CN111336710B - CO (carbon monoxide)2Refrigerant charge control system and method for optimal cycle performance - Google Patents

CO (carbon monoxide)2Refrigerant charge control system and method for optimal cycle performance Download PDF

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CN111336710B
CN111336710B CN202010121244.0A CN202010121244A CN111336710B CN 111336710 B CN111336710 B CN 111336710B CN 202010121244 A CN202010121244 A CN 202010121244A CN 111336710 B CN111336710 B CN 111336710B
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electromagnetic valve
pressure
temperature
outlet
refrigerant
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CN111336710A (en
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曹锋
王静
方健珉
殷翔
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Xian Jiaotong University
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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
    • F25B13/00—Compression machines, plants or systems, with reversible cycle
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating [HVAC] devices
    • B60H1/00357—Air-conditioning arrangements specially adapted for particular vehicles
    • B60H1/00385—Air-conditioning arrangements specially adapted for particular vehicles for vehicles having an electrical drive, e.g. hybrid or fuel cell
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating [HVAC] devices
    • B60H1/00642—Control systems or circuits; Control members or indication devices for heating, cooling or ventilating devices
    • B60H1/00814—Control systems or circuits characterised by their output, for controlling particular components of the heating, cooling or ventilating installation
    • B60H1/00878—Control systems or circuits characterised by their output, for controlling particular components of the heating, cooling or ventilating installation the components being temperature regulating devices
    • B60H1/00885—Controlling the flow of heating or cooling liquid, e.g. valves or pumps
    • 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
    • F25B40/00—Subcoolers, desuperheaters or superheaters
    • F25B40/06—Superheaters
    • 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
    • F25B45/00—Arrangements for charging or discharging refrigerant
    • 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
    • F25B2345/00—Details for charging or discharging refrigerants; Service stations therefor
    • F25B2345/003—Control issues for charging or collecting refrigerant to or from a cycle
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/80—Technologies aiming to reduce greenhouse gasses emissions common to all road transportation technologies
    • Y02T10/88—Optimized components or subsystems, e.g. lighting, actively controlled glasses

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Air Conditioning Control Device (AREA)

Abstract

The invention discloses a CO2The refrigerant charge amount control system with optimal cycle performance comprises a compressor, an auxiliary heat exchanger, a main heat exchanger, a two-way throttle valve, an outdoor heat exchanger, a heat regenerator, 2 liquid accumulators, a three-way valve, a four-way reversing valve, 2 electromagnetic valves and two dryness meters; the invention firstly provides a control method of the optimal charging amount of the air conditioning system after the operation condition of the air conditioning system changes, adopts negative feedback PI control logic, and combines the judgment criterion of the invention to accurately achieve the aim of always controlling the charging amount of the system to be the optimal value; the invention specifically provides a change rule of the system charge amount in the change of different operation conditions and a specific and accurate control method after the change. The invention has wide working condition change range covered by the adjustment control of the system charge, and can be suitable for the charge adjustment under any working condition change, so that the system always operates under the optimal performance, the unnecessary power consumption is reduced, and the energy is saved.

Description

CO (carbon monoxide)2Refrigerant charge control system and method for optimal cycle performance
Technical Field
The invention belongs to the field of transcritical carbon dioxide systems, and particularly relates to a system and a method for adjusting and controlling the filling amount of a new energy automobile air conditioning system under multi-environment working conditions.
Background
The new energy automobile overcomes the problem of fossil fuel dependence of fuel oil automobiles, is diversified in energy utilization, quiet and environment-friendly, and represents the development trend of future automobiles. The new energy automobile is different from a fuel automobile, no engine waste heat can be used for heating air in a compartment at low ambient temperature, so that the pure new energy automobile basically adopts PTC electric heating for heating in winter at present, however, the vehicle-mounted battery of the pure new energy automobile has limited electric storage capacity, and the driving range of the automobile is influenced by adopting electric heating for heating. Compared with electric heating, the heat pump type air conditioning system has the characteristics of high efficiency and energy conservation, and is more beneficial to the development of pure and new energy automobiles. The most widely used refrigerant of the conventional automobile air conditioning system is R134a, which has poor environmental protection performance, has been gradually eliminated,the automobile is in the driving process, and the environment is changeable, meets weather such as serious traffic jam condition, sleet and heavy fog, according to the road regulation, needs to reduce the speed of traveling as required, and the gas cooler amount of wind reduces, and it is higher to the vehicle air conditioner heating performance requirement, consequently to traditional working medium, also is a very big examination, is difficult to satisfy actual requirement. And CO2The refrigerant has obvious advantages as a natural refrigerant. Transcritical CO2The heat pump cycle has unique advantages, the temperature of the heat release process is high, and a considerable temperature slip (about 80-100 ℃) exists. The research shows that: under the environment working condition of 20 ℃ below zero, the transcritical carbon dioxide heat pump air conditioner still has considerable heating performance.
Because the automobile has changeable environment in the driving process, the automobile air conditioner is generally provided with a full fresh air mode and a full return air mode, when the automobile runs for a long time, the amount of fresh air in a carriage is reduced, and passengers are easy to feel uncomfortable, so that the full fresh air mode and the full return air mode are adopted, the inlet air temperature of the two working modes is greatly different, and the requirement of the system on the filling amount is greatly different; the environment temperature in summer is high, the air conditioner needs to realize the function of refrigeration, but the environment temperature span is large, the day and night temperature difference in one day can exceed 10 ℃ at most, the optimal charging quantity of the automobile air conditioner is greatly influenced by the environment temperature, the optimal charging quantity of the heat pump air conditioning system at the environment temperature of 30 ℃ in the evening or at night is completely inconsistent with the charging quantity required under the high-temperature environment working condition of 40 ℃ at noon, so that the refrigeration performance of the air conditioner is good and bad in one day, and the air conditioner cannot always run under the optimal performance; the ambient temperature is too low in winter, the automobile air conditioner needs to realize the heating function, the difference of the ambient working conditions of the heating working mode and the refrigerating working mode is huge, the requirement of the charging amount of the air conditioning system is also very different, and the same charging amount cannot simultaneously meet the requirement of the system on the optimal performance in the refrigerating working mode and the heating working mode.
Disclosure of Invention
The invention aims to provide CO2Refrigerant charge amount control system and method with optimal cycle performance, so as to adjust the charge amount of the system in time under different driving conditions to realizeThe goal of optimum comfort of the passenger compartment is reached under any condition.
In order to achieve the purpose, the invention adopts the following technical scheme:
CO (carbon monoxide)2A refrigerant charge control system with optimal cycle performance, comprising: the system comprises a compressor, an auxiliary heat exchanger, a four-way reversing valve, an outdoor heat exchanger, a heat regenerator, a two-way throttle valve, a main heat exchanger, a liquid storage device, a three-way valve, a liquid storage device, a first electromagnetic valve, a second electromagnetic valve and a plurality of temperature and pressure sensors;
the outlet of the compressor is connected with the inlet of the auxiliary heat exchanger, the outlet of the auxiliary heat exchanger is connected with the b interface of the four-way reversing valve, the a interface of the four-way reversing valve is connected with the inlet of the outdoor heat exchanger, the outlet of the outdoor heat exchanger is connected with the high-pressure side inlet of the heat regenerator, the high-pressure side outlet is connected with one end of the two-way throttle valve, the other end of the two-way throttle valve is connected with the inlet of the main heat exchanger, the outlet of the four-way reversing valve is connected with the c interface of the reservoir, the d interface is connected with the inlet of the reservoir, the outlet of the reservoir is connected with the a interface of the three-way valve, the b interface of the three-way valve and the low-pressure outlet of the heat regenerator.
Further, the liquid storage device is used for adjusting the stability of the operation of the system; the liquid storage device is used for adjusting the filling amount of the system; when the charging amount of the system is insufficient, the second electromagnetic valve is opened, the first electromagnetic valve is closed, the refrigerant stored in the liquid accumulator is sucked into the compressor and enters the system circulation to supplement the charging amount of the refrigerant; when the refrigerant in the system is overcharged, the first electromagnetic valve is opened, the second electromagnetic valve is closed, and the high-pressure refrigerant in the compressor is extruded and discharged into the liquid accumulator, so that the purpose of reducing the charging amount of the system is achieved.
Further, in the refrigeration mode, the dryness of the outlet of the evaporator is used as a standard for judging whether the system charging amount is proper or not; at the moment, the main heat exchanger is an evaporator, and the outdoor heat exchanger is a gas cooler; at this time, the dryness x of the outlet of the evaporatorinThe method comprises the following steps: the temperature of the high-pressure inlet of the regenerator,Pressure and enthalpy are respectively T1，P1And h1(ii) a The temperature, pressure and enthalpy of the high-pressure outlet of the heat regenerator are respectively T2，P2And h2(ii) a The temperature, pressure and enthalpy of the low-pressure inlet (i.e. the evaporator outlet) of the regenerator are respectively T3，P3And h3(ii) a The temperature, pressure and enthalpy of the low-pressure outlet of the heat regenerator are respectively T4，P4And h4. Then there are:
hx＝f(Tx,Px)，x＝1,2,4
h3＝h4-(h1-h2)
xin＝x3＝f(P3,h3)
in the heating mode, the superheat degree of the outlet of the evaporator is a standard for judging whether the system charge amount is appropriate. The outdoor heat exchanger (4) is an evaporator. The superheat degree of the outlet of the evaporator at this time is obtained by: the measured values of the temperature and the pressure at the outlet of the evaporator are respectively Tout-eva，Pout-evaThe saturation temperature at the evaporator outlet is:
Tsat＝f(Pout-eva)
the superheat degree at the outlet of the evaporator is:
ΔTsup＝Tout-eva-Tsat。
further, the method for judging whether the charge amount is appropriate is as follows:
under any working condition, the transcritical carbon dioxide circulation system has the optimal exhaust pressure value Popt, so that the performance of the system is optimal; the compressor all is equipped with safe exhaust temperature upper limit value: a maximum exhaust temperature value Tmax; in the refrigeration working mode, the evaporation temperature standard T of the systemc-evaThe air outlet temperature T required by the manufacturer or the clientairStandard correlation:
Tc-eva＝Tenv-5
in the heating working mode, the evaporation temperature standard T of the systemh-evaAnd ambient temperature TenvAnd (3) correlation:
Th-eva＝Tenv-12
the actual value of the measured evaporation temperature is the measured value of the post-valve temperature sensor: t isaft(ii) a The measured temperature values at the outlet of the evaporator are respectively Tin-evaAnd Tout-eva；
When the transcritical carbon dioxide system is in a refrigeration working mode, the main heat exchanger is an evaporator, the outdoor heat exchanger is a gas cooler, and the measured value of the outlet of the evaporator is Tin-eva(ii) a After the start-up operation is stable, the exhaust pressure of the opening control system of the bidirectional throttle valve is adjusted to be an optimal exhaust pressure value; if the opening of the two-way throttle valve is continuously reduced, the exhaust temperature T is taken asdisThe maximum discharge temperature value of the compressor, i.e. T, is reacheddis＝TmaxAt all times, the exhaust pressure does not reach the optimum exhaust pressure value, i.e. Pdis≤PoptThe suction pressure and the evaporation pressure are always too low, and the evaporation temperature is lower than a set value, namely Taft≤Tc-evaThe dryness of the refrigerant at the outlet of the main heat exchanger is 1, namely xinAt 1, the outlet of the refrigerant is severely superheated, i.e. Tin-eva≥TaftIf the system is in the low-charging state, the system is in the low-charging state;
when the system is started and stably operates, the exhaust pressure of the system is controlled to be the optimal exhaust pressure value, namely P, by adjusting the opening of the two-way throttle valvedis＝PoptAt the moment, the rotation speed of the compressor and the opening of the two-way throttle valve are continuously adjusted, the suction pressure and the pressure behind the valve are always overhigh, and the evaporation temperature is higher than a set value, namely Taft＞Tc-evaThe dryness x at the refrigerant outlet of the evaporator cannot meet the air outlet requirementinBelow 0.9, the refrigerant is severely two-phase, indicating that the system is being charged too much.
Further, when the system is in a heating working mode, the main heat exchanger and the auxiliary heat exchanger are gas coolers, the outdoor heat exchanger is an evaporator, and the measured value of the outlet of the evaporator is Tout-eva(ii) a After the start-up operation is stable, the exhaust pressure of the opening control system of the bidirectional throttle valve is adjusted to be an optimal exhaust pressure value; if the opening of the two-way throttle valve is continuously reduced, the exhaust gas is exhaustedTemperature TdisThe maximum discharge temperature value of the compressor, i.e. T, is reacheddis＝TmaxAt all times, the exhaust pressure does not reach the optimum exhaust pressure value, i.e. Pdis≤PoptThe suction pressure and the evaporation pressure are always too low, and the evaporation temperature is lower than a set value, namely Taft≤Th-evaDegree of superheat Δ T of outlet refrigerant of outdoor heat exchangersupThe temperature of the refrigerant outlet is not less than 2, and the serious overheating of the refrigerant outlet indicates that the charging quantity of the system is insufficient; when the system is started and stably operates, the exhaust pressure of the system is controlled to be the optimal exhaust pressure value, namely P, by adjusting the opening of the two-way throttle valvedis＝PoptAt the moment, the rotation speed of the compressor and the opening of the two-way throttle valve are continuously adjusted, the suction pressure and the pressure behind the valve are always overhigh, and the evaporation temperature is higher than a set value, namely Taft＞Th-evaThe air outlet requirement cannot be met, and the superheat degree delta T of the refrigerant outlet of the evaporatorsupIf 0, i.e., refrigerant two-phase, the system charge is excessive.
Furthermore, the control logic of the charging amount of the opening and closing control system of the first electromagnetic valve and the second electromagnetic valve adopts negative feedback PI control, the charging amount of the system is the input amount of the PI control, and the opening time length of the first electromagnetic valve and the second electromagnetic valve is the output amount; the opening degrees of the two electromagnetic valves are alpha, and the maximum opening degrees of the two electromagnetic valves are alpha when the two electromagnetic valves are fully openedmaxThe opening and closing control of the electromagnetic valve adopts a current pulse form; when the charging quantity of the system is adjusted, after a control signal is input, the electromagnetic valve plate is opened, and t0The electromagnetic valve is automatically closed after s, automatically opened after t's, and t0s, automatically closing, and repeating the steps in such a way, wherein each Ts is one regulation period; the control equation of the pulse signal is as follows:
Figure BDA0002392996390000051
wherein: t ═ T0+ t', k is a positive integer;
t s when the electromagnetic valve is opened, the system carries out an automatic flow regulation process, and t's when the electromagnetic valve is closed is a process of dynamic stabilization of the system again; if the system is stable and the filling amount is appropriate, a signal for closing the electromagnetic valve is input, the electromagnetic valve enters a closed state all the time, and the adjusting process is finished.
Further, the time interval of the pulse signal is set in relation to the pressure difference between the air suction end and the air discharge end of the compressor and the liquid storage device:
when the system is short of charge, the second electromagnetic valve (12) needs to be opened, and the pressure difference is the suction pressure P of the compressorsucWith pressure P in the reservoiraccDifference, i.e. Δ P ═ Psuc-Pacc(ii) a When the charging quantity of the system is excessive, the first electromagnetic valve (11) needs to be opened, and the pressure difference at the moment is the discharge pressure P of the compressordisWith pressure P in the reservoiraccDifference, i.e. Δ P ═ Pdis-Pacc(ii) a The time interval t is inversely proportional to the differential pressure Δ P, the refrigerant is mainly supplemented by the differential pressure of the refrigerant, and the larger the differential pressure is, the larger the amount of refrigerant supplement per unit time is, therefore, in order to prevent the refrigerant from being supplemented excessively, the opening time interval of the electromagnetic valve is determined by the following formula:
t＝k/ΔP
wherein: t is the opening time interval of the electromagnetic valve, and the unit of second(s);
Δ P-pressure differential in units of megapascals (MPa);
the inverse proportionality coefficient k of the time interval t and the differential pressure delta P is 10-30.
Further, the change in the demand for the charge amount occurs when the operating condition of the transcritical carbon dioxide changes:
1) conversion of internal and external circulation:
when the system is in refrigeration mode, when being turned into the extrinsic cycle by the inner loop, because the air inlet temperature of evaporimeter risees, the demand to the refrigerating output is bigger, and is also bigger to the demand of filling volume promptly, turns into the extrinsic cycle after, and the system is serious to be short of filling, carries out filling volume to the system this moment and supplements: the second electromagnetic valve is opened, and the first electromagnetic valve is closed; when the system is in the mode of heating operation, because the air inlet temperature of indoor gas cooler reduces suddenly, and the demand to the heating capacity of system increases suddenly, also increases suddenly to the demand of the charge volume of refrigerant promptly, so turn into the extrinsic cycle after, the system charge volume appears seriously not enough, carries out the charge volume to the system this moment and supplements: the second electromagnetic valve is opened, and the first electromagnetic valve is closed;
when the system is in refrigeration mode, when being turned into the inner loop by the extrinsic cycle, because the inlet air temperature of evaporimeter reduces, so the demand to the refrigerating output is littleer, and is also littleer to the demand of filling volume promptly, so turn into the inner loop after, the system filling volume appears seriously excessively, need reduce the filling volume of system this moment: the second electromagnetic valve is closed, and the first electromagnetic valve is opened; when the system is in the heating mode of operation, because the inlet air temperature of indoor gas cooler rises suddenly, the demand to the heating capacity of system reduces suddenly, and the demand to the charge volume of refrigerant also reduces suddenly promptly, so turn into the extrinsic cycle after, the system charge volume appears seriously excessive, needs to reduce the charge volume of system this moment: the second electromagnetic valve is closed, and the first electromagnetic valve is opened;
2) change of ambient temperature
A temperature sensor is arranged on the system, and the environmental temperature value T of the last working operation is collected and recordedpreAnd the ambient temperature T at the current start-upnouWhen the change value of the environmental temperature is T, T is the change value of the environmental temperaturenou-TpreWhen the system is in a working mode of refrigerating in summer or heating in winter, and the ambient temperature is increased from low temperature to high ambient temperature, if delta T is less than 3, the filling amount of the system does not need to be changed, and the system is kept in the original state to start working; if the delta T is larger than or equal to 3, reducing the filling amount: the second electromagnetic valve is closed, and the first electromagnetic valve is opened;
when the ambient temperature is increased from low temperature to high ambient temperature, if delta T is greater than-3, the charging quantity of the system does not need to be changed, and the system is maintained in the original state to start working. If the delta T is less than or equal to-3, reducing the filling amount: the first electromagnetic valve is closed, and the second electromagnetic valve is opened;
3) conversion of operating modes
When the system is switched from the refrigeration mode to the heating mode, the demand of the system for the charging quantity is lower, the second electromagnetic valve is closed, the first electromagnetic valve is opened, and the charging quantity in the system is reduced; when the system is switched from the heating mode to the cooling mode, the demand of the system for the charging amount is higher, the second electromagnetic valve is opened, the first electromagnetic valve is closed, and the charging amount in the system is increased.
Compared with the prior art, the invention has the following beneficial effects:
present vehicle air conditioner system, adopt fixed filling volume, in case fill the back promptly, no matter the car moves under what kind of operating mode, the filling volume of system can't all adjust, lead to vehicle air conditioner under many operating modes, can't reach optimum performance, it is more that the air conditioner not only consumes power to appear, and cooling volume/heating volume is too big when cooling volume/heating volume is not enough often, lead to the temperature in the carriage often too high often and too low, the passenger feels neglected to cool and neglected to heat, can't all satisfy best comfort level under all driving conditions.
Furthermore, the invention provides a specific control method of the system on the basis of providing the system with adjustable filling amount, and the timely and accurate filling amount adjustment can be realized according to the control logic and the method of the invention.
Furthermore, the invention provides a specific implementation mode of system charge amount adjustment in the actual driving working condition, and has clear and clear guiding significance in the actual application.
Drawings
FIG. 1 shows a CO according to the invention2The structural schematic diagram of the refrigerant charge amount control system with optimal cycle performance;
FIG. 2 shows a CO according to the invention2A logic control diagram for a refrigerant charge control method with optimal cycle performance.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Referring to FIG. 1, the present invention provides a CO2The refrigerant charge amount control system with optimal cycle performance comprises the following components: the system comprises a compressor 1, an auxiliary heat exchanger 2, a four-way reversing valve 3, an outdoor heat exchanger 4, a heat regenerator 5, a two-way throttle valve 6, a main heat exchanger 7, a liquid accumulator 8, a three-way valve 9, a liquid accumulator 10, an electromagnetic valve 11, an electromagnetic valve 12 and temperature and pressure sensors.
The outlet of the compressor 1 is connected with the inlet of the auxiliary heat exchanger 2, the outlet of the auxiliary heat exchanger 2 is connected with the interface b of the four-way reversing valve 3, the interface a of the four-way reversing valve 3 is connected with the inlet of the outdoor heat exchanger 4, the outlet of the outdoor heat exchanger 4 is connected with the high-pressure side inlet of the heat regenerator 5, the high-pressure side outlet is connected with one end of the two-way throttle valve 6, the other end of the two-way throttle valve 6 is connected with the inlet of the main heat exchanger 7, the outlet is connected with the interface c of the four-way reversing valve 3, the interface d is connected with the inlet of the liquid accumulator 8, the outlet of the liquid accumulator 8 is connected with the interface a of the three-way valve 9, the interface b of the three-way valve 9 and the low-pressure outlet of the heat regenerator 5 are converged and are connected with the air suction port of the compressor 1, the other end of the electromagnetic valve 12 is connected to the suction port of the compressor.
The invention provides CO2A refrigerant charge control method with optimal cycle performance, comprising: the reservoir 8 is accessed inside the system for adjusting the stability of the system operation. The reservoir 10 is used to adjust the filling amount of the system, and further improve the working condition adaptation range of the system. When the charging amount of the system is seriously insufficient, the electromagnetic valve 12 is opened, the electromagnetic valve 11 is closed, the refrigerant stored in the liquid accumulator 10 is sucked into the compressor and enters the system circulation to supplement the charging amount of the refrigerant. When the refrigerant in the system is overcharged, the electromagnetic valve 11 is opened, the electromagnetic valve 12 is closed, and the high-pressure refrigerant in the compressor is extruded and discharged into the liquid accumulator 10, so that the purpose of reducing the charging amount of the system is achieved.
The invention provides CO2A refrigerant charge control method with optimal cycle performance, comprising: in the cooling mode, the dryness of the outlet of the evaporator is used as a standard for whether the system charge is proper or not. In this case, the main heat exchanger 7 is an evaporator, and the outdoor heat exchanger 4 is a gas cooler. At this time, the dryness x of the outlet of the evaporatorinThe method comprises the following steps: the temperature, pressure and enthalpy of the high-pressure inlet of the regenerator are respectively T1，P1And h1(ii) a The temperature, pressure and enthalpy of the high-pressure outlet of the heat regenerator are respectively T2，P2And h2(ii) a Low pressure inlet of regeneratorThe temperature, pressure and enthalpy of the port (i.e. evaporator outlet) are each T3，P3And h3(ii) a The temperature, pressure and enthalpy of the low-pressure outlet of the heat regenerator are respectively T4，P4And h4. Then there are:
hx＝f(Tx,Px)，x＝1,2,4
h3＝h4-(h1-h2)
xin＝x3＝f(P3,h3)
in the heating mode, the superheat degree of the outlet of the evaporator is a standard for judging whether the system charge amount is appropriate. The outdoor heat exchanger 4 is an evaporator in this case. The superheat degree of the outlet of the evaporator at this time is obtained by: the measured values of the temperature and the pressure at the outlet of the evaporator are respectively Tout-eva，Pout-evaThe saturation temperature at the evaporator outlet is:
Tsat＝f(Pout-eva)
the superheat degree at the outlet of the evaporator is:
ΔTsup＝Tout-eva-Tsat
the method for judging whether the filling amount is proper or not in the invention comprises the following steps:
first, there are some standard values for transcritical carbon dioxide systems: the transcritical carbon dioxide circulation system has the optimal exhaust pressure value P under any working conditionoptThe performance of the system is optimized, and the value is determined by the physical properties of carbon dioxide itself. The compressors are all provided with a safe exhaust temperature upper limit value, namely a maximum exhaust temperature value TmaxWhen the exhaust temperature of the compressor exceeds the upper limit, the lubricating oil in the compressor is carbonized at high temperature, and the service life of the compressor is seriously influenced. When the transcritical carbon dioxide automobile air conditioning system is in a refrigeration working mode, the evaporation temperature standard T of the systemc-evaThe air outlet temperature T required by the manufacturer or the clientairStandard correlation:
Tc-eva＝Tair-5
in the heating working mode, the evaporation temperature standard T of the systemh-evaAnd ambient temperature TenvAnd (3) correlation:
Th-eva＝Tenv-12
the measured values of the key state parameter points of the system part are as follows: the actual value of the measured evaporation temperature is the measured value of the post-valve temperature sensor, i.e. Taft. The measured temperature values at the outlet of the evaporator are respectively Tin-eva(when the transcritical carbon dioxide automobile air conditioning system is in a refrigeration working mode, the main heat exchanger is an evaporator) and Tout-eva(when the transcritical carbon dioxide automotive air conditioning system is in a heating mode of operation, the outdoor air cooler is an evaporator).
When the transcritical carbon dioxide system is in a refrigeration working mode, the main heat exchanger 7 is an evaporator, the outdoor heat exchanger 4 is a gas cooler, and the auxiliary heat exchanger 2 does not work, so that the measured value of the outlet of the evaporator is Tin-eva. After the start-up operation is stable, the exhaust pressure of the system is controlled to be the optimal exhaust pressure value by adjusting the opening of the two-way throttle valve 6. If the opening of the two-way throttle valve is continuously reduced, the exhaust temperature T is taken asdisThe maximum discharge temperature value of the compressor, i.e. T, is reacheddis＝TmaxAt all times, the exhaust pressure does not reach the optimum exhaust pressure value, i.e. Pdis≤PoptThe suction pressure and the evaporation pressure are always too low, and the evaporation temperature is lower than a set value, namely Taft≤Tc-evaThe dryness of the refrigerant at the outlet of the main heat exchanger 7 is 1, i.e. xinAt 1, the outlet of the refrigerant is severely superheated, i.e. Tin-eva≥TaftThe system is not charged enough. When the system is started and stably operates, the exhaust pressure of the system is controlled to be the optimal exhaust pressure value, namely P, by adjusting the opening of the two-way throttle valve 6dis＝PoptAt the moment, the rotation speed of the compressor and the opening of the two-way throttle valve are continuously adjusted, the suction pressure and the pressure behind the valve are always overhigh, and the evaporation temperature is higher than a set value, namely Taft＞Tc-evaThe dryness x at the refrigerant outlet of the evaporator cannot meet the air outlet requirementinBelow 0.9, the refrigerant is severely two-phase, indicating that the system is being charged too much.
When the transcritical carbon dioxide system is in a heating working mode, the main heat exchanger 7 and the auxiliary heat exchanger 2 are gas coolers, the outdoor heat exchanger 4 is an evaporator, and therefore the measured value of the outlet of the evaporator is Tout-eva. And after the start-up operation is stable, the exhaust pressure of the opening control system of the bidirectional throttle valve is adjusted to be the optimal exhaust pressure value. If the opening of the two-way throttle valve is continuously reduced, the exhaust temperature T is taken asdisThe maximum discharge temperature value of the compressor, i.e. T, is reacheddis＝TmaxAt all times, the exhaust pressure does not reach the optimum exhaust pressure value, i.e. Pdis≤PoptThe suction pressure and the evaporation pressure are always too low, and the evaporation temperature is lower than a set value, namely Taft≤Th-evaDegree of superheat Δ T of refrigerant at outlet of main heat exchanger 7supAnd 2, the outlet of the refrigerant is seriously overheated, which indicates that the charging quantity of the system is insufficient. When the system is started and stably operates, the exhaust pressure of the system is controlled to be the optimal exhaust pressure value, namely P, by adjusting the opening of the two-way throttle valvedis＝PoptAt the moment, the rotation speed of the compressor and the opening of the two-way throttle valve are continuously adjusted, the suction pressure and the pressure behind the valve are always overhigh, and the evaporation temperature is higher than a set value, namely Taft＞Th-evaThe air outlet requirement cannot be met, and the superheat degree delta T of the refrigerant outlet of the evaporatorsupIf 0, i.e., refrigerant two-phase, the system charge is excessive.
The control logic of the filling amount of the opening and closing control system of the electromagnetic valve adopts negative feedback PI control, the filling amount of the system is the input amount of the PI control, the opening duration of the electromagnetic valve is the output amount, and the control logic block diagram is shown in figure 2.
The opening degrees of the two electromagnetic valves are alpha, and the maximum opening degrees of the two electromagnetic valves are alpha when the two electromagnetic valves are fully openedmaxThe opening and closing control of the electromagnetic valve adopts a current pulse form, namely when the charging quantity of the system needs to be regulated, after a control signal is input, the electromagnetic valve plate is opened, t0The electromagnetic valve is automatically closed after s, automatically opened after t's, and t0s is then automatically closed, and so on, one regulation cycle per Ts. The control equation of the pulse signal is as follows:
Figure BDA0002392996390000111
wherein: t ═ T0+ t', k is a positive integer.
The solenoid is opened t s and the system performs an automatic flow regulation process, and the closed t's is the process of dynamic stabilization of the system again for the sake of the appropriate charge of the system again more precisely. If the system is stable and the filling amount is appropriate, a signal for closing the electromagnetic valve is input, the electromagnetic valve enters a closed state all the time, and the adjusting process is finished.
The time interval of the pulse signal is set according to the pressure difference between the air suction end and the air discharge end of the compressor and the liquid storage device. When the system is short of charge, the second electromagnetic valve (12) needs to be opened, and the pressure difference is the suction pressure P of the compressorsucWith pressure P in the reservoiraccDifference, i.e. Δ P ═ Psuc-Pacc(ii) a When the charging quantity of the system is excessive, the first electromagnetic valve (11) needs to be opened, and the pressure difference at the moment is the discharge pressure P of the compressordisWith pressure P in the reservoiraccDifference, i.e. Δ P ═ Pdis-Pacc(ii) a The time interval t is inversely proportional to the differential pressure Δ P, the refrigerant is mainly supplemented by the differential pressure of the refrigerant, and the larger the differential pressure is, the larger the amount of refrigerant supplement per unit time is, therefore, in order to prevent the refrigerant from being supplemented excessively, the opening time interval of the electromagnetic valve is determined by the following formula:
t＝k/ΔP
wherein: t is the opening time interval of the electromagnetic valve, and the unit of second(s);
Δ P-pressure differential in units of megapascals (MPa);
the inverse proportionality coefficient k of the time interval t and the differential pressure delta P is 10-30.
After stating how to control the charge to the optimal amount for the system, the present invention describes the change in charge demand to guide the adjustment of actual engineering tests. The large demand change of the charging amount mainly occurs when the operation condition of the trans-critical carbon dioxide changes, such as the interconversion of pure internal circulation and external circulation, the change of external environment temperature and the working mode conversion caused by season alternation, and the following classification is explained in detail:
1) conversion of internal and external circulation:
when the transcritical carbon dioxide system is in a refrigeration working mode, the internal circulation is converted into the external circulation, the air inlet temperature of the evaporator is increased, so that the demand on the refrigeration capacity is larger, namely the demand on the charging capacity is also larger, and after the air inlet temperature is converted into the external circulation, the charging capacity of the system is seriously insufficient, so that the charging capacity of the system needs to be supplemented, namely the electromagnetic valve 12 is opened, and the electromagnetic valve 11 is closed. When the transcritical carbon dioxide system is in a heating working mode, the air inlet temperature of the indoor air cooler is suddenly reduced, the demand for the heating capacity of the system is suddenly increased, namely the demand for the filling amount of the refrigerant is also suddenly increased, so that after the system is converted into an external circulation, the filling amount of the system is seriously insufficient, and at the moment, the system needs to be supplemented with the filling amount, namely the electromagnetic valve 12 is opened, and the electromagnetic valve 11 is closed.
When the transcritical carbon dioxide system is in a refrigeration working mode, when the external circulation is converted into the internal circulation, the air inlet temperature of the evaporator is reduced, so that the demand on the refrigeration capacity is smaller, namely the demand on the charging capacity is smaller, and after the system is converted into the internal circulation, the charging capacity of the system is seriously excessive, so that the charging capacity of the system needs to be reduced, namely the electromagnetic valve 12 is closed, and the electromagnetic valve 11 is opened. When the transcritical carbon dioxide system is in a heating working mode, the intake air temperature of the indoor air cooler is suddenly increased, the demand for the heating capacity of the system is suddenly reduced, that is, the demand for the charging amount of the refrigerant is also suddenly reduced, so that after the system is converted into an external circulation, the charging amount of the system is seriously excessive, that is, the electromagnetic valve 12 is closed, and the electromagnetic valve 11 is opened.
2) Change of ambient temperature
Under the condition of the same season, the large change of the environmental temperature generally occurs in sudden change of weather or large day-night temperature difference in the same day. A temperature sensor is arranged on the system, and the environmental temperature value T of the last working operation is collected and recordedpreAnd the ambient temperature T at the current start-upnowWhen the change value of the environmental temperature is T, T is the change value of the environmental temperaturenow-TpreWhen the system is in a working mode of refrigerating in summer or heating in winter, the ambient temperature is increased from low temperature to high ambient temperature (namely delta T is more than 0), if delta T is less than 3, the ambient temperature is not greatly changed, the demand of refrigerating capacity is basically kept unchanged, the charging capacity of the system does not need to be changed, and the system is kept in an original state to start working. If the delta T is more than or equal to 3, the ambient temperature is obviously increased, the charging quantity demand of the refrigerant is reduced, namely the charging quantity in the system is excessive, the charging quantity needs to be reduced, namely the electromagnetic valve 12 is closed, and the electromagnetic valve 11 is opened.
When the ambient temperature is increased from low temperature to high ambient temperature (namely, delta T is less than 0), if delta T is greater than-3, the ambient temperature is not greatly changed, the requirement of refrigerating capacity is basically kept unchanged, the charging capacity of the system is not required to be changed, and the system is maintained in the original state to start working. If delta T is less than or equal to minus 3, the ambient temperature is obviously increased, the filling quantity demand of the refrigerant is reduced, namely the filling quantity in the system is excessive, the filling quantity needs to be reduced, namely the electromagnetic valve 11 is closed, and the electromagnetic valve 12 is opened.
3) Conversion of operating modes
Due to the change of seasons in one year, the air conditioner needs to meet the requirements of refrigeration in summer and heating in winter, when the system is switched from the refrigeration mode to the heating mode, the demand of the system for the charging amount is lower, the electromagnetic valve 12 is closed, the electromagnetic valve 11 is opened, and the charging amount in the system is reduced. On the contrary, when the system is switched from the heating mode to the cooling mode, the demand of the system for the charging quantity is higher, the electromagnetic valve (12) is opened, the electromagnetic valve (11) is closed, and the charging quantity in the system is increased.

Claims (6)

1. CO (carbon monoxide)2A refrigerant charge amount control system with optimal cycle performance, comprising: the system comprises a compressor (1), an auxiliary heat exchanger (2), a four-way reversing valve (3), an outdoor heat exchanger (4), a heat regenerator (5), a two-way throttle valve (6), a main heat exchanger (7), a first liquid storage device (8), a three-way valve (9), a second liquid storage device (10), a first electromagnetic valve (11), a second electromagnetic valve (12) and a plurality of temperature and pressure sensors;
the outlet of the compressor (1) is connected with the inlet of the auxiliary heat exchanger (2), the outlet of the auxiliary heat exchanger (2) is connected with the b interface of the four-way reversing valve (3), the a interface of the four-way reversing valve (3) is connected with the inlet of the outdoor heat exchanger (4), the outlet of the outdoor heat exchanger (4) is connected with the high-pressure side inlet of the heat regenerator (5), the high-pressure side outlet is connected with one end of a two-way throttle valve (6), the other end of the two-way throttle valve (6) is connected with the inlet of the main heat exchanger (7), the outlet is connected with the c interface of the four-way reversing valve (3), the d interface is connected with the inlet of a first reservoir (8), the outlet of the first reservoir (8) is connected with the a interface of a three-way valve (9), the b interface of the three-way valve (9) and the low-pressure outlet of the heat regenerator (5) are jointly connected with the, an inlet and an outlet of the second liquid storage device (10) are respectively connected with the first electromagnetic valve (11) and the second electromagnetic valve (12) and then are connected with the compressor (1) in parallel;
the first liquid storage tank (8) is used for adjusting the stability of the operation of the system; a second reservoir (10) for regulating the filling capacity of the system; when the charging amount of the system is insufficient, the second electromagnetic valve (12) is opened, the first electromagnetic valve (11) is closed, the refrigerant stored in the second liquid storage device (10) is sucked into the compressor and enters the system circulation to supplement the charging amount of the refrigerant; when the refrigerant in the system is overcharged, the first electromagnetic valve (11) is opened, the second electromagnetic valve (12) is closed, the high-pressure refrigerant in the compressor is extruded and discharged into the second liquid storage device (10), and the system charging amount is reduced;
in the refrigeration mode, the dryness of the outlet of the evaporator is used as a standard for judging whether the system charging amount is proper or not; at the moment, the main heat exchanger (7) is an evaporator, and the outdoor heat exchanger (4) is a gas cooler; at this time, the dryness x of the outlet of the evaporatorinObtained by the following method: the temperature, pressure and enthalpy of the high-pressure inlet of the regenerator are respectively T1、P1And h1(ii) a The temperature, pressure and enthalpy of the high-pressure outlet of the heat regenerator are respectively T2、P2And h2(ii) a The temperature, pressure and enthalpy of the low-pressure inlet of the regenerator are respectively T3、P3And h3(ii) a The temperature, pressure and enthalpy of the low-pressure outlet of the heat regenerator are respectively T4、P4And h4(ii) a Then there are:
hx＝f(Tx,Px)，x＝1,2,4
h3＝h4-(h1-h2)
xin＝x3＝f(P3,h3)
in the heating mode, the superheat degree of an evaporator outlet is a standard for judging whether the system charge amount is appropriate; the outdoor heat exchanger (4) is an evaporator, and the superheat degree of the outlet of the evaporator is obtained by the following method: the measured values of the temperature and the pressure at the outlet of the evaporator are respectively Tout-eva、Pout-evaThe saturation temperature at the evaporator outlet is:
Tsat＝f(Pout-eva)
the superheat degree at the outlet of the evaporator is:
ΔTsup＝Tout-eva-Tsat。
2. CO (carbon monoxide)2Method for controlling the charge of refrigerant with optimal cycle performance, characterized in that it is based on a CO according to claim 12The method for judging whether the charging amount is proper or not in the refrigerant charging amount control system with the optimal cycle performance comprises the following steps:
the transcritical carbon dioxide circulation system has the optimal exhaust pressure value P under any working conditionoptOptimizing the performance of the system; the compressor all is equipped with safe exhaust temperature upper limit value: maximum exhaust temperature value Tmax(ii) a In the refrigeration working mode, the evaporation temperature standard T of the systemc-evaThe air outlet temperature T required by the manufacturer or the clientairStandard correlation:
Tc-eva＝Tenv-5
in the heating working mode, the evaporation temperature standard T of the systemh-evaAnd ambient temperature TenvAnd (3) correlation:
Th-eva＝Tenv-12
the actual value of the measured evaporation temperature is the measured value of the post-valve temperature sensor: t isaft(ii) a The measured temperature values at the outlet of the evaporator are respectively Tin-evaAnd Tout-eva；
When the transcritical carbon dioxide system is in a refrigeration working mode, the main heat exchanger (7) is an evaporator, the outdoor heat exchanger (4) is a gas cooler, and the measured value of the outlet of the evaporator is Tin-eva(ii) a After the start-up operation is stable, the exhaust pressure of the opening control system of the bidirectional throttle valve is adjusted to be an optimal exhaust pressure value; if the opening of the two-way throttle valve is continuously reduced, the exhaust temperature T is taken asdisThe maximum discharge temperature value of the compressor, i.e. T, is reacheddis＝TmaxAt all times, the exhaust pressure does not reach the optimum exhaust pressure value, i.e. Pdis≤PoptThe suction pressure and the evaporation pressure are always too low, and the evaporation temperature is lower than a set value, namely Taft≤Tc-evaThe dryness of the refrigerant at the outlet of the main heat exchanger (7) is 1, namely xinAt 1, the outlet of the refrigerant is severely superheated, i.e. Tin-eva≥TaftIf the system is in the low-charging state, the system is in the low-charging state;
when the system is started and stably operates, the exhaust pressure of the system is controlled to be the optimal exhaust pressure value, namely P, by adjusting the opening of the two-way throttle valvedis＝PoptAt the moment, the rotation speed of the compressor and the opening of the two-way throttle valve are continuously adjusted, the suction pressure and the pressure behind the valve are always overhigh, the evaporation temperature is higher than a set value, namely Taft＞Tc-evaThe dryness x at the refrigerant outlet of the evaporator cannot meet the air outlet requirementinBelow 0.9, the refrigerant is severely two-phase, indicating that the system is being charged too much.
3. CO according to claim 22The refrigerant charge control method with the optimal cycle performance is characterized in that when the system is in a heating working mode, the main heat exchanger (7) and the auxiliary heat exchanger (2) are gas coolers, the outdoor heat exchanger (4) is an evaporator, and the measured value of the outlet of the evaporator is Tout-eva(ii) a After the start-up operation is stable, the exhaust pressure of the opening control system of the bidirectional throttle valve is adjusted to be an optimal exhaust pressure value; if the opening of the two-way throttle valve is continuously reduced, the exhaust temperature T is taken asdisThe maximum discharge temperature value of the compressor, i.e. T, is reacheddis＝TmaxAt all times, the exhaust pressure does not reach the optimum exhaust pressure value, i.e. Pdis≤PoptThe suction pressure and the evaporation pressure are always too low, and the evaporation temperature is lower than a set value, namely Taft≤Th-evaAnd the outlet superheat degree delta T of the outlet refrigerant of the outdoor heat exchanger (4)supThe temperature of the refrigerant outlet is not less than 2, and the serious overheating of the refrigerant outlet indicates that the charging quantity of the system is insufficient; when the system is started and stably operates, the exhaust pressure of the system is controlled to be the optimal exhaust pressure value, namely P, by adjusting the opening of the two-way throttle valvedis＝PoptAt the moment, the rotation speed of the compressor and the opening of the two-way throttle valve are continuously adjusted, the suction pressure and the pressure behind the valve are always overhigh, the evaporation temperature is higher than a set value, namely Taft＞Th-evaDegree of superheat Δ T of refrigerant outlet of evaporatorsupIf 0, i.e., refrigerant two-phase, the system charge is excessive.
4. CO according to claim 22The refrigerant charge control method with optimal cycle performance is characterized in that the control logic of the charge of an opening and closing control system of a first electromagnetic valve (11) and a second electromagnetic valve (12) adopts negative feedback PI control, the charge of the system is the input quantity of the PI control, and the opening duration of the first electromagnetic valve (11) and the second electromagnetic valve (12) is the output quantity; the opening degrees of the two electromagnetic valves are alpha, and the maximum opening degrees of the two electromagnetic valves are alpha when the two electromagnetic valves are fully openedmaxThe opening and closing control of the electromagnetic valve adopts a current pulse form; when the charging quantity of the system is adjusted, after a control signal is input, the electromagnetic valve plate is opened, and t0The electromagnetic valve is automatically closed after s, automatically opened after t's, and t0s, automatically closing, and repeating the steps in such a way, wherein each Ts is one regulation period; the control equation of the pulse signal is as follows:
Figure FDA0002808008940000041
wherein: t ═ T0+ t', k is a positive integer;
t s when the electromagnetic valve is opened, the system carries out an automatic flow regulation process, and t's when the electromagnetic valve is closed is a process of dynamic stabilization of the system again; if the system is stable and the filling amount is appropriate, a signal for closing the electromagnetic valve is input, the electromagnetic valve enters a closed state all the time, and the adjusting process is finished.
5. CO according to claim 22The refrigerant charging amount control method with optimal cycle performance is characterized in that the time interval of the pulse signal is set to be related to the pressure difference between a suction end and a discharge end of the compressor and a second liquid storage device:
when the system is short of charge, the second electromagnetic valve (12) needs to be opened, and the pressure difference is the suction pressure P of the compressorsucAnd the pressure P in the second reservoiraccDifference, i.e. Δ P ═ Psuc-Pacc(ii) a When the charging quantity of the system is excessive, the first electromagnetic valve (11) needs to be opened, and the pressure difference at the moment is the discharge pressure P of the compressordisAnd the pressure P in the second reservoiraccDifference, i.e. Δ P ═ Pdis-Pacc(ii) a The time interval t is inversely proportional to the differential pressure Δ P, the refrigerant is mainly supplemented by the differential pressure of the refrigerant, and the larger the differential pressure is, the larger the amount of refrigerant supplement per unit time is, therefore, in order to prevent the refrigerant from being supplemented excessively, the opening time interval of the electromagnetic valve is determined by the following formula:
t＝k/ΔP
wherein: t is the opening time interval of the electromagnetic valve, and the unit of second(s);
Δ P-pressure differential in units of megapascals (MPa);
the inverse proportionality coefficient k of the time interval t and the differential pressure delta P is 10-30.
6. CO according to claim 22The refrigerant charge control method with optimal cycle performance is characterized in that the change of the demand of the charge is realized when the operation condition of transcritical carbon dioxide is changed:
1) conversion of internal and external circulation:
when the system is in refrigeration mode, when being turned into the extrinsic cycle by the inner loop, because the air inlet temperature of evaporimeter risees, the demand to the refrigerating output is bigger, and is also bigger to the demand of filling volume promptly, turns into the extrinsic cycle after, and the system is serious to be short of filling, carries out filling volume to the system this moment and supplements: the second electromagnetic valve (12) is opened, and the first electromagnetic valve (11) is closed; when the system is in the mode of heating operation, because the air inlet temperature of indoor gas cooler reduces suddenly, and the demand to the heating capacity of system increases suddenly, also increases suddenly to the demand of the charge volume of refrigerant promptly, so turn into the extrinsic cycle after, the system charge volume appears seriously not enough, carries out the charge volume to the system this moment and supplements: the second electromagnetic valve (12) is opened, and the first electromagnetic valve (11) is closed;
when the system is in refrigeration mode, when being turned into the inner loop by the extrinsic cycle, because the inlet air temperature of evaporimeter reduces, so the demand to the refrigerating output is littleer, and is also littleer to the demand of filling volume promptly, so turn into the inner loop after, the system filling volume appears seriously excessively, need reduce the filling volume of system this moment: the second electromagnetic valve (12) is closed, and the first electromagnetic valve (11) is opened; when the system is in the heating mode of operation, because the inlet air temperature of indoor gas cooler rises suddenly, the demand to the heating capacity of system reduces suddenly, and the demand to the charge volume of refrigerant also reduces suddenly promptly, so turn into the extrinsic cycle after, the system charge volume appears seriously excessive, needs to reduce the charge volume of system this moment: the second electromagnetic valve (12) is closed, and the first electromagnetic valve (11) is opened;
2) change of ambient temperature
A temperature sensor is arranged on the system, and the environmental temperature value T of the last working operation is collected and recordedpreAnd the ambient temperature T at the current start-upnowWhen the change value of the environmental temperature is T, T is the change value of the environmental temperaturenow-TpreWhen the system is in a working mode of refrigerating in summer or heating in winter, and the ambient temperature is increased from low temperature to high ambient temperature, if delta T is less than 3, the filling amount of the system does not need to be changed, and the system is kept in the original state to start working; if the delta T is larger than or equal to 3, reducing the filling amount: the second electromagnetic valve (12) is closed, and the first electromagnetic valve (11) is opened;
when the ambient temperature is increased from low temperature to high ambient temperature, if delta T is greater than-3, the charging amount of the system does not need to be changed, and the system is maintained in the original state to start working; if the delta T is less than or equal to-3, reducing the filling amount: the first electromagnetic valve (11) is closed, and the second electromagnetic valve (12) is opened;
3) conversion of operating modes
When the system is switched from the refrigeration mode to the heating mode, the demand of the system for the charging quantity is lower, the second electromagnetic valve (12) is closed, the first electromagnetic valve (11) is opened, and the charging quantity in the system is reduced; when the system is switched from the heating mode to the cooling mode, the demand of the system for the charging quantity is higher, the second electromagnetic valve (12) is opened, the first electromagnetic valve (11) is closed, and the charging quantity in the system is increased.
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