume of the corresponding vessel in a first compartment comprising the inlet of the corresponding vessel and a second compartment comprising the outlet of the corresponding vessel.

9. Electric boiler (210) according to any one of the previous claims, wherein each one of the first and the second vessel, and optionally the third and the fourth vessel, comprises fastening means for assembling the respective vessels in an array of vessels, preferably wherein the fastening means comprise a frame configured for receiving the corresponding vessel and arranged for being fastened to a frame of another vessel.

10. Electric boiler (310) according to any one of the claims 1 to 9, further comprising a mixing valve (316) having a first mixing inlet, a second mixing inlet and a mixing outlet, wherein the first mixing inlet is in fluid communication with the main cold water inlet (318), the second mixing inlet is in fluid communication with the main hot water outlet (317), wherein the mixing valve (316) is arranged for mixing water from the main cold water inlet (318) and the main hot water outlet (317).

11. Electric boiler (310) according to claim 10, wherein the mixing valve (316) is arranged for mixing water such that the mixing valve outlet provides water having a temperature between 40 and 80 degrees Celsius, preferably 50 and 70 degrees Celsius and even more preferably about 60 degrees Celsius.

12. Electric boiler (210) according to any one of the claims 1 to 9, further comprising a buffer tank (211) configured for providing a hot water buffer, having a buffer tank outlet (212) arranged for providing hot water and a buffer tank inlet (214) arranged for receiving cold water, wherein the buffer tank (211) comprises a heat exchanger (216) comprising an inlet and an outlet, wherein the inlet of the heat exchanger is fluidly connected to the main hot water outlet (217) and the outlet of the heat exchanger is fluidly connected to the main cold water inlet (218).

13. Electric boiler (210) according to claim 12, wherein the buffer tank (211) further comprises a temperature sensor (222) arranged for sensing a buffer tank water temperature, and wherein the controller is configured to control a flow of water through the heat exchanger (216) based on the buffer tank water temperature and a buffer tank setpoint temperature.

14. Central heating system comprising an electric boiler (110) according to any one of claims 1 to 9, wherein a return line (215) of the central heating system is fluidly connected to the main cold water inlet (118) and a supply line (213) of the central heating system is fluidly connected to the main hot water outlet (117).

15. Central heating system comprising an electric boiler (210) according to claim 12 or 13, wherein a return line (215) of the central heating system is fluidly connected to the buffer tank inlet (214) and the supply line (213) of the central heating system is fluidly connected to the buffer tank outlet (212).

16. Water heating system comprising an electric boiler (110, 310) according to any one of the claims 1-11.

17. Use of the electric boiler according to any one of the claims 1 to 13, or of the central heating system according to claim 14 or 15, or of the water heating system according to claim 16, wherein the first vessel and the second vessel, and preferably the third vessel and the fourth vessel are mounted in a single room of a building.

18. Method of operating a boiler (110, 210, 310) according to any one of the claims 1 to 13, comprising the steps of heating the vessels (111) sequentially to reach a predetermined threshold temperature in each of the vessels (111).

19. Method of claim 18, comprising opening the shut off valve (113) of the vessels (111) that have reached the predetermined threshold temperature sequentially.

20. Method of claim 18, comprising opening the shut off valve

(113) of the vessels (111) that have reached the predetermined threshold temperature simultaneously.