A high-efficiency geothermal source high-temperature environment-friendly heat pump system with double-system collaborative optimization

Abstract

The present application belongs to the technical field of geothermal source utilization, and particularly relates to a high-efficiency geothermal source high-temperature environment-friendly heat pump system with double-system collaborative optimization. The system comprises a transcritical CO2 system and a refrigerant system coupled through a heat exchanger, and the refrigerant system uses R1233zd(E) refrigerant. Geothermal source water is connected to an evaporator in the refrigerant system and an evaporator in the CO2 system in sequence to complete a secondary heat release process. Heat recovery working medium is connected to an air cooler in the CO2 system and a condenser in the refrigerant system in sequence to complete a secondary heat absorption process. The present application makes full use of the characteristics of CO2 in the transcritical state and the advantages of R1233zd(E) to reduce the floor area of the system. Through reasonable setting of operating parameters and adjustment of load matching, geothermal source heat can be efficiently extracted, and while providing a 120 DEG C high-temperature heat source, a 20 DEG C geothermal return water basis can be completed, and the system COP is kept at greater than or equal to 2.5.

Description

Technical Field

[0001] This invention belongs to the field of geothermal source utilization technology, specifically relating to a high-efficiency geothermal source high-temperature environmentally friendly heat pump system with dual-system synergistic optimization. Background Technology

[0002] In practical applications combining geothermal energy and high-temperature heat pumps, the heat source end requires a large temperature drop of geothermal water, drawn from thousands of meters underground, to fully utilize geothermal energy, with the return water temperature not exceeding 20°C. The heat sink end, due to industrial application limitations, demands a heating temperature no lower than 120°C. This necessitates efficient heating under large temperature differences. Traditional high-temperature heat pump systems in this application scenario employ conventional R134a / R245fa cascade units, which suffer from low system energy efficiency (COP < 2.5), high refrigerant GWP, and environmental unfriendliness.

[0003] Achieving efficient production of 120°C hot water from low-temperature geothermal energy sources while ensuring deep heat extraction (return water temperature ≤ 20°C) is a comprehensive challenge that urgently needs to be overcome in this field. However, existing technologies often fall into the trap of compromising one aspect for another, making it difficult to simultaneously meet the multiple requirements of large temperature difference, high energy efficiency, and environmental protection.

[0004] The widespread use of environmentally friendly refrigerants such as CO2 (R744) and R1233zd (E) in the heat pump industry is mainly due to their environmental friendliness and high efficiency. With increasingly stringent environmental regulations and continuous technological advancements, the application prospects of environmentally friendly refrigerants in the heat pump industry will be even broader.

[0005] However, current single transcritical CO2 cycles are limited by the fact that supercritical CO2 has a high specific heat in the low-temperature region but a low specific heat in the high-temperature region, making it difficult to match heat exchange with water and thus unable to achieve efficient production of 120°C high-temperature water. Most existing transcritical CO2 high-temperature heat pumps only utilize heat from the high-temperature region, wasting a large amount of heat from the low-temperature region, resulting in a low overall COP of the system. While a single R1233zd(E) cycle can adapt to high-temperature heating, the evaporation pressure is lower than atmospheric pressure when the return water reaches 20°C on the evaporator side, leading to an excessively high system compression ratio, increased energy consumption, and inability to achieve the high-efficiency operation requirement of COP≥2.5. Furthermore, the equipment is bulky and too expensive.

[0006] If the transcritical CO2 cycle can be coupled with the R1233zd(E) cycle in a geothermal energy and high-temperature heat pump system, it is expected to improve the overall energy efficiency of the system and meet the heating demand with large temperature differences. How to specifically combine the advantages of both to achieve a system solution that is high-temperature, efficient, and stable in operation remains a technical problem to be solved. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention employs a system architecture design that forces the energy flow to match the working fluid characteristics, achieving optimal load distribution. This invention provides a highly efficient geothermal source high-temperature environmentally friendly heat pump system with dual-system synergistic optimization. By coupling a transcritical CO2 cycle and an R1233zd(E) cycle, it efficiently extracts heat from the geothermal source, maintaining a system COP ≥ 2.5 while providing 20°C return water and outputting 120°C hot water.

[0008] The technical solution adopted in this invention is as follows: A high-efficiency geothermal source high-temperature environmentally friendly heat pump system with dual-system synergistic optimization includes a transcritical CO2 system and a refrigerant system. The transcritical CO2 system includes a CO2 compressor, an air cooler, a CO2 electronic expansion valve, and a CO2 evaporator connected in sequence to form a loop. The refrigerant in the refrigerant system is R1233zd(E), and the refrigerant system includes a refrigerant compressor, a condenser, a refrigerant electronic expansion valve, and a refrigerant evaporator connected in sequence to form a loop. The transcritical CO2 system is coupled to the refrigerant system through a heat exchanger. The CO2 flowing out of the cold side outlet of the CO2 evaporator absorbs heat in the heat exchanger and then enters the CO2 compressor. The refrigerant flowing out of the electronic expansion valve releases heat in the heat exchanger and then enters the cold side of the refrigerant evaporator. The geothermal source water is sequentially connected to the hot side of the refrigerant evaporator and the hot side of the CO2 evaporator to complete the secondary heat release process; the heat recovery working fluid is sequentially connected to the cold side of the gas cooler and the cold side of the condenser to complete the secondary heat absorption process.

[0009] The energy efficiency of both cycles is improved simultaneously through heat exchanger coupling. The setting of secondary heat absorption / release determines the system's load distribution principle and specific pinch point temperature, which is crucial for achieving the system's COP≥2.5 target.

[0010] Furthermore, the refrigerant system also includes a flash buffer tank. After being throttled by the electronic expansion valve, the refrigerant enters the flash buffer tank for gas-liquid separation. The liquid refrigerant enters the heat exchanger to exchange heat with the CO2, while the gaseous refrigerant directly enters the refrigerant compressor for compression. This configuration, in addition to conventionally optimizing compressor work and improving compression efficiency, can further enhance the efficiency of the downstream coupled heat exchanger, serving the dual-cycle synergy.

[0011] Furthermore, in the refrigerant system, the refrigerant compressor includes a primary compressor and a secondary compressor, and the refrigerant electronic expansion valve includes a primary electronic expansion valve and a secondary electronic expansion valve. The primary and secondary compressors are connected in series, and the outlet of the secondary compressor is connected to the hot-side inlet of the condenser. The gaseous refrigerant separated by the flash buffer tank is connected between the primary and secondary compressors. The primary electronic expansion valve is located between the hot-side outlet of the condenser and the inlet of the flash buffer tank, and the secondary electronic expansion valve is located between the hot-side outlet of the heat exchanger and the cold-side inlet of the refrigerant evaporator. This configuration is designed to adapt to the high-pressure ratio conditions imposed on the R1233zd(E) cycle by this dual-cycle synergistic system, and utilizes the flash buffer tank to transform the efficiency improvement of this stage into synergistic effect on the transcritical CO2 cycle, which is one of the keys to achieving overall high-efficiency and stable operation of the system.

[0012] Furthermore, the transcritical CO2 system also includes an economizer. The hot-side inlet of the economizer is connected to the hot-side outlet of the gas cooler, and the hot-side outlet of the economizer is connected to the CO2 electronic expansion valve. The cold-side inlet of the economizer is connected to the cold-side outlet of the CO2 evaporator, and the cold-side outlet of the economizer is connected to the cold-side inlet of the coupled heat exchanger. This configuration improves the energy efficiency of the CO2 cycle and contributes to the overall COP improvement of the system.

[0013] Preferably, under nominal operating conditions, the CO2 system provides 35% to 40% of the total system heating load; the nominal operating conditions are as follows: geothermal water inlet temperature T1 is 50°C, geothermal water return temperature T3 is 20°C, heated water inlet temperature T4 is 15°C, and heated water outlet temperature T6 is 120°C.

[0014] The above technical solution can achieve high-temperature hot water output at 120℃ while efficiently extracting heat from the geothermal source. When the return water reaches 20℃, the system COP can still be maintained at ≥2.5, which is impossible to achieve in existing units.

[0015] This application differs from traditional cascade or parallel units by creatively placing the transcritical CO2 cycle in the low-temperature heating zone and the R1233zd(E) cycle in the high-temperature heating zone at the heat sink end; and placing the R1233zd(E) cycle in the high-temperature heat release zone and the transcritical CO2 cycle in the low-temperature heat release zone at the heat source end. Furthermore, the two cycles are deeply integrated through a coupled heat exchanger, and a bidirectional counter-current series energy flow network enables both working fluids to operate in their respective optimal temperature zones and achieves efficient internal energy recovery. The transcritical CO2 cycle, due to its large temperature glide characteristics, has significant advantages in heating hot water in the medium- and low-temperature range. Under moderate pressure, its transcritical cycle can achieve a large temperature rise through an air cooler, and it has a high COP, while perfectly avoiding the pressure ratio and exhaust temperature problems encountered when pursuing extreme high temperatures. The R1233zd(E) cycle is better suited for heating in the medium and high temperature range of hot water supply. In this temperature range, its working pressure is moderate and the pressure ratio is relatively reasonable, which enables it to stably and efficiently carry out phase change condensation and heat release, avoiding operation at excessively low evaporation temperatures.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: 1) A dual-cycle deep collaborative heat pump system with "temperature zone matching - two-stage relay heat exchange" was constructed. It makes full use of the advantages of transcritical CO2 and R1233zd(E) loop in their respective temperature zones. The two forced flow paths form the physical basis of two-stage relay heat exchange, locking the working boundaries of the two loops and ensuring that the entire system operates in the high-efficiency temperature zone, thus achieving passive optimization at the architecture level.

[0017] 2) By coupling transcritical CO2 and R1233zd(E) cycles, the high heat capacity and low-temperature adaptability of CO2 in the transcritical state, as well as the environmentally friendly and high-temperature compression resistant properties of R1233zd(E), can be fully utilized to effectively reduce the system's footprint. Through reasonable setting of operating parameters and adjustment of load matching, using ambient temperature water as the heat recovery medium, it can output 120℃ high-temperature hot water and efficiently extract heat from the geothermal source. Even with a 20℃ return water condition, the system's COP can still be guaranteed to be ≥2.5.

[0018] 3) A two-stage compression and secondary throttling design is adopted for the R1233zd(E) loop to reduce the compression ratio of the loop; an 8-loop regenerator design (economizer + coupling heat exchanger to form an 8-loop) is adopted for the transcritical CO2 loop to further improve the system energy efficiency, so that it can still stably achieve COP≥2.5 under the large temperature difference heat source-heat sink condition of 120℃ / 20℃, reaching a high-efficiency operation level that is difficult to achieve by conventional single-cycle units.

[0019] 4) Based on the wide temperature range thermodynamic characteristics of the two working fluids, with the goal of maximizing the system COP, the CO2 system is determined to bear 35% to 40% of the total heating load, thereby achieving optimal operating parameters and precise load allocation, and significantly improving the overall energy efficiency of the system.

[0020] 5) The coupled heat exchanger recovers waste heat, solving the problem of secondary flashing that easily occurs in the R1233zd(E) liquid circuit; at the same time, the recovered heat is used to increase the superheat of CO2 gas before entering the compressor, avoiding the problem of liquid slugging in the gas; this system fundamentally solves the defects that exist when the two working fluids are run alone, achieving a synergistic effect of 1+1>2, and greatly improving the system's operational safety and energy efficiency.

[0021] 6) The unit uses low-GWP refrigerant R1233zd(E) and natural working fluid CO2, making the whole unit green and low-carbon, which meets the requirements of energy conservation and environmental protection development. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the system structure of this application.

[0023] Figure 2 This is a schematic diagram of the working fluid parameters during the operation of the system in this application.

[0024] The meanings of the attached figures numbered in the diagram are as follows: 11-CO2 compressor, 12-air cooler, 13-CO2 electronic expansion valve, 14-CO2 evaporator, 15-economizer; 21-Refrigerant compressor, 211-First stage compressor, 212-Second stage compressor, 22-Condenser, 23-Refrigerant electronic expansion valve, 231-First stage electronic expansion valve, 232-Second stage electronic expansion valve, 24-Refrigerant evaporator, 25-Flash buffer tank; 30 - Heat exchanger.

[0025] T1 - Geothermal water inlet temperature, T2 - Geothermal water precooling temperature, T3 - Geothermal water return temperature, T4 - Heated water inlet temperature, T5 - Heated water preheating temperature, T6 - Heated water outlet temperature. Detailed Implementation

[0026] Unless otherwise stated, the terms used herein have the meanings commonly understood by those skilled in the art.

[0027] The technical solution of the present invention will be described in more detail below with reference to embodiments: Example 1 See Figure 1 A high-efficiency geothermal source high-temperature environmentally friendly heat pump system with dual-system synergistic optimization, wherein the heat pump system recovers heat from geothermal source water and supplies it to the heat recovery working fluid, including a transcritical CO2 system and a refrigerant system.

[0028] The transcritical CO2 system includes a CO2 compressor 11, an air cooler 12, a CO2 electronic expansion valve 13, and a CO2 evaporator 14 connected in sequence to form a loop; the refrigerant in the refrigerant system is R1233zd(E), and the refrigerant system includes a refrigerant compressor 21, a condenser 22, a refrigerant electronic expansion valve 23, and a refrigerant evaporator 24 connected in sequence to form a loop.

[0029] The transcritical CO2 system is coupled to the refrigerant system through a heat exchanger 30. The CO2 flowing out of the cold side outlet of the CO2 evaporator 14 absorbs heat in the heat exchanger 30 and then enters the CO2 compressor 11. The refrigerant flowing out of the refrigerant electronic expansion valve 23 releases heat in the heat exchanger 30 and then enters the cold side of the refrigerant evaporator 24.

[0030] The geothermal source water is sequentially connected to the hot side of the refrigerant evaporator 24 and the hot side of the CO2 evaporator 14 to complete the secondary heat release process; the heat recovery working fluid is sequentially connected to the cold side of the gas cooler 12 and the cold side of the condenser 22 to complete the secondary heat absorption process.

[0031] The refrigerant system also includes a flash buffer tank 25, and the refrigerant compressor 21 includes a primary compressor 211 and a secondary compressor 212. The refrigerant electronic expansion valve 23 includes a primary electronic expansion valve 231 and a secondary electronic expansion valve 232. The primary compressor 211 and the secondary compressor 212 are connected in series. The outlet of the secondary compressor 212 is connected to the hot-side inlet of the condenser 22. The primary electronic expansion valve 231 is located between the hot-side outlet of the condenser 22 and the inlet of the flash buffer tank 25, and the secondary electronic expansion valve 232 is located between the hot-side outlet of the heat exchanger 30 and the cold-side inlet of the refrigerant evaporator 24. After being throttled by the primary electronic expansion valve 231, the refrigerant enters the flash buffer tank 25 for gas-liquid separation. The liquid refrigerant separated by the flash buffer tank 25 enters the heat exchanger 30 to exchange heat with CO2, then enters the secondary electronic expansion valve 232 and then enters the cold side of the refrigerant evaporator 24 to absorb heat, and then enters the primary compressor 211 for compression. The outlet of the separated gaseous refrigerant is connected between the primary compressor 211 and the secondary compressor 212. The gaseous refrigerant mixes with the refrigerant compressed by the primary compressor 211 and then enters the secondary compressor 212 together.

[0032] The transcritical CO2 system is also equipped with an economizer 15. The hot side inlet of the economizer 15 is connected to the hot side outlet of the gas cooler 12, and the hot side outlet of the economizer 15 is connected to the CO2 electronic expansion valve 13. The cold side inlet of the economizer 15 is connected to the cold side outlet of the CO2 evaporator 14, and the cold side outlet of the economizer 15 is connected to the cold side inlet of the heat exchanger 30.

[0033] See Figure 2 In this system, by setting the operating parameters reasonably and matching the load well, the heat from the geothermal source can be extracted efficiently. When the water supply is 120℃ and the return water is 20℃, the system COP can still be maintained at ≥2.5.

[0034] Taking room temperature water as the working fluid for heat recovery as an example, specifically: The system monitors the inlet water temperature T4, preheating temperature T5, and heating temperature T6 in real time on the heat sink side. The heating temperature T6 is controlled by adjusting the heat sink water flow rate, and the preheating temperature T5 is controlled by adjusting the speed of CO2 compressor 11. While maintaining T6 at 120℃, T5 is ensured to be close to 55℃. Based on the temperature difference between (T6 and T5) and (T5 and T4), the speeds of primary compressor 211 and secondary compressor 212 are synchronously adjusted to match the operation of CO2 compressor 11, ensuring that the (T6-T5) / (T5-T4) value is close to 1.6.

[0035] The system monitors geothermal water temperature T1, precooling temperature T2, and return water temperature T3 in real time on the heat source side. The precooling temperature T2 is controlled by adjusting the geothermal water flow rate. When T1 is 50℃, T2 is kept close to 30℃ to ensure proper temperature distribution of geothermal water between refrigerant evaporator 24 and CO2 evaporator 14.

[0036] The refrigerant system monitors the evaporation pressure P3, the first-stage discharge pressure P4, and the condensation pressure P5 in real time. If P4 is too high, the speed of the first-stage compressor is reduced. If P4 is too low, the speed of the first-stage compressor 211 is increased. At the same time, the opening of the first-stage electronic expansion valve 231 is adjusted to reduce the amount of gas supplied. The pressure ratio of the first-stage compressor 211 and the second-stage compressor 212 is appropriate, and they operate efficiently.

[0037] Example 2 Taking a 700kW high-temperature hot water heat pump as an example, the operation process of this system is as follows: Geothermal source water circuit: At a flow rate of 3.94 kg / s (m5), geothermal water at 50℃ (T1) enters the refrigerant evaporator 24, where it exchanges heat with low-temperature R1233zd(E) and is cooled to 30℃ (T2) to complete the initial pre-cooling. Then, it enters the CO2 evaporator 14 and exchanges heat with low-temperature CO2, where it is cooled to 20℃ (T3) to complete the secondary cooling, thus achieving full recovery of geothermal heat.

[0038] Hot water circuit: A 1.6 kg / s (m1) flow rate of 15℃ (T4) hot water enters the air cooler 12, where it exchanges heat with high-temperature CO2 and is heated to 55℃ (T5) to complete the initial preheating. Then it enters the condenser 22 and exchanges heat with high-temperature R1233zd(E) and is heated to 120℃ (T6) to complete the secondary heating, thus achieving high-temperature heat load output at the heat sink end.

[0039] CO2 circuit: CO2 with a flow rate of 0.97 kg / s (m2) is pressurized to a supercritical state of 9000 kPa (P1) by CO2 compressor 11 and enters air cooler 12 to release heat. After entering economizer 15, it further recovers the waste heat of CO2. After being throttled to 3430 kPa (P2) evaporation pressure by CO2 electronic expansion valve 13, it enters CO2 evaporator 14. It flows out of CO2 evaporator 14 after being superheated, and then enters heat exchanger 30 after being superheated twice by economizer 15 to complete the figure-eight cycle. After being superheated twice, it returns to CO2 compressor 11.

[0040] Refrigerant (R1233zd(E)) circuit: After two-stage compression, the R1233zd(E) with a flow rate of 2.51 kg / s (m3) from the second-stage compressor 212 has an exhaust pressure of 1760 kPa (P5) and an exhaust temperature of 130℃. It releases heat in the condenser 22. The gas separated by the flash buffer tank 25 enters the second-stage compressor 212. The liquid with a flow rate of 2.09 kg / s (m4) is initially cooled by the heat exchanger 30 and enters the second-stage electronic expansion valve 232, where it is throttled to 140 kPa (P3) and enters the refrigerant evaporator 24 to evaporate and absorb heat. The superheated vapor returns to the first-stage compressor 211 and is pressurized to 500 kPa (P4). It then mixes with the separated gas and enters the second-stage compressor 212.

[0041] The above system absorbs heat on the heat sink side: ; Air cooler 12 provides heating: ; Condenser 22 provides heating: ; in: h1 is the mass enthalpy of CO2 at the hot side outlet of air cooler 12; h2 is the mass enthalpy of CO2 at the hot side inlet of air cooler 12; h3 is the mass enthalpy of R1233zd(E) at the hot side outlet of condenser 22; h4 is the mass enthalpy of R1233zd(E) at the hot side inlet of condenser 22; The values ​​of h1 to h4 can be found in the property query software.

[0042] Compressor power consumption: ; ; ; in: k1 / k2 is the actual gas adiabatic index; η is the adiabatic efficiency; The values ​​of ρ2 to ρ4 can be found using property lookup software.

[0043] Calculate the unit's COP: .

[0044] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-efficiency, high-temperature, environmentally friendly heat pump system based on dual-system synergistic optimization of geothermal source, wherein the heat pump system recovers heat from geothermal source water and supplies it to the heat recovery working fluid, characterized in that, The system includes a transcritical CO2 system and a refrigerant system. The transcritical CO2 system includes a CO2 compressor (11), an air cooler (12), a CO2 electronic expansion valve (13), and a CO2 evaporator (14) connected in sequence to form a loop. The refrigerant in the refrigerant system is R1233zd(E), and the refrigerant system includes a refrigerant compressor (21), a condenser (22), a refrigerant electronic expansion valve (23), and a refrigerant evaporator (24) connected in sequence to form a loop. The transcritical CO2 system is coupled to the refrigerant system through a heat exchanger (30). The CO2 flowing out of the cold side outlet of the CO2 evaporator (14) absorbs heat through the heat exchanger (30) and then enters the CO2 compressor (11). The refrigerant flowing out of the refrigerant electronic expansion valve (23) releases heat in the heat exchanger (30) and then enters the cold side of the refrigerant evaporator (24). The geothermal source water is connected in sequence to the hot side of the refrigerant evaporator (24) and the hot side of the CO2 evaporator (14) to complete the secondary heat release process; the heat recovery working fluid is connected in sequence to the cold side of the gas cooler (12) and the cold side of the condenser (22) to complete the secondary heat absorption process.

2. The high-efficiency geothermal source high-temperature environmentally friendly heat pump system with dual-system synergistic optimization as described in claim 1, characterized in that, The refrigerant system is also equipped with a flash buffer tank (25). After the refrigerant is throttled by the refrigerant electronic expansion valve (23), it enters the flash buffer tank (25) for gas-liquid separation. The liquid refrigerant enters the heat exchanger (30) to exchange heat with the CO2, and the gaseous refrigerant directly enters the refrigerant compressor (21) to complete the compression.

3. The high-efficiency geothermal source high-temperature environmentally friendly heat pump system with dual-system synergistic optimization as described in claim 2, characterized in that, In the refrigerant system, the refrigerant compressor (21) includes a primary compressor (211) and a secondary compressor (212), and the refrigerant electronic expansion valve (23) includes a primary electronic expansion valve (231) and a secondary electronic expansion valve (232). The primary compressor (211) and the secondary compressor (212) are connected in series. The outlet of the secondary compressor (212) is connected to the hot side inlet of the condenser (22). The gaseous refrigerant separated by the flash buffer tank (25) is connected between the primary compressor (211) and the secondary compressor (212). The primary electronic expansion valve (231) is located between the hot side outlet of the condenser (22) and the inlet of the flash buffer tank (25). The secondary electronic expansion valve (232) is located between the hot side outlet of the heat exchanger (30) and the cold side inlet of the refrigerant evaporator (24).

4. The high-efficiency geothermal source high-temperature environmentally friendly heat pump system with dual-system synergistic optimization as described in claim 1, characterized in that, The transcritical CO2 system is also equipped with an economizer (15), the hot side inlet of which is connected to the hot side outlet of the gas cooler (12), and the hot side outlet of which is connected to the CO2 electronic expansion valve (13); the cold side inlet of which is connected to the cold side outlet of the CO2 evaporator (14), and the cold side outlet of which is connected to the cold side inlet of the heat exchanger (30).

5. The high-efficiency geothermal source high-temperature environmentally friendly heat pump system with dual-system synergistic optimization as described in claim 1, characterized in that, Under nominal operating conditions, the transcritical CO2 system provides 35% to 40% of the heating load of the heat pump system; the nominal operating conditions are as follows: geothermal inlet temperature (T1) is 50°C, geothermal return temperature (T3) is 20°C, heated water inlet temperature (T4) is 15°C, and heated water outlet temperature (T6) is 120°C.

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