KR100779069B1 - Air conditioner utilizing carbon dioxide and mothod of control the same - Google Patents

Abstract

According to the present invention, an air conditioner using carbon dioxide includes a variable capacity compressor, a gas cooler for cooling carbon dioxide gas discharged from the discharge port of the compressor, and an evaporator for expanding the refrigerant cooled by the gas cooler to absorb latent heat of evaporation. And a connection tube constituting a closed circuit by connecting the compressor, the gas cooler and the evaporator, and a buffer vessel and a variable expansion valve installed in the connection pipe between the gas cooler and the evaporator, and the temperature of the outside air introduced into the gas cooler. Is sensed by the first sensor and converted into an optimal cooling pressure in accordance with the outside temperature in the controller to control the gas coolie pressure by controlling the compression ratio using the variable characteristics of the variable displacement compressor, the outlet temperature of the evaporator and evaporation Variable expansion valve by sensing the temperature difference by the second sensor and comparing it with the set reference superheat Control means for controlling the flow rate of the refrigerant by adjusting the opening degree of the.

Description

Air conditioner utilizing carbon dioxide and mothod of control the same

1 and 2 is a diagram showing a frozen P-H diagram of carbon dioxide,

3 is a view schematically showing an air conditioner according to the present invention;

4 is a block diagram illustrating the control of the pressure of the gas cooler according to the present invention;

5 is a block diagram illustrating controlling the degree of superheat of an evaporator.

The present invention relates to an air conditioner, and more particularly, to an air conditioner using carbon dioxide as a heat exchange medium and a control method thereof.

As environmental issues become a global concern due to global warming, automobile companies and automobile related organizations around the world are developing pollution-free cars to replace gasoline cars, which are considered to be the leading causes of pollution. In addition to such a trend, in the air conditioner for automobiles, the use of Freon-based heat exchange media that causes global warming is expanding, and carbon dioxide is drawing attention as being able to replace the Freon-based heat exchange media.

This is because the global warming index (GWP) is about 1,300 times higher than that of carbon dioxide in the case of R134a, which is currently used in automobile air conditioners.

The carbon dioxide used as the heat exchange medium of the air conditioner has a low operating compression ratio, which has good compression efficiency, and the gas cooler has a smaller temperature approach (temperature inlet temperature of the secondary fluid-outlet temperature difference of the refrigerant) than the conventional refrigerant. In the case of having a heat transfer characteristic is excellent enough to lower the temperature of the refrigerant to the temperature of the incoming air.

In addition, the thermodynamic properties are excellent, the volumetric cooling capacity of carbon dioxide (kJ / ㎥; capacity volume ratio = latent heat of evaporation x gas density) is 7 to 8 times compared to R134a. Therefore, the capacity of the compressor can be reduced, and the specific heat is large and the liquid viscosity is low to show excellent vaporization characteristics in the evaporator.

However, carbon dioxide has a lower critical temperature and a higher evaporation pressure than conventional refrigerant R134a. Therefore, the CO2 refrigeration cycle is a supercritical pressure cycle that exceeds the critical pressure, so each component must be redesigned to withstand high pressures, with 6 to 8 times higher evaporation and gas cooling pressures than conventional R134a refrigeration cycles.

1 shows a refrigeration cycle of carbon dioxide, which is such a heat exchange medium.

As shown, the lower the temperature of the heat exchange medium carbon dioxide at the outlet side of the gas cooler (corresponding to the existing air conditioning system) at the gas cooling pressure of P1 (90 bar), the better the freezing performance. That is, when the outlet temperature of the gas cooler is t1, the refrigerating cycle has a trajectory of 1-2-3-4-1, and the freezing effect at this time is Q1. However, if the temperature of the gas cooler outlet is t2 lower than t1, the freezing cycle draws a trace of 1-2-3'-4'-1, and the freezing effect is increased to Q2 which is larger than Q1, thereby increasing the freezing effect.

For this reason, in order to forcibly lower the temperature of the gas cooler outlet, an internal heat exchanger is installed to exchange heat with the refrigerant at the outlet of the low temperature evaporator.

In the carbon dioxide refrigeration cycle, when the outlet temperature of the gas cooler is constant at t1 and the carbon dioxide cooling pressure of the gas cooler is P1, the cycle is 1-2-3-4-1 and the refrigeration effect is Q1, but the cooling pressure of carbon dioxide is reduced. When P2 is lower than P1, the cycle becomes 1-2 "-3" -4 "-1, and the freezing effect is greatly reduced to Q3, and it can be seen that the performance difference increases with the change of pressure under the same temperature condition.

As can be seen from the refrigeration cycle of carbon dioxide as described above, in the air conditioner using carbon dioxide as a heat exchange medium, the outlet temperature of the gas cooler changes according to the outside temperature so that temperature control is impossible, and the refrigeration of the air conditioning system In order to optimally control the efficiency, the cooling efficiency can be optimized by controlling the gas cooling pressure.

In more detail, since there is a gas cooling pressure for optimizing the freezing efficiency according to the outside temperature, it can be controlled by using a predetermined control logic. In most cases, as the ambient temperature rises, the optimized gas cooling pressure also rises, but excessive increases in gas cooling pressure can reduce system performance. For example, as shown in FIG. 2, as the distance away from the critical point of the Ph diagram increases, the isentropy line increases gradually but the isothermal line increases rapidly, so the gas cooling pressure excessively increases the cycle abcda. The freezing effect is increased from Q4 to Q5, while the required power of the compressor is excessively increased from W1 to W2, and the overall refrigeration efficiency is drastically lowered. Therefore, in the air conditioning system using carbon dioxide, the cooling pressure of carbon dioxide should be controlled so that the optimum refrigeration efficiency can be exerted according to the change of the outside temperature.

The present invention is to solve the above problems by maximizing the refrigeration efficiency by controlling the gas cooling pressure of the carbon dioxide by using the variable characteristics of the variable capacity compressor in accordance with the ambient temperature introduced into the gas cooler, and also adjust the opening degree of the variable expansion valve It is an object of the present invention to provide an air conditioner and a control method using carbon dioxide to optimize the performance of the evaporator by controlling the flow rate of the refrigerant on the evaporator to have an appropriate superheat degree.

In order to achieve the above object, an air conditioner using carbon dioxide of the present invention includes a variable capacity compressor, a gas cooler for cooling the carbon dioxide discharged from the discharge port of the compressor, and expands the carbon dioxide cooled by the gas cooler to reduce the latent heat of evaporation. And a variable expansion valve installed at a connection pipe connecting the compressor and the gas cooler and the evaporator to form a closed circuit, and a connection pipe between the gas cooler and the evaporator.

The first sensor senses the temperature of the outside air flowing into the gas cooler, and adjusts the compression ratio of the variable displacement compressor to achieve the target gas cooling pressure corresponding to the outside temperature. The second sensor measures the difference between the outlet temperature of the evaporator and the evaporation temperature. And controlling means for optimizing the evaporation performance of the evaporator by controlling the amount of refrigerant to have a predetermined degree of superheat by controlling the opening degree of the variable expansion valve in comparison with the set reference superheat degree.

In the present invention, when the optimal gas cooling pressure is P and A1 and A2 are constants greater than 0, the optimum gas cooling pressure is expressed by the formula P (bar) = A1 x ambient temperature (° C) + A2. Is calculated. Here, the A1 value is 1 to 10, and the A2 value is 10 to 50. And a buffer vessel may be further installed in the connection pipe between the gas cooler and the evaporator.

A control method of an air conditioner using carbon dioxide of the present invention for achieving the above object is a variable capacity compressor, a gas cooler for cooling the carbon dioxide discharged from the discharge port of the compressor, and expands the carbon dioxide cooled by the gas cooler And an evaporator for absorbing latent heat of evaporation, a connecting pipe constituting a closed circuit by connecting the compressor, the gas cooler and the evaporator, and a variable expansion valve installed in the connection pipe between the gas cooler and the evaporator. In the control method of,

A first step of sensing a temperature of outside air flowing into the gas cooler and calculating a target gas cooling pressure by a controller;

A second step of maintaining a pressure in the gas cooler at the target gas cooling pressure by controlling a compression ratio by using a variable characteristic of the variable displacement compressor using the calculated cooling pressure;

And a third step of controlling the refrigerant flow rate by controlling the opening degree of the variable expansion valve so that the evaporator has a reference superheat degree by comparing the outlet temperature and the evaporation temperature difference of the evaporator and then setting the reference superheat degree.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 shows an embodiment of an air conditioner using carbon dioxide according to the present invention.

As illustrated, the air conditioner includes a variable capacity compressor 11, a gas cooler 13 connected by the variable capacity compressor 11, and a first connection pipe 12, and the gas cooler 13 and the first air conditioner. An evaporator 15 connected by two connecting pipes 14, a variable expansion valve 16 installed in the second connecting pipe 14 adjacent to the evaporator 15, an outlet side of the evaporator 15, It comprises a third connecting pipe 17 for connecting the inlet of the variable displacement compressor (11). An internal heat exchanger 18 for exchanging the gas cooler outlet and the evaporator outlet to forcibly lower the temperature of the gas cooler outlet is included. Here, the internal heat exchanger 18 includes an accumulator formed integrally therewith, but is not limited thereto. The accumulator may be installed separately from the internal heat exchanger. The variable capacity compressor 11 is controlled using the rotational speed of the drive motor or in the case of a swash plate type compressor to change the inclination angle of the swash plate to control the discharge amount, or bypass the suction side and the discharge side to increase the pressure of the crankcase. Any structure can be used as long as the pumping capacity can be varied, such as an adjustable type.

The variable expansion valve 16 may be an electronic expansion valve or a solenoid type electronic expansion valve with a stepping motor.

In addition, the air conditioner is provided with a control means 20, the control means 20 by the first sensor 21 and the first sensor 21 to determine the temperature of the outside air flowing into the gas cooler (13) And a controller 22 having a control logic for calculating and controlling an optimum target cooling pressure in the gas cooler 13 according to the sensed outside temperature.

The optimum target gas cooling pressure can be calculated by the following equation (1).

[Equation]

P (bar) = A1 x Ambient Temperature (℃) + A2

In the above equation, P is an optimal target gas cooling pressure, and A1 and A2 are constants greater than 0, wherein the A1 value is 1 to 10 and the A2 value is 10 to 50.

An outlet side of the gas cooler 13 is further provided with a pressure sensor 25 for sensing the gas cooling pressure and providing pressure information to the controller. And the control means 20 are respectively installed to detect the evaporation temperature and the outlet temperature of the evaporator 15 in order to control the evaporation pressure of the evaporator 15 compared to the reference superheat in the controller 22 Two second sensors 23. In the above-described configuration, the internal heat exchanger 18 serves to mutually heat exchange the carbon dioxide passed through the evaporator and the carbon dioxide cooled by the gas cooler to forcibly lower the refrigerant temperature at the outlet of the gas cooler, and the buffer vessel 24 ) Is a buffer container for balancing the optimum refrigerant flow rate on the evaporator side with the optimum refrigerant content on the gas cooler side.

The control method for controlling the air conditioning system configured as described above is based on the equation in the controller 22 by sensing the temperature of the outside air flowing into the gas cooler 13 as shown in FIG. The first step of calculating the target gas cooling pressure, and the compression ratio is controlled using the variable characteristics of the variable displacement compressor using the calculated cooling pressure to maintain the pressure in the gas cooler 13 at the pressure calculated in the first step It includes a second step. As shown in FIG. 5, the flow rate of the refrigerant is controlled by adjusting the opening degree of the variable expansion valve such that the evaporator 15 has a reference superheat degree by comparing the outlet temperature and the evaporation temperature difference of the evaporator 15 with the reference superheat degree set. It includes a third step of controlling. At this time, the gas expansion pressure is controlled by the variable capacity compressor such that the variable expansion valve adjusts the refrigerant flow rate so that the evaporator side has the optimum superheat degree, and the gas cooler side is the optimum cooling pressure. The buffer vessel 24 performs the function of storing the fluctuating refrigerant difference in the system to balance the refrigerant on the gas cooler side and the evaporator side.

The operation of the air conditioner for automobiles configured as described above and the control method will be described in more detail with reference to FIGS. 3 and 4 and 5 as follows.

The air conditioner using carbon dioxide as a heat exchange medium compresses the carbon dioxide evaporated from the evaporator 15 into the gas cooler 13 using a compressor. In this state, as shown in FIG. 4, the first sensor 21 of the control means 20 senses the outside air temperature passing through the gas cooler 13. Based on this temperature, the optimized gas cooling pressure is calculated by the control logic of the equation in the controller 22. This internal pressure calculates the cooling pressure at which the refrigeration efficiency is optimized as described in FIG. When the cooling pressure is calculated as described above, the pressure inside the gas cooler 13 can be maintained by changing the compression ratio by using the variable characteristics of the variable displacement compressor by the controller 22. At this time, the pressure sensor 25 installed at the outlet of the gas cooler 13 compares the outlet pressure of the gas cooler with the set pressure and maintains the optimum pressure state of the gas cooler.

When the degree of superheat increases excessively, the area occupied by the gas in the evaporator becomes excessively large compared to the area occupied by the liquid, so that the evaporator inlet temperature is low, but the evaporator outlet temperature is excessively increased and the overall evaporator surface temperature is increased. Is lowered. In addition, when there is almost no superheat, the flow rate of the refrigerant flowing inside the evaporator is high, but the overall evaporation pressure and temperature increase, which also increases the temperature of the evaporator surface, thereby degrading performance. Therefore, maintaining adequate superheat is a way to optimize evaporator performance. In order to use this principle, as shown in FIG. 5, the outlet temperature and the evaporation temperature of the evaporator 15 are sensed by two second sensors 23, and a predetermined reference superheat degree (about 5 ° C.) in the controller 22 is detected. After comparing with), the degree of superheat of the evaporator is controlled by controlling the refrigerant flow rate by adjusting the opening degree of the variable displacement expansion valve.

In the air conditioner and the control method using carbon dioxide according to the present invention by controlling the carbon dioxide cooling pressure by the gas cooler based on the outside air and controlling the superheat degree of the evaporator refrigeration efficiency and refrigeration within a range that does not increase the work amount of the compressor This has the advantage of significantly improving performance.

Although the present invention has been described with reference to the embodiments illustrated in the accompanying drawings, these are merely exemplary, and those skilled in the art may understand that various modifications and equivalent embodiments are possible. will be. Therefore, the true scope of protection of the present invention should be defined only by the technical spirit of the claims.

Claims (5)

A variable capacity compressor, a gas cooler for cooling carbon dioxide discharged from the discharge port of the compressor, an evaporator for expanding the refrigerant cooled by the gas cooler to absorb latent heat of evaporation, and connecting the compressor, the gas cooler, and the evaporator to a closed circuit And a variable expansion valve installed at a connection pipe between the gas cooler and the evaporator, and an internal heat exchanger to heat exchange the gas cooler outlet and the evaporator outlet. The first sensor senses the temperature of the outside air flowing into the gas cooler, adjusts the compression ratio of the variable displacement compressor to a target gas cooler pressure corresponding to the temperature of the outside air, and adjusts the difference between the outlet temperature of the evaporator and the evaporation temperature. And a control means for detecting the flow rate of the refrigerant by detecting the sensor and adjusting the opening degree of the variable expansion valve in comparison with the set reference superheat. delete The method of claim 1, And an accumulator integrated with an internal heat exchanger installed between the evaporator and the variable capacity compressor. The method of claim 1, And a buffer vessel installed at the connection pipe between the gas cooler and the evaporator. A variable capacity compressor, a gas cooler for cooling carbon dioxide discharged from the discharge port of the compressor, an evaporator for expanding the refrigerant cooled by the gas cooler to absorb latent heat of evaporation, and connecting the compressor, the gas cooler, and the evaporator to a closed circuit For a motor vehicle comprising a connecting pipe constituting a, a variable expansion valve installed in the connection pipe between the gas cooler and the evaporator, and an internal heat exchanger to heat exchange the gas cooler outlet and the inlet of the evaporator, In the control method, A first step of sensing a temperature of outside air flowing into the gas cooler and calculating a target gas cooling pressure by a controller; A second step of maintaining the pressure in the gas cooler as the target gas cooling pressure by controlling the compression ratio using the variable characteristics of the variable displacement compressor using the calculated cooling pressure; And a third step of controlling the refrigerant flow rate by sensing the difference between the outlet temperature and the evaporation temperature of the evaporator and comparing the set reference superheat with the evaporator having a reference superheat. Control method of the air conditioner using.

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