JP2010091135A - Two-stage compression type hot water supply device and method of controlling its start - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately control the opening degree of a supercooling valve to prevent liquid droplets from entering a high stage compressor and to prevent an excessive temperature rise of the high stage compressor. A hot water supply apparatus is provided.
An evaporator, a low-stage compressor that compresses a low-pressure refrigerant to an intermediate pressure, a high-stage compressor that compresses an intermediate-pressure refrigerant to a high pressure, a radiator, and a supercooler. The main expansion valve 112 that expands the high-pressure refrigerant to a low pressure, the supercooling valve 114 that expands the high-pressure refrigerant to an intermediate pressure, the main circuit 132 that reaches the main expansion valve, and the economizer circuit 134. And an expansion valve control unit 116. The expansion valve control unit 116 has a supercooling valve 114 so that the degree of superheat at the inlet of the high-stage compressor 106 or the outlet of the cooling channel 108b of the supercooler 108 becomes positive. To control the opening degree.
[Selection] Figure 1

Description

  The present invention relates to a two-stage compression hot water supply apparatus that supplies hot water using a two-stage compression heat pump and a start-up control method thereof.

  In recent years, heat pump hot water supply devices have been widely used from the viewpoint of effective use of energy and reduction of the emission amount of carbon dioxide, which is a greenhouse gas. By introducing a heat pump type hot water supply apparatus, it is possible to save about 30% of energy and reduce carbon dioxide emissions by about 50% as compared with a conventional combustion type hot water supply apparatus.

  Unlike a fuel type, the efficiency of a heat pump is significantly reduced when high heat is generated. Thus, how to increase the efficiency of the refrigerant cycle has been an old problem. Among them, a multi-stage cycle in which a plurality of compressors are provided in series and an intermediate pressure refrigerant is returned to a refrigerant being compressed is widely used. Multistage compression is advantageous for compressing to a desired temperature range with a relatively low pressure refrigerant. Multistage expansion is effective to recover the compressed heat and increase efficiency.

  The multistage cycle is described in Patent Document 1, for example. FIG. 12 is a diagram for explaining a conventional two-stage compression / one-stage expansion cycle. In the cycle shown in FIG. 12A, the refrigerant is divided on the downstream side of the radiator 803, and the second refrigerant flow passes through the subcooler 805 (referred to as an intermediate heat exchanger) and the main expansion valve 806. The first refrigerant flow is expanded by a supercooling valve 804 (referred to as an auxiliary expansion valve) and flows to the supercooler 805 for heat exchange, and then the low-stage compressor 801 is flowed to the evaporator 807. And the compressor 802 on the higher stage side. According to Patent Document 1, the specific enthalpy at the evaporator inlet can be reduced by cooling the second refrigerant flow with the first refrigerant flow, and the refrigeration effect can be increased. Further, since the amount of refrigerant (second refrigerant flow) compressed by the low-stage compressor is reduced, the compression power is reduced and the coefficient of performance is improved.

  In the two-stage compression cycle shown in FIG. 12 (a), it is necessary to adjust the subcooling valve 804 to control the intermediate pressure and to set the amount of refrigerant at the intermediate pressure after being reduced by the subcooling valve to the optimum flow rate. is there. In Patent Document 1, for example, the outlet temperature of the first refrigerant flow and the inlet temperature of the second refrigerant flow of the subcooler are within 5K, or the outlet temperature of the second refrigerant flow and the inlet of the first refrigerant flow. By setting the temperature within 5K, the temperature of the first or second refrigerant flow can be appropriately controlled.

  FIG. 12B is similar to the two-stage compression and one-stage expansion cycle, but the expansion side is an economizer circuit. In the economizer circuit, a flow is divided on the downstream side of the supercooler 805, and after expansion and cooling by the supercooling valve 804, heat exchange is performed by the supercooler. Since it is cooled by the subcooler 805 before expanding, further improvement in efficiency can be achieved.

By the way, natural refrigerants have been actively introduced into the heat pump refrigerants recently. A natural refrigerant is a natural product that is harmless to the environment, and carbon dioxide is most frequently used as such a natural refrigerant. As a result, it is possible to further reduce the environmental load. However, since carbon dioxide has a low critical point of about 31 ° C., when used as a refrigerant, a supercritical region where the boundary between gas and liquid disappears is used. For example, Patent Document 2 discloses a heat pump hot water supply apparatus that uses carbon dioxide (CO ₂ ), ethylene, ethane, nitrogen oxide, or the like as a refrigerant in a supercritical state.
JP 2006-242557 A JP 2001-263801 A

  However, in the technique described in Patent Document 1, since the temperature difference between one outlet temperature of the supercooler 805 and the other inlet temperature is controlled to be within a predetermined range, Both the temperatures may drop, and the wet refrigerant may be mixed into the high-stage compressor 802. If droplets are mixed in the compressor, the performance may be degraded, or the compressor may be damaged in some cases.

  On the other hand, the temperature of the refrigerant flowing from the supercooler 805 to the higher stage compressor 802 may rise together, and the degree of superheat in the higher stage compressor 802 may become too large. When the temperature of the compressor rises excessively, the compressor may be seized.

  When supercooling with an intermediate pressure refrigerant is used, the high-pressure refrigerant has a large heat dissipation amount in the supercooler and a small heat dissipation amount with respect to water in the radiator. Therefore, in a steady state, the water flow rate is small as compared with the high-stage refrigerant circulation amount. When the compressor is started with a small water flow rate, the response of the supercooling valve cannot catch up with the change in the refrigerant state, and the high-pressure refrigerant has a large amount of heat released to water and the high pressure tends to be too high. As the high pressure increases, the intermediate pressure (pressure between the low-stage compressor and the high-stage compressor) increases, and the possibility that the intermediate pressure approaches the critical pressure increases.

  When the intermediate pressure approaches the critical pressure, the wet area between the saturated vapor line and the saturated liquid line becomes narrow and the enthalpy that can absorb heat decreases, so the cooling capacity of the intermediate pressure refrigerant changes sensitively to changes in the intermediate pressure. To do. In order to adjust the supercooling capacity, it is necessary to increase the amount of change in the refrigerant flow rate, and thus it is necessary to adjust the supercooling valve opening rapidly.

  However, when the supercooling valve opening is rapidly adjusted, the refrigerant temperature (refrigerant flow rate) at the main expansion valve inlet also changes suddenly. In particular, when the refrigerant flow rate suddenly increases, the amount of refrigerant evaporation inside the evaporator is insufficient and the liquid phase remains. Then, there is a possibility that the compressor is damaged due to the inflow of droplets to the compressor suction port. Thus, when using supercooling with an intermediate pressure refrigerant, refrigerant control becomes unstable when the compressor is started, and the compressor may be damaged.

  When the refrigerant flow rate at the main expansion valve inlet changes suddenly, the opening of the main expansion valve also needs to be changed. Then, the low pressure of the refrigerant also fluctuates, and the intermediate pressure fluctuates accordingly. As a result, the outlet temperature of the subcooler changes, and it is necessary to adjust the opening degree of the supercooling valve in order to absorb this fluctuation. Need to adjust. Then, the refrigerant temperature at the main expansion valve inlet changes suddenly. Thus, there is a problem that the dependency relationship circulates, the fluctuation of the refrigerant pressure is not settled, and it is difficult to shift to the steady state.

  In view of such problems, the present invention appropriately controls the opening degree of the supercooling valve to prevent liquid droplets from being mixed into the high stage compressor and to prevent excessive temperature rise of the high stage compressor. An object of the present invention is to provide a two-stage compression hot water supply device that can be used.

  A typical configuration of a two-stage compression hot water supply apparatus according to the present invention includes an evaporator, a low-stage compressor that compresses a low-pressure refrigerant to an intermediate pressure, and a high-stage compressor that compresses an intermediate-pressure refrigerant to a high pressure. A radiator, a subcooler, a shunt, a main expansion valve that expands the high-pressure refrigerant to a low pressure, a supercooling valve that expands the high-pressure refrigerant to an intermediate pressure, and a cooled channel of the subcooler. An economizer circuit that joins between the low-stage compressor and the high-stage compressor through the main circuit from the shunt to the main expansion valve, and from the shunt through the subcooling valve and the cooling channel of the subcooler And an expansion valve control unit that controls the opening degree of the supercooling valve, the expansion valve control unit so that the degree of superheat at the inlet of the high-stage compressor or the outlet of the cooling channel of the supercooler becomes positive. The opening degree of the supercooling valve is controlled.

  Other representative configurations of the two-stage compression hot water supply apparatus according to the present invention include an evaporator, a low-stage compressor that compresses a low-pressure refrigerant to an intermediate pressure, and a high-stage compression that compresses an intermediate-pressure refrigerant to a high pressure. Machine, radiator, subcooler, shunt, main expansion valve that expands high-pressure refrigerant to low pressure, supercooling valve that expands high-pressure refrigerant to intermediate pressure, and subcooler flow The main circuit from the shunt to the main expansion valve through the channel and the shunt flows through the subcooling valve and the cooling passage of the subcooler and joins between the low stage compressor and the high stage compressor An economizer circuit and an expansion valve control unit that controls the opening degree of the supercooling valve are provided. The expansion valve control unit is a refrigerant having an intermediate pressure at the inlet of the high-stage compressor or the outlet of the cooling channel of the supercooler. The opening degree of the supercooling valve is controlled so as to be higher than the saturation temperature by a predetermined temperature or more.

  Other representative configurations of the two-stage compression hot water supply apparatus according to the present invention include an evaporator, a low-stage compressor that compresses a low-pressure refrigerant to an intermediate pressure, and a high-stage compression that compresses an intermediate-pressure refrigerant to a high pressure. Machine, radiator, subcooler, shunt, main expansion valve that expands high-pressure refrigerant to low pressure, supercooling valve that expands high-pressure refrigerant to intermediate pressure, and subcooler flow The main circuit from the shunt to the main expansion valve through the channel and the shunt flows through the subcooling valve and the cooling passage of the subcooler and joins between the low stage compressor and the high stage compressor An economizer circuit and an expansion valve control unit that controls the degree of opening of the supercooling valve. The expansion valve control unit has a temperature at the outlet of the cooled channel of the subcooler that is a predetermined temperature from the saturation temperature of the intermediate-pressure refrigerant. The opening degree of the supercooling valve is controlled to be within the range.

  According to any of the above configurations, it is possible to reliably prevent the wet refrigerant from entering the high stage compressor, and it is possible to prevent the performance of the high stage compressor from being deteriorated and the high stage compressor from being damaged.

  The saturation temperature of the intermediate pressure refrigerant may be obtained by detecting the temperature of the outlet of the supercooling valve. Thereby, it is not necessary to store the saturation temperature of the refrigerant in advance, and the saturation temperature of the intermediate pressure of the refrigerant that actually flows in the apparatus can be acquired.

  The refrigerant is carbon dioxide, and in the radiator, the refrigerant may radiate heat in a supercritical state. Carbon dioxide, which is a natural refrigerant, is a natural product and is harmless to the environment. Therefore, according to the said structure, it can be set as the heat pump which does not put a burden on an environment. In addition, since carbon dioxide has a low critical point of about 31 ° C., when used as a refrigerant, a supercritical region in which the boundary between gas and liquid is eliminated can be used. Thus, since no phase change (gas-liquid change) is performed within the operating temperature range, a wide and wide temperature range and a large heat transfer can be set.

  A second radiator disposed on the refrigerant circuit between the low-stage compressor and the high-stage compressor and upstream of the merged position of the refrigerant circuit and the economizer circuit; and disposed downstream of the radiator. You may provide a 3rd heat radiator. Thereby, the temperature change of the water with respect to the change of enthalpy can be made to follow the temperature change of the refrigerant, and the pressure of the refrigerant can be reduced. Therefore, the power of the compressor can be reduced and the COP can be reduced.

  In addition to the second and third radiators, a fourth radiator disposed on the refrigerant circuit between the supercooler and the main expansion valve may be further provided. This makes it possible to obtain a larger amount of heat from the air even though the work of the compressor is the same, and to further improve the COP of the heat pump cycle.

  A typical configuration of the start-up control method for a two-stage compression hot water supply apparatus according to the present invention is to increase the flow rate of water in a state where the supercooling valve is closed in the two-stage compression hot water supply apparatus having the above-described configuration. Start the low-stage compressor and the high-stage compressor until the refrigerant state is stable after a certain period of time and the refrigerant outlet temperature of the radiator falls within a predetermined range with the water inlet temperature of the radiator. Waiting and gradually opening the supercooling valve until the outlet pressure of the high stage compressor reaches a steady state high pressure, and reducing the flow rate of water until the outlet temperature of the radiator reaches a steady state temperature. To do.

  That is, at the time of starting the compressor, the supercooling valve is not opened until the temperature is within a predetermined range with respect to the water inlet temperature of the radiator. In other words, the supercooling valve is not opened until the intermediate pressure is less than a certain value (a pressure lower than the critical pressure by a predetermined amount or more). Then, after the refrigerant state becomes effective in cooling by the supercooler, gradually increasing the high pressure while gradually opening the supercooling valve and gradually decreasing the flow rate of water to raise the radiator outlet temperature , Transition to steady state. According to the start control method described above, the inlet temperature of the supercooling valve can be lowered when the compressor is started, and the refrigerant state and the water amount can be brought to a steady state at an early stage.

  When the outlet pressure of the high stage compressor is higher than the steady state pressure by a certain value or more, the increase in the supercooling valve opening or the decrease in the water flow rate may be prohibited to prevent an increase in the high pressure. . Similarly, when the intermediate pressure is higher than the steady-state pressure by a certain value or more (closer to the critical pressure), prohibit the increase of the subcooling valve opening or the decrease of the water flow rate. May be prevented from rising.

  Another representative configuration of the start-up control method for a two-stage compression hot water supply apparatus according to the present invention is that a low-stage compressor and a high-stage compressor are installed in a two-stage compression hot water supply apparatus with the supercooling valve closed. Start up at a lower rotational speed than the steady state, wait until the refrigerant state is stable after a certain period of time, and the outlet temperature of the radiator is within a predetermined range with the water inlet temperature of the radiator. Increase the rotation speed of the low and high stage compressors until the outlet temperature of the radiator reaches the steady state temperature while gradually opening the subcooling valve until the outlet pressure of the machine reaches the steady state high pressure. It is characterized by.

  Also with the above startup control method, the inlet temperature of the supercooling valve can be lowered when the compressor is started, and the refrigerant state and the water amount can be brought to a steady state at an early stage.

  According to the present invention, it is possible to appropriately control the opening degree of the supercooling valve to prevent liquid droplets from being mixed into the high stage compressor and to prevent the refrigerant control from becoming unstable when the compressor is started. A two-stage compression hot water supply apparatus can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  In the present embodiment, the configuration of the two-stage compression hot water supply device is first described, and then the operation of the expansion valve control unit and the activation control method are described.

[Configuration of two-stage compression hot water supply system]
FIG. 1 is a diagram illustrating a two-stage compression hot water supply apparatus according to the present embodiment. The two-stage compression hot water supply apparatus (hereinafter simply referred to as “hot water supply apparatus 100”) shown in the figure includes an evaporator 102, a low-stage compressor 104 that compresses a low-pressure refrigerant to an intermediate pressure, and an intermediate-pressure refrigerant to a high pressure. High-stage compressor 106 to be compressed, radiator 120, supercooler 108, flow divider 110, main expansion valve 112 that expands the high-pressure refrigerant to low pressure, and supercooling that expands the high-pressure refrigerant to intermediate pressure And a valve 114. A circuit from the flow divider 110 to the main expansion valve 112 through the cooled channel 108a of the subcooler 108 is referred to as a main circuit 132, and the subcooler 114 to the supercooling valve 114 and the cooling channel 108b of the subcooler 108 are referred to as the main circuit 132. A circuit that joins between the low-stage compressor 104 and the high-stage compressor 106 through the circuit is called an economizer circuit 134. The hot water supply device 100 includes an expansion valve control unit 116 that controls the opening degree of the supercooling valve 114. The hot water supply apparatus 100 is provided with a control unit 101 that controls the operation of each part of the whole.

  The radiator 120 exchanges heat with water and accumulates the heated hot water in the hot water storage tank 118. If necessary, hot water is taken out from the hot water storage tank 118 and used. Further, since a temperature gradient occurs in the hot water storage tank 118 and low temperature water is biased at the lower end, a discharge port may be provided at the lower end and circulated through the radiator 120.

  The low stage compressor 104 and the high stage compressor 106 are connected in series to the refrigerant, and compress the refrigerant in two stages. In this embodiment, as an example, a low-pressure refrigerant of 3 MPa is pressurized to an intermediate pressure of 5 MPa by the low-stage compressor 104 and further compressed to a high pressure of 8 MPa by the high-stage compressor 106.

  The flow divider 110 does not perform any special flow rate adjustment, and the amount of refrigerant flowing to the economizer circuit 134 is adjusted by the opening degree of the supercooling valve 114. The intermediate pressure also changes depending on the opening degree of the supercooling valve 114, and the degree of cooling in the supercooler 108 is also controlled.

  2A and 2B are diagrams for explaining a two-stage compression economizer cycle. FIG. 2A is a PH diagram, and FIG. 2B is a TH diagram. When the radiator 120 is cooled with water (ab), it is further subcooled by the subcooler 108 (bc). Then, the refrigerant that is divided and flows to the economizer circuit 134 is reduced in pressure and temperature in the supercooling valve 114 (c−j) and warmed in the supercooler 108 (j−k), and then the low stage compressor 104 and It merges between the high stage compressors 106 (kg). The refrigerant flowing in the main circuit 132 is expanded by the main expansion valve 112 (cd), heated by exchanging heat with air in the evaporator 102 (de), and then compressed by the low-stage compressor 104 ( e−f), merged with the intermediate pressure refrigerant (f−g), and compressed by the high stage compressor 106 (ga).

  When the economizer circuit 134 as described above is not provided, there is a problem that the compressor discharge pressure needs to be increased when the feed water temperature rises, so that the power consumption increases and the COP (operation coefficient) deteriorates. However, by cooling the high-pressure refrigerant by supercooling, a high discharge pressure is not necessary, and power consumption can be reduced. In addition, since a part of the refrigerant does not expand to a low pressure and is compressed from the intermediate pressure, the compression power can be reduced and power consumption can be reduced.

  Thus, even if the feed water temperature is high, heating can be performed without lowering the COP. Therefore, even when the medium-temperature water (about 15 to 40 ° C.) is reheated from the hot water storage tank 118, the COP does not decrease and can be suitably applied to a hot water storage type hot water supply apparatus. Moreover, even if hot water is supplied from a solar water heater or the like, power consumption can be reduced without lowering the COP. Therefore, an environment-friendly hot water supply apparatus using natural energy can be provided. Furthermore, the hot water in the hot water storage tank 118 may be heated by solar heat or the remaining hot water in the bath, or the intermediate pressure refrigerant may be heated by the remaining hot water in the bath.

  Note that the economizer circuit 134 does not always need to be operated, and the supercooling valve 114 may be opened when the outlet temperature of the radiator 120 becomes higher than the saturation temperature of the intermediate-pressure refrigerant to some extent.

[Opening control of supercooling valve]
As described above, the flow rate of the intermediate pressure refrigerant is controlled by the opening degree of the supercooling valve 114, whereby the intermediate pressure also fluctuates and the refrigerant state also changes. Note that the range in which the intermediate pressure fluctuates depending on the opening degree of the supercooling valve 114 is from the pressure by only the low stage compressor 104 to the pressure by the low stage compressor 104 and the high stage compressor 106. Therefore, in order to operate in a stable steady state, it is necessary to control the opening degree of the supercooling valve 114. It should be particularly noted that liquid droplets (wet refrigerant) are mixed in the high stage compressor 106 (when the inlet (g) of the high stage compressor 106 is in a wet region). This is because when the droplets are mixed into the compressor, the performance may be deteriorated or the compressor may be damaged in some cases. In addition, a damp refrigerant may be sufficient at the exit (k) of the cooling channel 108b of the subcooler 108, and it may be dry at the entrance (g) of the high stage compressor 106.

  The opening degree of the supercooling valve 114 is controlled by the expansion valve control unit 116. The expansion valve control unit 116 includes a sensor S1 that measures the temperature of the outlet (j) of the supercooling valve 114, a sensor S2 that measures the temperature of the inlet (g) of the high stage compressor 106, and the cooling flow of the supercooler 108. A sensor S3 that measures the temperature of the outlet (k) of the passage 108b and a sensor S4 that measures the temperature of the outlet (c) of the channel to be cooled 108a of the subcooler 108 are connected. In the present embodiment, one of the following controls is performed in order not to mix droplets in the high stage compressor 106.

(Control 1)
The expansion valve control unit 116 controls the degree of opening of the supercooling valve 114 so that the degree of superheat at the inlet (g) of the high stage compressor 106 or the outlet (k) of the cooling channel 108b of the supercooler 108 becomes positive. Control. Since the degree of superheat is positive means that the refrigerant is dry (in the gas phase), if the degree of superheat is positive in (g) or (k), the high-stage compressor 106 has droplets. Does not mix. 2B, the temperature at the inlet (g) of the high stage compressor 106 is always higher than the temperature at the outlet (k) of the cooling channel 108b of the supercooler 108.

  Specifically, the temperature of the refrigerant is measured using the sensor S2 or the sensor S3. The degree of superheat of these temperatures can be known from the type of refrigerant, the pressure of the economizer circuit 134, and the temperature of the refrigerant (g) or (k). When the expansion valve control unit 116 is opened, the intermediate pressure and temperature of the refrigerant are lowered, and when the expansion valve control unit 116 is throttled, the intermediate pressure and temperature are raised. Under the condition that the degree of superheat is positive, the expansion valve controller 116 may be narrowed down more. However, in actuality, the opening degree of the expansion valve controller 116 is controlled so that the degree of superheat becomes a predetermined temperature (for example, about 10K). It is preferable to do.

(Control 2)
The expansion valve control unit 116 controls the temperature of the inlet (g) of the high-stage compressor 106 or the outlet (k) of the cooling flow path 108b of the supercooler 108 to be higher than the saturation temperature of the intermediate-pressure refrigerant by a predetermined temperature or more. The opening degree of the supercooling valve 114 is controlled. The saturation temperature of the intermediate pressure refrigerant can be obtained if the intermediate pressure is determined. Further, the saturation temperature of the intermediate pressure refrigerant may be obtained by detecting the temperature of the outlet (j) of the supercooling valve 114. The refrigerant expanded in the supercooling valve 114 is in a wet region as shown in FIG. 2B, and the temperature of (j) is always the saturation temperature. If the temperature of (g) or the temperature of (k) is higher than the saturation temperature, that is, it is in the heating region (gas phase), it can be confirmed that it is dry.

  Specifically, the expansion valve control unit 116 detects the temperature of the sensors S1 to S3, determines whether or not the temperature of the sensor S2 or S3 is higher than the temperature of the sensor S1, and if lower, throttles the supercooling valve 114. If so, the supercooling valve 114 is controlled to open. At this time, the temperature of (g) or (k) may be controlled so as to be higher than the saturation temperature of the intermediate-pressure refrigerant by a predetermined temperature or more. In practice, the temperature difference is a predetermined temperature (for example, about 10K). It is preferable to control the opening degree of the expansion valve control unit 116 so as to be.

(Control 3)
The expansion valve control unit 116 controls the opening degree of the supercooling valve 114 so that the temperature of the outlet (c) of the channel to be cooled 108a of the supercooler 108 is within a predetermined temperature from the saturation temperature of the intermediate-pressure refrigerant. . As described above, the saturation temperature of the intermediate pressure refrigerant is equal to the temperature of the outlet (j) of the supercooling valve 114. As can be seen from the TH diagram in FIG. 2 (b), if the temperature difference between (c) and (j) is large, the isentropic line due to low-stage compression becomes shorter, so the temperature in (f) decreases and dry saturation occurs. There is a possibility that (g) may enter the wet region, together with the fact that the vapor line is widened.

  Specifically, the expansion valve control unit 116 detects the temperatures of the sensors S1 and S4 and controls the opening degree of the supercooling valve 114 so that the temperature difference is within a predetermined temperature. From the viewpoint of reducing the temperature difference, the supercooling valve 114 may be throttled. Actually, however, the opening degree of the expansion valve control unit 116 may be controlled so that the temperature difference becomes a predetermined temperature (for example, about 15K). preferable.

  According to any of the above control 1 to control 3, it is possible to reliably prevent droplets (humid air) from entering the high stage compressor 106, thereby reducing the performance of the high stage compressor 106 and damaging the high stage compressor. Can be prevented. Moreover, the opening degree of the supercooling valve 114 can be controlled by extremely simple temperature detection, and can be easily controlled.

[Startup control method of heat pump]
Next, start-up control of the hot water supply apparatus 100 having the above configuration will be described. The activation control is performed by the control unit 101 (see FIG. 1).

  When the heat pump is started, even if the refrigerant and water are circulated under the same conditions as in the steady state, the supercooling by the economizer circuit does not function. First, in the heat pump provided with the economizer circuit 134, since the heat radiation by the supercooler is large, the water flow rate is small with respect to the refrigerant flow rate in the steady state (heat radiation amount of the high-pressure refrigerant = heat absorption amount of water + supercooling). Endothermic amount of intermediate pressure refrigerant). Therefore, when the compressor is started at a steady water flow rate, the refrigerant temperature at the outlet of the radiator 120 increases, and the pressure on the high stage side increases.

  FIG. 3 is a diagram for explaining a start-up cycle, and FIG. 3 (a) is a diagram showing a cycle when the flow rate of water is small. The broken line shown in FIG. 3A is a steady-state cycle, and the cycle at the time of startup becomes high temperature and high pressure as shown by the solid line. Then, the cooling capacity in the supercooler 108 (the enthalpy through which the intermediate pressure refrigerant passes through the wet area) becomes small. For this reason, when the fluctuation occurs in the intermediate pressure, the fluctuation rate of the cooling capacity is large, the degree of opening control of the supercooling valve is not stable, and it is difficult to achieve a steady state. In particular, when the intermediate pressure is near the critical pressure, the cooling capacity fluctuates with respect to the pressure fluctuation, and it is difficult to achieve a steady state.

  Here, it is also conceivable to provide a refrigerant charge amount regulator and reduce the refrigerant charge amount at the time of start-up, thereby preventing an increase in high pressure and causing the economizer circuit to function from the time of start-up. FIG.3 (b) is a figure which shows the cycle at the time of providing a refrigerant | coolant filling amount regulator. However, the provision of the refrigerant charging amount adjuster increases the cost of the equipment, and the size of the apparatus increases, the installation area increases, and the control becomes more complicated. . Further, as shown in FIG. 3B, even if the economizer circuit is functioning, the cooling capacity by supercooling is small because the refrigerant charging amount is small, and it is difficult to be in a steady state.

  Therefore, in order to smoothly shift to a steady state in which the economizer circuit 134 functions, it is sufficient that the intermediate pressure does not become close to the critical pressure. For that purpose, the refrigerant outlet temperature of the radiator has only to be low, that is, the refrigerant outlet temperature of the radiator has to be within a predetermined range with respect to the water inlet temperature of the radiator. Therefore, it is conceivable to increase the ratio of the water flow rate to the refrigerant circulation amount on the higher stage side from the steady state. Therefore, a first start control method for increasing the flow rate of water at the time of startup compared to the steady state and a second start control method for reducing the number of rotations of the compressor at the start time than in the steady state can be considered.

  FIG. 4 is a timing chart for explaining the first activation control method. At the start of activation (time t1), the low-stage compressor 104 and the high-stage compressor 106 are activated by increasing the flow rate of water from the steady state with the supercooling valve 114 closed. The refrigerant state (refrigerant temperature and pressure) is stable after a certain period of time, and the refrigerant outlet temperature of the radiator is within a predetermined range with the water inlet temperature of the radiator (the intermediate pressure decreases). Until (time t2). Next, the subcooling valve 114 is gradually opened until the outlet pressure of the high stage compressor 106 reaches a steady state high pressure, and the water flow rate is decreased until the outlet temperature of the radiator reaches a steady state temperature (time t3). .

  FIG. 5 is a timing chart for explaining the second activation control method. At the start of activation (time t1), the low-stage compressor 104 and the high-stage compressor 106 are activated at a lower rotational speed than in the steady state with the supercooling valve 114 closed. Wait until a certain time has elapsed, the refrigerant state is stable, and the refrigerant outlet temperature of the radiator is within a predetermined range with the water inlet temperature of the radiator (until the intermediate pressure becomes low) (time t2). ). Next, the subcooling valve 114 is gradually opened until the outlet pressure of the high stage compressor 106 reaches a steady state high pressure, and the low stage compressor and the high stage compression are performed until the outlet temperature of the radiator 120 reaches a steady state temperature. The number of revolutions of the machine is increased (time t3).

  As described above, according to any of the above startup control methods, the ratio of the flow rate of water to the flow rate of the refrigerant can be made larger than the steady state at the start of startup. Therefore, the inlet temperature of the supercooling valve 114 can be lowered, and the refrigerant state and the water amount can be brought to a steady state at an early stage.

  In addition, according to the said starting control method, since the amount of water at the time of compressor starting is comparatively large, the radiator outlet water temperature is lower than required temperature (steady state outlet water temperature). In such a case, the hot water storage tank 118 may be caused to flow into the hot water storage tank 118 from the position corresponding to the internal temperature in the vertical direction (see FIG. 1). Thereby, the effect that the temperature stratification in the hot water storage tank 118 is not disturbed is obtained. Hot water is stored in the hot water storage tank 118, and has a temperature gradient in which the upper part is hot and the lower part is cold. Therefore, when low-temperature water is allowed to flow into the hot water storage tank 118, the high-temperature hot water staying above is not impaired by flowing from the inlet provided in the middle or lower direction in the vertical direction. Thereby, the user can use hot water at a desired temperature immediately.

[Other Embodiments]
FIG. 6 is a diagram illustrating another configuration of the two-stage compression hot water supply apparatus, and FIG. 7 is a PH diagram and a TH diagram of the cycle of FIG. A hot water supply apparatus 100 a shown in FIG. 6 includes a second radiator 122 between the low stage compressor 104 and the high stage compressor 106 in addition to the hot water supply apparatus 100 shown in FIG. A third radiator 124 is provided. Then, the water supply is diverted after passing through the third radiator 124, and passes through the radiator 120 and the second radiator 122.

  As for the second radiator 122, by radiating heat (cooling the refrigerant) with the intermediate-pressure refrigerant in this way, the enthalpy of the inlet (g) of the high stage compressor 106 as shown in the PH diagram of FIG. Can be lowered. As a result, the pressure of the high-stage compressor 106 can be reduced and the compressor input (input work) can be reduced, so that the COP can be improved.

  The third radiator 124 is in a region where the inclination of the isobar is smaller than those of the radiator 120 and the second radiator 122 in the TH diagram. Therefore, the third radiator 124 flows all the water, and the radiator 120 and the second radiator 122 in the region where the inclination of the isobars is large diverts and flows the water little. As a result, the outlet temperature as high as possible can be aimed as shown in the TH diagram of FIG. 7B (because there is little water, it can be close to the refrigerant temperature).

  In addition, by exchanging heat with water using a plurality of radiators, it is possible to divide the straight line of the temperature change of the hot water during the heat dissipation process (one straight line in FIG. 2B). Here, the straight line of the water temperature change has a enthalpy H dimension of (KJ / Kg), so the slope decreases as the flow rate increases (the straight line approaches 0 °), and the slope increases as the flow rate decreases. (The straight line approaches 90 °). Therefore, it can be seen that the water temperature change straight line can be greatly bent by flowing all the water in the third radiator 124 and diverting the water in the radiator 120 and the second radiator 122.

On the other hand, the constant pressure curve of the CO ₂ refrigerant follows a meandering path as if the S-shape was reversed. For example, as shown in FIG. 7B, the slope is large at a low temperature of about 0 to 30 ° C., the slope is small at a medium temperature of about 30 ° C. to 50 ° C., and the slope is large at a higher temperature (the numerical value is an example). ). Therefore, by bending the water temperature straight line as described above, this can be made to follow the constant pressure curve of the refrigerant. Thereby, it becomes difficult for the constant pressure curve to fall below the water temperature straight line, and the pressure of the compressor can be reduced.

  For example, the same amount of water can be divided. However, since the inlet (g) of the high stage compressor 106 needs to be in a dry region, the outlet (i) of the second radiator 122 does not enter the wet region excessively (do not cool too much). For that purpose, the amount of water flowing through the second radiator 122 may be controlled (restricted).

  FIG. 8 is a diagram illustrating another configuration of the two-stage compression hot water supply apparatus, and FIG. 9 is a PH diagram and a TH diagram of the cycle of FIG. A hot water supply device 100b shown in FIG. 8 includes a fourth radiator 126 on the upstream side of the main expansion valve 112 and the downstream side of the flow divider 110 in addition to the hot water supply device 100a shown in FIG. . Then, the water supply passes through the fourth radiator 126 and the third radiator 124 and then is diverted to pass through the radiator 120 and the second radiator 122.

  The cooling using the fourth radiator 126 draws a cycle similar to the conventional two-stage expansion as shown in the PH diagram shown in FIG. 9A, and is expanded when the main circuit 132 and the economizer circuit 134 are expanded. There is a difference in enthalpy. That is, although the work of the low stage compressor 104 and the high stage compressor 106 is the same, the enthalpy of the refrigerant is further lowered than the temperature of the outlet (c) of the cooled channel 108a of the supercooler 108. Thus, during evaporation, the evaporator 102 can acquire a larger amount of heat from the air. For this reason, COP of a heat pump cycle can be improved further.

  The fourth radiator 126 is effective when the temperature of water (water supply) is lower than the temperature of the outlet (c) of the channel to be cooled 108a of the supercooler 108. At this time, as shown in the TH diagram of FIG. 9 (b), the water temperature straight line can be made to follow the constant pressure curve of the refrigerant by preheating the low temperature water supply, and the pressure of the compressor can be reduced. Can be improved.

  In addition, when the temperature of water (water supply) is higher than the temperature of the outlet (c) of the channel to be cooled 108a of the supercooler 108, water may not be passed through the fourth radiator 126. This is to prevent reheating of the refrigerant due to water (water supply). Specifically, a circuit that bypasses the fourth radiator 126 and a sensor (not shown) that measures the temperature of the feed water are provided, and the temperature of the feed water is higher than the refrigerant temperature measured by the sensor S4. In such a case, the water may be supplied from the bypass circuit without passing through the fourth radiator 126.

  FIG. 10 is a diagram illustrating another configuration of the two-stage compression hot water supply apparatus. A hot water supply device 100c shown in FIG. 10A includes an ejector 128 and a gas-liquid separator 130 at the position of the evaporator 102 in addition to the hot water supply device 100a shown in FIG. The separated gaseous refrigerant is led to the low-stage compressor 104. Note that the hot water storage tank 118 is not shown.

  Referring to the TH diagram shown in FIG. 10B, it can be seen that the pressure at the inlet (e) of the low-stage compressor 104 is higher than the outlet (q) of the evaporator 102. Thereby, the work of the low-pressure compressor can be reduced, and the COP can be further improved.

  FIG. 11 is a diagram illustrating another configuration of the two-stage compression hot water supply apparatus. A hot water supply apparatus 100d shown in FIG. 11 (a) uses a low-stage compressor 104 and a high-stage compressor 106 as an integrated compressor 136 with a gas injection port, compared to the hot water supply apparatus 100 shown in FIG. The gas injection increases the efficiency by bypassing the gaseous refrigerant to the intermediate pressure part of the compressor, and is internally the same as the two-stage compression. Therefore, a high COP can be obtained by suitably combining with an economizer circuit. Above all, since the compressor is only one device, the cost and size of the device can be reduced.

  In addition, as shown in FIG. 11 (b), a high pressure can be obtained with a small amount of work (enthalpy) in appearance in contrast to the two-stage compression indicated by the broken line (similar to FIG. 2 (a)). COP can be improved.

  At this time, if droplets (wet refrigerant) are introduced into the injection port of the compressor 136, the efficiency of the compressor 136 may be reduced or a failure may occur. Therefore, by controlling the opening degree of the supercooling valve 114 as described above, it is possible to ensure that the refrigerant at the outlet (k) of the cooling flow path 108b of the supercooler 108 becomes a dry region.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  INDUSTRIAL APPLICABILITY The present invention can be used as a two-stage compression hot water supply apparatus that supplies hot water using a two-stage compression heat pump and a starting method thereof.

It is a figure explaining the two-stage compression type hot-water supply apparatus concerning embodiment. It is a figure explaining a two-stage compression economizer cycle. It is a figure explaining the cycle at the time of starting. It is a timing chart explaining the 1st starting control method. It is a timing chart explaining the 2nd starting control method. It is a figure explaining the other structure of a two-stage compression type hot water supply apparatus. FIG. 7 is a PH diagram and a TH diagram of the cycle of FIG. 6. It is a figure explaining the other structure of a two-stage compression type hot water supply apparatus. FIG. 9 is a PH diagram and a TH diagram of the cycle of FIG. 8. It is a figure explaining the other structure of a two-stage compression type hot water supply apparatus. It is a figure explaining the other structure of a two-stage compression type hot water supply apparatus. It is a figure explaining the conventional two-stage compression 1-stage expansion cycle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Hot-water supply apparatus 101 ... Control part 102 ... Evaporator 104 ... Low stage compressor 106 ... High stage compressor 108 ... Supercooler 108a ... Cooled flow path 108b ... Cooling flow path 110 ... Divider 112 ... Main expansion valve 114 ... Supercooling valve 116 ... Expansion valve controller 118 ... Hot water storage tank 120 ... Radiator 122 ... Second radiator 124 ... Third radiator 126 ... Fourth radiator 128 ... Ejector 130 ... Gas-liquid separator 132 ... Main circuit 134 ... Economizer circuit 136 ... Compressor

Claims (9)

An evaporator, a low-stage compressor that compresses a low-pressure refrigerant to an intermediate pressure, a high-stage compressor that compresses an intermediate-pressure refrigerant to a high pressure, a radiator, a subcooler, a shunt, and a high-pressure refrigerant A main expansion valve that expands the refrigerant to a low pressure, a supercooling valve that expands the high-pressure refrigerant to an intermediate pressure,
A main circuit that reaches the main expansion valve from the shunt through the cooled channel of the subcooler;
An economizer circuit that joins between the low-stage compressor and the high-stage compressor from the shunt through the supercooling valve and the cooling channel of the supercooler;
An expansion valve control unit for controlling the opening degree of the supercooling valve,
The expansion valve control unit controls the opening degree of the supercooling valve so that the degree of superheat at the inlet of the high stage compressor or the outlet of the cooling channel of the supercooler becomes positive. Stage compression hot water supply system. An evaporator, a low-stage compressor that compresses a low-pressure refrigerant to an intermediate pressure, a high-stage compressor that compresses an intermediate-pressure refrigerant to a high pressure, a radiator, a subcooler, a shunt, and a high-pressure refrigerant A main expansion valve that expands the refrigerant to a low pressure, a supercooling valve that expands the high-pressure refrigerant to an intermediate pressure,
A main circuit that reaches the main expansion valve from the shunt through the cooled channel of the subcooler;
An economizer circuit that joins between the low-stage compressor and the high-stage compressor from the shunt through the supercooling valve and the cooling channel of the supercooler;
An expansion valve control unit for controlling the opening degree of the supercooling valve,
The expansion valve control unit opens the supercooling valve so that the temperature at the inlet of the high stage compressor or the outlet of the cooling channel of the supercooler is higher than the saturation temperature of the intermediate pressure refrigerant by a predetermined temperature or more. A two-stage compression hot water supply device characterized by controlling the degree. An evaporator, a low-stage compressor that compresses a low-pressure refrigerant to an intermediate pressure, a high-stage compressor that compresses an intermediate-pressure refrigerant to a high pressure, a radiator, a subcooler, a shunt, and a high-pressure refrigerant A main expansion valve that expands the refrigerant to a low pressure, a supercooling valve that expands the high-pressure refrigerant to an intermediate pressure,
A main circuit that reaches the main expansion valve from the shunt through the cooled channel of the subcooler;
An economizer circuit that joins between the low-stage compressor and the high-stage compressor from the shunt through the supercooling valve and the cooling channel of the supercooler;
An expansion valve control unit for controlling the opening degree of the supercooling valve,
The expansion valve control unit controls the opening degree of the supercooling valve so that the temperature of the outlet of the cooled channel of the supercooler is within a predetermined temperature from the saturation temperature of the intermediate-pressure refrigerant. A two-stage compression hot water supply device.   The two-stage compression hot water supply apparatus according to claim 2 or 3, wherein the saturation temperature of the intermediate-pressure refrigerant is obtained by detecting the temperature of the outlet of the supercooling valve.   The two-stage compression hot water supply apparatus according to any one of claims 1 to 3, wherein the refrigerant is carbon dioxide, and the refrigerant radiates heat in a supercritical state in the radiator. . A second radiator disposed on the refrigerant circuit between the low-stage compressor and the high-stage compressor and upstream of the merging position of the refrigerant circuit and the economizer circuit;
The two-stage compression hot water supply device according to claim 1, further comprising a third heat radiator disposed downstream of the heat radiator.   The two-stage compression hot water supply device according to claim 6, further comprising a fourth radiator arranged on a refrigerant circuit between the supercooler and the main expansion valve. In the two-stage compression hot water supply device according to any one of claims 1 to 5,
With the supercooling valve closed, the flow rate of water is increased from the steady state to start the low-stage compressor and the high-stage compressor,
Wait until a certain time has passed and the refrigerant state is stable and the refrigerant outlet temperature of the radiator is within a predetermined range with the water inlet temperature of the radiator,
The flow rate of water is decreased until the outlet temperature of the radiator reaches a steady state temperature while gradually opening the supercooling valve until the outlet pressure of the high stage compressor reaches a steady state high pressure. A start-up control method for a two-stage compression hot water supply device. In the two-stage compression hot water supply device according to any one of claims 1 to 5,
With the supercooling valve closed, the low stage compressor and the high stage compressor are started at a lower rotational speed than the steady state,
Wait until a certain time has passed and the refrigerant state is stable, and the outlet temperature of the radiator is within a predetermined range with the inlet temperature of the water of the radiator,
The low-stage compressor and the high-stage compressor are gradually opened until the outlet temperature of the radiator reaches a steady-state temperature while gradually opening the supercooling valve until the outlet pressure of the high-stage compressor becomes a steady-state high pressure. The start-up control method of the two-stage compression type hot water supply apparatus characterized by increasing the rotation speed of the.

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