JP2002156163A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air conditioner the cooling power of which can be improved by lowering the enthalpy of a refrigerant before the refrigerant flows in an evaporator. SOLUTION: This air conditioner is provided with a compressor 1, a gas cooler 2 which condenses a CO2 refrigerant compressed by means of the compressor 1, and a pressure reducing means which reduces the pressure of the CO2 refrigerant condensed in the cooler 2. The air conditioner is also provided with the evaporator 4 which evaporates the CO2 refrigerant reduced in pressure by means of the pressure reducing means. In this air conditioner, an expander 3 which aggressively reduces the pressure of the CO2 refrigerant by expanding the refrigerant is used as the pressure reducing means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air conditioner using carbon dioxide as a refrigerant instead of a chlorofluorocarbon refrigerant.

[0002]

2. Description of the Related Art In recent years, interest in preserving the global environment has been increasing.
It is feared that a CFC refrigerant such as 134a promotes global warming. For this reason, research has been conducted on an air conditioner using a substance originally existing in the natural world, that is, a so-called natural refrigerant, as a substance replacing the chlorofluorocarbon refrigerant.

As a candidate for such an alternative CFC, carbon dioxide (hereinafter referred to as CO ₂ ) has been receiving attention. CO ₂
Is highly valued not only for its impact on global warming than fluorocarbons, but also for its non-flammability and basically harmlessness to the human body.

[0004] From such a background, a vapor compression refrigeration cycle using carbon dioxide (hereinafter referred to as a CO ₂ refrigeration cycle) has been proposed. The operation of this CO ₂ refrigeration cycle is the same as that of a conventional vapor compression refrigeration cycle using chlorofluorocarbon. That is, as shown in the Mollier diagram (pressure-enthalpy diagram) of FIG.
₂ (Gas state) is compressed by a compressor (A-B) to obtain a high temperature and high pressure gas phase state. Next, high-temperature and high-pressure CO ₂ (gas phase state) is condensed by a condenser (B-C) to obtain a high-temperature and high-pressure gas-liquid two-phase state. Next, the high-temperature and high-pressure CO ₂ (gas-liquid two-phase state) is depressurized by a pressure reducer (C-D) to obtain a low-temperature and low-pressure gas-liquid two-phase state. Next, low-temperature low-pressure CO ₂ (gas-liquid two-phase state) CO ₂ is evaporated by an evaporator (DA), and latent heat of evaporation generated at that time is taken from an external fluid such as air to cool the external fluid.

However, the critical temperature of CO ₂ is about 31
Since the temperature is lower than C ° and CFCs, when the outside air temperature is high, such as in summer, the temperature of CO ₂ on the condenser side becomes higher than the critical point temperature of CO ₂ . That is, CO ₂ does not condense on the condenser outlet side (the line segment BC does not cross the saturated liquid line SL).

[0006]

In the above-mentioned CO ₂ refrigeration cycle, for example, when the CO ₂ refrigeration cycle is applied to an air conditioner for an automobile, a sufficient discharge flow rate is required because the rotation speed of the compressor is reduced during idling. Therefore, there is a problem that a sufficient cooling capacity cannot be obtained because it is difficult to obtain the enthalpy difference.

The present invention has been made in view of the above circumstances, and has as its object to provide an air conditioner that can increase the cooling capacity by reducing the enthalpy before the refrigerant flows into the evaporator. I have.

[0008]

As means for solving the above-mentioned problems, an air conditioner having the following configuration is employed. That is, the air conditioner according to claim 1 of the present invention is a compressor for compressing a refrigerant, a condenser for condensing the refrigerant compressed by the compressor, and depressurizing the refrigerant condensed in the condenser. Decompression means, comprising an evaporator for evaporating the refrigerant decompressed by the decompression means,
An air conditioner comprising a refrigeration cycle using carbon dioxide as the refrigerant, characterized in that an expander for positively expanding and decompressing the refrigerant is used as the decompression means.

In the air conditioner according to the present invention, when the entropy is changed to be substantially constant by expanding and reducing the pressure of the refrigerant passing through the condenser by the expander, the entropy at the stage before flowing into the evaporator is increased. descend. Thereby, the enthalpy change amount in the evaporator becomes larger than before.

[0010] The air conditioner according to the second aspect is the first aspect.
In the air conditioner described above, a scroll compressor is used as the compressor, and a turbine expander is used as the pressure reducing means, and both are driven by the same drive source.

In the air conditioner according to the present invention, by driving the scroll compressor and the turbine expander with the same drive source, the structure of the device can be simplified and the power loss during operation can be reduced. .

The air conditioner according to the third aspect is the first aspect.
In the air conditioner described above, a scroll compressor is used as the compressor, and a scroll expander is used as the pressure reducing means, and both are driven by the same drive source.

Also in the air conditioner according to the present invention, by driving the scroll compressor and the scroll expander with the same drive source, the structure of the device can be simplified and the power loss during operation can be reduced. .

[0014] The air conditioner according to the fourth aspect is the second aspect.
Or the air conditioner according to 3, wherein a throttle means is provided between the condenser and the expander.

When the compressor and the expander are driven by the same drive source, it is necessary to make the discharge flow rate of the compressor equal to the suction flow rate of the expander, and two flow rates are set at the operating point set at the time of design. Is determined. However, in actual operation, when the operating point shifts, the two flow rates do not initially match, and thereafter the operating point settles where the flow rates match, and this operating point becomes the design operating point. Hardly ever. That is, the operating points of the two, the cooling capacity of the air conditioner, and the coefficient of performance (COP) are determined depending on the situation at that time.

Therefore, in the air conditioner according to the present invention, by providing a throttling means between the condenser and the expander, the refrigerant is appropriately depressurized at the stage preceding the expander, and the suction flow rate is changed. And the suction flow rate of the expander become equal. As a result, the operating point is adjusted to the designed point.

The air conditioner according to the fifth aspect is the first aspect.
In the air conditioner described above, the drive of the expander is individually controlled independently of the compressor.

In the air conditioner according to the present invention, by independently controlling the drive of the expander independently of the compressor, the expansion / reduction pressure of the refrigerant can be varied without affecting the drive of the compressor. Will be able to do it.

The air conditioner according to the sixth aspect is the fifth aspect.
The air conditioner according to claim 1, wherein a degree of superheat of the refrigerant between the evaporator and the compressor is measured, and driving of the expander is controlled according to the degree of superheat.

In the air conditioner according to the present invention, the drive of the expander is controlled in accordance with the degree of superheat of the refrigerant between the evaporator and the compressor, so that the desired degree of superheat cannot be obtained. For example, by driving the expander to change the discharge flow rate of the refrigerant, a desired cooling capacity can be obtained.

[0021] The air conditioner according to the seventh aspect is the fifth aspect.
In the air conditioner described above, the drive of the expander is controlled according to a low pressure value of the refrigerant in the refrigeration cycle.

In the air conditioner according to the present invention, the drive of the expander is controlled according to the low pressure value of the refrigerant,
If a desired low pressure value cannot be obtained, a desired cooling capacity can be obtained by driving the expander to change the discharge flow rate of the refrigerant.

According to an eighth aspect of the present invention, in the air conditioner of the fifth, sixth or seventh aspect, the driving of the compressor is controlled in accordance with a high pressure value of the refrigerant in the refrigeration cycle. Features.

In the air conditioner according to the present invention, the degree of superheat of the refrigerant near the outlet of the evaporator, the degree of superheat of the refrigerant near the suction port of the compressor, or the low pressure value of the refrigerant depends on either of By controlling the drive, and controlling the drive of the compressor according to the high pressure value of the refrigerant, by driving the compressor if the desired high pressure value is not obtained, to change the refrigerant pressure, A desired cooling capacity can be obtained.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment of an Air Conditioning Apparatus According to the Present Invention
The embodiment will be described with reference to FIGS. FIG. 1 shows a main configuration of an air conditioner constituting a refrigeration cycle using CO ₂ as a refrigerant instead of CFC as a refrigerant. The air conditioner shown in the figure is applied to, for example, an air conditioner of an automobile. Reference numeral 1 denotes a compressor for compressing a refrigerant, 2 denotes a gas cooler (condenser) for condensing the compressed refrigerant, and 3 denotes a condensed refrigerant. An expander 4 as a decompression means for decompressing the pressure is an evaporator (evaporator) for evaporating the depressurized refrigerant.

The compressor 1 is driven by obtaining a driving force from a driving source (for example, an engine mounted on an automobile) 5. The gas cooler 2 cools and condenses the refrigerant compressed by the compressor by exchanging heat with outside air. The expander 3 is driven by receiving a driving force from a driving source 5 similarly to the compressor 1,
The refrigerant condensed in is expanded, and the pressure is positively reduced.
The evaporator 4 evaporates the refrigerant decompressed by the expander 3 by exchanging heat with the air in the vehicle, and cools the air in the vehicle by the latent heat of vaporization when the refrigerant is vaporized.

In this embodiment, a scroll compressor is used as the compressor 1 and a turbine expander is used as the expander 3. The drive shaft 1a of the compressor 1 and the drive shaft 3a of the expander 3 are directly connected to each other, and via a power transmission mechanism (for example, a combination of gears, a combination of a pulley and a belt) 6 fixed to both drive shafts. The driving force is obtained from the driving source 1.

The thermodynamic change of the refrigerant in the air conditioner configured as described above will be described with reference to the Mollier diagram shown in FIG. First, the refrigerant is compressed by the compressor 1 in a low-temperature and low-pressure gaseous phase (A-B), and becomes a high-temperature and high-pressure gaseous state. Subsequently, the refrigerant is condensed and liquefied (B-C) in the gas cooler 2 to be in a gas-liquid two-phase state at a high temperature and a high pressure. The refrigerant in the two-phase state is positively expanded and decompressed (CD ′) in the expander 3 to be in a low-temperature, low-pressure gas-liquid two-phase state. Subsequently, the refrigerant evaporates and evaporates (D′-A) in the evaporator 4 to be in a low-temperature and low-pressure gas phase state. At this time, the air in the vehicle is cooled by the latent heat of vaporization.

In the above air conditioner, the entropy of the refrigerant changes while keeping it substantially constant in the process of expanding and depressurizing the refrigerant (C-D '), and the enthalpy at the stage before flowing into the evaporator 4 is reduced. descend. Thereby, the enthalpy change amount in the evaporator 4 becomes larger by Δi than in the conventional case. That is, since the latent heat of vaporization when the refrigerant is vaporized in the evaporator 4 increases, the air in the vehicle can be more strongly cooled. Therefore, even when the number of revolutions of the compressor is reduced, such as at the time of idling, or in the summertime when the outside air temperature is high, the air in the vehicle can be effectively cooled to realize a comfortable environment.

Further, by driving the compressor 1 and the expander 3 by the same drive source 5, the structure of the apparatus can be simplified and the power loss during operation can be reduced. This makes it possible to reduce costs and save energy during operation of the air conditioner.

In this embodiment, a turbine expander is used as the expander 3, but the air conditioner according to the present invention may employ a scroll expander instead of the turbine expander. May be employed. Further, a compressor other than the scroll compressor may be employed.

FIG. 3 shows, as a second embodiment, an example in which an expansion valve (throttle means) 7 is provided between the gas cooler 2 and the expander 3. When the expansion valve 7 is installed in this part,
The refrigerant is moderately decompressed in the stage preceding the expander 3 and the suction flow rate changes, so that the discharge flow rate of the compressor 1 matches the suction flow rate of the expander 3. As a result, the operating point is adjusted to the designed point, so that the air conditioner can exhibit the desired cooling capacity and coefficient of performance.

A third embodiment of the air conditioner according to the present invention will be described with reference to FIGS. In addition, the first
The same reference numerals are given to the components already described in the embodiments and the description is omitted. In the present embodiment, FIG.
As shown in FIG. 7, the expander 3 is driven by an independent motor 10 separate from the drive source 5. The rotation speed of the motor 10 is controlled by the control unit 11. In addition, a portion corresponding to a refrigerant outlet of the evaporator 4 is provided with a first pressure detecting refrigerant pressure.
And a first temperature sensor 13 for detecting the temperature of the refrigerant. Both sensors are connected to the control unit 11. In the air conditioner configured as described above, the same thermodynamic change as in the first embodiment occurs, and the air in the vehicle can be effectively cooled to realize a comfortable environment.

When the refrigerant vaporized in the evaporator 4 changes into a gaseous phase and is sucked into the compressor 1 in a state where the degree of superheat is further increased, the compressor 1 has to perform extra work. The coefficient of performance (COP) decreases. Further, if the refrigerant is sucked into the compressor 1 without leaving the gas-liquid two-phase state, not only the sufficient cooling capacity cannot be obtained, but also the compressor 1 that has sucked the mist-like refrigerant hinders driving. It is also expected that.

Therefore, in the present embodiment, the degree of superheat of the refrigerant is measured from the detection results of the first pressure sensor 12 and the first temperature sensor 13, and the motor 10 is operated in accordance with the degree of superheat.
To control the number of revolutions. As a result, the refrigerant enters a gaseous state at the outlet of the evaporator 4, and the superheat degree of the refrigerant is suppressed to a value close to zero.

Specifically, the processing shown in FIG. 5 is executed.
First, the pressure Pe-out near the outlet of the evaporator 4 is detected by the first pressure sensor 12 (step S1). Next, the temperature Te-out near the outlet of the evaporator 4 is detected by the first temperature sensor 13 (Step S2). Next, the saturation temperature Tsat is calculated based on the pressure Pe-out (step S3). Next, the temperature Te-out and the saturation temperature Tsat
To calculate the degree of superheat SH (step S
4). Next, a rotation speed command value of the motor 10 is calculated and output based on the superheat degree SH (step S5). afterwards,
If the operation stop command has not been issued, the process returns to step S1 to repeat the above-described processing, and if the operation stop command has been issued, the process ends (step S6).

As described above, according to the air conditioner,
Since the LP in the refrigeration cycle is kept constant by controlling the driving of the expander 3, it is possible to improve both the coefficient of performance and the cooling capacity.

In this embodiment, the first pressure sensor 12 and the first temperature sensor 13 are connected to the evaporator 4.
These sensors are installed near the refrigerant outlet, but these two sensors may be provided anywhere between the evaporator 4 and the compressor 1. For example, if both sensors are installed in front of the suction port of the compressor 1, it is not necessary to consider the condensation of the refrigerant after the measurement of the degree of superheat, so that the compressor 1 can be driven more safely.

A fourth embodiment of the air conditioner according to the present invention will be described with reference to FIG. In addition, the same reference numerals are given to the components already described in each of the above embodiments, and the description is omitted. In the present embodiment, the compressor 1 is also driven by the motor 20, similarly to the expander 3. Motor 2
The number of rotations of 0 is controlled by the control unit 11. Further, a second pressure sensor 14 for detecting the pressure of the refrigerant and a second temperature sensor 15 for detecting the temperature of the refrigerant are provided at a portion corresponding to the refrigerant inlet of the gas cooler 2. Both sensors are also connected to the control unit 11. In the air conditioner configured as described above, the same thermodynamic change as in the first embodiment occurs, and the air in the vehicle can be effectively cooled to realize a comfortable environment.

The evaporation of the refrigerant in the evaporator 4 normally proceeds while maintaining a constant pressure LP (low pressure value). However, when the discharge flow rate of the expander 3 or the suction flow rate of the compressor 1 changes, the evaporator 4 evaporates. The refrigerant in the evaporator 4 may not be able to maintain a constant pressure due to an excessive supply of the refrigerant or a shortage of the refrigerant. Gas cooler 2
The refrigerant condenses at a constant pressure HP (high pressure value) also proceeds, but when the discharge flow rate of the compressor 1 or the suction flow rate of the expander 3 changes, the refrigerant is excessively supplied into the gas cooler 2. In some cases, the pressure in the gas cooler 2 cannot be kept constant. In this case, it is expected that a sufficient coefficient of performance and cooling capacity cannot be obtained as in the case of the second embodiment.

Therefore, in the present embodiment, the low pressure target value SP (LP) is calculated from the detection results of the first pressure sensor 12 and the first temperature sensor 13, and the low pressure target value SP (LP) and the first pressure sensor SP (LP) are calculated. The detected value of the pressure sensor 12 is compared, and the rotation speed of the motor 10 is controlled so that the actual detected value approaches the low pressure target value SP (LP). Thereby, the discharge flow rate of the expander 3 changes, and the pressure in the evaporator 4 is kept constant.

The high pressure target value SP (HP) is calculated from the detection results of the second pressure sensor 14 and the second temperature sensor 15, and the high pressure target value SP (HP) and the detection of the second pressure sensor 14 are detected. Then, the rotation speed of the motor 20 is controlled so that the actual detection value approaches the high-pressure target value SP (HP). As a result, the discharge flow rate of the compressor 1 changes,
The pressure inside the gas cooler 2 is kept constant.

As described above, according to the air conditioner,
Since the LP and HP in the refrigeration cycle are kept constant by individually controlling the driving of the compressor 1 and the expander 3, it is possible to improve both the coefficient of performance and the cooling capacity.

In each of the above embodiments, the air conditioner for an automobile has been described. However, the air conditioner according to the present invention is not limited to this, and can be applied to general air conditioners for home use and business use. is there.

[0045]

As described above, according to the air conditioner of the present invention, the refrigerant passing through the condenser is expanded and decompressed by the expander, so that the entropy at the stage before flowing into the evaporator is reduced. As a result, the amount of change in enthalpy in the evaporator becomes larger than before, so that the cooling capacity can be improved.

According to the air conditioner of the second aspect, the scroll compressor and the turbine expander are driven by the same drive source, thereby simplifying the device configuration and reducing power loss during operation. be able to.

According to the air conditioner of the third aspect, the scroll compressor and the scroll expander are driven by the same drive source, thereby simplifying the structure of the device and reducing power loss during operation. be able to.

According to the air conditioner of the fourth aspect, by providing the throttling means between the condenser and the expander, the refrigerant is appropriately depressurized before the expander, the suction flow rate is changed, and Since the discharge flow rate of the compressor and the suction flow rate of the expander match, the operating point is adjusted to the designed point, so that the desired cooling capacity and coefficient of performance can be exhibited.

According to the air conditioner of the fifth aspect, by independently controlling the drive of the expander independently of the compressor, the expansion pressure of the refrigerant can be reduced without being affected by the drive of the compressor. Since it can be performed variably, the cooling capacity can be improved.

According to the air conditioner of the sixth aspect, if the desired degree of superheat cannot be obtained in the refrigerant, the expansion device is driven to change the discharge flow rate of the refrigerant, thereby increasing the desired cooling capacity. Can be demonstrated.

According to the air conditioner of the present invention, if the desired low pressure value cannot be obtained in the refrigerant, the expansion device is driven to change the discharge flow rate of the refrigerant, thereby achieving the desired cooling capacity. Can be demonstrated.

According to the air conditioner of the present invention, if the desired high pressure value cannot be obtained, the desired cooling capacity can be exhibited by driving the compressor to change the refrigerant pressure. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a first embodiment of an air-conditioning apparatus according to the present invention.

FIG. 2 is a Mollier diagram of a refrigeration cycle realized by the air-conditioning apparatus of the first embodiment.

FIG. 3 is a schematic configuration diagram illustrating a second embodiment of the air-conditioning apparatus according to the present invention.

FIG. 4 is a schematic configuration diagram illustrating a third embodiment of the air-conditioning apparatus according to the present invention.

FIG. 5 is a flowchart illustrating a method of controlling a motor in the air-conditioning apparatus according to the third embodiment.

FIG. 6 is a schematic configuration diagram showing a fourth embodiment of the air-conditioning apparatus according to the present invention.

FIG. 7 is a Mollier diagram of a refrigeration cycle realized by a conventional air conditioner using carbon dioxide as a refrigerant.

[Description of Signs] 1 compressor 2 gas cooler (condenser) 3 expander (decompression means) 4 evaporator (evaporator) 5 drive source 6 power transmission mechanism 7 expansion valve 10 motor 11 controller 12 first pressure sensor 13 first 1 temperature sensor 14 2nd pressure sensor 15 2nd temperature sensor

Claims (8)

[Claims] 1. A compressor for compressing a refrigerant, a condenser for condensing the refrigerant compressed by the compressor, a decompression device for decompressing the refrigerant condensed in the condenser, and a decompression device for decompressing the refrigerant. An evaporator for evaporating the refrigerant, wherein the air conditioner constitutes a refrigeration cycle using carbon dioxide as the refrigerant, wherein the decompression means actively expands and decompresses the refrigerant. An air conditioner characterized by using: 2. A scroll compressor as the compressor,
The air conditioner according to claim 1, wherein both of the pressure reducing means are driven by the same drive source using a turbine expander. 3. A scroll compressor as the compressor,
The air conditioner according to claim 1, wherein a scroll expander is used as the pressure reducing means, and both are driven by the same drive source. 4. The air conditioner according to claim 2, wherein a throttle means is provided between the condenser and the expander. 5. The air conditioner according to claim 1, wherein the drive of the expander is individually controlled independently of the compressor. 6. The air according to claim 5, wherein the degree of superheat of the refrigerant between the evaporator and the compressor is measured, and the driving of the expander is controlled according to the degree of superheat. Harmony equipment. 7. The air conditioner according to claim 5, wherein the drive of the expander is controlled according to a low pressure value of the refrigerant in the refrigeration cycle. 8. The air conditioner according to claim 5, wherein driving of the compressor is controlled in accordance with a high pressure value of the refrigerant in the refrigeration cycle.