Heat pump, systems, and methods for operating the same

Abstract

A heat pump, heat pump system, and method for operating the same is provided. The heat pump preferably operates using a supercritical working fluid, from which heat is extracted through a multi-stage heat exchanger. Heat is extracted from the working fluid to supply at least two heat sinks, such as a hot water system or space heating system of a building and a working fluid re-heater or economizer. The configuration of the multi-stage heat sinks facilitates the heat pump to serve as a drop-in replacement for traditional fossil-fuel powered boilers or the like and to provide heat at temperatures typically provided by these traditional systems, eliminating the need for excess or replacement infrastructure when retrofitting or upgrading existing installations. The working fluid is expanded twice to limit flashing of the working fluid during expansion and to facilitate recirculation of such gases without damaging components of the system.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 621,579 filed on Jan. 16, 2024, and U.S. Provisional Application No. 63 / 621,583 filed on Jan. 17, 2024, the entire contents of which are herein incorporated by reference.TECHNICAL FIELD

[0002] The present specification relates to an improved heat pump, corresponding control system, and methods and systems for operating the same.BACKGROUND

[0003] With the effects of global warming being increasingly felt throughout the world, environmental sustainability and emission reductions are becoming more important, both from an engineering and a marketing standpoint. The cost and feasibility of replacing existing, inefficient systems is often the primary hurdle which hampers the adoption and implementation of more sustainable solutions.

[0004] Heating and cooling accounts for more than 13% of total carbon emissions worldwide, and heating alone is the largest single source of carbon emissions in the UK, making up more than one-third of the total. Decarbonizing heat is one of the biggest energy challenges in tackling the climate emergency, particularly because it requires actions in millions, if not billions, of individual homes. In the UK alone, only one million of the UK's approximate twenty-seven million homes has low-carbon source of heat.

[0005] Gas and fossil fuel-fired boilers are at best only 85% efficient, burning approximately 1.18 kWh of input energy for every 1.0 kW of thermal output. This means that the Coefficient of Performance (COP) of these boilers is less than 1, because the amount of heat energy generated is less than the amount of energy input into the system. In contrast, traditional chlorofluorocarbon / hydrofluorocarbon (CFC / HFC)-based air and / or ground source heat pumps have higher COPs, typically in the range of 1-3.

[0006] The maximum temperatures produced by air and / or ground source heat pumps are generally too low to effectively power standard home systems, such as radiators and hot water tanks. To use these heat pumps in homes or businesses for such purposes, significant additional infrastructure—like enhanced insulation or larger heat transfer devices—is often required. This extra infrastructure can be costly and challenging to install, particularly when retrofitting existing buildings. Consequently, the potential cost savings of using a heat pump are often negated by the expenses involved in upgrading or modifying existing systems.

[0007] It is therefore desirable to have a cost-effective replacement for gas or fossil fuel-fired boilers and / or less efficient / capable heat pump systems that both reduces reliance on the combustion of fossil or biomass fuels and also meets the energy and temperature requirements for domestic and commercial buildings.

[0008] The disclosures herein provide for an improved heat pump system which uses CO2 as a working fluid and has enhanced energy efficiency, reduced greenhouse gas emissions, and optimized performance in home, business, and industrial applications. By leveraging those improvements described herein, functional systems have been able to achieve COPs of 7 or higher—meaning that for every unit of energy input, the heat pump “produces” 7 units of heat output. Embodiments described herein have the advantage that the heat pump system may serve as a “drop-in” replacement for existing gas or oil burners, such that the heat pump system can make use of existing radiators, pipework, flue systems, and the like, thereby eliminating the need for costly additional infrastructure and reducing installation and capital costs. An aesthetic benefit may also be realized, as the heat pump systems designed herein may omit outdoor evaporation units, such that the systems may be installed without affecting the aesthetic qualities of a building or without necessitating additional effort to hide industrial-looking components that some may find to be an eyesore.SUMMARY

[0009] The present disclosure provides for an improved heat pump, system, and method for operating the same, that may use supercritical carbon dioxide (CO2) as a working fluid.

[0010] In one embodiment, the heat pump comprises a multi-stage heat exchanger for providing heat to a plurality of heat sinks, preferably a hot water system or a space heating system of a building and a working fluid re-heater or economizer. The multi-stage heat exchanger arrangement facilitates the heat pump system to operate at temperatures consistent with those typically provided by traditional fossil-fuel fired boilers. As a result, the heat pump may serve as a “drop in” replacement for these traditional systems without requiring the additional infrastructure typically needed when attempting similar retrofits with conventional heat pump systems.

[0011] In another embodiment, the heat pump is provided with an oil separator, reservoir, and accompanying valve assembly to extract lubricant from the working fluid and feed said lubricant back to the compressor at a pressure which is higher than the inlet pressure of the compressor.

[0012] In another embodiment, the working fluid is expanded through multiple stages to limit flashing of the working fluid to a subcritical gas during expansion and to facilitate venting of any such gases which do form to the compressor suction inlet, again improving the efficiency and reliability of the heat pump.

[0013] These and additional features provided by the embodiments of the present disclosure will be more fully understood in view of the following detailed description, in conjunction with the drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the disclosure. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0015] FIG. 1 depicts an exemplary schematic view of a transcritical heat pump circuit according to the embodiments discussed herein;

[0016] FIG. 2 depicts an exemplary process chart for the operation of a heat pump according to the embodiments discussed herein;

[0017] FIG. 3 depicts an exemplary method for operating a heat pump according to the embodiments discussed herein;

[0018] FIG. 4 depicts a series of profile view of a heat pump according to the embodiments discussed herein;

[0019] FIG. 5A depicts a view of a housing for a heat pump according to the embodiments discussed herein;

[0020] FIG. 5B depicts a view of a housing for a heat pump according to the embodiments discussed herein;

[0021] FIG. 5C depicts a view of a housing for a heat pump according to the embodiments discussed herein;

[0022] FIG. 5D depicts a view of a housing for a heat pump according to the embodiments discussed herein; and

[0023] FIG. 6 depicts an exemplary schematic view of a heat pump system according to the embodiments discussed herein.DETAILED DESCRIPTION

[0024] The embodiments of the disclosure herein include a heat pump, corresponding system, controls, and methods for operating the same.

[0025] The heat pump may operate using CO2 as a working fluid, which has excellent thermodynamic properties and can efficiently transfer heat. Through the course of the cycle facilitated by the heat pumps disclosed herein, the working fluid is transitioned between subcritical and supercritical states in order to achieve the titular “pumping,” or transfer, of heat.

[0026] Subcritical and supercritical CO2 are two distinct states of carbon dioxide, defined by their temperature and pressure in relation to CO2's critical point. The critical point for CO2 is approximately 31.1° C. (87.8° F.) and 73.8 bar (1071 psi). When CO2 is below this critical temperature and pressure, it is considered subcritical. In the subcritical state, CO2 can exist as either a gas or a liquid, depending on specific conditions. At low pressures and temperatures, CO2 is gaseous, while at higher pressures but below the critical temperature, it becomes a liquid. In this subcritical state, there is a clear distinction between liquid and gas phases, often with a visible interface if both are present.

[0027] Supercritical CO2, on the other hand, exists at temperatures and pressures above its critical point, where it transitions into a supercritical fluid. In this state, CO2 exhibits properties that make it highly advantageous for advanced energy systems. It combines the density of a liquid, which allows it to carry significant thermal energy, with the low viscosity of a gas, enabling efficient flow through turbines and heat exchangers. Additionally, its high diffusivity improves heat transfer and overall system performance.

[0028] However, while preferred embodiments make use of CO2 as a working fluid, such a preference is not to be construed as a limitation. It is contemplated that any working fluid with similar properties and / or characteristics at notable points in the refrigeration cycle, such as air or argon, or any suitable working fluid cognizable to a person of ordinary skill in the art, may be usable or used with those systems herein to achieve a comparable effect.

[0029] Turning now to FIG. 1, a simplified, exemplary heat pump system is depicted in schematic form. The heat pump 10 may include a compressor 20, one or more heat exchangers 30, one or more controllable expansion valves 41-42, a liquid receiver 50, one or more pressure valves 52, one or more heat exchangers, or evaporators 61-62, and a fan 63. The heat pump 10 forms a largely closed or hermetically sealed loop, whereby the working fluid may pass through these components and undergo the cycle described below.

[0030] As set forth herein, and solely for the purposes of explanation and orientation, any relative positional description of components as “upstream” or “downstream” of one another, specifically, is to be considered broken by a conceptual boundary between the compressor 20 and the inlet or suction side of the compressor 20, even though no such physical boundary exists. For example, as shown in FIG. 1, the compressor is “upstream” of the first heat exchanger 30a, but the evaporator stage 60 is not. As another example, and again as shown in FIG. 1, the second heat exchanger 30b (or at least a portion thereof) is “downstream” of the evaporator stage 60, but the compressor 20 is not. Any other relative positional descriptions (e.g., X is between Y and Z, X is before Y) are to be given their plain and ordinary meaning as would be understood by a person of ordinary skill in the art.

[0031] At the start of the cycle, compressor 20 is used to compress the working fluid from a subcritical state to a supercritical state. The compressor 20 may be embodied as a piston compressor, rolling piston compressor, swing compressor, scroll compressor, vane compressor, screw compressor, reciprocating compressor, and / or any other type of compressor known in the art which is suitable for compressing a working fluid as described herein from a subcritical to a supercritical state. The compressor 20 may be a single stage compressor or a multi-stage compressor.

[0032] Once the working fluid leaves the compressor, it may then pass to a first heat exchanger 30a. The first heat exchanger 30a is used to extract heat from the supercritical working fluid, thereby cooling the supercritical working fluid to some extent, and transfer that heat to a first heat sink. This transfer may be direct or indirect by way of another medium or intermediate coolant. An exemplary intermediate coolant may include water or a water / glycol mixture. Preferably, the working fluid is maintained at a constant pressure as it passes through the first heat exchanger 30a.

[0033] It is preferable that the first heat exchanger 30a transfers heat from the working fluid to a first heat sink embodied as a hot water system 81, such as a domestic hot water system (e.g., that which might supply showers, baths, laundries or the like). For example, the extracted heat may be used to heat up a hot water tank or provide in-line heating to a hot water line. The hot water system 81 may also be a commercial or industrial hot water system, such that which supplies hot water used for industrial processes or the like. As above, this transfer of heat to the hot water system 81 may be direct, such as by passing the water of the hot water system 81 through the heat exchanger 30a, or indirect, such as by passing an intermediate coolant through the heat exchanger 30a which passes through another heat exchanger to ultimately provide heat to the hot water system 81.

[0034] The first heat sink may also be embodied as a space heating system, such as that which provides heat for a home / building via hot water radiators or via forced air systems.

[0035] Next, the working fluid exits the first heat exchanger 30a and passes into a second heat exchanger 30b. That is to say, the second heat exchanger 30b may be provided in series with the first heat exchanger 30a. The second heat exchanger 30b may also be referred to as an economizer. The second heat exchanger 30b may, as above, transfer, directly or indirectly, heat from the supercritical working fluid to subcritical working fluid later on in the cycle in a pre-heating step, before the subcritical working fluid is fed back into the compressor. This step is discussed in further detail below. Again, preferably, the working fluid is maintained at a constant pressure as it passes through the second heat exchanger 30b.

[0036] Efficiency of the thermodynamic cycle may be increased by lowering the temperature of the supercritical working fluid before any expansion step. Efficiency of the thermodynamic cycle may also be increased by increasing the temperature of the subcritical working fluid after evaporation has occurred. The second heat exchanger 30b, or economizer, achieves both conditions simultaneously, further increasing the overall efficiency of the heat pump 10.

[0037] As a result of this multi-stage process, a building, such as a home or business, may be provided with hot water for one or both of the hot water system 81, hot air or water for a space heating system, or the like at temperatures and capacities which are typically provided by traditional gas and / or fossil fuel boilers. This means that these traditional gas and / or fossil fuel boilers can be replaced with the heat pump 10 described herein without needing to also replace existing infrastructure such as pipes / ducts, heat exchangers, and the like as may be required for conventional heat pump systems.

[0038] The heat exchangers 30a-b may be embodied as heat exchangers comprising micro-channels of less than 1 mm in width, diameter, and / or spacing. The heat exchangers 30a-b may be formed from metal and, advantageously, may be 3D printed. The use of 3D printing allows for the creation of three-dimensional surface features which, combined with the high surface area density and optimized fluid pathways of the micro-channel configuration, results in a heat exchanger 30 with high thermal exchange, low weight, and low pressure drops. As a result, the overall heat pump system is made more compact, lighter, easier to install, more efficient, and cheaper to manufacture.

[0039] After leaving the second heat exchanger 30b, the working fluid passes through a expansion stage 40 which includes a first expansion valve 41, a liquid receiver 50, and a second expansion valve 42. The first and second expansion valves may each be embodied as a controllable expansion valve, such as a stepper motor-controlled or servo-controlled valve or any other known expansion device.

[0040] As the high pressure, supercritical working fluid passes through the first expansion valve 41, the pressure of the working fluid is reduced, which has the result of converting the supercritical fluid to a subcritical liquid. The subcritical liquid is then collected in the liquid receiver 50 before undergoing further expansion.

[0041] While residing in the liquid receiver 50, it is possible that some of the supercritical fluid or subcritical liquid vaporizes / evaporates / flashes into a subcritical gas which also occupies the liquid receiver 50. To avoid overpressure conditions, the liquid receiver is provided with a bypass line 51 on which is arranged a pressure valve 52 via which subcritical gas may be vented to the suction line 22 of the compressor 20. The pressure valve 52 may be a controlled valve (e.g., stepper motor, servo, or the like), active valve, passive valve, or any other known type of pressure control valve. The pressure valve 52 is attached to the liquid receiver 50 and controlled in a manner that ensures that any fluid which passes to the suction line of the compressor 20 is a gas and not a liquid.

[0042] Next, the working fluid, in its subcritical liquid form, passes from the liquid receiver 50 and through a second expansion valve 42. Optionally, second expansion valve 42 may instead be embodied as a powered expansion device, such as one that may be independently driven or driven along with the compressor 20 via the compressor shaft. In either case, the working fluid is further expanded to a pressure which corresponds well to the prevailing ambient air temperature to better facilitate subsequent evaporation steps. This degree of expansion may be dynamically adjusted, in real time, to account for changes in ambient air temperatures, thereby ensuring safe and efficient operation and improving the overall COP of the heat pump.

[0043] Additionally, a filter 53 may be disposed downstream of the liquid receiver 50 and upstream of the second expansion valve 42.

[0044] Once the working fluid is expanded to the desired pressure, the working fluid passes to an evaporation stage 60 whereby the working fluid is converted from a subcritical liquid to a subcritical gas. Heat for evaporating the working fluid in this manner may be extracted from, for example, ambient air.

[0045] The evaporation stage 60 is provided with at least one evaporator 61, 62 and a fan 63, such as a cyclone fan. The fan 63 is configured to force—pushing or pulling—ambient air over the evaporator 62 to exchange heat with the working fluid contained within. The evaporator 61, 62 is preferably embodied as a finned micro-channel heat exchanger. Preferably, the micro-channels are less than 1 mm in width, diameter, and / or spacing. Use of a finned micro-channel heat exchanger has advantages in that the internal volumes are lower, requiring less working fluid, corrosion resistance is better, approach temperatures are closer, and the airside pressure drop is lower.

[0046] As the ambient air passes through the evaporator 62, the ambient air is cooled. However, the degree of cooling here may be significant, which can lead to icing of the evaporator 62 and a reduction in performance of the same. The impact of this phenomenon can be reduced by executing defrosting cycles or by lowering the pitch of the fins, but this significantly reduces the heat transfer rate of the evaporator 62.

[0047] Another solution to the icing problem is to provide a second evaporator, such that air would first pass over the first evaporator 62 and then pass over the second evaporator. In such a configuration, the first evaporator 62 may instead be provided with larger fins and / or a lower fin density while the second evaporator is provided with smaller fins and / or a higher fin density. This has the result that most, if not all, of the moisture in the ambient air would condense on the fins of the first evaporator 62, leaving little to no moisture left in the air to condense on the fins of the second evaporator, and thereby delaying the accumulation / formation of frost. The larger fins / lower fin density of the first evaporator 62 would also permit the condensation to flow / drip away from the first evaporator 62 more quickly under the force of gravity or the like.

[0048] This two-stage arrangement has the effect of increasing defrost intervals and reducing defrost time, as the second evaporator would only be subject to icing in the most extreme weather conditions. Additionally, hydrophobic coatings may be applied to the surfaces of the first and / or second evaporators to further mitigate the formation of frost. Frost which does form over such a coating tends to have poor adhesion and is easier to dislodge from the evaporators.

[0049] For both single and multi-stage evaporator configurations, defrost cycles may be incorporated whereby hot gas is passed through either / both the first and second evaporators to melt / dislodge any accumulated frost.

[0050] Evaporators 61, 62 may also be referred to as heat exchangers, gas coolers, or described using other terms of art.

[0051] A gas accumulator 80 or other working fluid storage device may optionally be arranged downstream of the evaporation stage, so as to collect subcritical working fluid gases for subsequent use by the compressor 20.

[0052] A controller 90 comprising any number of processors, memory units, storage units, network interfaces, user interfaces, data / control / PID interfaces, sensor interfaces, displays, audio inputs / outputs may be provided. Additionally / alternatively, the controller may be formed as an application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or any other computing / control system. The controller may be a plurality of controllers and / or microcontrollers which are in operative communication with one another.

[0053] The controller 90 may be configured to or may execute software which causes the controller to control operation of the heat pump 10. The heat pump 10 may be provided with any number of sensors, which may include temperature and / or pressure sensors measuring static and / or total quantities, vibration sensors, microphones, flow rate sensors, electrical sensors (e.g., voltage, resistance, current), rotational speed sensors, clocks / timers, humidity / moisture sensors, and the like and provided at any point on, in, around (such as to measure environmental quantities, such as ambient temperatures / pressures), and / or between components of the heat pump 10 circuit shown in FIG. 1. Feedback and / or measurements from any combination of these sensors may be used in the control of the heat pump 10 by the controller.

[0054] In most configurations, control of the heat pump 10 by the controller may be exercised by adjusting the speed of the compressor 20 and the degree of expansion of the working fluid carried out at the expansion stage by the first expansion valve 41 and / or the second expansion valve 42.

[0055] It is further contemplated that any number of valves, check valves, pressure valves, controlled valves, or the like may be disposed at various points along the heat pump circuit to facilitate the injection / venting of working fluid, control of working fluid as it passes through the circuit, servicing of any of the components arranged along the circuit (e.g., valves may be disposed in a manner, such as at the inlet / outlet ports / flanges / etc. of a component, that a given component may be isolated from the rest of the circuit to make the component easier to service), and the like.

[0056] Additionally, additional receivers, accumulators, storage tanks, or the like may be disposed at various points along the heat pump circuit, such as directly or substantially directly before the compressor 20, to collect working fluid, to ensure any downstream components have available sufficient working fluid to operate, and / or the like as required by a given installation.

[0057] Lubrication of the compressor may be ensured by way of an oil system 100. For the purposes of descriptions herein, “oil” refers to any suitable oil or lubricant and is thus not necessarily limited only to “oils.” An oil separator 102 may be provided downstream of a muffler 101 which, in turn, is downstream of compressor 20. The oil separator has the effect of separating any oil from the working fluid once the working fluid leaves the compressor 20.

[0058] Once oil is detected in the separator 102 by an optical switch or the like, oil valve 103, which is controlled by a solenoid or comparable control mechanism, opens to permit any such oil to pass to an oil receiver 104 or other storage tank. The pressure within the oil receiver 104 is maintained via a pressure valve 105 to be just above the compressor inlet pressure, thereby ensuring that oil may be fed to the compressor 20 during operation.

[0059] When a compressor oil level switch 106 or the like signals that more oil is required by the compressor 20, another oil valve 106a, which is controlled by a solenoid or comparable control mechanism, opens to permit any such oil to pass into the compressor 20. An oil filter 107 may be arranged between the compressor and another oil valve 106a.

[0060] Turning now to FIG. 2, a flow chart describing an energy transfer method utilizing the heat pump 10 is shown.

[0061] In step 200, the working fluid is compressed by a compressor 20 from a subcritical state, preferably a subcritical gas, to a supercritical state at the exit of the compressor.

[0062] In step 210, the working fluid passes into a first heat exchanger 30a, at which point heat is exchanged, directly or indirectly, between the working fluid and a first heat sink, such as hot water system 81 or a space heating system.

[0063] In step 220, the working fluid passes into a second heat exchanger 30b, at which point heat is exchanged, directly or indirectly, between the working fluid in a supercritical state and the working fluid in a subcritical state at a later point in the thermodynamic cycle.

[0064] Throughout steps 210 and 220, the supercritical working fluid is maintained at a high pressure to sustain the supercritical state. Preferably, the supercritical working fluid is maintained at a constant pressure through steps 210 and 220.

[0065] Because the supercritical nature of the working fluid may complicate the expansion process—enhancing the effects of the expansion process, causing higher energy losses and prematurely generating subcritical vapor—if the temperature of the working fluid is above the critical temperature as the working fluid leaves the second heat exchanger 30b, a two-stage expansion process may be employed in addition to the provision of an evaporation stage 60.

[0066] In step 230, the working fluid is expanded a first time by a first expansion valve 41, thereby effecting a phase change and transitioning the supercritical working fluid to a subcritical liquid state. The first expansion valve 41 may be a controlled valve, such as a stepper motor-controlled valve, whereby the size of an orifice of the valve is adjustable to control the pressure drop across the first expansion valve 41.

[0067] In step 240, the working fluid is received and held in the liquid receiver 50.

[0068] As the working fluid is expanded from the supercritical fluid state to the subcritical liquid state, it is likely that some subcritical vapor may be generated as well. This flash or bypass gas may be vented from the liquid receiver 50 by way of a pressure valve 52. Pressure valve 52 may be an actively controlled valve (e.g., motor / servo controlled), a passively actuated valve (e.g., one that opens at a certain pressure), or the like.

[0069] In step 250, the working fluid, which is now in a subcritical liquid state, is expanded again through a second expansion valve 42 or expansion device. Preferably, the working fluid is expanded by the second expansion valve 42 or expansion device to an extent that the working fluid begins to boil or is near or at a boiling point.

[0070] In step 260, heat is transferred from ambient air to the working fluid by way of an evaporation stage 60 comprising one or more evaporators 61, 62. Optionally, a fan 63 may be provided to force an ambient airflow through and / or over the evaporators 61, 62. This causes the working fluid to boil, such that, by the time the working fluid exits the evaporation stage, the working fluid has fully or substantially fully undergone a phase change from a subcritical liquid to a subcritical gas.

[0071] In step 270, the working fluid in its subcritical gas form is passed back through the second heat exchanger 30b to, as above, exchange heat with the supercritical working fluid earlier in the cycle. This has the effect of increasing the temperature of the working fluid in its subcritical gas state prior to entering the compressor, which increases overall performance of the heat pump 10.

[0072] Finally, gases may be retained in an accumulator 80 before being passed to the compressor 20.

[0073] In additional advantageous embodiments, it is contemplated that the hot water system 81 and / or the space heating system may be replaced with other process systems which are well suited to the temperatures achievable at these respective stages of the heat pump 10. Such other process systems may include in-floor or other forms of home / building heating, driveway heating, laundry, water purification, thermal energy storage devices, thermal power or electricity, industrial and / or commercial process, chemical processes / reactors, and the like.

[0074] In another advantageous embodiment, it is contemplated that the heat pump 10 may further be used to supply cool air and / or air conditioning to the same home or building to which it supplies heat. In such an embodiment, air which is to be circulated through the building may be passed through the evaporation stage 60 with or instead of the ambient air. In a similar fashion, the air which is to be circulated through the building may undergo a dehumidification process as moisture in the air condenses upon the evaporators 61, 62. This air conditioning may be achieved either directly or indirectly by way of an intermediate coolant and / or may be provided as a step instead of or in addition to the evaporation stage 60 discussed above. In this way, the heat pump 10 may provide both heating and cooling to a building.

[0075] In another advantageous embodiment, the hot water system 81 may be provided with one or more heat exchangers by way of which heat contained within the hot water system may be rejected to the atmosphere. In this manner, the capacity or ability of the hot water system 81 to accept heat from the supercritical working fluid may be maintained. In those scenarios in which the ambient temperature may be too high to adequately or effectively reject heat to the atmosphere, the hot water system 81 may instead reject this heat to one or more cold water return lines.

[0076] In additional advantageous embodiments, the heat pump 10, hot water system 81, and / or space heating system may interface, directly or indirectly, with a low temperature reservoir (e.g., a pond / lake or other body of water, geothermal or in-ground thermal reservoir, or the like), phase change material (PCM) unit, or other dedicated heat sink (e.g., cooling tower or the like). In such a configuration, the heat pump 10 may be provided with one or more additional heat exchangers 30, in series or parallel, at any point with any of the first or second heat exchangers 30a-b discussed above. Such configurations facilitate the ability to reject additional heat from the system to maintain desirable operating conditions and / or parameters of the heat pump 10 and / or ensure that the hot water system and / or space heating system are able to accept a sufficient amount of heat from the supercritical working fluid without exceeding operating parameters, safety margins or requirements, or the like.

[0077] In another advantageous embodiment, the heat pump 10 may be provided with a CO2 concenter, whereby CO2 may be extracted from an environment in / around the heat pump 10 and used within the heat pump 10 or stored for safety purposes (e.g., in the event of leaks or the like to avoid harming technicians).

[0078] Turning now to FIG. 3, a flow chart showing an exemplary control scheme for a heat pump 10 is shown. As discussed above, the exemplary circuit of FIG. 1 provides for three primary control points for adjusting the operating parameters of the heat pump 10: the speed of the compressor 20, the degree of expansion facilitated by the first expansion valve 41, and the degree of expansion facilitated by the second expansion valve 42 or expansion device. As further discussed above, the second expansion valve 42 may be embodied as an actively driven expansion device, whereby rotational input power, either with or independent of the shaft of the compressor 20, drives expansion of the working fluid.

[0079] Accordingly, in step 300, the speed of the compressor may be adjusted to affect the temperature and / or pressure of the supercritical working fluid as it exits the compressor 20. One or more temperature and / or pressure sensors may be provided at and / or near an inlet and / or an outlet of the compressor 20, and measurement data collected from the same may be used by the controller and / or any software / circuit configurations to control the speed of the compressor 20, or a motor or otherwise which drives the functional elements of compressor 20, to achieve a target temperature and / or pressure of the working fluid at the exit of the compressor 20 and / or inlet to the first heat exchanger 30a.

[0080] In step 310, the degree to which the first expansion valve 41 is opened is adjustable to achieve a target pressure within the liquid receiver 50 and / or a condition of the working fluid which advantageously reduces the generation of any excess vapor which might need to be vented from the liquid receiver 50. Likewise, any number of pressure and / or temperature sensors may be provided before and / or after the first expansion valve 41 and / or in / near / around the liquid receiver 51, such that measurement data collected by the same may be used by the controller and / or any software / circuit configurations to control the degree to which the first expansion valve 41 is opened.

[0081] In step 320, the degree to which the second expansion valve 42 is opened or speed at which a second expansion device is operated are adjustable to reach a target temperature and / or pressure downstream of the second expansion valve / device and / or upstream of the evaporation stage 60. As discussed above, it is preferable to target a pressure and / or temperature at this point which corresponds to prevailing ambient conditions to ensure efficient heat transfer between the ambient air and the working fluid in the evaporation stage 60. Likewise, any number of pressure and / or temperature sensors may be provided before and / or after the second expansion valve / device, in / near / around the evaporation stage 60, and / or around the heat pump 10 (e.g., to measure environmental / ambient conditions) such that measurement data collected by the same may be used by the controller and / or any software / circuit configurations to control the degree to which the second expansion valve 42 is opened or speed at which a second expansion device is operated.

[0082] It may be appreciated that any of steps 300, 310, and / or 320 may be carried out in isolation and / or independent of any other step, in combination with any other step, and / or simultaneously and / or asynchronously with any other step depending on the operating needs of the heat pump, such that the sequential listing shown in FIG. 3 is intended to be non-limiting.

[0083] Turning now to FIG. 4, various profile views of a housing 400 or cabinet for containing / protecting the heat pump 10 is shown. One or more removable and / or openable panels 410 are provided for accessing the heat pump 10 within the housing 400. Additionally, one or more feet 420 or wheels, such as caster wheels, are provided to facilitate mounting of the heat pump 10, vibration dampening, transport, and the like as necessary. On the front of the housing 400, an opening 430 is provided for receiving the controller 90 and / or any suitable interfaces, displays, buttons, or the like for operating the controller. However, it is also contemplated that the controller 90 may be disposed anywhere accessible or appropriate for interfacing with the heat pump as the installation requires. One or more flanges may be provided for interfacing the heat pump with any hot water systems 81, space heating systems, reservoirs, or the like as needed.

[0084] The housing 400 may be formed as or with a mechanical frame constructed from welded, riveted, and / or bolted folded steel sheets which are optimized to accommodate vibrational and mechanical loads.

[0085] Turning now to FIGS. 5A-D, a series of profile views of a heat pump 10, predominantly the transcritical circuit 500 of the heat pump 10, according to any of the foregoing embodiments is shown.

[0086] The heat pump 10 may be provided with any of a discharge line muffler 501, one or more oil reservoirs 502, one or more oil separators 566, a compressor 544, an evaporator 545, a gas cooler 546, an economizer 547, a liquid receiver 568, and an air blast cooler 575 consistent with those descriptions set forth above.

[0087] Turning now to FIG. 6, another schematic view of a heat pump system 600 according to any of the foregoing embodiments is shown. The transcritical circuit 500 is shown contained within housing 400 in the center of the diagram.

[0088] One or more hot water loops 610 may extend from the housing 400 to interface with any hot water systems 612, one or more heat rejection devices or gas coolers 614, PCM units 616, or the like for extracting heat from the supercritical working fluid. While the supercritical working fluid may be passed to each of these devices for direct heat extraction, it is preferable to use an intermediate coolant, such as a water / glycol mixture, to indirectly transfer heat to / from the transcritical circuit 500.

[0089] Likewise, one or more cold water loops 620 may extend from the housing to interface with any number of evaporators 622, thermal reservoirs 624, or the like to serve as heat inputs to the subcritical working fluid in liquid form to boil the subcritical working fluid. As above, while the supercritical working fluid may be passed to each of these devices for direct heat input, it is preferable to use an intermediate coolant, such as a water / glycol mixture, to indirectly transfer heat to / from the transcritical circuit 500.

[0090] Any number of valves 630 may be provided to direct and / or otherwise control the flow of intermediate coolant to / from the transcritical circuit 500 and any attached devices.

[0091] It is noted that the terms “substantially” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0092] While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.

Claims

1. A heat pump circuit, comprising:a compressor for compressing a working fluid;an expansion stage for expanding the working fluid;a first heat exchanger arranged downstream of the compressor and upstream of the expansion stage, wherein the first heat exchanger is configured to exchange heat between the working fluid and a first heat sink;a second heat exchanger arranged downstream of the first heat exchanger and upstream of the expansion stage, wherein the second heat exchanger is configured exchange heat with the working fluid after the working fluid exits an evaporation stage but before the working fluid re-enters the compressor; andthe evaporation stage arranged downstream of the expansion stage, wherein the evaporation stage is configured to exchange heat between the working fluid and ambient air.

2. The heat pump according to claim 1, wherein the first heat sink is a hot water system of a building.

3. The heat pump according to claim 1, wherein the first heat sink is a space heating system of the building.

4. The heat pump according to claim 1, wherein the expansion stage comprises a first expansion valve, a second expansion valve, and a liquid receiver therebetween.

5. The heat pump according to the claim 4, further comprising a bypass line and a pressure valve via which gaseous subcritical working fluid may be vented from the liquid receiver to a suction line of the compressor.

6. The heat pump according to claim 4, wherein the first and second expansion valves are independently controlled.

7. The heat pump according to claim 1, wherein the evaporation stage comprises a first evaporator and a fan which is configured to force the ambient air over the at least one evaporator.

8. The heat pump according to claim 1, further comprising an accumulator arranged downstream of the evaporation stage for holding the working fluid in a gaseous form.

9. The heat pump according to claim 1, further comprising an oil system for providing a lubricant to the compressor.

10. The heat pump according to claim 9, wherein the oil system comprises an oil separator arranged downstream of the compressor and upstream of the first heat exchanger.

11. The heat pump according to claim 10, wherein the oil system further comprises an oil reservoir, andwherein the lubricant passes from the oil separator to the oil reservoir via an oil valve which is configured to open when lubricant is detected in the oil separator.

12. The heat pump according to claim 11, wherein a pressure in the oil reservoir is maintained, via control of an oil pressure valve that is in fluidic connection with the oil reservoir, to be greater than an inlet pressure of the compressor.

13. The heat pump according to claim 1, further comprising at least a third heat exchanger arranged downstream of the compressor and upstream of the expansion stage.

14. A heat pump system comprising:the heat pump according to claim 1; anda controller, the controller comprising at least one processor,wherein the controller is configured to adjust a speed of the compressor and a state of the expansion stage to set an operating point of the heat pump.

15. The heat pump system according to claim 14, further comprising a hot coolant loop for circulating an intermediate coolant,wherein the hot coolant loop is fluidically separate from a transcritical loop which circulates the working fluid, andwherein the hot coolant loop exchanges heat between the first heat exchanger and the first heat sink.

16. The heat pump according to claim 1, wherein the working fluid is carbon dioxide.

17. The heat pump system according to claim 16, wherein the intermediate coolant is a water-glycol mixture.

18. A method for operating a heat pump, comprising the steps of:compressing a working fluid in a compressor;exchanging heat between the working fluid and a first heat sink via a first heat exchanger, the first heat exchanger arranged downstream of the compressor and upstream of an expansion stage;exchanging heat between the working fluid in a supercritical state and the working fluid in a subcritical state via a second heat exchanger, the second heat exchanger arranged downstream of the first heat exchanger and upstream of the expansion stage;expanding the working fluid in the expansion stage; andevaporating the working fluid in an evaporation stage by exchanging heat between the working fluid and ambient air.

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