Radiant heat dissipation and collection of heat for cold and hot central air conditioning systems

Abstract

This application discloses a central air conditioning system that uses radiant heat dissipation and radiant heat collection. The system includes a compressor (3), a liquid reservoir (4), an indoor unit (1), and an outdoor unit (2) connected in sequence. The outdoor unit (2) includes a radiant heat collector (20). The radiant heat collector (20) includes a protective plate (200), a heat absorption plate (201), and a plate core (202). The heat absorption plate (201) is located between the plate core (202) and the protective plate (200). The plate core (202) includes an inlet end (204) of a heat exchange medium and an outlet end (205) of the heat exchange medium. The heat absorption plate (201) transfers the absorbed heat to the heat exchange medium circulating within the plate core (202). The heat absorption plate (201) collects heat and then transfers it to the heat exchange medium circulating in the plate core (202). The heated heat exchange medium is compressed by the compressor (3) and then enters the indoor unit (1) for heat exchange. When light of a suitable wavelength and temperature difference are provided, the radiant heat collector (20) collects heat by light radiation or temperature difference radiation.

Description

[Technical field]

[0001] The present invention relates to the field of air conditioning, and in particular to a central air conditioning system for cooling and heating using radiant heat dissipation and radiant heat collection. [Background technology]

[0002] Air conditioners account for a large proportion of the energy consumption of buildings. Air conditioners are used frequently in both winter and summer every year. In the current situation of energy shortage, high energy consumption, and prominent environmental pollution problems, energy conservation and emission reduction are requirements for the sustainable development of society. In the natural world in which we live, the solar energy resource reserves are very abundant, and by making full use of these renewable energies in our lives and production, the problems of energy shortage and high energy consumption can be greatly alleviated, which is very worthy of consideration and research. Summary of the Invention [Problem to be solved by the invention]

[0003] In addition, in high-rise buildings, whether freon or ammonia is used as the refrigerating working medium, due to the characteristics of high density, high viscosity, and small pressure difference, the installation head between the indoor unit and the outdoor unit is small, the piping distance is short, and the range of use is limited. The pressure generated by the conventional cold air conditioning system itself cannot transport the refrigerant to the rooms of a high-rise building to directly perform cooling and heating, so it is necessary to use the cheapest water medium to cooperate to transport energy and transport the cold or hot heat generated by the cold air conditioning system to the high-rise air-conditioned room. A large-power water pump is installed, so the power consumption is high. In addition, when the conventional freon air conditioner and ammonia air conditioner are applied to heating, they always have the defect of high energy consumption.

[0004] SUMMARY OF THE DISCLOSURE In order to overcome the shortcomings of the prior art, the present invention aims to provide a central air conditioning system using radiant heat dissipation and radiant heat collection, which is capable of both cooling and heating, has high efficiency, and consumes little energy. [Means for solving the problem]

[0005] The technical proposal of the present invention for the central air conditioning system using radiant heat dissipation and radiant heat collection is as follows: A central air conditioning system for cooling and heating using radiant heat dissipation and radiant heat collection, comprising a compressor, a liquid storage tank, an indoor unit and an outdoor unit connected in sequence, the outdoor unit including a radiant heat collector, the radiant heat collector including a protective plate, a heat absorption plate and a plate core, the heat absorption plate being located between the plate core and the protective plate, the plate core including an inlet end of a heat exchange medium and an outlet end of the heat exchange medium, and the heat absorption plate transferring absorbed heat to the heat exchange medium circulating and flowing within the plate core.

[0006] Preferably, the plate core is disposed so as to be in close contact with the heat absorbing plate, the other surface of the plate core is provided with glass wool, and the heat absorbing plate is a solar heat collecting plate.

[0007] Preferably, the protective plate is made of tempered glass, the plate core is made of a serpentine coil pipe, and a plurality of radiant heat collectors are connected in series to form a heat collection module.

[0008] Preferably, the radiant collector further comprises a heat exchanger made of copper tubes and fins.

[0009] Preferably, the indoor unit includes a heat exchange medium circulation pipeline installed in a high-rise building, the high-rise building includes a plurality of indoor spaces, the indoor spaces are provided with indoor heat exchangers, a first throttle valve is provided at an inlet end and / or an outlet end of each indoor heat exchanger, and a second throttle valve is provided in the pipeline of each floor of the building.

[0010] Preferably, the outdoor unit includes a flash evaporative heat exchanger connected in parallel to the radiant heat collector, a first solenoid valve being provided in a pipe line of the radiant heat collector, and a second solenoid valve being provided in a pipe line of the flash evaporative heat exchanger.

[0011] Preferably, the flash evaporative heat exchanger includes a housing, a heat exchange means, a water atomization device, a blower, and a heat exchange medium flow pipe, the blower is provided outside the housing and is used to create negative pressure inside the housing, the heat exchange means and the water atomization device are provided inside the housing, and a coil pipe in the heat exchange means is connected to the heat exchange medium flow pipe.

[0012] Preferably, the water mist device is provided with a control device for controlling the water mist device to open or close, the control device is connected to a control center, and the control center randomly selects the water mist device to be opened or closed according to a random function based on the opening degree of a predetermined water mist device for a predetermined time.

[0013] Preferably, the heat exchange means further includes a heat exchange fin, and the coil pipe is drilled through the heat exchange fin; The water atomization device includes an ultrasonic atomization device and a water tank, the ultrasonic atomization device is disposed in the water tank, A heat exchanger is formed by stacking a plurality of heat exchange means installed in a drawer type, and the housing is a sealed housing; The compressor and liquid reservoir are located in one cabinet and the flash evaporative heat exchanger is also located in another cabinet.

[0014] Preferably, the central air conditioning system further includes a first four-way valve and a second four-way valve, the four connection ports of the first four-way valve are respectively connected to the intake end of the compressor, the exhaust end of the compressor, the outdoor unit, and the indoor unit, and the four connection ports of the second four-way valve are respectively connected to the outdoor unit, the liquid supply port of the liquid reservoir, the liquid outlet of the liquid reservoir, and the indoor unit; a check valve is provided in a pipeline between the liquid reservoir and the second four-way switching valve, and a third throttle valve is provided in a pipeline between the outdoor unit and the second four-way switching valve; The central air conditioning system is a single-stage carbon dioxide circulation system, which uses carbon dioxide as the single circulating working medium. Effect of the Invention

[0015] The implementation of the present invention includes the following technical advantages: According to the present invention's central air conditioning system using radiation heat dissipation and radiation heat collection, the heat absorbing plate collects heat, then transfers it to the heat exchange medium flowing in the plate core, and the heated heat exchange medium is compressed by the compressor and enters the indoor unit to exchange heat. Any object has the function of continuously emitting, absorbing and emitting electromagnetic waves, and when equipped with light of the corresponding wavelength, the radiation collector collects heat by the way of light emission or temperature difference radiation, and the central air conditioning system of the present invention can heat even at ultra-low temperatures. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of a central air conditioning system using radiant heat dissipation and radiant heat collection according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a structural schematic diagram of a radiant heat collector according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a schematic cross-sectional view taken along the line A-A in FIG. 2. [Figure 4] FIG. 2 is a schematic diagram of the structure of a planar core. [Diagram 5] FIG. 2 is a structural schematic diagram of a flash evaporator heat exchanger. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will be described in detail below in conjunction with the embodiments and drawings, in which the described embodiments do not have any limiting effect but are only for understanding the present invention.

[0018] Referring to FIG. 1, the cold and hot central air conditioning system using radiant heat dissipation and radiant heat collection provided by this embodiment includes a compressor 3, a liquid storage tank 4, an indoor unit 1 and an outdoor unit 2 connected in sequence; referring to FIG. 2 and FIG. 4, the outdoor unit 2 includes a radiant heat collector 20, the radiant heat collector 20 includes a protective plate 200, a heat absorption plate 201 and a plate core 202, the heat absorption plate 201 is located between the plate core 202 and the protective plate 200, the plate core 202 includes an inlet end 204 of the heat exchange medium and an outlet end 205 of the heat exchange medium, and the heat absorption plate 201 transfers the collected heat to the heat exchange medium circulating and flowing within the plate core 202. The plate core 202 is arranged in close contact with the heat absorption plate 201, and the protective plate 200 protects the heat absorption plate 201. After the heat absorption plate 201 collects heat, it directly transfers the heat to the heat exchange medium circulating within the plate core 202. After being compressed by the compressor 3, the heated heat exchange medium enters the indoor unit 1 to perform heat exchange, and the heat exchange medium of the central air conditioner directly exchanges heat with the heat absorption plate, which is one of the inventive features of this embodiment.

[0019] Specifically, the protective plate 200 is made of tempered glass, and the tempered glass has excellent light transmittance. The heat absorbing plate 201 may be selected as a solar heat collecting plate. The other side of the plate core 202 is provided with glass wool 203, which has a heat retention effect and reduces the heat exchange between the heated heat exchange medium and the outside. Referring to FIG. 4, the plate core 202 is a serpentine coil pipe, which increases the heat exchange area between the plate core 202 and the heat absorbing plate 201. A heat collecting module is formed by connecting a plurality of radiant heat collectors 20 in series. Any object has the function of continuously emitting, absorbing and emitting electromagnetic waves. With the development of technology, a preferred solar heat collecting plate is provided with light of a corresponding wavelength, and the solar heat collecting plate collects the heat radiated from the light, and the central air conditioning system of this embodiment can heat even at ultra-low temperatures. Preferably, the radiant collector further includes a heat exchanger consisting of copper tubes and fins, and the fins collect heat in the air, and when there is a temperature difference between the outside air and the heat exchange medium, the fins can collect air heat.

[0020] Referring to FIG. 1, an indoor unit 1 includes a heat exchange medium circulation pipeline installed in a high-rise building, the high-rise building has a hierarchical structure, each floor includes a plurality of indoor spaces, the indoor spaces are provided with indoor heat exchangers 10 connected in parallel or in series, a first throttle valve 11 is provided at the inlet end and / or outlet end of each indoor heat exchanger 10, a second throttle valve 12 is provided in the pipeline of each floor building, for the first throttle valve 11 and the second throttle valve 12, an electronic expansion valve unit is preferable, and the end refrigeration temperature is adjusted by adjusting the intake pressure of the compressor 3 and the opening degree of the electronic expansion valve, and the temperature adjustment range can reach -25℃~30℃.

[0021] Referring to FIG. 1, in order to realize switching between cooling and heating, the central air conditioning system further includes a first four-way switching valve 5 and a second four-way switching valve 6, the four connection ports of the first four-way switching valve 5 are respectively connected to the intake end of the compressor 3, the exhaust end of the compressor 3, the outdoor unit 2, and the indoor unit 1, and the four connection ports of the second four-way switching valve 6 are respectively connected to the outdoor unit 2, the liquid supply port of the liquid reservoir 4, the liquid outlet of the liquid reservoir 4, and the indoor unit 1. FIG. 1 is a schematic diagram of the connections in heating mode. In heating mode, the first four-way switching valve 5 connects the exhaust end of the compressor 3 to the indoor unit 1, and connects the outdoor unit 2 to the intake end of the compressor 3. The second four-way switching valve 6 connects the outdoor unit 2 to the liquid reservoir 4, and connects the liquid reservoir 4 to the indoor unit 1. The heat exchange medium flows through the compressor 3, the first four-way switching valve 5, the indoor unit 1, the liquid reservoir 4, the second four-way switching valve 6, and the outdoor unit 2 in that order to complete heating. In the cooling mode, the first four-way valve 5 connects the exhaust end of the compressor 3 to the outlet end of the outdoor unit 2, and connects the outlet end of the indoor unit 1 to the intake end of the compressor 3. The second four-way valve 6 connects the outlet end of the outdoor unit 2 to the inlet end of the liquid reservoir 4, and connects the outlet end of the liquid reservoir 4 to the inlet end of the indoor unit 1. The heat exchange medium flows through the compressor 3, the first four-way valve 5, the outdoor heat exchanger, the second four-way valve 6, the liquid reservoir 4, and the indoor heat exchanger 10 in order to complete the cooling. Specifically, a check valve 8 is provided in the pipe of the liquid reservoir 4 and the second four-way valve 6. The check valve 8 can only flow in one direction and has a pressure regulating function, so as to always keep the pressure of the central air conditioner within an appropriate range and ensure the efficient operation of the system. A third throttle valve 7 is provided in the pipeline between the outdoor unit 2 and the second four-way switching valve 6, and is preferably an electronic expansion valve having a throttle / pressure reducing function.

[0022] The outdoor unit 2 further includes a flash evaporation heat exchanger 21 connected in parallel with the radiant heat collector 20, and a first solenoid valve 206 is provided in the pipe of the radiant heat collector 20, which controls whether the heat exchange medium flows through the radiant heat collector 20. A second solenoid valve 217 is provided in the pipe of the flash evaporation heat exchanger 21, which controls whether the heat exchange medium flows through the flash evaporation heat exchanger 21. In summer, when operating for cooling, the second solenoid valve 217 is opened, the first solenoid valve 206 is closed, and the flash evaporation heat exchanger 21 is dissipating heat, and in winter, when operating for heating, the second solenoid valve 217 is closed, the first solenoid valve 206 is opened, and the radiant heat collector 20 is heating.

[0023] The sun radiates and transmits energy to the outside in the form of electromagnetic waves, and according to the present embodiment of the central air conditioning system using radiation and collection of heat, when it is sunny, the heating is performed using solar heat, which is environmentally friendly, and when it is not sunny, the radiation collector can collect part of the heat by thermal radiation, or the air energy collector can collect heat, and the flash evaporative heat exchanger 21 can be started to take heat, so as to meet the demand for heating. The radiation collector or flash evaporative heat exchanger is used to collect radiation heat by light energy, collect radiation heat by temperature difference, and collect radiation heat by mist droplets in the flash evaporative heat exchanger, which greatly improves the heating efficiency of the central air conditioner. When cooling, the flash evaporative heat exchanger is used to take heat from the room by radiation between the heat exchange medium and mist droplets.

[0024] The heat exchange medium may be selected from freon, ammonia, carbon dioxide, etc., and in this embodiment, carbon dioxide is preferably used as the cooling and heating medium of the central air conditioner. Carbon dioxide as the circulating working medium has the advantages of large pressure difference, good fluidity, small density, and supercritical phase transition, and can be applied to high-rise buildings. The indoor heat exchange medium circulating pipe is connected to a single-stage carbon dioxide circulating system using carbon dioxide as the single circulating working medium, and the single stage means that unlike a cascade system, only carbon dioxide medium is used for circulation and no cascade is required. The multi-type central air conditioning system of this embodiment uses carbon dioxide as the working medium, provides cooling or heating to a higher floor in vertical height, and when applied to a flat floor, it can circulate to a longer distance and operate more indoor units. The evaporating temperature is controlled by controlling the intake pressure of the compressor 3, for example, the evaporating temperature is controlled between 6 and 10 degrees, and the bodily sensation effect is better. Compared with traditional air conditioners, the central air conditioning system of this embodiment is more efficient and more energy-saving, and the efficiency is improved by more than two times, saving more than 50% of energy.

[0025] Specifically, referring to Fig. 5, the flash evaporative heat exchanger 21 includes a housing 210, a heat exchange means 211, a water atomizing device 212, a blower 213, and a heat exchange medium flow pipe 214, the blower 213 is provided outside the housing 210 to form a negative pressure inside the housing 210, the heat exchange means 211 and a plurality of independent water atomizing devices 212 are provided inside the housing 210, specifically, a coil pipe in the heat exchange means 211 is connected to the heat exchange medium flow pipe 214. The heat exchange means 211 further includes a heat exchange fin, and the coil pipe is drilled into the heat exchange fin. The water atomizing device 212 is provided with a control device for controlling the water atomizing device 212 to open or close, and the control device is connected to the control center. The control center randomly selects the water atomization devices 212 that need to be opened or closed according to a random function based on a predetermined time (e.g., 1 second to 200 seconds) and the opening degree of a predetermined water atomization device 212 (e.g., opening the water atomization device 212 10% to 90%), and randomly opens or closes each water atomization device 212, thereby achieving the effect of making the atomized liquid in the housing 210 uniform. During actual operation, when the heating requirement can be met by only opening the spray head 50%, the conventional way is to completely close the water atomization device 212; operating in this manner will inevitably result in uneven distribution of the atomized liquid in the housing 210, which will affect the heat exchange effect; and manually closing part of the water atomization device 212 will be inconvenient; in this embodiment, the control center randomly closes part of the water atomization device 212 (a conventional random control device can also be used) at regular intervals (e.g., 30 seconds), so that the probability of each water atomization device 212 being randomly opened or closed is similar, and the atomized liquid in the housing 210 is always in a uniform state.

[0026] The water atomizing device 212 atomizes the liquid, and the atomized liquid spreads around the heat exchanging means 211, and the liquid micelles complete radiative heat exchange with the heat exchanging medium in the heat exchanging means 211 under the action of negative pressure, and then are extracted from the housing 210 by the blower 213. For the water atomizing device 212, an ultrasonic atomizing device is preferred, and the ultrasonic atomizing device is installed in a water tank.

[0027] A heat exchanger is formed by stacking a plurality of heat exchange means 211 installed in a drawer type, which is convenient for installation and maintenance. When a heat exchange means 211 is broken, the broken heat exchange means 211 can be removed for maintenance or replacement. Preferably, the housing 210 is a sealed housing, and the blower 213 forms a predetermined negative pressure value in the sealed housing 210 to achieve more efficient heat exchange. The exhaust volume of the blower 213 is greater than the evaporation volume of the atomized liquid in the housing 210, and the steam in the housing 210 is sufficiently exhausted to improve the evaporation efficiency of the atomized liquid while maintaining a negative pressure environment in the housing 210. Here, unlike the principles of the conventional air-cooled heat exchanger and the evaporative cooling heat exchanger, the flash evaporative heat exchanger of this embodiment is under negative pressure conditions, and there is no external gas mixed in except for the external gas mixed in the pressure regulating device, and there is no influence on heat exchange even under high temperature and high humidity conditions, so that it can be normally used under different climatic conditions.

[0028] Preferably, the compressor 3, the control valve and the liquid reservoir 4 are provided in one cabinet, the flash evaporative heat exchanger is arranged in a modular manner, and the flash evaporative heat exchanger 21 is also provided in another cabinet.

[0029] According to the flash evaporative heat exchanger of this embodiment, the cooling requirements of the air conditioner can be met by single-stage circulation of carbon dioxide, and the circulation of carbon dioxide medium can be completed in high-rise buildings of more than 100 meters, and the refrigeration efficiency COP of the central air conditioner is greater than 4.5. Carbon dioxide has a GWP of 1 and an ODP of 0, and is a highly environmentally friendly refrigerant with good safety and chemical stability, non-toxic, non-flammable, suitable for various lubricants, good thermal properties, large refrigeration capacity per unit volume, low kinetic viscosity, and excellent flow and heat transfer properties. However, because carbon dioxide has a low critical temperature (31.1°C), it can easily be kept in a gaseous state at the ambient temperature in summer, and its critical pressure is high (7.38MPa), and the pressure in the gaseous state is high, which increases the operating pressure of the system and increases the throttle loss. Based on the characteristics of carbon dioxide, the technical solution of this embodiment can ensure that the pressure in the central air conditioner is maintained within an appropriate range, and can ensure that CO2 is in a liquid state when it is located at the outlet of the outdoor unit 2, thereby improving the heat exchange effect in the end heat exchanger, and allowing one master device to operate more end heat exchangers (more than 100 units), thereby ensuring the safe and normal operation of the system.

[0030] Finally, the above embodiments do not limit the protection scope of the present invention, but are merely intended to describe the technical solution of the present invention. The present invention has been described in detail with reference to preferred embodiments. However, as can be understood by those skilled in the art, the technical solution of the present invention may be modified or replaced with equivalents, and such modifications or replacements do not depart from the substance and scope of the technical solution of the present invention. [Explanation of symbols]

[0031] 1. Indoor unit; 10...indoor heat exchanger; 11 First throttle valve; 12 - second throttle valve; 2 Outdoor unit; 20...Radiant collector; 200...protective plate; 201 ···Heat absorbing plate; 202 ···Plate core; 203 ···Glass wool; 204 ···Inlet end of heat exchange medium; 205 ···Outlet end of heat exchange medium; 206 ···First solenoid valve; 21 ···Flash evaporative heat exchanger; 210 ···Housing; 211 ...heat exchange means; 212...Water atomization device; 213 ···Blower; 214 ...Heat exchange medium distribution pipe; 217 ···Second solenoid valve; 3 ···Compressor; 4 Liquid reservoir; 5 ···First four-way valve; 6 ···Second four-way valve; 7 ···Third throttle valve; 8. Check valve.

Claims

1. A central air conditioning system for cooling and heating using radiant heat dissipation and radiant heat collection, comprising a compressor, a liquid storage tank, an indoor unit, and an outdoor unit, all of which are connected to each other, the outdoor unit including a radiant heat collector, the radiant heat collector including a protective plate, a heat absorbing plate, and a plate core, the heat absorbing plate being located between the plate core and the protective plate, the plate core including an inlet end of a heat exchange medium and an outlet end of the heat exchange medium, and the heat absorbing plate transferring absorbed heat to the heat exchange medium circulating and flowing within the plate core, The central air conditioning system further includes a first four-way switching valve and a second four-way switching valve, the four connection ports of the first four-way switching valve being respectively connected to an intake end of a compressor, an exhaust end of the compressor, an outdoor unit, and an indoor unit, and the four connection ports of the second four-way switching valve being respectively connected to an outdoor unit, a liquid supply port of a liquid reservoir, a liquid outlet port of the liquid reservoir, and the indoor unit; The outdoor unit includes a flash evaporation heat exchanger connected in parallel with the radiant heat collector, a first solenoid valve is provided in a pipe of the radiant heat collector, and the first solenoid valve controls whether the heat exchange medium flows through the radiant heat collector; a second solenoid valve is provided in a pipe of the flash evaporation heat exchanger, and the second solenoid valve controls whether the heat exchange medium flows through the flash evaporation heat exchanger; The flash evaporative heat exchanger includes a housing, a heat exchange means, a water atomizing device, a blower, and a heat exchange medium flow pipe, the blower is provided outside the housing and is used to create a negative pressure inside the housing, the heat exchange means and the water atomizing device are provided inside the housing, and a coil pipe in the heat exchange means is connected to the heat exchange medium flow pipe, The water mist generation device is provided with a control device for controlling the water mist generation device to be opened or closed, the control device is connected to a control center, and the control center randomly selects the water mist generation device to be opened or closed according to a random function based on the opening degree of a predetermined water mist generation device at a predetermined time.

2. The plate core is disposed so as to be in close contact with the heat absorbing plate, The other surface of the plate core is provided with glass wool, The central air conditioning system using radiant heat dissipation and radiant heat collection according to claim 1, wherein the heat absorption plate is a solar heat collection plate.

3. The protective plate is made of tempered glass, The plate core is a serpentine coil pipe, 2. The central air conditioning system using radiant heat dissipation and radiant heat collection according to claim 1, wherein a heat collection module is formed by connecting a plurality of radiant heat collectors in series.

4. The central air conditioning system using radiant heat dissipation and collection according to claim 1 , wherein the radiant heat collector further comprises a heat exchanger made of copper tubes and fins.

5. The cooling and heating central air conditioning system using radiant heat dissipation and radiant heat collection as described in claim 1, characterized in that the indoor unit includes a heat exchange medium circulation pipeline installed in a high-rise building, the high-rise building includes a plurality of indoor spaces, the indoor spaces are provided with indoor heat exchangers, a first throttle valve is provided at an inlet end and / or an outlet end of each indoor heat exchanger, and a second throttle valve is provided in the pipeline of each floor building.

6. The heat exchange means further includes a heat exchange fin, and the coil pipe is drilled through the heat exchange fin; The water atomization device includes an ultrasonic atomization device and a water tank, the ultrasonic atomization device is disposed in the water tank, A plurality of heat exchange means are stacked to form a heat exchanger, and the housing is a sealed housing; 2. The central air conditioning system using radiant heat dissipation and radiant heat collection as claimed in claim 1, wherein the compressor and the liquid reservoir are installed in one cabinet, and the flash evaporative heat exchanger is also installed in another cabinet.

7. a check valve is provided in a pipeline between the liquid reservoir and the second four-way switching valve, and a third throttle valve is provided in a pipeline between the outdoor unit and the second four-way switching valve; The central air conditioning system using radiant heat dissipation and radiant heat collection as claimed in any one of claims 1 to 6, characterized in that the central air conditioning system is a single-stage carbon dioxide circulation system using carbon dioxide as the sole circulating working medium.

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