FIELD OF THE INVENTION

The present invention relates to heating ventilation and air conditioning and more particularly to water heating. CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application claims priority from and is related to U.S. Provisional Patent Application Serial Number 61/954,658, filed 03/18/2014, this U.S. Provisional Patent Application incorporated by reference in its entirety herein.

BACKGROUND OF THE INVENTION Heat pumps are used extensively in heating and air conditioning devices. A heat pump is a heat exchange circuit designed to move heat to the opposite direction of spontaneous flow, absorbing heat from a cold space and releasing it to a warmer one. More commonly heat pumps are used for cooling, as in freezers where the heat is removed from the cooled space to the warmer environment. When heat pumps are used for heating, heat is absorbed from the cooler environment and released in the heated space. In many air conditioning applications the heat pump is designed to operate in both directions, depending on whether the air condition is used for cooling or heating.

Heat pumps use intermediate fluid referred to as a refrigerant, to absorb heat where it vaporizes, in the evaporator, and then to release heat where the refrigerant condenses, in the condenser. The refrigerant flows through insulated pipes between the evaporator and the condenser, allowing for efficient thermal energy transfer at relatively long distances. The heat pump compresses the refrigerant on the side to be warmed (condenser), and releases the pressure at the side where heat is absorbed (evaporator). When the heat pump is operated in heating mode, the outdoor coil is an evaporator, while the indoor is a condenser. Compressing and circulating the refrigerant requires input of energy, usually electricity. The ratio of the heat energy transferred to the input energy is called system coefficient of performance COP. The COP of a heat pump can be 3 or 4. If alternatively the input electrical energy was converted to heat in standard resistance heater the COP would then equal to 1. The COP can be regarded as a measure of system efficiency and hence for the purpose of heating a heat pump is an efficient heating device.

Water heating is a significant portion of domestic energy consumption, and in certain industrial and commercial use. Hot water for domestic use is sometimes provided by central heating or storage water heaters installed residentially, whereas industrial hot water is usually provided by storage water heaters installed in a facility. Water heaters consist of a cylindrical vessel or container that keeps water continuously hot and ready for use. Conventional storage water heaters may use electricity, natural gas, propane, heating oil, or solar energy. Alternatively, storage water heaters can operate at higher COP using heat pump which is energetically more favorable.

There are ample examples of domestic hot water heat pumps, for example US department of Energy (DOE) provides overview of the technology and a guide for selecting a DHW HP device according to user needs http://energy.gov/energysaver/articles/heat-pump-water-heate rs.

One of the drawbacks of the current technology is that domestic hot water heaters are integral with the heat pump while there is a significant number of installed conventional storage water heaters. Therefore, there is a need to provide a "retrofit" solution for the installed base of storage water heaters in the sense to be adapted to be heated by the heat pump.

SUMMARY OF I VENTION

According to a first aspect of the present invention there is provided a heat pump water heater comprising: a heat exchange circuit comprising: a heat absorber; and a heat exchanger configured to be immersed in water within a water storage container, said heat absorber configured to transfer heat to refrigerant in said heat exchanger and said heat exchanger configured to transfer heat from the refrigerant to water. The heat pump water heater may further comprise a resistive heater, immersed in the water and configured to heat the water.

The immersed heat exchanger may be of elongated shape and essentially circular profile configured to fit into a vertically oriented water storage container with a flange. The immersed heat exchanger may comprise at least one vertical tube, said tube is folded for circulating the refrigerant, and a plurality of planar fins attached radially along the length of said tube, and the plane of said fins may be inclined to the horizontal; wherein said fins are configured to conduct heat from said tube to the water.

The at least one vertical tube may comprise a plurality of tubes, said tubes are corrugated to maximize contact area with water.

The heat absorber may comprise an evaporator configured to absorbs heat from the outside environment.

The evaporator may comprise a coil constructed in circular shape having a plurality of loops and located on the perimeter of the heat absorber. The evaporation coil may be coated with hydrophilic coating to increase wettability.

The water heater may further comprise a control unit and a temperature sensor positioned in a water storage container, said control unit configured to monitor water temperature measured by said temperature sensor; said control unit further configured to regulate water temperature by switching the current between said heat pump water heater and said resistive water heater. The heat absorber may comprise a motorized compressor configured to heat the refrigerant.

The control unit may comprise an adjustable electrical inverter adapted to provide variable speed of refrigerant flow by controlling the speed of the compressor motor.

The control unit may comprise a programmable logic controller configured to be accessed remotely. The control unit may be accessed remotely from the electrical-grid control center wherein the pump water heater and resistive water heater are activated remotely during low electricity load and deactivated remotely during high electricity load.

The heat exchanger may comprise a coil shaped from a single tube. The heat exchanger may comprise a curved refrigerant carrying pipe firmly attached to a metal plate.

The heat exchanger may comprise double walls.

The curved refrigerant carrying pipe may be sandwiched between two metal plate sheets.

The heat exchanger may comprise a plurality of stacked tube plates connected serially or in parallel by refrigerant pipes.

The heat pump water heater may further comprise an illuminated indicator display.

The illuminated indicator display may comprise one of LED and display screen.

The illuminated indicator display may comprise at least one of heating status indicator, water temperature indicator and temperature set point. The heat pump water heater may further comprise a light source for illumination and visibility.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings.

With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings:

Fig. 1 is a schematic configuration of the domestic hot water heater comprising a heat pump constructed of external heat absorber and immersion heat exchanger unit configured to heat the water, and a control unit. The heat absorber and the immersion heat exchanger are connected via refrigerant tubing.

Fig 2A and Fig 2B are side view and cross sectional view of water immersed condenser constructed of vertical tubes carrying the refrigerant and planar fins inclined to the horizon and running the length of the tubing.

Fig. 3 is a side view of water immersed condenser constructed of inclined tubes carrying the refrigerant and planar fins attached perpendicularly and running the length of the tubing.

Fig. 4A and Fig. 4B are isometric and side views of immersion condenser constructed of corrugated tubes carrying the refrigerant.

Fig 5 is a water-immersed condenser of coiled shaped tube .

Fig 6 is a tube plate condenser comprises of curved pipe firmly attached to a meal plate. Fig 7 is a water immersion heat exchanger formed of a tube plate condenser curved into a spool of a rectangular cross section.

Fig 8A is a double wall tube plate condenser comprise of curved pipe firmly attached and sandwiched between two meal plates

Fig 8B is a cross section of double wall tube plate condenser of Fig 8 A Fig 9 is water immersion heat exchanger comprised of stack of tube plate condensers wherein the flow of refrigerant to and out of individual tube plates is in parallel via manifolds.

Fig 10 is water immersion heat exchanger comprised of stack of tube plate condensers wherein the flow of refrigerant through individual tube plates is in series. Fig 11 is schematic of circular evaporation coil located within external heat absorber.

Fig 12 is a schematic of enclosure for co-installation of outdoor heat absorbing unit of a water heater and outdoor unit of an air conditioning system.

Fig 13 is a schematic of heat pump water heater integrated in a variable refrigerant flow (VRF) air condoning unit. Fig 14 is a block diagram of the control unit that comprises a programmable logic controller that has a remote access in addition to local user interface. The control unit controls the water temperature by switching on and off the current to a heat pump and resistive heater.

DESCRIPTION OF PREFERRED EMBODIMENTS Reference is made to Fig 1 , which is a simplified pictorial illustration of the domestic hot water (DHW) heater and storage, based on air-to-water heat pump technology constructed and operative in accordance with embodiments of the invention. As seen in Fig 1, the DHW system 100 comprises a heat exchange circuit ("heat pump") comprising an external heat absorber 110, which is configured to absorbs heat from outdoor air and transfers it to a heat exchanger 109 immersed in water contained in a storage container 140. The heat exchange cycle is achieved as follows: the refrigerant flows from the evaporator 113 through pipe 114 to the condenser 109 after the fluid's temperature has been elevated by compressing it in the compressor 112. The evaporator 113 is the outdoor coil where heat (designated by an arrow)105 is absorbed from the outside air, while the condenser 109 is the indoor coil where thermal energy is transferred to water 106 (indicated by arrows). The refrigerant is then transferred via pipe 115 and allowed to expand, cool, and absorb heat to reheat to the outdoor temperature in the outside evaporator 113, and the cycle repeats. For better heat absorbing efficiency from the outdoor air the heat absorbing unit also comprises an electrical fan 111. Optionally the heat absorbing unit may be provided with illuminated indicator display 1 16 such as for example LED and /or display screen. Such indications may for example be "heating on" and / or "heating off cycles, water temperature indicator, temperature set point, etc., which can be clearly seen at a remote distance. In addition, because the heat absorbing unit is installed outdoors in certain embodiment it can also be provided with a light source, such as for example LED for illumination

and visibility.

The coefficient of performance (COP) of a heat pump is the ratio of the heat delivered to the hot water per input of electrical energy. Generally heat pumps are efficient devices for heating, and COP of 3 or greater is not uncommon; however the COP decreases with increasing temperature difference between the outdoor temperature and space or water heated. For weather conditions where the temperature difference may become large, the DHW is preferably a hybrid type, i.e., provided with a resistive heater element 125 that can operate independently of the heat pump. The resistive heater is seen to be electrically wired by an electrical cable 123 to a control unit 120. Similarly, the heat absorber 110 is also electrically wired by electrical cable 121 to the control unit 120. The DHW is further provided with a temperature sensor 126, also electrically wired 124 to the control unit 120.

The DHW can be considered as configured with an internal section which fits into the water storage container and is immersed into water, comprising the immersion heat exchanger, the resistive heater, and the temperature sensor, and an extemal section comprising the heat absorber and the control unit.

As seen in the Fig. 1 the water immersed components are adapted to fit to conventional water storage 140 with a flange 130 and may also be immersed in other open or close liquid vessels, such as hot tub, or industrial water tank. The flange has a feed-through insert 131 to allow the hot refrigerant inlet pipe 114 into a water immersed heat exchanger 109 and a second insert 132 to allow refrigerant flow from the water immersed heat exchanger. The flange is also adapted with other feed -through inserts to accommodate the resistive heater 125 and the temperature sensor 126. In the refrigerant flow circuitry the water immersed heat exchanger is a condenser where the refrigerant gas condenses into a liquid and thereby releases heat into the surrounding water. In the description below water -immersed (or immersed in short) heat exchanger and water- immersed condenser are used interchangeably.

In one embodiment the water - immersed condenser shown in Fig. 2A is constructed of tubes where refrigerant flows 210, typically constructed of copper or other alloys of efficient heat conduction properties. Because water can be corrosive the tubes can be coated by corrosion- resistant material (e.g., by nickel). The tubes extend from the hot refrigerant inlet 131 on the flange, folded, and run in parallel as to from a closed round to the outlet 132 located on the flange. To achieve high surface for efficient heat exchange thin fins 220 constructed of copper, or other alloys of efficient heat conduction properties are arranged around the tubing 210 and running the length of the tubes. Similar to the tubing, the fins are coated to protect against water corrosion. The fins are firmly attached to maximize heat conduction. On the one hand, the number of fins along the length of the tube needs to be sufficiently large to deliver high surface area; on the other hand, the spacing between fins needs to be sufficiently large to allow efficient water circulation around the facets of the fins. Typically the density of fins can be between 4 fins per 1 inch of tube length, to 12 fins per inch. Because the water stored in the container forms layers according to their respective temperature, with layers of hot water raising above layers of colder water, the preferred installation of the storage container is vertically, along the cylinder axis. Equally, to allow water circulation and prevent stagnation on the fins surface, the fins may be inclined at an angle such that the surface plane is not perfectly horizontal.

In another embodiment shown in Fig. 3 the fins are shown to be largely perpendicular to the tubing, wherein the entire structure of heat exchanger is tilted such that tubes are aligned at an angle to the vertical which results in fins being inclined to the horizon. The fins are constructed to form large surface contact with water. They are essentially of planar geometry, the shape of the fin can be circular as depicted in Fig. 2B, but can assume any other shape, octagonal, hexagonal, square or rectangular. Since the immersion condenser is designed to fit into conventional hot water storage the lateral size is limited to the opening allowed by the particular type of storage. The exact number of tubes and their pattern across fin plane is not particular but can follow the standard tubing adopted in heating, ventilation, and air conditioning (HVAC) industry. In another embodiment of the immersion condenser shown in Fig. 4 A and side view in Fig. 4B the large surface area, required for better heat exchange is achieved by corrugated shape of the tubing. Such tubing shape offers high surface area of the immersed tube with the surrounding water that minimizes the flow impedance of the refrigerant and yet maintains small cross section area to fit a water storage container. Similar to the previous embodiment the tubing are coated with corrosion resistant material.

In another embodiment the immersed condenser shown in Fig 5 is a coil shaped from a single tube such as to from large surface area contact with the surrounding water. In certain

arrangements the refrigerant carrying tube is a double walled pipe, such as for example Bundy pipe, manufactured by rolling a strip through 720 degrees and brazing the overlapped seam.

A tube plate condenser shown in Fig 6, comprises of curved refrigerant carrying pipe 610 firmly attached to a metal plate 620. With high surface area of the metal plate the heat is transferred efficiently from the refrigerant to the surrounding water. Preferably the refrigerant carrying tubes comprise a double walled pipe, such as for example Bundy pipe described above. In one preferred embodiment the immersed heat exchanger shown in Fig 7 is constructed by curving a tube plate condenser described in greater detail in Fig 6 to a shape that fits the water container. As with other water immersed condenser described above the tube plate condenser is coated with enamel, epoxy resin or with corrosive resistive paint.

In certain embodiments the immersed condenser should have a double walled barrier between the refrigerant and the heated water. The tube plate condenser depicted in Figs 8A and 8B is constructed of a curved pipe 810 firmly attached and sandwiched between a first metal plate sheet 820 and a second metal plate sheet 830. The metal sheet plates extend over the pipe and are brazed or welded together over the edge 840. The protruding pipes are set in an external sleeve 850 which is also brazed to the metal sheets. The tube plate condenser may also be provided with holes 860 through the metal sheets for stacking a number of condenser plates as will be described later below. In a simplest arrangement a single tube plate condenser is used as the immersion condenser provided it is fitted to the water cylinder container. Generally it is desired to increase the surface area contact with the water so as to increase the heat transfer efficiency. In tube plate panel is shown to be curved into a spool of rectangular shape but the shape of the panel can have a cylindrical shape adapted to fit into the water container.

In still another embodiment the immersion heat exchanger shown schematically in Fig 9 is constructed of stacked tube plates 910 of essentially planar geometry. The individual tube plates are stacked by means of threaded rods 920 inserted through holes drilled in the tube plates as explained above. The stack array is secured and fastens by spacers 930 between the tube plates and nuts 940.

In a first configuration shown in Fig 9 the inflow to the individual tube plates is in parallel. Each tube plate is provided with individual inflow pipe 911 and outflow pipe 912. Inflow of the hot refrigerant to the individual tube plates is via a manifold 950 fed from the main inflow pipe 114. Similarly the outflow of the cold refrigerant from the individual tube plates is via manifold 960 coupled to the main outflow pipe 115. In one embodiment the inflow manifold 950 and outflow manifold 960 are water immersed, located within the water container, wherein the main inflow pipe 114 and main outflow pipe 115 are fed-through the sealing flange 130. In a second configuration the manifolds are located outside the water container wherein the inflow pipes 920 and outflow pipes of the individual tube plates are inserted through the flange. Similar to other arrangements the flange is also provided with other feed-through inserts to accommodate resistive heater and the temperature sensor.

In a second configuration shown if Fig 10 the individual tube plates are connected in series: The hot refrigerant inflows from the main inflow pipe 114 into first tube plate 1010. After circulating in the first tube plate the refrigerant flows to a second tube plate 1020 through connecting pipe 1015; the second tube plate and the third tube plate 1030 are connected in the same manner through pipe 1025. The outflow of cold refrigerant to the main outflow pipe 115 is done from the last tube plate. Returning to Fig. 1, the heat absorbing unit 110 contains an evaporation coil 113 where the cool refrigerant absorbs heat from the outside environment. The coil shown in greater detail in Fig. 11 is constructed of metal tubing formed in a shape of a plurality of loops as to from large surface area contact with the outside air, has circular shape and is located at the perimeter of the absorbing unit. If the fan 111 located within the heat absorbing unit 110 is configured to force air out of the unit ("blow out") as indicated by air flow 1 101 , the flow of outside air 1 102 into the heat absorbing unit is directed towards the coil, making heat absorption more efficient. Very often during operation the surface of the evaporation coils is colder that the dew-point temperature of the outside air. Therefore, moisture condenses and accumulates on the surface of the coil which has detrimental effect on the efficiency of heat absorption and hence of water heating. For this reason the evaporating coil is usually coated with hydrophilic coating to enhance wettability and improve the condensate drainage from the coil surface.

Sometimes the water storage heater is installed in a site which also contains split type air conditioner (AC). In a split type AC the inside heat exchanger unit is separated by some distance from the outside heat exchanger unit. It may be desirable to locate the external heat absorbing unit of the storage water heater of the present invention under the same enclosure containing the AC outside heat exchanger. Shown in Fig 12 is an integrated outdoor unit 1210 that comprises the AC unit outdoor coil 1220, the AC compressor 1230, the outdoor evaporation coil of the water heating unit 1240, water heating compressor 1250 and a fan 1260. The refrigerant piping of the AC unit 1221 is connected to the AC indoor unit 1222 while the refrigerant piping of the water heater 1241 is connected to the immersed condenser 1242 found in the water storage container 1243.

When the AC operates in cooling mode cooling the indoor space heat is exhausted at the AC outdoor coil. This heat is removed by a fan that blows outside air over the AC outdoor coil. In Fig 12 the water heater outdoor evaporation coil 1240 is placed behind the AC outdoor coil such that it can benefit from the hot air forced by the fan 1260 located in front of the AC outdoor coil. When the AC unit operates in heating mode, similar to the water heating heat pump the AC outdoor coil absorbs heat from the environment. When operated in heating mode, in cold outdoor conditions frost or ice may build up on the outdoor coil reducing considerably the heat pump efficiency. In AC one strategy to overcome this is to operate the unit in cooling cycle reversing the flow of refrigerant. At the point when the hot refrigerant that circulates in the outdoor coil melts the accumulated frost or ice the AC unit is switched back to normal heating mode. Placing the water heater outdoor coil after the AC outdoor coil is advantageous in circumstances where the water heater coil requires running the defrost mode.

Some split type air conditioners are of so called variable refrigerant flow (VRF) technology. VRF AC can use refrigerant as the cooling and heating medium. This refrigerant is conditioned by a single outdoor condensing unit, and is circulated within multiple indoor units. In certain configurations VRF AC is adapted to simultaneously heat certain zones while cooling others. The VRF system can be regarded as high efficiency heat pump circuit since a heat extracted from zones requiring cooling is put to use in the zones requiring heating. In one preferred

embodiment of the present invention the storage water heater is not provided with an outdoor unit, instead the immersed condenser is connected with the outdoor unit of a VRF AC system. The water immersed condenser is operated as one of the multiple units of the VRF system, and particularly, a heating unit utilized for water heating. Fig 13 is a schematic of VRF AC system 1300 which comprises an outdoor unit 1310 and a plurality of indoor units; some indoor units are shown in cooling mode (1320, 1325) and another indoor unit is shown in heating mode 1330. Similarly, the immersed heat condenser 1340 within the water storage 1350 is also an indoor unit of the VRF heat pump system which functions similar to an AC indoor unit in a heating mode.

According to embodiments of the present invention the DHW control unit comprises several components as depicted schematically in Fig 14. A programmable logic controller ("controller") 1400 which can be accessed locally via user interface, and/or remotely regulates the heating and thereby water temperature by activating and deactivating water heating. This is achieved by switching on/off the current to the heat pump 121, and/or the current 123 to resistive heater. The controller is provided with a non-volatile memory such that the controller is programmable to execute stored programs of water heating schedules. The controller also monitors water temperature by receiving a signal from the temperature sensor 122 located within the water container via cable 122, and in addition it is configured to set the desired water temperature, "setpoint". The controller acts as "thermostat", namely it is operative to maintain water temperature near a desired setpoint by a feedback signal for the temperature sensor. Optionally, the system may be provided with additional "thermostat" units as a safety means to prevent hazardous overheating. The thermostat may be configured such that the heating is shut off when the temperature exceeds any factory preset setpoint. Shown in Fig. 1 is yet another safety measure wherein the water storage is provided with a pressure relief valve 141.

The control unit also contains the electrical terminals from a power supply. Certain components within the control unit, and generally within the DHW system may require input voltages other than provided by the power supply, such as for example most electronic components are adapted to operate under direct current (DC) in contrast to alternating current (AC) based electrical grid. Thus the electrical system may contain AC to DC convertors and voltage reduction components to lower the voltage required to various components within the system. Particularly the DHW may incorporate what is known as "inverter technology", where-in the compressor is driven by variable speed by an adjustable electrical inverter 1410. In this manner the speed of the compressor is controlled to provide variable flow of the refrigerant which results in a more efficient heating (higher COP) of water.

In one scenario the controller is programmed to execute heating cycles scheduled by the user, on a daily weekly or indefinite routine. In another scenario the DHW is switched on/off by a remote user which schedules the availability of hot water to her or his convenience. The remote access is by any readily available standard means such as communication cable, wi-fi or cellular communication with corresponding modem.

In another scenario the controller is accessed remotely from the control center of the electrical grid such as to equalize electricity load and reduce the strain on electric power plant. Electric power plants must match generation and load of electricity in real time, with tight tolerances. Transitions from low load to high load occur on long time scales such as the transition ramp from low load during night hours to peak demand during morning hours, or fast transitions that may occur over time scale of minutes. As a result, both electricity plant stress and consequently prices can vary considerably throughout the day. Returning to Fig. 1 the water storage cylinder wall 142 is constructed of high thermal insulation against heat loss to the environment. High insulation means that the water remains hot over relatively extended period of time. In terms of electricity management it would therefore be advantageous to schedule the heating during the low electricity loads, say during night hours, while providing the user with hot water upon demand. Accordingly, during hours of low demand the water heaters namely, the heat pump and the resistive heater are activated and the water is heated. During period of high demand the heaters are switched off. Such load management is not limited to long cycles of heating or switch offs and can be implemented momentary so as to follow the real-time electricity demand.

Yet in another scenario the controller is programmed in adaptive mode, namely according to a typical partem of usage. Operating in this mode the first stage is "learning": the controller records the heating cycles over a predetermined period of time. After sufficient data has been collected (over a period of say a few weeks) a typical pattern can be recognized. Such a pattern can be stored, or further optimized according to electricity tariffs, or using other weighting criteria as defined by the user. The controller than executes heating cycles according to the optimized heating cycle.

Finally, as shown in Fig 14 when the outdoor unit is provided with a display or other illuminated indicator/s or a light source the controller also provides the output for such a display and/or light source.

It will be appreciated that operation of DHW is not limited to scenarios described hereinabove, rather these are described in greater detail as exemplary situations of efficient management of water heating brought about by the configuration and construction of DHW of the present invention.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims