JP7603329B2 - Heat Pump System - Google Patents

Description

The present disclosure relates to heat pumps. In particular, the present disclosure relates to heat pumps for heating and/or cooling systems, such as air conditioning systems, refrigeration systems, or cryogenic systems.

Heat pump ("HP") technologies are gaining commercial support in heating, ventilation, and air conditioning ("HVAC") applications. They can provide energy savings and emissions reductions, and are typically provided for heating and cooling systems in buildings, automotive applications, and the like.

There are several types of heat pumps. Most existing technologies utilize a refrigerant in an expansion/compression cycle, and many heat pumps are classified by the heat source, for example air source heat pumps or ground source heat pumps. The same is true for the basic technologies used in heat pumps. Air source heat pumps are limited in performance at low temperatures (at -18°C, the CoP tends to be close to 1 (by Carnot), so electrical resistance heating is more effective, and at higher operating temperatures the CoP can reach 4). Ground source heat pumps have a more stable inlet temperature, but conventional technologies are limited by the coefficient of performance ("CoP").

There is a need to decarbonize heating and cooling in buildings globally. Heating typically burns carbon-based fuels, releasing carbon into the atmosphere. Cooling and air conditioning can be major electrical loads in warmer climates. Heat pumps could potentially provide heating and cooling from a single package. In cases where heat pumps use renewable electricity, they can be a zero-emission technology. Conventional heat pump technology is generally undesirable because it uses refrigerants that have high global warming potential and can be highly toxic. Fans and pumps have noise that can be intrusive.

Conventional HP technology has a CoP of 3-4. By increasing the CoP, power consumption can be reduced, which reduces carbon emissions when using non-renewable power. Furthermore, conventional HP technology may have a CoP that is affected by the ambient air temperature, which is undesirable. US Patent Publication No. 20160084544 (Radermacher et al.) discloses a heat pump system that uses material tubes made of SMA, which are filled with other tubes or rods of unknown material to occupy the volume, thus helping to remove dead thermal mass and increase the efficiency of the system. China Patent Publication No. 106052190 (Qian et al.) discloses a refrigeration system that uses an SMA core with NiTi tubes. Fluid passes through the tubes and flow devices to increase heat transfer, and the core needs to be mechanically connected for work recovery. However, this configuration suffers from poor thermal efficiency.

Heat pumps can be a clean alternative to fossil fuel heating technologies that are currently used in most air conditioning and refrigeration. Hence, the heat pump market is growing. Heat pumps are fundamentally unable to operate at partial load and are less efficient during periods when partial load is required. Cooling requires a lot of energy and maximizing efficiency for cooling has a big impact on generating capacity and grid strengthening. The use of inverter/variable speed operation improves partial load performance but can increase the price of the product by up to 40%.

An object of the present invention is to provide a heat pump system with a significantly improved coefficient of performance (CoP) .

The heat pump system of the present invention is a core having a shape memory alloy (SMA) or a negative thermal expansion material (NTE) or a thermoelastic material arranged inside a housing , the core having a first core, a second core and a third core, each of the first core, the second core and the third core absorbing heat and storing energy, and each of the first core, the second core and the third core changing state depending on an applied stress , the first core and the second core being connected in series to allow fluid to communicate with each other, and the second core and the third core being connected in series to allow the fluid to communicate with each other, and the heat pump system is provided with a control system that controls the supply of the fluid discharged from the first core to the second core and controls the supply of the fluid discharged from the second core to the third core , the control system being configured to discharge the fluid from the first core at a first pressure, discharge the fluid from the second core at a second pressure lower than the first pressure, and discharge the fluid from the third core at a third pressure lower than the second pressure .

Work recovery is fundamental in achieving a good system CoP. The present invention provides a system and method for maximizing work recovery in systems operated by hydraulic or electric load actuator systems. Minimizing back pressure returned to the tank means a dramatic improvement in system CoP.

In one embodiment, each of the cores has a positive pressure gradient in sequence, and the pressure obtained in the first core is utilized to reach equilibrium at a lower pressure.

In one embodiment, an accumulator is provided, and the pressure is accumulated in the accumulator for release to the load-bearing portion of the core, maximizing the rate of thermal change.

In one embodiment, the control system includes a booster.

In one embodiment, the booster comprises a counter booster having an interconnection area that receives the pressure.

In one embodiment, the booster is configured to be in communication with the first core, the second core, and the third core.

In one embodiment, the system is equipped with a hydraulic motor and a generator, and the pressure is converted into effective electricity, which is used to operate the heat pump system.

In one embodiment, the series of cores provide a temperature change to the fluid to activate either the first core, the second core, or the third core such that the cycle time for operating at least one of the cores is reduced.

The heat pump system according to the present invention is a core in which a shape memory alloy (SMA) or a negative thermal expansion material (NTE) or a thermoelastic body is disposed inside a housing, the core having a first core, a second core, a third core and a fourth core, the first core, the second core, the third core and the fourth core each absorbing heat and storing energy, and the first core, the second core, the third core and the fourth core each changing their state in response to an applied stress, the first core and the second core being connected in series to allow fluid to communicate with each other, and the second core and the third core being connected in series to allow the fluid to communicate with each other. The fluid discharged from the first core is connected in series to be able to communicate with the second core, and the control system controls the supply of the fluid discharged from the second core to the third core, and controls the supply of the fluid discharged from the third core to the fourth core, and the control system is configured to discharge the fluid from the first core at a first pressure, discharge the fluid from the second core at a second pressure lower than the first pressure, discharge the fluid from the third core at a third pressure lower than the second pressure, and discharge the fluid from the fourth core at a fourth pressure lower than the third pressure .

In one embodiment, multiple hydraulic cavities of a multi-core system are provided for load sharing and energy recovery. When the core is loaded in compression or tension, a portion of this stored energy can be recovered. However, when two cores with one cavity each are load shared (one loaded and one unloaded at time=0), there is only a pressure balance when the two cores are connected, which means a maximum energy recovery of 50%. If each core has multiple hydraulic chambers (i.e. numbers 1-2-3) of various working surface areas, each core can recover more than 50%.

In one embodiment, a control system is provided that couples two or more cores together, in this example the pistons are coupled in time 1-3, 2-2, 3-1, where 1 is the smallest surface area and 3 is the largest. Any number may be used, but in the present invention we have a multi-core hydraulic piston area and dynamically change this coupling between the cores during the cycle.

In another embodiment, the core is made of a shape memory alloy (SMA) or a negative thermal expansion material (NTE) or a thermoelastic body, the core is arranged inside a housing to absorb heat and store energy, the housing is configured to receive a fluid from an inlet at a first temperature to change the state of the core at an activation temperature, pressure via a hydraulic circuit acts on the core, the core changes from a first state to a second state at an activation point, and a control device is provided that applies the pressure to the core in the housing to change the core from the first state to the second state, and the control device is configured to initially apply the pressure below the activation point.

The present invention provides a heat pump that provides high part-load efficiency by controlling the applied load. This provides significantly higher part-load efficiency than can be achieved with conventional vapor compression (VC) heat pumps, with little increase in cost (unlike VC heat pumps, which can increase costs by 40%). For example, energy stored in the hydrostatic transmission can be used to "soft start" the heat pump, avoiding large starting loads that can be problematic for grid managers.

In one embodiment, the control device has the hydraulic circuit.

In one embodiment, the hydraulic circuit has an electronic proportional control valve/regulator that variably controls the hydraulic pressure or flow to apply stress to the core.

In one embodiment, the electronic proportional control valve/regulator is configured to adjust and circulate the pressure in response to variable temperature of the fluid.

In one embodiment, the hydraulic circuit includes a first hydraulic ram that applies the pressure to the core. The hydraulic circuit includes a hydraulic ram configured to provide a controlled stress to the core.

In one embodiment, the electronic proportional control valve/regulator is configured to regulate the pressure of the first hydraulic ram using a load regulator.

In one embodiment, the hydraulic circuit includes one or more sensors to obtain information to determine the pressure or a response to adjust the downstream fluid.

In one embodiment, the hydraulic circuit has a second hydraulic ram that applies the pressure to the core.

In one embodiment, the electronic proportional control valve/regulator is configured to control the first and second hydraulic rams in response to one or more sensor readings.

In one embodiment, the electronic proportional control valve/regulator is configured to control the second hydraulic ram in response to readings from one or more sensors.

In one embodiment, the control circuit includes an accumulator suitable for storing energy, the stored energy being used to provide energy for applying the pressure.

In one embodiment, the SMA or NTE or elastocaloric material core is suitable for absorbing or releasing heat and/or storing energy in response to applied hydraulic load/pressure.

The pressure or stress applied to the one or more cores can be applied by a hydraulic circuit. In addition to this configuration, pressure can be applied by other mechanisms such as pneumatics, linear/electromechanical actuators, rotary/screw actuators, SMA actuators, etc.

FIG. 1 shows a heat pump system consisting of multiple cores made of SMA or NTE or thermoelastic material. FIG. 2 is an operating cycle of one embodiment, which is an ideal temperature-entropy diagram for a heat pump cycle of a thermoelastic material. FIG. 3 is a diagram illustrating multiple cores of a heat pump system arranged in series in accordance with the operation of the present invention. FIG. 4 is a diagram illustrating multiple cores of a heat pump system arranged in series in accordance with the operation of the present invention. FIG. 5 is a diagram illustrating multiple cores of a heat pump system arranged in series in accordance with the operation of the present invention. FIG. 6 is a diagram illustrating multiple cores of a heat pump system arranged in series, in accordance with the operation of the present invention. FIG. 7 is a diagram illustrating a booster connected to the first core, the second core, and the third core in one embodiment. FIG. 8 illustrates an example of an embodiment in which hydraulic fluid from an unloaded core can be pumped directly to the inlet of a hydraulic pump. FIG. 9-1 illustrates a portion of a multi-core system in one embodiment, where eight cores are shown utilizing a single hydraulic pump and a single pressure distribution link valve. FIG. 9-2 illustrates a portion of a multi-core system in one embodiment, where eight cores are shown utilizing a single hydraulic pump and a single pressure distribution link valve. FIG. 10-1 illustrates a portion of a multi-core system, with four cores operating through a single pump, in one embodiment. FIG. 10-2 illustrates a portion of a multi-core system, with four cores operating through a single pump, in one embodiment. FIG. 10-3 illustrates a portion of a multi-core system, with four cores operating through a single pump, in one embodiment. FIG. 11-1 illustrates a portion of a 12-core system that utilizes several crossover valves with a single pump in one embodiment. FIG. 11-2 illustrates a portion of a 12-core system that utilizes several crossover valves with a single pump in one embodiment. FIG. 11-3 illustrates a portion of a 12-core system that utilizes several crossover valves with a single pump in one embodiment. FIG. 11-4 illustrates a portion of a 12-core system utilizing several crossover valves with a single pump in one embodiment. FIG. 11-5 illustrates a portion of a 12-core system utilizing several crossover valves with a single pump in one embodiment. FIG. 11-6 illustrates a portion of a 12-core system utilizing several crossover valves with a single pump in one embodiment. FIG. 12 is a diagram showing the relationship between material stress and strain in the operation cycle of FIG. FIG. 13 illustrates a tank circuit or similar device placed in series between the first and second cores in one embodiment. FIG. 14 illustrates an ideal operating cycle outlined as Ts in one embodiment.

For a clearer understanding of the present invention, an exemplary embodiment of the present invention will be described in detail below with reference to the drawings. The present invention relates to a novel heat pump cycle that utilizes latent heat from phase transformation in a material made of SMA or NTE or a thermoelastic body. The following describes an implementation of the present invention in an SMA as a preferred embodiment, but the same applies to implementations of materials made of NTE or a thermoelastic body.

The present invention can use SMAs consisting of multiple elements or wires arranged in close proximity to define a core. SMA materials can be in two crystalline states, martensite and austenite, and can reversibly transform from one phase to the other. The transformation from austenite to martensite in SMAs is exothermic. The transformation from martensite to austenite in SMAs is endothermic. The temperature at which the phase transition occurs can be manipulated by application of stress to the SMA material.

Shape memory alloys (SMAs) are alloys that exhibit a shape memory effect, meaning that once deformed, they return to their original shape when heated. These materials are a lighter, solid-state alternative to traditional actuators such as hydraulic, pneumatic, and motor-based systems.

The present invention relates to a heat pump system and method that can use either a plurality of shape memory alloys (SMAs) or a plurality of negative thermal expansion materials (NTEs) or a material made of a thermoelastic body. In one embodiment, an SMA system can be used that is made of a material made of SMA. In one example, a plurality of elements (or a group of elements) or a plurality of wires are arranged in close proximity to define a core. In another example, the core can be defined by one or more of rods, blocks, ribbons, strips or plates, 3D printed elements, etc., any of which can function as a core by being subjected to axial or lateral compression, compressive and natural loads, and torsional stresses.

Heat pumps have two phases: heat absorption and heat release. A machine cycle is defined as a complete heat absorption phase (endothermic) and a complete heat release phase (exothermic).

The heat absorption phase sets the stress applied to the material to a suitable value lower than that used in the cycle operation that allows the transfer of heat into the SMA material. As a result, the austenite start (As) and austenite finish (Af) activation temperatures are set to values lower than the input temperature of the fluid flow. A thermal gradient exists that allows heat transfer into the SMA by thermal conduction and thermal convection. Once the material has fully or partially transformed to austenite (i.e. the temperature of the SMA material is higher than Af), the heat absorption phase is complete.

After increasing the stress on the material made of austenitic SMA, the heat release phase begins. This increases the activation temperatures of martensite start (Ms) and martensite finish (Mf) for the reverse transformation back to martensite. Once the value of Ms rises above the temperature of the input fluid flow, the reverse transformation begins. It is completed only when Mf is also higher than the temperature of the fluid flow. Latent heat is then released by the material made of SMA to the fluid flow, increasing its temperature. The rate at which the release of heat occurs is a function of various thermodynamic conditions of the fluid flow such as thermal gradients, flow velocity, and turbulence.

A single fluid temperature input can be used in the system, and a series of valves can be used at the output from the fluid chamber to direct the flow of cooler fluid from the heat absorption phase back to the fluid source while directing the warmer fluid from the heat release phase to the object to be heated. Multiple fluid temperature inputs can also be used.

Figure 1 illustrates a heat pump system incorporating what is known as an SMA actuation system, but in reverse operation, and is incorporated herein by reference in unpublished PCT Patent Application No. PCT/EP2019/052300 filed by Exergyn Limited. As shown in Figure 1, a low pressure accumulator is applied to the SMA material in the martensitic state. When fluid is input to the fluid chamber containing the SMA material at a temperature greater than As and Af, the SMA material is enabled to absorb heat.

Figure 2 shows an idealized temperature-entropy diagram for a heat pump cycle made of a thermoelastic material according to one embodiment of the present invention, illustrating the operating cycle. The cycle removes heat from a heat transfer fluid (HTF) at temperature Tc between points 5-6, and releases heat to a higher temperature fluid Th between points 2-3. Heat is absorbed by the heat recovery circuit between points 3-4, causing the material to cool, and is reabsorbed by the material between points 6-1, causing it to heat.

Work recovery is the primary process required to achieve maximum CoP in a solid/SMA/elastic heating heat pump/refrigeration system. This can be achieved by introducing the pressure exhausted from one SMA core chamber (first core) into the next core chamber (second core) that is preparing or undergoing cycle component load application. The end result is a lowering of the input work required to the system to operate the second core while maintaining the same Qout. Hence, the coefficient of performance increases.

However, under normal circumstances, the maximum pressure that can be transferred from one core to the next is 50% (assuming no losses in the transfer line). This is because both cores compress against each other and reach equilibrium at which point the thrust to perform work drops to zero. Therefore the remaining 50% of the pressure discharged from the first core must be returned to the tank.

The present invention improves work recovery. In a first embodiment, the heat pump system includes a continuous build-up of back pressure in a series core. In a second embodiment, the present invention utilizes a back booster that converts low pressure to high pressure, thus adding pressure to a second core. In a third embodiment, the heat pump system uses an electric conversion unit.

In a first aspect of the present invention, the improvement in work recovery is achieved by distributing the effective back pressure among a series of cores that are in sequential communication with the first core.

The invention works by providing at least three cores arranged in sequence. The net effect is that each core in turn has a positive pressure gradient and reaches equilibrium at a lower pressure, thus utilizing more of the back pressure available in the first core.

3 shows a heat pump system 10 with four cores C1, C2, C3 and C4 connected by valves 11. The four cores work in sequence as follows (assuming ideal conditions, no losses and core pressure expressed as a percentage of the initial core pressure):
[Initial Cycle]
Step 1 (C2-C4 closed): C1=100, C2=0, C3=0, C4=0 is shown in FIG.
Step 2 (C2 open, C3-C4 closed): C1=50, C2=50, C3=0, C4=0 is shown in FIG.
Step 3 (C2 closed, C3 open, C4 closed): C1=25, C2=50, C3=25, C4=0 is shown in FIG.
Step 4 (C2-C3 closed, C4 open): C1=12.5, C2=50, C3=25, C4=12.5 is shown in FIG.

After step 4, the remaining 12.5% of the exhaust pressure at C1 is discharged to tank (if it is not utilized elsewhere in the system, such as to generate electrical energy when running the recovery motor). The pressure at C2 needs to be increased by 50%, which is sourced from the input pump. However, in the second cycle, it is more preferable that the system is as follows:
In the second cycle, each core does the following:
Step 1 (C1 is discharged to the tank, and C2 is pumped up to 100%): C1 = 0, C2 = 100, C3 = 25, C4 = 12.5
Step 2 (Close C1, Open C3, Close C4): C1 = 0, C2 = 62.5, C3 = 62.5, C4 = 12.5)
Step 3 (Close C1+C3, Open C4): C1=0, C2=37.5, C3=62.5, C4=37.5
Step 4 (C1 open, C3-C4 closed): C1 = 18.75, C2 = 18.75, C3 = 62.5, C4 = 37.5

This trend continues until the core pressure balance is balanced according to the following relationship:
Maximum ideal work recovery (%) = 100 - 100 / number of cores in the work distribution sequence (Equation 1)

Therefore, for a 4-core sequence, the maximum achievable work recovery is 75% and for an 8-core sequence it is 87.5%. Adding additional cores results in additional pressure transmission losses and entropy of the overall system, and therefore in realistic scenarios a point is reached where the benefits of increasing the number of sequence cores are balanced by some gain.

Activation of the valves associated with the C1-C4 cores can be configured to fix some pressure in each or some of the cores and select the best back pressure exchange between the cores to maximize recovery.

In some embodiments, it may be necessary to store the built-up pressure in a small pressure accumulator in preparation for release into the core when loading is required to ensure that the heating rate, and therefore the final temperature of the SMA, is maximized.

To further enhance work recovery, a back booster can be used to use a portion of the pressure discharged to the tank. In the case of an ideal four-core sequence, the pressure discharged to the tank (and therefore needs to be replenished by the pump) is 25% of the initial pressure of the core (once the system has stabilized). The actuation of one or more of the valves can be configured to fix the pressure in a portion of the core and select the best back pressure exchange between the cores to maximize recovery.

The reverse booster utilizes two interconnected areas that are subjected to pressure as shown in Figure 7. The ratio of the larger surface area to the smaller surface area represents the ideal pressure increase that can be achieved by utilizing the device.

The cost of pressure "boosting" is volume loss. Such a system can be used between hydraulic fluid being discharged to tank and the next core in the sequence requiring higher pressure. The system then increases the pressure of the following core while reducing the back pressure discharged to tank. This increases system efficiency. The end result of a four-core sequence would be a favorable shift of required work input from the hydraulic pump.

Considering Equation 1 above, the four-core sequencing system described above achieves a maximum work recovery of 75%, with 25% being lost and needing to be replenished as work input. The reverse booster increases the maximum work recovery to >75%, therefore the loss is <25%.

A single intensifier in a multicore sequence is used at rotational speed, and due to the cyclical nature of its usage, it is not necessary to have a single intensifier installed on each core in the system.

An alternative to using a pressure intensifier is to utilize the residual pressure in a hydraulic motor and generator setup, where the pressure is converted into useful electricity, offsetting the electrical load required to run the system.

[Hydraulic embodiment]
8 illustrates an embodiment in which hydraulic fluid from the unloading core is pumped directly to the inlet of a hydraulic pump. The pressure differential required by the pump is reduced as the fluid initially enters at high pressure and gradually decreases as the core is fully unloaded.

According to FIG. 8, the hydraulic cylinders of the two cores 20 and 21 are connected through valves 22. When one core is unloaded, it first supplies pressure and fluid directly to the second core, similar to the embodiment described above. When the pressures are equalized, the remaining fluid is sent to the inlet 23 of the hydraulic pump 24 to increase the fluid pressure and provide the required remaining pressure to the load-applying core. This embodiment reduces the number of valves required to achieve work recovery. Besides this configuration, multiple valves may be used in the circuit to increase the direct supply between the cores and reduce the operating flow rate of the hydraulic motor.

Figure 9 illustrates a multi-core system with eight cores shown utilizing a single hydraulic pump 30, a single pressure distribution link valve 31 between the cores, and hydraulic check valves 32 to prevent back pressure from the cores when not desired. In this embodiment, each core operates 1/8 out of phase to ensure a constant supply to the hydraulic pump and to ensure a constant supply from the hydraulic pump.

Figure 10 illustrates how four cores operate through a single pump with no core crossovers, eliminating the need for check valves and therefore making the system more efficient. Figure 10 shows a circuit with 12 cores, each operated by a single motor with a single pump for a nested four-core configuration.

Figure 11 illustrates a 12-core system utilizing several crossover valves with only a single pump, with each core operating 1/12 out of phase. Five cores are used to distribute pressure directly before the final fluid is fed to the hydraulic pump for recirculation.

[Heat Pump Load Control Embodiment]
FIG. 12 illustrates the operating cycle of FIG. 2 from the material stress and strain points in one embodiment. Between points 6 and 1, the material stress increases. However, the load does not activate the martensite phase operating point (Ms') because doing so would dump heat into the heat recovery circuit, thus reducing the efficiency of the system. The same applies to points 3 and 4, where the load reduction prevents the initiation of the austenite operating point (As's), which would remove heat from the heat recovery circuit. Meanwhile, between points 1 and 2, the load increases to cause heat dump, but must remain constant between 2 and 3 for isothermal heat dump. Also, between points 4 and 5, the load must drop below As' and then remain constant between 5 and 6.

To achieve these types of load profiles in hydraulic circuits, electronic proportional control valves/regulators are implemented to control the hydraulic pressure or flow and therefore material stress. The electronic proportional control valves/regulators can adjust cycle pressure to accommodate variable temperature or heat demands. Also, in situations where the heat recovery circuit must be reheated due to heat losses, this device can be used to control material heat rejection between 6 to 1 or heat absorption between 3 to 4.

Figure 13 shows a hydraulic circuit configured to achieve the required level of control for a single hydraulic ram without work recovery in one embodiment. Figure 13 shows hydraulic fluid stored at low pressure in a hydraulic tank 40 and pumped through a hydraulic pump 41 when pressure rises. This high pressure fluid is stored in an accumulator 42 until needed. The load regulator 43 is operated by a control system that uses readings from both upstream/downstream pressure sensors and/or other sensors 44. The sensors 44 may be located on the housing or at the inlet or outlet. The sensors determine the appropriate response to adjust downstream pressure or fluid. A solenoid valve 45 may also be included downstream. The valve 45 regulates pressure to the hydraulic ram 46 to the load regulator or releases it to the hydraulic tank 40 to remove all load. During each cycle, the hydraulic ram 46 applies the appropriate stress to the core at the right time.

As an alternative to Figure 13, where more than one cylinder is required, a configuration is shown in Figure 14. In this configuration, the solenoids are located in three locations. Moving the valve to the far left applies a load from the main regulator to the right core and completely unloads the left core. Moving to the far right loads the left ram and completely unloads the right. When the valve is in the center position, all ports are closed. A second regulator between the cores can be used to control the load application between the cores for work recovery at points 3-4 and 6-1 in Figure 12. The regulator position is controlled by a control system that uses pressure sensor readings on each core and possibly temperature and time.

The heat pump systems and methods described herein have many applications and can be used for heating (space heating, thermal boiler systems, or hot water), cooling (air conditioning water coolers, process cooling), reversible heating and cooling (building or automotive applications), refrigeration (domestic or commercial/retail), and cryogenic cooling. The heat pump systems and methods can be effectively applied to any heating and cooling system.

In this specification, the words "comprise, comprise, comprised, comprised of" or any variations thereof, and the words "include, include, include, including, comprised of, any variations thereof, are interchangeable and should be given the broadest possible interpretation.

The present invention is not limited to the embodiments described above, and various modifications can be made to the configuration and details.

Claims (2)

a first core, a second core, and a third core, each of the first core, the second core, and the third core absorbing heat and storing energy, and each of the first core, the second core, and the third core changing state in response to an applied stress ; the first core and the second core being connected in series to allow fluid to communicate with each other, and the second core and the third core being connected in series to allow the fluid to communicate with each other; and a control system controlling a supply of the fluid discharged from the first core to the second core and a supply of the fluid discharged from the second core to the third core , the control system being configured to discharge the fluid from the first core at a first pressure, discharge the fluid from the second core at a second pressure lower than the first pressure, and discharge the fluid from the third core at a third pressure lower than the second pressure . A core in which a shape memory alloy (SMA) or a negative thermal expansion material (NTE) or a thermoelastic body is disposed inside a housing, the core having a first core, a second core, a third core and a fourth core , each of the first core, the second core, the third core and the fourth core absorbing heat and storing energy, and each of the first core, the second core, the third core and the fourth core changing state in response to an applied stress, the first core and the second core being connected in series to be able to communicate with a fluid, and the second core and the third core being connected in series to be able to communicate with the fluid, A heat pump system comprising a control system that controls the supply of the fluid discharged from the first core to the second core, controls the supply of the fluid discharged from the second core to the third core, and controls the supply of the fluid discharged from the third core to the fourth core, wherein the control system is configured to discharge the fluid from the first core at a first pressure, discharge the fluid from the second core at a second pressure lower than the first pressure, discharge the fluid from the third core at a third pressure lower than the second pressure, and discharge the fluid from the fourth core at a fourth pressure lower than the third pressure .

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