KR20080095635A - Air conditioner utilizing carbon dioxide refrigerant - Google Patents

Abstract

An air conditioner utilizing carbon dioxide refrigerant is provided to control precisely through system analysis in supercritical refrigerating cycle using carbon dioxide as refrigerant. An air conditioner utilizing carbon dioxide refrigerant comprises a compressor(11) taking in carbon dioxide refrigerant and then compressing it; a gas cooler(13) cooling refrigerant discharged from a outlet of the compressor; a throttling unit(16) controlling refrigerant flow rate while expanding refrigerant discharged from the gas cooler and then reducing pressure; an evaporator(15) evaporating refrigerant passing through the throttling unit by heat exchanging with blast air; a refrigerant temperature sensing unit(24) detecting the refrigerant temperature on outlet side of the gas cooler; an outdoor temperature sensing unit(25) sensing outdoor temperature outside a vehicle; a refrigerant flow rate sensing unit(26) sensing current flow rate of refrigerant; and a control unit(22) controlling the compressor or the throttling unit.

Description

Air conditioner utilizing carbon dioxide refrigerant

1 is a view showing an air conditioner according to the present invention.

2 is a graph showing the relationship between the system target refrigerant circulation flow rate according to the outside air temperature flowing into the gas cooler and the gas cooler outlet side refrigerant temperature according to the present invention.

3 is a control flowchart according to the present invention.

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

11: compressor

13: gas cooler

15: evaporator

16: throttling means

18: internal heat exchanger

22: control means

24: refrigerant temperature detection means

25: outside temperature sensing means

26: refrigerant flow rate detection means

The present invention relates to an air conditioner using a carbon dioxide refrigerant, and more specifically, a target refrigerant circulation flow rate value is calculated according to the outlet temperature and the outside temperature of the gas cooler so that the current refrigerant circulation flow rate value is the target refrigerant circulation flow rate value. The air conditioner using the carbon dioxide refrigerant to improve the cooling performance and the cooling efficiency by controlling the discharge capacity of the compressor or the opening degree of the expansion valve which is the throttling means to reach.

As conventional refrigerants such as R134a are known to be the main culprit of environmental destruction such as ozone layer destruction and global warming, there is a growing interest in the development of alternative refrigerants to protect the environment. Critical refrigeration cycles are drawing attention.

Carbon dioxide as a refrigerant has two major advantages, which have a low compression ratio and excellent compression efficiency, and because of its excellent heat transfer characteristics, a temperature approach (inlet temperature of the secondary fluid, the outlet temperature of the refrigerant) is known. It is much smaller than the refrigerant. This means that the heat is easily transferred even though the temperature difference between the refrigerant and the air is excellent because of its excellent heat transfer characteristics, which is why carbon dioxide is attracting much attention as an operating refrigerant of a heat pump that needs to absorb heat from cold outside air in winter. In addition, carbon dioxide has many advantages over conventional refrigerant R134a, which has a lower critical temperature and higher evaporation pressure than conventional refrigerant R134a. Therefore, it can be predicted that the supercritical refrigeration cycle using carbon dioxide as a refrigerant is a cycle over a critical pressure. In addition, since carbon dioxide has excellent thermodynamic properties, the volumetric cooling rate of carbon dioxide (capacity volume ratio = evaporation latent heat × gas density) is 7 to 8 times higher than that of R134a. Can be greatly reduced. In addition, carbon dioxide has an excellent boiling heat transfer due to its small surface tension, and has a favorable 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 evaporation pressure as well as the gas cooling pressure (conventional condensation pressure) compared to a general refrigeration cycle using R134a as a refrigerant. That is, in the supercritical refrigeration cycle, the evaporation pressure is approximately 10 times higher than that of the normal refrigeration cycle, and the gas cooling pressure is about 7 times higher (about 120 bar). For this reason, researches have been conducted on devices and systems for protecting each component (compressor, gas cooler, etc.) from high pressure, and research on system control technology considering overall cooling efficiency has been conducted.

As such, in the supercritical refrigeration cycle, optimal system control is essential due to the high pressure operating conditions and various characteristics of carbon dioxide. This is because the compression ratio is small, but the suction pressure is high, so the work required for the overall compression process may be higher than that of R134a. Therefore, even if the cooling performance is excellent, there is much room for efficiency reduction.

In addition, the supercritical refrigeration cycle is characterized by the amount of refrigerant discharged from the compressor by various signals transmitted from sensors for optimum efficiency control (gas cooler inlet temperature sensor, gas cooler outlet temperature sensor, gas cooler outlet pressure sensor, evaporator outlet pressure sensor, etc.). Although it is designed to adjust the expansion valve opening, there are so many such sensors that not only increases the construction cost of the supercritical refrigeration cycle, but also the complicated control logic of the system makes it difficult to precisely control the system. It is very difficult to calculate and apply the driving torque of the, and in the case of the embodiment controlled by the outside temperature, there is a problem that it is not an optimal control method because the heat exchange efficiency according to the amount of air flowing into the radiator is not considered.

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

The present invention was created to solve the above problems, the target refrigerant circulation flow rate value is calculated according to the refrigerant temperature and the outside temperature of the outlet side of the gas cooler so that the current refrigerant circulation flow rate value reaches the target refrigerant circulation flow rate value By controlling the discharge capacity of the compressor or the opening degree of the expansion valve as the throttling means, it is possible to improve the cooling performance and the cooling efficiency, and can effectively control the whole system, and the system in the supercritical refrigeration cycle using carbon dioxide as a refrigerant The aim is to provide an air conditioner using carbon dioxide refrigerant that enables the implementation of a new system design and control logic that enables simple and precise control through analysis.

An air conditioner using a carbon dioxide refrigerant according to the present invention for achieving the above object comprises a compressor for sucking and compressing carbon dioxide which is a refrigerant; A gas cooler for cooling the refrigerant discharged from the discharge port of the compressor; Throttling means for expanding the refrigerant discharged from the gas cooler to adjust the refrigerant flow rate while reducing pressure; An evaporator for evaporating the refrigerant passing through the condensation means by heat exchange with blowing air; Refrigerant temperature sensing means for sensing an outlet refrigerant temperature of the gas cooler; Outside temperature sensing means for sensing an outside temperature of the vehicle; Refrigerant flow rate sensing means for sensing a current flow rate through which the refrigerant flows; The target refrigerant circulation flow rate value is calculated based on the refrigerant temperature at the outlet side of the gas cooler 13 and the outside air temperature to satisfy the maximum cooling efficiency, and the current refrigerant circulation flow rate value reaches the calculated target refrigerant circulation rate value. 11) or control means 22 for controlling the throttling means 16.

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

1 is a view showing an air conditioner according to the present invention, Figure 2 is a graph showing the relationship between the system target refrigerant circulation flow rate according to the outside air temperature flowing into the gas cooler and the gas cooler outlet side refrigerant temperature according to the present invention 3 is a control flowchart according to the present invention.

As shown in FIG. 1, the air conditioner using the carbon dioxide refrigerant according to the present invention includes a compressor 11 for sucking and compressing carbon dioxide, which is a refrigerant, and a gas for cooling the refrigerant discharged from the discharge port of the compressor 11. The cooler 13, the throttling means 16 for expanding the refrigerant discharged from the gas cooler 13 to regulate the refrigerant flow rate while reducing the pressure, and the refrigerant passing through the throttling means 16 by heat exchange with the blowing air. An evaporator 15 for evaporating, an internal heat exchanger 18 for exchanging a refrigerant flowing from the evaporator 15 to the compressor 11 and a refrigerant flowing from the gas cooler 13 to the throttling means 16; Refrigerant temperature sensing means 24 for sensing the temperature of the refrigerant on the outlet side of the gas cooler 13, outside temperature sensing means 25 for sensing the outside air temperature of the vehicle, and detects the current circulation flow rate through which the refrigerant flows Refrigerant flow rate It comprises an index stage 26 and, the control means 22.

Here, it is preferable to use a variable displacement type compressor having a variable discharge capacity as the compressor 11.

The outside air detected by the outside air temperature detecting means 25 is air when the outside air of the vehicle or the outside air passes through the gas cooler 13.

The control means 22 calculates a target refrigerant circulation flow rate value at the outlet side refrigerant temperature and the outside air temperature of the gas cooler 13 to satisfy the maximum cooling efficiency (COP), and the current refrigerant circulation flow rate value is calculated as the target. The compressor 11 or the throttling means 16 is controlled to reach the refrigerant circulation flow rate value.

The target refrigerant circulation flow rate value is represented by the following equation, M = a x T _gc + b x T _amb + C, where M = target refrigerant circulation flow rate value [kg / h], T _gc = gas cooler outlet refrigerant temperature. [° C], T _amb = outside temperature [° C], a, b, c = constant).

Herein, it is preferable that the constant a is (20.5 ± 1), the constant b is − (16.9 ± 1), and the constant c is − (115 ± 10).

This formula was obtained by the applicant based on experiments under various conditions.

That is, as shown in FIG. 2, when the outside air temperature flowing into the gas cooler is 43 ° C., the detected gas cooler outlet refrigerant temperature is approximately 45 ° C., and the target refrigerant circulation flow rate value (◆ Shape) has a linear relationship like line 1.

When the outside air temperature flowing into the gas cooler is 35 ° C, the gas cooler outlet side refrigerant temperature is approximately 37 ° C. As the refrigerant temperature increases or decreases, the target refrigerant circulation flow rate value is linear as in line 2. It was found out.

That is, it can be seen that the target refrigerant circulation flow rate value (M) has a linear relationship with the gas cooler outlet side refrigerant temperature and the outdoor air temperature flowing into the gas cooler, and the target refrigerant circulation flow rate value described above through the refrigerant temperature and the outside air temperature. The above-described equation for obtaining (M) can be derived.

Referring to the operation of the present invention configured as described above are as follows.

The compressor 11 sucks carbon dioxide in a low temperature low pressure state, which is a refrigerant, and compresses and discharges the sucked refrigerant into a supercritical state to have a high pressure higher than a critical pressure.

The high temperature and high pressure supercritical refrigerant discharged from the compressor 11 passes through the inside of the gas cooler 13 and is blown to the outside air blown to pass through the outer surface of the gas cooler 13 by the cooling fan 13a. It cools down and changes to low temperature.

The internal heat exchanger 18 heats the low temperature refrigerant discharged from the gas cooler 13 with the low temperature refrigerant discharged after passing through the inside of the evaporator 15, thereby lowering the temperature to a lower temperature than the external air.

Here, the internal heat exchanger 18 is a first heat exchanger for allowing the refrigerant discharged from the gas cooler 13 to be supplied to the throttling means 16, and the refrigerant discharged from the evaporator 15 passes through the compressor. It consists of a second heat exchanger to be returned, the refrigerant is heat exchanged with each other in the first heat exchanger and the second heat exchanger.

Next, the throttling means 16 is discharged from the gas cooler 13 and expands the refrigerant passing through the internal heat exchanger 18 to depressurize and reduce the temperature so that the refrigerant is changed to a state of low pressure lower than the critical pressure to the evaporator 13. It is a function of controlling the flow rate of the refrigerant while controlling the flow, which is used as a variable expansion valve as the throttling means (16), which is an electronic expansion valve or a solenoid type electronic expansion valve with a built-in stepping motor There is an expansion valve.

Finally, the evaporator 15 is air (indoor or outdoor air) blown to pass through the outer surface of the refrigerant supplied from the electronic expansion valve, which is the throttling means 16, and flows therein by the blower 15a. Heat exchanger) to evaporate the refrigerant and at the same time reduce the temperature of the blowing air to make it cold. The blowing air changed into cold by the evaporator 15 is supplied to the vehicle interior through an open vent (not shown) of the air conditioning case (not shown) according to the air conditioning mode to cool the vehicle interior.

In addition, the refrigerant discharged from the evaporator 15 lowers the temperature of the refrigerant passing through the first heat exchanger while the heat exchanger passes through the second heat exchanger of the internal heat exchanger 18 and passes through the first heat exchanger. Is returned to the compressor (11).

In the air conditioner constituting the supercritical refrigeration cycle of the present invention as described above, the control means 22 is a target refrigerant at the exit refrigerant temperature and the outside air temperature of the gas cooler 13 to satisfy the maximum cooling efficiency. The circulation flow rate value is calculated and the compressor 11 or the throttling means 16 is controlled such that the current refrigerant circulation flow rate value reaches the calculated target refrigerant circulation flow rate value.

In more detail with reference to the flow chart of Figure 3 as follows.

As shown in FIG. 3, the refrigerant temperature input step S1 is performed in which data on the gas cooler outlet side refrigerant temperature detected by the refrigerant temperature sensing means 24 is input to the control means 22.

At the same time as performing the step (S1) to perform the outside temperature temperature input step (S2) that the data on the outside temperature sensed by the outside air temperature sensing means 25 is input to the control means (22).

Subsequently, the step (S1) (S2) is carried out so that the control means 22 the target refrigerant circulation flow rate value (M) by the outlet temperature and the outside temperature of the gas cooler 13 to satisfy the maximum cooling efficiency The calculation (S3) is performed based on one formula.

After the step S3, the current refrigerant circulation flow rate value input step S4 in which data on the current refrigerant flow rate value sensed by the refrigerant flow rate detection means 26 is input to the control means 22 is performed. Perform.

After performing the step S4, the step of determining the magnitude of the current refrigerant circulation flow rate value and the target refrigerant circulation flow rate value is proceeded.

As a result of the determination in step S5, when the current refrigerant circulation flow rate value is smaller than the target refrigerant circulation flow rate value, the discharge capacity of the compressor 11 is increased or the opening degree of the throttling means 16 is increased. Proceed to step S6.

On the other hand, as a result of the determination in step S5, when the current refrigerant circulation flow rate value is larger than the target refrigerant circulation flow rate value, the discharge capacity of the compressor 11 is reduced or the opening degree of the throttling means 16 is reduced. The control to proceed to step (S7).

Therefore, by controlling the discharge capacity of the compressor or the opening degree of the expansion valve which is the throttling means, it is possible to improve the cooling performance and the cooling efficiency, and to effectively control the entire system.

As described above, the present invention minimizes the number of detection means in the supercritical refrigeration cycle using carbon dioxide as a means of detecting the outlet temperature, the outside temperature, and the current refrigerant flow rate of the gas cooler. System analysis enables new system design and control logic to enable simple and precise control.

The target refrigerant circulation flow rate value is calculated by using the outlet side refrigerant temperature and the outside air temperature of the gas cooler so as to satisfy the maximum cooling efficiency, and the current refrigerant circulation flow rate value reaches the calculated target refrigerant circulation rate value. By controlling the throttling means, it is possible to effectively control over the entire system.

In the present invention, the control means 22 controls the compressor 11 to control the discharge capacity. However, when the throttle means 16 uses the electronic expansion valve, the discharge capacity of the compressor 11 is controlled or At the same time, the opening amount of the throttling means 16 can be variably controlled.

As described above, according to the present invention, the discharge capacity of the compressor or the discharge capacity of the compressor is calculated so that the target refrigerant circulation flow rate value reaches the target refrigerant circulation flow rate value by calculating the target refrigerant circulation flow rate value according to the outlet temperature of the gas cooler and the ambient air temperature. By controlling the opening degree of the expansion valve which is the throttling means, the cooling performance and the cooling efficiency can be improved, and it is possible to effectively control over the whole system.

In addition, the present invention, it is possible to implement a new system design and control logic capable of simple and precise control through system analysis in a supercritical refrigeration cycle using carbon dioxide as a refrigerant.

Claims (4)

A compressor 11 for sucking and compressing carbon dioxide which is a refrigerant; A gas cooler (13) for cooling the refrigerant discharged from the discharge port of the compressor (11); Throttling means (16) for expanding the refrigerant discharged from the gas cooler (13) to control the refrigerant flow rate while reducing pressure; An evaporator (15) for evaporating the refrigerant having passed through the throttling means (16) by heat exchange with blowing air; Refrigerant temperature sensing means (24) for sensing an outlet side refrigerant temperature of the gas cooler (13); An outside air temperature sensing means 25 for sensing an outside air temperature of the vehicle; Refrigerant flow rate detection means (26) for sensing a current flow rate through which the refrigerant flows; The target refrigerant circulation flow rate value is calculated based on the refrigerant temperature at the outlet side of the gas cooler 13 and the outside air temperature to satisfy the maximum cooling efficiency, and the current refrigerant circulation flow rate value reaches the calculated target refrigerant circulation rate value. 11) or an air conditioner using a carbon dioxide refrigerant, characterized in that it comprises a control means (22) for controlling the throttling means (16). The method of claim 1, The target refrigerant circulation flow rate value is, M = a × T _gc + b × T _amb + C, (M = target coolant circulation flow rate value, T _gc = gas cooler outlet coolant temperature, T _amb = outside temperature, a, b, c = constant) Air conditioning apparatus using a carbon dioxide refrigerant, characterized in that calculated by. The method of claim 2, The constant a is 20.5 ± 1, the constant b is-(16.9 ± 1), the constant c is-(115 ± 10) air conditioning apparatus using a carbon dioxide refrigerant. The method of claim 1, When the current refrigerant circulation flow rate value is smaller than the target refrigerant circulation flow rate value, the discharge capacity of the compressor 11 is increased or the opening degree of the throttling means 16 is increased. If the current refrigerant circulation flow rate value is greater than the target refrigerant circulation flow rate value, the air using the carbon dioxide refrigerant, characterized in that the discharge capacity of the compressor 11 is reduced or the opening degree of the throttling means 16 is controlled to be reduced. Conditioner.

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