WO2011051379A2

WO2011051379A2 - A water heater for heating domestic water

Info

Publication number: WO2011051379A2
Application number: PCT/EP2010/066333
Authority: WO
Inventors: Troels Gottfried Pedersen
Original assignee: Colipu A/S
Priority date: 2009-10-30
Filing date: 2010-10-28
Publication date: 2011-05-05
Also published as: WO2011051379A3; BR112012010177A2

Abstract

The invention provides a water heater for heating domestic water in a building and a method of heating domestic water. The water heater comprises a water reservoir for storage of water and a heat structure for heating water in the reservoir. The heat structure is adapted to extract thermal energy from air in an ambient space in which the water heater is located and to deliver energy to water in the reservoir. In that way, the contribution of room heating provided by the water heater can be reduced or eliminated completely. This improves the ability to control indoor climate and it may reduce energy consumption in the building.

Description

A WATER HEATER FOR HEATING DOMESTIC WATER Introduction

The present invention relates to a water heater with a water reservoir and a heat structure for heating water in the reservoir. Background

Commercially available water heaters typically include an electrical water heater, or a water heater which receives hot water from a boiler or solar collector etc. Generally, the existing water heaters consume energy which is received from outside the building and converts the consumed energy to hot water. In spite of various attempts to thermally isolate the water heaters, the known types of water heaters contribute to the general heating of the building due to heat loss across the wall of the water heater. Sometimes, this contribution to the heating of the building is counteracted by the general heating of the building which then delivers less energy than necessary without the contribute from the water heater. Since, however, heating of the building is not always desired, and since the contribution to the heating which is achieved by the heat loss through the wall of the water heater is typically not cost efficient compared with the heating provided by the heating system of the building, the heat loss generally increases the energy consumption and it is therefore unwanted. As mentioned, isolation of the wall counts as one attempt to reduce the heat loss from water heaters. Even though isolation may reduce the problem, a certain heat loss will remain, and due to the isolation, the water heater becomes larger which is not always desirable. In another attempt to reduce the heat loss, the water heater is combined with a boiler such that at least a part of the heat loss occurs directly into the boiler. This, however, limits the freedom to select temperatures for the boiler and temperatures for the water heater independently. In yet another attempt to reduce the impact of the water heater on the indoor temperature, the water heater is installed outside the building. This is not a good solution in cold areas where the water may freeze, and in general, it is not an acceptable solution seen from an architectural point of view. Description of the invention

It is an object of the invention to provide a water heater and a method of heating domestic water for a building by which the heating of water may occur without heating the ambient space around the water heater. According to a first aspect, the invention provides a water heater with a heat structure which can extract thermal energy from air in an ambient space in a building in which the water heater is located and which can deliver energy to water in the reservoir and thereby heat the water.

Since thermal energy is extracted, air can be returned to the ambient space at a temperature which is lower than the temperature of the air which is received from the ambient space. The water heater according to the invention can therefore be installed and operated inside a building without contributing to the heating of the building.

It should be understood that thermal energy is extracted from the air in the building without exhausting the cooled air to the outdoor environment. Thus, thermal energy is extracted from the air which stays in ambient space in which the water heater is positioned, whereby this space is cooled. Herein 'ambient space' is a space inside the building in which the water heater is positioned.

The water heater is able to influence the thermal energy level of the building without exchanging air with the surroundings outside the building in which the water heater is positioned.

The water reservoir could be of the kind which is well known for heating water, e.g. a steel or plastic reservoir with an inlet in a bottom end of the reservoir, an outlet in the top of the reservoir and optionally a return inlet at a position between the inlet and outlet.

The heat structure could comprise a refrigerating system for extraction of thermal energy from air in the ambient space and a separate water heater for heating up the water in the reservoir and thereby deliver energy to the water, e.g. a traditional electrical heating element.

To reduce the size of the water heater, to reduce complexity and/or to reduce manufacturing, assembly and maintenance costs, the refrigeration system and water heater may be combined into one unit capable of transferring the extracted heat directly to the water in the reservoir. This combined unit may constitute the only source of heating the water, or it may be used in combination with traditional water heaters such as electrical water heaters, etc.

The heat structure could be dimensioned with a fixed capacity such that a fixed amount of thermal energy is removed from the ambient space. A control structure may control operation of the water heater e.g. based on at least one of the temperature in the ambient space, the temperature of the water, the consumption of water, the time of the day, weather forecast data, etc. In particular, such a control system may be able to receive a desired temperature in the ambient space and/or a desired amount of thermal energy to be extracted from the ambient space, e.g. given as a function of temperature of the ambient space, or to receive a desired temperature of the water in the reservoir. The control structure may be adapted, based on at least one of the mentioned desired temperatures and based on an energy-consumption-criteria to determine the rate of extraction of thermal energy from the ambient space. The energy-consumption-criteria may relate to the energy price, or the amount of energy used for the extraction, or both. The control structure may e.g. control an effect of the heat structure, i.e. the amount of thermal energy which is extracted from air in the ambient space and/or an amount of thermal energy which is delivered to water in the reservoir.

The control structure may also be capable of predicting or calculating a heat loss from the hot water in the reservoir to the ambient space. This prediction could be based on a temperature difference between the temperature of the water in the reservoir and the temperature of the ambient space. The control structure could be capable, based on the heat loss, to control the extraction of thermal energy such that the thermal energy which is extracted from air in the ambient space compensates for the loss, i.e. such that the water heater becomes neutral in the ambient space which means that it receives and delivers the same amount of thermal energy.

The control structure may further be adapted to control the effect based on combinations of any of the above mentioned input, e.g. a combination between an hour of the day and a temperature in the ambient space or a combination between temperature of the water in the reservoir and temperature in the ambient space etc. The control structure may further be programmable, e.g. in a manner where two or more standard programs can be selected, where each standard program determines the control activity e.g. based on one or more of the above mentioned input. As an example, one program could be a summer program, one could be a winter program, one could be an "away from the house" program, or different programs could be provided for different geographical locations. Additionally, the control structure may comprise a user interface allowing user programming of additional control activities, or a user interface which communicates with an external server, e.g. over the internet, by radio signals etc. and to automatically adapt settings which are suitable for a weather or power price condition, or simply to download programs suitable for a specific geographical location.

The effect can be controlled either by starting or stopping the heat structure or by controlling a power rate of the heat structure. If the heat structure is constituted by a two-phase gas compressor system, the compressor effect could be controlled by controlling the speed of the compressor or by starting and stopping the compressor. If the heat structure is constituted by a solid state heat pump, such as a Peltier element, the effect can be controlled by switching the solid state heat pump on and off or by varying the electrical power which is consumed by the solid state heat pump element.

The heat structure may comprise an outer heat exchanger arranged outside the reservoir for exchanging thermal energy with the air and an inner heat exchanger arranged inside the reservoir for exchanging thermal energy with the water. The control structure may further be adapted to control the heat structure so that the temperature of the outer heat exchanger is kept above the dew point temperature to avoid moisture.

In an alterative embodiment the control structure may be adapted to control the heat structure so that the temperature of the outer heat exchanger is kept below the dew point temperature. This may be done either to achieve a higher effect and to be able to utilise the energy of water condensing or it may be done to ensure reduction of the absolute humidity of the air in the ambient space. In any event, the control system may use a temperature sensor for sensing the temperature of the ambient space, a humidity sensor for sensing the humidity of the ambient air, and/or air pressure sensors for determining the dew point, and

subsequently to control the heat structure with the incentive to obtain a desired temperature of the outer heat exchanger.

To be able to collect the moisture released if the heat structure is kept below the dew point temperature, the water heater may comprise a moisture receiver, e.g. a bottle, a tray, or the like. The moisture receiver may be connected to a drain so that overflow of the moisture receiver can be avoided. Furthermore, the moisture receiver may comprise a level measuring structure to facilitate measuring of the level of the moisture in the receiver. The control structure may in one embodiment be able to control the heat structure dependent on the level of moisture in the receiver, whereby it may be assured that heat structure is controlled so that the temperature of the outer heat exchanger is raised to above the dew point temperature if the level of moisture approaches the top of the moisture receiver.

The control structure may be further be arranged so that it is possible to switch between operation above and below the dew point temperature, as this makes is possible to select the 'below-dew-point-temperature-mode', e.g. if it is desired to reduce the humidity in the ambient space or simply if adequate disposal of the waste moisture is available.

The control structure may comprise a temperature sensing structure and a storage structure for storing limit values relating to the temperature of the air in the ambient space, the control structure being adapted to prevent extraction of energy from the air upon sensing of an air temperature below a limit value stored in the storage structure.

In one embodiment, the control structure is adaptive such that the consumption of water from the reservoir is monitored over time, and if a consumption below a limit value is observed, the temperature of the water is reduced, e.g. in combination with a reduction of the extraction of thermal energy from the ambient space. The water heater may comprise an air duct and optionally also a ventilator for establishing a forced air flow from the ambient space into the duct and from the duct back to the ambient space. In this case, extraction of thermal energy from air may take place in the duct such that air can be returned to the ambient space at a temperature which is lower than the temperature of the air which is received from the ambient space. The duct enables better control of the extraction of thermal energy from the ambient space and enables the returned, cold, air to be guided to a specific location in the ambient space.

The duct may comprise at least two different openings with a possibility of switching between these two openings. One opening may be in communication with the room in which the water heater is positioned and the other opening may e.g. be in communication with the outdoor. This enables switching between a summer mode and a winter mode of operation, as the air during summertime may be taken from the room to cool the room. During wintertime the air may be taken from the outside, a basement, or a loft, so that the room itself (the ambient space) is not cooled.

To reduce complexity in the installation of the water heater, the duct may communicate air directly between the ambient space and the air duct, e.g. such that air is received into the duct from an upwards direction via an inlet pointing in an upwards direction when the water reservoir is installed, and e.g. such that air is also returned from the duct to the ambient space in an upwards direction. In this way, the water heater may utilise the hot air which is typically accumulated under the roof of a building and, by returning the cold air in the upwards direction, the water heater may stir the hot air and improve the indoor climate.

In an alternative embodiment, the air duct forms a U-shape and the water heater is adapted for use in an orientation where the U shaped air duct has the free ends in a downwards direction. This facilitates release of condensed water from the duct.

The air duct may either be thermally isolated or have a surface towards the ambient space which is very small, e.g. a polished surface, such that thermal exchange by convection or radiation between the duct and the ambient space is reduced or prevented.

In one embodiment, the air duct extends through a passage within the reservoir such that the duct is encircled by water in the reservoir and such that thermal energy which is lost from the duct and heat structure is received by water in the reservoir.

In an alternative embodiment, the duct surrounds the reservoir such that thermal energy which is lost from the reservoir heats up the air in the duct and thus improves the efficiency of the heat structure. In this embodiment, the water heater may comprise an inner tank forming the reservoir and an outer tank housing the inner tank, where the inner tank is sufficiently smaller than the outer tank to provide space there between. This space could constitute the duct, and openings, e.g. in the top and bottom of the outer tank could form passages into and out of the duct.

If the water heater is provided with a duct and/or a ventilator, the heat structure and ventilator could be dimensioned relative to each other such that a temperature difference between the temperature of the returned air and the temperature of the air in the ambient space becomes fixed, e.g. at most 10 degrees Celsius, or such that the difference is fixed to another desirable level. This could be achieved by implementation of a control system which controls operation of the heat structure and/or ventilator, e.g. such that the temperature difference is controlled by controlling a speed of the ventilator e.g. while the effect of the heating structure is constant.

For transporting the thermal energy to the water in the reservoir, the heat structure may comprise a heat pipe or a thermo siphon. The use of a heat pipe or a thermo siphon may increase the efficiency of the heat structure by separating the hot water in the reservoir from the hot side of the heat structure. If the heat structure comprises a solid state heat pump, such as a Peltier element, this will highly increase the efficiency of the Peltier elements, and in this embodiment, the heat pipe or thermo siphon may be arranged directly in connection with the hot side of the Peltier element. Additionally, the use of a heat pipe may prevent heat loss through the heat structure when the heat structure is inactive.

The heat structure may comprise an outer heat exchanger arranged outside the reservoir for exchanging thermal energy with the air and an inner heat exchanger arranged inside the reservoir for exchanging thermal energy with the water. In one embodiment, at least one of the heat exchangers has a heat capacity in the range of 0.2 - 0.8 J/K per Watt.

The inner and outer heat exchangers may further have a total heat capacity in the range of 100 J/K - 400 J/K, and the inner heat exchanger may have a heat capacity in the range of 5- 50 percent of the heat capacity of the outer heat exchanger. The heat structure may comprise a solid state heat pump, such as a Peltier element, e.g. being controllable between two different modes with different energy consumption based on a temperature difference between a temperature in the ambient space and a desired temperature of the water. The use of Peltier elements as a heat pump may be advantageous due to the silent operation and simple structure without moving components. One and the same Peltier element may function to extract thermal energy from the ambient space and to heat water in the reservoir. In one embodiment, the Peltier elements form part of a wall of the reservoir. In another embodiment, the Peltier elements are fixed directly to an outer surface of the wall of the reservoir, and heat from the hot side of the Peltier element propagates through the wall into the water in the reservoir. For this purpose, the wall of the reservoir may preferably have a good thermal conductivity, e.g. corresponding to that of cobber, aluminium, bronze, or similar.

Alternatively or additionally, the heat structure may comprise a 2-phase gas compressor system e.g. of the kind known from refrigerators etc. The use of a 2 phase gas compressor as a heat pump may include a C0₂, Propane, R134a, isobutene, CH3 compressor. Alternatively or additionally, the heat structure may comprise a Stirling machine. This may enable a compact water heater with a large capacity.

An evaporation refrigeration system may be used as a heat pump for providing absorption cooling of the ambient space.

In a second aspect, the invention provides a method for heating domestic water in a building where air in the building is cooled down while the domestic water is heated. It should be understood, that the above-mentioned features of the first aspect of the invention may also be applicable in relation to the method for heating domestic water in a building according to the second aspect of the invention. Thus, the second aspect may comprise any combination of features and elements of the first aspect of the invention. According to the method, the cooling and heating can be carried out such that a ratio between energy corresponding to the cooling and energy corresponding to the heating becomes predictable, and the method may comprise the step of predicting this ratio. For this purpose, the cooling and heating could be carried out such that the ratio becomes constant or almost constant, e.g. within plus/minus one percent. The thermal energy could be transferred from the air to the water by use of at least a first transfer structure and a second transfer structure, the first transfer structure being selected from the group consisting of a solid state heat pump, such as a Peltier structure, a 2-phase compressor based refrigeration structure, and a Stirling structure, and the second transfer structure is selected from the group consisting of a heat pipe structure and a thermo siphon structure.

The second transfer structure could be arranged such that a heat transfer medium is guided along a transfer passage from a start location to an end location, the end location being located below the start location in vertical direction.

In one aspect, the thermal energy from air in the building is transferred to water and the air is subsequently released inside the building such that the heat loss from the water heating becomes compensated by heat extraction from the ambient space. Accordingly, the invention, in a third aspect, provides a method for preventing unwanted room heating during heating of water by use of a water heater as described above.

In a fourth aspect, the invention provides a method for refrigerating a building where thermal energy from air in the building is transferred to water and the air is subsequently released inside the building.

In a fifth aspect, the invention provides a method for reducing humidity in a building where thermal energy from air in the building is transferred to water and the air is subsequently released inside the building. It should be understood, that the water heater of the first aspect of the invention including any of the features mentioned in relation hereto may also be applicable in relation to the methods according to the third, fourth, and fifth aspects of the invention. Thus, the third, fourth, and fifth aspects may comprise any combination of features and elements of the first aspect of the invention.

In a sixth aspect, the invention provides a building comprising a water heater according to the first aspect of the invention, wherein the heat structure is adapted to extract thermal energy from air in an ambient space in the building in which the water heater is located and to deliver energy to water in the reservoir without exchanging air with a surrounding space outside the building.

In general the loss of heat through the insulation of water heaters may not be regarded as a problem. However, losses count for a high annual loss, expenses and pollution. This is primarily because domestic water is usually kept warm, i.e. ready for usage all day. This is also the case during cold days, where the temperature or the air surrounding the water heater in the building may be as low as 15 degrees or lower. Having 60 degrees of hot water inside a water heater produces a major heat loss even though the water heater is insulated towards the ambient. As an example, a traditional 100 litres reservoir for domestic hot water loses approximately 1 kWh per day, having an ambient temperature of 20 degrees and a reservoir temperature of 60 degrees inside the reservoir. This correspond to an annually loss of 365 kWh. The total usage of hot water when using 100 litres of hot water/day creates a usage of 1680 kWh/year when heating the water to 60 degrees. A loss of 365 kWh per year corresponds to an 18% loss compared to a total usage of 100 litres of hot water per day.

In some regions of the world e.g. in southern parts of Europe, many water heaters are placed in rooms, e.g. machine rooms, inside the building which are kept unheated. During winter times e.g. in Spain or Italy, the temperature may become as low as 0 degrees in these machine rooms, increasing losses from 1 to 1.5 kWh per day during wintertime. This is also the case if the water heater is placed in a cold cellar where the general temperature may never exceed 15 degrees through the year. Losses from water heaters in these rooms can be seen as wasted electricity creating pollution and increased electric bills.

In many buildings piping furthermore counts for substantial losses as pipes leading from a water reservoir is heated during flow of the domestic water. Another aspect is moisture in e.g. bathrooms. Moisture is in general a problem where much water is used, such as in kitchens and bathrooms. By use of a water heater with a heat pump in these rooms it is possible to reuse the heat of evaporated water and by the same time remove moisture from the room. It is a further object of the invention to regain this heat dispersed from the water reservoir, together with waste heat generated by e.g. other electric devices such as washing machines, tumble dryers, or boilers for central heating.

Detailed description The invention will now be described in further details with reference to the drawing in which Figs. 1 - 6 illustrate water heaters according to the invention.

It should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Fig. 1 illustrates a water heater 1 comprising a reservoir 2 enclosed in an insulation 4 and a cabinet 3. The reservoir and enclosure may be attached to the wall 100 of a building or it may stand on the floor. The reservoir 2 is equipped with means that allows water to enter and to leave the reservoir for domestic hot water usage. The reservoir 2 may comprise a pipe connection 5 in the bottom of the reservoir 2 and a pipe connection 6 connected in a way that allows the tap water to be taken from the top of the reservoir 2.

The system further comprises a duct 7 e.g. placed on the back side of the reservoir 2 between the insulation 4 and the wall 100. In the duct 7, a first heat exchanger 10 is placed in order to remove heat from the ambient air passing the heat exchanger. The heat exchanger 10 is thermally connected with one or more Peltier elements 8, performing a heat pump effect. Further, the Peltier elements 8 are in thermal contact with either the outside enclosure of the reservoir 2, or a second heat exchanger 9 which is in thermal

communication with the reservoir, or which is arranged in the reservoir.

In one embodiment the second heat exchanger 9 is placed inside the reservoir 2 without a cut out in the enclosure of the reservoir 2.

The system further comprises a ventilation fan 11 that allows air to be circulated in the room where the system is placed - the room air temperature is thereby reduced. The temperature of the room, i.e. the ambient air temperature, is defined as T₀, and the average temperature in the reservoir is defined as T_x. The system may also comprise one or more vents 12 that can suppress the convection of air around the first heat exchanger. This will take place whenever the reservoir 2 is hot, and the solid state heat pumps in the form of Peltier elements 8 are cut off. In this situation heat will flow from the reservoir back into the first heat exchanger. Thus, the first heat exchanger 10 will become hotter than the ambient temperature T₀ and convection will start removing heat from the reservoir 2 into the ambient air. To prevent this unwanted heat loss, one or more vents 12 are placed to shut of the duct whenever the system is not cooling/heating.

The vents 12 may be driven by the airflow created by the fan 11, or they may be operated in another way, e.g. electrically. Finally, the system comprises a control unit 13 also having a power supply to supply the Peltier elements.

The control unit 13 may have an interface allowing users to program or adjust the function of the system, or allowing the system to gain information concerning temperatures in the surroundings, weather forecasts from the internet or prices on electric power in order to decide different modes of operation.

In one embodiment of the invention, the control unit 13 can operate in different modes in order to gain special properties of the system.

In one mode the system is working with full power to the Peltier elements in order for them to produce as much cooling of the ambient space as possible, though this means that the reservoir is heated rapidly and that the system is working quite inefficiently, i.e. with a low COP.

In another mode the system is working to optimize the utilization of the electric energy by controlling the current in the Peltier elements to be as low as possible while still performing extraction of thermal energy from air in the ambient space. Fig. 2 illustrates another embodiment of a system according to the invention comprising a reservoir 2 enclosed in an insulation 4 and a cabinet 3. The reservoir and enclosure may be attached to the wall 100 of a building or it may stand on the floor.

The reservoir 2 is equipped with means that allows water to enter and to leave the reservoir for e.g. usage in the form of domestic hot water. This can be done by having a pipe connection 5 in the bottom of the reservoir 2 and a pipe connection 6 connected in a way that allows the tap water to be taken from the top of the reservoir 2. The system further comprises a duct 7 e.g . placed on the back side of the reservoir 2 between the insulation 4 and the wall 100. In the duct a first heat exchanger 10 is placed in order to remove heat from the ambient air passing the heat exchanger. The heat exchanger 10 is connected to the compressor 8a so that evaporated gas in the heat exchanger 10 can be lead back to the compressor 8a . The compressor 8a is further connected through piping to a condenser 9a . The condenser may be wrapped around the wall 2 of the reservoir, or it could be placed inside the reservoir 2 in order to transfer heat from the gas entering from the compressor to the water or liquid inside the reservoir.

The system further comprises a fan 11 that allows air to be circulated in the room where the system is placed to thereby cool the air in the room .

A control unit 13 is controlling the start and stop of the compressor 8a on basis of different strategies concerning temperatures T_x in the reservoir 2 and the ambient temperature T₀

The heat exchanger 10 may have a large thermal constant Ci in order for the system to work efficiently. To minimize delay of cooling e.g . due to de-icing of the heat exchanger, the heat exchanger 10 is normally made with as low a weight as possible. The provision of a heat exchanger 10 with a large thermal constant has, however, shown to make the control of the air cooling much more precise in relation to the compressor 8a . At least if the system must be kept simple and without expensive regulation of the compressor.

Thus, the compressor can be started and stopped repeatedly as a simple way to regulate the cooling power, without having large fluctuations on the cooled air (for a give flow of air), leading to sudden condensation of water on surfaces exposed to the cold air flow T₂.

Fig . 3 illustrates another water heater 1 comprising a reservoir 2 enclosed in an insulation 4 and a cabinet 3. The reservoir and enclosure may be attached to the wall 100 of a building or it may stand on the floor. The reservoir 2 is equipped with means that allows water to enter and to leave the reservoir for domestic hot water usage. This may comprise a pipe connection 5 in the bottom of the reservoir 2 and a pipe connection 6 connected in a way that allows the hottest tap water in top of the reservoir 2 to be drained .

The system further comprises a thermo encapsulation 14, which helps to collect heat that is lost from the reservoir 2 through part of the insulation 4. At least a part of the insulation 4 will be between the reservoir 2 and the thermo encapsulation 14. The thermo encapsulation 14 will be in thermodynamic contact with the bottom of the reservoir 2 through the heat pump element 8' and a second heat exchanger 9 inside the reservoir. If the heat pump element 8' is not in use, there will still be a continued transportation of heat from the thermo encapsulation 14 to the reservoir 2 as long as the water in the bottom part of the reservoir is kept cold, e.g. by continuously entering of fresh cold water.

The system further comprises a second heat pump element 8" which is connected to an outside first heat exchanger 10 that collects heat from the surroundings.

The use of two heat pumps in series - 8" and 8' - makes it possible to control the

temperature and heat flux so that the thermo encapsulation 14 is kept about room

temperature T₀ or just above. This minimizes the loss of heat from the reservoir 2, even though the temperature in the top of the reservoir 2 may be very high, such as about 60 degrees.

Air is forced to pass the first heat exchanger 10. Alternatively, the circulation of air may be based on convection.

The system further comprises a control unit 13 that may help to control the power or capacity of the heat pumps 8' and 8". As an example, the control unit 13 may control the current running in the heat pump 8' being a thermo electric heat pump so that the mean temperature T₂ of the thermo encapsulation 14 is only 5 degrees higher than that of the outside temperature T₀, absorbing as much waste heat as possible. Furthermore, the control unit 13 may control the current running in the second thermo electric heat pump 8", so that the there is no backflow of heat from the thermo encapsulation 14 and the first heat exchanger 10. Whenever T_x decreases in the bottom of the reservoir 2, or when much domestic hot water is needed, the control unit 13 may increase the current running to the two heat pumps 8' and 8" to create a flow of heat from the first heat exchanger 10 to the second heat exchanger 9.

Fig. 4 illustrates a water heater 1 comprising a reservoir 2 enclosed in an insulation 4 and a cabinet 3. The reservoir and enclosure may be attached to the wall 100 of a building or it may stand on the floor. The reservoir 2 is divided into two separated chambers 2a and 2b connected with e.g. an orifice or tube 15 which allows water to pass - at least - from reservoir 2b into 2a. The system further comprises connections 5 that enable fresh cold water to enter the reservoir 2b. Further the reservoir 2a is equipped with a connection 6 that allows for hot water to leave the reservoir 2a which is considered to be the hottest. In the insulation 4 a thermo encapsulation 14 is positioned. The thermo encapsulation is adapted to gather waste heat from the reservoir 2. The thermo encapsulation may be made of metal, e.g. of copper or aluminium. The system further comprises a heat pump or a heat pipe/conductor 8'. The heat pump 8' is connected to a second heat exchanger 9b inside the lower reservoir 2b. The system also comprises a control unit 13 which may help adjusting the current or which may comprise a programmed current to ensure that the heat pump 8' may always keep the thermo encapsulation 14 cold enough to minimize losses towards the surroundings.

In addition the top reservoir 2a is heated by a second heat pump 8" which collects waste heat from the surroundings, e.g. from waste of heat in pipes outside the system, by a first heat exchanger 10 and a hot second heat exchanger 9a. The control unit 13 may further control the current or start stop of the heat pump 8". As the connection 15 between the two reservoirs 2a and 2b is small, the mixture of hot and cold water is only enabled when preheated water from the lower reservoir 2b is pressed into the upper reservoir 2a. This happens during usage of hot water, as fresh cold water enters the lower reservoir from the supply line and connection 5.

It should be understood that even though thermo electric heat pumps, such as Peltier elements, are within the preferred embodiment of the invention, any other type of heat pump may be used. This includes 2 phase gas/liquid heat pumps, gas heat pumps, and any other type of heat pumps.

Fig. 5 illustrates a water heater 1 comprising a reservoir 2 enclosed in an insulation 4 and a cabinet 3. The reservoir and enclosure may be attached to the wall 100 of a building or it may stand on the floor. The reservoir 2 is divided into two separated chambers 2a and 2b connected thermally by e.g. a heat pipe or heat pumps 8". The system further comprises connections 5 that enable fresh cold water to enter the reservoir 2a. Furthermore, the reservoir 2a is equipped with a connection 6 that allows for hot water to leave the reservoir 2a, the water being taken from the hottest area of the reservoir 2a. The lower reservoir 2b is connected to a secondary heat pump 8' which is thermally in contact with a second heat exchanger 9 inside the reservoir 2b. A first heat exchanger 10 outside the reservoir 2b enables collection of waste heat from the surroundings by forcing air from the surroundings to pass the heat exchanger 10. The reservoir 2b may comprise a liquid being water or another liquid mixture. Alternatively, the reservoir 2b may comprise a solid material or a material changing from a solid state to a liquid state during heating within the available temperature range.

A control unit 13 may be adapted to control the current to the heat pumps 8' and 8" in embodiments, where the heat pumps are thermo electric heat pumps. In case the heat pumps are of another type, the control unit may control e.g. the speed of a compressor in order to control the heat transfer of the heat pump.

I should be understood that the heat pump 8' or 8" may also includes additional thermo elements to secure e.g. that heat is not lost in a heat back flow from the reservoir 2a to 2b or from 2b to the surroundings. This may include heat pipes of different types or different types of thermo siphons.

Fig. 6 illustrates a water heater 1 comprising a reservoir 2 enclosed in an insulation 4 and a cabinet 3. The reservoir and enclosure may be positioned below a table with a sink, it may stand on the floor, or it may work as part of a building. The reservoir 2 is heated by a heat pump 8' or by an additional heating device or heat source illustrated by the element 16. The heat pump 8' transfers heat from the surroundings by a second heat exchanger 9 connected to the warm outlet of the heat pump 8', and a first heat exchanger 10 connected to the cold side of the heat pump 8'. A device for circulating air, e.g. a fan of ventilator 18 driven by an electric motor, may be applied. Furthermore, the water heater 1 may comprise a drain and water collector 19, that helps colleting condensed moisture and guide it e.g. to a drain somewhere in the building or the room. This drain may be a drain for a sink or bathtub. The water heater 1 may be directly connected to only one single tap 17, e.g. placed nearby. In this embodiment the water reservoir 2 may have a small volume as only one tap must be supported. As the water heater 1 is placed close to the tap, the loss of heat from the pipes connecting the water heater and the pipe is minimized. A further benefit is to have instant hot water whenever needed.

The system comprises a simple or advanced control unit 13. The water in the reservoir 2 may be heated by a simple on/off of the heat pump 8' whenever the temperature in the reservoir exceeds a lower level. If the heat pump is a thermo electric heat pump like Peltier, the control could be a simple on/off of maximum of predetermined current running in the Peltier element or elements.

In other cases the control unit 13 may apply a more intelligent control which determines the heat transferred by the heat pump 8' by use of different sets of data. The set of data may comprise on/off at different temperatures, depending on the time of the day. As an example the temperature may drop during night-time. The data could also comprise knowledge of prices of electricity e.g. collected through the internet or in some other way. The control unit may then calculate the optimal time for heating, or how rapidly the water should be heated. As the heat pump 8' decreases the capacity of transferring waste heat from the surroundings back the reservoir 2, the efficiency of the heat pump may increase though the time of heating may also increase. As an example, the control unit may calculate that during nighttime when electricity is inexpensive and usage of domestic hot water is low, the heat pump is driven most efficient as possible with a low capacity, until 7 a.m. from which time the system should work with highest capacity in order to always fulfil needs for instant hot water. By 11 p.m. it could then go back into high efficiency mode.

The control unit 13 may also have different modes where one is e.g. high capacity, one is high efficiency, and one is normal. The control unit 13 may also control a supportive heat element 16 which may be applied whenever the need for instant heating is high, and the capacity of the heat pump 8' is not high enough.

Furthermore, the control unit 13 may be adaptive and learn how the usage of domestic hot water is at a particular tap, so that heat is normally only generated when needed or just before.

Claims

1. A water heater (1) for heating domestic water in a building, the water heater comprises a water reservoir (2) for storage of water and a heat structure (8, 9, 10) for extracting water in the reservoir, wherein the heat structure (8, 9, 10) is adapted to extract thermal energy from air in an ambient space (T₀) in the building in which the water heater is located and to deliver energy to water in the reservoir (2).

2. A water heater according to claim 1, comprising a control structure (13) adapted to control an effect of the heat structure (8, 9, 10).

3. A water heater according to claim 2, wherein the effect is controlled based on a

temperature (T₀) of the ambient space.

4. A water heater according to claim 2 or 3, wherein the effect is controlled based on a temperature of water in the reservoir (2).

5. A water heater according to any of claims 2-4, wherein the effect is controlled based on a signal from a clock.

6. A water heater according to any of claims 2-5, wherein the effect is controlled based on a determined or estimated heat loss from the water to air in the ambient space.

7. A water heater according to any of claims 2-6, wherein the effect is controlled based on a weather condition.

8. A water heater according to any of claims 2-7, wherein the effect is controlled based on an energy price.

9. A water heater according to any of claims 2-8, wherein the effect is controlled based on a determined or estimated consumption of water from the reservoir (2).

10. A water heater according to any of claims 2-9, wherein the control structure comprises a temperature sensing structure and a storage structure for storing limit values relating to the temperature of the air in the ambient space, the control structure being adapted to prevent extraction of energy from the air upon sensing of an air temperature below a limit value stored in the storage structure.

11. A water heater according to any of the preceding claims, comprising an air duct (7) with an inlet for receiving air from the ambient space and an outlet for returning the air to the ambient space, the heat structure being arranged to extract the thermal energy from air in the air duct.

12. A water heater according to claim 11, comprising a ventilator (11) for establishing a forced air flow through the duct.

13. A water heater according to claim 11 or 12, wherein the air duct extends between an intake and a discharge which are formed to communicate air directly between the ambient space and the air duct.

14. A water heater according to any of claims 11-13, wherein the air duct is adapted to prevent thermal exchange by convection or radiation with the ambient space.

15. A water heater according to any of claims 11-14, wherein the air duct forms a U-shape and the water heater is adapted for use in an orientation where the U-shaped air duct has the free ends in a downwards direction.

16. A water heater according to any of claims 11-15, wherein at least one of the ventilator and heat structure are dimensioned such that a temperature difference between the temperature of the returned air and the temperature of the air in the ambient space is at most 10 degrees Celsius.

17. A water heater according to claim 16, comprising a control structure adapted to the control the temperature difference by controlling a speed of the ventilator.

18. A water heater according to any of the preceding claims, wherein the heat structure comprises a heat pipe or a thermo siphon.

19. A water heater according to any of the preceding claims, wherein the heat structure comprises a outer heat exchanger arranged outside the reservoir for exchanging thermal energy with the air and an inner heat exchanger arranged inside the reservoir for exchanging thermal energy with the water, at least one of the heat exchangers having a heat capacity in the range of 0.2 - 0.8 J/K per Watt.

20. A water heater according to claim 19, wherein the inner and outer heat exchangers have a total heat capacity in the range of 100 J/K - 400 J/K.

21. A water heater according to claim 19 or 20, wherein the inner heat exchanger has a heat capacity in the range of 5-50 percent of the heat capacity of the outer heat exchanger.

22. A water heater according to any of the preceding claims, wherein the heat structure comprises a solid state heat pump, such as a Peltier element.

23. A water heater according to claim 22, wherein the solid state heat pump is controllable between two different modes with different energy consumption based on a temperature difference between a temperature in the ambient space and a desired temperature of the water.

24. A water heater according to any of the preceding claims, wherein the heat structure comprises a outer heat exchanger arranged outside the reservoir for exchanging thermal energy with the air and an inner heat exchanger arranged inside the reservoir for exchanging thermal energy with the water, the water heater further comprising a control structure adapted to control the temperature of the outer heat exchanger.

25. A water heater according to claim 24, wherein the temperature of the outer heat exchanger is control based on a dew point temperature of the ambient space.

26. A water heater according to any of the preceding claims, wherein the heat structure comprises a 2-phase gas compressor system.

27. A water heater according to any of the preceding claims, wherein heat structure comprises a Stirling machine.

28. A water heater according to any of the preceding claims, further comprising a thermo encapsulation being adapted to collect thermal energy which is transmitted from the water reservoir to the ambient space.

29. A method for heating domestic water in a building where air in the building is cooled down while the domestic water is heated.

30. A method according to claim 29, wherein the cooling and heating is carried out such that a ratio between energy corresponding to the cooling and energy corresponding to the heating becomes predictable.

31. A method according to claim 30, comprising the step of predicting the ratio.

32. A method according to claim 30 or 31, wherein the cooling and heating is carried out such that the ratio becomes constant.

33. A method according to any of claims 30-32, wherein the air is cooled at most 10 degrees Celsius.

34. A method according to any of claims 29-34, wherein thermal energy is transferred from the air to the water by use of at least a first transfer structure and a second transfer structure, the first transfer structure being selected from the group consisting of a solid state heat pump, such as a Peltier structure, a 2-phase compressor based refrigeration structure, and a Stirling structure, and the second transfer structure is selected from the group consisting of a heat pipe structure and a thermo siphon structure.

35. A method according to claim 34, wherein the second transfer structure is arranged so that a heat transfer medium is guided along a transfer passage from a start location to an end location, the end location being located below the start location.

36. A method for refrigerating a building where thermal energy from air in the building is transferred to water and the air is subsequently released inside the building.

37. A method for reducing humidity in a building where thermal energy from air in the building is transferred to water and the air is subsequently released inside the building.

38. A method for preventing unwanted transfer of thermal energy to a room, the method comprising the use of a water heater according to any of claims 1-28.

39. A building comprising a water heater according to any of claims 1-28, wherein the heat structure (8, 9, 10) is adapted to extract thermal energy from air in an ambient space (T₀) in the building in which the water heater is located and to deliver energy to water in the reservoir (2) without exchanging air with a surrounding space outside the building.