JP2002168536A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air conditioner which enables the operation at an optimum balance point corresponding with cooling load by regulating the quantity of a refrigerant circulating within the system. SOLUTION: The air conditioner is equipped with a compressor 1 for compressing the refrigerant, a gas cooler 2 for condensing the compressed refrigerant, first and second control valves 3 and 4 for depressurizing the condensed refrigerant, and an evaporator 5 for evaporating the depressurized refrigerant; and constitutes a freezing cycle using carbon dioxide as the refrigerant. A liquid reserving container 8 for temporarily reserving the liquid-phase components of the refrigerant is installed between the first and second control valves 3 and 4 arranged in series. Also a refrigerant pipe 6a having passed through the second control valve 4 is passed into the liquid reserving container 8. The refrigerant gas at middle pressure within the liquid reserving container 8 is cooled for condensation, so as to regulate the quantity of the liquid refrigerant within the container by the temperature difference between the saturation temperature at middle pressure and the evaporation temperature.

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 fluorocarbon, carbon dioxide (hereinafter referred to as CO2) has been receiving attention. CO
No. 2 is highly evaluated for not only having much less impact on global warming than CFCs, but also being nonflammable and basically harmless to the human body.

[0004] From such a background, a vapor compression refrigeration cycle using carbon dioxide (hereinafter referred to as a CO2 refrigeration cycle) has been proposed. The operation of this CO2 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.
(A gas phase state) is compressed by a compressor (A-B) to obtain a supercritical state of high temperature and high pressure. Next, high temperature and high pressure CO2 (gas phase state) is cooled by a condenser (B-C). Next, high-temperature and high-pressure CO2 (supercritical state) is depressurized by a decompressor (C-
D) A low-temperature low-pressure gas-liquid two-phase state is set. Next, low-temperature and low-pressure CO2 (gas-liquid two-phase state) CO2 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.

[0005] However, the critical temperature of CO2 is about 31
° C and lower than CFC, when the outside air temperature is high, such as in summer, the temperature of CO2 on the condenser side becomes higher than the critical point temperature of CO2. That is, CO2 is not condensed on the condenser outlet side (the line segment BC changes to the saturated liquid line SL).
Does not intersect).

[0006]

In the refrigeration cycle under supercritical pressure as described above, the refrigerant does not condense on the so-called high pressure side (between the condenser and the expansion valve) where the refrigerant exhibits a high pressure value. It does not make sense to install a receiver (gas-liquid separator) on the. Therefore, proposals have been made to increase the amount of change in enthalpy by installing a receiver on a so-called low pressure side (between the evaporator and the compressor) where the refrigerant exhibits a low pressure value.

However, in the above case, there is a problem that the state of the refrigerant on the side of the evaporator is determined by the effect of the outside air temperature, the set conditions in the room, and the like, and stable operation cannot be performed.

The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances, and is intended to adjust the amount of refrigerant circulating in the system of a CO2 refrigeration cycle to enable air to be operated at an optimum balance point corresponding to a cooling load. It aims at providing a harmony device.

[0009]

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. First and second decompression means,
An evaporator for evaporating the refrigerant decompressed by the first and second decompression means, wherein the air conditioner constitutes a refrigeration cycle using carbon dioxide as the refrigerant, and is arranged in series. A liquid reservoir is installed in the refrigerant pipe between the first and second decompression means, a lower part of the liquid reservoir and the refrigerant pipe are connected by a connecting pipe, and the second decompression means and the evaporation A part of a refrigerant pipe between the reservoir and the inside of the reservoir is passed through the inside of the reservoir, and a gas phase component of the refrigerant in the reservoir is cooled by the refrigerant decompressed by the second pressure reducing means. It is characterized by being changed and stored.

[0010] The air conditioner according to the second aspect is the first aspect.
In the air conditioner described above, the first pressure reducing means located on the side of the condenser is a control valve capable of adjusting an opening degree, and the opening degree of the valve is controlled based on a refrigerant temperature after passing through the condenser. It is characterized by doing.

[0011] The air conditioner according to the third aspect is the first aspect.
Or the air conditioner according to 2, wherein the second pressure reducing means located on the side of the evaporator is a control valve capable of adjusting an opening degree, and the opening degree of the valve is determined based on a refrigerant temperature after passing through the evaporator. Control.

In the air conditioner according to the present invention, the refrigerant flowing into the liquid storage container is cooled and condensed by the refrigerant whose temperature has been further lowered through the second pressure reducing means. Thereby, the refrigerant is stored in the state of the saturated liquid inside the liquid reservoir. The amount of refrigerant to be stocked is first,
A refrigerant pressure (intermediate pressure) saturation temperature between the second pressure reducing means,
The larger the difference from the refrigerant pressure (evaporator inlet pressure) saturation temperature through the second pressure reducing means, the larger the difference.

[0013] The refrigerant pressure on the high pressure side decreases, and the throttle amount (valve opening) of the first pressure reducing means is increased to increase the refrigerant pressure to a target value.
When the pressure is reduced, the refrigerant pressure (intermediate pressure) between the first and second decompression means provided with the liquid reservoir decreases, and the pressure balance with the refrigerant in a gaseous state stored in the liquid reservoir is maintained. The liquid-phase refrigerant is extruded from the liquid reservoir. As a result, the amount of refrigerant in the system increases, and the refrigerant pressure on the high pressure side increases.

When the pressure of the refrigerant on the high pressure side rises and the throttle amount of the first pressure reducing means is increased in order to reduce the refrigerant pressure to the target value, the intermediate pressure rises and the gaseous phase accumulated in the liquid storage container increases. In order to maintain the pressure balance with the refrigerant in the liquid state, the refrigerant in the liquid state is sucked into the liquid reservoir. As a result, the amount of refrigerant in the system decreases, and the refrigerant pressure on the high pressure side decreases.

On the other hand, when the degree of superheat of the refrigerant after passing through the evaporator increases, and the amount of throttle of the second pressure reducing means is increased in order to approach the target value, the intermediate pressure decreases, and the refrigerant is stored in the reservoir. In order to maintain the pressure balance with the accumulated refrigerant in the gas phase, the refrigerant in the liquid phase is extruded from the reservoir. As a result, the amount of refrigerant in the system increases, and the refrigerant pressure on the high pressure side increases.

[0016]

FIG. 1 shows an embodiment of an air conditioner according to the present invention. FIG. 1 shows a main configuration of an air conditioner constituting a refrigeration cycle using CO2 as a refrigerant instead of CFC as a refrigerant. The air conditioner shown in FIG. 1 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 and 4 denote condensates. First and second control valves (decompression means) for decompressing the cooled refrigerant, 5
Is an evaporator that evaporates the depressurized refrigerant
It is. These constitute a refrigerant circulation system closed by the pipe 6.

The compressor 1 is driven by obtaining a driving force from a driving source (for example, an engine mounted on an automobile). The gas cooler 2 cools and condenses the refrigerant compressed by the compressor 1 by exchanging heat with outside air. First and second expansion valves 3,
4 expands the refrigerant condensed in the gas cooler 2,
Reduce pressure. The evaporator 5 includes first and second expansion valves 3,
The refrigerant decompressed by the heat exchanger 4 evaporates by exchanging heat with the air inside the vehicle, and cools the air inside the vehicle by latent heat of vaporization when the refrigerant is vaporized.

Between the gas cooler 2 and the first control valve 3,
An intercooler 7 is provided. Intercooler 7
Is a low-temperature refrigerant which has been evaporated by the evaporator 5 and further cools a high-temperature and high-pressure refrigerant (supercritical state) cooled by the gas cooler 2 to increase the cooling capacity.

Between the first and second control valves 3 and 4, there is provided a liquid reservoir 8 for temporarily storing the refrigerant circulating in the system. The lower part of the liquid reservoir 8 is connected to the refrigerant pipe 6 between the first and second control valves 3 and 4 by a connecting pipe 8a. In order to cool the refrigerant inside the reservoir 8, a part of the refrigerant pipe 6 a between the second control valve 4 and the evaporator 5 is passed through the interior of the reservoir 8. The liquid reservoir 8 captures a gas phase component contained in the refrigerant that has been expanded and decompressed by the first control valve 3 and removes the liquid phase component from the evaporator 5.
It also has a function as a receiver to send to

Between the high-pressure gas cooler 2 and the intercooler 7, a temperature sensor 9 for detecting the refrigerant temperature on the high-pressure side in the CO2 refrigeration cycle is provided. The opening degree of the first control valve 3 is controlled based on the refrigerant temperature detected by the temperature sensor 9 so that the refrigerant pressure on the high pressure side approaches a target value.

Between the evaporator 5 and the intercooler 7, a temperature sensor 10 for detecting a low-pressure side refrigerant temperature in the CO2 refrigeration cycle is provided. The degree of opening of the second control valve 4 is controlled based on the refrigerant temperature detected by the temperature sensor 10 so that the degree of superheat of the refrigerant on the low pressure side approaches a target value.

A pipe 6a between the second control valve 4 and the evaporator 5 is once led inside the liquid reservoir 8, and after exposing the surface of the pipe to the refrigerant inside the container, it goes out of the container. It is connected to the evaporator 5. The space inside the liquid reservoir 8 and the inside of the pipe 6a are completely separated, so that the refrigerant does not flow in and out between them.

In the air conditioner configured as described above, when the refrigerant pressure on the high pressure side is reduced in the CO2 refrigeration cycle, the first pressure is set to increase the pressure to the target value.
Of the control valve 3 is reduced. At this time, the reservoir 8
The phenomenon that takes place inside the device will be described with reference to FIG. In the drawing, P0 is the refrigerant pressure (high pressure) before being depressurized by the first control valve 3, and P1 is depressurized by the first control valve 3 and is the second pressure.
Pressure (intermediate pressure) before pressure reduction by the control valve 4 of P2, P2
Is the refrigerant pressure (evaporation pressure) after being depressurized by the second control valve 4, T1 is the temperature of the refrigerant showing the intermediate pressure, and T2 is the temperature of the refrigerant showing the evaporation pressure of the second control valve 4. G indicates a gas layer inside the liquid reservoir 8.

When the opening degree of the first control valve 3 is reduced, the refrigerant pressure (intermediate pressure) P1 between the first and second control valves 3 and 4 decreases, and the saturation temperature inside the liquid reservoir 8 is reduced. Since T1 is reduced, the temperature difference (T1-T2) between the refrigerant pipe 6a and the refrigerant pipe 6a becomes small, and it becomes difficult for heat exchange with the refrigerant in the gaseous state stored in the liquid reservoir 8 to proceed, so that the refrigerant does not condense. For this reason, the refrigerant liquid is pushed out of the liquid reservoir 8 so that the gas pressure inside the liquid reservoir 8 is balanced with the refrigerant pressure P1 (see FIG. 3A). As a result, the amount of refrigerant in the system increases, and the refrigerant pressure on the high pressure side increases.

When the refrigerant pressure on the high pressure side rises, the valve opening of the first control valve 3 is opened to reduce the pressure to the target value. When the valve opening of the first control valve 3 is opened,
The intermediate pressure P1 rises and the saturation temperature T1 inside the liquid reservoir 8 increases.
Therefore, the temperature difference (T1-T2) between the refrigerant pipe 6a and the refrigerant pipe 6a increases, and heat exchange with the refrigerant in the gaseous state stored in the liquid reservoir 8 easily proceeds, and the refrigerant condenses. Therefore, the amount of liquid in the reservoir 8 increases, and the refrigerant is sucked into the reservoir 8 until the gas pressure in the reservoir 8 balances with the refrigerant pressure P1 (FIG. 3B).
reference). As a result, the amount of refrigerant in the system decreases, and the refrigerant pressure on the high pressure side decreases.

On the other hand, the second control valve 4 detects the degree of superheat of the refrigerant after leaving the evaporator 5 based on the information from the temperature sensor 10, and when the degree of superheat is large, the amount of the liquid refrigerant is insufficient. Therefore, the valve opening of the second control valve 4 is opened so as to approach the target value (= 0). When the valve opening of the second control valve 4 is opened, the refrigerant pressure P1 decreases, and the saturation temperature T1 inside the liquid reservoir 8 decreases, so that the temperature difference (T1-T2) with the refrigerant pipe 6a decreases. In addition, heat exchange with the refrigerant in a gaseous state stored in the liquid reservoir 8 becomes difficult to progress, and the refrigerant does not condense. Therefore, the refrigerant liquid is pushed out of the liquid reservoir 8 so that the gas pressure inside the liquid reservoir 8 is balanced with the refrigerant pressure P1 (the same as in FIG. 3A). As a result, the amount of liquid refrigerant entering the evaporator 5 increases, and the degree of superheat decreases.

When the refrigerant pressure on the high-pressure side rises, this is detected and the valve opening of the first control valve 3 is also slightly opened, so that the intermediate pressure and the refrigerant flow rate are settled to an appropriate state, and the optimum pressure suitable for the cooling load is obtained. Operation at an appropriate balance point becomes possible.

In this embodiment, the second control valve 4
Is effective when the superheat degree of the refrigerant passing through the evaporator 5 is controlled to be an appropriate size by using
When a fixed throttle is used instead of the control valve 4, the refrigerant pipe on the outlet side of the evaporator 5 may be passed through the liquid reservoir.

The present invention is not limited to the above embodiment, and it goes without saying that the design can be changed without departing from the spirit of the invention.

[0030]

As described above, according to the air conditioner of the present invention, the refrigerant in the liquid phase is stocked in the liquid reservoir, and the refrigerant circulates in the system in accordance with the high / low pressure control. By changing the amount, the intermediate pressure and the flow rate of the refrigerant can be settled in an appropriate state, and the operation at the optimum balance point corresponding to the cooling load can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an embodiment of an air conditioner according to the present invention.

FIG. 2 is a Mollier diagram of a refrigeration cycle realized by a conventional air conditioner using carbon dioxide as a refrigerant.

FIG. 3 is a state explanatory view showing a phenomenon occurring inside the liquid reservoir.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Compressor 2 Gas cooler (condenser) 3,4 First and second control valve (decompression means) 5 Evaporator (evaporator) 6 Piping 7 Intercooler 8 Liquid storage container 9,10 Temperature sensor

Claims (3)

[Claims] 1. A compressor for compressing a refrigerant, a condenser for condensing the refrigerant compressed by the compressor, first and second decompression means for decompressing the refrigerant condensed in the condenser, An evaporator for evaporating the refrigerant decompressed by the first and second decompression means, wherein the air conditioner constitutes a refrigeration cycle using carbon dioxide as the refrigerant, and is arranged in series. A liquid reservoir is installed in the refrigerant pipe between the first and second decompression means, a lower part of the liquid reservoir and the refrigerant pipe are connected by a connecting pipe, and the second decompression means and the evaporation A part of a refrigerant pipe between the reservoir and the inside of the liquid reservoir is passed through the inside of the liquid reservoir, and a gas phase component of the refrigerant inside the liquid reservoir is cooled by the refrigerant depressurized by the second decompression means. An air conditioner characterized by being changed into a storage. 2. The method according to claim 1, wherein the first pressure reducing means located on the condenser side is a control valve capable of adjusting an opening degree, and the valve opening degree is controlled based on a refrigerant temperature after passing through the condenser. The air conditioner according to claim 1, characterized in that: 3. The method according to claim 2, wherein the second pressure reducing means located on the side of the evaporator is a control valve capable of adjusting an opening degree, and the opening degree of the valve is controlled based on a refrigerant temperature after passing through the evaporator. The air conditioner according to claim 1 or 2, wherein: