CN111912131A - Multistage cooling carbon dioxide refrigeration air conditioner and refrigeration method - Google Patents

Multistage cooling carbon dioxide refrigeration air conditioner and refrigeration method Download PDF

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CN111912131A
CN111912131A CN202010549715.8A CN202010549715A CN111912131A CN 111912131 A CN111912131 A CN 111912131A CN 202010549715 A CN202010549715 A CN 202010549715A CN 111912131 A CN111912131 A CN 111912131A
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pressure
evaporator
valve
outlet
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CN111912131B (en
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曹锋
叶祖樑
王驿凯
宋昱龙
殷翔
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Xian Jiaotong University
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
    • F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
    • F25B9/008—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant the refrigerant being carbon dioxide
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/62—Control or safety arrangements characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values
    • F24F11/63—Electronic processing
    • F24F11/65—Electronic processing for selecting an operating mode
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
    • F24F11/72—Control systems characterised by their outputs; Constructional details thereof for controlling the supply of treated air, e.g. its pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
    • F24F11/80—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air
    • F24F11/83—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling the supply of heat-exchange fluids to heat-exchangers
    • F24F11/84—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling the supply of heat-exchange fluids to heat-exchangers using valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
    • F24F11/80—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air
    • F24F11/86—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling compressors within refrigeration or heat pump circuits
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B31/00—Compressor arrangements
    • F25B31/002—Lubrication
    • F25B31/004—Lubrication oil recirculating arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B49/00—Arrangement or mounting of control or safety devices
    • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B5/00—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity
    • F25B5/02—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity arranged in parallel

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Abstract

The invention discloses a multi-stage cooling carbon dioxide refrigeration air conditioner and a refrigeration method thereof.A high-pressure stage compressor outlet is connected with a gas cooler inlet, a gas cooler outlet is connected with a high-pressure expansion valve inlet, a high-pressure expansion valve outlet is connected with a flash tank inlet, a flash tank upper outlet is connected with a high-pressure stage compressor inlet, a flash tank lower liquid outlet is connected with a first stage evaporator inlet, a second stage evaporator inlet and a third stage evaporator inlet; the outlet of the third-stage evaporator is connected with the inlet of the low-pressure-stage compressor, the outlet of the low-pressure-stage compressor and the outlet of the second-stage evaporator are connected with the inlet of the medium-pressure-stage compressor together, and the outlet of the medium-pressure-stage compressor, the outlet of the first-stage evaporator and the outlet of the upper part of the flash tank are connected with the inlet of the high-pressure-stage compressor together. The system can adopt different operation modes according to actual operation conditions, is suitable for application occasions with large load change, and ensures the energy-saving effect of long-term operation by matching with capacity and pressure control.

Description

Multistage cooling carbon dioxide refrigeration air conditioner and refrigeration method
Technical Field
The invention belongs to the field of refrigeration air conditioners, and particularly relates to a multistage cooling carbon dioxide refrigeration air conditioner and a refrigeration method.
Background
In the field of refrigeration air conditioners and heat pumps, HFC refrigerants widely used at present have no destructive effect on the ozone layer, but have high global warming potential and certain influence on the aggravation of the greenhouse effect. Therefore, the refrigerant replacement work has been continuously conducted in recent years, and research on refrigerants having better environmental protection properties has been advanced. As a natural working medium, carbon dioxide (CO)2) Has excellent environment-friendly performance, the ozone layer destruction potential value ODP of the composite material is 0, and the global warming potential value GWP of the composite material is 1. Meanwhile, the carbon dioxide is safe, non-toxic, non-combustible and stable in chemical property. As refrigerant, CO2Large refrigerating capacity per unit volume, high heat conductivity, good heat transfer effect, low viscosity and small flow loss. Due to these advantages and properties of carbon dioxide, it has become an important choice for refrigerant replacement in recent years.
However, due to CO2When the external environment temperature on the heat sink side is higher, the cycle enters a transcritical state, namely the pressure of the high-pressure side of the system is higher than the critical pressure, and the pressure of the low-pressure side is lower than the critical pressure. At this time, unlike the conventional refrigerant, supercritical CO2Does not undergo phase change in the exothermic process, temperature andthe pressures are independent of each other. A large number of studies have shown that CO2The performance of the refrigeration system is limited by the ambient temperature, and when the ambient temperature is high, the CO is present2The performance of the system may be significantly inferior to that of conventional refrigerant systems. In addition, for some application occasions requiring the great reduction of the air temperature on the evaporation side, such as data center machine room air conditioner, airport ground air-conditioned vehicle and the like, common CO2High performance operation of the refrigeration system is also difficult to achieve.
Disclosure of Invention
The invention aims to provide a multistage cooling carbon dioxide refrigeration air conditioner and a refrigeration method, so as to solve the problem of the common CO mentioned above2When the temperature of the external environment is higher and the temperature of the air on the evaporation side needs to be greatly reduced, the performance of the refrigerating system is insufficient.
In order to achieve the purpose, the invention adopts the following technical scheme:
a multi-stage cooled carbon dioxide refrigeration air conditioner comprising: the system comprises a high-pressure stage compressor, a gas cooler, a high-pressure expansion valve, a flash tank, a first-stage evaporator, a second-stage evaporator, a third-stage evaporator, an intermediate-pressure stage compressor and a low-pressure stage compressor;
the outlet of the high-pressure stage compressor is connected with the inlet of the gas cooler, the outlet of the gas cooler is connected with the inlet of the high-pressure expansion valve, the outlet of the high-pressure expansion valve is connected with the inlet of the flash tank, the outlet of the upper part of the flash tank is connected with the inlet of the high-pressure stage compressor, and the liquid outlet of the lower part of the flash tank is connected with the inlet of the first-stage evaporator, the inlet of the second-stage evaporator and the inlet of the third-;
the outlet of the third-stage evaporator is connected with the inlet of the low-pressure-stage compressor, the outlet of the low-pressure-stage compressor and the outlet of the second-stage evaporator are connected with the inlet of the medium-pressure-stage compressor together, and the outlet of the medium-pressure-stage compressor, the outlet of the first-stage evaporator and the outlet of the upper part of the flash tank are connected with the inlet of the high-pressure-stage compressor together.
Furthermore, an outlet of the high-pressure stage compressor is connected with an inlet of the oil-gas separator, and a working medium outlet of the oil-gas separator is connected with an inlet of the gas cooler.
Further, a bottom lubricating oil outlet of the oil-gas separator is connected with an inlet of the oil reservoir;
an outlet of the oil reservoir is respectively connected with an oil return port of the high-pressure stage compressor, an oil return port of the medium-pressure stage compressor and an oil return port of the low-pressure stage compressor through a first oil path electromagnetic valve, a second oil path electromagnetic valve and a third oil path electromagnetic valve.
Further, an outlet at the upper part of the flash tank is connected with an inlet of the high-pressure stage compressor through a flash gas bypass valve; the liquid outlet at the lower part of the flash tank is respectively connected with the inlet of the first-stage evaporator, the inlet of the second-stage evaporator and the inlet of the third-stage evaporator through a first-stage throttle valve, a second-stage throttle valve and a third-stage throttle valve.
Further, a first electromagnetic valve is connected between the outlet of the first-stage evaporator and the outlet of the second-stage evaporator; and a second electromagnetic valve is connected between the outlet of the second-stage evaporator and the outlet of the third-stage evaporator.
Further, the environment side fan is arranged on the gas cooler, and the evaporation side fan is arranged at an air outlet of the cooling air duct; a first air valve and a second air valve are arranged in the evaporation side cooling air duct; the first air valve and the second air valve are controlled by the position limiter, are parallel to the air channel when opened and are vertical to the air channel when closed.
Further, the multistage cooling carbon dioxide refrigeration air conditioner comprises the following operation modes: a single-evaporator single-stage cooling mode, a double-evaporator double-stage cooling mode, a triple-evaporator double-stage cooling mode, and a triple-evaporator triple-stage cooling mode;
under the single-evaporator single-stage cooling mode, the high-pressure stage compressor operates, and the medium-pressure stage compressor and the low-pressure stage compressor are stopped; the first-stage throttle valve is opened, and the second-stage throttle valve and the third-stage throttle valve are closed; the first electromagnetic valve and the second electromagnetic valve are closed; the first air valve is closed, and the second air valve is opened;
under the single-stage cooling mode of the double-evaporator, the high-pressure stage compressor operates, and the medium-pressure stage compressor and the low-pressure stage compressor are stopped; the first-stage throttle valve and the second-stage throttle valve are opened, and the third-stage throttle valve is closed; the first electromagnetic valve is opened, and the second electromagnetic valve is closed; the first air valve and the second air valve are opened;
in a double-evaporator double-stage cooling mode, the high-pressure stage compressor and the medium-pressure stage compressor run, and the low-pressure stage compressor stops; the first-stage throttle valve and the second-stage throttle valve are opened, and the third-stage throttle valve is closed; the first electromagnetic valve and the second electromagnetic valve are closed; the first air valve and the second air valve are closed;
in a three-evaporator two-stage cooling mode, a high-pressure stage compressor and a low-pressure stage compressor run, and a medium-pressure stage compressor stops; the first-stage throttle valve, the second-stage throttle valve and the third-stage throttle valve are opened; the first electromagnetic valve is opened, and the second electromagnetic valve is closed; the first air valve and the second air valve are opened;
under the three-stage cooling mode of the three evaporators, the high-pressure stage compressor, the medium-pressure stage compressor and the low-pressure stage compressor operate; the first-stage throttle valve, the second-stage throttle valve and the third-stage throttle valve are opened; the first electromagnetic valve and the second electromagnetic valve are closed; the first and second dampers are closed.
Further, the working medium pressure at the outlet of the gas cooler is controlled by controlling the opening degree of the high-pressure expansion valve, and when the return air temperature of the cooling air channel reaches a set value, the control target value of the working medium pressure at the outlet of the gas cooler is calculated according to the external environment temperature, as follows:
Figure BDA0002542085110000031
wherein, PgcThe control target value of the outlet working medium pressure of the gas cooler is unit MPa; t isambIs the external ambient temperature in units;
controlling the pressure in the flash tank by controlling the opening of the flash gas bypass valve, wherein the pressure in the flash tank is calculated according to the evaporation temperature of the first stage evaporator, and the pressure is as follows:
Figure BDA0002542085110000041
wherein, PmFor controlling the pressure of working medium in flash tanksTarget value in MPa; t ise1The temperature is the working medium evaporation temperature of the first-stage evaporator in unit ℃.
Further, the gas cooler, the first-stage evaporator, the second-stage evaporator and the third-stage evaporator are fin tube type heat exchangers or micro-channel heat exchangers.
A refrigeration method of a multistage cooling carbon dioxide refrigeration air conditioner comprises the following steps:
when the air quantity at the evaporation side is less than 33% of the maximum value, if the air temperature at the evaporation side is reduced to be less than 12 ℃, adopting a single-stage cooling mode of a single evaporator; if the temperature drop of the air at the evaporation side is more than or equal to 12 ℃, adopting a double-evaporator double-stage cooling mode;
when the air quantity at the evaporation side is more than or equal to 33% of the maximum value and less than 66% of the maximum value, if the air temperature at the evaporation side is reduced to be less than 12 ℃, adopting a single-stage cooling mode of a single evaporator; if the temperature drop of the air at the evaporation side is more than or equal to 12 ℃ and less than 24 ℃, adopting a double-evaporator double-stage cooling mode; if the temperature drop of the air at the evaporation side is more than or equal to 24 ℃, adopting a three-evaporator three-level cooling mode;
when the air quantity at the evaporation side is greater than or equal to 66% of the maximum value, if the air temperature at the evaporation side is reduced to be less than 12 ℃, adopting a single-stage cooling mode of the double evaporators; if the temperature drop of the air at the evaporation side is more than or equal to 12 ℃ and less than 24 ℃, adopting a three-evaporator two-stage cooling mode; if the temperature drop of the air at the evaporation side is more than or equal to 24 ℃, a three-evaporator three-level cooling mode is adopted.
Furthermore, the switch of the oil-way electromagnetic valve is controlled by an oil level sensor arranged on each compressor so as to ensure that the oil level of the compressor is normal.
Furthermore, in the early stage of starting the system, when the return air temperature of the cooling air duct is higher than a set value, the pressure of the working medium at the outlet of the gas cooler is controlled at a higher value, so that the rapid cooling of large refrigerating capacity is realized.
Furthermore, the high-pressure compressor can adopt a plurality of start-stop controls and a single variable frequency control to realize capacity control according to application scenes. The medium-pressure stage compressor and the low-pressure stage compressor are controlled by frequency conversion. When the high-pressure stage compressor works, the evaporation temperature of the first stage evaporator is controlled; when the medium-pressure stage compressor works, the evaporation temperature of the second-stage evaporator is controlled; and when the low-pressure stage compressor works, the evaporation temperature of the third stage evaporator is controlled.
Furthermore, when the first-stage throttling valve, the second-stage throttling valve and the third-stage throttling valve work, the superheat degree of working media at the outlets of the first-stage evaporator, the second-stage evaporator and the third-stage evaporator is respectively used as a control target.
Further, the refrigeration air conditioner provided by the invention adopts carbon dioxide R744 as a refrigerant.
Compared with the prior art, the invention has the following beneficial effects:
the carbon dioxide refrigeration air conditioner provided by the invention adopts natural working media as refrigerants, the ozone layer damage potential value is 0, the global warming potential value is 1, and the environmental protection advantage is obvious. Compared with the refrigerant used by the existing refrigeration air-conditioning system, the refrigerant has obviously improved environmental protection performance and has important significance for the increasingly severe global warming problem.
By adopting the flash tank and the flash gas bypass valve, the two-phase working medium obtained by throttling through the high-pressure expansion valve is subjected to gas-liquid separation, so that the enthalpy value of the working medium entering the evaporator is reduced, the dryness is reduced, the liquid content is increased, the heat exchange effect and the refrigerating capacity of the evaporator are improved, and the performance of the system is improved. Through adopting the structure of multistage evaporimeter for the system can satisfy the evaporation side and need reduce the application demand under the wind temperature scene by a wide margin, improves the temperature matching of heat transfer between working medium and the air, reduces the irreversible loss among the heat transfer process, makes the system performance further improve.
The system can adopt different cooling modes according to the actual working condition, so that the carbon dioxide refrigeration air conditioner provided by the invention can be suitable for application occasions with large load change. According to the operating condition, the pressure of the working medium in the outlet of the gas cooler and the pressure of the working medium in the flash tank are controlled, and the capacity control of the compressor is matched, so that the system can operate in an optimized state when being stable, and the energy-saving effect of long-term operation is ensured. The system is different from a system adopting a traditional refrigerant, the temperature and the pressure of the supercritical high-pressure side of the carbon dioxide refrigerating system are mutually independent, and the rapid cooling of large refrigerating capacity can be realized by controlling the pressure of the working medium at the outlet of the gas cooler in the starting-up stage of the system.
Drawings
FIG. 1 is a schematic structural diagram of a multistage cooling carbon dioxide refrigeration air conditioner of the invention;
the reference numbers in the figures are: 1 high-pressure stage compressor, 2 oil-gas separator, 3 gas cooler, 4 high-pressure expansion valve, 5 flash tank, 6 flash gas bypass valve, 7 first-stage throttle valve, 8 second-stage throttle valve, 9 third-stage throttle valve, 10 first-stage evaporator, 11 second-stage evaporator, 12 third-stage evaporator, 13 medium-pressure stage compressor, 14 low-pressure stage compressor, 15 first electromagnetic valve, 16 second electromagnetic valve, 17 oil storage device, 18 first oil way electromagnetic valve, 19 second oil way electromagnetic valve, 20 third oil way electromagnetic valve, 21 environment side fan, 22 evaporation side fan, 23 first air valve, 24 second air valve.
Fig. 2 is a schematic flow diagram of a selected operating mode of a multi-stage cooled carbon dioxide refrigeration air conditioner of the present invention.
Detailed Description
Referring to fig. 1, the invention provides a multistage cooling carbon dioxide refrigeration air conditioner, which comprises a high-pressure stage compressor 1, an oil-gas separator 2, a gas cooler 3, a high-pressure expansion valve 4, a flash tank 5, a flash gas bypass valve 6, a first-stage throttle valve 7, a second-stage throttle valve 8, a third-stage throttle valve 9, a first-stage evaporator 10, a second-stage evaporator 11, a third-stage evaporator 12, an intermediate-pressure stage compressor 13, a low-pressure stage compressor 14, a first electromagnetic valve 15, a second electromagnetic valve 16, an oil reservoir 17, a first oil-way electromagnetic valve 18, a second oil-way electromagnetic valve 19, a second oil-way electromagnetic valve 20, an environment side fan 21, an evaporation side fan 22, a first air valve 23 and a second air valve 24.
The outlet of the high-pressure stage compressor 1 is connected with the inlet of the oil-gas separator 2, the working medium outlet of the oil-gas separator 2 is connected with the inlet of the gas cooler 3, the outlet of the gas cooler 3 is connected with the inlet of the high-pressure expansion valve 4, the outlet of the high-pressure expansion valve 4 is connected with the inlet of the flash tank 5, the outlet of the upper part of the flash tank 5 is connected with the inlet of the flash gas bypass valve 6, the liquid outlet of the lower part of the flash tank 5 is connected with the inlets of the first-stage throttle valve 7, the second-stage throttle valve 8 and the third-stage throttle valve 9, the outlet of the first-stage throttle valve 7 is connected with the inlet of the first-stage evaporator 10, the outlet of the second-stage throttle valve 8 is connected with the inlet of the second-stage evaporator 11, the outlet of the third-stage throttle valve 9 is connected with the inlet of the third-stage evaporator 12, the outlet of the intermediate-pressure stage compressor 13, the outlet of the first stage evaporator 10 and the outlet of the flash gas bypass valve 6 are connected with the inlet of the high-pressure stage compressor 1. The first solenoid valve 15 is connected to the outlets of the first stage evaporator 10 and the second stage evaporator 11, and the second solenoid valve 16 is connected to the outlets of the second stage evaporator 11 and the third stage evaporator 12.
The bottom lubricating oil outlet of the oil-gas separator 2 is connected with the inlet of an oil reservoir 17, the outlet of the oil reservoir 17 is connected with the inlets of a first oil way electromagnetic valve 18, a second oil way electromagnetic valve 19 and a third oil way electromagnetic valve 20, and the outlets of the first oil way electromagnetic valve 18, the second oil way electromagnetic valve 19 and the third oil way electromagnetic valve 20 are respectively connected with the oil return ports of the compressor 1, the medium-pressure connecting compressor 13 and the low-pressure connecting compressor 14 in a high-pressure mode. The opening and closing of the first oil solenoid valve 18, the second oil solenoid valve 19 and the third oil solenoid valve 20 are controlled by oil level sensors installed on the respective compressors to ensure that the oil levels of the compressors are normal.
The environment-side fan 21 is mounted on the gas cooler 3, and the evaporation-side fan 22 is mounted on the air outlet of the cooling air duct. The return air temperature of the cooling air duct is controlled by controlling the evaporation side fan 22 to change the air volume of the cooling air duct. A first air valve 23 and a second air valve 24 are installed in the evaporation side cooling air duct. The position of the air valve is controlled by the limiter, the air valve is parallel to the air channel when the air valve is opened, and the air valve is vertical to the air channel when the air valve is closed.
Referring to fig. 2, the refrigeration method of the system is selected according to the operation condition:
when the air quantity at the evaporation side is less than 33% of the maximum value, if the air temperature at the evaporation side is reduced to be less than 12 ℃, adopting a single-stage cooling mode of a single evaporator; if the temperature drop of the air at the evaporation side is more than or equal to 12 ℃, a double-evaporator double-stage cooling mode is adopted.
When the air quantity at the evaporation side is more than or equal to 33% of the maximum value and less than 66% of the maximum value, if the air temperature at the evaporation side is reduced to be less than 12 ℃, adopting a single-stage cooling mode of a single evaporator; if the temperature drop of the air at the evaporation side is more than or equal to 12 ℃ and less than 24 ℃, adopting a double-evaporator double-stage cooling mode; if the temperature drop of the air at the evaporation side is more than or equal to 24 ℃, a three-evaporator three-level cooling mode is adopted.
When the air quantity at the evaporation side is greater than or equal to 66% of the maximum value, if the air temperature at the evaporation side is reduced to be less than 12 ℃, adopting a single-stage cooling mode of the double evaporators; if the temperature drop of the air at the evaporation side is more than or equal to 12 ℃ and less than 24 ℃, adopting a three-evaporator two-stage cooling mode; if the temperature drop of the air at the evaporation side is more than or equal to 24 ℃, a three-evaporator three-level cooling mode is adopted.
Referring to table 1, the control of the actuators in each operating mode is as follows:
TABLE 1 executive component control table for multi-stage cooling carbon dioxide refrigeration air conditioner in different operation modes
Figure BDA0002542085110000081
In the single-evaporator and single-stage cooling mode, the high-pressure stage compressor 1 operates, and the medium-pressure stage compressor 13 and the low-pressure stage compressor 14 are stopped; the first stage throttle valve 7 is opened, and the second stage throttle valve 8 and the third stage throttle valve 9 are closed; the first solenoid valve 15 and the second solenoid valve 16 are closed; the first damper 23 is closed and the second damper 24 is opened. In this mode, only the first stage evaporator 10 provides the cooling effect.
In the double-evaporator single-stage cooling mode, the high-pressure stage compressor 1 is operated, and the medium-pressure stage compressor 13 and the low-pressure stage compressor 14 are stopped; the first-stage throttle valve 7 and the second-stage throttle valve 8 are opened, and the third-stage throttle valve 9 is closed; the first solenoid valve 15 is open and the second solenoid valve 16 is closed; the first and second dampers 23 and 24 are opened. In this mode, the first stage evaporator 10 and the second stage evaporator 11 provide a cooling effect at the same evaporation temperature.
In the double-evaporator double-stage cooling mode, the high-pressure stage compressor 1 and the medium-pressure stage compressor 13 operate, and the low-pressure stage compressor 14 stops; the first-stage throttle valve 7 and the second-stage throttle valve 8 are opened, and the third-stage throttle valve 9 is closed; the first solenoid valve 15 and the second solenoid valve 16 are closed; the first damper 23 and the second damper 24 are closed. In this mode, the first stage evaporator 10 and the second stage evaporator 11 provide cooling at two different evaporating temperatures.
In the three-evaporator two-stage cooling mode, the high-pressure stage compressor 1 and the low-pressure stage compressor 14 operate, and the medium-pressure stage compressor 13 stops; the first stage throttle valve 7, the second stage throttle valve 8 and the third stage throttle valve 9 are opened; the first solenoid valve 15 is open and the second solenoid valve 16 is closed; the first and second dampers 23 and 24 are opened. In this mode, the first stage evaporator 10 and the second stage evaporator 11 provide cooling effects at the same evaporation temperature and the third stage evaporator 12 at different evaporation temperatures.
In the three-evaporator three-stage cooling mode, the high-pressure stage compressor 1, the medium-pressure stage compressor 13 and the low-pressure stage compressor 14 operate; the first stage throttle valve 7, the second stage throttle valve 8 and the third stage throttle valve 9 are opened; the first solenoid valve 15 and the second solenoid valve 16 are closed; the first damper 23 and the second damper 24 are closed. In this mode, the first stage evaporator 10, the second stage evaporator 11, and the third stage evaporator 12 provide cooling effects at different evaporation temperatures, respectively.
In order to optimize the system performance, the working medium pressure at the outlet of the gas cooler 3 is controlled by controlling the opening degree of the high-pressure expansion valve 4, and when the return air temperature of the cooling air channel reaches a set value, the control target value of the working medium pressure at the outlet of the gas cooler 3 is calculated according to the external environment temperature, as follows:
Figure BDA0002542085110000091
wherein, PgcIs a control target value of the outlet working medium pressure of the gas cooler 3, and has unit MPa; t isambIs the ambient temperature in units of ℃.
The pressure in the flash tank 5 is controlled by controlling the opening of the flash gas bypass valve 6, the pressure in the flash tank 5 being calculated from the evaporation temperature of the first stage evaporator 10 as follows:
Figure BDA0002542085110000092
wherein, PmThe target value of the working medium pressure control in the flash tank 5 is unit MPa; t ise1The working medium evaporation temperature of the first stage evaporator 10 is unit ℃.
And in the earlier stage of starting the system, when the return air temperature of the cooling air duct is higher than a set value, the pressure of the working medium at the outlet of the gas cooler 3 is controlled at a higher value so as to realize the rapid cooling of large refrigerating output.
According to the application scene, the high-pressure compressor 1 can adopt a plurality of start-stop controls and a single variable frequency control to realize capacity control. The medium-pressure stage compressor 13 and the low-pressure stage compressor 14 adopt frequency conversion control. When the high-pressure stage compressor 1 works, the evaporation temperature of the first stage evaporator 10 is controlled; when the medium-pressure stage compressor 13 works, the evaporation temperature of the second-stage evaporator 11 is controlled; the low pressure stage compressor 14 operates to control the evaporating temperature of the third stage evaporator 12. When the first-stage throttling valve 7, the second-stage throttling valve 8 and the third-stage throttling valve 9 work, the superheat degree of working media at the outlets of the first-stage evaporator 10, the second-stage evaporator 11 and the third-stage evaporator 12 is respectively taken as a control target. The gas cooler 3, the first-stage evaporator 10, the second-stage evaporator 11 and the third-stage evaporator 12 are fin tube type heat exchangers or micro-channel heat exchangers.
The refrigeration air conditioner adopts carbon dioxide R744 as a refrigerant.
Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and all changes that come within the scope of the invention or that are equivalent to the scope of the invention are intended to be embraced therein.

Claims (10)

1. The utility model provides a multistage cooling carbon dioxide refrigeration air conditioner which characterized in that includes: the system comprises a high-pressure stage compressor (1), a gas cooler (3), a high-pressure expansion valve (4), a flash tank (5), a first-stage evaporator (10), a second-stage evaporator (11), a third-stage evaporator (12), an intermediate-pressure stage compressor (13) and a low-pressure stage compressor (14);
an outlet of the high-pressure stage compressor (1) is connected with an inlet of the gas cooler (3), an outlet of the gas cooler (3) is connected with an inlet of the high-pressure expansion valve (4), an outlet of the high-pressure expansion valve (4) is connected with an inlet of the flash tank (5), an outlet of the upper part of the flash tank (5) is connected with an inlet of the high-pressure stage compressor (1), and a liquid outlet of the lower part of the flash tank (5) is connected with an inlet of the first-stage evaporator (10), an inlet of the second-stage evaporator (11) and an inlet of the third-stage evaporator (12);
the outlet of the third-stage evaporator (12) is connected with the inlet of the low-pressure-stage compressor (14), the outlet of the low-pressure-stage compressor (14) and the outlet of the second-stage evaporator (11) are jointly connected with the inlet of the medium-pressure-stage compressor (13), and the outlet of the medium-pressure-stage compressor (13), the outlet of the first-stage evaporator (10) and the outlet of the upper part of the flash tank (5) are jointly connected with the inlet of the high-pressure-stage compressor (1).
2. The multistage cooling carbon dioxide refrigeration air conditioner as claimed in claim 1, characterized in that the outlet of the high-pressure stage compressor (1) is connected with the inlet of the oil-gas separator (2), and the working medium outlet of the oil-gas separator (2) is connected with the inlet of the gas cooler (3).
3. The multistage cooling carbon dioxide refrigeration air conditioner as claimed in claim 2, characterized in that the bottom lubricating oil outlet of the oil-gas separator (2) is connected with the inlet of the oil reservoir (17);
an outlet of the oil reservoir (17) is respectively connected with an oil return port of the high-pressure stage compressor (1), an oil return port of the medium-pressure stage compressor (13) and an oil return port of the low-pressure stage compressor (14) through a first oil path electromagnetic valve (18), a second oil path electromagnetic valve (19) and a third oil path electromagnetic valve (20).
4. The multi-stage cooling carbon dioxide refrigeration air conditioner as claimed in claim 1, characterized in that the outlet of the upper part of the flash tank (5) is connected with the inlet of the high-pressure stage compressor (1) through the flash gas bypass valve (6); the liquid outlet at the lower part of the flash tank (5) is respectively connected with the inlet of a first-stage evaporator (10), the inlet of a second-stage evaporator (11) and the inlet of a third-stage evaporator (12) through a first-stage throttling valve (7), a second-stage throttling valve (8) and a third-stage throttling valve (9).
5. A multi-stage cooling carbon dioxide refrigeration air conditioner according to claim 4, characterized in that a first electromagnetic valve (15) is connected between the outlet of the first stage evaporator (10) and the outlet of the second stage evaporator (11); a second electromagnetic valve (16) is connected between the outlet of the second-stage evaporator (11) and the outlet of the third-stage evaporator (12).
6. The multi-stage cooling carbon dioxide refrigeration air conditioner as claimed in claim 5, characterized in that the environment side fan (21) is installed on the gas cooler (3), and the evaporation side fan (22) is installed at the air outlet of the cooling air duct; a first air valve (23) and a second air valve (24) are arranged in the evaporation side cooling air channel; the first air valve (23) and the second air valve (24) are controlled by the position limiter to be parallel to the air channel when opened and to be vertical to the air channel when closed.
7. The multi-stage cooled carbon dioxide refrigeration air conditioner as claimed in claim 6, characterized in that it comprises the following modes of operation: a single-evaporator single-stage cooling mode, a double-evaporator double-stage cooling mode, a triple-evaporator double-stage cooling mode, and a triple-evaporator triple-stage cooling mode;
under the single-evaporator single-stage cooling mode, the high-pressure stage compressor (1) operates, and the medium-pressure stage compressor (13) and the low-pressure stage compressor (14) are stopped; the first-stage throttle valve (7) is opened, and the second-stage throttle valve (8) and the third-stage throttle valve (9) are closed; the first solenoid valve (15) and the second solenoid valve (16) are closed; the first air valve (23) is closed, and the second air valve (24) is opened;
under the double-evaporator single-stage cooling mode, the high-pressure stage compressor (1) operates, and the medium-pressure stage compressor (13) and the low-pressure stage compressor (14) are stopped; a first-stage throttle valve (7) and a second-stage throttle valve (8) are opened, and a third-stage throttle valve (9) is closed; the first electromagnetic valve (15) is opened, and the second electromagnetic valve (16) is closed; the first air valve (23) and the second air valve (24) are opened;
in a double-evaporator double-stage cooling mode, the high-pressure stage compressor (1) and the medium-pressure stage compressor (13) operate, and the low-pressure stage compressor (14) stops; a first-stage throttle valve (7) and a second-stage throttle valve (8) are opened, and a third-stage throttle valve (9) is closed; the first solenoid valve (15) and the second solenoid valve (16) are closed; the first air valve (23) and the second air valve (24) are closed;
in a three-evaporator two-stage cooling mode, a high-pressure stage compressor (1) and a low-pressure stage compressor (14) operate, and a medium-pressure stage compressor (13) stops; a first-stage throttle valve (7), a second-stage throttle valve (8) and a third-stage throttle valve (9) are opened; the first electromagnetic valve (15) is opened, and the second electromagnetic valve (16) is closed; the first air valve (23) and the second air valve (24) are opened;
in the three-evaporator three-stage cooling mode, a high-pressure stage compressor (1), a medium-pressure stage compressor (13) and a low-pressure stage compressor (14) operate; a first-stage throttle valve (7), a second-stage throttle valve (8) and a third-stage throttle valve (9) are opened; the first solenoid valve (15) and the second solenoid valve (16) are closed; the first air valve (23) and the second air valve (24) are closed.
8. The multistage cooling carbon dioxide refrigeration air conditioner as claimed in claim 7, characterized in that the opening degree of the high-pressure expansion valve (4) is controlled to control the working medium pressure at the outlet of the gas cooler (3), when the return air temperature of the cooling air duct reaches a set value, the control target value of the working medium pressure at the outlet of the gas cooler (3) is calculated according to the outside environment temperature as follows:
Figure FDA0002542085100000031
wherein, PgcIs a control target value of the outlet working medium pressure of the gas cooler (3) in unit MPa; t isambIs the external ambient temperature in units;
controlling the pressure in the flash tank (5) by controlling the opening of the flash gas bypass valve (6), the pressure in the flash tank (5) being calculated from the evaporation temperature of the first stage evaporator (10) as follows:
Figure FDA0002542085100000032
wherein, PmThe target value of the working medium pressure control in the flash tank (5) is in MPa; t ise1Is the working medium evaporation temperature of the first-stage evaporator (10) in unit ℃.
9. The multi-stage cooling carbon dioxide refrigeration air conditioner as claimed in claim 1, characterized in that the gas cooler (3), the first stage evaporator (10), the second stage evaporator (11) and the third stage evaporator (12) are fin tube heat exchangers or microchannel heat exchangers.
10. A refrigeration method of a multistage cooling carbon dioxide refrigeration air conditioner is characterized in that the multistage cooling carbon dioxide refrigeration air conditioner based on claim 7 comprises the following steps:
when the air quantity at the evaporation side is less than 33% of the maximum value, if the air temperature at the evaporation side is reduced to be less than 12 ℃, adopting a single-stage cooling mode of a single evaporator; if the temperature drop of the air at the evaporation side is more than or equal to 12 ℃, adopting a double-evaporator double-stage cooling mode;
when the air quantity at the evaporation side is more than or equal to 33% of the maximum value and less than 66% of the maximum value, if the air temperature at the evaporation side is reduced to be less than 12 ℃, adopting a single-stage cooling mode of a single evaporator; if the temperature drop of the air at the evaporation side is more than or equal to 12 ℃ and less than 24 ℃, adopting a double-evaporator double-stage cooling mode; if the temperature drop of the air at the evaporation side is more than or equal to 24 ℃, adopting a three-evaporator three-level cooling mode;
when the air quantity at the evaporation side is greater than or equal to 66% of the maximum value, if the air temperature at the evaporation side is reduced to be less than 12 ℃, adopting a single-stage cooling mode of the double evaporators; if the temperature drop of the air at the evaporation side is more than or equal to 12 ℃ and less than 24 ℃, adopting a three-evaporator two-stage cooling mode;
if the temperature drop of the air at the evaporation side is more than or equal to 24 ℃, a three-evaporator three-level cooling mode is adopted.
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