Dual-mode evaporators, methods, software, and systems for optimizing performance of solar-assisted heat pumps

Abstract

In some aspects, dual-mode evaporators, for example, for solar-assisted heat pumps, are disclosed that are configured for optimizing both radiative and convective heat collection. In some embodiments, a dual-mode evaporator includes at least one radiation collector and at least one convection collector, wherein the radiation collector(s) is / are optimized for radiative collection and the convection collector(s) is / are optimized for convective collection. For example, a radiation collector(s) of an evaporator can have fewer airflow-disturbance features than the convection collector(s) of the same evaporator. In some aspects, control methods for solar-assisted heat pumps are disclosed. In some embodiments, the control methods are configured to operate solar-assisted heat pumps in a manner that optimizes their efficiencies based on the amount of heat available in the environments of their evaporators as determined in any one or more of a variety of ways.

Description

DUAL-MODE EVAPORATORS, METHODS AND SOFTWARE FOR OPTIMIZING PERFORMANCE OF SOLAR-ASSISTED HEAT PUMPS, AND SYSTEMS INCORPORATING ONE OR MORE OF THE SAMERELATED APPLICATION DATA

[0001] The present application claims the benefit of priority of U.S. Provisional Patent Application Serial No. 63 / 489,627, filed on March 10, 2023, and titled “DUAL-MODE EVAPORATORS, METHODS AND SOFTWARE FOR OPTIMIZING PERFORMANCE OF SOLAR-ASSISTED HEAT PUMPS, AND SYSTEMS INCORPORATING ONE OR MORE OF THE SAME”, which is incorporated herein by reference in its entirety.FIELD OF THE INVENTION

[0002] The present disclosure relates to solar-assisted heat pumps. More particularly, this disclosure relates to dual-mode evaporators, methods and software for optimizing performance of solar-assisted heat pumps, and systems incorporating one or more of the same.BACKGROUND

[0003] Despite many advances in energy-efficient solutions for buildings and homes, domestic hot water heating remains a large source of energy consumption.

[0004] “Hybrid” air source heat-pump-type-water heaters incorporate a heat pump design that has an evaporator located on top of the storage tanks. Such an evaporator is warmed by a supply of warm room air fed by a fan. The cold evaporator coil absorbs heat energy from the warm air while expelling cold air to the surroundings. In many applications the consumption of room air that is heated by conventional means is not desirable. Moreover, these water heaters have a noisy fan and require an external means to remove condensate that is produced as moisture-laden air is passed through the cold evaporator.

[0005] A newer, more energy-efficient heat pump water heater design also uses an air source heat pump design to heat water. The evaporator, however, is located outdoors and relies on surface area and exposure to sunlight (not fan-assisted air movement) to provide heat energy to aid the refrigeration cycle and to reduce the load on the compressor. These heaters are commonly referred to as “solar-assisted heat pump”-type water heaters. These evaporators often comprise a large roll- bonded aluminum panel having a pattern of channels through which a refrigerant (working fluid) passes and are painted black to absorb radiation from the sun. Alternatively, the evaporator maycomprise conventional refrigeration tubing mounted to a black rigid panel. The refrigerant typically enters the evaporator in mixed-phase form and evaporates due to the temperature of the evaporator’s physical structure being above the refrigerant’s boiling point at the operating pressure within the evaporator. This design will function at night and in cold conditions, but the COP (coefficient of performance) of the entire system is improved when the evaporator is at an elevated temperature.

[0006] The current state-of-the-art solar-assisted heat pump design also incorporates a simple controller that turns the system’s compressor on or off based on the tank temperature. Typically, the controller will start the compressor when the tank temperature drops below 120°F and then turns the compressor off when the tank temperature exceeds 130°F. These conditions can occur at any time of the day or during cold and sunless conditions. Accordingly, the system COP may be poor during the winter months and / or during nighttime operation.

[0007] Therefore, it is advantageous to further increase the efficiency of solar-assisted heat pump water heaters.SUMMARY

[0008] In one implementation, the present disclosure is directed to an evaporator for use with a working fluid, which includes a working-fluid circuit that carries the working fluid during use of the evaporator; a radiation collector containing a first portion of the working-fluid circuit and designed and configured to capture radiation energy and transfer the radiation energy to the working fluid in the first portion of the working-fluid circuit during use, the radiation collector designed and configured to, during use, favor collecting the radiation energy from an environment of the evaporator over collecting thermal energy in air surrounding the evaporator; and a convection collector containing a second portion of the working-fluid circuit and designed and configured to capture convection energy and to transfer the convection energy to the working fluid in the second portion of the working-fluid circuit during use, the convection collector designed and configured to, during use, favor collecting the thermal energy from the air surrounding the evaporator.

[0009] In one implementation, the present disclosure is directed to a method of manufacturing an evaporator for use with a working fluid. The method includes providing a first roll-bonded sheet having a first fluid-channel pattern comprising at least one fluid channel; providing a second roll- bonded sheet having a second fluid-channel pattern comprising at least one second fluid channel; forming a number of convection fins in the first roll-bonded sheet; mechanically connecting the first and second roll-bonded sheets to one another; and fluidly connecting the at least one first fluidchannel and the at least one second fluid channel into a working-fluid circuit for carrying the working fluid during use.

[0010] In one implementation, the present disclosure is directed to a method of operating a water heater comprising a solar-assisted heat pump and a storage tank. The method includes intermittently operating the solar-assisted heat pump to provide a series of sample-testing periods; determining an instantaneous coefficient of performance (COP) of the water heater during the each of the sample-testing periods; determining whether the instantaneous COP satisfies a continue- operation threshold; and if the current COP satisfies the continue-operation threshold, then continue operating the solar-assisted heat pump to heat water in the storage tank to a temperature above a baseline temperature.

[0011] In one implementation, the present disclosure is directed to a method of operating a water heater comprising a solar-assisted heat pump and a storage tank having a minimum temperature set point. The method includes monitoring an amount of time that the solar-assisted water heater operates in a minimum tank temperature mode; and adjusting the minimum temperature set point as a function of the amount of time that the solar-assisted water heater operates in the minimum tank temperature mode.

[0012] In one implementation, the present disclosure is directed to a method of operating a water heater comprising a solar-assisted heat pump that includes an evaporator. The method includes receiving weather-forecast data for weather to which the evaporator is exposed during deployment of the water heater; determining an instantaneous coefficient of performance (COP) of the water heater; determining a future COP based on the weather forecast data, wherein the future COP occurs at a future time relative to when the instantaneous COP is determined; and

[0013] when the instantaneous COP is less than the future COP, delay operating the solar- assisted heat pump until the future time.

[0014] In one implementation, the present disclosure is directed to a method of operating a water heater comprising a solar-assisted heat pump that includes an evaporator. Te method includes tracking time of day; storing a start time that indicates when the solar-assisted heat pump is to be operated; comparing the time of day to the start time; and when the time of day is equal to the start time, operate the solar-assisted heat pump for a fixed period of time.

[0015] In one implementation, the present disclosure is directed to a method of operating a water heater comprising a solar-assisted heat pump that includes an evaporator and a condenser in fluid communication with one another. The method includes collecting inlet temperatures and outlet temperatures at, respectively, a fluid inlet and a fluid outlet of at least one of the condenser and the evaporator when the solar-assisted heat pump is operating; calculating temperature deltas between respective sets of the inlet and outlet temperatures; determining from the temperature deltas one or more periods during which it is most efficient to operate the solar-assisted heat pump; and controlling operation of the solar-assisted heat pump based on the one or more periods.

[0016] In one implementation, the present disclosure is directed to a machine-readable medium containing machine-executable instruction for performing any one or more of the methods as described above.

[0017] In one implementation, the present disclosure is directed to a water-heater system, which includes a water storage tank; a solar-assisted heat pump in fluid communication with the water storage tank; and a controller operatively connected to the solar-assisted heat pump, wherein, when operating, the controller executes any one or more of the methods described above.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] For the purpose of illustration, the accompanying drawings show aspects of one or more embodiments of the disclosure. However, it should be understood that the scope of this disclosure is / are not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

[0019] FIG. lAis a partial isometric view and partial schematic diagram of an example paneltype dual-mode (DM) evaporator unit made in accordance with aspects of the present disclosure;

[0020] FIG. IB is a front view of an example louver that can be used on a convection collector of a DM evaporator of the present disclosure;

[0021] FIG. 1C is an enlarged partial cross-sectional view of the louver of FIG. IB, as taken along line 1C-1C;

[0022] FIG. ID is a plan view of an example collector panel that can be used as either a radiation collector or a convection collector, depending on the amount it is processed to include flow-disturbance features;

[0023] FIG. 2 is a high-level partial block diagram and partial schematic diagram of an example solar-assisted heat-pump (SAHP) system of the present disclosure in the form of a hot water generation and storage system;

[0024] FIG. 3 is a flow diagram of an example control method for controlling an SAHP system of the present disclosure, such as the SAHP system of FIG. 2; and

[0025] FIG. 4 is a flow diagram of another example control method for controlling an SAHP system of the present disclosure, such as the SAHP system of FIG. 2, wherein the control method includes a scheduled adaptive water-heating cycle.DETAILED DESCRIPTION

[0026] In some aspects, the present disclosure is directed to dual -mode (DM) evaporators for solar-assisted heat pumps for applications such as water heaters. A DM evaporator of the present disclosure is configured for optimizing heating of a working fluid by both solar-radiation heating and air-convection heating. For example, some embodiments of a DM evaporator of the present disclosure include a radiation collector designed and configured to favor solar-radiation heating and a convection collector designed and configured to favor air-convection heat transfer, where, at its broadest level, the term “favor” connotes a difference in design as between the radiation collector and the convection collector to account for the differing manners of heat collection.

[0027] In some embodiments, this difference in design may be expressed in terms of disturbances to the boundary layer at the surface(s) of the working components of each of the radiation collector and the convection collector. For the radiation collector, it is desirable to minimize disturbing the boundary layer so as to maintain the temperature of the radiation collector as high as possible. It is also desirable that the surface(s) of the radiation detector be optimized for maximizing the heat gain from the radiation, which for solar radiation correlates to having an absorptive color, such as black. For the convection collector, in contrast, it is desirable to maximize disturbing the boundary layer so as to maximize the convective transfer of heat from the surrounding air. Those skilled in the art will readily appreciate that the terms “optimize”, “maximize”, “minimize”, and like terms in these contexts are not absolute but rather are relative to a particular design, corresponding design parameters, and other practical considerations.

[0028] In some embodiments, the convection-versus-radiation design differences can be expressed in terms of a convection :radiati on disturbance-feature-per-unit-area ratio, R, with disturbance features being physical features of the respective collector that act to disturb theboundary layer of that collector. For panel -type collectors, each disturbance-feature-per-unit-area value, DV, is determined by dividing the total number of boundary -lay er disturbance features on the respective collector by the “plan” area of the panel. For example, a completely flat collector panel would have a disturbance-feature-per-unit-area value DV of 0 (zero), and thus function optimally as a radiation collector, while a collector panel having one or more fins and / or other boundary-layer- disturbance features would have a disturbance-feature-per-unit-area value of greater than zero. Consequently, with a convection collector of a DM evaporator of the present disclosure being desired to have relatively more boundary -layer-disturbance features than the radiation collector of the DM evaporator, the convection: radiati on disturbance-feature-per-unit-area ratio R for a paneltype DM evaporator would be in a range of > 1 to00, i.e., R = DVc / DVr, wherein DVc is the DV for the convection collector and DVr is the DV for the radiation collector. In some embodiments R is in a range of about 2 to00, in a range of about 10 to00, or in a range of about 20 to00, among others. As those skilled in the art will readily understand, R = 00 simply means that the radiation collector does not include any disturbance features, such as when the radiation collector is a flat panel or a curved panel, among other shapes not having any disturbance features. It is also noted that R =00does not allow for both the convection collector and the radiation collector to have zero disturbance features, as zero divided by zero is undefined. Consequently, when the DVr is 0, DVc must be 1 or greater.

[0029] In some aspects, the present disclosure is directed to control methods, and corresponding algorithms, for controlling operation of a solar-assisted heat pump type water heater that includes a solar-assisted heat pump, a hot-water storage tank, and a control system implementing one or more control methods of the present disclosure. In some embodiments, the solar-assisted heat pump comprises an evaporator, a condenser, and a compressor for compressing a working fluid in the heat exchanger. For such embodiments, control methods of the present disclosure may involve heating the water to a higher-than-baseline temperature when the operating efficiency of the solar-assisted heat pump is relatively high, such as when solar and / or convective heat gain via the evaporator is relatively high. In some embodiments, control methods of the present disclosure may involve controlling operation of the solar-assisted heat pump as a function of both a current energy efficiency and current hot water usage profile. In some embodiments, control methods and algorithms of the present disclosure may involve controlling operation of the compressor based on weather forecast data. In some embodiments, control methods of the present disclosure may be tooperate the solar-assisted heat pump for a fixed period every day when outdoor conditions are known, on average, to be advantageous, such as between 1 PM and 4 PM, to create an elevated tank temperature. In some embodiments of such a fixed-period daily operation, a maximum tank temperature may be set to avoid overheating the water. In some embodiments, the maximum tank temperature may be 10°F to 15°F above a target water temperature, but it can be any other suitable elevated values.

[0030] In some embodiments, a control system for a solar-assisted water heater may implement two or more of the foregoing control methods. It is noted that the evaporator of a solar-assisted heat pump of the present disclosure is preferably, but need not be, a DM evaporator of the present disclosure. It is further noted that a solar-assisted heat pump of the present disclosure may include more than one each of an evaporator, a condenser, a compressor, and a hot water storage tank, among other components. A control system of the present disclosure may have a centralized architecture or a distributed architecture, or a hybrid of both of these architectures.

[0031] The foregoing and other aspects and embodiments of the present disclosure are described below and / or are exemplified in this disclosure, including in the appended example claims, which are incorporated into this Detailed Description section by reference.

[0032] EXAMPLE PANEL-TYPE DUAL-MODE EVAPORATOR

[0033] Referring now to the drawings, FIG. 1A illustrates an example panel -type DM evaporator 100 made in accordance with aspects of the present disclosure. In this example, the DM evaporator 100 is particularly designed for being mounted in a vertical orientation as suggested by FIG. 1 A. However, those skilled in the art will readily appreciate that DM evaporators of the present disclosure, such as the DM evaporator 100 of FIG. 1A, can be designed for being mounted in any one or more orientations, including orientations other than vertical, including horizontal and sloped, for example, to match the pitch of a roof on which the DM evaporator is mounted. The DM evaporator 100 includes a radiation collector 104 and a convection collector 108 each mounted to a support frame 106. Both of the radiation collector 104 and the convection collector 108 have the same “plan” area as one another, which consists of the length times the height of their overall rectangular regions within the respective support frames 106. In this embodiment, the radiation collector 104 comprises 7 horizontally extending solid (i.e., non-segmented) louvers 104L(l) through 104L(7) that are tilted upward to optimize their orientation for receiving solar radiation. In this example, the solid louvers 104L(l) through 104L(7) are fixed, but in other embodiments theymay be rotatable to further optimize the incident angle of the solar radiation as the sun (not shown) changes location in the sky throughout the day. In other embodiments, the number of solid louvers can be greater or fewer than the 7 solid louvers 104L(l) through 104L(7) shown, including zero, e g., is a solid panel, for example, if the entire radiation collector 104 panel can be oriented to face the sun. As noted above, each solid louver 104L(l) through 104L(7) may have a suitable coating comprising solar-radiation-absorbing material.

[0034] The convection collector 108 in this example comprises 6 horizontally extending finned (segmented) full louvers 108L(2) through 108L(7) and 2 finned half-louvers 108L(l) and 108(8), each having fins 108F (only a few labeled to avoid cluttering the figure) as additional boundarylayer-disturbance features (in addition to the louvers themselves) and that extend substantially laterally from the longitudinal axes (not labeled) of the corresponding finned louvers 108L(l) through 108L(8). The fins 108F may be oriented in any one or more other directions as desired for a particular design, perhaps to further optimize the design, such as for a predominant direction of air flow, and / or to suit physical constraints, such as size and / or thickness of the DM evaporator 100, among other things. In some embodiments, the fins 108F may vary in their radial extension direction along each finned louver 108L( 1 ) through 108L(8) or from finned louver to finned louver, or both, to suit a particular design. In some embodiments, the fins 108F and / or finned louvers 108L(l) through 108L(8) may be pivotable, manually or automatically, so as to change their orientation, for example, to adapt / adjust to air-flow conditions at the installation site and / or to suit a particular installation orientation of the convection collector 108, among other things. In this example, each finned full louver 108L(2) through 108L(7) includes 110 fins 108F (55 on each side) and each finned half louver 108L(l) and 108L(8) has 55 fins. In other embodiments, the fins 108F may be provided in a different number, extend in one or more differing directions, have differing shapes, be replaced by other boundary -lay er flow disturbing features, among other things, and any combination thereof. The fins 108F of the finned louvers 108L(l) through 108L(8) may or may not have a radiation-absorbing color. For example, if the arrangement of the radiation collector 104 and the convection collector 108 are such that when the evaporator 100 is deployed the convection collector is always shaded by the radiation collector, then the fins 108F on the finned louvers need not have a radiation-absorbing color. However, if, when the evaporator 100 is deployed, the fins 108F will be exposed to sunlight radiation, then it can be desirable that the fins have a radiationabsorbing color.

[0035] Applying the convection: radiati on disturbance-feature-per-unit-area ratio R discussed above to the example DM evaporator 100 of FIG. 1A, with the “plan” areas of the radiation collector 104 and the convection collector 108 being identical (so as to drop out of the calculation), the disturbance-feature-per-unit-area value DVc of the convection collector is (7 x 110) = 770 (i.e., the equivalent number of finned full louvers (6 full louvers 108L(2) through 108L() + 2 half louvers 108L(l) and 108L(8)) times the number of fins 108F per louver), and the disturbance-feature-per- unit-area value DVr of the radiation collector 104 is 7 (i.e., the number of solid louvers 104L(l) through 104L(7)), making the disturbance-feature-per-unit-area ratio R = 770:7, or 110, i.e., DVc / DVr.

[0036] The example DM evaporator 100 of FIG. 1A may be made, for example, starting with two identical roll-bonded panels 104P and 108P (only shown after processing to create the solid louvers 104L(l) through 104L(7) and finned louvers 108L(l) through 108L(7)), each having the same serpentine working-fluid passageway 104FP and 108FP (internal, but highlighted for illustration, only some labeled to avoid cluttering the figure) formed therein in the usual manner. The serpentine working-fluid passageways 104FP and 108FP are shown in FIG. 1A as being fluidly connected to one another at the upper end of the DM evaporator 100 via a connector tube 112, and the bottom end of the DM evaporator includes a working-fluid inlet 1041 and a working-fluid outlet 1080 on the radiation collector 104 and the convection collector 108, respectively. Overall, the working-fluid pathway through the entire DM evaporator 100 makes up the working-fluid circuit 116 of the DM evaporator. It is noted that in alternative working-fluid circuits (see, e.g., FIG. ID, described below), the working-fluid passageways 104FP and 108FP in the radiation and convection collectors 104 and 108 may be configured in any suitable manner, such as using one or more headers, one or more branching points, one or more collection points, etc., and the working-fluid passageways may be connected in another manner, such as in a parallel manner instead of a series manner as between the convection collector and the radiation collector. In addition, the workingfluid inlet 1041 and outlet 1080 may be reversed in their locations and / or located elsewhere on the DM evaporator 100. Those skilled in the art will understand that the particular arrangement and design of the working-fluid circuit can be highly variable without departing from the scope of the present disclosure.

[0037] Starting with the two identical roll-bonded panels 104P and 108P (shown only after processing described herein), each of the radiation and convection collectors 104 and 108 may be made by suitably cutting patterns in non-fluid-passageway regions of the roll-bonded panels to formvarious elements (here, the support frame 106, the solid and finned louvers 104L(l) through 104(7) and 108L(l ) through 108L(8), and fins 108F) and then bending at least some of the elements (e.g., the louvers and fins), or portion(s) thereof, to orient them as desired. The patterns may be cut using any suitable method(s), such as but not limited to, laser cutting, plasma cutting, saw cutting, roll cutting, etc. Bending may also be accomplished using any suitable automated and / or manual method(s). As can be seen in FIG. 1 A, in this embodiment the straight segments of the workingfluid passageways 104FP and 108FP are located within the solid and finned louvers 104L(l) through 104(7) and 108L(l) through 108L(8), and the direction-changing segments of the workingfluid passageways are present in the vertical sides of the support frame 106.

[0038] In this example, the radiation and convection collectors 104 and 108 are spaced apart from one another and are in registration with one another. Also shown, but which need not be present in a finished DM-evaporator unit 120, is an optional mounting frame 124 to which the radiation and convection collectors 104 and 108 are attached, for example via their own support frames 106. In some embodiments, the radiation and convection collectors 104 and 108 may be located differently relative to one another, such as side-by-side, spaced laterally apart, or overlapping, among others. In some embodiments, the radiation and convection collectors 104 and 108 need not be mounted to a mounting frame, such as the mounting frame 124, but rather may be mounted separately and joined with one another only via one or more components of the workingfluid circuit 116. In some embodiments, the overall shapes of the radiation and convection collectors 104 and 108 may be any shapes suitable for a particular design, including planar, curved, polygonal, non-polygonal, and other shapes in any suitable view of each collector.

[0039] In some embodiments, the radiation and convection collectors 104 and 108 need not be provided in separate panels 104P and 108P. For example, a single panel (not shown) can include both types of collectors and / or in any suitable number of each. In some embodiments, one or both of the radiation and convection collectors 104 and 108 may be made using multiple discrete components, such as tubing for the working-fluid passageways, individual plates / sheets for the solid louvers, and individual plates / sheets for the fins, among other things, and such components may be joined with one another using any suitable thermally conductive connections, such as welding, brazing, roll bonding, and adhesive bonding, among others.

[0040] In some embodiments, any louver or like element provided, such as any of the solid louvers 104L(l) through 104L(7) of the radiation collector 104 in FIG. 1A and the finnedlouvers 108L(l) through 108L(8), may have more than one working-fluid passageway and / or one or more working-fluid passageways that are non-linear (e.g., serpentine). If one or more non-linear working-fluid passageways are present, then the directionality of the working-fluid flow in such passageway(s) may be described by an “overall-flow vector” that relates the aggregate flow to the overall element (e.g., louver). For example and referring to FIG. 1A, if the straight portion of the working-fluid passageway 104FP in each of the solid louvers 104L(l) through 104L(7) of the radiation collector 104 were replaced by a single serpentine passageway (not shown) within that solid louver, then the overall-flow vector would resolve the serpentine flow to a vector extending along the straight working-fluid passageway shown. In some embodiments, a DM evaporator of the present disclosure may include any one or more or combination of features of any of the embodiments discussed above.

[0041] During operation of the example DM evaporator 100 of FIG. 1 A, in “solar mode” a working fluid (not shown, but present within the fluid passageways 104FP and 108FP and flowing therethrough between the fluid inlet 1041 and fluid outlet 1080, is primarily warmed via the solid louvers 104L(l) through 104L(7) that are angled towards the sun. The working fluid then may experience a secondary, more modest, heat gain from pure air convection as it travels through the shaded finned louvers 108L(l) through 108L(8) on the rear of the DM evaporator 100. In non-solar or “convection mode” operating conditions, the working fluid experiences a generally modest air-to- working-fluid heat gain from passage through the front solid louvers 104L(l) through 104L(7) but then experiences a greater heat gain as it passes through the rear-finned louvers 108L(l) through 108L(8) that have the many fins 108F that improves the convective performance.

[0042] FIG. IB illustrates a louver 140 that is similar to the finned louvers 108L(l) through 108L(8) of FIG. 1A. However, instead of having the discrete fins 108F as the flow-disturbance features like each of the finned louvers 108L(l) through 108L(8) of FIG. 1A, the louver 140 of FIG. IB has flow-disturbance features 144 that result from the louver including wings 148(1) and 148(2) that each have an undulating surface profile 152, which is shown in more detail in FIG. 1C. The louver 140 may be constructed in any of a variety of ways. For example, it may be constructed by sandwiching a discrete working-fluid conduit 156 inside two sheets of material that are brazed together at the wings 148(1) and 148(2) and are brazed to the working-fluid conduit. In another example, the louver 140 may be made by a set of cutting and stamping operations upon a brazed-type flat panel that form the wings 148(1) and 148(2) and form the undulating surface profile. Those skilled in the art will readily understand how to make the louver 140.

[0043] FIG. ID illustrates another example roll-bonded flat panel 160 that can be used to form either a radiation collector or a convection collector depending on the amount of processing to form flow-disturbance features or not. Examples of such processing include, but are not limited to, punching, cutting, stamping, and shearing, among others. In this example, the flat panel 160 includes a working-fluid inlet 164 and a working-fluid outlet 168 fluidly connected to one another by internal working-fluid passageways 172. Those skilled in the art will readily understand that the flat panel 160 is merely another example of a roll-bonded panel and that other panels, including other roll-bonded panels, can be used to form radiation collectors and / or convection collectors of DM evaporators of the present disclosure, such as DM evaporator 120 of FIG. 1A.

[0044] EXAMPLE SOLAR-ASSISTED HEAT-PUMP SYSTEM AND EXAMPLECONTROL METHODS FOR SUCH A SYSTEM

[0045] The efficiency of solar-assisted heat pumps is primarily a function of the environmental conditions at the evaporator-mounted outdoors. Sun, temperature, wind, and humidity all affect evaporator performance, which in turn affects the capacity and efficiency of an entire solar-assisted heat-pump type (SAHP) system, such as a solar-assisted heat-pump water heater. In practice, it is not uncommon to see very wide variations in heat-pump efficiency on a daily basis. Control methods and algorithms that appropriately maximize heat-pump run time when conditions are favorable will have a very significant electricity savings benefit relative to simplistic existing designs.

[0046] FIG. 2 illustrates an example solar-assisted heat-pump (SAHP) system 200 that is in the form of a hot water generation and storage system for supplying domestic hot water. Consequently, the SAHP system 200 includes a water-storage tank 204 that holds water 208, typically under pressure, during normal operation of the SAHP system. The water-storage tank 204 may be any suitable water-storage tank, including tanks of conventional designs. Not shown for the sake of brevity are related components, such as a cold-water inlet, a hot-water outlet, an optional mixing valve, and any necessary fittings, among others. The SAHP system 200 also includes a solar- assisted heat pump, or SAHP, 210 that includes a condenser 212, an evaporator 216, and a compressor 220 that, during operation of the SAHP system, compresses and circulates a working fluid 224 through the condenser and evaporator when controlled to do so. The working fluid 224 may be any suitable working fluid known in the field of heat pumps and SAHPs. The SAHP system 200 further includes a controller 228 that controls the operation of the SAHP 210, forexample, as discussed below in more detail in connection with the example control method 300 ofFIG. 3.

[0047] Referring still to FIG. 2, in this example, the condenser 212 is located externally to the water-storage tank 204. In this example, the condenser 212 is of the counterflow type in which the working fluid 224 and water 208 from the tank are passed through the condenser in generally opposite directions, with the movement of the water through the condenser being provided by a suitable pump 230. The condenser 212 has an inlet end 2121 that receives water 208 from proximate to the bottom of the water-storage tank 204 where the water is relatively cooler and an outlet end 2120 that returns the water heated by the condenser to a location higher up on the water-storage tank where the water is relatively hotter. Condenser types suitable for use as the condenser 212 of the SAHP system 200, such as coaxial types and brazed-plate types, among others, are well known, such that further explanation of the condenser need not be provided for those skilled in the art to practice the subject matter of the present disclosure to its fullest scope.

[0048] The evaporator 216 may be any suitable evaporator, such as a conventional solar-type evaporator or a DM evaporator of the present disclosure, such as any of the DM evaporators described herein, such as the DM evaporator 100 of FIG. 1A, among others. Whether the evaporator 216 is a conventional solar-type evaporator or a DM evaporator of the present disclosure, it will be located in a suitable location, such as, for example, on a rooftop or exterior wall of a building that the SAHP system 200 serves, among other locations, whereat it experiences the relevant environmental conditions, which include circadian conditions and weather conditions.

[0049] The compressor 220 may be any suitable compressor for the type of the working fluid 224 used in the SAHP system 200. In some embodiments, the compressor is electrically powered. Compressors suitable for use as the compressor 220 of the SAHP system 200 are well known, such that further explanation of the compressor need not be provided for those skilled in the art to practice the subject matter of the present disclosure to its fullest scope.

[0050] Those skilled in the art will readily appreciate that while FIG. 2 shows the SAHP system 200 as having only one component of each type, for example, one water-storage tank 204, one condenser 212, one evaporator 216, and one compressor 220, an SAHP system of the present disclosure may include two or more of any one or more of such components.

[0051] In this example, the controller 228 includes a microprocessor 232 and memory 236 that is in operative communication with the microprocessor and contains machine-executable instructions 238 for performing, among other things, any one or more algorithms, such as a SAHP- control algorithm(s) 240 and one or more optional evaporator-control algorithms 244, perhaps among others. There is fundamentally no limitation on the type of the microprocessor 232 other than it be suitable for the application at issue and can be determined by anyone having ordinary skill in the art. For example, the processor 232 may be a general processing unit, an application-specific integrated circuit, a field programmable gate array, among others, and may, for example, be part of a system on chip, among other things. The memory 236 in this example is, collectively, any and all hardware memory deployed in the controller 228. Examples of such hardware memory include, but are not limited to, RAM, ROM, cache memory, magnetic storage memory, solid-state memory, and optical memory, to name a few. Fundamentally, there is no limitation on the nature and number of hardware storage memories that can make up the memory 236 other than practical limitations of other hardware provided for the controller. The memory 236 may be considered a “machine- readable hardware storage medium”, which is distinct from the term “machine-readable medium” in that the former is directed to hardware memory and excludes transitory signals, such as carrier waves encoded with digital information and pulsed signals encoded with digital information, while the latter includes such transitory signals.

[0052] Detailed examples of control methods, such as the control methods 300 and 400 of FIGS. 3 and 4, respectively, that may be embodied in the compressor-control algorithm(s) 240 are described below. In some embodiments of the controller 228, such as an embodiment that executes either of the exampled control methods 300 and 400 of FIGS. 3 and 4, the controller requires temperature inputs for various temperatures of the water 208 inside the water-storage tank 204 and an electrical-power-determining input to measure electrical power that the compressor 220 consumes, as these inputs are needed to determine a coefficient of performance (COP), described below, used in the example control methods.

[0053] Accordingly, the example SAHP system 200 includes several temperature sensors, here, a condenser-inlet temperature sensor 248, a condenser-outlet temperature sensor 252, and one or more general -tank-temperature sensors 256. The locations of the condenser-inlet and -outlet temperature sensors 248 and 252 are self-explanatory. The location(s) of the general-tanktemperature sensor(s) 256 is / are selected to provide a suitable value representative of the temperature of the water 208. The example SAHP system 200 also includes an electrical-currentsensor 260 that measures the electrical current drawn by the compressor 220. Knowing the value electrical current that the compressor 220 draws, the controller 228 can use this value along with a fixed supply voltage (such as a mains voltage), to calculate the power consumption of the compressor. In other embodiments, one or more other or additional sensors or transducers can be used to determine the power that the compressor 220 consumes. The use of these sensors 248, 252, 256, and 260 in the context of the control methods 300 and 400 of FIGS. 3 and 4 is described below.

[0054] If provided, the evaporator-control algorithm 244 may be configured to control the orientation of the evaporator 216, or portion(s) thereof, such as louvers (not shown), to maximize exposure of the radiation collector (not shown) to the sun’s radiation. In some embodiments, the evaporator-control algorithm 244 may be based on known positional data for the sun based on time of day and calendar date or may be based on sensor data, such as from a sensor (not shown) located onboard the evaporator.

[0055] In some embodiments involving SAHP water heaters, such as the SAHP system 200 of FIG. 2, control methods, and corresponding algorithms and software embodying the algorithms and methods, of this disclosure continuously monitor operation of the solar-assisted heat pump, such as the SAHP 210 of FIG. 2, and compare the hot-water energy production of the SAHP with the electrical energy consumed. For the sake of illustration, these control methods, algorithms, and software, are described in the contexts of FIGS. 2 through 4. However, those skilled in art will readily appreciate that the overarching features and functionalities described below are not limited to these contexts.

[0056] Turning now to FIG. 3, with references being made to the SAHP system 200 of FIG. 2, these methods are exemplified by the example control method 300 of FIG. 3. At a high level, the control method 300 operates the SAHP 210 to heat the water 208 in the water-storage tank 204 to a higher-than-baseline temperature when the controller 228 determines that it is comparatively economical to do so. In this manner, the water-storage tank 204 is “loaded” with heat to a higher degree when the cost to operate the SAHP 210 is relatively low than when the operating cost is higher, for example, due to poorer environmental conditions of the evaporator 216. Regardless of the efficiency benefits of operating the SAHP 210 only when the conditions are favorable, a minimum storage temperature of the water 208 inside the storage-tank 204 must be maintained so that hot water is always available for the site. This, in turn, means that the SAHP 210 must turn on when the temperature of the water 208 in the water-storage tank 204 drops below the minimumstorage temperature regardless of operating efficiency. When properly implemented, the control strategy just described will minimize the duration of the “minimum tank-temperature mode” of operation during which the SAHP 210 is operating in an attempt to maintain the minimum temperature of the water 208 within the water-storage tank 204.

[0057] In some embodiments, the control method 300 requires measuring temperatures of both the incoming and outgoing (or “cold” and “hot”, respectively) water 208 at the working-fluid-to- water heat exchanger (i.e., the condenser 212) as well as determining the electrical consumption of the compressor 220. The controller 228 may acquire such temperatures from the condenser-inlet temperature sensor 248 and the condenser-outlet temperature sensor 252 located, respectively, at the inlet 2121 and the outlet 2120 of the condenser 212 and may determine the electrical consumption of the compressor 220 using the electrical current that the compressor draws, as measured using the electrical current sensor 260. The controller 228 may then calculate an instantaneous COP value by dividing the heat energy produced by the electrical energy consumed as follows:COP = (water mass x temperature difference) / electricity consumption wherein, for a heat pump: the “water mass” is the flow rate at the condenser 212 and is a known fixed value based on the water circulator type and frictional losses in the water piping (not shown) and condenser; the “temperature difference” is the measured difference in temperatures as between the incoming and outgoing (cold and hot, respectively) water 208 at the condenser 212 measured, in this example, via, respectively, the condenser-inlet and -outlet sensors 248 and 252; and the “electricity consumption” is the power consumed by the compressor 220 determined, for example, by multiplying a measured electrical current, measured via the electrical-current sensor 260, by the supply voltage (e.g., 120 VAC mains voltage in the U.S.).

[0058] With a COP-determination capability, the controller 228 may regularly sample the operating conditions by operating intermittently (e.g., periodically and / or on a fixed or variable schedule, among other possibilities) for a brief period, for example, once every hour, and then calculate a corresponding operating COP value for that sampling period. In an example, when the controller 228 determines a high operating COP value in any given sampling period, it will continue to operate the SAHP 210 after the sample period to heat the water 208 in the water-storage tank 204to a temperature higher than a baseline target storage temperature and thus store “less expensive” hot water for later usage at the site. In some embodiments, a graduated scale of target storage temperatures is implemented, with higher instantaneous operating COP values causing the controller 228 to shift the target storage temperature to a higher value based on a programmed lookup table of COP versus target storage temperature values. The Table below illustrates an example lookup table of instantaneous COP values and corresponding target tank temperature values. The above high-level methodology is illustrated in the control method 300 of FIG. 3.TABLE - Instantaneous COPs Versus Target Tank TemperaturesCOP 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9Target TankTemp (°F) 125 126 127 128 129 130 131 132 133 134 135 136 137

[0059] Referring particularly to FIG. 3, the example control method 300 includes block 305 at which the controller 228 determines whether or not the current temperature Tc of water 208 in the storage tank 204 is below a minimum storage temperature, Tmin. As noted above, in the context of the SAHP system 200 of FIG. 2, this current temperature Tc may be acquired using the one or more general -tank-temperature sensors 256. When the current temperature Tc is less than the minimum storage temperature Tmin, at block 310 the controller 228 controls the SAHP 210 to operate to raise the temperature of the water 208 to a setpoint temperature Ts above the minimum storage temperature Tmin.

[0060] When the current temperature Tc is equal to or greater than the minimum storage temperature at block 305, the controller 228 implements an intermittent looping branch 315 for determining whether or not it is economical for the SAHP 210 to heat the water 208 to a temperature above the minimum storage temperature Tmin to take advantage of favorable environmental conditions for efficient operations of the evaporator 216. Within the intermittent looping branch 315, at block 320 the controller 228 determines an instantaneous COP value, COPinst, that it then, at block 325, compares to a threshold COP value, COPthresh, which is a value at and above which it has been determined that it is economical, from an energy-efficiency standpoint, to the SAHP 210 and heat the water 208 to a temperature higher than minimum storage temperature Tmin. Consequently, when, at block 325, COPinst < COPthresh, the control method 300 simply loops back to block 305. However, when, at block 325, COPinst > COPthresh, the control method 300 proceeds to block 330 at which the controller 228 controls the SAHP 210 to operate, until a shutoff conditionoccurs, to raise the temperature of the water 208 to take advantage of the energy savings that can occur by extending the time that the temperature of the water remains about the minimum storage temperature Tmin and, therefore, the time that the SAHP must run to maintain the water at the proper temperature for use, regardless of how poor the environmental conditions of the evaporator 216 may be.

[0061] The controller 228 keeps the SAHP 210 operating until a shutoff condition occurs, other than the COPinst falling below the COPthresh, which is accounted for at block 325 in a loop. In an example, the shutoff condition can be the water 208 reaching a maximum temperature, Tmax. To avoid the controller 228 unnecessarily restarting the SAHP 210 on the next path through looping branch 315, the controller executes a block 335 at which the controller obtains the current water temperature Tc and compares it to the maximum temperature Tmax. While the current temperature Tc remains greater than or equal to the maximum temperature Tmax, the controller 228 remains in a loop with block 335. When the current temperature Tc falls below the maximum temperature Tmax, the control method 300 loops back to block 305. As those skilled in the art will readily understand, the control method 300 may be embodied into the SAHP-control algorithm(s) 240 and coded into corresponding machine-executable instructions that are part of the machine-executable instructions 238.

[0062] FIG. 4 illustrates another example control method 400 that can be executed by a controller of an SAHP water heater, such as the controller 228 of the SAHP system 200 of FIG. 2. For ease of illustration only and not limitation, the control method 400 is described in the context of SAHP system 200. At block 405, the controller 228 compares a current temperature, Tc, of the water 208 in the storage tank 204 to a minimum temperature, Tmin, that is the minimum delivery temperature of the water 208 within the water-storage tank 204. As discussed above with the control method 300 of FIG. 3, the controller 228 may determine the minimum temperature Tmin using the general-tank-temperature sensor(s) 256. When the current temperature Tc is lower than the minimum temperature Tmin, at block 410 the controller 228 turns on and runs the SAHP 210 until the current temperature Tc reaches an upper setpoint temperature Tsetup, which is a predetermined level above the minimum temperature Tmin to prevent the controller 228 from needing to operate the SAHP 210 too frequently, as would occur if the setpoint temperature at block 410 were only the minimum temperature Tmin. Once the controller 228 determines at block 410 that the current temperature Tc reaches the upper setpoint temperature Tsetup, the control method 400 returns to block 405.

[0063] When at block 405 the current temperature Tc is not less than the minimum temperature Tmin, at block 415 the controller starts a scheduled adaptive water-heating cycle in which, when the environmental conditions of the evaporator 216 are favorable for heating the water 208 in the tank 204 higher than the upper setpoint temperature Tsetup, the controller 228 will cause the SAHP 210 to operate until a then-current temperature Tc of the water reaches an increased upper setpoint temperature, Tincr.

[0064] In some embodiments, the increased upper setpoint temperature Tincr is a fixed value that has been predetermined to provide the SAHP system 200 with a higher-than-conventional operating efficiency, measured in terms of electrical-power consumption. In some embodiments, the increased upper setpoint temperature Tincr is variable in any one or more of a variety of ways. For example, the controller 228 may increase the increased upper setpoint temperature Tincr when the instantaneous COP, COPinst, is relatively high. In some embodiments, the values of such variable increased upper setpoint temperature Tincr may vary in a predetermined relationship with the values of the COPinst, such as an increasing linear relationship or an increasing polynomial relationship, among others. Those skilled in the art will readily understand how to implement a variable increased upper setpoint temperature Tincr for the situation at hand.

[0065] In some embodiments, the controller 228 may include learning logic 264 that monitors the amount of time that the SAHP 210 operates in the minimum-water-temperature mode of block 405. Operating in this minimum-water-temperature mode means that the SAHP 210 must operate to maintain enough hot water for the site regardless of the presence or absence of a favorable instantaneous COPinst. In an example, when the amount of time that the SAHP is operating in the minimum-water-temperature mode is relatively significant because of a relatively high hot-water- usage profile, the learning logic 264 adjusts a lookup table 268 of COPinst values versus Tincr values. That is, the learning logic 264 adjusts such values so that, at relatively high hot water usage profiles, the controller 228 controls the SAHP 210 to heat the water 208 in the water-storage tank 204 to a higher increased upper setpoint temperature Tincr with lower COPinst values than for lower hot water usage profiles. A goal is to minimize the periods during which the SAHP 210 operates in its minimum tank temperature mode at block 405 during which a poor COPinst, and corresponding high electricity consumption, may be occurring.

[0066] Conversely, for a site that has less hot water consumption (i.e., a lower hot-water usage profile) and less frequent and less severe tank temperature drops, the learning logic 264 may adjustits lookup table 268 of COPinst values versus Tincr values to maximize higher-COP water heating. That is, the learning logic 264 may adjust the COPinst values versus Tincr values so that the SAHP 210 heats the water 208 in the water-storage tank 204 to a higher temperature only when higher COPinst values are occurring during the sampling periods. This ensures that a low-hot- waterconsumption site is consuming a larger proportion of “high COP” hot water, i.e., less expensively heated hot water.

[0067] In some embodiments, the controller 228 may include a weather-data interface 272 that receives and processes weather forecast information (e.g., in a weather forecast data stream 272S) to allow the learning logic 264 to make weather-forecast-informed determinations about operating the SAHP 210 to heat the water 208 in the water-storage tank 204 to a higher increased upper setpoint temperature Tincr value in the future. In some embodiments, the controller 228 anticipates the COPtarg that should be attainable based on sun, wind, temperature, precipitation, and / or humidity forecast data and then controls the operation of the SAHP 210 based on the lookup table 268 of COPinst values versus Tincr values. In some embodiments, this functionality can entail continual adjustment to the values in the look-up table 268. For example, the controller 228 may determine not to operate the SAHP 210 during current favorable environmental conditions of the evaporator 216 due to a high probability of even more favorable conditions forecast to occur several hours later. Other weather-based adjustments to the look-up table 268 are possible, as those skilled in the art will appreciate.

[0068] Returning to the control method 400, in this example the scheduled adaptive waterheating cycle of block 415 involves periodically sampling the COPinst to determine whether or not the environmental conditions of the evaporator 216 are favorable for increasing the current temperature Tc of the water 208 above the minimum temperature Tmin. Consequently, at block 420 the controller 228 determines the amount of time that has passed since the last sample. In this example, the control method 400 is set up to sample the COPinst every hour to determine whether the environmental conditions have changed. The sampling period may be different and / or may be variable, such as variable to depend upon the time of day, for examples with longer sampling periods being employed overnight when the environmental conditions are less likely to impact efficiency than daytime environmental conditions when solar radiation can provide a significant boost to efficiency. When, at block 420, an hour has not yet passed since the last sample, the control method 400 loops back to block 405. However, when, at block 420, an hour has passed, at block 425 thecontroller 228 causes the SAHP 210 to operate and calculates the COPinst, for example, as described above relative to the control method 300 of FIG. 3.

[0069] At block 430, the controller 228 determines whether or not the COPinst is greater than a target COP, COPtarg, such as a 5-day moving-average COP, among other methodologies for determining a COPtarg. When the COPinst is not greater than the COPtarg at block 430, the control method 400, at block 435, shuts-off the SAHP 210 and loops back to block 405. When the COPinst is greater than the COPtarg at block 430, the control method 400 proceeds to block 440, at which the controller continues operating the SAHP 210 until the current water temperature Tc reaches the increased upper setpoint temperature Tincr or until COPinst falls below the COPtarget, whichever occurs first. Once the controller 228 determines that one of the two conditions is satisfied and shuts- off the SAHP 210 at block 440, the control method 400 loops back to block 405. As those skilled in the art will readily understand, the control method 400 may be embodied into the SAHP-control algorithm(s) 240 and coded into corresponding machine-executable instructions that are part of the machine-executable instructions 238.

[0070] With referenced to FIG. 2 for convenience of explanation, a further example control method for operating the SAHP system 200 uses inlet and outlet temperature data from the condenser 212, such as water inlet and outlet temperatures measured, respectively, using the water inlet and outlet temperature sensors 248 and 252, collected over time to determine the best time period(s) to operate the SAHP system. In another example, working-fluid inlet and outlet temperatures of the working fluid 224 at either the condenser 212 or the evaporator 216 may be used. For example, the controller 228 may initially be controlled to operate during a variety of time periods throughout each day and to collect inlet and outlet temperature data, which the controller may then use to determine corresponding temperature deltas, i.e., the temperature differences between the inlet and outlet temperatures at the respective measurement times. The controller 228 may then use these temperature deltas to effectively determine one or more time periods, for example, for each day, during which it is most efficient to operate the SAHP 210. As those skilled in the art will readily appreciate, periods with higher temperature deltas means that the evaporator 216 is collecting more heat, such that the operation of the SAHP 210 will be more efficient during these periods. Once enough data has been collected to determine the most-efficient operating period(s), the controller 228 may change over from a schedule-building mode for creating an efficient operating schedule to an operating-schedule mode where it then controls the SAHP 210 based on the schedule built during the schedule-building mode. In some embodiments, the controller228 may intermittently and / or periodically re-enter the schedule-building mode, for example, to account for longer-term efficiency -affecting trends, such as seasonal weather changes and / or to account for the possibility of unusual weather occurring during the initial schedule building.

[0071] Various modifications and additions can be made without departing from the spirit and scope of this disclosure. Features of each of the various embodiments described above may be combined with features of other described embodiments as appropriate in order to provide a multiplicity of feature combinations in associated new embodiments. Furthermore, while the foregoing describes a number of separate embodiments, what has been described herein is merely illustrative of the application of the principles of the present invention. Additionally, although particular methods herein may be illustrated and / or described as being performed in a specific order, the ordering is highly variable within ordinary skill to achieve aspects of the present disclosure. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.

[0072] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.

[0073] The subject matter of the appended claims is incorporated by reference into this DetailedDescription section so as to have the effect of being literally present in this section.

Claims

What is claimed is:1 . An evaporator for use with a working fluid, comprising: a working-fluid circuit that carries the working fluid during use of the evaporator; a radiation collector containing a first portion of the working-fluid circuit and designed and configured to capture radiation energy and transfer the radiation energy to the working fluid in the first portion of the working-fluid circuit during use, the radiation collector designed and configured to, during use, favor collecting the radiation energy from an environment of the evaporator over collecting thermal energy in air surrounding the evaporator; and a convection collector containing a second portion of the working-fluid circuit and designed and configured to capture convection energy and to transfer the convection energy to the working fluid in the second portion of the working-fluid circuit during use, the convection collector designed and configured to, during use, favor collecting the thermal energy from the air surrounding the evaporator over collecting the radiation energy from the environment of the evaporator.

2. The evaporator of claim 1, wherein the radiation collector is located in series with the convection collector relative to the working-fluid circuit.

3. The evaporator of claim 2, comprising a plurality of radiation collectors and a plurality of convection collectors interspersed with the plurality of radiation collectors.

4. The evaporator of claim 1, wherein the evaporator is configured as a unitary assembly that contains the working-fluid circuit, the radiation collector, and the convection collector, and includes a working-fluid inlet designed and configured to connect the working-fluid circuit to a working-fluid feed line and includes a working-fluid outlet designed and configured to connect the working fluid circuitry to a working-fluid output line.

5. The evaporator of claim 1, wherein the first portion of the working-fluid circuit comprises a first plurality of elongate flow passageways each extending in a first overall-flow-vector direction, with the first overall-flow-vector directions of the first plurality of elongate flow passageways being substantially parallel to and in spaced relation with one another.

6. The evaporator of claim 5, wherein the radiation collector comprises a plurality of elongate louver fins, the first plurality of elongate flow passageways are contained within the plurality ofelongate louver fins, and corresponding respective ones of the first overall -flow-vector directions extend along the plurality of elongate louver fins.

7. The evaporator of claim 5 or 6, wherein each of the first plurality of elongate flow passageways is substantially linear.

8. The evaporator of claim 5 or 6, wherein each of the first plurality of elongate flow passageways is serpentine.

9. The evaporator of claim 6, wherein each of the elongate louver fins is a roll-bonded louver fin.

10. The evaporator of claim 1 or claim 6, wherein the second portion of the working-fluid circuit comprises a second plurality of elongate flow passageways each extending in a second overall- flow-vector direction, with the second overall-low-vector directions being substantially parallel to and in spaced relation with one another.

11. The evaporator of claim 10, wherein the convection collector comprises a plurality of fins spaced apart from one another along each of the elongate flow passageways in the second plurality of flow passageways.

12. The evaporator of claim 11, wherein each of the plurality of fins extends radially from the corresponding elongate flow passageway.

13. The evaporator of claim 1, wherein the radiation collector lies in a first plane and the convection collector lies in a second plane parallel to the first plane.

14. The evaporator of claim 13, wherein the first and second planes are spaced apart from one another and the radiation and convection collectors are in at least partial registration with one another.

15. The evaporator of claim 13, wherein the radiation collector comprises a plurality of louver fins each having a radiation collection surface, and the evaporator is designed and configured to be mounted so that the radiation collection surface is oriented to receive sunlight during daylight hours.

16. The evaporator of claim 15, wherein the evaporator is designed and configured so that the convection collector is located in a shadow of the radiation collector during use.

17. The evaporator of claim 1, wherein both of the radiation and convection collectors are formed from a roll-bonded sheet.

18. The evaporator of claim 1, wherein the convection collector is formed in a first roll-bonded sheet, the radiation collector is formed in a second roll-bonded sheet, and the first and second roll-bonded sheets are mechanically connected to one another.

19. The evaporator of claim 18, wherein the first roll-bonded sheet has a first fluid-channel pattern and the second roll-bonded sheet has a second fluid-channel pattern that is identical to the first- fluid-channel pattern.

20. The evaporator of claim 19, wherein the first roll-bonded sheet has a number of convection fins formed by cutting and bending portions of the first roll-bonded sheet.

21. The evaporator of claim 20, wherein the second roll-bonded sheet has a number of radiation fins formed by cutting and bending portions of the second roll-bonded sheet, wherein the number of convection fins is greater than the number of radiation fins.

22. A method of manufacturing an evaporator for use with a working fluid, the method comprising: providing a first roll-bonded sheet having a first fluid-channel pattern comprising at least one fluid channel; providing a second roll-bonded sheet having a second fluid-channel pattern comprising at least one second fluid channel; forming a number of convection fins in the first roll-bonded sheet; mechanically connecting the first and second roll-bonded sheets to one another; and fluidly connecting the at least one first fluid channel and the at least one second fluid channel into a working-fluid circuit for carrying the working fluid during use.

23. The method of claim 22, wherein the forming of the number of convection fins includes cutting and bending portions of the first roll-bonded sheet.

24. The method of claim 22, further comprising forming radiation fins in the second roll-bonded sheets in a number fewer than the number of the convection fins.

25. The method of claim 24, wherein the forming of the number of radiation fins includes cutting and bending portions of the second roll-bonded sheet.

26. The method of any one of claims 22 through 25, wherein the first fluid-channel pattern is substantially the same as the second fluid-channel pattern.

27. A method of operating a water heater comprising a solar-assisted heat pump and a storage tank, the method comprising: intermittently operating the solar-assisted heat pump to provide a series of sample-testing periods; determining an instantaneous coefficient of performance (COP) of the water heater during the each of the sample-testing periods; determining whether the instantaneous COP satisfies a continue-operation threshold; and if the current COP satisfies the continue-operation threshold, then continue operating the solar- assisted heat pump to heat water in the storage tank to a temperature above a baseline temperature.

28. The method of claim 27, wherein the solar-assisted heat pump comprises an evaporator of any one of claims 1 through 21.

29. A method of operating a water heater comprising a solar-assisted heat pump and a storage tank having a minimum temperature set point, the method comprising: monitoring an amount of time that the solar-assisted water heater operates in a minimum tank temperature mode; and adjusting the minimum temperature set point as a function of the amount of time that the solar- assisted water heater operates in the minimum tank temperature mode.

30. The method of claim 29, wherein the solar-assisted heat pump comprises an evaporator of any one of claims 1 through 21.

31. A method of operating a water heater comprising a solar-assisted heat pump that includes an evaporator, the method comprising: receiving weather-forecast data for weather to which the evaporator is exposed during deployment of the water heater; determining an instantaneous coefficient of performance (COP) of the water heater; determining a future COP based on the weather forecast data, wherein the future COP occurs at a future time relative to when the instantaneous COP is determined; andwhen the instantaneous COP is less than the future COP, delay operating the solar-assisted heat pump until the future time.

32. The method of claim 31, wherein the solar-assisted heat pump comprises an evaporator of any one of claims 1 through 21.

33. A method of operating a water heater comprising a solar-assisted heat pump that includes an evaporator, the method comprising: tracking time of day; storing a start time that indicates when the solar-assisted heat pump is to be operated; comparing the time of day to the start time; and when the time of day is equal to the start time, operate the solar-assisted heat pump for a fixed period of time.

34. The method of claim 33, further comprising: monitoring a temperature of water heated by the solar-assisted heat pump during the fixed period of time; and when the temperature reaches a preset maximum temperature, stopping operation of the solar- assisted heat pump.

35. The method of claim 33 or claim 34, wherein the solar-assisted heat pump comprises an evaporator of any one of claims 1 through 21.

36. A method of operating a water heater comprising a solar-assisted heat pump that includes an evaporator and a condenser in fluid communication with one another, the method comprising: collecting inlet temperatures and outlet temperatures at, respectively, a fluid inlet and a fluid outlet of at least one of the condenser and the evaporator when the solar-assisted heat pump is operating; calculating temperature deltas between respective sets of the inlet and outlet temperatures; determining from the temperature deltas one or more periods during which it is most efficient to operate the solar-assisted heat pump; and controlling operation of the solar-assisted heat pump based on the one or more periods.

37. The method of claim 36, wherein the fluid inlet and the fluid outlet are, respectively, a water inlet and a water outlet.

38. The method of claim 36, wherein the fluid inlet and the fluid outlet are, respectively, a workingfluid inlet and a working-fluid outlet.

39. The method of and one of claims 36-38, wherein the solar-assisted heat pump comprises an evaporator of any one of claims 1 through 21.

40. A machine-readable medium containing machine-executable instruction for performing the method of any one or more of claims 27, 29, 31, 33, 34, and 36.

41. A water-heater system, comprising: a water storage tank; a solar-assisted heat pump in fluid communication with the water storage tank; and a controller operatively connected to the solar-assisted heat pump, wherein, when operating, the controller executes the method of any one or more of claims 27, 29, 31, 33, 34, and 36.

42. The water-heater system of claim 41, wherein the solar-assisted heat pump comprises an evaporator of any one of claims 1 through 21.

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