KR20040073325A - A supercritical cooling-heating cycle - Google Patents

Abstract

PURPOSE: A supercritical cooling and heating cycle is provided to improve the performance and efficiency of a cooling cycle by controlling the quantity of refrigerant discharge of a compressor and opening of a throttle element. CONSTITUTION: A variable displacement compressor(100) absorbs a refrigerant, carbon dioxide for compressing the refrigerant into a supercritical state. A gas cooler(110) cools the refrigerant of high temperature and high pressure discharged from the compressor. A throttling element(150) controls refrigerant flux while reducing pressure by expanding the refrigerant discharged from the gas cooler. An evaporator(140) evaporates the refrigerant discharged from the throttling element by exchanging heat with ventilated air. An inner heat exchanger(120) exchanges heat between the refrigerant flowing from the evaporator to the compressor, and the refrigerant flowing from the gas cooler to the throttling element. An accumulator(160) is installed between the evaporator and the inner heat exchangers for executing phase separation for the refrigerant to supply only gaseous refrigerant to the compressor. A discharge control valve(170) controls the quantity of refrigerant discharge of the compressor. A plurality of refrigerant pressure sensors(101,102) sense refrigerant pressure of the compressor. A temperature sensor senses a refrigerant discharge temperature of the evaporator.

Description

A supercritical cooling-heating cycle

The present invention relates to a supercritical cooling and heating cycle, and more particularly, by controlling by simple control logic using a refrigerant discharge temperature sensor of an evaporator and a refrigerant pressure detecting means of a compressor, thereby adjusting the refrigerant discharge amount of the compressor and the opening degree of the throttling means. Therefore, the present invention relates to a supercritical cooling and heating cycle capable of maximally improving the performance and efficiency of a refrigeration cycle and additionally improving heating performance.

As is well known, as conventional refrigerants, such as R134a, are known to be the main culprit of environmental destruction such as ozone layer destruction and global warming, usage regulations are being expanded to protect the environment, and carbon dioxide may be substituted for the refrigerant. Supercritical refrigeration cycles using this carbon dioxide have attracted attention.

The carbon dioxide refrigerant has two major advantages, the compression ratio is low due to the low operating compression ratio, and the temperature approach (inlet temperature of the secondary fluid air-the outlet temperature difference of the refrigerant) is a conventional refrigerant due to its excellent heat transfer characteristics. Compared with the gas cooler, the heat transfer characteristics are excellent enough to lower the temperature of the refrigerant to the temperature of the incoming air.

In addition, due to its excellent thermal role, the volumetric cooling capacity of carbon dioxide (capcity volume ratio = evaporation latent heat x gas density) is 7 to 8 times higher than that of R134a. Can be greatly reduced.

In addition, carbon dioxide has excellent surface heat transfer because of its small surface tension, and has a particular advantage over R134a even under pressure drop due to its high specific heat and low liquid viscosity.

However, the supercritical refrigeration cycle using carbon dioxide as a refrigerant has a much higher gasoline pressure (conventional condensation pressure) as well as the evaporation pressure as compared to the normal refrigeration cycle using R134a as a refrigerant.

That is, in the supercritical refrigeration cycle, the evaporation pressure is about 10 times higher than the general refrigeration cycle, and the gas cooling pressure is about 7 times higher (about 120 bar).

For this reason, research is being conducted on devices and systems for protecting each component (compressor, gas cooler, etc.) from high pressure.

1 shows a refrigeration cycle using carbon dioxide, which is 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) under the gas cooling pressure of P1, 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 is Q1.

However, when the temperature of the gas cooler outlet is t2 lower than t1, the refrigeration cycle draws a 1-2-3'-4'-1 trajectory, and the freezing effect is increased to Q2 compared to 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 that exchanges heat with the low temperature evaporator outlet refrigerant is installed.

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. When the pressure is P2 lower than P1, the cycle becomes 1-2'-3'-4'-1, and the freezing effect is greatly reduced to Q3, so the performance difference increases with the change of pressure under the same temperature condition.

In the air conditioner using carbon dioxide as a heat exchange medium, as can be seen from the refrigeration cycle of carbon dioxide as described above, 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 gas cooling pressure can be controlled to improve the refrigeration efficiency.

As an example of a refrigeration cycle using carbon dioxide as a refrigerant as described above, there is Japanese Patent Application Laid-Open No. 2001-194017 (2002.7.17; published), which is shown in FIG. 2.

As shown, the refrigerant evaporates and compresses heat to transfer heat from the low temperature side to the high temperature side, and at the same time, a supercritical steam compressor type refrigeration cycle in which the refrigerant pressure on the high pressure side is equal to or greater than the grain boundary pressure of the refrigerant. (10), a gas cooler (20) for cooling the refrigerant discharged from the compressor (10), a pressure control valve (30) capable of reducing the pressure of the refrigerant flowing out of the gas cooler (20) and controlling the opening degree; And an evaporator 40 for evaporating the refrigerant depressurized by the pressure control valve 30, a high pressure refrigerant temperature detection means for detecting the refrigerant temperature on the high pressure side, a cycle control means 70, and a set temperature input means 66. A supercritical steam compressor refrigeration cycle is disclosed.

In the refrigeration cycle, an internal heat exchanger must be added to forcibly lower the refrigerant temperature at the radiator outlet through heat exchange between the gas cooler outlet temperature and the evaporator outlet temperature in order to improve capacity and efficiency (COP). In the case of Japanese Patent Application Laid-Open No. 2001-194017, the internal heat exchanger is excluded from the system, and sensors for optimum efficiency control (gas cooler inlet temperature sensor 64, gas cooler outlet temperature sensor 61, gas cooler outlet pressure sensor 62). ), The amount of refrigerant discharged from the compressor and the opening of the pressure control valve are controlled by various signals transmitted from the evaporator outlet pressure sensor 63, the outflow air temperature sensor 65, and the like.

However, the conventional technology not only increases the configuration cost of the supercritical refrigeration cycle due to the large number of sensors, but also the complicated control logic of the system, which makes it difficult to precisely control the system. It is difficult to calculate and apply.

Therefore, a new system design and control logic are urgently required for simple and precise control through system analysis in a refrigeration cycle using carbon dioxide as a refrigerant.

The present invention has been made to solve the above problems, by controlling by simple control logic using the refrigerant discharge temperature sensor of the evaporator and the refrigerant pressure detection means of the compressor, to adjust the refrigerant discharge amount of the compressor and the opening degree of the throttling means. Therefore, the object of the present invention is to provide a supercritical heating and cooling cycle to maximize the performance and efficiency of the refrigeration cycle, and additionally improve the heating performance.

1 is a diagram showing a P-H diagram of a refrigeration cycle using carbon dioxide.

Figure 2 is a schematic diagram of a supercritical refrigeration cycle according to the prior art.

3 is a block diagram of a supercritical air conditioning cycle according to an embodiment of the present invention.

4 is a control flowchart of FIG. 3.

5 is a block diagram of a supercritical air conditioning cycle according to another embodiment of the present invention.

6 is a control flowchart of FIG. 5.

<Description of the symbols for the main parts of the drawings>

100: compressor

110: gas cooler

120: internal heat exchanger

140: evaporator

150: throttling means

190 controller

The present invention for achieving the above object, a variable displacement compressor that sucks carbon dioxide which is a refrigerant and compresses to a supercritical state, the compression capacity is controlled; A gas cooler for cooling the high temperature, high pressure refrigerant discharged from the compressor; Throttling means for expanding the refrigerant discharged from the gas cooler to control the refrigerant flow rate while decompressing the refrigerant; An evaporator for evaporating the refrigerant passing through the condensation means by heat exchange with blowing air; An internal heat exchanger configured to exchange heat between the refrigerant flowing from the evaporator to the compressor and the refrigerant flowing from the gas cooler to the throttling means; An accumulator installed between the evaporator and the internal heat exchanger to phase-separate the refrigerant so that only the gaseous refrigerant is supplied to the compressor; A discharge amount control valve controlling a discharge amount of the compressor; Refrigerant pressure sensing means for sensing a refrigerant pressure of the compressor; And a temperature sensor for sensing a refrigerant discharge temperature of the evaporator, wherein the refrigerant pressure sensing unit detects a refrigerant suction pressure of the compressor in a cooling mode, and compares the error between the refrigerant suction pressure of the compressor and a set low pressure pressure. A pressure comparison unit, a discharge amount control signal output unit for outputting a signal for adjusting the opening degree of the discharge amount control valve by the error, and a refrigerant saturation temperature calculated by the refrigerant discharge temperature of the evaporator and the refrigerant suction pressure of the compressor A calculation unit for calculating a refrigerant superheat degree, an overheat degree comparison unit comparing an error between the superheat degree of the refrigerant and the set refrigerant superheat degree, and an overheat degree control signal for outputting a signal for adjusting the opening degree of the throttling means by the error. Characterized in that it comprises a controller consisting of an output unit.

Hereinafter, a preferred embodiment of the supercritical air conditioning cycle according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram of a supercritical air conditioning cycle according to an embodiment of the present invention, FIG. 4 is a control flowchart of FIG. 3, and FIG. 5 is a block diagram of a supercritical air conditioning cycle according to another embodiment of the present invention. 6 is a control flowchart of FIG. 5.

As shown in FIG. 3, a variable displacement compressor (100) in which a carbon dioxide, a refrigerant, is compressed into a supercritical state, and a compression capacity is controlled, and a gas for cooling a high temperature and high pressure refrigerant discharged from the compressor (100). The cooler 110, the throttling means 150 for adjusting the refrigerant flow rate while expanding and decompressing the refrigerant discharged from the gas cooler 110, and the refrigerant passing through the throttling means 150 by heat exchange with the blowing air An evaporator 140 for evaporating, an internal heat exchanger 120 for exchanging a refrigerant flowing from the evaporator 140 to the compressor, and a refrigerant flowing from the gas cooler 110 to the throttling means 150, and the evaporator 140. And an accumulator 160 installed between the internal heat exchanger 120 to separate the refrigerant to supply only the gaseous refrigerant to the compressor 100, and a discharge amount control valve controlling the discharge amount of the compressor 100. 170) And a refrigerant pressure detecting means (101) (102) for detecting a refrigerant pressure of the compressor (100), a temperature sensor (141) for detecting a refrigerant discharge temperature of the evaporator (140), and a controller (200). Include.

The controller 200 outputs a signal for comparing the error between the refrigerant suction pressure and the set low pressure of the compressor 100 and a signal for adjusting the opening degree of the discharge amount control valve 170 by the error. Computation unit 210 for calculating the refrigerant superheat degree by comparing the discharge amount control signal output unit 221, the refrigerant discharge temperature of the evaporator 140 and the refrigerant saturation temperature calculated by the refrigerant suction pressure of the compressor 100 And an overheat degree comparison unit 211 for comparing an error between the superheat degree of the refrigerant and a set refrigerant superheat degree, and a superheat control signal output unit 212 for outputting a signal for adjusting the opening degree of the throttling means by the error. It consists of a controller 200 made of.

The internal heat exchanger 120 may be integrally provided with the accumulator 160 or may be separately installed.

The throttling means 150 uses an electromagnetic expansion valve in a preferred embodiment.

When the present invention is to be used in the cooling mode, the refrigerant pressure sensing means 101 detects the refrigerant suction pressure of the compressor 100.

Here, the pressure comparison unit 220 compares the error between the refrigerant suction pressure and the set low pressure pressure of the compressor 100, the set low pressure pressure is greater than or equal to 33 bar, by setting the reference to be less than or equal to 37 bar Doom is preferred.

In addition, the pressure comparison unit 220 is referred to as a first pressure comparison unit 220 hereinafter.

The superheat degree comparator 211 compares an error of the refrigerant superheat degree and the set refrigerant superheat degree of the evaporator 140 calculated by the operation unit 210. The set refrigerant superheat degree is greater than or equal to 0k and 4k. It is preferable to set the criterion to be smaller or equal.

On the other hand, the present invention can be applied in the cooling mode as described above, as shown in Figure 5, in the heating mode, the refrigerant pressure sensing means detects the refrigerant discharge pressure of the compressor (100). The controller 200 includes a second pressure comparison unit 230 for comparing the error between the refrigerant discharge pressure and the target high pressure of the compressor 100; The second discharge amount control signal output unit 231 for outputting a signal for adjusting the opening degree of the discharge amount control valve 170 by the error is further provided.

The control method of the cooling and heating cycle of the present invention configured as described above with reference to Figure 4 as follows.

First, it is determined whether the compressor is on (S10).

As a result of the determination in step S10, when the compressor is turned on, the first pressure comparing unit 220 is detected by the suction pressure sensor 101 and measured (S30), and the refrigerant suction pressure and the set low pressure pressure of the compressor 100 are measured. Compare the error of (S40).

Here, the set low pressure pressure is in the range of greater than or equal to 33 bar and less than or equal to 37 bar.

Thereafter, after the step S40, the first discharge amount control signal output unit outputs a signal for adjusting the opening degree of the discharge amount control valve 170 by an error compared by the first pressure comparator 220. The discharge amount of the compressor 100 is varied (S50).

After performing step S50, the refrigerant discharge temperature of the evaporator 140 is measured based on the signal input to the temperature sensor 141.

After proceeding to the step (S60), the calculating unit 210 calculates the refrigerant superheat degree by the measured refrigerant discharge temperature of the evaporator 140 and the refrigerant suction pressure of the compressor (S70).

After the step S70, the superheat degree comparator 211 compares the error between the superheat degree of the refrigerant and the set refrigerant superheat degree.

Here, the set refrigerant superheat degree is greater than or equal to 0k and less than or equal to 4k.

After the step (S80), the superheat control signal output unit 212 outputs a signal for adjusting the opening degree of the throttling means 150 by the error to adjust the amount of refrigerant (S90).

Hereinafter, the operation of the present invention will be described.

First, the carbon dioxide evaporated from the evaporator 140 is compressed using the compressor 100 into the gas cooler 13.

The method of controlling the gas cooling pressure by the compressor 100 may include adjusting the opening degree of the discharge amount control valve 170 by the first pressure comparing unit 220 and the first discharge amount control signal output unit 220. In this case, the discharge amount of the gas may be varied. In this case, the refrigerant compression ratio may be varied so that the pressure inside the gas cooler 110 may be maintained at an optimally set pressure.

In this state, on the basis of the refrigerant discharge temperature of the evaporator 140 sensed by the temperature sensor 141, the calculating unit 210 of the controller 200 is connected to the refrigerant discharge temperature of the evaporator 140 and the refrigerant suction pressure of the compressor. After the coolant superheat degree is calculated, the superheat degree control signal output unit 212 uses the error of the coolant superheat degree and the set coolant superheat degree compared by the first superheat degree comparing unit 211 to determine the throttling means 150. The amount of refrigerant is adjusted by outputting a signal for adjusting the opening degree.

In this case, since the flow rate of the refrigerant is adjusted to have an optimal degree of superheat on the evaporator 140 side, the gas cooling pressure is adjusted by the compressor 100 to have an optimal cooling pressure on the gas cooler 110 side.

Here, when the degree of superheat is excessively increased, the area occupied by the gas in the evaporator 140 becomes excessively larger than the area occupied by the liquid, so that the inlet temperature of the evaporator 140 is low but the outlet temperature of the evaporator 140 is increased. The excessive rise in the surface temperature of the evaporator 140, so the performance of the evaporator 140 is reduced.

In addition, when there is almost no superheat, the flow rate of the refrigerant flowing inside the evaporator 140 is high, but the overall pressure and temperature of the evaporator 140 increases, which also increases the surface temperature of the evaporator 140, thereby degrading performance. do.

As a result, it is possible to maintain the optimum degree of superheat in the evaporator 140 as described above to optimize the refrigeration efficiency of the evaporator to improve the cooling performance.

Referring to the present invention described so far P-H diagram of the refrigeration cycle using FIG. 1 as follows.

The lower the temperature of carbon dioxide, the heat exchange medium at the outlet side of the gas cooler (corresponding to the existing air conditioning system) at the gas cooling pressure, the better the freezing performance.

That is, when the outlet temperature of the gas cooler is t1, the refrigerating cycle forms a trajectory of 1-2-3-4-1, and the freezing effect at this time is Q1.

However, when the outlet of the gas cooler is t2 lower than t1, the refrigeration cycle draws a 1-2-3'-4'-1 trajectory and the cooling effect is increased to Q2 compared to Q1, indicating that the freezing effect is increased. Can be.

For this reason, in order to forcibly lower the temperature of the outlet of the gas cooler, an internal heat exchanger is installed in which the heat exchanger is performed 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 and the refrigeration effect is Q1. When P2 is lower than P1, the cycle is 1-2'3'-4'-1, and the freezing effect is greatly reduced to Q3, and the performance difference becomes larger according to the pressure change under the same temperature conditions.

Therefore, as described above, the present invention can maximize the refrigeration efficiency by controlling the cooling pressure of the gas cooler in an optimal state.

Meanwhile, the cooling mode of the present invention has been described so far, and the heating mode of the present invention will be described below with reference to FIG. 6.

First, it is determined whether the compressor is on (S10).

As a result of the determination in step S10, if the compressor is on, it is determined whether the heating mode is present (S20), and when it is determined that the heating mode, the second pressure comparison unit 230 is measured by the discharge pressure sensor 102 (S21) The error between the refrigerant discharge pressure and the target high pressure of the compressor 100 is compared.

After the step S21, the discharge amount of the compressor 100 is varied by outputting a signal for adjusting the opening degree of the discharge amount control valve 170 by the error compared in the second pressure comparing unit 230. S23)

By advancing as mentioned above, this invention is effective at the time of heating as well as cooling.

As described above, according to the present invention, by controlling by simple control logic using the refrigerant discharge temperature detection sensor of the evaporator and the refrigerant pressure detection means of the compressor, by adjusting the refrigerant discharge amount of the compressor and the opening degree of the throttling means of the performance of the refrigeration cycle And maximum efficiency, and additionally, heating performance can be improved.

Claims (5)

A variable displacement compressor (100) that sucks carbon dioxide, which is a refrigerant, compresses it into a supercritical state, and has a compression capacity controlled; A gas cooler (110) for cooling the high temperature and high pressure refrigerant discharged from the compressor (100); Throttling means for expanding the refrigerant discharged from the gas cooler 110 to control the refrigerant flow rate while reducing pressure; An evaporator 140 for evaporating the refrigerant passing through the condensation means by heat exchange with blowing air; An internal heat exchanger (120) for heat-exchanging the refrigerant flowing from the evaporator (140) to the compressor and the refrigerant flowing from the gas cooler (110) to the throttling means; An accumulator (160) installed between the evaporator (140) and the internal heat exchanger (120) to phase-separate the refrigerant so that only the gaseous refrigerant is supplied to the compressor (100); A discharge amount control valve 170 for controlling the discharge amount of the compressor 100; Refrigerant pressure sensing means for sensing a refrigerant pressure of the compressor (100); It is provided with a temperature sensor 141 for detecting the refrigerant discharge temperature of the evaporator 140, In the cooling mode, the refrigerant pressure sensing means detects the refrigerant suction pressure of the compressor 100, A pressure comparator 220 for comparing the error between the refrigerant suction pressure and the set low pressure pressure of the compressor 100, and a discharge amount control signal output unit for outputting a signal for adjusting the opening degree of the discharge amount control valve 170 by the error; 221, a calculation unit 210 for calculating a refrigerant superheat degree by comparing the refrigerant discharge temperature of the evaporator 140 with the refrigerant saturation temperature calculated by the refrigerant suction pressure of the compressor 100, and the superheat of the refrigerant. The controller 200 includes an overheat degree comparison unit 211 for comparing an error between a degree of a set refrigerant and a superheat degree, and an overheat degree control signal output unit 212 for outputting a signal for adjusting the opening degree of the throttling means by the error. Supercritical air-conditioning cycle, characterized in that consisting of. The method of claim 1, The set low pressure pressure is greater than or equal to 33 bar, supercritical heating and cooling cycle, characterized in that less than or equal to 37 bar. The method of claim 1, The set refrigerant superheat degree is greater than or equal to 0k, supercritical air conditioning cycle, characterized in that less than or equal to 4k. The method of claim 1, Supercritical air conditioning cycle, characterized in that the throttling means is an electronic expansion valve (150). The method according to any one of claims 1 to 4, In the heating mode, the refrigerant pressure sensing means detects the refrigerant discharge pressure of the compressor 100, The controller 200 includes a second pressure comparison unit 230 for comparing the error between the refrigerant discharge pressure and the target high pressure of the compressor 100; And a second discharge amount control signal output unit (231) for outputting a signal for adjusting the opening degree of the discharge amount control valve (170) by the error.