Patent Application
20120017620
The present invention relates to a refrigeration cycle apparatus including an expansion mechanism and compression mechanisms, and used in a hot water heater, an air conditioner, and the like.
In recent years, a power recovery type refrigeration cycle apparatus has been proposed as a refrigeration cycle apparatus for achieving more efficient performance. In a refrigeration cycle apparatus of this type, an expansion mechanism is used instead of an expansion valve to recover as mechanical energy the pressure energy of a refrigerant in its expansion process and reduce the electric power required for driving a compression mechanism by the amount of the recovered power. Such a refrigeration cycle apparatus includes an expander-compressor unit, in which a motor, a compression mechanism, and an expansion mechanism are coupled to each other by a shaft.
Since the expander-compressor unit includes the compression mechanism and the expansion mechanism coupled to each other by the shaft, it is subject to a so-called “constraint of constant density ratio”, under which the ratio between the density of a refrigerant drawn into the compression mechanism and the density of a refrigerant drawn into the expansion mechanism is fixed at a constant ratio determined by their suction volumes. Therefore, the displacement of the compression mechanism or the displacement of the expansion mechanism may be insufficient under certain operating conditions. In order to retain the recovered power even under the operating conditions that may cause an insufficient displacement of the compression mechanism so as to keep the coefficient of performance (COP) of the refrigeration cycle apparatus high, there has been proposed a refrigeration cycle apparatus including a secondary compressor in addition to an expander-compressor unit (see, for example, PTL 1).
The refrigeration cycle apparatus described in PTL 1 further is provided with a bypass passage 160 for bypassing the expansion mechanism 103 and an injection passage 150 for supplying additional refrigerant to the expansion mechanism 103 during the expansion process of the refrigerant. These bypass passage 160 and injection passage 150 are provided with a bypass valve 161 and an injection valve 151, respectively, to regulate the flow rate of the refrigerant. In this refrigeration cycle apparatus of PTL 1, the bypass valve 161 is closed and the injection valve 151 is opened during the winter season. The opening of the injection valve 151 is determined based on the outside air temperature and other factors. Such a configuration allows the refrigeration cycle apparatus to deal with an insufficient displacement of the expansion mechanism 103.
In the above-mentioned refrigeration cycle apparatus in which the compression mechanisms are placed in parallel, it is conceivable to rotate the first motor in the expander-compressor unit and the second motor in the second compressor at the same rotational frequency.
Generally, in a refrigeration cycle apparatus, the pressure on the lower pressure side in the winter season becomes lower than that in the intermediate season such as spring or autumn, as shown, for example, in
For example,
On the other hand, in the refrigeration cycle apparatus provided with the injection passage, the refrigerant flowing through the injection passage is expanded to some extent in the injection valve unless the injection valve is opened fully. Therefore, a part of the expansion energy cannot be recovered.
These results show that the injection loss varies significantly depending on the injection flow rate, that is, the opening of the injection valve. Therefore, it is preferable that the opening of the injection valve is in a fully closed state or in a fully opened state. It is preferable that the opening of the injection valve is in the fully closed state or in the fully opened state also during the start-up operation.
In the case where the table shown in
The present invention has been made in view of the above problems, and it is an object of the present invention to keep the injection loss low during a start-up operation in a refrigeration cycle apparatus including an expansion mechanism and compression mechanisms and provided with an injection passage.
In order to solve the above problems, the present invention provides a refrigeration cycle apparatus including:
a first compressor including: a first compression mechanism for compressing a refrigerant; an expansion mechanism for recovering power from an expanding refrigerant; a first motor coupled to the first compression mechanism and the expansion mechanism by a shaft; and a first closed casing for accommodating the first compression mechanism, the expansion mechanism and the first motor;
a second compressor including: a second compression mechanism for compressing the refrigerant, the second compression mechanism being connected in parallel with the first compression mechanism in a refrigerant circuit; a second motor coupled to the second compression mechanism by a shaft; and a second closed casing for accommodating the second compression mechanism and the second motor;
a radiator for radiating heat from the refrigerant discharged from the first compression mechanism and the second compression mechanism;
an evaporator for evaporating the refrigerant discharged from the expansion mechanism;
a first pipe for guiding the refrigerant from the first compression mechanism and the second compression mechanism to the radiator;
a second pipe for guiding the refrigerant from the radiator to the expansion mechanism;
a third pipe for guiding the refrigerant from the expansion mechanism to the evaporator;
a fourth pipe for guiding the refrigerant from the evaporator to the first compression mechanism and the second compression mechanism;
an injection passage, branched from the second pipe, for supplying the refrigerant additionally to the expansion mechanism during an expansion process;
an opening-adjustable injection valve provided in the injection passage;
an outside air temperature sensor for detecting an outside air temperature; and
a controller for determining a target rotational frequency of the first motor and a target rotational frequency of the second motor for a start-up operation and determining whether an opening of the injection valve should be in a fully opened state or in a fully closed state during the start-up operation, based on the outside air temperature detected by the outside air temperature sensor, and performing the start-up operation by controlling rotational frequencies of the first motor and the second motor to be the determined target rotational frequencies while maintaining the opening of the injection valve in the fully opened state or in the fully closed state.
The fully closed state here means a state in which the flow of the refrigerant substantially is shut off by the injection valve, for example, a state in which the opening is 5% or less. The fully opened state means a state in which the flow of the refrigerant substantially is not impeded by the injection valve, for example, a state in which the opening is 95% or more.
With the configuration as described above, the refrigeration cycle apparatus of the present invention can keep the injection loss low during the start-up operation.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
The expander-compressor unit 1 has a first closed casing 10 for accommodating a first compression mechanism 11, a first motor 12 and an expansion mechanism 13 that are coupled to each other by a first shaft 15. The second compressor 2 has a second closed casing 20 for accommodating a second compression mechanism 21 and a second motor 22 that are coupled to each other by a second shaft 25. The first compression mechanism 11 and the second compression mechanism 21 are connected to the radiator 4 via the first pipe 3a having two branch pipes and a main pipe connected thereto. The radiator 4 is connected to the expansion mechanism 13 via the second pipe 3b. The expansion mechanism 13 is connected to the evaporator 5 via the third pipe 3c. The evaporator 5 is connected to the first compression mechanism 11 and the second compression mechanism 21 via the fourth pipe 3d having a main pipe and two branch pipes connected thereto. In the refrigerant circuit 30, the first compression mechanism 11 and the second compression mechanism 21 are placed in parallel. In other words, the first compression mechanism 11 and the second compression mechanism 21 are connected in parallel to each other in the refrigerant circuit 30.
The refrigerant compressed in the first compression mechanism 11 and the refrigerant compressed in the second compression mechanism 21 are discharged respectively from the first and second compression mechanisms 11 and 21 to the first pipe 3a, and then join in the first pipe 3a. The joined refrigerant is guided to the radiator 4. The refrigerants compressed in the compression mechanisms 11 and 21 may be discharged once into the closed casings 10 and 20 separately and then discharged from the closed casings 10 and 20 to the first pipe 3a. The refrigerant guided to the radiator 4 radiates heat there, and then is guided to the expansion mechanism 13 through the second pipe 3b. The refrigerant guided to the expansion mechanism 13 expands there. At the same time, the expansion mechanism 13 recovers power from the expanding refrigerant. The expanded refrigerant is guided to the evaporator 5 through the third pipe 3c. The refrigerant guided to the evaporator 5 absorbs heat there, and then is split into two streams in the fourth pipe 3d, which are guided to the first compression mechanism 11 and the second compression mechanism 21.
It is preferable that the displacement volume of the first compression mechanism 11 is the same as that of the second compression mechanism 21. In this case, it is possible to construct the first and second compression mechanisms 11 and 12 with common members, which reduces the cost.
The refrigeration cycle apparatus further includes an injection passage 6, branched from the second pipe 3b, for supplying the refrigerant additionally to the expansion mechanism 13 in the expansion process of the refrigerant. An opening-adjustable injection valve 61 for regulating the flow rate is provided at an intermediate point of this injection passage 6.
The refrigeration cycle apparatus of the present embodiment is used as a heat pump unit for heating water to generate hot water, in a hot water heater for supplying hot water stored in a hot water tank 200 to a hot water tap 201. Specifically, the radiator 4 serves as a heat exchanger for exchanging heat between water and a refrigerant to heat the water, and includes a refrigerant passage 41 through which the refrigerant flows and a water passage (fluid passage) 42 through which the water (fluid) flows. The water flowing through the water passage 42 receives heat from the refrigerant flowing through the refrigerant passage 41. The refrigeration cycle apparatus further includes a supply pipe 91 for supplying the water from the hot water tank 200 to the water passage 42, and a return pipe 92 for returning the water (hot water) from the water passage 42 to the hot water tank 200.
The refrigeration cycle apparatus includes a controller 7 for controlling mainly the rotational frequencies of the first motor 12 and the second motor 22 as well as the opening of the injection valve 61. In the present embodiment, the controller 7 is connected to an outside air temperature sensor 82 for detecting the outside air temperature, a fluid temperature sensor 93 for detecting the temperature of water flowing through the supply pipe 91, and a refrigerant temperature sensor 81 for detecting the temperature of the refrigerant guided to the radiator 4 through the first pipe 3a (to be more specific, the temperature of the joined refrigerant).
The refrigerant circuit 30 is filled with a refrigerant that reaches a supercritical state in the high-pressure side thereof (specifically, in a path from the first compression mechanism 11 and the second compression mechanism 21 to the expansion mechanism 13 through the radiator 4). In the present embodiment, the refrigerant circuit 30 is filled with carbon dioxide (CO2) as such a refrigerant. It should be noted that the type of the refrigerant is not particularly limited. The refrigerant may be a refrigerant that does not reach a supercritical state during operation (for example, a fluorocarbon refrigerant).
Next, the control performed by the controller 7 is described. As shown in
Immediately before the start-up operation, the controller 7 obtains a predetermined preset discharge temperature of the refrigerant guided to the radiator 4 through the first pipe 3a, the outside air temperature detected by the outside air temperature sensor 82, and the water temperature detected by the fluid temperature sensor 93 (Step S1). Then, the controller 7 determines the target rotational frequency F1 of the first motor 12 and the target rotational frequency F2 of the second motor 22 for the start-up operation and determines whether the opening X of the injection valve 61 should be in the fully closed state or in the fully opened state during the start-up operation, based on the obtained preset discharge temperature, outside air temperature and water temperature (Steps S2 to S4).
Specifically, tables for respective preset discharge temperatures (for example, from 80 deg C. to 140 deg C. in increments of 5 deg C.) and respective water temperatures (for example, from 10 deg C. to 30 deg C. in increments of 2 deg C.), as shown in
The preset discharge temperature is related to a target temperature of water to be heated (a temperature of hot water to be generated) in the radiator 4. A desired value of the preset discharge temperature is selected previously in accordance with the intended use or environment, and the selected value is stored in a memory of the controller 7. For example, in order to generate hot water of 90 deg C., a preset discharge temperature of 110 deg C. is selected. The controller 7 reads the preset discharge temperature from the memory to obtain that temperature. It also is possible to determine a preset discharge temperature to be obtained, on a case-by-case basis, based on the target temperature of water to be heated in the radiator 4 and the outside air temperature.
The controller 7 identifies, among the tables, a group of tables corresponding to the obtained preset discharge temperature, immediately before it starts the start-up operation. The controller 7 further selects, from among the identified group of tables, a table involving a water temperature closest to the water temperature detected by the fluid temperature sensor 93 (Step S2). Subsequently, by using the selected table, the controller 7 determines the target rotational frequency F1 of the first motor 12 and the target rotational frequency F2 of the second motor 22 for the start-up operation based on the outside air temperature detected by the outside air temperature sensor 82 (Step S3). In the case where the detected outside air temperature coincides with the outside air temperature listed in the selected table, the target rotational frequencies F1 and F2 are determined to be the values defined in this table. In the case where the detected outside air temperature is between the two temperatures listed in the table, the target rotational frequencies F1 and F2 each are determined to be the value calculated on a prorated basis using the two values corresponding to the two temperatures. In the case where the detected outside air temperature is beyond the range of outside air temperatures listed in the table, the target rotational frequencies F1 and F2 are determined to be the values defined in a table in association with the closest outside air temperature. In the case where the detected outside air temperature is between the two temperatures listed in the table, the values corresponding to one of the two temperatures closer to the detected temperature may be adopted to determine the target rotational frequencies F1 and F2.
The controller 7 determines the target rotational frequency F1 of the first motor 12 and the target rotational frequency F2 of the second motor 22 for the start-up operation, and simultaneously determines whether the opening X of the injection valve 61 should be in the fully closed state or in the fully opened state during the start-up operation based on the outside air temperature detected by the outside air temperature sensor 82, by using the selected table (Step S4). In the present embodiment, if the detected outside air temperature is 9 deg C. or lower, the controller 7 determines that the opening X of the injection valve 61 should be in the fully closed state (0%), and if the detected outside air temperature is higher than 9 deg C., the controller 7 determines that the opening X of the injection valve 61 should be in the fully opened state (100%). As described above, in the case where the detected outside air temperature coincides with the threshold temperature, it is preferable to determine that the opening X of the injection valve 61 should be in the fully closed state in order to prevent the pressure loss in the injection passage 6.
The threshold temperature that defines a switching point between the fully closed state and the fully opened state for the opening X of the injection valve 61 does not necessarily have to be 9 deg C. The threshold temperature can be determined appropriately. For example, the threshold temperature may be determined in the following manner. As shown in
The values defined in the tables are described below in detail.
In the present embodiment, each of the target rotational frequencies F2 of the second motor 22 in the tables is higher than the corresponding rotational frequency F2′ of the second motor 22 in a steady operation table for an ideal steady operation derived from a preset discharge temperature, an outside air temperature and a water temperature. The ideal steady operation here means a state in which the rotational frequency of one of the first motor 12 and the second motor 22 is increased and that of the other is decreased until the opening X of the injection valve 61 becomes 0% or 100% from the opening X that is optimized assuming that the rotational frequency of the first motor 12 is the same as that of the second motor 22 (see
As shown in
In order to generate rapidly a pressure difference between the high pressure side and the low pressure side of the refrigeration cycle, start-up operation tables, in which the rotational frequencies of the first motor 12 also are higher than those in the steady operation table, may be used. It is preferable that the ratio F1/F2 of each of the target rotational frequencies F1 of the first motor 12 to the counterpart target rotational frequency F2 of the second motor 22 in the start-up operation tables is lower than the corresponding ratio F1′/F2′ of the rotational frequency F1′ of the first motor 12 to the rotational frequency F2′ of the second motor 22 in the steady operation table. With such a configuration, the rotational frequency of the expander-compressor unit 1 can be reduced relative to that of the second compressor 2. Therefore, the apparent specific volume of the expansion mechanism 13 decreases relative to those of the compression mechanisms 11 and 21, and as a result, a pressure difference can be generated rapidly between the high pressure side and the low pressure side of the refrigeration cycle.
Alternatively, each of the target rotational frequencies F1 of the first motor 12 in the start-up operation tables may be set lower than the corresponding rotational frequency F1′ of the first motor 12 in the steady operation table, while each of the target rotational frequencies F2 of the second motor 22 in the start-up operation tables is maintained to be equal to the corresponding rotational frequency F2′ of the first motor 22 in the steady operation table. It is preferable to use a start-up operation table in which at least the rotational frequencies of the second motor 22 are set higher than those in the steady operation table, because a sufficient amount of refrigerant can be circulated through the refrigerant circuit 30 during the start-up operation and thereby the constituent members of the refrigeration cycle apparatus can be heated quickly.
It is preferable that the difference between each of the target rotational frequencies F1 of the first motor 12 and the counterpart target rotational frequency F2 of the second motor 22 in the start-up operation tables is smaller than the upper limit value (for example, 40 Hz) of the allowable driving range under any conditions (i.e., at any preset discharge temperature, at any water temperature, and at any outside air temperature). Furthermore, it is preferable that the ratio F1/F2 of each of the target rotational frequencies F1 of the first motor 12 to the counterpart target rotational frequency F2 of the second motor 22 in the start-up operation tables is in a range between the lower limit value (for example, 0.5) and the upper limit value (for example, 2) of the allowable driving range. The allowable driving range here means a range that is determined arbitrarily based on factors to be considered from a design viewpoint, such as the allowable lowest rotational frequency and the allowable highest rotational frequency of the compression mechanism 11 and 21, and the degree of imbalance between the lubricating oil level in the closed casing 10 and that in the closed casing 20 generated from a difference between the rotational frequency of the first motor 12 and that of the second motor 22.
The controller 7 determines the target rotational frequency F1 of the first motor 12 and the target rotational frequency F2 of the second motor 22 for the start-up operation, and simultaneously determines whether the opening X of the injection valve should be in the fully opened state or in the fully closed state during the start-up operation, by using the start-up operation tables stored previously in the controller 7. Subsequently, the controller 7 drives the first and second motors 12 and 22 to start the start-up operation (Step S5). Then, the controller 7 performs the start-up operation by controlling the rotational frequencies f1 and f2 of the first motor 12 and the second motor 22 to be the determined target rotational frequencies F1 and F2 respectively until a predetermined time period for the start-up operation has elapsed (Step S6). In the present embodiment, the controller 7 increases continuously the rotational frequencies f1 and f2 of the first motor 12 and the second motor 22 to the determined target rotational frequencies F1 and F2 respectively, as shown in
In addition, when the controller 7 determines that the opening of the injection valve 61 should be in the fully closed state, it performs the start-up operation while maintaining the opening X of the injection valve 61 in the fully closed state. It should be noted that when the controller 7 determines that the opening of the injection valve 61 should be in the fully opened state, it performs the start-up operation while maintaining the opening X of the injection valve 61 in the fully opened state. When the controller 7 determines that the opening of the injection valve 61 should be in the fully opened state, it may control the opening of the injection valve to be in the fully closed state for a predetermined period of time after the start of the start-up operation and then switched to the fully opened state. With such a configuration, a pressure difference can be generated rapidly between the high pressure side and the low pressure side of the refrigeration cycle, and a time required to shift from the start-up operation to the steady operation can be reduced.
After the start-up operation is completed, the controller 7 performs the steady operation. Specifically, the controller 7 changes the rotational frequencies f1 and f2 of the first motor 12 and the second motor 22 to the rotational frequencies F1′ and F2′ respectively determined based on the steady operation table shown in
As described above, in the refrigeration cycle apparatus of the present embodiment, the start-up operation is performed while the opening X of the injection valve 61 is maintained in the fully closed state or in the fully opened state under any conditions. Therefore, the injection loss can be kept low during the start-up operation. In particular, if the opening X of the injection valve 61 is maintained at 0% or 100% as in the case of the present embodiment, the injection loss can be prevented from occurring.
In the above embodiment, the controller 7 increases continuously the rotational frequencies f1 and f2 of the first motor 12 and the second motor 22, as shown in
Specifically, the controller 7 divides the time period of the start-up operation into time-based control sections (for example, every 180 seconds). Then, the controller 7 increases both the rotational frequency f1 of the first motor 12 and the rotational frequency f2 of the second motor 22 so as to bring the sum of the rotational frequencies f1 and f2 of the first motor 12 and the second motor 22 closer to the sum of the determined target rotational frequencies F1 and F2 of the first motor 12 and the second motor 22 step by step as the control section shifts from one to another. A rapid increase in the rotational frequencies f1 and f2 of the first motor 12 and the second motor 22 may cause in some cases a so-called overshoot, in which the actual discharge temperature of a refrigerant exceeds a preset discharge temperature. In contrast, if the rotational frequencies f1 and f2 of the first motor 12 and the second motor 22 are increased step by step, as described above, such an overshoot can be prevented.
It is preferable that the controller 7 calculates a difference between the preset discharge temperature and the refrigerant temperature detected by the refrigerant temperature sensor 81 every time the control section shifts from one to another, and when the difference is a relatively large value, increases relatively significantly the sum of the rotational frequency f1 of the first motor 12 and the rotational frequency f2 of the second motor 22. With such a configuration, the high pressure of the refrigeration cycle can be brought closer to the target value rapidly, and thereby the time period of the start-up operation can be reduced.
In the example shown in
In this case, it is preferable that the controller 7 calculates a difference between the preset discharge temperature and the refrigerant temperature detected by the refrigerant temperature sensor 81 every time the control section shifts from one to another, and when the difference is a relatively large value, increases the rotational frequency ratio f1/f2 at a slow rate. With such a configuration, a sufficient amount of refrigerant can be circulated through the refrigerant circuit 30 during the start-up operation, and a pressure difference can be generated rapidly between the high pressure side and the low pressure side. Therefore, the constituent members of the refrigeration cycle apparatus can be heated quickly, and thereby the actual discharge temperature of the refrigerant can be increased rapidly to the preset discharge temperature.
In the above embodiment, the controller 7 terminates the start-up operation when a predetermined time period has elapsed. The controller 7 may, however, terminate the start-up operation when the actual discharge temperature of the refrigerant exceeds the preset discharge temperature. Furthermore, the controller 7 may perform the start-up operation several times successively. In this case, a start-up operation table may be prepared for each start-up operation to repeat the procedure from Step S2 through Step S6 of
In the above embodiment, the controller 7 uses the preset discharge temperature to determine the target rotational frequencies F1 and F2 of the first motor 12 and the second motor 22 as well as the opening X of the injection valve 61 for the start-up operation. The controller 7 may, however, use a target temperature of water to be heated (temperature of hot water to be generated) in the radiator 4, instead of the preset discharge temperature.
Furthermore, in the above embodiment, the refrigeration cycle apparatus includes the fluid temperature sensor 93. However, the water temperature as a value that varies with the season may be inputted previously into the controller 7. The water temperature also may be a fixed value.
In the above embodiment, the radiator 4 serves as a heat exchanger for exchanging heat between a refrigerant and water. The radiator 4 may, however, be a heat exchanger for exchanging heat between a refrigerant and a fluid (for example, air) other than water.
The refrigeration cycle apparatus may be used in an air conditioner. In this case, the radiator 4 does not have the water passage 42 and dissipates heat from the refrigerant into the atmosphere.
The refrigerant circuit provided in the refrigeration cycle apparatus of the present invention is not limited to the refrigerant circuit 30 for allowing the refrigerant to flow in one direction only. It may be a refrigerant circuit in which the flow direction of the refrigerant can be changed, for example, a refrigerant circuit including four-way valves and thereby capable of switching between a heating operation and a cooling operation.
The refrigeration cycle apparatus of the present invention is useful as a power recovery system for recovering the expansion energy of a refrigerant in a refrigeration cycle as mechanical energy.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-009707 | Jan 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/007020 | 12/18/2009 | WO | 00 | 7/15/2011 |
