IN A BOILER

Field of the Invention

The present invention relates to the field of hot water installations. More particularly, the invention relates to thermostatic control of the water temperature in hot water installations.

Background of the Invention

As industry and population number grow, the demand for electricity also grows. In recent years there has been much investment in systems for saving electricity by controlling the temperature of the water in hot water installations. Generally, reducing water heating level in hot water installations and enhancing heating efficiency saves electricity.

Domestic hot water installations typically include a hot water tank which may be situated within a house or apartment or, alternatively, on the roof thereof. In countries wherein the sun can be relied on to shine for most days of the year it is very common to provide hot water, at least in part, by solar heating. A solar panel is provided on the roof of the building and hot water is contained in a storage tank adjacent to the solar panel. Water is fed to the domestic hot water supply system via a thermally insulated pipe running from the storage tank on the roof of the building and gaining entrance to the domestic hot water supply.

Whether the water is heated using solar power or other means, some electrical backup is also normally provided in the form of an electrical immersion heater disposed within the hot water tank. The immersion electrical heater is fully controlled by a person wishing to bring the water to a comfortable shower temperature relatively quickly in the absence of sun or when the he speculates that the hot water temperature is inadequate.

The person wishing to take a shower mixes hot water from the tank with cold water in order to achieve a comfortable shower temperature, typically, between 40°C and 45°C. However, there is no way to know the actual temperature or amount of the hot water in the storage tank. Therefore, the decision to boost the hot water temperature by the electrical immersion heater is mostly based on a guess and very often results in unnecessary activation of the electrical immersion heater. This is, clearly, an extravagant waste of energy.

Furthermore, owing to the high cost of electricity, it is obviously desirable to use an electrical immersion heater in order to boost the water temperature only to the extent that is absolutely required. For example, a person who wishes to boost the water temperature prior to taking a shower, clearly, has no need to electrically heat the entire water tank to the highest temperature enabled by the boiler thermostat. It is sufficient to heat the water tank such that, when the hot water in the tank is mixed with cold water, the resulting hot water temperature is around 40 to 45°C for a desired time or number of showers.

However, since the amount and temperature of the water exists in the tank cannot be predicted in advance, users tend to unnecessary boost the water temperature prior to taking a shower using the electrical immersion heater. Besides the waist of energy and the unnecessary time users wait for the water to get hot, electrical heating causes scale build-up in the hot water pipes and around the immersion heater. In many cases even when the user estimates correctly the required heating time, he forget to turn-off the electrical heater. Thus, it is extremely desired to boost the water temperature only to the extent required for saving energy and enhancing the life of the hot water installation.

JP 20050098102 (Nobuo) discloses a residual hot water quantity display device for a storage type water boiler capable of correctly displaying hot water quantity of set temperature or higher, and hot water quantity that can be boiled by a heat pump unit. Nobuo discloses temperature sensors to detect hot water temperature in the hot water storage tank, comparing means to compare detected temperature by the temperature sensors with prescribed temperature to output if hot water of prescribed temperature or higher exists or not, and display means corresponding to the output of the comparing means. The prescribed temperature is changed in accordance with situations such as set supply water temperature and open air temperature.

Nobuo's device, as several other prior art devices, places several temperature sensors at predetermined heights within the hot water tank so that their respective readings give the user an indication of the local temperature of the water in the vicinity of the sensor. Such affixing of temperature sensors at different heights within the water tank is preferably performed during manufacture of the tank itself. To the extent that they are inserted after the tank is manufactured, this can be done only by boring holes through the wall of the tank, inserting the temperature sensors and then sealing the holes against water leakage in a manner which will withstand the water pressure in the tank. This is clearly an involved procedure which adds to the cost of the tank and may detract from its reliability.

Another method known in the art is discloses in WO/2000/058668 (Cohen). Cohen provides a hot water tank and method for estimating an available quantity of usable water having a desired water temperature therein. Cohen provides at least three temperature sensors disposed at respective heights of the tank for measuring local water temperature at respective points thereof. Each of the temperature sensors is bonded to the wall so as to form a thermocouple at a respective point of contact.

The method discloses by Cohen utilizes thermocouples (temperature sensors) located on the tank's wall, and have no direct contact with the water. It is known from heat transfer analysis that hot water has a temperature radial gradient. Therefore, measuring the temperature employing a thermocouple at the tank's wall does not provide a precise measurement as measuring the temperature of the water itself in a central location. Furthermore, hot water usage profile indicates that most of the people intended to use the same shower-room (family or hotel guests) are likely to take their showers in the same time period (e.g., in most families, all family members take their showers between 19:00 to 22:00 PM). Cohen fails to provide a system that considers the hot water in the tank and the water usage profile to provide a requested number of showers.

US 2007/0005190 (David) discloses a system for predicting the availability of hot water for bathing. Based on a hot water consumption rate and/or determination of a current hot water availability condition, a projection is made to whether there will be adequate hot water to fill the bathtub to a desired level or volume at a desired temperature. However, David fails to provide the number of showers available to the user. The sensors in David's invention are located at the distal end of the water tank. Thus, the measurement does not consider the temperature gradient of the water. In addition, David fails to measure the flow and temperature of the cold water inserting the tank. Therefore, his calculations lack the weather impact over the hot water consumption.

Another method for thermostatic control discloses in WO/2008/152645 (Yatir). This method determines the amount of warm water in a water tank, comprising: pre-determining various situation graphs, each graph describing the variation of the water temperature as a function of time; determining for each graph section the percentage of warm water in the tank; storing in a memory said graph sections, and the corresponding percentage of warm water in the tank; during the operation of the heating system, sampling periodically the temperature in the tank; for each sequence of samples, finding the most similar graph section, and the percentage of warm water that corresponds to said graph section; and displaying to the user said present percentage of warm water in the tank. Yatir fails to provide the number of showers available to the user. The percentage of the hot water in the tank is far from indicating the number of showers available. The number of the showers available depends on many factors such as, usage profile, cold water temperature, cold water flow, and other parameters which are not considered at all. In addition, Yatir provides a single temperature sensor. Surely, a single measurement can not provide an accurate and immediate measurement of the entire water tank.

In winter when the cold water is at a much lower temperature than in the summer, a householder will naturally mix less cold water from the cold water supply with the hot water in the tank than he or she would do in summer. Therefore, the nominal volume of hot water available in the tank translates into different actual quantities of usable water depending on the cold water temperature. Prior art systems addresses the problem of estimating a volume of available water in the tank having a specified average temperature, but does not appear to take into consideration that what is of interest to the user is the actual volume of usable hot water, which may well be considerably more than the nominal hot water volume in the tank. In addition prior art systems typically consider only the water temperature in one or more points inside the boiler. However, they do not provide accurate and extensive information regarding the hot water available for different utilizations, such as, showers, baths, washing dishes, and etc.

None of the currently available techniques provide a satisfying solution for thermostatically controlling the water temperature in a hot water installation. A need therefore exists in the art for a system retrofitted to any water tank, adapted to boost the water temperature only to the extent amount of water absolutely required for preset utilizations.

It is therefore an object of the present invention to provide a system for controlling the water temperature in a hot water installation while saving energy and enhancing the life period of the hot water installation.

Another object of the present invention is to control the water temperature according to user request, and to display the number of utilizations currently available.

Yet another object of the present invention is to provide a system adapted to retrofit to any water tank which does not require changing the structure of the water tank.

An additional object of the present invention is to provide an automatic heating control, adjustable during usage. Still an object of the present invention is to provide a method for learning the water usage profile.

Other objects and advantages of the invention will become apparent as the description proceeds.

Summary of the Invention

In a first aspect, the invention is directed to a system for controlling the temperature of water in a hot water installation, comprising: (a) an array of one or more temperature sensors, arranged to measure accurately the water temperature in a water tank; (b) a user interface adapted to receive input from a user; (c) a heating member for heating the water in said water tank; and (d) a control unit adapted to receive information from said sensors array and/or user interface, said unit controls the operation of said heating member, wherein said system is retrofitted to most hot water installations, adapted to heat a precise amount of water according to the input requested by said user, said system further considers usage profile, for minimizing the heating time and power consumption.

In an embodiment of the invention the hot water installation may be a solar heating system provided with an electrical backup in the form of an electrical immersion heater disposed within the hot water tank.

In one embodiment, the system further comprises a connector installed between the tank's cold water inlet and cold water supply pipe, said connector encompasses a flow meter and a temperature sensor for sensing flow and temperature of water entering the water tank.

In an embodiment of the invention connecting the control unit to the sensors array, user interface, and connector is made via an interface taken from the group of: USB, wire line, wireless network, cellular interface, Bluetooth, and Ethernet.

In an embodiment of the invention the sensors array may be positioned in a central location between the wall of the water tank and the heating member, said sensors array measures the water temperature in one or more locations along said water tank to receive a precise measurement.

In an embodiment of the invention the sensor array may be inserted to the water tank through its cold water inlet.

In one embodiment, the system further comprises a float attached to the sensors array, said float stretches said array along the water tank, for spreading the sensors at equally spaced intervals.

In one embodiment, the system further comprises one or more electronic valves mounted on one or more closed loop pipes entering into the water tank, said electronic valves are connected to the control unit, and are adapted to be closed upon activating the electrical immersion heater for preventing heating the fluid in the closed loop pipes.

In an embodiment of the invention the user interface may be installed inside the user's house, typically on the shower room wall.

In an embodiment of the invention the input from the user may be taken from the group consisting of: number of showers, number of baths, number of dishes, number of piles of dishes, activation timer, shower time, tank's size, and liters of hot water. In an embodiment of the invention the user interface may display information regarding the hot water availability, said information is taken from the group consisting of: number of showers, number of baths, number of dishes, and number of piles of dishes.

In an embodiment of the invention the control unit may be installed in proximity to said water tank.

In one embodiment the control unit further comprises a processor for calculating the required heating time, and a memory unit for saving data to create a usage profile for future calculations.

In a second aspect, the invention is directed to a method of controlling the temperature of water in a hot water installation, for minimizing heating time and power consumption, comprising: (a) inserting one or more temperature sensors to a water tank; (b) connecting a control unit to a user interface, a tank heating member, and to the temperature sensors; (c) receiving input from a user; and (d) heating a precise amount of water according to the input received by said user, and to temperature sensors measurements.

In one embodiment, the method further comprises saving data to create a usage profile for future calculations.

In one embodiment, the method further comprises configuring the control unit by setting parameters defining the hot water installation, said parameters are taken from the group consisting of: tank's size, number of sensors, and sensors location. The temperature sensors are inserted to said water tank inside a thin sleeve for isolating said sensors from the water.

Brief Description of the Drawings

The above and other characteristics and advantages of the invention will be better understood through the following illustrative and non-limitative detailed description of preferred embodiments thereof, with reference to the appended drawings, wherein:

Fig. 1 schematically illustrates a hot water tank having a control unit according to one embodiment of the invention;

Fig. 2 illustrates the user interface; and

Fig. 3 schematically illustrates an embodiment of the system in an apartment building.

Detailed Description of the Invention

The subject invention is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the subject invention. It may be evident, however, that the subject invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the subject invention.

Fig. 1 schematically illustrates a hot water tank having a control unit according to one embodiment of the invention. The water tank 101 has cold water inlet 102 providing cold water to the tank, hot water outlet 103 supplying hot water to the house, an electrical immersion heater 104 electrically controlled by a control unit 105, and a standard thermostat 106 generally, turns the electrical heater 104 on and off according to the temperature measured by the standard thermostat. The electrical immersion heater 104 is typically surrounded with a prolonged sleeve 120 allowing heating a small amount of water fast. When the electrical heater is turned-on, water is heated inside the prolonged sleeve and rise to the top of the tank. In the same time cold water from the bottom of the tank enters the sleeve to be heated. This way a temperature gradient is formed inside the tank, wherein, the hot water presents in top of the tank and cold water in its bottom.

In one embodiment, a sensors array 107 is inserted to the water tank through the cold water inlet 102. In another embodiment the boiler is manufactured comprising a sleeve having an external outlet, to which the sensor array is inserted. The sensors array is used for measuring the water temperature in several spots along the tank, it is adapted to be installed on any tank, namely, retrofit to any exist tank without drilling it or forming any change in its structure. In one embodiment a float 108 is attached to the sensors array stretching it along the tank. When the sensors array is stretched the sensors 109-112 are spread at equally spaced intervals, and provide a temperature profile through the tank. In another embodiment the sensors array is inserted inside a thin sleeve for isolating the sensors from the water and providing it a rigid structure which also spares the float.

In one embodiment, a connector 113 is inserted between the tank's cold water inlet, cold water supply pipe 114, and control unit 105. The connector comprises a single sensor 115 for sensing the temperature of the cold water entering the tank during hot water usage. In one embodiment the single sensor 115 is part of the sensors array 107. The control unit is adapted to consider the temperature profile through the tank and the temperature of the cold water entering the tank, and calculates the minimal heating time require for providing a desired number of showers.

In one embodiment the connector is also equipped with a water flow meter 116. The flow meter measure the water flow into the tank, therefore, it is capable of indicating the number of liters consumed from the water tank every minute. The flow meter may be implemented by a thermistor (a type of resistor whose resistance varies significantly with temperature), immersed in the water pipe. The thermistor is constantly connected to a voltage source through a serially connected fixed resistor that causes current to flow through it, while measuring the voltage drop on the the thermistor. If there is no water flow in the pipe, the thermistor will be overheated and its resistance will rise, while causing the voltage drop to increase. If there is water flow in the pipe, the thermistor will be cooled and its resistance willdrop, while causing the voltage drop to decrease.

The control unit is adapted to receive measurements from the water flow meter and calculate accordingly the ratio of hot water to cold water. Typically, the pipes from the water tank to the shower head are fill with cold water, the user who wishes to receive hot water, fully opens the hot water valve. After the cold water is wasted, the user mixes the hot with cold water. The control unit is adapted to receive the flow measured at both cases, namely, initial and normal operation. The control unit calculates accordingly the cold water consumption. In one embodiment the control unit subtracts the second measurement from the first measurement, namely, the measurement during normal operation is subtracted from the flow measurement during the beginning of the shower. In another embodiment the control unit subtracts the flow measurement durin normal operation from a predefined average flow value to calculate the ratio of hot water to cold water.

Besides measuring the cold water flow to the tank, the flow meter is also responsible for notifying the control unit of the water usage. Such communication helps the control unit to immediately response to hot water usage, this is extremely important in cases wherein the hot water amount is limited, and there is no margin between the requested and the available number of showers. Another advantage of this communication is the fact that the control unit does not require to constantly check the temperature in the sensors array to detect change in the water temperature, but rather initiate a check only when cold water go through the flow meter. This mechanism helps to save unnecessary calculations and power consumption.

The control unit saves all the data collected regarding the hot and cold usage profile, and the water usage per shower. The control unit identifies the end of a shower according to the data received from the flow meter. After a long time in which no water is consumed, the control unit assumes that the shower is over. If the control unit detects that the user does not mix the water according to its expectations or uses more water than expected it updates the number of residual showers. Additionally, the control unit automatically turns on the electrical immersion heater to heat enough water to satisfy the request number of showers. The control unit collects (shower duration, change in temperature gradient, cold water flow), and adjusts its calculations accordingly.

The control unit is adapted to receive input from the user interface, comprising the user requirements. The control unit calculates the required heating time according to the profile of the hot water in the tank and according to the usage profile statistic collected. In order to minimize the energy consumption the control unit is adapted to identify usage patterns. The usage patterns include many types, for example, given a family in which both parents take a shower between 20:00 PM to 21:00 Pm, and the average hot water consumption of both showers is 50 liters, the control unit saves this information and uses it in cases where 2 showers are set in the control panel between 20:00 PM to 21:00 Pm. Even though setting 2 showers typically causes to a heating of 100 liters, the present invention recognizes that at this time in the evening two showers require only 50 liters, and saves energy by heating only 50 liters.

Another parameter that is considered for the usage statistic is the number of showers requested. The software in the control unit is adapted to record the consumption values for the different number of showers requested. It is well understood that the average water consumption per shower also depends on the number of showers required. The software in the control unit is also adapted to change the heating profile according to the time in the day and season. The different usage patterns may be learned during boiler operations, or may be inserted by the user. For example, assuming that the user takes a shower every Tuesday evening around 21:00 PM, the user may set the boiler to heat-up enough water for one shower every Tuesday at 21:00 PM. In winter time the user may enlarge the amount of water heated-up for an average shower.

Besides connecting to the flow meter, the control unit is also connected to the sensors array comprises one or more temperature sensors. In one embodiment, the single sensor 115 is part of the sensor array, and the sensors array comprises at least two sensors. In this embodiment the sensors array comprises four sensors. Installing the system is very simple, the sensors array, and water flow meter are assembled between the cold water inlet 102 and the cold water supply pipe 115. The control unit 105 is connected to the water flow meter 113, to the thermostat 106, to the electrical immersion heater 104, and to the user interface (not shown). The control unit 105 is connected to the user interface through the existing power-lines 140, which typically connects the on/off switch to the electrical immersion heater. According to this embodiment, dada transfer from the sensors array to the control unit through the flow meter. In another embodiment the flow meter and the single sensor are removed, and the calculations are based merely on the changes in the temperatures measurements. According to this embodiment, the control unit detects end of shower when sequential temperatures measurements show the same temperature for a couple of minutes after a fast cooling of the water.

Fig. 2 schematically illustrates the user interface 121. Typically, the user interface is installed by the bath-room door, where the traditional on-off switch of the boiler is usually installed. The user interface comprises a control panel 122 for selecting the type of heating required. In this embodiment the control panel presents three heating functions, bath 123, shower 124, and dishes 125. In one embodiment the user set a number of dishes, in another embodiment the user set a number of piles of dishes, typically, the water that are heated for one pile of dishes is enough for washing a sink full of dishes. A select button 126 is located on the control panel for transferring the user input to a micro-processor 127. A reset button 128 is available for resetting the program set by the user, the reset also use for resetting the statistics collected during former operations. A short press resets the program set by the user, and an extended press resets the statistics collected during former operations. The control panel in this embodiment, further comprises an enter button 139. Once the user sets all his requirements, he pushes the enter button 139 for sending data to the control unit 105 in Fig. 1. In this embodiment the user interface comprises two display screens 129- 130. One screen 129 uses for presenting the user requests and the water tank status. For example, given a user who wishes to heat up enough water for two showers, in the first step, the user selects the shower option (by pressing the shower option button 124), in the second step, the user sets the number 2 by using up/down buttons 131a-131b on the quantity adjustment panel 131. After the setting is over, the user presses the select button 126 for transferring his request to the micro-processor 127. During the adjustment step, the display 129 presents the input from the user. During normal operation the display presents the water tank status, in this example the display presents the number of showers available. In order to view the user settings during normal operation, the user is required to press one of the buttons over the adjustment panel 131.

A second display screen 130 is provided for presenting the delay requested by the user. The delay can be set to each operation requested bath/shower/dishes. In one embodiment the delay is set in hours. In another embodiment the user can build a program for activating the heating system automatically. For example, the user may set a program for heating an amount of water required for two showers every day at 20:00PM, and for dishing one pile of dishes every day at 14:00PM. As mentioned hereinabove, after several operations the system 'learns' the usage profile, and adapted to heat a more precise amount of water, thus, saves energy.

The micro-processor 127 according to this embodiment is used for preparing commands which encompasses the input from the user. The commands are sent to another micro-processor located in the control unit 105 in Fig. 1, which is located by the water tank and uses for calculating the required heating time based on the water-tank status and the user requirements received from the micro-processor 127. In another embodiment, the water tank status is sent from the control unit 105 in Fig. 1 to the micro-processor 127 in the user interface. The micro-processor 127 perform the required calculations and turns the electrical heater 104 in Fig. 1 on and off accordingly.

According to this embodiment, data, namely commands from the microprocessor, transfer between the user interface and the control unit over the existing power-lines 140 of the house. Installing the present invention does not require wiring new wires. The data is transmitted over the existing power-line between the traditional on-off switch, and the water tank. In one embodiment data is transferred over the power-line during its normal operation, namely, data transfer over a live power-line. In another embodiment, a switching mechanism 141 is implemented for disconnecting the existing power-lines 140 from the power source 142 during data transfer. According to this embodiment, once the power source is disconnected, the user interface provides an acoustical or visual feedback to the user, the user program the interface, and press the select 126 button to transfer the data to the micro-processor 127. In order to prevent current leakage from the power-line 140 to the micro-processor, a filter 143 is placed between them.

The switching is controlled by a switch 144 located in the user interface. When the user wishes to insert his preferences he needs to switch off the power source. Once the power is off, a LED 146 placed over the switch, blinks to indicate to user to insert his requirements. After the data is inserted the user reconnects the power by switching the switch on. When the switch is on the LED 146 turns on for indicating that the power is connected. A speaker 147 is placed over the user interface for providing an acoustic feedback (e.g., a horn sound) at different cases. The system is adapted to provide an acoustic feedback when input from the user is required, in another case the acoustic feedback is provided when the water tank is ready for use. The speaker 147 may also provide an acoustic feedback in the case that one user consumes more than the amount calculated for him. In such cases an acoustic feedback is provided and the control unit starts reheating.

As mentioned before the communication between the user interface and the control unit may transfer over a live power-line or after switching off the power. If the last option is employed it means that the user has no communication with the control unit, and has no way of knowing whether the control unit completed the heating. To overcome this problem the current in the line is measured. In one embodiment a magnetic core, made of ferromagnetic metal is surrounded with a coil 151 of the power-line 140. When current flows in the power-lint, the magnetic core creates a strong magnetic field which detects by a magnetic sensor 152. The magnetic sensor notifies the microprocessor whether current flows in the line or not. Accordingly the microprocessor turns on and off an 'active' 160 and 'ready' 161 lights. For example, when the control unit turns on the electrical immersion heater 104 in Fig. 1, current flows in the coil 151, and the 'active' indication is on. When the control unit finishes the heating operation and the electrical immersion heater is turned off, current does not flow in the line, the magnetic sensor does not sense any magnetic field, and the microprocessor turns on the 'ready' indication.

In another embodiment a standard ammeter is connected to the power- line. The ammeter measures the electric current in the line and provides indication to the microprocessor. According to the ammeter measurement, the microprocessor turns on and off an 'active' 160 and 'ready' 161 lights The user interface 121 is located in a house, providing control over the water temperature while saving energy, as a result the life period of the hot water installation is enhanced. Another advantage of the system is its ability to retrofit to most water tanks. After installation the system is configured, different parameters relevant for the calculation (e.g., tank's size, number of sensors, sensors location) are defined through the control unit, and the system is ready for usage.

Fig. 3 schematically illustrates an embodiment of the system in an apartment building. In large apartment buildings 300 it is impossible to provide a collector for each resident. Therefore, those buildings employ a system of collectors 301 shared by all the apartments in the building. Typically, a shared set of collectors is utilized to heat a close thermo- siphon system of pipes 302. In close thermo-siphon systems a fluid (e.g., water) circulates through a close loop. The fluid is heated in the collectors 301 and flows in a close system of pipes 302. The close system of pipes goes into a layer 305 which surrounds the water tank 306, and transfer heat to the water in the inner layer of the tank. In some water tanks, the close thermo-siphon system of pipes goes inside the inner layer of the water tank, and transfers heat to the water in tank. In both cases, the contact of the hot pipes with the water inside the water tank heats the water.

One of the problems in such systems is the fact that the close system of pipes is shared by all the residents in the building. Therefore, when one resident turns on his boiler to heat the water inside his water tank, using the electrical heater 303, he needs to close a valve 307 mounted on the inlet and/or outlet of the closed system pipes, for preventing an opposite heating operation in which the water in the tank is getting hotter, and heat is transfer to the fluid in the close system of pipes throughout all the building. Another drawback exist in such systems is that pump 304 which circulates the fluid in the closed system is not controlled by the residents. Therefore, there are cases in which the fluid surrounding a water tank of one of the residents is hotter then the fluid in the rest of the system and the pump circulates the water. Such scenario will cause the hot water in the tank of that resident to get colder.

In order to prevent the drawbacks mentioned hereinabove, the system comprises one or more electronic valves mounted on one or more closed loop pipes entering into the water tank, the electronic valves are connected to the control unit, and are adapted to be closed upon activating the electrical immersion heater for preventing heating the fluid in the closed loop pipes. In one embodiment the electronic valves are adapted to sense the temperature of the fluid in the closed system and to send it back to the control unit. The control unit is adapted to close the electronic valves for preventing waste of energy due to circulating the fluid in the closed system when the water in the tank are hotter then the fluid in the closed system.

This mechanism is adapted to provide a solution to the problem of opposite heating operation mentioned above. In this embodiment the control unit is also connected to an electronic valve 307, mounted on the inlet of the cold fluid pipe which goes into the water tank 308. The control unit is adapted to close the valve for preventing circulation of the fluid in the closed loop 302. Thus, whenever the control unit decides to boost the hot water temperature by activating the electrical immersion heater 303, it closes the electronic valve 307. This operation saves energy in cases that the user forgets to turn of the electrical heating.

According to another embodiment of the invention, the control unit may be wirelessly connected to a server of the electricity provider, which continuously transmits data regarding hours with lower rate. The control unit then calculates the required heating time period and delays or advance its start time, to overlap with the hours with lower rate. In addition, the electricity provider may disable the supply voltage to the boiler during hours with over-consumption. In this case the control unit will verify that the supply voltage is enabled before starting heating. In case when the supply voltage is disabled after starting heating, the control unit will calculate the time left to complete the required heating time and will resume heating when the supply voltage is enabled back again.

According to another embodiment of the invention, the control unit may track and learn the daily hot water consumption pattern of the family and heat the boiler to optimally match it.

The above examples and description have of course been provided only for the purpose of illustration, and are not intended to limit the invention in any way. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the invention.