KR101811957B1 - Cascade Heat Pump with Two Stage Expansion Structure using CO2 Refrigerant and Method for Circulating thereof - Google Patents

Abstract

Provided are a cascade heat pump with a two stage expansion structure using carbon dioxide refrigerant and a method for circulating the same. According to an embodiment, in the cascade heat pump with a two stage expansion structure having a compressor, a condenser, a vapor-liquid separator, an expansion device, and an evaporator, a first expansion device is formed between the condenser and the vapor-liquid separator to decrease pressure of refrigerant passing through the condenser. The refrigerant is expanded from high pressure to intermediate pressure by the first expansion device, and is expanded from the intermediate pressure to low pressure by the expansion device to perform a two stage expansion process.

Description

Technical Field [0001] The present invention relates to a multi-stage heat pump having a two-stage expansion structure using CO2 refrigerant and a circulation method thereof,

The following embodiments relate to a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant and a circulation method thereof. More particularly, the present invention relates to a multi-stage heat pump having a two-stage expansion structure using a CO ₂ refrigerant using a mixed refrigerant in which CO ₂ and other refrigerants are mixed, and a circulation method thereof.

In general, a heat pump is a device that compresses, condenses, expands, and evaporates a refrigerant to cool or heat the indoor space. The heat pump includes a compressor, a condenser, an expansion valve, and an evaporator. The refrigerant is evaporated in the evaporator to absorb heat from the surroundings and become a gas. The refrigerant is again liquefied by releasing heat around the condenser.

General refrigerants such as R134a used in these heat pumps are known to be the main cause of environmental destruction such as ozone layer destruction and global warming. Accordingly, a supercritical refrigeration cycle using carbon dioxide (CO ₂ ) for replacing the refrigerant has attracted attention.

The carbon dioxide (CO ₂ ) refrigerant has an excellent compression efficiency due to its low operating compression ratio, and because of its excellent heat transfer characteristics, the temperature approach (inlet temperature of the secondary fluid - temperature difference of the outlet of the refrigerant) In the case of the high temperature and high pressure side heat exchanger, there is an advantage that the heat transfer characteristic is excellent enough to lower the temperature of the refrigerant up to the temperature of the incoming air.

The volume capacity ratio (capacity volume ratio) of the carbon dioxide is 7 to 8 times higher than that of R134a because of its excellent thermodynamic properties. Therefore, the volume volume of the compressor constituting the supercritical refrigeration cycle is greatly reduced .

In addition, carbon dioxide has excellent boiling heat transfer due to its small surface tension, and has a high specific heat and low liquid viscosity, which is more advantageous than R134a even under pressure.

However, the supercritical refrigeration cycle using carbon dioxide as the refrigerant is very high in comparison with the general refrigeration cycle in which R134a is refrigerant as well as the evaporation pressure and the high-temperature high-pressure side heat exchanger pressure (conventional condensation pressure). That is, in the supercritical refrigeration cycle, the evaporation pressure is about 10 times higher than that of the general refrigeration cycle, and the high-temperature and high-pressure heat exchanger pressure is about 7 times (about 120 bar) higher.

For example, the condensing process of the high pressure refrigerant gas of the freezer is cooled by air or water. When CO ₂ is applied to the refrigerator, a high pressure of 120 to 130 bar higher than the critical point should be applied. Accordingly, hot water or heating function of about 90 ° C can be obtained by using heat on the high-pressure side.

The equipment using this condensation heat is called a heat pump, and the COP (coefficient of performance), which indicates the refrigerating cycle efficiency of the heat pump, is added to the refrigerator COP by 1.0, so that the COP becomes 3 ~ 4. This means that the energy of Electricity 1 is applied and the heat is used three to four times.

However, since the CO ₂ heat pump has a high pressure of about 30 bar on the side of the low-pressure evaporator, the evaporator vaporization temperature of about 0 ° C is obtained. Therefore, if the outdoor air temperature is low in winter, the refrigerant vaporization of the outdoor unit (evaporator) can not be performed. The heat of these outdoor units can be used for refrigeration or air conditioning, but they can not provide sustained load.

Korean Patent Laid-Open No. 10-2012-0055065 relates to an industrial heat pump system using the carbon dioxide refrigerant and a performance evaluation method thereof, and relates to an industrial heat pump using a low-carbon eco-friendly carbon dioxide refrigerant and a technology for evaluating a performance of the heat pump system .

Embodiments describe a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant and a circulating method thereof, and more specifically, a method of increasing the efficiency of heating and / or refrigeration using a mixed refrigerant in which CO ₂ and another refrigerant are mixed Technology.

Embodiments having a two-stage expansion structure using a condenser and the reservoir thereby to install the expansion device between the separator to expand the working fluid chain refrigerant, CO ₂ refrigerant to get a low-temperature refrigerant that can be easily evaporated even in winter low outside air in the evaporator A multi-stage heat pump and a circulation method thereof.

Embodiments can increase the CO ₂ to 50 to 90% by using CO ₂ and HFC mixed refrigerants having different boiling points, and it is possible to apply a lower pressure to the high pressure side, thereby providing the effect of the hot water for heating Stage heat pump using a CO ₂ refrigerant capable of saving energy and a circulation method thereof.

A multi-stage heat pump having a two-stage expansion structure including a compressor, a condenser, a liquid separator, an expansion device, and an evaporator according to an embodiment, the multi-stage heat pump comprising: Wherein the refrigerant is inflated from a high pressure to an intermediate pressure by the first expansion device and expanded from the intermediate pressure to a low pressure by the expansion device to perform a two stage expansion process .

Here, the refrigerant may be a mixed refrigerant in which carbon dioxide (CO ₂ ) and at least one other refrigerant are mixed.

The refrigerant is composed of carbon dioxide (CO ₂ ) and HFC-based mixed refrigerant having different boiling points, and the ratio of the carbon dioxide (CO ₂ ) is increased from 50% to 90% to lower the pressure at the high pressure, Available.

The refrigerant is composed of two or more mixed refrigerants, and functions as a heat pump that uses the heat of the condenser as hot water for heating. At the same time, the low temperature of the evaporator can be evaporated by the heat of the outside air or applied to a refrigerating device.

The liquid-liquid separator separates a part of the other refrigerant and the carbon dioxide (CO ₂ ) having a low boiling point into a liquid as the pressure of the refrigerant passing through the condenser is lowered by the first expansion device, and the remaining CO 2 ₂ ) can be separated into gas.

Further comprising a second precooler for cooling the refrigerant that has passed through the liquid separator, wherein the expansion device is disposed between the liquid separator and the second precooler, A second expansion device for lowering the pressure of carbon dioxide (CO ₂ ); And in the second precooling group it is disposed between the evaporator and the reservoir of liquid in the other refrigerant and to lower the evaporator pressure and then a portion of the carbon dioxide (CO ₂₎ the cooling of the second example, cold air discharged from the separator And a third expansion device for discharging the refrigerant.

The evaporator can vaporize the other refrigerant passing through the third expansion device and a part of the carbon dioxide (CO ₂ ) by the outside air heat.

And a first precooler connected to a discharge port of the evaporator and a discharge port of the condenser, wherein the first precooler is configured to mix the refrigerant vaporized in the evaporator and the carbon dioxide (CO ₂ ) passing through the condenser, And then to the compressor.

And an ejector or an evaporator pressure regulator (EPR) for correcting different pressure differences between the refrigerant discharged from the second cold air and the refrigerant discharged from the evaporator to the compressor.

Wherein the refrigerant is inflated from a high pressure to an intermediate pressure by the first expansion device and then expanded to a low pressure from the intermediate pressure by the third expansion device so as to perform a heating function even when the outdoor air temperature is low. The refrigerant having undergone the expansion process may be introduced and the vaporization temperature may be lowered.

In another aspect of the present invention, there is provided a circulation method of a multi-stage heat pump having a two-stage expansion structure, comprising: condensing a refrigerant mixed with carbon dioxide (CO ₂ ) discharged from a compressor and at least one other refrigerant in a condenser; Expanding the refrigerant passing through the condenser using a first expansion device to lower the pressure; Separating the refrigerant having passed through the first expansion device from the other refrigerant having a low boiling point and a part of the carbon dioxide (CO ₂ ) into a liquid using a liquid separator and separating the remaining carbon dioxide (CO ₂ ) into a gas ; Expanding the carbon dioxide (CO ₂ ) in a gaseous state at a high pressure discharged from the liquid-liquid separator using a second expansion device to lower the pressure and moving the _second carbon dioxide to a second precooler; Cooling the second refrigerant and the carbon dioxide (CO ₂ ) in the _second liquid cooler discharged from the liquid-liquid separator by using the third expansion device to lower the pressure of the refrigerant and discharge it to the evaporator, Vaporizing a part of the other refrigerant and the carbon dioxide (CO ₂ ) by outside heat; And a step in which the carbon dioxide (CO ₂ ) passed through the second precooler, the other refrigerant vaporized by the evaporator, and a part of the carbon dioxide (CO ₂ ) are exchanged with each other and then transferred to the compressor.

Here, the refrigerant may be composed of carbon dioxide (CO ₂ ) and HFC-based mixed refrigerant having different boiling points, and the ratio of the carbon dioxide (CO ₂ ) may be increased to 50% to 90% to lower the pressure at the high pressure It becomes possible to provide hot water for heating.

According to the embodiments, by providing an expansion device between the condenser and the liquid-liquid separator to expand the refrigerant as a working oil, a two-stage expansion structure using a CO ₂ refrigerant, which can obtain a low-temperature refrigerant that can easily evaporate even in low- And a circulation method thereof.

According to the embodiments, CO ₂ can be increased to 50 to 90% by using CO ₂ and HFC mixed refrigerants having different boiling points, so that it is possible to apply lower pressure on the high pressure side, To provide a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant capable of saving energy and a circulation method thereof.

Further, according to the embodiments, it is possible to increase CO ₂ to 50 to 90% by using CO ₂ and HFC mixed refrigerants having different boiling points, thereby providing a heat pump using refrigerant of environmentally friendly carbon dioxide, It is possible to contribute to the reduction of greenhouse gas emission by replacing the heat pump using the refrigerant having a low temperature and the high pressure of the low pressure evaporator generated from the heat pump using the carbon dioxide as the refrigerant, If the outdoor air temperature is low in winter, the refrigerant vaporization of the outdoor unit (evaporator) can not be performed, thereby solving the problem of requiring a supplementary heat source.

1 is a view schematically showing a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment.
2 is a view schematically showing a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant including an ejector according to another embodiment.
3 is a view for explaining a two-stage expansion process of a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment.
FIG. 4 is a diagram illustrating a COP change according to an intermediate pressure of a two-stage expansion according to an embodiment. FIG.
5 is a flowchart showing a circulation method of a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to another embodiment.

Hereinafter, embodiments will be described with reference to the accompanying drawings. However, the embodiments described may be modified in various other forms, and the scope of the present invention is not limited by the embodiments described below. In addition, various embodiments are provided to more fully describe the present invention to those skilled in the art. The shape and size of elements in the drawings may be exaggerated for clarity.

In the following examples, an expansion device is installed between a condenser and a liquid separator, and a two-stage expansion process is applied. By using the CO ₂ refrigerant capable of obtaining a low-temperature refrigerant that can be easily evaporated even in a low- It is possible to provide a multi-stage heat pump (Cascade Heat Pump) having a simple expansion structure. Also, CO ₂ can be increased to 50 to 90% by using CO ₂ and HFC mixed refrigerants having different boiling points, so that the pressure at a high pressure side can be applied at a low level, and hot water for heating can be provided.

As a result, it is possible to apply a pressure as high as 60 ~ 80bar, which is much lower than the CO ₂ heat pump process of 130 bar, and it is possible to use a heat pump function using condenser heat as hot water by applying two or more mixed refrigerants, Can be applied to freezing. In addition, it is possible to perform the heating function by easily sucking the outside heat by sucking the outside heat even in the winter when the evaporator is low in the vaporization temperature, and it is possible to improve the COP (coefficient of performance) Can be provided.

1 is a view schematically showing a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment.

1, a multi-stage heat pump 100 having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment includes a compressor 110, a condenser 120, a first expansion device 140, a liquid separator 150, a second expansion device 141, a third expansion device 142, and an evaporator 160. In addition, according to the embodiment, the multi-stage heat pump 100 having the two-stage expansion structure using the CO 2 refrigerant may further include at least one of the first cooling air 130 and the second cooling air 131.

The compressor 110 sucks the refrigerant as a working fluid, compresses the refrigerant to a state higher than the critical point, and discharges the compressed refrigerant.

Here, the refrigerant may be a mixed refrigerant in which carbon dioxide (CO ₂ ) and at least one or more other refrigerants are mixed.

More specifically, the refrigerant is composed of carbon dioxide (CO ₂ ) having different boiling points and HFC-based mixed refrigerant, thereby increasing the CO ₂ ratio from 50% to 90% to lower the pressure at high pressure to provide hot water for heating, .

Further, the refrigerant is composed of two or more mixed refrigerants, and functions as a heat pump that uses the heat of the condenser as hot water for heating, and at the same time, the low temperature of the evaporator is applicable to the refrigerating apparatus.

The condenser 120 condenses the refrigerant discharged from the compressor and can heat the refrigerant using the heat generated in the condenser. In particular, when a refrigerant containing CO ₂ is used as the refrigerant, a high pressure higher than the critical point is applied to CO ₂ , so that hot water or a heating function can be obtained by using the heat on the high pressure side.

For example, when CO ₂ is applied to a heat pump, a high pressure of 120 to 130 bar higher than the critical point is applied, and hot water or heating function of about 90 degrees can be obtained by using the heat on the high pressure side.

In this condenser 120, a refrigerant having a predetermined pressure and a low boiling point at a predetermined temperature may exist in a gaseous state above the critical point.

For example, refrigerant CO ₂ gas at a pressure of 60 to 80 bar at 40 ° C in the condenser 120 and other refrigerant having a low boiling point may exist in a gaseous state above the critical point.

The first cool air 130 may be disposed between the condenser 120 and the first expansion device 140 and may also be connected to the discharge port of the evaporator 160. The first cold air 130 is an apparatus for improving performance, and may be omitted.

The first expansion device 140 may be configured between the condenser and the liquid separator to expand the refrigerant that has passed through the condenser to lower the pressure.

Thus, the refrigerant is expanded from the high pressure to the intermediate pressure by the first expansion device 140, expanded from the intermediate pressure to the low pressure by the expansion device, and the two-stage expansion process can be performed.

Reservoir separator 150 includes a first expansion device (140) according to Sikkim lowering the pressure of the refrigerant passing through the condenser 120 by separate parts from other low-boiling point refrigerant and CO ₂ in the liquid, and the remaining CO ₂ Gas can be separated.

Unlike a conventional automatic multi-stage system, after condensing process, according to one embodiment a first portion of when lowering the pressure in the expansion device 140, other low boiling point refrigerant full with CO ₂ is in a liquid, and the remaining CO ₂ is a reservoir with a gas Separator 150 as shown in FIG.

The second example cooling air 131 can cool the lower refrigerant liquid of the liquid-liquid separator 150.

More specifically, the second example cooling air 131 can cool a part of CO ₂ and other refrigerant in a liquid state discharged from the liquid-liquid separator 150. In addition, the pressure of the high-pressure gaseous CO ₂ discharged from the liquid-liquid separator 150 by the second expansion device 141 can be lowered to the final pressure and then passed through the second pre-cooler 131.

For example, high-pressure gaseous CO ₂ can expand the pressure to about 8 to 12 bar and make the liquid at -20 캜 gas, thereby subcooling the liquid of the liquid-liquid separator in the second example cold air.

The expansion device may include a second expansion device (141) and a third expansion device (142).

The second expansion device 141 is disposed between the liquid crystal separator 150 and the second preliminary cooling air 131 and expands the high pressure gaseous carbon dioxide (CO ₂ ) discharged from the liquid crystal separator 150 to lower the pressure . The refrigerant having passed through the second expansion device (141) may be introduced into the second cooling air (131).

The third expansion device 142 is disposed between the second warm air cooler 131 and the evaporator 160 to convert a portion of CO ₂ and other refrigerant in a liquid state discharged from the liquid cooler separator 150 to a second cool air 131 The pressure of the refrigerant can be lowered and discharged to the evaporator 160.

The evaporator 160 can vaporize a part of CO ₂ and other refrigerant passing through the third expansion device 142 by the outside air heat.

For example, the precooled refrigerant liquid may be evaporated by the outside air heat in the evaporator 160 because the pressure of the precooled refrigerant is expanded to 10 bar and the temperature is lowered to about -15 ° C.

More specifically, the evaporator 160 is a two-stage expansion process in which the refrigerant is expanded from the high pressure to the intermediate pressure by the first expansion device 140, and then expanded from the intermediate pressure to the low pressure by the third expansion device 142 The evaporation can be easily performed even when the temperature of the outside air is low because the vaporization temperature is lowered due to the flow of the refrigerant.

Thereafter, the refrigerant vaporized in the evaporator 160 and the CO ₂ gas passing through the second expansion device 141 and passing through the second refrigerant 131 may be mixed and moved to the compressor 110. Here, the refrigerant vaporized in the evaporator 160 and the CO ₂ gas passing through the second expansion device 141 and passed through the second refrigerant 131 are transferred to the compressor 110, It is possible to move to the compressor 110 after passing through the first example cooler 130. In this case,

In the first example cooler 130, the mixed gas that is sucked into the compressor 110 from the evaporator 160 and the mixed refrigerant that has passed through the condenser 120 are heat-exchanged. That is, the high-pressure refrigerant that has passed through the condenser 120 is cooled by the cool gas sucked from the evaporator 160 to the compressor 110.

For example, the refrigerant vaporized in the evaporator 160 may be combined with the CO ₂ gas, passed through the first refrigerant 130, and then compressed by the compressor 110 so that the discharge temperature may be 120-130 ° C.

The first example cooler 130 can precool about 5 degrees Celsius, for example, the outlet temperature of the evaporator 160 can be heated by 5 degrees, and the temperature of the condenser 120 can be reduced by 5 degrees.

As described above, the present embodiments improve the auto multistage cycle, and an expansion device is installed between the condenser and the liquid separator, and the expansion process can be configured in two stages. That is, it can be constituted by a high-pressure-intermediate-low-pressure two-stage expansion structure.

According to the embodiments, CO ₂ and HFC mixed refrigerants having different boiling points may be used in the same manner, and CO ₂ may be increased to 50 to 90%. Therefore, it is possible to apply a pressure as high as 60 to 80 bar on the high pressure side.

In addition, by applying two or more mixed refrigerants, it is possible to apply a low temperature of the evaporator to the refrigerator while simultaneously using the condenser heat as a hot water, and evaporate at the evaporator 160 in the winter even at a low temperature of the evaporator, It is possible to perform a heating function, and a high COP efficiency of 3.0 to 4.0 can be obtained.

2 is a view schematically showing a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant including an ejector according to another embodiment.

Referring to FIG. 2, a multi-stage heat pump 200 having a two-stage expansion structure using CO ₂ refrigerant including an ejector according to another embodiment includes a compressor 210, a condenser 220, a first expansion device 240, A liquid crystal separator 250, a second expansion device 241, a third expansion device 242, an evaporator 260, and an ejector 270 or an EPR (evaporation pressure control device). The multi-stage heat pump 200 having the two-stage expansion structure using the CO ₂ refrigerant including the ejector according to the embodiment may further include at least one of the first cooling air 230 and the second cooling air 231 .

Here, the multi-stage heat pump 200 having the two-stage expansion structure using the CO ₂ refrigerant including the ejector according to another embodiment has the two-stage expansion structure using the CO ₂ refrigerant according to the embodiment described with reference to FIG. 1 The description of the structure of the multi-stage heat pump partially overlapping with that of the multi-stage heat pump will be omitted, and different structures will be mainly described.

The ejector 270 can correct the differential pressure difference between the refrigerant discharged from the second cold air 231 and the refrigerant discharged from the evaporator 260 and then introduce the refrigerant whose pressure difference has been corrected into the compressor 210 have.

In this way, in the multi-stage heat pump 200 having the two-stage expansion structure using the CO ₂ refrigerant including the ejector or the EPR according to another embodiment, the ejector 270 can be additionally installed in order to further lower the evaporator temperature. The ejector 270 can be used to correct a small pressure difference when the pressures are different from each other.

For example, in order to lower the evaporator temperature to below -20 캜, a pressure difference occurs in which the low-pressure side pressure is lower than 8 to 12 bar which is a CO ₂ gas pressure of 6 bar, so that the ejector 270 or the EPR can be applied for suction.

In this way, the ejector 270 is intended to correct a small pressure difference within 5 bar, which is significantly different from the function of the main driving high pressure ejector of the refrigerator, which is applied to the conventional ejector-applied CO ₂ heat pump system.

3 is a view for explaining a two-stage expansion process of a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment.

Referring to FIG. 3A, a multi-stage heat pump 300 having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment includes a compressor 310, a condenser 320, The first expansion device 340 includes the cold air 330, the first expansion device 340, the liquid separator 350, the second expansion device 341, the third expansion device 342, the second example cooling device 331, and the evaporator 360 Lt; / RTI >

FIG. 3B shows the ph diagram in the case where the ratio of the mixed refrigerant of CO ₂ and R 143a is 85:15.

As shown in FIG. 3B, refrigerant CO ₂ gas at the pressure of 70 bar and 40 ° C (point 1) in the condenser and other refrigerant having a low boiling point may exist in the gas state above the critical point.

The gas at point 1 is sub-cooled to point 2 by the amount of energy at points 11 to 12, which is the outlet gas of the evaporator 360 at the first example cooler 330. [

The subcooled gas (point 2) expands (point 3) to a medium pressure 25 bar and is collected in the liquid separator 350. The enthalpy of liquid in the liquid separator 350 is point 7, which is a saturated liquid, and the gas is point 4, which is a saturated gas.

The CO ₂ gas at point 4 expands to point 5, which is the final pressure of 12 bar, to become a temperature -13 ° C gas, then subcooling point 4 to the point 8 in the second example cool air 331, It becomes point 6.

The liquid at the subcooled point 8 is expanded at the second expansion device 342 to the final pressure 12 bar to become the point 9, and is vaporized by the outside air heat to become the saturated gas at the point 10.

The gas at the point 11 is mixed with the superheated gas at the point 6, becomes the gas at the point 11, and then is taken to the point 12 from the first cool air 330 to be sucked into the compressor 310.

And is compressed by the isentropic process from the compressor 310 to 70 bar to become the gas at the temperature of the point 13 at 130 ° C. This gas acts as a heat pump in the condenser for hot water or heating and becomes cold gas at point 1. Here, the other refrigerant refers to a refrigerant other than CO ₂ , and may be composed of at least one refrigerant. For example, various alternative refrigerants such as R143A, R410A, R152A, R32, R717 and R290 may be used as other refrigerants.

Unlike a conventional automatic multi-stage system, a portion of the condensation process after the first expansion device is decreased when the pressure across the other low boiling point refrigerant and the CO ₂ is in a liquid, and the remaining CO ₂ may be obtained from the reservoir with a gas separator.

The gas CO ₂ at high pressure can expand the pressure to about 8 to 12 bar to make the liquid at -20 ° C. gas and subcooled the liquid of the liquid separator at the second example cold air.

First example: It is possible to precool about 5 캜 in cold air. For example, the evaporator outlet temperature may be heated by 5 degrees and the condenser temperature may be decreased by 5 degrees. Here, the first precooler is a facility for improving the performance and may be omitted.

In the following, performance evaluation of a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment can be confirmed.

For example, the thermodynamic properties (enthalpy, entropy, pressure, temperature, etc.) of the refrigerant and the performance evaluation can be calculated using engineering equation solver (EES) software or the like.

Table 1 shows the case where only CO ₂ is applied to the existing CO ₂ heat pump as refrigerant.

[Table 1]

As shown in Table 1, COP (coefficient of performance) indicating the refrigerating cycle efficiency of the heat pump according to the high and low pressures can be confirmed when only CO ₂ is applied to the existing CO ₂ heat pump.

Here, the COP (coefficient of performance) indicating the refrigeration cycle efficiency of the heat pump can be calculated by dividing the amount of heat radiation in the condenser by the amount of compression of the compressor in the high temperature and the low temperature.

For example, COP = Qc / W of the heat pump and COP = Qe / W of the refrigerating device. At this time, the heat pump represents the condenser heat quantity / compression quantity, and the refrigerating device can represent the evaporator suction quantity / compression quantity.

Table 2 shows a case where CO ₂ and another refrigerant are mixed with a refrigerant in a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment.

[Table 2]

Referring to Table 2, CO ₂ and R 143 a are applied as mixed refrigerant to a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment, in which the high pressure, intermediate pressure, and low pressure The COP (coefficient of performance) indicating the refrigerating cycle efficiency of the heat pump according to the present invention can be confirmed.

When referring to Table 1 and Table 2, comparing the case where the high pressure / low pressure of 70bar / 12bar, COP of the conventional CO ₂ heat pumps are multi-stage having a two-stage expansion structure using a CO ₂ refrigerant according to 1.3725, while the embodiment The heat pump is improved by 245% to 3.3635 even at low pressure, and it is confirmed that the COP becomes 3.3606 even with the short expansion without the two-stage expansion.

Therefore, the multi-stage heat pump having a two-stage expansion structure using a CO ₂ refrigerant according to the embodiment has a COP increase effect than using CO ₂ refrigerant and the other only by applying the CO ₂ to the mixed refrigerant.

FIG. 4 is a diagram illustrating a COP change according to an intermediate pressure of a two-stage expansion according to an embodiment. FIG.

Referring to FIG. 4, when CO ₂ and R143a are mixed in 70:30 as a mixed refrigerant in a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment, when the intermediate expansion pressure of the second stage expansion is 25 bar The maximum COP can be obtained.

Therefore, when CO ₂ and other refrigerant are used as the mixed refrigerant in the multi-stage heat pump having the two-stage expansion structure using the CO ₂ refrigerant according to the embodiment, the maximum COP can be obtained at the intermediate pressure of the two-stage expansion.

In addition, when a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to an embodiment is applied as a heat pump, the evaporation temperature of the evaporator as an outdoor unit is low to -10 to -15 ° C., Can function as a heating and hot water heat pump without. Thus, the energy saving effect can be obtained by improving the COP and decreasing the compression power.

5 is a flowchart showing a circulation method of a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to another embodiment.

Referring to FIG. 5, in a circulation method of a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to another embodiment, a refrigerant in which carbon dioxide (CO ₂ ) discharged from a compressor and at least one other refrigerant are mixed (510) condensing in the condenser, expanding the refrigerant passing through the condenser by using a first expansion device to reduce the pressure (520), cooling the refrigerant passing through the first expansion device to a low boiling point another refrigerant and the carbon dioxide separation part of the (CO ₂₎ in liquid, and the remaining carbon dioxide step 530, the gas phase of the discharged high-pressure in the reservoir separator carbon dioxide (CO ₂₎ separating the (CO ₂₎ in a gaseous second when expanded by using the expansion device cools the part of step 540, the liquid refrigerant and the other carbon dioxide discharged from the separator reservoir (CO ₂₎ for moving the second group precooling by reducing the pressure in the second example Frost After the third to the expansion using the expansion device to lower the discharge to the evaporator pressure and, passing from the evaporator other refrigerants as carbon dioxide (CO ₂₎ step 550 of vaporizing by some heat air in, and the second precooling a group CO ( CO ₂ ) and the other refrigerant vaporized by the evaporator and a portion of the carbon dioxide (CO ₂ ) are exchanged with each other and then transferred to the compressor (step 560).

According to the embodiments, by providing an expansion device between the condenser and the liquid-liquid separator to expand the refrigerant as a working oil, a low-temperature refrigerant liquid that can be easily evaporated even in low outside temperatures in winter can be obtained. In addition, CO ₂ can be increased to 50 to 90% by using CO ₂ and HFC mixed refrigerants having different boiling points, so that it is possible to apply a lower pressure on the high pressure side, thereby providing the effect of hot water for heating Energy can be saved.

Hereinafter, a circulation method of a multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant according to another embodiment will be described in more detail with an example.

The circulation method of the multi-stage heat pump having the two-stage expansion structure using the CO ₂ refrigerant according to another embodiment is more specifically described using the multi-stage heat pump having the two-stage expansion structure using the CO ₂ refrigerant described in FIGS. 1 to 4 . Here, the multi-stage heat pump having a two-stage expansion structure using CO ₂ refrigerant may include a compressor, a condenser, a first expansion device, a liquid separator, a second expansion device, a third expansion device, and an evaporator. Also, according to the embodiment, the multi-stage heat pump having the two-stage expansion structure using the CO ₂ refrigerant may further include at least one of the first example cooler, the second cooler, and the ejector or EPR. On the other hand, the circulation method of the multi-stage heat pump having a two-stage expansion structure using a CO ₂ refrigerant can be shown how a refrigerant is circulated, including the CO ₂ refrigerant as the working fluid.

In step 510, the condenser may condense refrigerant in which CO ₂ discharged from the compressor and at least one or more other refrigerants are mixed.

Here, the refrigerant may be a mixed refrigerant in which carbon dioxide (CO ₂ ) and at least one or more other refrigerants are mixed.

More specifically, the refrigerant is composed of carbon dioxide (CO ₂ ) having different boiling points and HFC-based mixed refrigerant, thereby increasing the ratio of CO ₂ to 50% to 90%, thereby lowering the pressure at high pressure to provide hot water for heating.

In step 520, the first expansion device may inflate the refrigerant that has passed through the condenser to reduce the pressure.

As described above, the refrigerant expands from the high pressure to the intermediate pressure by the first expansion device, and is expanded from the intermediate pressure to the low pressure by the expansion device, so that the two-stage expansion process can be performed.

In step 530, the liquid separator separates the refrigerant having passed through the first expansion device from other refrigerant having a low boiling point and a part of CO ₂ into liquid, and separates remaining CO ₂ into gas.

In step 540, the second expansion device may expand the high pressure gaseous CO ₂ discharged from the liquid-liquid separator to lower the pressure and transfer it to the second precooler.

In step 550, the third expansion device may cool a portion of CO ₂ and other refrigerant in a liquid state, which is discharged from the liquid-liquid separator, in the second pre-cooler and then expand it to lower the pressure and discharge it to the evaporator.

Then, other refrigerant and a part of CO _{2 in} the evaporator can be vaporized by the outside air heat.

In step 560, the CO ₂ passed through the second quencher and the other refrigerant vaporized by the evaporator and a portion of CO ₂ can be exchanged with each other and moved to the compressor.

At this time, the pressure difference between the refrigerant discharged from the second cold air and the refrigerant discharged from the evaporator may be corrected using an ejector or an EPR (evaporation pressure control device), and the refrigerant may be moved to the compressor.

Passed through the first quencher, cooled, and then moved to the compressor.

In the first precooler, the refrigerant vaporized in the evaporator and the CO ₂ passing through the condenser are heat-exchanged with each other, so that the low-temperature gas sucked into the compressor further lowers the temperature of the condenser exhaust gas.

As described above, according to the embodiments, an expansion device is installed between the condenser and the liquid-liquid separator to expand the refrigerant as a working oil, and CO ₂ is increased to 50 to 90% by using CO ₂ and HFC mixed refrigerants having different boiling points , Since the pressure of the low-pressure evaporator generated from the heat pump using the carbon dioxide as the refrigerant is high, the evaporator vaporization temperature of about 0 ° C is obtained. Therefore, if the outdoor air temperature is low in winter, the refrigerant vaporization of the outdoor unit (evaporator) Can be solved.

Accordingly, by providing a heat pump that uses eco-friendly carbon dioxide as a refrigerant, it can contribute to reduction of greenhouse gas emissions by replacing a heat pump using a refrigerant that adversely affects the ozone layer.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Or even if it is an HCFC-based refrigerant that affects ozone instead of HFC or is replaced or replaced by ammonia (R717), propane (R290) or the like as an equivalent or equivalent refrigerant.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (10)

In a multi-stage heat pump having a two-stage expansion structure,
A compressor for compressing a mixed refrigerant composed of carbon dioxide (CO ₂ ) having different boiling points and at least one or more other refrigerants;
A condenser disposed next to the compressor for condensing the refrigerant passing through the compressor;
A first expansion device disposed downstream of the condenser, the first expansion device expanding the refrigerant passing through the condenser to lower the pressure;
And a second expansion device disposed downstream of the first expansion device to separate a part of the other refrigerant having a low boiling point and a part of the carbon dioxide (CO ₂ ) into a liquid as the pressure of the refrigerant passing through the condenser is lowered by the first expansion device A liquid separator for separating the remainder of the carbon dioxide (CO ₂ ) into gas;
A second cold air cooler disposed next to the liquid cooler separator to cool the coolant having passed through the liquid cooler separator;
A second expansion device disposed between the liquid crystal separator and the second preliminary cooling device for expanding the gaseous carbon dioxide (CO ₂ ) discharged from the liquid crystal separator to lower the pressure;
And a second precooler disposed between the second precooler and the evaporator for expanding the other refrigerant in the liquid state and a part of the carbon dioxide (CO ₂ ) To the third expansion device; And
A first example cooler disposed between the condenser and the first expansion device and connected to the discharge port of the evaporator,
Lt; / RTI >
The mixed refrigerant may include,
A heat pump function using the heat of the condenser as hot water for heating and a low temperature of the evaporator can be applied to a refrigeration apparatus,
Wherein the evaporator comprises:
Stage expansion process in which the refrigerant is inflated from the high pressure to the intermediate pressure by the first expansion device and then expanded from the intermediate pressure to the low pressure by the third expansion device so as to perform the heating function even when the outdoor air temperature is low The carried refrigerant is introduced and the vaporization temperature is lowered,
The refrigerant vaporized in the evaporator and the carbon dioxide (CO ₂ ) passing through the second expansion device are mixed with each other, and then the refrigerant is heat-exchanged with the refrigerant passing through the condenser in the first preliminary cooling air, cooled and then moved to the compressor
Stage expansion mechanism. delete The method according to claim 1,
The mixed refrigerant may include,
(CO ₂ ) and HFC-based mixed refrigerant having different boiling points, and the ratio of the carbon dioxide (CO ₂ ) is increased from 50% to 90% to lower the pressure at the high pressure to provide hot water for heating and hot air
Stage expansion mechanism. delete delete delete delete The method according to claim 1,
An ejector or an evaporation pressure control device (EPR) for correcting different pressure differences between the refrigerant discharged from the second cold air and the refrigerant discharged from the evaporator and sending the corrected differential pressure to the compressor,
Stage expansion mechanism. delete delete

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