JP2003322421A - High pressure side pressure control method in supercritical vapor compression circuit and circuit device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive circuit device and a control method for controlling high pressure side pressure in a supercritical vapor compression circuit using an oil feeding type screw compressor. <P>SOLUTION: This supercritical vapor compression circuit device is composed of the oil feeding type screw compressor, an oil separator, a gas cooler, an expansion valve, a closed circuit including an evaporator, and a circuit for resupplying oil supplied to the compressor, included in delivery gas, and separated by the oil separator to the compressor, and is provided with at least one of an adjusting means for adjusting at least one of a flow rate or a temperature of the supply oil or an adjusting means for adjusting an oil quantity in the oil separator by supplying the oil from an external part in the oil separator or taking out the oil to the external part in the circuit for supplying the oil to the compressor, and is provided with a control means for controlling these adjusting means so that COP becomes optimal. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor compression circuit such as a refrigeration, air conditioning, and heat pump which is equipped with a refueling screw compressor and is operated under supercritical conditions, and more specifically, when external conditions change. Maintain and secure the refrigeration capacity of
Also, the present invention relates to a control method and a circuit device for controlling the pressure on the high-pressure side so as to operate with maximum efficiency in response to changes in external conditions.

[0002]

2. Description of the Related Art Refueling type screw compressors are excellent in reliability and durability, have less vibration, and have low cost.
It is often used in refrigerators. Conventionally, halogenated hydrocarbon (CFC) refrigerants, which have been frequently used as refrigerants for refrigeration systems, air conditioners, and heat pumps, are regulated as a causative agent that causes destruction of the ozone layer. Various devices and operation methods for vapor compression refrigeration cycle using ₂ ) as a refrigerant have been proposed. CO ₂ has conventionally been used as a refrigerant in some refrigeration systems, but its critical temperature is 31 ° C, which is the critical temperature for CFCs that have been widely used in the past (for example, about 12 ° C for R12).
Since it is lower than that of the refrigerant, the high pressure side exceeded the critical point of the refrigerant in order to secure the cooling capacity in summer when the temperature of the cooling water or cooling air entering the radiator (condenser) that cools the compressed refrigerant is high. It is operated as a supercritical vapor compression cycle in which the state is reached.

FIG. 4 shows the pressure of the supercritical vapor compression cycle--
An enthalpy diagram (Ph diagram) is shown. In the figure, K
Is the critical point of the refrigerant, and in the case of CO ₂ , the temperature T _K is 31.0
5 ° C., the critical pressure P _K is 7.39MPa. The SK line is a saturated liquid line, the KV line is a saturated vapor line, and T _I , T _K , T _X , T _Y , T
_Z, T _W lines are isotherms. In the figure, the horizontal axis is the specific enthalpy (enthalpy per unit mass), but is simply described as enthalpy. Hereinafter, in the present specification, the specific enthalpy is simply referred to as enthalpy. A-B-C-D show one supercritical vapor compression cycle, which is slightly superheated than saturated vapor.
The refrigerant at the point A is sucked into the compressor, and the refrigerant is compressed by the compressor to increase the pressure and temperature, and the state becomes the point B. When the compressed refrigerant is cooled to the temperature T _X by the cooling medium by the gas cooler, the state becomes point C. The gas at the point C is throttled by an expansion valve (throttle valve) and undergoes an isenthalpic change, the pressure and temperature drop, and a wet vapor state at the point D is reached. The liquid phase component of the wet vapor takes evaporation latent heat from the medium to be cooled in the evaporator and evaporates, and becomes a state of point A of the temperature T _I that is slightly overheated due to the heat taken from the medium to be cooled, and the refrigerant Is again sucked into the compressor and compressed. In this cycle, h ₁ is the increase in the enthalpy of the refrigerant in the evaporator, that is, the amount of heat removed from the medium to be cooled, and H ₁ is the decrease in the enthalpy of the refrigerant in the gas cooler, that is, the amount of heat released to the cooling medium.

The temperature of water or air, which is the cooling medium of the gas cooler, is high, and the refrigerant temperature at the outlet of the gas cooler is T _X
If it can only cool to a higher T _Y than
A-B-C'-D ', the amount of heat taken from the medium to be cooled in the evaporator is reduced to h ₂ , and the amount of heat released to the cooling medium in the gas cooler is
Reduced to H ₂ . Pressure at the compressor outlet is higher than point B
When the B ", cycle A-B-C '' - D '' , and the deactivating amount of heat from the cooling medium in the evaporator is h _3, the heat radiation amount of the cooling medium in the gas cooler becomes H ₃ , And both are almost equal in the case of cycles A-B-C-D.

As described above, the refrigerating capacity can be enhanced by increasing the pressure on the high pressure side of the refrigerating cycle. As a method for increasing the pressure on the high pressure side, a device for changing the pressure by changing the mass of the refrigerant charged on the high pressure side by operating a throttle valve by providing a low pressure refrigerant receiver between the evaporator and the compressor inlet is disclosed in Japanese Patent Publication No.
No. -18602, a separate expansion container is provided between the throttle valve and the evaporator to adjust the refrigerant storage amount of the container to change the mass of the refrigerant charged in the circuit and change the pressure on the high pressure side. The device is disclosed in Japanese Patent No. 2804844. Further, in the apparatus disclosed in Japanese Patent Publication No. 7-18602, the refrigerant temperature at the gas cooler outlet is detected and throttled so that the coefficient of performance (COP) of the refrigeration cycle is the maximum pressure side with respect to the temperature. A high-side pressure regulation method for operating a valve is disclosed in Japanese Patent No. 2931668. Further, a supercritical vapor compression circuit device provided with a variable volume element for changing the high-pressure side circuit volume by moving a movable partition means provided inside the gas cooler and the throttle valve is provided. It is disclosed.

[0006]

However, in any of the above disclosures, in order to adjust the pressure on the high-pressure side,
It is necessary to newly provide a low pressure refrigerant receiver, a separate expansion container, or a variable volume element. For example, in a supercritical vapor compression circuit using CO ₂ as a refrigerant, the pressure is considerably high even on the low pressure side, so these containers require considerable pressure resistance and require a considerable amount of space. It becomes a factor of. An object of the present invention is to provide a control method and a circuit device that can always operate with high efficiency by adjusting the high-pressure side pressure without newly providing a container or the like in a refrigeration cycle circuit using a refueling screw compressor. Is.

[0007]

A method for controlling a high-pressure side pressure in a supercritical vapor compression circuit according to the present invention is a closed circuit including a refueling type screw compressor, an oil separator, a gas cooler, an expansion valve and an evaporator. And a circuit for supplying again the compressor the oil supplied to the compressor and contained in the discharge gas and separated by the oil separator, wherein the high-pressure side of the closed circuit operates at a supercritical pressure. In the high-pressure side pressure control method in a vapor compression circuit, the discharge gas temperature of the compressor is adjusted by adjusting at least one of the flow rate or temperature of oil supplied to the compressor, and the high-pressure side is adjusted by adjusting the discharge gas temperature. It is characterized by adjusting the pressure of.

The oil-filled screw compressor contributes to the lubrication of the rotor by injecting oil between the compressor rotors, and the sealability between the rotors and between the rotor and the casing is improved so that internal leakage is small, and during compression. Since the gas is cooled by oil, the compression power is saved. The oil injected into the gas is separated by the oil separator after being discharged and is supplied to the compressor again, and the gas separated from the oil is supplied to a predetermined place. The temperature of the discharge gas can be changed by changing at least one of the flow rate and the temperature of the oil supplied to the compressor.

In the supercritical vapor compression circuit, the high-pressure side is always a gas, so if the volume and temperature of a gas of a certain mass are determined, its pressure will be determined. The circuit volume is determined at the time of design, and the circuit volume on the high voltage side is usually much larger than that on the low voltage side. The refrigerant mass filled in the circuit is constant,
Even if the refrigerant mass in the low-pressure side circuit changes slightly depending on the operating conditions, the high-pressure side circuit volume is significantly larger than the low-pressure side circuit volume as described above, so the refrigerant mass in the high-pressure side circuit changes almost depending on the operating conditions. do not do. Therefore, the pressure on the high pressure side of the circuit can be changed by changing the temperature of the refrigerant discharged from the compressor. That is, the temperature of the refrigerant discharged from the compressor can be increased by increasing the temperature of the oil supplied to the oil supply type screw compressor or by decreasing the flow rate to increase the pressure on the high pressure side. Thus, the refrigerating capacity can be increased, that is, the refrigerating capacity can be prevented from decreasing due to the rise in the inlet temperature of the cooling medium of the gas cooler.

According to a second aspect of the present invention, a refueling screw compressor, an oil separator, a gas cooler, an expansion valve, a closed circuit including an evaporator, and a discharge gas supplied to the compressor and included in discharge gas. And a circuit for supplying the oil separated by the oil separator to the compressor again, wherein the high pressure side of the closed circuit is operated at a supercritical pressure, and the high pressure side pressure control method in a supercritical vapor compression circuit comprises: A circuit volume on the high-pressure side is adjusted by adjusting the amount of oil in the separator by supplying oil to the outside or extracting the oil from the outside, and the pressure on the high-pressure side is adjusted by adjusting the circuit volume on the high-pressure side. To do.

Since the oil separated by the oil separator of the vapor compression circuit using the oil supply type screw compressor circulates between the oil separator and the compressor, the oil separation is neglected if some wear of the oil during that time is ignored. The amount of oil in the vessel is kept constant during operation. Since the oil separator is arranged between the discharge port of the compressor and the gas cooler, the space volume occupied by the refrigerant gas in the oil cooler is included in the high pressure side circuit volume. Therefore, if oil is externally supplied to the oil separator to increase the amount of oil in the oil separator, the volume occupied by the refrigerant gas in the oil separator decreases, and the high-pressure side circuit volume decreases. As described above, since the mass of the refrigerant existing on the high pressure side is substantially constant, the high pressure side pressure can be increased by reducing the high pressure side circuit volume.

According to a third aspect of the present invention, the high pressure side pressure and the high pressure side in the operating state which are preset so that the coefficient of performance (COP) is optimized corresponding to the refrigerant temperature at the gas cooler outlet in the actual operating state. It is characterized in that the high pressure on the operating side is adjusted by comparing at least one of the flow rate or the temperature of the oil supplied to the compressor so that the difference is within a specified range. . Further, in the invention described in claim 4, the high-pressure side circuit volume is adjusted by adjusting the amount of oil in the oil separator, and the high-pressure side pressure control in the operating state is performed similarly to the third aspect.

Coefficient of performance (COP) of vapor compression refrigeration cycle
And the compressor discharge pressure (gas cooler outlet refrigerant pressure, that is, high-pressure side pressure) have a relationship as shown in FIG. 5, for example. In the supercritical vapor compression cycle, the refrigerant is in the vapor phase in the condenser (radiator) in the normal vapor compression cycle, so the condenser (radiator) is generally called a gas cooler. The figure shows the calculation results when CO ₂ is used as a refrigerant, the evaporation temperature in the evaporator is set to a saturated state of −15 ° C., and the adiabatic efficiency and mechanical efficiency of the compressor are both 100%. From the figure, the higher the refrigerant temperature at the gas cooler outlet, the higher the COP
It can be seen that the discharge pressure that maximizes the pressure is high, and that the COP decreases when the pressure exceeds that pressure. However, when the CO ₂ temperature at the gas cooler (radiator) outlet is 30 ° C or higher, the COP changes gradually with respect to the discharge pressure change near the COP maximum point. Since high discharge pressure puts a burden on the compressor and piping, it is not a good idea to increase the discharge pressure unnecessarily to reduce the COP improvement gain. Therefore, the discharge pressure (high-pressure side pressure) that is lower than the discharge pressure that maximizes the COP and that also has a high COP is set as the optimum high-pressure side pressure in advance according to the refrigerant temperature at the gas cooler outlet, and the high pressure in the operating state is set. It is preferable to control the high pressure side pressure so that the difference between the side pressure and the optimum high pressure side pressure set as described above falls within a specified range. The specified range is set to, for example, ± 0.1 MPa or the like in which a change in COP due to a change in high-pressure side pressure within that range is allowable.

FIG. 5 shows the adiabatic effect of the compressor at a constant evaporation temperature.
It is the result of calculation assuming that the rate is 100%.
Compressed polytrope when the oil flow rate or temperature to be supplied is changed
If the index changes and the evaporation temperature in the evaporator changes, the pressure
The compressor inlet temperature is different, and the discharge temperature that maximizes COP is
Affected by them. In Figure 4, the state of the refrigerant from A to B
Work required to compress up to (H₁−h₁) And frozen
The coefficient of performance (COP) of is h ₁/ (H₁−h₁) Is defined by. Salary
In case of oil type screw compressor, compressed gas is
Is cooled by the oil injected to the rotor,
Polytropic index of contraction is adiabatic index (isoentropic index)
Smaller, compression work less than in adiabatic compression
Become. The lower the oil temperature, the lower the degree of cooling by this oil.
The larger the oil flow rate is, the larger it becomes.

Therefore, in such a case, not only the refrigerant temperature at the gas cooler outlet but also at least one of the compressor inlet refrigerant temperature or pressure and the outlet refrigerant temperature, pressure and COP
Is calculated and the optimum gas cooler outlet refrigerant pressure is set for those values in the above-mentioned sense, and at least one of the operating high pressure side pressure, gas cooler outlet temperature, compressor inlet temperature or pressure is set. It is preferable to control the high-pressure side pressure so that the difference between the optimum pressure and the high-pressure side pressure corresponding to the detected temperature and outlet temperature and pressure falls within the specified range. Since the compressor inlet refrigerant temperature is set to a temperature slightly higher than the saturated vapor temperature of the refrigerant at the inlet pressure, if that amount is estimated in advance, either the compressor inlet temperature or the pressure will be either the pressure or the temperature. The other can be calculated by detecting. For applications where the inlet temperature changes significantly, the optimum high-pressure side pressure corresponding to the gas cooler outlet refrigerant temperature and the compressor inlet refrigerant temperature is set, and the high-pressure side pressure in operation and the gas cooler outlet temperature detection value and The pressure on the high-pressure side may be controlled so that the difference between the detected value of the compressor inlet temperature or the pressure of 1 and the optimum pressure on the high-pressure side falls within a specified range.

According to a sixth aspect of the present invention, a refueling type screw compressor, an oil separator, a gas cooler, an expansion valve, a closed circuit including an evaporator, and a compressor which is supplied to the compressor and is included in discharge gas. In a supercritical vapor compression circuit device comprising a circuit for supplying the oil separated by the oil separator to the compressor again, at least one of the flow rate or temperature of the supplied oil is supplied to the circuit for supplying the oil to the compressor. The invention according to claim 7 is characterized in that adjustment means for adjusting is provided, and the adjustment means for adjusting the amount of oil in the oil separator is provided by supplying or extracting oil from the outside into the oil separator. It is a circuit device characterized by that. According to the eighth aspect of the invention, the oil flow rate and temperature adjusting means as well as the oil amount adjusting means for the oil separator are provided.

According to a ninth aspect of the present invention, there is provided a high pressure side pressure detecting means, a refrigerant temperature detecting means at the gas scooter outlet,
The coefficient of performance (COP) is optimum in accordance with the gas cooler outlet refrigerant temperature detected by the detecting means by at least one adjusting means for adjusting the flow rate or temperature of the oil supplied to the compressor or the oil amount in the oil separator. And a control means for comparing the high-pressure side pressure set in advance with the high-pressure side pressure in the operating state and controlling the difference so as to fall within a specified range. With such an invention, the high-side pressure of the present invention is automatically controlled, and the optimum CO
High COP operation can be performed at P, that is, at the low side pressure as low as possible.

According to a tenth aspect of the present invention, the optimum high-pressure side pressure is set in consideration of not only the gas cooler outlet temperature but also at least one of the refrigerant temperature or pressure at the compressor inlet and the refrigerant temperature or pressure at the outlet. The optimum high-side pressure is automatically controlled in response to these detected values during operation.When the refrigerant temperature at the compressor inlet changes significantly depending on operating conditions, or when compression by the compressor It adapts even when the polytropic index changes, and always provides the optimum CO
High COP operation can be performed at P, that is, at the low side pressure as low as possible. The refrigerant used in the supercritical vapor compression circuit device is carbon dioxide.

In a twelfth aspect of the present invention, in a CO ₂ supercritical vapor compression circuit using a screw compressor as a compression element, liquid injection is performed during compression by the compressor to change the discharge gas temperature and the circuit. Is a method for controlling the pressure on the high-pressure side, and the pressure on the high-pressure side of the circuit is controlled by controlling the temperature and amount of the injection liquid. The screw compressor may be a non-lubricating type or a refueling type. According to a thirteenth aspect of the present invention, there is provided a circuit device for carrying out this control method, which comprises means for performing liquid injection into the screw compressor and means for separating the injection liquid from the gas discharged from the compressor.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples.

FIG. 1 (A) shows an embodiment of a supercritical vapor compression circuit device of the present invention, in which 1 is a refueling type screw compressor,
2 is a gas cooler, 3 is an evaporator, 4 is a throttle valve, 5 is an oil separator, and these constitute a series closed circuit. 2a
Indicates the flow of the cooling medium that cools the refrigerant by the gas cooler 2, and 3a indicates the flow of the cooled medium that is cooled by the evaporator 3. The refrigerant gas sucked from the evaporator 3 to the compressor 1 and compressed and heated includes oil supplied to the compressor, and the oil is separated from the refrigerant gas by the oil separator 5, and the oil is The separated refrigerant gas is cooled by the cooling medium 2a in the gas cooler 2 and is throttled by the throttle valve 4 to reduce the pressure and temperature to become wet vapor composed of a liquid phase and a gas phase, and the medium to be cooled in the evaporator 3 is cooled. The heat is taken from 3a to evaporate, and is made slightly superheated than the saturated steam and sucked into the compressor 1.

The oil separated by the oil separator 5 is cooled by an oil cooler 6 and supplied to the compressor 1. This oil not only lubricates the rotor of the compressor, the rotor and the casing, and the bearings, but also cools the refrigerant gas in the compression process. A three-way control valve 8 for adjusting the temperature of the oil supplied to the compressor by adjusting the amount of oil that bypasses the oil cooler is provided in the downstream of the oil cooler 6, and the three-way control valve 8 A control valve 7 for adjusting the flow rate of oil supplied to the compressor is provided in the wake. Since the pressure in the oil separator is higher than the low pressure side of the compressor to which the oil is supplied, the oil is supplied by the pressure difference, and the oil flow rate is adjusted by adjusting the opening degree of the control valve 7. It In the oil-filled screw compressor, since the effect of cooling the refrigerant in the compression process by the oil injected to the rotor is great, it is possible to change the temperature of the refrigerant gas discharged from the compressor by changing at least one of the oil temperature and the flow rate. it can. Since the high-pressure side volume of the circuit is constant and the charged mass of the high-pressure side refrigerant is substantially constant regardless of the operating state, the high-pressure side pressure of the circuit can be changed by changing the discharge temperature of the refrigerant gas.

FIG. 1B shows another embodiment of the present invention,
The oil separator 5 is provided with adjusting means for supplying oil from the outside or taking oil out of the oil separator 5. The adjusting means includes an oil tank 10, an oil pump 11, and an opening / closing valve 12, and when increasing the amount of oil in the oil separator 5, the oil pump 11 transfers oil from the oil tank to the oil separator 5. When supplying and reducing the amount of oil in the oil separator 5, the on-off valve 12 is opened and the oil in the oil separator 5 is taken out to the oil tank 10. Since the pressure inside the oil separator 5 is higher than the pressure inside the tank 10, the oil inside the oil separator 5 flows out to the tank 10 when the on-off valve 12 is opened. Since the refrigerant gas space volume in the oil separator 5 constitutes a part of the high-pressure side volume of the circuit, the refrigerant gas space in the oil separator 5 can be changed by changing the amount of oil in the oil separator 5. The volume can be varied and the high side volume of the circuit can be varied. As described above, since the charged mass of the high-pressure side refrigerant is substantially constant regardless of the operating state, the high-pressure side pressure of the circuit is changed by changing the high-pressure side volume of the circuit by changing the refrigerant gas space volume in the oil separator 5. be able to.

FIG. 2 shows the apparatus of the present invention, which is constructed so that the coefficient of performance (COP) of refrigeration is automatically controlled so that it is always operated optimally. A symbol surrounded by a circle indicates the temperature and pressure detecting means at that position, or the temperature, pressure, or control signal at that position. Compressor 1
Although the discharge pressure and the outlet pressure of the gas cooler 2 differ by the amount of the line resistance between them, since this resistance is usually small, they are ignored and the compressor discharge pressure and the gas cooler outlet pressure are the same.

Refrigerant temperature T ₃ and pressure P _{2 at} the outlet of the gas cooler ₂
A detection means for detecting is detected at the refrigerant outlet of the gas cooler 2, and the detected value is sent to the control means 20. The control means 20
Compares the predetermined optimum high-pressure side pressure corresponding to the detected temperature T ₃ with the detected high-pressure side pressure P _2, and controls the three-way control valve 8 so that the difference falls within the regulation. signal
The pressure on the high-pressure side is adjusted by sending C ₂ to adjust the temperature of the oil supplied to the compressor 1, or the flow rate of the oil supplied to the compressor ₁ by sending a control signal C ₁ to the control valve 7. To adjust the high pressure side by adjusting the
Alternatively, the control signal C ₄ or C ₃ is sent to the open / close valve 12 to adjust the amount of oil in the oil separator 5 to adjust the circuit volume on the high pressure side to adjust the pressure on the high pressure side.

As described above, the optimum high-pressure side pressure is the high-pressure side pressure at which the COP is close to the maximum without unnecessarily increasing the high-pressure side pressure with respect to the rise in the gas cooler outlet refrigerant temperature. The pressure is preset in accordance with. The relationship between the optimum high-pressure side pressure and the gas cooler outlet refrigerant temperature is input to the control means as a map.

Since the high pressure side pressure adjusting effect by the control of the three-way control valve 8 and the high pressure side pressure adjusting effect by the opening / closing valve 7 are different, although not shown, the oil temperature and the oil flow rate are detected and input to the control means 20. A map indicating which and to what extent these values are adjusted according to the detected values and the required adjustment amount of the high-pressure side pressure is input to the control means 20 and selected according to the map. Compressor 1 as shown in FIG.
In the case of a circuit device capable of adjusting the high pressure side pressure by adjusting the oil temperature and oil flow rate to be supplied to the oil separator and the high pressure side pressure adjustment by adjusting the oil amount in the oil separator 5, the oil level of the oil separator 5 is not shown. It is detected and input to the control means 20, and a map for selecting the adjustment means is created according to the oil temperature, the oil flow rate, and the necessary adjustment amount of the oil surface and the high-pressure side pressure, and is input to the control means. For example, if the oil temperature is higher than the specified value, the adjustment to increase the oil temperature is not performed, and if the oil flow rate is lower than the specified value, the adjustment to reduce the oil flow rate is not performed.

FIG. 3 is different from FIG. 2 in the gas cooler 2 inlet refrigerant pressure, temperature (compressor discharge pressure, temperature) P ₂ , T ₂ and evaporator 3 outlet refrigerant pressure, temperature (compressor suction pressure, temperature). P ₁ ,
T _I and T _I are additionally input to the control means 20.
If the refrigeration load changes significantly, for example due to refrigeration, T _I
Is operated at -20 ° C and T _I is 20 ° C due to cooling
The pressure on the high-pressure side at which the COP is maximized is different for the same gas cooler outlet refrigerant temperature, and therefore the pressure to be set as the optimum high-pressure side pressure is also different from the case of operating at. In such a case, the gas cooler outlet refrigerant temperature
A map of the optimum high-pressure side pressure with respect to T ₃ and the evaporator outlet refrigerant temperature T _I is created and input to the control means 20,
The optimum high-side pressure is controlled according to the detected values of T ₃ and T _I.

When the temperature and flow rate of the oil supplied from the oil separator 5 to the compressor 1 are adjusted to change the compressor discharge temperature to adjust the high-pressure side pressure, the polytopotope index of the compressor is changed to compress the oil. Machine work changes, which affects the gas cooler outlet refrigerant pressure where COP is maximized. Work required to compress (in FIG. 4 (H ₁ -h ₁₎ or _{(H 2 -h 2), (} H 3 -h 3)) is
Since it is determined by P ₁ , T _I , P ₂ , and T ₂ , the high-pressure side pressure that maximizes COP for the same gas cooler outlet refrigerant temperature depends on these pressures and temperatures, and is therefore set as the optimum high-pressure side pressure. The pressure to be used will also be different.
In that case, in addition to the gas cooler outlet refrigerant temperature T ₃ , create a map of the optimum high-side pressure for these, including the refrigerant pressure at the evaporator inlet and outlet, and the temperatures P ₁ , T _I , P ₂ , and T _2. It is input to the control means 20 and T ₃ , P ₁ , T _I , P ₂ ,
The optimum high-side pressure is controlled according to the detected value such as T ₂ . The evaporator outlet refrigerant temperature (compressor inlet temperature) T _I is operated at a temperature slightly higher than the saturated vapor temperature of the refrigerant at the pressure P _1, so if you anticipate that amount in advance, if P ₁ is known, then T _{If I} knows, on the other hand, if T _I knows, P ₁ knows. Therefore, the control means 2 is provided with a detection means for detecting either P ₁ or T _I.
You may enter 0.

As shown in FIG. 5, when the gas cooler (radiator) outlet temperature becomes lower, the discharge pressure (high-pressure side pressure) at which COP becomes maximum becomes lower. When the temperature of the refrigerant at the outlet of the gas cooler (radiator) becomes lower than the critical temperature of the refrigerant, the refrigerant becomes a liquid phase and the density rapidly increases, so the high-pressure side pressure also drops, but the refrigerant in the liquid phase becomes a radiator. Since there is only the refrigerant near the outlet and most of the refrigerant is in the vapor phase, the pressure drop on the high-pressure side is not large. According to the method of adjusting the amount of oil in the oil separator of the present invention to adjust the high-pressure side pressure, the high-pressure side pressure can be sufficiently reduced, and the gas cooler (radiator) outlet temperature becomes equal to or lower than the critical temperature. High if
The high-side pressure can be controlled so that the COP can be operated.

In FIG. 2 or 3, CO is used as the refrigerant.
_When using 2, the inlet refrigerant temperature of the gas cooler 2 is 90
Since the temperature is raised to about 110 ° C, if the cooling medium 2a of the gas cooler 2 is water, the outlet temperature can be raised to about 80 to 90 ° C, and the gas cooler can be used as a heat source for supplying hot water. In that case, the cooling medium 2
Although it is difficult to always keep the temperature and flow rate of a constant for the refrigeration system, the circuit device and the control method of the present invention can always operate with a high COP against these variations.

[0032]

The present invention is carried out in the form as described above and has the following effects.

By adjusting the temperature and flow rate of the oil supplied from the oil separator to the oil supply screw compressor, the temperature of the refrigerant discharged from the compressor can be adjusted to adjust the high pressure side pressure. Further, by adjusting the amount of oil in the oil separator by supplying oil from the outside or taking it out to the outside, the high-pressure side volume of the circuit can be adjusted and the high-pressure side pressure can be adjusted. Then, by detecting the temperature and pressure during operation,
The COP at these temperatures and pressures can be automatically controlled so that the pressure on the high-pressure side effectively raises the COP to near the maximum. The circuit device of the present invention does not need to be added with a tank or the like exposed to high pressure, and can be easily configured by adding a control valve or the like to the conventional circuit device.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a supercritical vapor compression circuit device according to an embodiment of the present invention.

FIG. 2 is an example of a control system diagram of a supercritical vapor compression circuit device according to an embodiment of the present invention.

FIG. 3 is another example of the control system diagram of the supercritical vapor compression circuit device according to the embodiment of the present invention.

FIG. 4 is a pressure-enthalpy diagram of a refrigerant.

FIG. 5 is a diagram showing a relationship between a high pressure side pressure and a coefficient of performance (COP) using a radiator outlet refrigerant temperature as a parameter.

[Explanation of symbols]

1 Lubricating screw compressor 2 gas cooler (radiator) 3 evaporator 4 Throttle valve 5 oil separator 6 oil cooler 7 control valve 8 three-way control valve 10 oil tank 11 oil pump 12 open / close valve

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F25B 1/047 F25B 1/047 RT 43/02 43/02 N (72) Inventor Yuji Murase Midori Ward, Nagoya City, Aichi Prefecture 1 at 20 Kitakanyama, Otakacho Chubu Electric Power Co., Inc. Energy Research Laboratory (72) Inventor Katsumi Fujima 2-13-1 Botan, Koto-ku, Tokyo Maekawa Works, Ltd. (72) Inventor Asahi Yoshikawa Iku 2-13-1 Botan, Koto-ku, Tokyo Stock company Maekawa Works (72) Inventor Hirokazu Yoneda 2-3-1 Botan, Koto-ku, Tokyo Maekawa Works Co., Ltd.

Claims (13)

[Claims] 1. A closed circuit including a refueling screw compressor, an oil separator, a gas cooler, an expansion valve, and an evaporator,
A supercritical vapor compression circuit comprising a circuit for supplying the oil supplied to the compressor and contained in the discharge gas and separated by the oil separator to the compressor again, and the high-pressure side of the closed circuit operates at a supercritical pressure. In the high pressure side pressure control method for a circuit, the discharge gas temperature of the compressor is adjusted by adjusting at least one of the flow rate or temperature of the oil supplied to the compressor, and the high pressure side pressure is adjusted by adjusting the discharge gas temperature. A pressure control method for a high pressure side in a supercritical vapor compression circuit, characterized in that: 2. A closed circuit including a refueling screw compressor, an oil separator, a gas cooler, an expansion valve, and an evaporator,
A supercritical vapor compression circuit comprising a circuit for supplying the oil supplied to the compressor and contained in the discharge gas and separated by the oil separator to the compressor again, and the high-pressure side of the closed circuit operates at a supercritical pressure. In the high-pressure side pressure control method in a circuit, the circuit volume on the high-pressure side is adjusted by adjusting the amount of oil in the oil separator by externally supplying or extracting oil, and by adjusting the circuit volume on the high-pressure side. A high pressure side pressure control method in a supercritical vapor compression circuit, characterized by adjusting the high pressure side pressure. 3. A high pressure side pressure preset so that the coefficient of performance (COP) is optimized corresponding to the refrigerant temperature at the gas cooler outlet in an actual operating state and a high pressure side pressure in an operating state are compared. 2. The supercritical pressure according to claim 1, wherein at least one of the flow rate or temperature of oil supplied to the compressor is adjusted so that the difference falls within a specified range to adjust the high-pressure side pressure in the operating state. High pressure side pressure control method in vapor compression circuit. 4. The high pressure side pressure preset to optimize the coefficient of performance (COP) corresponding to the refrigerant temperature at the gas cooler outlet in an actual operating state is compared with the high pressure side pressure in the operating state. 3. The high-pressure side pressure in the operating state is adjusted by adjusting the amount of oil in the oil separator and adjusting the high-pressure side circuit volume so that the difference falls within a specified range. A method for controlling a high-pressure side pressure in the described supercritical vapor compression circuit. 5. The coefficient of performance (COP) corresponds to at least one of the gas cooler outlet refrigerant temperature, the compressor inlet refrigerant temperature or pressure, and the outlet refrigerant temperature and pressure, in addition to the gas cooler outlet refrigerant temperature. The high pressure side pressure control method in a supercritical vapor compression circuit according to claim 3 or 4, wherein the pressure is set to be optimum. 6. A closed circuit including a refueling screw compressor, an oil separator, a gas cooler, an expansion valve, and an evaporator,
A circuit for supplying oil to the compressor, in a supercritical vapor compression circuit device comprising a circuit for supplying again the oil supplied to the compressor and contained in discharge gas and separated by the oil separator. A supercritical vapor compression circuit device, characterized in that an adjusting means for adjusting at least one of the flow rate and the temperature of the supplied oil is provided in the. 7. A closed circuit including a refueling screw compressor, an oil separator, a gas cooler, an expansion valve, and an evaporator,
In a supercritical vapor compression circuit device comprising a circuit that supplies oil to the compressor and is contained in discharge gas and separated by the oil separator, and supplies the oil again to the compressor, an oil is externally supplied into the oil separator. A supercritical vapor compression circuit device, characterized in that adjustment means is provided for adjusting the amount of oil in the oil separator by supplying or extracting the oil to the outside. 8. A closed circuit including a refueling screw compressor, an oil separator, a gas cooler, an expansion valve, and an evaporator,
A circuit for supplying oil to the compressor, in a supercritical vapor compression circuit device comprising a circuit for supplying again the oil supplied to the compressor and contained in discharge gas and separated by the oil separator. And an adjusting means for adjusting at least one of the flow rate or the temperature of the supplied oil and an adjusting means for adjusting the amount of oil in the oil separator by supplying or extracting oil from the outside into the oil separator. A supercritical vapor compression circuit device characterized in that 9. A high-pressure side pressure detecting means, a refrigerant temperature detecting means at the gas scooter outlet, and at least one adjusting means for adjusting the flow rate or temperature of oil supplied to the compressor or the amount of oil in the oil separator. The coefficient of performance (CO
And a control means for comparing the high-pressure side pressure preset to optimize P) with the high-pressure side pressure in the operating state and controlling the difference so as to fall within a specified range. The supercritical vapor compression circuit device according to any one of claims 6 to 8. 10. A high pressure side pressure detecting means, a detecting means for detecting at least one of a refrigerant temperature at the gas scooter outlet, a refrigerant temperature or pressure at the compressor inlet, and an outlet refrigerant temperature and pressure, and the compressor. At least one adjusting means for adjusting the flow rate or temperature of the oil to be supplied or the oil amount in the oil separator is used to optimize the coefficient of performance (COP) in accordance with the refrigerant temperature and pressure detected by the detecting means. 9. A control means for comparing a preset high pressure side pressure with an operating high pressure side pressure and controlling the difference so as to fall within a prescribed range.
The supercritical vapor compression circuit device according to any one of 1. 11. The supercritical vapor compression circuit device according to claim 6, wherein the refrigerant used is carbon dioxide. 12. A CO using a screw compressor as a compression element.
_{2 In the} supercritical vapor compression circuit, the high pressure side pressure in the supercritical vapor compression circuit characterized by controlling the high pressure side pressure of the circuit by changing the discharge gas temperature by performing liquid injection during compression by the compressor Control method. 13. CO using a screw compressor as a compression element
_{2. In the} supercritical vapor compression circuit device, the compressor is provided with a means for performing liquid injection and a means for separating the injection liquid contained in the discharge gas.