Patent Application
20250164167
The present disclosure relates to a refrigeration cycle device and a control method.
There has been generally known a refrigeration device (referred to also as a refrigeration cycle device) that controls a supercooling level by using an expansion valve (see Patent Reference 1, for example),
Patent Reference 1: International Publication No. WO 2021/054463
The configuration of the refrigeration device disclosed in the Patent Reference 1 is effective only in a refrigerant amount range in which the control of the supercooling level (referred to also as supercooling level control) is possible. Thus, there is a problem in that the supercooling level cannot be controlled appropriately and the refrigeration device is likely to fail in a case where the supercooling level control does not work out well.
An object of the present disclosure is to appropriately control the supercooling level even in a case where the supercooling level control does not work out well.
A refrigeration cycle device in the present disclosure includes:
A control method in the present disclosure is a control method for controlling an expansion valve in a refrigeration cycle device including a compressor to compress a refrigerant, a condenser, the expansion valve to regulate a flow rate of a refrigerant, and a control device to control the expansion valve, the control method including:
According to the present disclosure, the supercooling level can be controlled appropriately even in a case where the supercooling level control does not work out well.
A refrigeration cycle device 1 according to the present disclosure will be described below with reference to the drawings. Incidentally, components assigned the same reference character in the drawings are components identical or corresponding to each other, which commonly holds in the entirety of this patent specification.
As shown in
The compressor 3 is a device that compresses and discharges the refrigerant taken in from the accumulator 7. The compressor 3 can also be a compressor whose displacement (the amount of the refrigerant sent out per unit time) is changed by arbitrarily changing its drive frequency by using a non-illustrated inverter circuit or the like, for example.
The condenser 4 is placed on a discharge side of the compressor 3. The condenser 4 is a device that performs heat exchange between the refrigerant and air, which condenses and Liquefies the refrigerant while heating air.
The expansion valve 5 is provided in the piping 8 between the condenser 4 and the evaporator 6 in the refrigerant circuit 9. The expansion valve 5 is formed with an expansion valve whose degree of opening is variable such as an electronic expansion valve, for example, and regulates the pressure and the flow rate of the refrigerant.
The evaporator 6 is placed in the piping 8 on the discharge side of the expansion valve 5. The evaporator 6 is a device that performs the heat exchange between the refrigerant and air, which evaporates and gasifies the refrigerant while cooling air.
The accumulator 7 is placed in the piping 8 on an intake side of the compressor 3. The accumulator 7 separates the refrigerant taken in into liquid refrigerant and gas refrigerant so as to make the compressor 3 take in the gas refrigerant only. The accumulator 7 has a function as a liquid reservoir that reserves surplus refrigerant while avoiding a failure of the compressor 3 caused by liquid compression by preventing the compressor 3 from taking in the liquid refrigerant.
As shown in
As shown in
As shown in
The control processing device 21 can be formed with a microcomputer or the like including a control arithmetic processing device such as a CPU (Central Processing Unit), for example. The storage device 23 holds data obtained by programming a processing procedure to be executed by the control processing device 21. The control arithmetic processing device implements the control by executing a process based on the data of the program. Incidentally, each device can be formed with a dedicated device (hardware).
The control device 2 is configured to calculate an expansion valve opening degree for making the discharge temperature follow an upper limit of the discharge temperature and an expansion valve opening degree for making the supercooling level follow a supercooling level target valve and control the expansion valve opening degree at a higher one of the expansion valve opening degrees when changing the expansion valve opening degree to a calculated opening degree. The expansion valve opening degree means the degree of opening (opening degree) of the expansion valve 5. In the present application, the “upper limit” means a determined valve. In the present application, a “lower limit” means a predetermined value. The upper Limit of the discharge temperature means, for example, the upper limit of the temperature of the refrigerant that can be used by the Compressor 3. The upper limit of the discharge temperature is referred to also as a discharge temperature upper limit.
Referring to
Gaseous refrigerant compressed by the compressor 3 and thereby entering a high-temperature and high-pressure state is discharged through a discharge port of the compressor 3 and flows into the condenser 4. The gaseous refrigerant that flows into the condenser 4 radiates heat in the condenser 4, liquefies under high pressure, and flows out from the condenser 4. The refrigerant that flows out from the condenser 4 is decompressed by the expansion valve 5, shifts to a low-temperature two-phase state, and flows into the evaporator 6. The refrigerant in the low-temperature two-phase state that flows into the evaporator 6 absorbs heat in the evaporator 6, gasifies under low pressure, and flows out from the evaporator 6. The refrigerant that flows out from the evaporator 6 flows into the accumulator 7. The refrigerant that flows into the accumulator 7 is separated into a gas phase and a liquid phase, and the gas-phase refrigerant is discharged from the accumulator 7. The refrigerant discharged from the accumulator 7 is taken into the compressor 3 and is compressed again. By repeating such an operation, the refrigeration cycle of the refrigeration cycle device 1 is implemented.
Incidentally, the refrigerant circuit 9 shown in
As shown in
The supercooling level controller 21 calculates an opening degree (referred to also as a “first opening degree”) of the expansion valve 5 such that the supercooling level of the refrigerant follows the target value and outputs the calculation result. The supercooling level controller 21 is a PI controller (referred to also as a “first PI controller”), for example. In this case, the PI controller forming the supercooling level controller 21 is a PI controller of a positional type that outputs an opening degree of the expansion valve 5 such that the supercooling level follows the supercooling level target value as a refrigerant temperature being a control target. The supercooling level controller 21 obtains a deviation between a present supercooling level calculated from a sensor value and the predetermined supercooling level target value and outputs the expansion valve opening degree that makes the supercooling level follow the supercooling level target value.
An example of a method for calculating the supercooling level will be described below. First, from a high-pressure pressure sensed by the high-pressure sensor 13, a saturation liquid temperature at the pressure is calculated by using a physical property value of the refrigerant. The difference between the calculated saturation liquid temperature and the temperature sensed by the outlet temperature sensor 12 is the supercooling level. The method for calculating the supercooling level is not limited to this method. For example, the supercooling level may be calculated as the difference between a temperature sensed by a temperature sensor placed in a two-phase region of the condenser 4 and the temperature sensed by the outlet temperature sensor 12.
The PI controller forming the supercooling level controller 21 has an anti-reset windup function and is configured so that the output of the supercooling level controller 21 does not diverge. For example, the output of the supercooling level controller 21 does not diverge even when the maximum selector 23 does not output the output of the supercooling level controller 21.
The anti-reset windup function means a function of inhibiting an integral value calculated inside the PI controller from diverging when the output of the PI controller and the opening degree of the expansion valve 5 differ from each other due to the selection by the maximum selector 23 or upper/lower limit restriction on the opening degree of the expansion valve 5. Such a function is effective especially in a configuration in which PI controllers are arranged in parallel and the output of one of the PI controllers is selected.
The supercooling level target value may be either a constant value or a variable value that is set properly depending on actual operational status. When the supercooling level target value is set as a variable value, the supercooling level target value may be set as a valve obtained by multiplying the difference between a condensation temperature and an ambient temperature of the condenser 4 by a coefficient, for example
The supercooling level controller 21 does not necessarily have to be a controller but can also be a dynamic feedback controller such as a P controller, a PID controller or a model prediction controller, or a dynamic or static controller abiding by a previously set table or the like.
Further, the supercooling level controller 21 does not necessarily have to be a controller of the positional type but. can also be a controller of a velocity type. Even in this case, the inputs to the maximum selector 23 are the expansion valve opening degrees.
The discharge temperature controller 22 calculates an opening degree (referred to also as “second opening degree”) of the expansion valve 5 such that the temperature of the refrigerant discharged from the compressor 3 (referred to also as a “discharge temperature”) follows the upper limit and outputs the calculation result. The discharge temperature controller 22 is a PI controller (referred to also as a “second PI controller”), for example. In this case, the PI controller forming the discharge temperature controller 22 is a PI controller of the positional type that outputs an opening degree of the expansion valve 5 such that the discharge temperature follows the discharge temperature upper limit as a refrigerant temperature being a control. The discharge temperature controller 22 obtains a deviation between the discharge temperature acquired from the discharge temperature sensor 11 and the predetermined discharge temperature upper limit and outputs the expansion valve opening degree for making the discharge temperature follow the discharge temperature upper Limit.
The PI controller forming the discharge temperature controller 22 has the anti-reset windup function and is configured so that the integral value does not diverge. For example, the integral value as the output of the discharge temperature C stroller 22 does not diverge even when the maximum selector 23 does not output the output of the discharge temperature controller 22. Therefore, when an operating condition has changed and a refrigerant deficiency level has changed, the control is switched immediately and the refrigeration cycle device 1 can be shifted to operational status in which the efficiency is stably high.
The discharge temperature upper limit may be either determined based on restriction on the hardware or set based on an empirical rule or the like.
The discharge temperature controller 22 does not necessarily have to be a PI controller but can also be a dynamic feedback controller such as a P controller, a PID controller or a model prediction controller, or a dynamic or static controller abiding by a previously set table or the like.
Further, the discharge temperature controller 22 does not necessarily have to be a controller of the positional type but can also be a controller of the velocity type. Even in this case, the inputs to the maximum selector 23 are the expansion valve opening degrees.
The maximum selector 23 compares the output of the supercooling level controller 21 with the output of the discharge temperature controller 22 and outputs one of the outputs at a greater value. In other words, the maximum selector 23 selects and outputs the maximum value out of the output of the supercooling level controller 21 and the output of the discharge temperature roller 22.
The control device 2 controls the expansion valve 5 by using the value outputted from the maximum selector 23. By this process, the open degree of the expansion valve 5 is controlled appropriately.
A parameter of each of the first PI controller and the second PI (stroller is calculated by using the result of system identification by a step response or the like, Therefore, the load of designing the first PI controller and the second PI controller can be reduced.
As described above, the control method for controlling the expansion valve 5 includes the following steps:
The discharge temperature is shifting under the upper limit and the supercooling level is following the target value, In this case, the supercooling level controller 21 is outputting the opening degree for maintaining the supercooling level at the target value. The discharge temperature controller 22 is outputting a lower opening degree in order to make the discharge temperature converge on the upper Limit. As a result, the maximum selector 23 selects the output of the supercooling level controller 21 and the control is in progress at the opening degree for controlling the supercooling level at the target
The discharge temperature is following the upper Limit and the supercooling level is shifting under the target value. In this case, the opening degree for maintaining the discharge temperature at the upper limit is being outputted as the discharge temperature control output. The supercooling level controller 21 is outputting a lower opening degree in order to make the supercooling level rise to the target value, As a result, the maximum selector 23 selects the output of the discharge temperature controller 22 and the control is in progress at the opening degree for controlling the discharge temperature at the upper limit.
As shown in
As shown in
First, problems in cases where the refrigerant amount becomes insufficient will be described below. In a refrigeration cycle device including an accumulator, the supercooling level is generally controlled by the expansion valve. However, when the refrigerant amount becomes insufficient, a problem arises in that narrowing down the expansion valve opening degree hardly works to turn on the supercooling level, the supercooling level becomes uncontrollable, and thus it becomes impossible to determine the appropriate value of the expansion valve opening degree. Further, when the refrigerant amount becomes insufficient, a problem arises in that an intake superheating level of the compressor increases, the discharge temperature of the compressor rises, and heat expansion of the compressor can cause a failure.
Against the above-described problems, in the configuration according to the first embodiment, the supercooling level can be controlled appropriately and high-efficiency and energy-saving operation can be realized in an operating condition in which the refrigerant is well sufficient. On the other hand, in an operating condition in which the refrigerant is insufficient due to a factor such as a great piping length and the supercooling level control does not work out well, a stable and high-efficiency operation is maintained since the control is automatically and continuously switched to the discharge temperature control, the rise in the discharge temperature is inhibited, and the opening degree of the expansion valve 5 appropriate for the inhibition is calculated constantly. Further, since controllers like the continuous PI controllers having the anti-reset windup function is used, hunting does not occur and a stable operation can be realized even when the refrigerant amount is intermediate and the operation is performed at a point where the target that should be controlled is switched between the supercooling level and the discharge temperature. Furthermore, since the discharge temperature can be accurately controlled at the upper limit, protection of the device can be realized with high accuracy, The above-described advantages ace obtained by employing continuous control such as PI control for not only the supercooling level control as main control but also subordinate control such as protection as above.
Further, since the supercooling level controller 21 and the discharge temperature controller 22 are controllers already established in terms of control engineering such as PI controllers, techniques for designing the parameters of these controllers have already been established by a lot of existing research. Thus, there is also an advantage of reducing design load on the controllers. For example, while a technique like a design technique using the result of system identification by a step response can be considered as the method of designing the parameters of the controllers and the parameters are calculated by a mathematical procedure basically from properties obtained by the system identification, it is also possible to consider a configuration for learning the parameters of the controllers from input-output data at times of the actual operation. Incidentally, there is no restriction on whether the aforementioned system identification is online identification or offline identification,
A configuration and operation different from those in the first embodiment will be described below.
In the second embodiment, the control device 2 further includes a switch 24. The second embodiment differs from the first embodiment shown in
The switch 24 is arranged between the supercooling level controller 21 and the maximum selector 23. The switch 24 receives the output from the supercooling level controller 21. An output from the switch 24 enters the maximum selector 23.
The switch 24 determines whether the state of the refrigerant existing at the outlet of the condenser 4 is the Liquid phase or the two-phase state based on the supercooling level, for example. When the state of the refrigerant existing at the outlet of the condenser 4 is determined to be the liquid phase, the switch 24 outputs a value equal to the output of the supercooling level controller 21. In contrast, when the state of the refrigerant existing at the outlet of the condenser 4 is determined to be the two-phase state, the switch 24 outputs an invalid signal.
When the invalid signal is received by the maximum selector 23, the maximum selector 23 outputs the maximum value out of the outputs inputted to the maximum selector 23 excluding the invalid signal.
For example, the switch 24 determines whether or not the supercooling level from the supercooling level controller 21 is higher than or equal to a predetermined threshold value. In this case, if the supercooling level from the supercooling level controller 21 is higher than or equal to the predetermined threshold value, the switch 24 directly outputs the output of the supercooling level controller 21. If the supercooling level from the supercooling level controller 21 is less than the predetermined threshold value, the switch 24 outputs the invalid signal.
It is also possible for the switch 24 to determine whether or not the supercooling level is on (i.e., the supercooling level is taking on a positive value). In this case, the switch 24 receives the supercooling level as an input and when the switch 24 determines that the supercooling level is on, the switch 24 directly outputs the output of the supercooling level controller 21. When the switch 24 determines that the supercooling level is not on, the switch 24 outputs the invalid signal.
When the invalid signal is inputted to the maximum selector 23, the maximum selector 23 outputs the maximum value out of the inputs excluding the invalid signal. For example, when the output of the switch 24 is the invalid signal and the output of the discharge temperature controller 22 is “100”, the switch 24 outputs “100”.
The judgment on whether the supercooling level is on or not is made based on whether the supercooling level is over a certain threshold value or not. For example, the supercooling level is determined to be on when the supercooling level is higher than or equal to 2° C., and the supercooling level is determined to be not on when the supercooling level is less than 2° C. The threshold value of the supercooling level is set in consideration of piping pressure loss, mounting positions of the sensors, measurement errors of the sensors, or the like.
The judgment by the switch 24 may also be made by a different means. For example, it is also possible to estimate a dryness level of the refrigerant existing at the outlet of the condenser 4, determine that the supercooling level is on if the dryness level is less than or equal to zero, and determine that the supercooling level is not on if the dryness level is higher than zero.
In the example shown in
In the example shown in
According to the second embodiment, when the supercooling level is not on, the control is executed at the opening degree of the expansion valve 5 for making the discharge temperature follow the upper limit. Therefore, the throttling of the expansion valve 5 in the region where the supercooling level is not on becomes faster and the time until the stabilization can be shortened. Consequently, an effect such as a rapid heating/cooling effect or an energy-saving effect can be obtained.
The configuration of the control device 2 in the third embodiment is the same as the configuration of the control device 2 in the first embodiment. Operation different from that in the first embodiment will be described below.
For example, the third embodiment differs from the first embodiment (e.g., the operation shown in
In the third embodiment, the discharge temperature controller 22 does not make the temperature of the refrigerant discharged from the compressor 3 follow the predetermined upper limit but appropriately controls the intake superheating level of the compressor 3 and makes the temperature of the refrigerant discharged from the compressor 3 follow the target value of the discharge temperature at which the energy saving performance increases. The temperature of the refrigerant discharged from the compressor 3 is referred to also as the discharge temperature.
For example, the discharge temperature controller 22 makes the discharge temperature follow a predetermined target value other than the predetermined upper limit.
The target value of the discharge temperature is set at a valve at which the intake superheating level of the compressor 3 is made appropriate and the energy saving performance increases. For example, the target value of the discharge temperature is set at a temperature when the intake superheating level of the compressor 3 is assumed to be 5° C. at high and low pressures before and after the compressor at that time, The intake superheating level of the compressor 3 does not necessarily have to be 5° C. but is permissible as long as it is a value greater than or equal to zero. The target value of the discharge temperature may be either determined according to a previously set table or calculated each time by using a formula of a polytropic change.
According to the third embodiment, the intake superheating level of the compressor 3 can be controlled at an appropriate valve. If the intake superheating level is appropriate, the efficiency of the refrigeration cycle is optimized and the coefficient of performance (COP) increases. Thus, according to the third embodiment, more high-efficiency and energy-saving operation can be realized even in a state in which the refrigerant is so insufficient that the supercooling level is uncontrollable.
A configuration and operation different from those in the first embodiment will be described below.
The evaporator differential temperature controller 31 calculates an expansion valve opening degree (referred to also as a third opening degree) that makes an evaporator differential temperature follow a predetermined upper limit and outputs the calculation result. The evaporator differential temperature controller 31 is formed with a PI controller of the positional type that outputs an expansion valve opening degree such that the evaporator differential temperature follows the evaporator differential temperature upper Limit as a refrigerant temperature being a control target. The evaporator differential temperature controller 31 obtains a deviation b ween a present evaporator differential temperature calculated from a sensor value and the predetermined evaporator differential temperature upper limit and outputs the expansion valve opening degree that makes the evaporator differential temperature follow the evaporator differential temperature upper limit.
The orator differential temperature is calculated as the difference between the temperature of the refrigerant exiting from the operator 6 and the temperature of the refrigerant entering the evaporator 6. For example, the evaporator differential temperature is calculated as the difference between the value of a temperature sensor placed in the vicinity of the evaporator outlet and the value of a temperature sensor placed in the vicinity of the evaporator inlet. The calculation of the evaporator differential temperature is not limited to this method. For example, the difference between the temperature at the evaporator outlet and a saturation gas temperature calculated from a low-pressure pressure may also be defined as the evaporator differential temperature.
The evaporator differential temperature upper limit is set at 2° C., for example. The evaporator differential temperature upper Limit does not necessarily have to be 2° C., For example, the evaporator differential temperature upper Limit may be set based on the relationship between permissible dryness of the evaporator 6 and the evaporator differential temperature while taking into account factors such as installation positions of sensors.
The evaporator differential temperature controller 31 does not necessarily have to be a PI controller. For example, the evaporator differential temperature controller 31 can also be a dynamic feedback controller such as a P controller, a PID controller or a model prediction controller, or a dynamic or static controller abiding by a previously set table or the like,
The evaporator differential temperature controller 31 does not necessarily have to be a controller of the positional type. For example, the evaporator differential temperature controller 31 can also be a controller of the velocity type. Even in the case where the evaporator differential temperature controller 31 is a controller of the velocity type, the inputs to the maximum selector 23 are the expansion valve opening degrees.
The discharge superheating level lower limit controller 32 calculates an expansion valve opening degree (referred to also as a fourth opening degree) that makes a discharge superheating level follow a lower limit and outputs the calculation result. The discharge superheating level lower limit controller 32 is formed with a PI controller of the positional type that outputs the expansion valve opening degree that makes the discharge superheating level follow the discharge superheating level lower limit as a refrigerant temperature being a control target, The discharge superheating level lower limit controller 32 obtains a deviation between a present discharge superheating level calculated from a sensor value and the predetermined discharge superheating level lower limit and outputs the expansion valve opening degree that makes the discharge superheating level follow the discharge superheating level lower limit.
The discharge superheating level is calculated as the difference between the value of the discharge temperature sensor 11 and the value of a temperature sensor placed in the two-phase region of the condenser 4. The calculation of the discharge superheating level is not Limited to this method. For example, the difference between the temperature sensed by the discharge temperature sensor 11 and a saturation gas temperature calculated from the high-pressure pressure may also be defined as the discharge superheating level.
The discharge superheating level lower limit is set at 10° C., for example. The discharge superheating level lower limit does not necessarily have to be 10° C. For example, the discharge superheating level lower limit may be set based on a discharge superheating level condition for preventing liquid backflow while taking into account an operation guarantee condition or the like of the compressor The discharge superheating level lower limit may be set so as to include a tolerance.
The discharge superheating level lower limit controller 32 does not necessarily have to be a PI controller. The discharge superheating level lower Limit controller 32 can also be a dynamic feedback controller such as a P controller, a PID controller or a model prediction controller, or a dynamic ox static controller abiding by a previously set table or the like.
The discharge superheating level lower limit controller 32 does not necessarily have to be a controller of the positional type. For example, the discharge superheating level lower limit controller 32 can also be a controller of the velocity type, Even in the case where the discharge superheating level lower limit controller 32 is a controller of the velocity type, the inputs to the minimum selector 34 are the expansion valve opening degrees.
The discharge superheating level upper limit controller 33 calculates an expansion valve opening degree (referred to also as a fifth opening degree) that makes the discharge superheating level follow an upper limit and outputs the calculation result. The discharge superheating level upper Limit controller 33 is formed with a PI controller of the positional type that outputs the expansion valve opening degree that makes the discharge superheating level follow the discharge superheating level upper limit as a refrigerant temperature being a control target. The discharge superheating level upper limit controller 33 obtains a deviation bet wee n a present discharge superheating level calculated from a sensor value and the predetermined discharge superheating level upper limit and outputs the expansion valve opening degree that makes the discharge superheating level follow the discharge superheating level upper limit.
The discharge superheating level is calculated as the difference between the value of the discharge temperature sensor 11 and the value of the temperature sensor placed in the two-phase region of the condenser 4. The calculation of the discharge superheating level is not limited to this method. For example, the difference between the temperature sensed by the discharge temperature sensor 11 and the saturation gas temperature calculated from the high-pressure pressure may also be defined as the discharge superheating level.
The discharge superheating level upper limit is set at 60° C., for example. The discharge superheating level upper Limit does not necessarily have to be 60° C. For example, the discharge superheating level upper limit may be set as an upper limit for maintaining appropriate operational status based on device specifications or the operating condition of the compressor 3. The discharge superheating level upper limit may be set so as to include a tolerance.
The discharge superheating level upper Limit controller 33 does not necessarily have to be a PI controller. For example, the discharge superheating level upper limit controller 33 can also be a dynamic feedback controller such as a P controller, a PID controller or a model prediction controller, or a dynamic or static controller abiding by a previously set table or the like.
The discharge superheating level upper limit controller 33 does not necessarily have to be a controller of the positional type. For example, the discharge superheating level upper limit controller 33 can also be a controller of the velocity type. Even in the case where the discharge superheating level upper limit controller 33 is a controller of the velocity type, the inputs to the second maxis um selector 35 are the expansion valve opening degrees.
The maximum selector 23 (first maximum selector 23) receives the output of the supercooling level controller 21 and the output of the evaporator differential temperature controller 31. The maximum selector 23 selects and outputs the maximum value out of the output of the supercooling level controller 21 and the output of the evaporator differential temperature controller 31.
The minimum selector 34 is arranged between the maximum selector 23 (first maximum selector 23) and the maximum selector 35 (second maximum selector 35), The minimum selector 34 receives the output of the maximum selector 23 and the output of the discharge superheating level lower Limit controller 32. The minimum selector 34 selects and outputs the minimum value out of the output of the maximum selector 23 and the output of the discharge superheating level lower limit controller 32.
The maximum selector 35 (second maximum selector 35) receives the output of the minimum selector 34, the output of the discharge temperature controller 22 and the output of the discharge superheating level upper limit controller 33, The maximum selector 35 selects and outputs the maximum value out of the output of the minimum selector 34, the output of the discharge superheating level upper limit controller 33 and the output of the discharge temperature controller 22.)
The control device 2 controls the expansion valve 5 by using the valve outputted from the second maximum selector 35. By this process, the opening degree of the expansion valve 5 is controlled appropriately.
In the fourth embodiment, the control device 2 may include at least one switch 24 described in the second embodiment. In this case, the switches 24 are connected respectively to the supercooling level controller 21, the disc controller 22, the evaporator differential temperature controller 31, the discharge superheating level lower limit controller 32 and the discharge superheating level upper limit controller 33, for example.
In the case where the control device 2 includes these switches 24 in the fourth embodiment, the input valve to the switch 24 is outputted to the evaporator differential temperature controller 31 when the evaporator differential temperature is higher than or equal to 2° C., and the invalid signal is outputted to the evaporator differential temperature controller 31 when the evaporator differential temperature is less than 2° C., for example. On the other hand, the state of the refrigerant existing at the outlet of the evaporator 6 is estimated, the input value to the switch 24 is outputted when the state of the refrigerant is the gas phase, and the invalid signal is outputted when the state of the refrigerant is the two-phase state. The switch 24 connected to the discharge superheating level lower limit controller 32 outputs the input value to the switch 24 when the discharge superheating level is less than or equal to 15° C., and outputs the invalid signal when the discharge superheating level is higher than 15° C. The threshold value used for the judgment on the discharge superheating level does not necessarily have to be 15° C.
While the discharge temperature upper limit is used as the input to the discharge temperature controller 22 in the fourth embodiment, it is also possible to use the discharge temperature target valve as the input to the discharge temperature controller 22 as in the third embodiment.
A control parameter for each of the supercooling level controller 21, the discharge temperature controller 22, the evaporator differential controller 31, the discharge superheating level lower limit controller 32 and the discharge superheating level upper limit controller 33 can also be a parameter that is variable depending on the present operational status in the actual operation in order to increase the control performance of each controller. For example, the control parameter may vary depending on the refrigerant flow rate. Specifically, it is possible to decrease a control gain when the refrigerant flow rate is low and increase the control gain when the refrigerant flow rate is high.
In general, when the refrigerant amount has become insufficient, a region on the evaporator's side occupied by the gas-phase refrigerant increases in size, the performance becomes insufficient, and accordingly the temperature difference between the gas-phase region and the two-phase region of the evaporator piping increases. As a result, a temperature/humidity difference occurs between airflows respectively passing through the regions, moisture is condensed in air, and consequently, dew is blown out. If the control is configured complexly in consideration of such various states, the discharge superheating level of the compressor, which should normally be maintained in a predetermined permissible region, might deviate from its upper or lower limit. Therefore, the discharge superheating level also needs to be controlled with high accuracy.
With the configuration according to the fourth embodiment, not only the discharge temperature but also the evaporator differential temperature can be controlled within the upper limit with high accuracy. Accordingly, the temperature difference between the gas-phase region and the two-phase region in the piping of the evaporator 6 can be reduced and the blowing out of the dew can be avoided. Further, since it becomes possible to execute the control in an expansion valve opening degree range that maintains the upper limit and the lower limit of the discharge superheating level, the discharge superheating level can be avoided from deviating from the upper limit or the lower Limit and reliability of the refrigeration cycle device 1 can be increased.
Features in the embodiments described above can be combined with each other,
1: refrigeration cycle device, 2: control device, 3: compressor, 4: condenser, 5: expansion valve, 6: evaporator, 7: accumulator, 0: piping, 9: refrigerant circuit, 11: discharge temperature sensor, 12: outlet temperature sensor, 13: high-pressure pressure sensor, 21: supercooling level controller, 22: discharge temperature controller, 23: maximum selector (first maximum selector), 24: switch, 31; evaporator differential temperature controller, 32: discharge superheating level lower limit controller, 33: discharge superheating level upper limit controller, 34: minimum selector, 35: maximum selector (second maximum selector)
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/004153 | 2/3/2022 | WO |
