Cascade type low-temperature air source heat pump unit and control method thereof

Abstract

The invention provides a cascade type low-temperature air source heat pump unit which is composed of a low-temperature loop and a high-temperature loop, the low-temperature loop and the high-temperature loop exchange heat through an intermediate heat exchanger, the heating function and the refrigerating function can be achieved at the same time, the defrosting effect is greatly improved, and long-term reliable operation of a device is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of heat pump air conditioners, and in particular to a cascade low-temperature air source heat pump unit and a control method thereof. Background Art

[0002] Conventional air source heat pump devices use a single-stage compression method, and their heating capacity and energy efficiency ratio decrease as the outdoor temperature drops and the water temperature in the water tank rises. Generally speaking, the lower the ambient temperature, the greater the demand for heat. When the ambient temperature drops, the heating capacity of a single-stage compression heat pump decreases seriously, the compressor exhaust temperature increases, and the heat pump device cannot operate normally. It cannot even start normally when the ambient temperature is as low as -20°C. For a single-stage compression heat pump, increasing the hot water temperature will lead to adverse effects such as increased condensing pressure, increased compression ratio, reduced compressor volumetric efficiency, reduced heating capacity, and reduced heating performance coefficient. Excessively high condensing temperature will also lead to problems such as excessively high exhaust temperature, excessively high exhaust pressure, and failure of lubricating oil, which seriously affect the safe and normal operation of the unit.

[0003] At present, in order to increase the temperature difference between the condenser and the evaporator, a multi-stage compression refrigeration cycle and a cascade cycle with an intercooler are used. The advantages of the cascade air source heat pump cycle are: the air source heat pump that combines a single-stage cycle with a cascade cycle can still achieve the requirements of a small compression ratio, low exhaust temperature, and high heating capacity when the outdoor temperature is very low. Under low temperature conditions, the energy utilization efficiency of the cascade cycle operation is higher than that of the single-stage operation.

[0004] However, the existing cascade air source units have the following defects: (1) The units only have heating function and cannot realize cooling function; (2) During heating and defrosting in winter, the fin coil is defrosted by switching between the low-temperature and high-temperature systems through a four-way valve, which has the disadvantages of poor defrosting effect and poor stability of the heating system, and the reliability of long-term operation is difficult to guarantee. Summary of the invention

[0005] The object of the present invention is to provide a cascade low-temperature air source heat pump unit and a control method thereof which has both heating and cooling functions, greatly improves the defrosting effect, and ensures long-term reliable operation.

[0006] In order to achieve the above object, the present invention is implemented by the following technical solutions: A cascade low-temperature air source heat pump unit, composed of a low-temperature loop and a high-temperature loop, the low-temperature loop and the high-temperature loop exchange heat through an intermediate heat exchanger, the low-temperature loop also includes a low-temperature compressor, a four-way valve, a first one-way valve, a second one-way valve, a third one-way valve, a liquid storage device, an economizer, a first electronic expansion valve, a second electronic expansion valve, a fourth electronic expansion valve, a fin coil, and a low-temperature gas-liquid separator, the low-temperature compressor exhaust port is connected to the four-way valve D port, the four-way valve C port is connected to the fin coil gas side interface, the four-way valve S port is connected to the low-temperature gas-liquid separator inlet, the four-way valve The valve E port is connected to the intermediate heat exchanger A port and the third one-way valve outlet respectively, the fin coil liquid side interface is connected to the second one-way valve inlet and the first electronic expansion valve respectively, the liquid reservoir inlet is connected to the first one-way valve outlet and the second one-way valve outlet respectively, the liquid reservoir outlet is connected to the economizer A port, the economizer B port is connected to the first electronic expansion valve, the second electronic expansion valve, and the fourth electronic expansion valve respectively, the economizer C port is connected to the low-temperature compressor air supply port, the economizer D port is connected to the second electronic expansion valve, and the low-temperature gas-liquid separator outlet is connected to the low-temperature compressor suction port; The high-temperature loop also includes a high-temperature compressor, a water-side heat exchanger, a third electronic expansion valve, and a high-temperature gas-liquid separator. The high-temperature compressor exhaust port is connected to the water-side heat exchanger A port, the high-temperature compressor suction port is connected to the high-temperature gas-liquid separator outlet, the water-side heat exchanger B port is connected to the third electronic expansion valve, and the water-side heat exchanger CD channel is used as a refrigerant channel; The intermediate heat exchanger A port is connected to the four-way valve E port and the third one-way valve outlet respectively, the intermediate heat exchanger B port is connected to the first one-way valve inlet, the intermediate heat exchanger C port is connected to the high-temperature gas-liquid separator inlet, and the intermediate heat exchanger D port is connected to the third electronic expansion valve.

[0007] Furthermore, the interior of the fluorine side of the water-side heat exchanger is a plurality of independent heat exchange spaces, which are respectively connected to the low-temperature loop and the high-temperature loop.

[0008] Furthermore, the interior of the intermediate heat exchanger is a plurality of independent heat exchange spaces, which are respectively connected to the low-temperature loop and the high-temperature loop.

[0009] Furthermore, the intermediate heat exchanger may be a plate heat exchanger, a shell and tube heat exchanger, or a shell and tube heat exchanger.

[0010] Furthermore, the low temperature stage compressor or the high temperature stage compressor may be a scroll compressor, a screw compressor or a centrifugal compressor.

[0011] A control method for a cascade low-temperature air source heat pump unit, when the unit is in heating mode, the high-temperature and high-pressure gas at the outlet of the low-temperature compressor is guided into the A port of the intermediate heat exchanger through a four-way valve, and condenses into a high-pressure medium-temperature liquid refrigerant after heat exchange with the high-temperature refrigerant in the intermediate heat exchanger and flows out from the B port, passes through the first one-way valve and the liquid storage device in sequence and flows into the economizer to increase the degree of supercooling, and then is throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant through the first electronic expansion valve and enters the fin coil, evaporates from the air to absorb heat to become a low-temperature and low-pressure gaseous refrigerant, and then flows through the four-way valve and the low-temperature gas-liquid separator to return to the suction port of the low-temperature compressor; at the same time, the high-temperature and high-pressure gaseous refrigerant discharged from the high-temperature compressor enters the water-side heat exchanger, discharges heat to the hot water on the user side, and then condenses into a high-pressure liquid refrigerant, and then is throttled into the intermediate heat exchanger through the third electronic expansion valve, evaporates from the low-temperature refrigerant to absorb heat to become a low-temperature and low-pressure gaseous refrigerant, and then flows through the high-temperature gas-liquid separator to return to the suction port of the high-temperature compressor, and the cycle repeats; When the unit is in the refrigeration mode, the high-temperature and high-pressure gas at the outlet of the low-temperature compressor is guided into the fin coil through the four-way valve to release heat to the atmosphere and then condense into a high-pressure medium-temperature liquid refrigerant, and then passes through the second one-way valve and the liquid storage device in turn and flows into the economizer to increase the degree of supercooling, and then is throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant through the fourth electronic expansion valve, and then enters the water-side heat exchanger to absorb heat from the user-side chilled water and evaporate into a low-temperature and low-pressure gaseous refrigerant, and finally flows through the third one-way valve, the four-way valve, and the low-temperature gas-liquid separator in turn and returns to the compressor suction port; When the unit is in defrost mode, the high-temperature and high-pressure gas at the outlet of the low-temperature compressor is guided into the fin coil through the four-way valve for hot gas defrosting. After the refrigerant is condensed into a high-pressure liquid, it passes through the second one-way valve, the liquid receiver, the economizer, and then enters the water-side heat exchanger through the fourth electronic expansion valve throttling. It evaporates and absorbs heat from the user's hot water to become a low-temperature and low-pressure gaseous refrigerant, and finally flows through the third one-way valve, the four-way valve, and the low-temperature gas-liquid separator in sequence and returns to the compressor suction port.

[0012] Furthermore, when the unit is operating in heating mode or cooling mode, part of the high-pressure liquid refrigerant at the main outlet B of the economizer is diverted to the second electronic expansion valve to be throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant, and then absorbs heat from the main liquid refrigerant in the economizer to evaporate into a medium-pressure gas refrigerant and then returns to the low-temperature compressor air supply port.

[0013] Compared with the prior art, the present invention has the following advantages: The present invention discloses a cascade low-temperature air source heat pump unit and a control method thereof, which have both heating and cooling functions. The low-temperature refrigeration system absorbs heat from hot water during defrosting, greatly improving the defrosting effect and ensuring long-term reliable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1It is a schematic diagram of the control principle of the present invention.

[0015] Figure numerals: 1. low-temperature compressor; 2. four-way valve; 3. intermediate heat exchanger; 4. first one-way valve; 5. second one-way valve; 6. liquid storage tank; 7. economizer; 8. first electronic expansion valve; 9. fourth electronic expansion valve; 10. fin coil; 11. low-temperature gas-liquid separator; 12. second electronic expansion valve; 13. high-temperature compressor; 14. water-side heat exchanger; 15. third electronic expansion valve; 16. high-temperature gas-liquid separator; 17. third one-way valve. DETAILED DESCRIPTION

[0016] The embodiments of the present invention are described in further detail below in conjunction with the accompanying drawings.

[0017] The specific embodiments of the present invention are described in detail as follows. Figure 1 .

[0018] (I) When the unit is operating in heating mode The low-temperature compressor 1, the high-temperature compressor 14, the first electronic expansion valve 8, the second electronic expansion valve 12, and the third electronic expansion valve 15 are working; the fourth electronic expansion valve 9 is not working; at the same time, the D port of the four-way valve 2 is connected to the E port, and the C port is connected to the S port.

[0019] The high-temperature and high-pressure gas at the outlet of the low-temperature compressor 1 is guided into the A port of the intermediate heat exchanger 3 through the four-way valve 2, and condenses into a high-pressure medium-temperature liquid refrigerant after heat exchange with the high-temperature refrigerant in the intermediate heat exchanger 3 and flows out from the B port, and then passes through the first one-way valve 4 and the liquid storage tank 6 in sequence and flows through the economizer 7 to increase the supercooling degree, and then is throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant through the first electronic expansion valve 8, enters the fin coil 10 to evaporate and absorb heat from the air to become a low-temperature and low-pressure gaseous refrigerant, and finally flows through the four-way valve 2 and the low-temperature gas-liquid separator 11 and returns to the air intake port of the low-temperature compressor 1; a small part of the high-pressure liquid refrigerant at the main outlet B of the economizer 7 is diverted to the second electronic expansion valve 12 to be throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant, and then absorbs heat from the main liquid refrigerant in the economizer 7 to evaporate into a medium-pressure gaseous refrigerant and then returns to the air supply port of the low-temperature compressor 1.

[0020] At the same time, the high-temperature and high-pressure gaseous refrigerant discharged from the high-temperature compressor 13 enters the water-side heat exchanger 14, discharges heat to the hot water on the user side, and then condenses into liquid refrigerant, and then enters the intermediate heat exchanger 3 through the throttling of the third electronic expansion valve 15, evaporates and absorbs heat from the low-temperature refrigerant to become low-temperature and low-pressure gaseous refrigerant, and finally flows through the high-temperature gas-liquid separator 16 and returns to the air intake of the high-temperature compressor 13, repeating the cycle.

[0021] (II) When the unit is operating in cooling mode The low-temperature machine compressor 1, the second electronic expansion valve 12, and the fourth electronic expansion valve 9 are working; the high-temperature compressor 13, the first electronic expansion valve 8, and the third electronic expansion valve 15 are not working; at the same time, the D port of the four-way valve 2 is connected to the C port, and the E port is connected to the S port.

[0022] The high-temperature and high-pressure gas discharged from the compressor 1 is guided into the fin coil 10 through the four-way valve 2 to release heat to the atmosphere and then condense into a high-pressure medium-temperature liquid refrigerant, and then passes through the second one-way valve 5 and the liquid storage tank 6 in sequence and flows through the economizer 7 to increase the supercooling degree, and then is throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant through the fourth electronic expansion valve 9, and then enters the water-side heat exchanger 14 to absorb heat from the user-side chilled water and evaporate into a low-temperature and low-pressure gaseous refrigerant, and finally flows through the third one-way valve 17, the four-way valve 2, and the low-temperature gas-liquid separator 11 in sequence to return to the suction port of the low-temperature compressor 1; a small part of the high-pressure liquid refrigerant at the main outlet B of the economizer 7 is diverted to the second electronic expansion valve 12, and after being throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant, it absorbs heat from the main liquid refrigerant in the economizer 7 and evaporates into a medium-pressure gaseous refrigerant, and finally returns to the air supply port of the low-temperature compressor 1.

[0023] When the unit is in defrost mode The low-temperature machine compressor 1 and the fourth electronic expansion valve 9 are working; the second electronic expansion valve 12, the high-temperature compressor 13, the first electronic expansion valve 8, and the third electronic expansion valve 15 are not working; at the same time, the D port of the four-way valve 2 is connected to the C port, and the E port is connected to the S port.

[0024] The high-temperature and high-pressure gas discharged from the low-temperature compressor 1 is guided into the fin coil 10 through the four-way valve 2 for hot gas defrosting. After the refrigerant is condensed into a high-pressure liquid, it passes through the second one-way valve 5, the liquid storage tank 6, the economizer 7 in sequence, and then enters the water-side heat exchanger 14 through the fourth electronic expansion valve 9 throttling, evaporates from the user's hot water and absorbs heat to become a low-temperature and low-pressure gaseous refrigerant, and finally flows through the third one-way valve 17, the four-way valve 2, and the low-temperature gas-liquid separator 11 in sequence to return to the intake port of the low-temperature compressor 1.

[0025] The above description is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the concept of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A cascade low-temperature air source heat pump unit, consisting of a low-temperature loop and a high-temperature loop, the low-temperature loop and the high-temperature loop exchange heat through an intermediate heat exchanger, characterized in that: The low-temperature loop also includes a low-temperature compressor, a four-way valve, a first one-way valve, a second one-way valve, a third one-way valve, a liquid reservoir, an economizer, a first electronic expansion valve, a second electronic expansion valve, a fourth electronic expansion valve, a fin coil, and a low-temperature gas-liquid separator. The low-temperature compressor exhaust port is connected to the four-way valve D port, the four-way valve C port is connected to the fin coil gas side interface, the four-way valve S port is connected to the low-temperature gas-liquid separator inlet, the four-way valve E port is respectively connected to the intermediate heat exchanger A port and the third one-way valve outlet, the fin coil liquid side interface is respectively connected to the second one-way valve inlet and the first electronic expansion valve, the liquid reservoir inlet is respectively connected to the first one-way valve outlet and the second one-way valve outlet, the liquid reservoir outlet is connected to the economizer A port, the economizer B port is respectively connected to the first electronic expansion valve, the second electronic expansion valve, and the fourth electronic expansion valve, the economizer C port is connected to the low-temperature compressor air supply port, the economizer D port is connected to the second electronic expansion valve, and the low-temperature gas-liquid separator outlet is connected to the low-temperature compressor suction port; The high-temperature loop also includes a high-temperature compressor, a water-side heat exchanger, a third electronic expansion valve, and a high-temperature gas-liquid separator. The high-temperature compressor exhaust port is connected to the water-side heat exchanger A port, the high-temperature compressor suction port is connected to the high-temperature gas-liquid separator outlet, the water-side heat exchanger B port is connected to the third electronic expansion valve, and the water-side heat exchanger CD channel is used as a refrigerant channel; The intermediate heat exchanger A port is connected to the four-way valve E port and the third one-way valve outlet respectively, the intermediate heat exchanger B port is connected to the first one-way valve inlet, the intermediate heat exchanger C port is connected to the high-temperature gas-liquid separator inlet, and the intermediate heat exchanger D port is connected to the third electronic expansion valve.

2. A cascade low-temperature air source heat pump unit according to claim 1, characterized in that: The fluorine side of the water-side heat exchanger is internally provided with a plurality of independent heat exchange spaces, which are respectively connected to the low-temperature loop and the high-temperature loop.

3. The cascade low-temperature air source heat pump unit according to claim 1, characterized in that: The interior of the intermediate heat exchanger is a plurality of independent heat exchange spaces, which are respectively connected to the low-temperature loop and the high-temperature loop.

4. The cascade low-temperature air source heat pump unit according to claim 3, characterized in that: The intermediate heat exchanger may be a plate heat exchanger, a sleeve heat exchanger or a shell and tube heat exchanger.

5. The cascade low-temperature air source heat pump unit according to claim 1, characterized in that: The low temperature stage compressor or the high temperature stage compressor may be a scroll compressor, a screw compressor or a centrifugal compressor.

6. A control method for a cascade low-temperature air source heat pump unit, characterized in that: When the unit is in heating mode, the high-temperature and high-pressure gas at the outlet of the low-temperature compressor is guided into the A port of the intermediate heat exchanger through the four-way valve, and condenses into high-pressure medium-temperature liquid refrigerant after heat exchange with the high-temperature refrigerant in the intermediate heat exchanger and flows out from the B port, passes through the first one-way valve and the liquid storage device in turn and flows into the economizer to increase the degree of subcooling, and then is throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant through the first electronic expansion valve and enters the fin coil, evaporates from the air and absorbs heat to become a low-temperature and low-pressure gas refrigerant, and then flows through the four-way valve and the low-temperature gas-liquid separator and returns to the suction port of the low-temperature compressor; At the same time, the high-temperature and high-pressure gaseous refrigerant discharged from the high-temperature compressor enters the water-side heat exchanger, discharges heat to the hot water on the user side, condenses into high-pressure liquid refrigerant, and then enters the intermediate heat exchanger through the throttling of the third electronic expansion valve, evaporates from the low-temperature refrigerant, absorbs heat to become low-temperature and low-pressure gaseous refrigerant, and then flows through the high-temperature gas-liquid separator and returns to the high-temperature compressor suction port, repeating the cycle; When the unit is in the refrigeration mode, the high-temperature and high-pressure gas at the outlet of the low-temperature compressor is guided into the fin coil through the four-way valve to release heat to the atmosphere and then condense into a high-pressure medium-temperature liquid refrigerant, and then passes through the second one-way valve and the liquid storage device in turn and flows into the economizer to increase the degree of supercooling, and then is throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant through the fourth electronic expansion valve, and then enters the water-side heat exchanger to absorb heat from the user-side chilled water and evaporate into a low-temperature and low-pressure gaseous refrigerant, and finally flows through the third one-way valve, the four-way valve, and the low-temperature gas-liquid separator in turn and returns to the compressor suction port; When the unit is in defrost mode, the high-temperature and high-pressure gas at the outlet of the low-temperature compressor is guided into the fin coil through the four-way valve for hot gas defrosting. After the refrigerant is condensed into a high-pressure liquid, it passes through the second one-way valve, the liquid receiver, the economizer, and then enters the water-side heat exchanger through the fourth electronic expansion valve throttling. It evaporates and absorbs heat from the user's hot water to become a low-temperature and low-pressure gaseous refrigerant, and finally flows through the third one-way valve, the four-way valve, and the low-temperature gas-liquid separator in sequence and returns to the compressor suction port.

7. The control method of a cascade low-temperature air source heat pump unit according to claim 6, characterized in that: When the unit is operating in heating mode or cooling mode, part of the high-pressure liquid refrigerant at the main outlet B of the economizer is diverted to the second electronic expansion valve to be throttled into low-temperature and low-pressure gas-liquid two-phase refrigerant, and then absorbs heat from the main liquid refrigerant in the economizer to evaporate into medium-pressure gas refrigerant and then return to the low-temperature compressor air supply port.

Images