Patent Application
20070068178
1. Field of the Invention
The present invention relates to heat pumps useful for hot water heaters, air-conditioners, and the like, and more particularly to a heat pump furnished with a mechanism for recovering energy with an expander.
2. Description of the Related Art
A heat pump employing an expander in place of an expansion valve can recover the expansion energy of refrigerant as electric power or mechanical power. As the expander, in many cases a positive displacement expander is used that has a space with a variable capacity for introducing and expanding the refrigerant therein. The energy recovery with the expander has a significant value, particularly in the transcritical cycle of carbon dioxide in which the high pressure reaches a supercritical state of the refrigerant.
Because of its structure, the expander cannot recover energy unless the refrigerant passes through it in a predetermined direction. The heat pump used for an air-conditioner, however, requires that the refrigerant should flow in opposite directions when in a cooling operation and when in a heating operation because it is necessary to use the heat exchanger installed indoors as a radiator during the heating operation but as an evaporator during the cooling operation.
JP 2001-66006A discloses a heat pump capable of energy recovery with an expander in both cooling and heating operations. This heat pump is designed so that the refrigerant can flow through the expander in the same direction in both cooling and heating operations by switching in a four-way valve. Furthermore, in this heat pump, the expander and the compressor are connected to a common axis of rotation. In other words, they are directly coupled, in order to use the energy recovered by the expander directly for operating the compressor.
In the heat pump in which the expander and the compressor are directly coupled, the expander and the compressor operate at the same rotational speed and therefore it is impossible to vary the ratio between the displacement of the expander and the displacement of the compressor according to operation conditions. In other words, the heat pump of this type has the constraint of constant density ratio. For that reason, the heat pump in which the expander and the compressor are coupled directly has difficulty in performing a smooth operation according to operation conditions, although it has good efficiency in energy recovery. JP 2003-121018A discloses a heat pump that alleviates this difficulty.
As illustrated in
In the heat pump disclosed in JP 2003-121018A, an expansion valve (bypass valve) 107 is disposed in a bypass circuit 112 disposed in parallel with the expander 103, and an expansion valve 106 is also disposed in series with the expander 103. The opening of the expansion valve 106 or the expansion valve 107 is controlled according to the operation condition. A receiver 100 prevents excessive flow of the refrigerant into the expander 103 by temporarily reserving the refrigerant.
As discussed above, although the heat pump in which the expander and the compressor are coupled directly is advantageous in energy recovery, it cannot change the displacement ratio between the expander and the compressor according to operation conditions. For example, if the expander is designed based on the standard condition in a cooling operation, the displacement of the expander will be too large in a heating operation with respect to the required value. For that reason, in the heat pump disclosed in JP 2003-121018A, the expansion valve 107 is fully closed during a heating operation, while the opening of the expansion valve 106 is controlled as appropriate. On the other hand, during a cooling operation, the displacement of the expander 103 may become less than the required value. When this is the case, the expansion valve 106 is fully opened, while the opening of the expansion valve 107 is controlled as appropriate.
In this way, the heat pump disclosed in JP 2003-121018A avoids the constraint of constant density ratio and makes possible smooth cycling operations according to operation conditions by adjusting the opening of one of the expansion valves 106 and 107 while keeping the opening of the other one in a fully opened or fully closed state.
As described above, in the heat pump disclosed in JP 2003-121018A, when the displacement of the expander 103 becomes less than the required value, the expansion valve 107 is opened to allow a portion of the refrigerant to flow into the bypass circuit 112. However, as the flow rate of the refrigerant flowing in the bypass circuit 112 is increased, the difference between the high pressure PH and the low pressure PL in the refrigeration cycle reduces, and correspondingly, the degree to which the refrigerant flowing into the compressor 101 is superheated (degree of superheat) also decreases.
This change also is shown in
When the degree of superheat SH of the refrigerant reduces, it becomes difficult to perform a stable operation and at the same time ensure the reliability of the compressor 101. The reason is that, when the degree of superheat SH is low, a portion of the refrigerant remaining in a liquid state flows into the compressor 101, and liquid compression, which should be avoided, may take place in the compressor 101.
In the control process disclosed in JP 2003-121018A, the openings of the expansion valves 106 and 107 are adjusted for ensuring smooth operations, and as a result, the high pressure PH is varied. However, the high pressure PH in a refrigeration cycle affects the coefficient of performance (COP) of the heat pump, and therefore, it is desirable that the control of the expansion valves should be conducted appropriately not just from the viewpoint of ensuring smooth operations but also from the viewpoint of improving the coefficient of performance.
It should be noted here that the coefficient of performance (COP) is a dimensionless numerical value representing the ratio of the energy obtained relative to the energy put into the heat pump.
It is therefore an object of the present invention to enable efficient operations in a heat pump in which the expander and the compressor are coupled directly, and at the same time ensure the reliability of the compressor.
A heat pump according to the present invention includes: a compressor; a radiator; an expander; an evaporator; a piping that forms a circulation passage in which refrigerant circulates through the compressor, the radiator, the expander, and the evaporator in that order, and a bypass passage in which the refrigerant flows from the radiator to the evaporator without flowing through the expander; a first throttling device having a variable opening and disposed in the circulation passage between the radiator and the expander or between the expander and the evaporator; a second throttling device having a variable opening and disposed in the bypass passage; and a control device for adjusting the opening of the first throttling device and the opening of the second throttling device. In this heat pump, the compressor and the expander are connected to a common rotation shaft, and rotate at the same rate. The compressor and the expander may be connected to a single-piece rotation shaft or a multi-piece rotation shaft.
Further, in the heat pump of the present invention, the control device executes a first controlling in which, when the difference between a high pressure PH of the refrigerant circulating in the circulation passage and a predetermined value PHT determined based on a value at which the coefficient of performance of the heat pump is optimized is outside a predetermined range PHDR, the opening of the second throttling device is varied so that the absolute value of the difference between the pressure PH and the predetermined value PHT becomes smaller. After completing the first controlling, the control device executes a second controlling in which, when the difference between a degree of superheat SH of the refrigerant flowing into the compressor and a predetermined positive value SHT is outside a predetermined range SHDR, the opening of the first throttling device is varied so that the absolute value of the difference between the degree of superheat SH and the predetermined value SHT becomes smaller.
In the present invention, when the second throttling is adjusted to attempt an improvement in the coefficient of performance while ensuring smooth cycling operations, the first throttling device subsequently is adjusted to control the degree of superheat of the refrigerant. This controlling allows even the heat pump in which the compressor and the expander are coupled directly to perform smooth and efficient operations according to operation conditions while ensuring the reliability of the compressor.
FIGS. 3 is a flowchart illustrating one example of the control process executed by the control device.
Hereinbelow, preferred embodiments of the present invention are described with reference to the drawings. In the following description, the same components and steps may be designated with the same reference numerals to avoid repetitive description.
The refrigerant circulates in the direction indicated by the arrows in
In the heat pump 71, a first expansion valve 6, which serves as the first throttling device, is disposed between the radiator 2 and the expander 3, and a second expansion valve 7, which serves as the second throttling device, is disposed in the bypass passage. In terms of the relationship with the expander 3, the first expansion valve 6 is disposed in series with the expander 3, while the second expansion valve 7 is disposed in parallel with the expander 3. The openings of the expansion valves 6 and 7 can be controlled by a control device (controller) 30. When the controller 30 sets the opening of the second expansion valve 7 to be minimum (in other words, to be in a fully closed state), the circulating refrigerant does not flow in the bypass passage but the entire refrigerant flows into the expander 3.
In the heat pump 71, a temperature sensor (first temperature sensing means) 23 for measuring the temperature of the refrigerant flowing into the compressor 1 is disposed between the evaporator 4 and the compressor 1, and the evaporator 4 is provided with a temperature sensor (second temperature sensing means) 24 for detecting the temperature of the refrigerant in the evaporator 4. By identifying the temperature of the refrigerant flowing into the compressor 1 and the temperature at which the refrigerant evaporates in the evaporator (refrigerant evaporation temperature), it is possible to calculate the degree of superheat SH of the refrigerant. Thus, in order to specify the degree of superheat SH, the heat pump further may have a first temperature sensing means for detecting the temperature of the refrigerant flowing into the compressor and a second temperature sensing means for detecting the temperature of the refrigerant in the evaporator.
The heat pump 71 also is furnished with a temperature sensor 25 for measuring outside air temperature T. As will be described later, as the outside air temperature T rises, the necessity of increasing the opening of the second expansion valve 7 intensifies. Thus, the heat pump further may have a third temperature sensing means for detecting the temperature outside the system. Specifically, an appropriate example of “the temperature outside the system” includes the temperature of a medium that flows into the radiator 2 and is heated there, such as the temperature of outside air or the temperature of the water flowing into the radiator.
The heat pump 71 is provided with a pressure sensor 21 disposed between the compressor 1 and the radiator 2, for measuring pressure Pd of the refrigerant discharged from the compressor 1. The pressure Pd corresponds to the high pressure PH in the refrigeration cycle. Thus, in order to specify the pressure PH, the heat pump further may have a pressure sensing means for detecting the pressure of the refrigerant discharged from the compressor.
The high pressure PH in the refrigeration cycle can be calculated from measurement values other than the pressure Pd. For example, it is possible to calculate the pressure PH from temperatures T and Td by measuring an outside air temperature T and a temperature Td of the refrigerant discharged from the compressor 1. Installing a temperature sensor is less expensive than installing a pressure sensor. Moreover, when a pressure sensor is installed, refrigerant tends to leak easily from the location at which the pressure sensor is mounted. For these reasons, it is desirable that only temperature sensors be used to specify the pressure PH.
An example of the heat pump for implementing this calculation is illustrated in
All of the pressure sensor 21 and the temperature sensors 22, 23, 24, and 25 are connected to the controller 30, and in response to signals from these sensors, the controller 30 adjusts the openings of the expansion valves 6 and 7. Conventionally known sensors may be used for these sensors. For example, the temperature sensors may be thermistors.
Hereinbelow, controlling of the heat pump 72 (cf.
The number of revolutions of the expander 3, which is directly coupled to the compressor, cannot be controlled separately from the number of revolutions of the compressor 1. For this reason, when the required value becomes too large, it becomes necessary to open the second expansion valve 7 and allow a portion of the refrigerant to flow into the bypass passage, to ensure a smooth operation. Nevertheless, when a portion of the refrigerant flows into the bypass passage, the high pressure PH in the refrigeration cycle lowers, and the degree of superheat SH of the refrigerant flowing into the compressor 1 decreases correspondingly. The decrease of the degree of superheat SH may cause the refrigerant in a liquid state to flow into the compressor, making it impossible to ensure the reliability of the compressor. Moreover, as the high pressure PH lowers, the coefficient of performance (COP) of the heat pump changes correspondingly.
In the control process described below referring to
First, an outside air temperature T is input by a signal from the temperature sensor 25 (step 1: S1). Next, the outside air temperature T is compared to a predetermined temperature Ta, and if the outside air temperature T is equal to or higher than the temperature Ta, the process proceeds to step 3, whereas if the outside air temperature T is lower than the temperature Ta, the process returns to step 1 (step 2: S2). If the outside air temperature T is equal to or higher than the temperature Ta, the second expansion valve 7, which has been closed, is opened, and a portion of the refrigerant flows into the piping 12, which forms the bypass passage (step 3: S3).
At step 3, the second expansion valve 7 may be opened to a predetermined opening, or the second expansion valve 7 may be opened to an opening corresponding to the temperature difference (T−Ta). The temperature Ta preferably may be determined based on, for example, the ratio of the cylinder volume of the expander 3 to the cylinder volume of the compressor 1.
Herein, if the outside air temperature T is lower than the temperature Ta, the second expansion valve 7 is fully closed so that the whole amount of the refrigerant flows into the expander 3. This control process is advantageous for enhancing the energy recovery efficiency by the expander 3. However, this is merely illustrative, and a portion of the refrigerant may be introduced into the bypass passage prior to the execution of step 3. In this case, step 3 is not a control process in which “the second expansion valve that has been closed is opened”, but it is a control process in which “the opening of the second expansion valve is increased”.
Subsequently, a high pressure PH in the refrigeration cycle is calculated based on the signals from the temperature sensors 22 and 25 (step 4: S4). In the case of the heat pump 71 equipped with the pressure sensor 21, a value obtained by the sensor 21 may be used as it is. Next, the pressure PH is compared to a predetermined target pressure PHT, and if the pressure PH does not match the target pressure PHT, the process moves to steps 6 and onward, whereas if they match, the process moves to steps 9 and onward (step 5: S5).
The high pressure PH can be calculated, for example, based on the relationship diagram shown in
The target pressure PHT is determined based on a value at which the coefficient of performance of the heat pump is optimized. A pressure value at which the coefficient of performance of a heat pump is optimized varies depending on the heating capability of the radiator (which is a value such as 4.5 kW, 6.0 kW, etc, in the case of a hot water heater), the outside air temperature (which corresponds to incoming water temperature in the case of a hot water heater), and the like. A typical factor that affects the coefficient of performance is the outside air temperature. It is recommended that the target pressure PHT be determined by measuring a value at which the coefficient of performance is optimized through an experiment in advance, and defining the target pressure PHT as a function of a predetermined variable (for example, outside air temperature) based on the result of the experiment.
It is desirable that the target pressure PHT be set at a value that matches a value (optimum value) at which the coefficient of performance of the heat pump is optimized in the operation conditions applied to the heat pump; however, the target pressure PHT need not precisely or always match the optimum value. For example, it is possible to set one target pressure PHT for outside air temperatures in a predetermined range. In this case, the target pressure PHT varies in a stepwise manner depending on the changes of the outside air temperature or incoming water temperature. The relationship between the target pressure PHT and a predetermined variable, represented by outside air temperature, is input to the controller 30 in advance, and the target pressure PHT is determined based on the variable determined according to an operation condition.
If the pressure PH and the target pressure PHT are not equal, it is determined whether or not the pressure PH is greater than the target pressure PHT (step 6: S6). Then, if it is found that the pressure PH is greater than the target pressure PHT, the opening of the second expansion valve 7 is increased (step 7: S7), whereas if it is found that the pressure PH is less than the target pressure PHT, the opening of the second expansion valve 7 is decreased (step 8: S8).
When the process goes through step 7, the pressure PH reduces, whereas when the process goes through step 8, the pressure PH rises. Thereafter, the process returns to step 4, at which the pressure PH is calculated again, and the calculated pressure PH is compared to the target pressure PHT at step 5. Thus, the loop control of steps 4 to 8 is repeated until the pressure PH matches the target pressure PHT.
In this loop control, it is recommended that the degree of variation of the opening in step 7 or 8 be kept very small. The reason is that, if the opening is changed greatly at one time, it becomes difficult for the pressure PH to converge on the target pressure PHT.
If a match between the pressure PH and the target pressure PHT is verified at step 5, the control of the high pressure PH in the refrigeration cycle (first controlling) is suspended temporarily, and controlling of the degree of superheat SH of refrigerant (second controlling) is executed.
In the second controlling, the degree of superheat SH is calculated first (step 9: S9). In the heat pump 72, the degree of superheat SH is calculated based on the temperature measured by the temperature sensor 23, referring to the saturated vapor line of the refrigerant (specifically, referring to the refrigerant evaporation temperature measured by the temperature sensor 24). Next, the degree of superheat SH is compared to a predetermined target degree of superheat SHT, and if the degree of superheat SH does not match the target degree of superheat SHT, the process moves to steps 11 and onward, whereas if they match, the process returns to step 4 (step 10: S10).
Although the predetermined value SHT that is the target degree of superheat may be determined as appropriate depending on the type of heat pump, the type of refrigerant, expected use conditions, and so forth, and a value within a range higher than 0° C. but lower than or equal to 20° C. is generally suitable. The degree of superheat can be expressed as a temperature difference, as mentioned above, but the above-mentioned temperature difference is, to be precise, the difference between the temperature of the superheated refrigerant and the temperature indicated by the intersection point with the saturated vapor line at the pressure of that refrigerant (the boiling point at that pressure).
In order to ensure the reliability of the compressor, it is desirable that the degree of superheat SH be higher than a certain degree. However, if the degree of superheat SH is too high, the mechanical power to be input to the compressor will be too large. When taking these into account, it is preferable that the predetermined value SHT be equal to or higher than 5° C., and more preferably 10° C. or lower. Controlling the degree of superheat SH within an appropriate range ensures the reliability of the compressor 1 and at the same time prevents the input of mechanical power to the compressor 1 from becoming larger than is necessary. Appropriate controlling of the degree of superheat SH serves not only to ensure the reliability of the compressor 1 but also to further improve the coefficient of performance of the heat pump.
If the degree of superheat SH and the target degree of superheat SHT are not equal, it is determined whether or not the degree of superheat SH is higher than the target degree of superheat SHT (step 11: S11). Then, if the degree of superheat SH is found to be higher than the target degree of superheat SHT, the opening of the first expansion valve 6 is increased (step 12: S12), whereas if the degree of superheat SH is found to be less than the target degree of superheat SHT, the opening of the first expansion valve 6 is decreased (step 13: S13).
When the process goes through step 12, the degree of superheat SH reduces, whereas when the process goes through step 13, the degree of superheat SH rises. For the same reason as explained concerning steps 7 and 8, it is recommended that the degree of variation of the opening(s) in step 12 or 13 be kept very small. This is because the degree of superheat SH reliably should be brought closer to the target degree of superheat SHT by way of step 12 or step 13.
After executing step 12 or 13, the process returns to step 4 to perform the control of the pressure PH again. Thus, in the control process shown in
If it is necessary to control only the high pressure PH, the control process as disclosed in JP 2003-121018A will be sufficient, in which the opening of one of the expansion valves is adjusted while the other one is kept in a fully opened or fully closed state. In contrast, in the control process shown in
In the heat pumps 71 and 72 as well, the control process in which the opening of the first expansion valve 6 is adjusted while the second expansion valve 7 is kept fully closed may be executed in a temperature range in which the volume flow rate of the refrigerant flowing into the expander 3 is smaller than the cylinder volume of the expander 3, although not shown in
In the control process shown in
In the example of the control process shown in
Various modifications may be made to the control of the pressure PH and the control of the degree of superheat SH other than the modification illustrated in
For example, in the foregoing, the subject of decision was a match between the pressure PH and the target pressure PHT, in other words, whether or not the difference between the pressure PH and the target pressure PHT is zero; however, in place of this, it also is possible to make the decision as to whether the difference between the pressure PH and the target pressure PHT falls within a predetermined range PHDR. In this case, in place of step 5, a decision may be made as to whether or not the difference between the pressure PH and the target pressure PHT falls within the predetermined range PHDR. The decision as to whether or not the difference falls within the predetermined range PHDR need not be made by directly calculating the difference, but it may be made by, for example, calculating a ratio and determining whether or not the ratio falls within a predetermined range PHDR that is converted for the ratio. The control of the degree of superheat SH also may be conducted in a similar manner.
Although the predetermined ranges PHDR and SHDR may be set as appropriate depending on, for example, the use of the heat pump, it is desirable that they should be in a very limited range. An example of the predetermined range PHDR is preferably from −1.2 MPa to 1.2 MPa, and more preferably from −0.8 MPa to 0.8 MPa, as expressed by a value obtained by subtracting the target pressure PHT (MPa) from the pressure PH (MPa). It is preferable that the predetermined range SHDR be within a range higher than −(SHT)° C. but lower than or equal to 20° C., and more preferably a range higher than −(SHT)° C. but lower than or equal to 10° C., as expressed by a value obtained by subtracting the target degree of superheat SHT (° C.) from the degree of superheat SH (° C.); however, the predetermined range SHDR may be set to be a value exceeding 0° C. in order that the just-mentioned value does not become negative. In the case that the target degree of superheat SHT is 10° C., the range “higher than −(SHT)° C. but lower than or equal to 20° C.” means a range “higher than −10° C. but lower than or equal to 20° C.”.
In addition, for example, a step of determining whether or not the second expansion valve 7 is fully closed may be added after step 8, and if it is determined that the second expansion valve 7 is fully closed in the additional step, the process may return to step 1. If it is determined that the second expansion valve 7 is not fully closed in the additional step, the control process returns to step 4 and is repeated.
Moreover, for example, step 9 may be executed subsequent to step 3 in order to execute the control of degree of the superheat SH prior to the control of the pressure PH. In this case, the degree of superheat SH is controlled first, then the pressure PH is controlled, and thereafter the degree of superheat SH is controlled again. Depending on the use and design of the heat pump, the control process may be started from step 4 or 9 without executing steps 1 to 3.
As has been described above, the controller (control device) 30 executes the control of pressure (first controlling) in which, if the difference between a high pressure PH of the refrigerant and a predetermined target value PHT is outside a predetermined range PHDR, the opening of the second expansion valve (second throttling device) 7 is varied so that the absolute value of the difference between the pressure PH and the predetermined value PHT becomes smaller (so that the pressure PH is brought closer to the predetermined value PHT) (S4 to S8).
Then, after completing the first controlling, the controller 30 executes the control of the degree of superheat (second controlling) in which, if the difference between a degree of superheat SH of the refrigerant flowing into the compressor and a predetermined positive value SHT is outside a predetermined range SHDR, the opening of the first expansion valve (first throttling device) 6 is varied so that the absolute value of the difference between the degree of superheat SH and the predetermined value SHT becomes smaller (so that the degree of superheat SH is brought closer to the predetermined value SHT) (S9 to S13).
In the first controlling, it is preferable that the control device vary the opening of the second throttling device so that the difference between the pressure PH and the predetermined value PHT falls within the predetermined range PHDR. In the second controlling, the control device may vary the opening of the first throttling device so that the difference between the degree of superheat SH and the predetermined value SHT falls within the predetermined range SHDR.
In an example of the control process described above, the control device further may execute the first controlling after completing the second controlling, if the difference between the pressure PH and the predetermined value PHT is outside the predetermined range PHDR. The purpose is to control the pressure PH again, taking into account the variation of the pressure PH resulting from the second controlling.
As illustrated in the foregoing, a specific controlling may be as follows; in the first controlling, when the pressure PH is higher than the predetermined value PHT and the difference between the pressure PH and the predetermined value PHT is outside the predetermined range PHDR, the opening of the second throttling device is increased; and when the pressure PH is lower than the predetermined value PHT and the difference between the pressure PH and the predetermined value PHT is outside the predetermined range PHDR, the opening of the second throttling device is decreased.
In addition, in the second controlling, when the degree of superheat SH is higher than the predetermined value SHT and the difference between the degree of superheat SH and the predetermined value SHT is outside the predetermined range SHDR, the opening of the first throttling device is increased; and when the degree of superheat SH is lower than the predetermined value SHT and the difference between the degree of superheat SH and the predetermined value SHT is outside the predetermined range SHDR, the opening of the first throttling device is decreased.
In the control processes shown in
For example, by measuring a ratio RV of the volume flow rate of the refrigerant flowing into the compressor 1 to the volume flow rate of the refrigerant flowing into the expander 3, it is possible to execute the control of the high pressure PH based on the ratio RV and a ratio RC of the volume of the expander 3 to the volume of the compressor 1. The magnitude relationship between the ratio RV and the ratio RC is an alternative parameter RP associated with the high pressure PH, and with this parameter, it also is possible to set a control target RPT associated with the target pressure PHT.
Thus, in the just-described control process, the control device may determine whether or not the difference between the pressure PH and the predetermined value PHT is within the predetermined range PHDR by comparing a predetermined characteristic RP associated with the pressure PH and a predetermined value RPT concerning the characteristic RP, the predetermined value RPT being associated with the predetermined value PHT, without directly comparing the pressure PH and the predetermined value PHT.
It should be noted that, as shown in
The configurations to which the present invention is applicable are not limited to the illustrative examples of
Moreover, a plurality of controllers may share the function of the controller 30. In a heat pump 76, illustrated in
Furthermore, it also is possible to employ a heat pump in which four-way valves 51 and 53 are provided. A heat pump 77, illustrated in
In the control processes illustrated above, the pressure Pd (PH) of the refrigerant discharged from the compressor is measured, or the temperature of the refrigerant discharged from the compressor is measured, in order to calculate the pressure PH. By utilizing this, abnormality management of the heat pump may be performed. The abnormality management can be executed as follows. In a heat pump having a configuration as illustrated above, if the pressure PH exceeds a predetermined limit pressure and/or if the temperature of the refrigerant discharged from the compressor 1 exceeds a predetermined limit temperature, the controller 30 recognizes the abnormality and performs adjustment to increase the opening(s) of the first expansion valve 6 and/or the second expansion valve 7 to a predetermined opening or greater. Here, it is preferable that the predetermined opening be set at an opening that exceeds the control ranges determined in the first controlling and the second controlling. Such an action makes it possible to reduce the pressure and temperature of the refrigerant quickly.
Even if the high pressure PH or the temperature of the refrigerant reaches an abnormal value due to an abrupt change in the operation condition or some other cause, the just-described control process makes it possible to eliminate the abnormal value in a short time. It should be noted that although the limit pressure and limit temperature may vary depending on such factors as the refrigerant and the configuration of the heat pump, illustrative examples of the limit pressure and the limit temperature may be given as 12 MPa and 115° C., respectively, in the case of using carbon dioxide as the refrigerant.
In order to execute the abnormality management as described above, it is preferable that, in the heat pump of the present invention, if the pressure PH exceeds a predetermined limit pressure or if the temperature of the refrigerant discharged from the compressor exceeds a predetermined limit temperature, the control device greatly varies at least one opening selected from the opening of the first throttling device and the opening of the second throttling device beyond the variation ranges of the openings in the first controlling and the second controlling.
The present invention has great utility value as it achieves an improvement in the heat pump, which is useful for air-conditioners, hot water heaters, dish dryers, garbage drying disposers, and the like.
The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-356560 | Dec 2004 | JP | national |
This application is a continuation of prior pending International Application Number PCT/JP2005/022655, filed on Dec. 9, 2005, which designated the United States.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP05/22655 | Dec 2005 | US |
| Child | 11537089 | Sep 2006 | US |
