JP3929067B2 - heat pump - Google Patents

Description

  The present invention relates to a heat pump useful as an air conditioner, a water heater, and the like, and more particularly, to a heat pump provided with a mechanism for recovering energy by an expander.

  In a heat pump using an expander instead of the expansion valve, the energy for expanding the refrigerant can be recovered as electric power or power. As the expander, a positive displacement expander having a variable capacity space for introducing and expanding a refrigerant is often used. Energy recovery by an expander is particularly significant in a transcritical cycle in which carbon dioxide is used as a refrigerant and the high pressure side reaches a supercritical state.

  Due to its structure, the expander cannot recover energy unless the refrigerant passes along a predetermined direction. However, in a heat pump used as an air conditioner, it is necessary to use a heat exchanger installed indoors as a radiator during heating operation and as an evaporator during cooling operation. It is necessary to flow the refrigerant in reverse.

  Japanese Patent Application Laid-Open No. 2001-66006 discloses a heat pump capable of recovering energy by an expander during both cooling operation and heating operation. This heat pump is designed so that the refrigerant flows through the expander in the same direction during both cooling and heating operations by switching the four-way valve. In this heat pump, in order to spend the energy recovered by the expander as it is for the operation of the compressor, the expander and the compressor are connected to the same rotating shaft, that is, directly connected.

  In a heat pump in which an expander and a compressor are directly connected, since the expander and the compressor operate at the same rotational speed, the displacement volume ratio between the expander and the compressor cannot be changed according to operating conditions. That is, this type of heat pump has a constant density ratio. For this reason, the heat pump in which the expander and the compressor are directly connected is excellent in energy recovery efficiency, but it is difficult to smoothly operate according to the operating conditions. JP2003-121018 discloses a heat pump that alleviates this difficulty.

  As shown in FIG. 14, Japanese Patent Laid-Open No. 2003-121018, like Japanese Patent Laid-Open No. 2001-66006, arranges two four-way valves 151, 153 in the tube body 111, and switching the four-way valves 151, 153, A heat pump is disclosed in which the refrigerant is designed to flow through the expander 103 and the compressor 101 in the same direction during any heating operation (see FIG. 4). In the air conditioner using this heat pump, during heating, a path indicated by a solid line is selected in the four-way valves 151 and 153, the indoor heat exchanger 152 functions as a radiator, and the outdoor heat exchanger 154 serves as an evaporator. Function. In this air conditioner, during cooling, a path indicated by a broken line is selected in the four-way valves 151, 153, the indoor heat exchanger 152 functions as an evaporator, and the outdoor heat exchanger 154 functions as a radiator. In this heat pump, the expander 103 and the compressor 101 are directly connected to share one rotating shaft, and the rotating shaft is driven by the motor 105.

  In the heat pump disclosed in Japanese Patent Laid-Open No. 2003-121018, an expansion valve (bypass valve) 107 is arranged in a bypass circuit 112 arranged in parallel with the expander 103, and an expansion valve 106 is also arranged in series with the expander 103. Has been. Then, the opening degree of the expansion valve 106 or the expansion valve 107 is controlled according to the operating conditions. The receiver 100 prevents the refrigerant from excessively flowing into the expander 103 by temporarily storing the refrigerant.

  As described above, the heat pump in which the expander and the compressor are directly connected is excellent in terms of energy recovery, but the displacement volume ratio between the expander and the compressor cannot be changed according to the operating conditions. . For example, if the expander is designed on the basis of standard conditions during cooling operation, the displacement volume of the expander is too large for the required value during heating operation. For this reason, in the heat pump disclosed in Japanese Patent Laid-Open No. 2003-121018, during the heating operation, the expansion valve 107 is fully closed, and the opening degree of the expansion valve 106 is appropriately controlled. On the other hand, during the cooling operation, the displacement volume of the expander 103 may be smaller than the required value. In this case, the expansion valve 106 is fully opened, and the opening degree of the expansion valve 107 is appropriately controlled.

  As described above, the heat pump disclosed in Japanese Patent Laid-Open No. 2003-121018 avoids the restriction of a constant density ratio by adjusting the opening degree of the other in a state where one of the expansion valves 106 and 107 is fully opened or fully closed, Smooth cycle operation according to operating conditions is possible.

FIG. 15 is a Mollier diagram showing the refrigeration cycle in the heat pump shown in FIG. 14, where the horizontal axis H represents enthalpy and the vertical axis P represents pressure. The refrigerant in the high pressure PH state a discharged from the compressor 101 radiates heat to the state b in the indoor heat exchanger 152 or the outdoor heat exchanger 154 functioning as a radiator. The refrigerant is expanded in an equal enthalpy state by the expansion valve 106 to state c, and further isentropically expanded in the expander 103 to reach a state d of low pressure PL. The refrigerant absorbs heat in the outdoor heat exchanger 154 or the indoor heat exchanger 152 functioning as an evaporator, reaches the state f that is in the superheated steam state beyond the intersection (state e) with the saturated vapor line, and then again. It flows into the compressor 101. In this heat pump, energy corresponding to the enthalpy difference W ₂ between the state c and the state d is recovered by the expander 103. Therefore, in this heat pump, basically, by introducing power corresponding to the value obtained by subtracting the enthalpy difference W ₂ from the enthalpy difference W ₁ between the states a and state f (W ₁ -W ₂₎ to the compressor 101 It's enough.

  As described above, in the heat pump disclosed in Japanese Patent Application Laid-Open No. 2003-121018, when the displacement volume of the expander 103 becomes smaller than the required value, the expansion valve 107 is opened and a part of the refrigerant flows into the bypass circuit 112. However, as the flow rate of the refrigerant flowing through the bypass circuit 112 is increased, the difference between the high-pressure side pressure PH and the low-pressure side pressure PL of the refrigeration cycle is reduced, and accordingly, the refrigerant flowing into the compressor 101 is superheated (superheat). The degree (degree of superheat) also decreases.

  This change is also shown in FIG. When the opening degree of the expansion valve 107 is increased, the refrigeration cycle (af) shifts to the refrigeration cycle (a'-f '). As shown in FIG. 15, with this transition, the high-pressure side pressure decreases from PH to PH ′, and the low-pressure side pressure increases from PL to PL ′. Then, the enthalpy difference between the state f indicating the degree of superheat of the refrigerant and the state e decreases from SH to SH ′.

  When the superheat degree SH of the refrigerant decreases, it becomes difficult to perform a stable operation while ensuring the reliability of the compressor 101. This is because if the degree of superheat SH is small, a part of the refrigerant flows into the compressor 101 as a liquid, and liquid compression that should be avoided in the compressor 101 may occur.

  Further, in the control disclosed in Japanese Patent Application Laid-Open No. 2003-121018, the opening degree of the expansion valves 106 and 107 is adjusted to ensure smooth operation, and as a result, the high pressure side pressure PH varies. However, since the high pressure PH of the refrigeration cycle affects the coefficient of performance (COP) of the heat pump, the control of the expansion valve not only ensures smooth operation but also improves the coefficient of performance. It is desirable to do it properly.

  The coefficient of performance (COP) is a dimensionless numerical value indicating the ratio of the obtained energy to the energy input to the heat pump.

  Therefore, an object of the present invention is to enable efficient operation while ensuring the reliability of a compressor in a heat pump in which an expander and a compressor are directly connected.

The heat pump of the present invention includes a compressor, a radiator, an expander, an evaporator, the compressor, the radiator, the expander, and a circulation path through which the refrigerant circulates through the evaporator in this order. And a tube forming a bypass path through which refrigerant flows from the radiator to the evaporator without going through the expander, and between the radiator and the expander or between the expander and the evaporator A first throttle device having a variable opening degree disposed in the circulation path between the first throttle device and a second throttle device having a variable opening degree disposed in the bypass path; And a control device for adjusting the opening and the opening of the second throttling device. In this heat pump, the compressor and the expander are directly connected so as to rotate at the same rotational speed .

Furthermore, in the heat pump of the present invention, the control device includes a high side pressure PH of the refrigerant circulating through the circulation path, the difference between the predetermined value PH _T which is determined based on the value the coefficient of performance becomes optimum heat pump If not within the predetermined range PH _DR, the absolute value of the difference between the pressure PH and the predetermined value PH _T changes the opening degree of the second throttle device so as to reduce, to implement the first control. Then, after finishing the first control, and the superheat degree SH of the refrigerant flowing into the compressor, when the difference between the predetermined value SH _T is not within the predetermined range SH _DR is a positive predetermined value Performs a second control in which the opening degree of the first expansion device is changed so that the absolute value of the difference between the superheat degree SH and the predetermined value SH _T becomes small.

  In the present invention, when the second expansion device is adjusted to improve the coefficient of performance while ensuring a smooth cycle operation, the first expansion device is continuously adjusted to control the degree of superheat of the refrigerant. did. With this control, even in a heat pump in which the compressor and the expander are directly connected, smooth and efficient operation according to the operation conditions can be performed while ensuring the reliability of the compressor.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the same members and steps are denoted by the same reference numerals, and duplication of description may be avoided.

  In FIG. 1, the block diagram of one form of the heat pump of this invention is shown. The heat pump 71 includes the compressor 1, the radiator 2, the expander 3, and the evaporator 4 as main components for exhibiting basic functions of the heat pump. These main components are connected by a tube 11 that forms a circulation path through which the refrigerant circulates through the compressor 1, the radiator 2, the expander 3, and the evaporator 4 in this order. One end of the tube body 12 is connected to the tube body 11 between the radiator 2 and the expander 3, and the other end is connected to the tube body 11 between the expander 3 and the evaporator 4. The tubular body 12 forms a bypass path through which the refrigerant flows from the radiator 2 to the evaporator 4 without going through the expander 3.

  While the refrigerant circulates in the direction indicated by the arrow in FIG. 1, the heat absorbed by the evaporator 4 is released by the radiator 2. As a result, this system functions as a heat pump that pumps heat from the evaporator 4 to the radiator 2. The compressor 1 and the expander 3 are connected to one rotating shaft (shaft) 10. The compressor 1 is operated by power supplied from the electric motor 5 connected to the shaft 10 and power recovered by the expander 3. Since the heat pump in which the compressor 1 and the expander 3 are directly connected and rotate at the same rotation speed cannot be controlled independently of the rotation speed of the compressor 1, the heat pump is subjected to a so-called constant density ratio constraint. . In order to avoid this restriction, in the heat pump 71, the pipe body 12 forms a bypass path for the refrigerant, and the expansion valve 7 is disposed in the bypass path.

  In the heat pump 71, a first expansion valve 6 that is a first expansion device is disposed between the radiator 2 and the expander 3, and a second expansion valve 7 that is a second expansion device is disposed in the bypass path. . If it expresses paying attention to the relationship with the expander 3, the first expansion valve 6 is arranged in series with the expander 3, and the second expansion valve 7 is arranged in parallel with the expander 3. The opening degree of the expansion valves 6 and 7 can be controlled by a control device (controller) 30. When the opening degree of the second expansion valve 7 is set to the minimum by the controller 30 (that is, when the second expansion valve 7 is fully closed), the circulating refrigerant does not flow through the bypass path but flows into the expander 3.

  The heat pump 71 is provided with a temperature sensor (first temperature detecting means) 23 for measuring the temperature of the refrigerant flowing into the compressor 1 between the evaporator 4 and the compressor 1. A temperature sensor (second temperature detecting means) 24 for detecting the temperature of the refrigerant in the evaporator 4 is disposed. If the temperature of the refrigerant flowing into the compressor 1 and the temperature at which the refrigerant evaporates in the evaporator (refrigerant evaporation temperature) can be specified, the superheat degree SH of the refrigerant can be calculated. Thus, the heat pump further includes first temperature detecting means for detecting the temperature of the refrigerant flowing into the compressor and second temperature detecting means for detecting the temperature of the refrigerant in the evaporator in order to specify the degree of superheat SH. You may do it.

  The heat pump 71 is also provided with a temperature sensor 25 that measures the outside air temperature T. As will be described later, when the outside air temperature T increases, the necessity of increasing the opening degree of the second expansion valve 7 increases. Thus, the heat pump may further include third temperature detection means for detecting the temperature outside the system. Specifically, the “outside system temperature” is suitably the temperature of the medium that flows into the radiator 2 and is heated, for example, the temperature of the outside air or the temperature of the flowing water.

  In the heat pump 71, a pressure sensor 21 that measures the pressure Pd of the refrigerant discharged from the compressor 1 is disposed between the compressor 1 and the radiator 2. The pressure Pd corresponds to the high-pressure side pressure PH of the refrigeration cycle. Thus, the heat pump may further include a pressure detection unit that detects the pressure of the refrigerant discharged from the compressor in order to specify the pressure PH.

  The high-pressure side pressure PH of the refrigeration cycle can also be calculated from measured values other than the pressure Pd. For example, the outside temperature T and the temperature Td of the refrigerant discharged from the compressor 1 can be measured, and the pressure PH can be calculated from these temperatures T and Td. The temperature sensor can be installed at a lower cost than the pressure sensor. Moreover, if a pressure sensor is installed, it will become easy to leak a refrigerant | coolant from the attachment part of a pressure sensor. For this reason, it is desirable to specify the pressure PH using only the temperature sensor.

  A heat pump for carrying out this calculation is illustrated in FIG. In the heat pump 72, a temperature sensor 22 that measures the temperature Td of the refrigerant discharged from the compressor 1 is disposed between the compressor 1 and the radiator 2 instead of the pressure sensor 21. Thus, the heat pump further includes the third temperature detecting means for detecting the temperature outside the system and the fourth temperature detecting means for detecting the temperature of the refrigerant discharged from the compressor in order to specify the pressure PH. You may have.

  The pressure sensor 21 and the temperature sensors 22, 23, 24, and 25 are all connected to the controller 30, and the controller 30 adjusts the opening degree of the expansion valves 6 and 7 based on signals from these sensors. As these sensors, those conventionally known may be used. The temperature sensor may be a thermistor, for example.

  Hereinafter, control of the heat pump 72 (see FIG. 2) by the controller 30 will be described. Here, the control when the cylinder volume of the expander 3 (more precisely, the ratio of the cylinder volume of the expander 3 to the cylinder volume of the compressor 1) is determined based on winter cycle conditions is illustrated. In this case, the required value for the displacement volume of the expander 3 increases as the ambient temperature outside the system (outside air temperature T) increases, and when the outside air temperature T reaches a predetermined temperature, the required value decreases the displacement volume of the expander 3. Exceed. That is, when the outside air temperature T becomes equal to or higher than a predetermined value, the volume flow rate of the refrigerant that flows into the expander 3 becomes larger than the cylinder volume.

  The rotational speed of the expander 3 directly connected to the compressor cannot be controlled separately from the rotational speed of the compressor 1. For this reason, when the required value is excessive as described above, it is necessary to ensure smooth operation by opening the second expansion valve 7 and allowing a part of the refrigerant to flow through the bypass path. However, when a part of the refrigerant flows into the bypass path, the high-pressure side pressure PH of the refrigeration cycle decreases, and accordingly, the superheat degree SH of the refrigerant flowing into the compressor 1 also decreases. When the degree of superheat SH decreases, there is a risk that liquid refrigerant flows into the compressor, and the reliability of the compressor cannot be ensured. In addition, the coefficient of performance (COP) of the heat pump changes as the high pressure side pressure PH decreases.

  In the control described below with reference to FIG. 3, the high-pressure side pressure PH is controlled to an appropriate value, and the refrigerant superheat degree SH is also controlled.

  First, the 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 with 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, and if the outside air temperature T is less than the temperature Ta, the process returns to step 1 (step 2; S2). When the outside air temperature T is equal to or higher than the temperature Ta, the closed second expansion valve 7 is opened, and a part of the refrigerant flows into the tubular body 12 forming the bypass path (step 3; S3).

  In step 3, the second expansion valve 7 may be opened to a predetermined opening degree that is determined in advance, or the second expansion valve 7 may be opened to an opening degree that corresponds to the temperature difference (T-Ta). . The temperature Ta 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.

  Here, when the outside air temperature T is lower than the temperature Ta, the second expansion valve 7 is fully closed so that the entire amount of the refrigerant flows into the expander 3. This control is advantageous for improving the energy recovery efficiency of the expander 3. However, the present invention is not limited to this, and a part of the refrigerant may be introduced into the bypass path before performing Step 3. In this case, step 3 is not “open the second expansion valve that has been closed” control but “control the degree of opening of the second expansion valve”.

Subsequently, the high-pressure side pressure PH of 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 provided with the pressure sensor 21, the value obtained by the sensor 21 may be used as it is. Next, the pressure PH is compared with a predetermined target pressure PH _T, and if the pressure PH does not match the target pressure PH _T , the process proceeds to step 6 or later, and if it matches, the process proceeds to step 9 or later (step 5). S5).

  The high pressure side pressure PH can be calculated based on, for example, the relationship diagram shown in FIG. If the outside air temperature T and the temperature of the refrigerant discharged from the compressor (the discharge refrigerant temperature of the compressor) Td are determined, the pressure of the refrigerant discharged from the compressor (the discharge refrigerant pressure of the compressor) Pd can be obtained. It is.

Target pressure PH _T is determined based on the value that optimizes the coefficient of performance of the heat pump. The pressure value at which the coefficient of performance of the heat pump is optimal is, for example, the heating capacity of the radiator (takes values such as 4.5 kW or 6.0 kW for a water heater), the outside temperature (corresponds to the incoming water temperature for a water heater) It changes according to the etc. A typical factor that affects the coefficient of performance is the outside temperature. The value coefficient of performance becomes optimum, measured beforehand by experiment, based on the results, as a function of predetermined variables (e.g., outside air temperature), it is sufficient to set the target pressure PH _T.

Target pressure PH _T is desirably set to a value coefficient of performance of the heat pump in the operating conditions applicable to the heat pump coincides with the optimum value serving (optimum value), it is not necessary to exactly match the optimal value, or It is not always necessary to match. For example, it is possible to set one of the target pressure PH _T for each outside air temperature in a predetermined range. In this case, the target pressure PH _T in response to changes in ambient temperature or entering water temperature will vary stepwise. Thus predetermined relationship between the variable and the target pressure PH _T represented by the outside air temperature is previously inputted to the controller 30, the target pressure PH _T is determined based on the variable which is determined according to the operating conditions.

If the pressure PH and the target pressure PH _T not equal, whether the pressure PH is larger than the target pressure PH _T is determined (Step 6; S6). If the pressure PH is larger than the target pressure PH _T, the opening degree of the second expansion valve 7 is greatly changed (step 7; S7). If the pressure PH is smaller than the target pressure PH _T , the second expansion valve 7 is opened. The degree is changed small (step 8; S8).

When passing through step 7, the pressure PH decreases, and when passing through step 8, the pressure PH increases. Thereafter, the calculated again pressure PH returns to Step 4, the pressure PH calculated in step 5 is compared with the target pressure PH _T. Thus, until the pressure PH coincides with the target pressure PH _T, it is repeated loop control comprising steps 4-8.

In this loop control, it is preferable that the degree of change in the opening degree in step 7 or 8 is very small. Larger changes at once the opening, because the pressure PH is less likely to converge to the vicinity of the target pressure PH _T.

When a match between the pressure PH and the target pressure PH _T is confirmed in step 5, the control (first control) of the high side pressure PH of the refrigeration cycle is temporarily terminated, the control of the superheat degree SH of the refrigerant (the second control) Is implemented.

In the second control, first, the superheat degree SH is calculated (step 9; S9). In the heat pump 72, based on the temperature measured by the temperature sensor 23, the superheat degree SH is calculated by referring to the saturated vapor line of the refrigerant (specifically, referring to the refrigerant evaporation temperature measured by the temperature sensor 24). Is done. Then, the degree of superheat SH and a predetermined target degree of superheat SH _T is compared, the degree of superheat SH is proceeds to step 11 and subsequent to be equal to the target degree of superheat SH _T, in step 4 if the match Return (step 10; S10).

The predetermined value SH _{T as the} target superheat degree may be determined as appropriate depending on the type of heat pump and refrigerant, assumed use conditions, etc., but usually a value in the range of more than 0 ° C. and not more than 20 ° C. is suitable. . The degree of superheat can be indicated by the temperature difference as described above. To be precise, the temperature difference is calculated from the temperature of the superheated refrigerant and the saturated vapor line at the pressure of the refrigerant. It is the difference from the temperature indicated by the intersection (boiling point at the pressure).

In order to ensure the reliability of the compressor, it is desirable that the degree of superheat SH is greater than a certain level. However, if the superheat degree SH is too large, the power to be input to the compressor increases. Considering this, the predetermined value SH _T is preferably a value of 5 ° C. or more, and more preferably a value of 10 ° C. or less. When the superheat degree SH is controlled within an appropriate range, the reliability of the compressor 1 can be ensured, and the power input to the compressor 1 can be prevented from becoming unnecessarily large. Appropriate control of the superheat degree SH contributes not only to the reliability of the compressor 1 but also to further improvement of the coefficient of performance of the heat pump.

When the degree of superheat SH and unequal and the target degree of superheat SH _T is whether the degree of superheat SH is larger than the target degree of superheat SH _T is determined (step 11; S11). Then, the degree of superheat SH is the opening degree of the first expansion valve 6 is larger than the target degree of superheat SH _T is changed greatly (Step 12; S12), a first expansion if the degree of superheat SH is smaller than the target degree of superheat SH _T The opening degree of the valve 6 is changed to be small (step 13; S13).

If it goes through step 12, superheat degree SH will fall, and if it goes through step 13, superheat degree SH will rise. For the reasons described in steps 7 and 8, the degree of change in the opening degree in step 12 or 13 should be very slight. By way of step 12 or step 13, reliably superheat degree SH is so that closer to the target degree of superheat SH _T.

  After execution of step 12 or 13, it returns to step 4 and control of pressure PH is implemented again. As described above, in the control shown in FIG. 3, after the control of the superheat degree SH (second control) is completed, the control of the high-pressure side pressure PH (first control) is further performed.

  If only the high-pressure side pressure PH is to be controlled, as disclosed in Japanese Patent Application Laid-Open No. 2003-121018, it is sufficient to carry out control to adjust the opening of the other with one of the expansion valves fully opened or fully closed. In contrast, in the control shown in FIG. 3, after the first control for appropriately adjusting the opening degree of the second expansion valve 7 is completed, the opening degree of the second expansion valve 7 is left as it is (that is, changed). Without the adjustment), the opening degree of the first expansion valve 6 is adjusted in the second control.

  Although not shown in FIG. 3, also in the heat pumps 71 and 72, the second expansion valve 7 is set in a temperature range where the volume flow rate of the refrigerant to be flown into the expander 3 is smaller than the cylinder volume of the expander 3. You may implement control which adjusts the opening degree of the 1st expansion valve 6, hold | maintaining the state closed fully. This control can be performed between these steps when returning from step 2 to step 1.

In the control shown in FIG. 3, although the pressure PH is shifted to the control of the target pressure PH _T ends its control after checking the agreement between to superheat SH, the superheat degree SH is the target degree of superheat SH _T The control is terminated without confirming the coincidence and the control returns to the control of the pressure PH. This is a result of placing more emphasis on appropriate control of the high-pressure side pressure PH of the refrigeration cycle. However, the present invention is not limited to this, the degree of superheat SH also, may end its control after confirming the match between the target degree of superheat SH _T. A flowchart for performing this control is illustrated in FIG.

In the control example shown in FIG. 5, after step 12 or 13 is finished, the process returns to step 9 and the control is continued. In this case, the second control is also a loop control that is repeated until the degree of superheat SH matches the target value SH _T. If the loop control, whether the determination in step 10 coincides with the target value, but not carried out whether the difference between the degree of superheat SH and the target value SH _T is within a predetermined range SH _DR, by It may be more appropriate to do this. Other steps of the control shown in FIG. 5 are performed in the same manner as the control example of FIG.

  In addition to the changes illustrated in FIG. 5, various changes can be made to control the pressure PH and the superheat degree SH. The control of the present invention is not limited to the control examples shown in FIGS.

For example, in the above, consistent with the target pressure PH _T for the pressure PH, in other words, although whether or not the difference between the pressure PH and the target pressure PH _T is 0 and the determination target, instead of this, the pressure PH and it may be determined subject to the difference between the target pressure PH _T is within a predetermined range PH _DR. In this case, instead of step 5, the difference between the pressure PH and the target pressure PH _T may be judged whether it is within a predetermined range PH _DR. The difference is whether within a predetermined range PH _DR determination may not be performed by calculating the difference directly, for example, to calculate the ratio, the ratio is within a predetermined range PH _DR which is converted to the ratio This may be done by determining whether or not. The same applies to the control of the superheat degree SH.

The sizes of the predetermined ranges PH _DR and SH _DR may be set as appropriate depending on the use of the heat pump and the like, but are desirably limited to a very limited range. For example, the predetermined range PH _DR is expressed by a value obtained by subtracting the target pressure PH _T (MPa) from the pressure PH (MPa), and is −1.2 MPa or more and 1.2 MPa or less, and further −0.8 MPa or more. 0.8 MPa or less is suitable. The predetermined range SH _DR is expressed by a value obtained by subtracting the target superheat degree SH _T (° C.) from the superheat degree SH (° C.), and exceeds − (SH _T ) ° C. and 20 ° C. or less, and further − (SH _T ) ° C. exceeding 10 ° C. or less, and it is preferable range determined to be, so that the value does not become negative, for example, a predetermined range SH _DR may be defined as a value exceeding 0 ° C.. “− (SH _T ) ° C. over 20 ° C.” is a range of “−10 ° C. over 20 ° C.” when the target superheat degree SH _T is 10 ° C.

  Further, for example, after step 8, a step of determining whether or not the second expansion valve 7 is fully closed is added, and if it is determined in this additional step that the second expansion valve 7 is fully closed. It is good also as returning to step 1. If it is determined in the additional step that the second expansion valve 7 is not fully closed, the control returns to step 4 and is repeated.

  In addition, for example, step 9 may be performed after step 3 in order to control the superheat degree SH prior to the control of the pressure PH. In this case, the superheat degree SH is controlled, the pressure PH is continuously controlled, and then the superheat degree SH is controlled again. Depending on the use and design content of the heat pump, control may be started from step 4 or 9 without performing steps 1 to 3.

As described above, the controller (control device) 30, when the difference between the predetermined value PH _T to high side pressure PH and the target refrigerant is not within the predetermined range PH _DR, the pressure PH and a predetermined value PH _T Pressure control (first control) is performed to change the opening of the second expansion valve (second expansion device) 7 so that the absolute value of the difference between the two becomes smaller (so that the pressure PH approaches the predetermined value PH _T ). (S4 to S8).

Then, after finishing the first control, when the difference between the predetermined value SH _T is a positive predetermined value and the degree of superheat SH of the refrigerant entering the compressor is not within the predetermined range SH _DR is overheated The opening degree of the first expansion valve (first expansion device) 6 is changed so that the absolute value of the difference between the degree SH and the predetermined value SH _T becomes smaller (so that the superheat degree SH approaches the predetermined value SH _T ). Superheat degree control (second control) is performed (S9 to S13).

In the first control, the control device, so that the difference between the pressure PH and the predetermined value PH _T falls within a predetermined range PH _DR, it is preferable to change the degree of opening of the second throttle device. In the second control, the control device, so that the difference between the degree of superheat SH and a predetermined value SH _T falls within a predetermined range SH _DR, may change the opening degree of the first throttle device.

As in the above control example, the control device, after finishing the second control, when the difference between the pressure PH and the predetermined value PH _T is not within the predetermined range PH _DR is to further implement the first control Also good. This is because the pressure PH is re-controlled in consideration of the change in the pressure PH due to the second control.

As exemplified above, a specific control, in a first control pressure PH is higher than the predetermined value PH _T, and when the difference between the pressure PH and the predetermined value PH _T is not within the predetermined range PH _DR the degree of opening of the second throttle device is large and the pressure PH is lower than the predetermined value PH _T, and the difference between the pressure PH and the predetermined value PH _T not within a predetermined range PH _DR is second The opening degree of the expansion device is reduced.

In the second control, superheat degree SH is higher than the predetermined value SH _T, and when the difference between the degree of superheat SH and a predetermined value SH _T is not within the predetermined range SH _DR, open the first throttle device degree is large and the degree of superheat SH is lower than the predetermined value SH _T, and the difference between the degree of superheat SH and a predetermined value SH _T is not within the predetermined range SH _DR is, the opening degree of the first throttle device is small Is done.

  In the control illustrated in FIGS. 3 and 5, the values of the pressure PH and the superheat degree SH are specifically specified, and the expansion valve is adjusted based on the values, thereby controlling the pressure PH and the superheat degree SH. However, the control of the pressure PH and the superheat degree SH can be performed indirectly using alternative parameters associated with the pressure PH or the superheat degree SH.

For example, the control of the high-pressure side pressure PH of the refrigeration cycle is performed by measuring the ratio RV of the volume flow rate of the refrigerant flowing into the compressor 1 with respect to the volume flow rate of the refrigerant flowing into the expander 3. It is also possible to carry out based on the ratio RC of the volume of the compressor 1 to the volume of. Magnitude relationship between the ratio RV and specific RC is an alternative parameter RP associated with high side pressure PH, it is also possible to set the control target RP _T associated for this parameter to the target pressure PH _T.

Thus, in the above control, the control device, without comparing the pressure PH and the predetermined value PH _T directly, a predetermined characteristic RP associated with the pressure PH, is associated with a predetermined value PH _T, the characteristic RP by comparison, the predetermined value RP _T for, whether the difference between the pressure PH and the predetermined value PH _T is within a predetermined range PH _DR, determines, it is also possible.

FIG. 6 shows changes in the refrigeration cycle by the above control. Initially the refrigeration cycle (a ₁ ~f _1), when the opening degree of the second expansion valve 7 to reduce the high pressure side pressure is changed greater than the target pressure PH _T in the first control, the refrigeration cycle (a ₂ ~f ₂₎ to shift to. This refrigeration cycle shifts to the refrigeration cycle (a _{3 to} f ₃ ) when the opening of the first expansion valve 6 is changed to be small in order to ensure a relatively large degree of superheat in the second control. This refrigeration cycle shifts to the refrigeration cycle (a _{4 to} f ₄ ) when the opening degree of the second expansion valve 7 is greatly changed in order to reduce the high-pressure side pressure in the first control performed again.

  As shown in FIG. 6, when the high-pressure side pressure of the refrigeration cycle is in a supercritical state, the high-low pressure difference in the refrigeration cycle increases, and the contribution of the energy recovery function of the expander 3 increases. In order to realize this, the compressor may be a heat pump that compresses the refrigerant so that the refrigerant discharged from the compressor is in a supercritical state.

  The configuration of the heat pump to which the present invention can be applied is not limited to the examples shown in FIGS. For example, in FIGS. 1 and 2, the tubular body 12 forms a bypass path that bypasses the expander 3 and the first expansion valve 6, but the tubular body 11 forms a bypass path that bypasses only the expander 3. It is good also as the heat pump 73 connected to (refer FIG. 7). Alternatively, the first expansion valve 6 may be a heat pump 74 disposed not on the upstream side of the expander 3 but on the downstream side (see FIG. 8). Furthermore, the pipe body 12 may form a bypass path that bypasses only the expander 3, and the first expansion valve 6 may be a heat pump 75 arranged on the downstream side of the expander 3 (see FIG. 9). Also in these configurations, the high-pressure side pressure PH and the superheat degree SH can be appropriately controlled by applying the same control as described above.

  A plurality of controllers may share the functions of the controller 30. In the heat pump 76 illustrated in FIG. 10, the first controller 31 has a function of adjusting the opening degree of the first expansion valve 6 and the second expansion valve 7 in order to control the pressure PH and the superheat degree SH (S4 to S8, S10 to S13), the second controller 32 receives the signals from the temperature sensors 23 and 24 and calculates the superheat degree SH (S9), and the third controller 33 measures the outside air temperature T, and according to the result. And controls the opening of the second expansion valve 7 (S1 to S3).

  Moreover, it is good also as a heat pump which has arrange | positioned the four-way valves 51 and 53. FIG. The heat pump 77 illustrated in FIG. 11 can be used as an air conditioner that can select a heating operation and a cooling operation by switching the four-way valves 51 and 53. During the heating operation, the path indicated by the solid line is selected in the four-way valves 51 and 53, and the indoor heat exchanger 52 functions as a radiator and the outdoor heat exchanger 54 functions as an evaporator. During the cooling operation, the paths indicated by broken lines are selected in the four-way valves 51 and 53, the outdoor heat exchanger 54 functions as a radiator, and the indoor heat exchanger 52 functions as an evaporator. Also in this heat pump 77, if the control as exemplified above is applied, the high pressure side pressure PH and the superheat degree SH can be appropriately controlled.

  In the control exemplified 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. This may be used to deal with an abnormality in the heat pump. Specifically, in the case of a heat pump having the above-described configuration, the response to an abnormality is performed when the pressure PH exceeds a predetermined limit pressure and / or the temperature of the refrigerant discharged from the compressor 1 reaches a predetermined limit temperature. If it exceeds, the controller 30 recognizes that it is abnormal, and can be implemented by adjusting the opening of the first expansion valve 6 and / or the second expansion valve 7 to be larger than a predetermined opening. Here, the predetermined opening degree may be set to an opening degree that exceeds a control range determined by the first control and the second control. With this measure, the pressure and temperature of the refrigerant can be quickly reduced.

  By controlling in this way, even when the high pressure side pressure PH or temperature of the refrigerant reaches an abnormal value due to a sudden change in the operating state or some factor, the abnormal value can be eliminated in a short time. The limit pressure and limit temperature vary depending on the refrigerant and the configuration of the heat pump. However, when carbon dioxide is used as the refrigerant, the limit pressure can be exemplified as 12 MPa and the limit temperature as 115 ° C.

  In order to cope with the above-described abnormality, the heat pump of the present invention provides a control device when the pressure PH exceeds a predetermined limit pressure or when the temperature of the refrigerant discharged from the compressor exceeds a predetermined limit temperature. However, it is preferable that at least one of the openings selected from the first throttle device and the second throttle device is largely changed beyond the opening change range in the first control and the second control.

12 and 13, when carbon dioxide is used as the refrigerant and the pressure on the high pressure side of the refrigeration cycle is set to exceed the critical pressure of carbon dioxide (FIG. 12), and when chlorofluorocarbon is used as the refrigerant (FIG. 13). ) Shows the temperature change between the refrigerant in the evaporator and the air (heated medium). In either case, the refrigerant flows into the radiator at the temperature T ₀ and heats the air by heat exchange with the air. The temperature difference ΔT when carbon dioxide is used as the refrigerant is larger than the temperature difference ΔT when fluorocarbon is used as the refrigerant. This is because, unlike Freon, carbon dioxide does not change phase in the radiator. Carbon dioxide is suitable as a refrigerant for heating the heated medium to a high temperature.

  INDUSTRIAL APPLICABILITY The present invention has a high utility value as an improvement of a heat pump useful as an air conditioner, a water heater, a tableware dryer, a garbage drying processor, and the like.

It is a figure which shows an example of a structure of the heat pump of this invention. It is a figure which shows another example of a structure of the heat pump of this invention. It is a flowchart which shows an example of the control which a control apparatus implements. It is a figure which shows the relationship between the outside temperature T and the discharge refrigerant | coolant pressure Pd of a compressor for every discharge refrigerant | coolant temperature Td of a compressor. It is a flowchart which shows another example of the control which a control apparatus implements. It is a Mollier diagram which illustrates the change of the refrigerating cycle accompanying control performed by a control device. It is a figure which shows another example of a structure of the heat pump of this invention. It is a figure which shows another example of a structure of the heat pump of this invention. It is a figure which shows another example of a structure of the heat pump of this invention. It is a figure which shows another example of a structure of the heat pump of this invention. It is a figure which shows the example of a structure of the heat pump of this invention provided with the four-way valve. It is a figure which shows the relationship between the position of the refrigerant | coolant in a heat radiator, and the temperature of a refrigerant | coolant at the time of using CFC as a refrigerant | coolant. It is a figure which shows the relationship between the position of the refrigerant | coolant in a heat radiator, and the temperature of a refrigerant | coolant at the time of using a carbon dioxide as a refrigerant | coolant. It is a figure which shows the structure of the conventional heat pump. It is a Mollier diagram which shows the change of the refrigerating cycle accompanying the control implemented in the conventional heat pump.

Claims (13)

A compressor, a radiator, an expander, an evaporator,
The refrigerant flows from the radiator to the evaporator without passing through the compressor, the radiator, the expander, and the circulation path through which the refrigerant circulates in this order, and without passing through the expander. A tube forming a bypass path;
A first expansion device that is arranged in the circulation path between the radiator and the expander or between the expander and the evaporator;
A second expansion device arranged in the bypass path and having a variable opening;
A controller for adjusting the opening of the first throttle device and the opening of the second throttle device;
The compressor and the expander are directly connected to rotate at the same rotational speed ,
The control device is
Wherein the high-pressure side pressure PH of the refrigerant circulating through the circulation path, when the difference between the predetermined value PH _T coefficient of performance of the heat pump is determined based on the values for the optimization is not within a predetermined range PH _DR, the pressure PH the absolute value of the difference between the predetermined value PH _T changes the opening degree of the second throttle device so as to reduce, and performing a first control and,
After finishing the first control,
And the degree of superheat SH of the refrigerant flowing into the compressor, when the difference between the predetermined value SH _T is a positive predetermined value is not within a predetermined range SH _DR, the said degree of superheat SH predetermined value SH Changing the opening of the first throttling device so that the absolute value of the difference from _T is small, and performing a second control;
heat pump. The control device is
Wherein the first control, as the difference between the predetermined value PH _T and the pressure PH is within the predetermined range PH _DR, changing the opening of the second throttle device, a heat pump according to claim 1. The control device is
In the second control, as the difference between the degree of superheat SH and the predetermined value SH _T is within the predetermined range SH _DR, changing the opening of the first throttle device, a heat pump according to claim 1 . The control device is
After finishing the second control,
If the difference between the predetermined value PH _T and the pressure PH is not within a predetermined range PH _DR is
The heat pump according to claim 1, further performing the first control. In the first control,
It said pressure PH is higher than the predetermined value PH _T, and if the difference between the pressure PH and the predetermined value PH _T is not within said predetermined range PH _DR is the opening of the second throttle device are greatly ,
Wherein when the pressure PH is lower than the predetermined value PH _T, and the difference between the pressure PH and the predetermined value PH _T is not within said predetermined range PH _DR is the opening of the second throttle device is small The
The heat pump according to claim 1. In the second control,
The degree of superheat SH is higher than the predetermined value SH _T, and if the difference between the degree of superheat SH and the predetermined value SH _T is not within said predetermined range SH _DR is the opening of the first throttle device Enlarged,
The degree of superheat SH is lower than the predetermined value SH _T, and if the difference between the degree of superheat SH and the predetermined value SH _T is not within said predetermined range SH _DR is the opening of the first throttle device Made smaller,
The heat pump according to claim 1. Wherein the predetermined value SH _T and values in the range of 20 ° C. or less exceed 0 ° C., a heat pump according to claim 1.   The first temperature detection means for detecting the temperature of the refrigerant flowing into the compressor and the second temperature detection means for detecting the temperature of the refrigerant in the evaporator in order to specify the degree of superheat SH. The heat pump described in 1.   The heat pump according to claim 1, further comprising pressure detection means for detecting a pressure of refrigerant discharged from the compressor in order to specify the pressure PH.   The apparatus further comprises third temperature detecting means for detecting a temperature outside the system and fourth temperature detecting means for detecting the temperature of the refrigerant discharged from the compressor in order to specify the pressure PH. The heat pump described in 1. The control device is
Without comparing the predetermined value PH _T and the pressure PH directly,
By comparing the predetermined characteristic RP associated with the pressure PH with the predetermined value RP _T for the characteristic RP associated with the predetermined value PH _T ,
Wherein whether or not the difference between the pressure PH and the predetermined value PH _T is within said predetermined range PH _DR, determining the heat pump according to claim 1. When the pressure PH exceeds a predetermined limit pressure, or when the temperature of the refrigerant discharged from the compressor exceeds a predetermined limit temperature,
The control device largely changes at least one opening selected from the first throttle device and the second throttle device beyond a change range of the opening in the first control and the second control. The heat pump according to 1.   The heat pump according to claim 1, wherein the compressor compresses the refrigerant so that the refrigerant discharged from the compressor is in a supercritical state.

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