JP4313083B2 - Screw refrigeration equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a screw refrigeration apparatus using an economizer.
[0002]
[Prior art]
Conventionally, a screw refrigeration apparatus using an economizer is known (see, for example, Patent Documents 1 and 2).
[0003]
[Patent Document 1]
JP-A-7-83525 (FIG. 1)
[Patent Document 2]
Japanese Patent Laying-Open No. 2003-21089 (FIG. 1)
[0004]
Patent Document 1 discloses a screw refrigeration apparatus using an oil-cooled screw compressor, which guides refrigerant gas evaporated by an economizer into a rotor chamber, and is used as a cooling heat source for oil cooling. A screw refrigeration apparatus is disclosed in which a gas is introduced into a rotor chamber closer to the discharge port than the refrigerant gas.
[0005]
Patent Document 2 discloses a screw refrigeration apparatus using a two-stage screw compressor, provided with an economizer, and driving to rotate the first-stage compressor and the second-stage compressor at the same rotational speed. There is disclosed a screw refrigeration apparatus formed so that the capacity of a two-stage screw compressor can be changed by controlling the number of rotations of a motor.
[0006]
[Problems to be solved by the invention]
In the case of a screw refrigeration system using a screw compressor, the economizer system can be easily incorporated into the screw refrigeration system by allowing the refrigerant from the economizer flow path to flow into the compression space of the screw compressor, that is, the intermediate pressure section. Furthermore, since the refrigeration capacity and COP (coefficient of performance (= refrigeration capacity / power consumption)) can be improved even if the rotation speed of the motor that is the drive unit of the screw compressor is constant, the economizer The refrigeration apparatus incorporating is widely used than before.
[0007]
The screw refrigeration apparatus disclosed in Patent Document 1 uses an economizer, and the screw refrigeration apparatus disclosed in Patent Document 2 uses an economizer and a motor whose rotational speed is controlled via an inverter. There is also a point where improvement can be expected. However, these refrigeration devices have been found to have the following problems.
[0008]
First, the first problem is that the performance in a region where the rotational speed of the motor is low is lowered. That is, as is well known, the screw compressor has a structure in which a pair of male and female screw rotors mesh with each other and rotate to compress the gas, and as illustrated in FIG. Adiabatic efficiency (compression efficiency during adiabatic compression) decreases. In FIG. 5, the horizontal axis represents the rotational speed ratio expressed with reference to the rated rotational speed of the screw rotor, and the vertical axis represents the thermal insulation efficiency ratio expressed with reference to the thermal insulation efficiency at the rated rotational speed. As shown in the figure, when the rotation speed ratio is about 25%, the heat insulation efficiency is reduced by about 20%. As the cooling heat load is reduced, even if the rotational speed of the screw rotor is reduced, there is a surplus in the heat exchange capacity of the evaporator, so if the compression efficiency of the screw compressor is constant, Improvement of refrigeration capacity is expected. However, as shown in FIG. 6, with respect to the COP ratio, the screw speed becomes maximum at around 50% of the rated speed, and as the cooling heat load decreases, that is, as the speed of the screw rotor decreases, There is a problem that the performance of the compressor is lowered, that is, the heat insulation efficiency is lowered, and the COP ratio is also lowered. In FIG. 6, the horizontal axis represents the rotational speed ratio expressed in the same manner as described above, and the vertical axis represents the COP ratio expressed with reference to the COP at the rated rotational speed.
[0009]
The second problem is a problem in the condenser or the evaporator. That is, the state of the refrigerant circulating in the screw refrigeration system is high pressure gas from the screw compressor to the condenser, high pressure liquid / gas mixed state in the condenser, high pressure from the condenser to the main expansion valve through the economizer. Low-pressure liquid / gas mixed state from the main expansion valve to the evaporator outlet, low-pressure gas from the evaporator to the screw compressor, and intermediate-pressure liquid / gas mixture from the auxiliary expansion valve for the economizer to the economizer outlet State, the gas from the economizer to the screw compressor is an intermediate pressure gas. Normally, the balance of gas and liquid outside the evaporator is substantially constant, but when the screw rotor of the screw compressor falls below a certain number of rotations, it becomes easy to separate the gas and liquid in the evaporator. The liquid that stays inside increases. Therefore, in order to continue stable and high-performance operation, it is necessary to provide a liquid receiver that absorbs fluctuations in the liquid amount or to increase the charging amount of the refrigerant at the expense of performance under rated conditions.
[0010]
FIG. 7 shows the required refrigerant quantity when the rotational speed is changed, with the horizontal axis representing the same rotation speed ratio as above and the vertical axis representing the required refrigerant quantity based on the required refrigerant quantity at the rated rotation speed. An example of the measurement result obtained about a change is represented. As shown in the figure, when the rotational speed ratio is 25%, 110% of the refrigerant required for the rated conditions is required. Accordingly, it is necessary to provide a liquid receiver that absorbs the change in the refrigerant amount or to perform a rated operation in a state of being overfilled by 10%. In the latter case of 10% overfilling, when the condenser is of the plate type or in-pipe condensing type, the overfilled refrigerant stays in the liquid state in the condenser, and accordingly the condenser There is a problem in that the area and volume of the portion that performs heat exchange in the heat exchanger are reduced and the performance of the condenser is reduced.
The present invention has been made with the object of eliminating such conventional problems, and an object of the present invention is to provide a screw refrigeration apparatus that can always maintain good performance and COP regardless of changes in heat load. .
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the first invention includes a refrigerant circulation passage returning from the screw compressor to at least the condenser, the economizer, the main expansion valve and the evaporator, and returning to the screw compressor, the condenser, and the main A screw refrigeration apparatus comprising: an economizer flow path for guiding a part of the refrigerant between the expansion valve and the economizer through an auxiliary expansion valve of the economizer to an intermediate pressure portion in a rotor chamber of the screw compressor. When it is determined that the compression function force is excessive based on a motor having a variable rotation speed provided as a drive unit, a thermal load detection means for detecting a thermal load, and a thermal load signal from the thermal load detection means A rotation speed controller that lowers the rotation speed of the motor and increases the rotation speed when it is determined that the compression function force is insufficient, and maintains the rotation speed in other cases; Up If the rotational speed has fallen below a predetermined rotational speed COP ratio of the case of the normally open when the said auxiliary expansion valve was normally closed with the auxiliary expansion valve is both substantially equivalent, the auxiliary expansion The valve is closed, and in other cases, a valve opening / closing control unit that keeps the auxiliary expansion valve open is provided.
[0012]
In the second aspect of the invention, in addition to the first configuration, the thermal load detection means is a temperature detector that detects the temperature of the liquid to be cooled that has exited the evaporator.
[0013]
In the third aspect of the invention, in addition to the first configuration, the thermal load detection means is a temperature detector that detects the temperature of hot water that has exited the condenser.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a screw refrigeration apparatus 1 according to the present invention. The screw refrigeration apparatus 1 includes a screw compressor 11, a condenser 12, a receiver 13, an economizer 14, a main expansion valve 15, and an evaporator 16. A refrigerant circulation passage L1 that returns to the compressor 11 and an economizer passage L2 that leads from the economizer 14 to an intermediate pressure portion in the rotor chamber of the screw compressor 11 are provided.
[0015]
The screw compressor 11 has a pair of male and female screw rotors that are rotatably accommodated to be engaged with each other, and is driven by a motor 21 having a variable number of rotations. Further, a rotation speed control unit 25 including a calculation unit 23 and an inverter 24 is interposed between the motor 21 and the power source 22.
The condenser 12 is a well-known vertical one-pass counter-flow type plate type, and a cooling water passage 26 passes through the condenser 12. As shown in the figure, the refrigerant discharged from the screw compressor 11 flows in from the upper part of the condenser 12 and flows out from the lower part, whereas the cooling water in the cooling water flow path 26 flows in from the lower part of the condenser 12, It flows out from the upper part, and heat exchange is performed between the refrigerant and the cooling water in the condenser 12. And by this heat exchange, the refrigerant is deprived of heat and condensed and flows out of the condenser 12, and the cooling water absorbs heat and flows out of the condenser 12 as hot water.
[0016]
The liquid receiver 13 is disposed below the condenser 12, and the refrigerant liquid condensed in the condenser 12 immediately flows down into the liquid receiver 13 without staying here. Thus, since the liquid receiver 13 is arrange | positioned under the condenser 12, since the condensed refrigerant | coolant liquid immediately flows out of the condenser 12, favorable heat exchange is maintained in the condenser 12. .
[0017]
The economizer 14 branches from the portion of the refrigerant circulation flow path L1 between the condenser 12 and the main expansion valve 15, and the economizer flow path L 2 in which the auxiliary expansion valve 27 is interposed and the secondary of the auxiliary expansion valve 27. On the side, the heat exchanger 28 is configured to exchange heat between the refrigerant in the refrigerant circulation passage L1 and the refrigerant in the economizer passage L2. In general, only the heat exchanging unit 28 may be referred to as an economizer, but in the embodiment of the present invention, the economizer is defined as described above. In the heat exchanging section 28, the refrigerant circulation flow path L1 and the economizer flow path L2 are respectively arranged so as to face each other, and heat exchange is efficiently performed between the two. Then, the high-pressure refrigerant that has been diverted from the refrigerant circulation flow path L1 is decompressed by the auxiliary expansion valve 27, is vaporized and then flows into the heat exchange unit 28, and after supercooling the refrigerant in the refrigerant circulation flow path L1, It is supplied to the intermediate pressure part in the screw compressor 11 by the economizer flow path L2. The auxiliary expansion valve 27 is formed so as to be opened and closed by a valve opening / closing control unit 29.
[0018]
On the other hand, the refrigerant liquid supercooled by the economizer 14 is guided to the main expansion valve 15, where the refrigerant liquid is depressurized and vaporized, and then goes to the evaporator 16.
The evaporator 16 is provided with a to-be-cooled liquid passage 31 that penetrates the refrigerant flowing from the bottom to the top so as to form a counter flow. Heat exchange is efficiently performed with the liquid to be cooled in the coolant flow path 31. As a result of this heat exchange, the liquid to be cooled in the liquid flow path 31 flows out from the cooled evaporator 16, the refrigerant evaporates, returns to the screw compressor 11 in a gas state, and It circulates while repeating the same state change.
[0019]
A temperature detector 32 for detecting the temperature of the liquid to be cooled is provided as a means for detecting a thermal load at the outlet side portion of the liquid flow path 31 to be cooled that has exited from the evaporator 16. A temperature signal indicating the temperature is sent to the calculation unit 23. In the calculation unit 23, based on the input temperature signal, the rotation speed of the motor 21 is calculated by PID calculation so that the temperature of the liquid to be cooled at the outlet side portion of the liquid flow path 31 to be cooled becomes a preset temperature. , And a control signal for setting the rotational speed is output to the inverter 24, and the rotational speed control of the motor 21 is performed via the inverter 24. That is, the rotational speed control of the motor 21 is performed so as to correspond to the cooling heat load.
[0020]
Further, a control signal for opening and closing the auxiliary expansion valve 27 according to the number of rotations of the motor 21 is output from the calculation unit 23 to the valve opening / closing control unit 29, and the auxiliary expansion valve 27 is connected via the valve opening / closing control unit 29. Can be opened and closed. Specifically, the auxiliary expansion valve 27 is closed when the rotation number of the motor 21 is equal to or less than a predetermined rotation number near 50% of the rated rotation number, and the auxiliary expansion valve 27 is opened at other times. It is supposed to be. The predetermined number of revolutions here will be described later with reference to FIGS.
[0021]
2 and 3 are diagrams for explaining changes in the COP ratio and the necessary refrigerant amount ratio with respect to the rotation speed ratio in the screw refrigeration apparatus 1 according to the present invention. A curve X indicated by a broken line is the screw refrigeration apparatus 1 and the auxiliary expansion valve 27 is normally closed, and a curve Y indicated by a solid line is a case where the auxiliary expansion valve 27 is normally open. .
As can be seen from FIG. 2, the COP ratio is substantially equal at a predetermined rotational speed in the vicinity of the rotational speed ratio of 50% (indicated by a one-dot chain line in the figure), and the function of the economizer 14 is stopped below that. In the curve X indicating the COP ratio, the COP ratio is further improved, and this becomes more remarkable as the rotational speed ratio becomes smaller. The curve Y in FIG. 2 is the same as the curve in FIG.
[0022]
Further, as can be seen from FIG. 3, the required amount of refrigerant in the curve X is smaller than that in the curve Y, the rotation speed ratio is less than a predetermined rotation speed near 50%, and as the rotation speed ratio becomes smaller Has become prominent. The curve Y in FIG. 3 is the same as the curve in FIG.
The characteristics of the COP ratio and the necessary refrigerant amount ratio are such that when the rotational speed becomes low, the function of the economizer 14 is stopped, thereby reducing the amount of refrigerant subcooling on the primary side of the main expansion valve 15. This is because the amount of flash gas at the inlet of the evaporator 16 is increased, and as a result, the amount of refrigerant liquid staying in the evaporator 16 is decreased, and the range of change in the refrigerant amount necessary for repeating the refrigeration cycle is reduced. It is estimated that
[0023]
The screw refrigeration apparatus 1 according to the present invention utilizes the characteristics of the COP ratio and the necessary refrigerant amount ratio with respect to the motor rotation speed. That is, in the screw refrigeration apparatus 1 according to the present invention, as described above, when the rotational speed of the motor 21 becomes equal to or less than the predetermined rotational speed near 50% of the rated rotational speed, the auxiliary expansion valve 27 is closed and the other In this case, the auxiliary expansion valve 27 is opened, but by doing so, the COP ratio of the screw refrigeration apparatus 1 is larger than the above-mentioned predetermined rotational speed, according to the curve Y in FIG. Below a predetermined number of revolutions, it will change according to the curve X in FIG. Further, the required refrigerant amount ratio of the screw refrigeration apparatus 1 is changed according to the curve Y in FIG. 3 when it is larger than the above-mentioned predetermined rotational speed, and according to the curve X in FIG.
[0024]
FIG. 4 shows another screw refrigeration apparatus 2 according to the present invention, which is substantially the same as the above-described screw refrigeration apparatus 1 except that the configuration of the economizer 14 is different. Are given the same numbers and their explanation is omitted.
In the screw refrigeration apparatus 2, the branch point of the economizer flow path L <b> 2 from the refrigerant circulation flow path L <b> 1 is between the liquid receiver 13 and the heat exchange unit 28.
Similarly to the above, based on the temperature signal from the temperature detector 32, the rotational speed of the motor 21 is controlled by the rotational speed controller 25, and the auxiliary expansion valve 27 is opened and closed by the valve opening / closing controller 29.
[0025]
Note that the screw refrigeration apparatus of the present invention may be applied to a system that uses hot water from a condenser, that is, a so-called heat pump. In the screw refrigeration apparatus in that case, as shown by a dotted line and a two-dot chain line in each of FIGS. 1 and 4, as a means for detecting a thermal load, the cooling from the condenser 12 is used instead of the temperature detector 32. A temperature detector 33 is provided at the outlet side of the water flow path 26, and a temperature signal indicating the detected temperature is sent from the temperature detector 33 to the calculation unit 23.
Further, in the screw refrigeration apparatuses 1 and 2, the liquid receiver 13 plays a role as a cushion tank that absorbs a change in the refrigerant amount necessary for repeating the refrigeration cycle, but the liquid receiver 13 is not necessarily required. You can omit it.
1 and 4 show an example in which the liquid receiver 13 is provided between the condenser 12 and the economizer 14, the present invention is not limited to this, and the liquid receiver 13 is connected to the economizer 14 and the economizer 14. It may be provided between the evaporator 16 or between the evaporator 16 and the screw compressor 11.
By the way, it is preferable to use a non-azeotropic refrigerant mixture as the refrigerant. When this non-azeotropic refrigerant mixture is used, since the refrigerant is supercooled by the economizer 14, the evaporation start temperature of the refrigerant in the evaporator 16 is lowered, so that the heat exchange efficiency in the evaporator 16 is improved.
[0026]
An oil-cooled screw compressor may be used as the screw compressor constituting the screw refrigeration apparatus of the present invention. In that case, an oil separator / recovery unit is interposed between the screw compressor 11 and the condenser 12, and the rotor chamber of the screw compressor passes through the oil cooler from the oil reservoir at the bottom of the oil separation / recovery unit. It is desirable to provide an oil supply flow path for supplying oil to the shaft seal portion, the bearing and the like.
Further, the screw compressor 11 is not limited to the one having only one stage of the compressor body, but includes one having a plurality of stages of compressor bodies arranged in series. The pressure part between the suction pressure of the compressor body of the first stage and the discharge pressure of the compressor body of the final stage is meant. That is, with respect to the multistage compressor body, the position where the economizer flow path L2 joins the refrigerant flow space in the screw compressor 11 is at the suction port of the first stage compressor body and the final stage compressor body. It suffices if it is between the discharge outlet.
[0027]
【The invention's effect】
As is clear from the above description, according to the first invention, in the screw refrigeration apparatus using the screw compressor and provided with the economizer, a motor with a variable rotation speed provided as a drive unit of the screw compressor, Based on the thermal load detection means for detecting the load and the thermal load signal from the thermal load detection means, when it is determined that the compression function force is excessive, the rotational speed of the motor is reduced and the compression function force is reduced. When it is determined that the rotation speed is insufficient, the rotation speed is increased, and in other cases, the rotation speed control unit that maintains the rotation speed, and the rotation speed causes the auxiliary expansion valve to be normally closed. When the auxiliary expansion valve is normally open, the auxiliary expansion valve is closed when the COP ratio is equal to or less than a predetermined number of rotations that are substantially equal to each other. Keep expansion valve open There a structure in which a switching control section.
According to the second invention, in addition to the configuration of the first invention, the thermal load detecting means is a temperature detector for detecting the temperature of the liquid to be cooled that has exited the evaporator.
Furthermore, according to the third invention, in addition to the structure of the first invention, the thermal load detecting means is a temperature detector that detects the temperature of the hot water that has exited the condenser.
[0028]
For this reason, when the rotational speed of the motor for driving the screw compressor is reduced, the function of the economizer is stopped, the amount of refrigerant liquid remaining in the evaporator is reduced, and the change in the amount of refrigerant necessary for the refrigeration cycle is reduced. As a result of the reduction of the width, there is an effect that it is possible to always maintain good performance and COP regardless of the change of the cooling heat load.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of a screw refrigeration apparatus according to the present invention.
FIG. 2 is a diagram for explaining a relationship between a rotation speed ratio of a motor (screw rotor) and a COP ratio in the screw refrigeration apparatus according to the present invention.
FIG. 3 is a diagram for explaining a relationship between a rotation speed ratio of a motor (screw rotor) and a necessary refrigerant amount ratio in the screw refrigeration apparatus according to the present invention.
FIG. 4 is a diagram showing an overall configuration of another screw refrigeration apparatus according to the present invention.
FIG. 5 is a diagram showing a relationship between a rotation speed ratio of a motor (screw rotor) and heat insulation efficiency in a general screw compressor.
FIG. 6 is a diagram showing a relationship between a rotational speed ratio of a motor (screw rotor) and a COP ratio in a conventional screw refrigeration apparatus.
FIG. 7 is a diagram showing a relationship between a rotation speed ratio of a motor (screw rotor) and a necessary refrigerant amount ratio in a conventional screw refrigeration apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 2 Screw refrigeration apparatus 11 Screw compressor 12 Condenser 13 Receiver 14 Economizer 15 Main expansion valve 16 Evaporator 21 Motor 22 Power supply 23 Calculation part 24 Inverter 25 Rotational speed control part 26 Cooling water flow path 27 Auxiliary expansion valve 28 Heat Replacement part 29 Valve opening / closing control part 31 Cooled liquid flow path 32, 33 Temperature detector L1 Refrigerant circulation flow path L2 Economizer flow path

Claims (3)

Refrigerant circulation path returning from the screw compressor to at least the condenser, the economizer, the main expansion valve and the evaporator and returning to the screw compressor, and a part of the refrigerant between the condenser and the main expansion valve. In the screw refrigeration apparatus comprising an economizer flow path that leads to an intermediate pressure portion in the rotor chamber of the screw compressor after passing through the auxiliary expansion valve of
A motor with a variable number of revolutions provided as a drive unit of the screw compressor;
Thermal load detection means for detecting thermal load;
When it is determined that the compression function force is excessive based on the heat load signal from the heat load detection means, the number of rotations of the motor is decreased, and when it is determined that the compression function force is insufficient. A rotation speed control unit that increases the rotation speed and maintains the rotation speed in other cases;
If the COP ratio between the case where the auxiliary expansion valve is normally closed and the case where the auxiliary expansion valve is normally open is equal to or less than a predetermined rotation number where both are substantially equal, A screw refrigeration apparatus comprising: a valve opening / closing control unit that keeps the expansion valve closed and in other cases maintains the auxiliary expansion valve open.   The screw refrigeration apparatus according to claim 1, wherein the thermal load detection means is a temperature detector that detects the temperature of the liquid to be cooled that has exited the evaporator.   The screw refrigeration apparatus according to claim 1, wherein the thermal load detection means is a temperature detector that detects the temperature of hot water that has exited the condenser.

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