Heat source system

Abstract

The objective is to provide a heat source system that can suppress the temperature drop of the heat transfer medium supplied to the load. [Solution] The heat source system of the embodiment comprises a first heat source unit and a second heat source unit, and a first control unit and a second control unit. The first and second heat source units heat a heat transfer medium supplied to the load. The first heat source unit is a heat pump. When the first control unit determines that defrosting of the air heat exchanger is necessary, it transmits a defrost preparation signal. When the second control unit receives the defrost preparation signal, it increases the output of the second heat source unit as a defrost preparation operation, using a control target value related to the output of the second heat source unit. After a first predetermined time has elapsed since transmitting the defrost preparation signal, the first control unit starts to decrease the output of the heating operation of the first heat source unit in preparation for the defrost operation of the first heat source unit. The temperature of the heat transfer medium supplied to the load is defined as the load supply temperature. The second control unit sets the control target value based on the load supply temperature.

Description

Technical Field

[0001] Embodiments of the present invention relate to a heat source system.

Background Art

[0002] A heat source system that supplies hot water to loads such as temperature control equipment is used. The heat source system has a first heat source machine and a second heat source machine that heat a heat medium (water) supplied to the load. The first heat source machine is a heat pump in which a refrigerant circulates through a compressor, a switching valve, a water heat exchanger, an expansion valve, and an air heat exchanger. The second heat source machine is a heating device such as a boiler.

[0003] When frost forms on the air heat exchanger of the first heat source machine, the first heat source machine performs a defrosting operation. Due to the defrosting operation of the first heat source machine, the temperature of the heat medium supplied to the load decreases. There is a need for a heat source system that can suppress a decrease in the temperature of the heat medium supplied to the load.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide a heat source system that can suppress a decrease in the temperature of the heat medium supplied to the load.

Means for Solving the Problems

[0006] The heat source system of this embodiment includes a first heat source unit and a second heat source unit, and a first control unit and a second control unit. The first and second heat source units heat the heat transfer medium supplied to the load. The first control unit controls the operation of the first heat source unit, and the second control unit controls the operation of the second heat source unit. The first heat source unit is a heat pump through which a refrigerant circulates a compressor, a flow direction switching device, a first heat exchanger, an expansion device, and an air heat exchanger. When the first control unit determines that defrosting of the air heat exchanger is necessary, it transmits a defrost preparation signal. When the second control unit receives the defrost preparation signal, it increases the output of the second heat source unit as a defrost preparation operation, using a control target value related to the output of the second heat source unit. After a predetermined time has elapsed since transmitting the defrost preparation signal, the first control unit starts to reduce the output of the heating operation of the first heat source unit in preparation for the defrost operation of the first heat source unit. The temperature of the heat transfer medium supplied to the load is defined as the load supply temperature. The second control unit sets the control target value based on the load supply temperature. [Brief explanation of the drawing]

[0007] [Figure 1] Circuit diagram of the heat source system in the embodiment. [Figure 2] Circuit diagram of the heat source system in a first modified embodiment. [Figure 3] Circuit diagram of the heat source system in a second modified embodiment. [Figure 4] Block diagram of the heat source system. [Figure 5] A flowchart for the defrost control method of a heat source system. [Figure 6] First timing chart for defrost control method of heat source system. [Figure 7] Second timing chart for defrost control method of heat source system. [Figure 8] Third timing chart for defrost control method of heat source system. [Figure 9] Fourth timing chart for defrost control method of heat source system. [Figure 10] Timing chart of the defrost control method for a heat source system in a fifth modified example of the embodiment. [Figure 11]Timing chart of the defrost control method for a heat source system in a sixth modified example of the embodiment. [Figure 12] Timing chart of the defrost control method for a heat source system in a seventh modified example of the embodiment. [Figure 13] Timing chart of the defrost control method for a heat source system in the eighth modified example of the embodiment. [Modes for carrying out the invention]

[0008] The heat source system of the embodiment will be described below with reference to the drawings. Figure 1 is a circuit diagram of the heat source system 1 in an embodiment. The heat source system 1 supplies a heat transfer medium that has been temperature-controlled to a high temperature to a load 40. The heat transfer medium is, for example, water. The load 40 is, for example, temperature control equipment such as a hot water bath, floor heating, or a constant temperature bath used in a factory production process. The heat source system 1 includes a tank 30, a temperature sensor T, a first heat source unit 10, and a second heat source unit 20.

[0009] Tank 30 stores the heat transfer medium. A heat transfer medium flow path F is installed between Tank 30 and the load 40. The heat transfer medium is supplied from Tank 30 to the load 40. The heat transfer medium may circulate between Tank 30 and the load 40. Tank 30 suppresses rapid changes in the temperature of the heat transfer medium supplied to the load 40 (sometimes called the load supply temperature).

[0010] The temperature sensor T is installed in the heat transfer medium flow path F between the tank 30 and the load 40. The temperature sensor T outputs a signal corresponding to the load supply temperature.

[0011] The first heat source unit 10 is a heat pump driven by electrical energy. A heat transfer medium channel F is installed between the first heat source unit 10 and the tank 30. The heat transfer medium circulates between the first heat source unit 10 and the tank 30. The first heat source unit 10 heats the heat transfer medium flowing through the heat transfer medium channel F.

[0012] The second heat source device 20 is a heating device other than a heat pump that does not require a defrosting operation, for example, a boiler. The second heat source device 20 is driven by energy such as oil or gas. A heat medium flow path F is installed between the second heat source device 20 and the tank 30. The heat medium circulates between the second heat source device 20 and the tank 30. The second heat source device 20 heats the heat medium flowing through the heat medium flow path F.

[0013] The heat source system 1 is a hybrid heat source system that heats a heat medium by the first heat source device 10 and the second heat source device 20. By using the first heat source device 10 in combination, the consumption of fossil fuel in the second heat source device 20 is suppressed. By using the second heat source device 20 in combination, a decrease in the load supply temperature associated with the defrosting operation of the first heat source device 10 is suppressed.

[0014] FIG. 2 is a circuit diagram of the heat source system 1 in the first modification of the embodiment. The heat source system 1 of the first modification is different from the above-described embodiment in that it does not have a tank 30. In the first modification, the first heat source device 10, the second heat source device 20, and the load 40 are connected in series by the heat medium flow path F. The temperature sensor T is installed in the heat medium flow path F between the second heat source device 20 and the load 40.

[0015] FIG. 3 is a circuit diagram of the heat source system 1 in the second modification of the embodiment. The heat source system 1 of the second modification is different from the above-described first modification in that the intermediate heat exchanger 32, the second heat source device 20, and the load 40 are connected in series by the heat medium flow path F. An intermediate heat medium flow path Fm is installed between the intermediate heat exchanger 32 and the first heat source device 10. The first heat source device 10 heats the intermediate heat medium flowing through the intermediate heat medium flow path Fm. In the intermediate heat exchanger 32, the intermediate heat medium flowing through the intermediate heat medium flow path Fm heats the heat medium flowing through the heat medium flow path F. The first heat source device 10 heats the heat medium indirectly via the intermediate heat medium.

[0016] FIG. 4 is a block diagram of the heat source system 1. The heat source system 1 includes a first heat source device 10, a first control unit 10c, a second heat source device 20, and a second control unit 20c.

[0017] The first heat source machine 10 has a compressor 11, a switching valve (flow direction switching device) 12, a water heat exchanger (first heat exchanger) 13, an expansion valve (expansion device) 14, and an air heat exchanger 15. The first heat source machine 10 is a heat pump in which a refrigerant circulates through these devices.

[0018] The compressor 11 compresses the low-pressure gaseous refrigerant taken into it into a high-temperature and high-pressure gaseous refrigerant. The switching valve 12 switches the flow direction of the refrigerant in the water heat exchanger 13, the expansion valve 14, and the air heat exchanger 15. In FIG. 4, the flow direction of the refrigerant when the first heat source machine 10 performs a heating operation is indicated by a solid-line arrow, and the flow direction of the refrigerant when performing a defrosting operation is indicated by a broken-line arrow.

[0019] When the first heat source machine 10 performs a heating operation, the refrigerant discharged from the compressor 11 circulates in the order of the switching valve 12, the water heat exchanger 13, the expansion valve 14, the air heat exchanger 15, and the switching valve 12, and returns to the compressor 11. At this time, the water heat exchanger 13 functions as a condenser (radiator), and the air heat exchanger 15 functions as an evaporator (heat absorber).

[0020] When the first heat source machine 10 performs a defrosting operation, the refrigerant discharged from the compressor 11 circulates in the order of the switching valve 12, the air heat exchanger 15, the expansion valve 14, the water heat exchanger 13, and the switching valve 12, and returns to the compressor 11. At this time, the air heat exchanger 15 functions as a condenser (radiator), and the water heat exchanger 13 functions as an evaporator (heat absorber).

[0021] The condenser dissipates heat from the high-temperature and high-pressure gaseous refrigerant discharged from the compressor 11 to convert the high-temperature and high-pressure gaseous refrigerant into a high-pressure liquid refrigerant. The expansion valve 14 reduces the pressure of the high-pressure liquid refrigerant sent from the condenser to convert the high-pressure liquid refrigerant into a low-temperature and low-pressure gas-liquid two-phase refrigerant. The evaporator converts the gas-liquid two-phase refrigerant sent from the expansion valve 14 into a low-pressure gaseous refrigerant. When the low-pressure gas-liquid two-phase refrigerant vaporizes in the evaporator, it absorbs the heat of vaporization from the surroundings.

[0022] When the first heat source unit 10 is performing heating operation, the water heat exchanger 13 functions as a condenser, and the refrigerant flowing through the water heat exchanger 13 releases heat. As a result, the refrigerant flowing through the water heat exchanger 13 heats the heat transfer medium flowing through the heat transfer medium channel F (see Figure 1). On the other hand, the air heat exchanger 15 functions as an evaporator, and the refrigerant flowing through the air heat exchanger 15 absorbs heat from the outside air. As a result, frost adheres to the air heat exchanger 15 (frost formation).

[0023] Frost formation on the air heat exchanger 15 reduces the operating efficiency of the first heat source unit 10. Therefore, when frost forms on the air heat exchanger 15, the first heat source unit 10 performs a defrosting operation.

[0024] When the first heat source unit 10 performs defrosting operation, the air heat exchanger 15 functions as a condenser, and the refrigerant flowing through the air heat exchanger 15 releases heat. As a result, the frost adhering to the air heat exchanger 15 melts and is removed. Meanwhile, the water heat exchanger 13 functions as an evaporator, and the refrigerant flowing through the water heat exchanger 13 absorbs heat. As a result, the first heat source unit 10 absorbs heat from the heat transfer medium flowing through the heat transfer medium channel F (see Figure 1) during defrosting operation, thereby cooling the heat transfer medium.

[0025] The first control unit 10c and the second control unit 20c include, for example, a processor such as a CPU (Central Processing Unit) connected by a bus, memory, and auxiliary storage device. The first control unit 10c and the second control unit 20c read and execute a program from, for example, the auxiliary storage device. The auxiliary storage device is configured using a storage medium such as a magnetic hard disk drive or a semiconductor storage device. For example, the auxiliary storage device is configured using a non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read-Only Memory).

[0026] All or part of the first control unit 10c and the second control unit 20c may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), or FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. Computer-readable recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program may be transmitted via a telecommunications line.

[0027] The first control unit 10c controls the operation of the first heat source unit 10. The first control unit 10c is formed integrally with the first heat source unit 10, but may be formed separately. The first control unit 10c performs heating operation of the first heat source unit 10 during normal operation of the heat source system 1. The first control unit 10c includes a defrost control unit 18 and an output port 19.

[0028] The defrost control unit 18 detects the degree of frost accumulation on the air heat exchanger 15 during the heating operation of the first heat source unit 10. The degree of frost accumulation is detected based on the temperature of the refrigerant flowing out of the air heat exchanger 15. To detect this temperature, a temperature sensor is installed in the refrigerant flow path at the outlet of the air heat exchanger 15. The defrost control unit 18 determines whether defrosting of the air heat exchanger 15 is necessary. The defrost control unit 18 determines that defrosting of the air heat exchanger 15 is necessary when the degree of frost accumulation on the air heat exchanger 15 exceeds a preset threshold.

[0029] The defrost control unit 18 outputs a defrost preparation signal when it determines that defrosting of the air heat exchanger 15 is necessary. The defrost preparation signal is transmitted from the output port 19 to the second control unit 20c. After a first predetermined time has elapsed since transmitting the defrost preparation signal, the defrost control unit 18 starts reducing the output of the heating operation of the first heat source unit 10 in preparation for defrosting. The output adjustment of the first heat source unit 10 is performed by adjusting the rotational speed of the compressor 11, etc. The defrost control unit 18 detects the load supply temperature of the heat medium based on the signal received from the temperature sensor T. The defrost control unit 18 sets a first predetermined time based on the load supply temperature.

[0030] The second control unit 20c controls the operation of the second heat source unit 20. The second control unit 20c is formed integrally with the second heat source unit 20, but may be formed separately. The second control unit 20c detects the load supply temperature based on the signal received from the temperature sensor T. The second control unit 20c adjusts the output of the second heat source unit 20 so that the load supply temperature approaches the target temperature. Specifically, the output of the second heat source unit 20 is adjusted so that the load supply temperature is maintained between the lower limit (referred to as the allowable lower temperature limit) and the upper limit (referred to as the allowable upper temperature limit) of the allowable temperature range centered on the target temperature. The output adjustment of the second heat source unit 20 is carried out by adjusting the amount of fuel supplied to the second heat source unit 20, etc.

[0031] When the second control unit 20c receives a defrost preparation signal from the first control unit 10c, it increases the output of the second heat source unit 20 as a defrost preparation operation, using a control target value related to the output of the second heat source unit 20. Note that starting the operation of the second heat source unit 20 is also one form of increasing the output of the second heat source unit 20. The increase in the output of the second heat source unit 20 increases the amount of heat transferred to the heat transfer medium by the second heat source unit 20. As mentioned above, the first heat source unit 10 absorbs heat from the heat transfer medium during defrost operation. The increase in the amount of heat transferred to the heat transfer medium by the second heat source unit 20 compensates for the heat absorbed from the heat transfer medium by the first heat source unit 10. This makes it possible to suppress the decrease in the load supply temperature of the heat transfer medium.

[0032] The defrost control method for heat source system 1 will be described in detail. Figure 5 is a flowchart of the defrost control method for heat source system 1. Figures 6-9 are the 1st to 4th timing charts of the defrost control method for heat source system 1. In the example in Figure 6-9, the target temperature of the load supply temperature is set to 70°C. The allowable lower temperature centered on the target temperature is set to 68°C, and the allowable upper temperature is set to 72°C.

[0033] During normal operation of the heat source system 1, the first control unit 10c performs heating operation of the first heat source unit 10 (S10). The defrost control unit 18 of the first control unit 10c detects the degree of frost on the air heat exchanger 15 during the heating operation of the first heat source unit 10 (S12). The defrost control unit 18 determines whether defrosting of the air heat exchanger 15 is necessary (S14). If the determination in S14 is NO, the defrost control unit 18 repeats the detection of the degree of frost on the air heat exchanger 15 (S12). If the determination in S14 is YES, the defrost control unit 18 sends a defrost preparation signal (turns it ON) (S16). In the example in Figure 6, the defrost control unit 18 sends the defrost preparation signal at time t1.

[0034] During normal operation of the heat source system 1, the second control unit 20c operates the second heat source unit 20 normally so that the load supply temperature approaches the target temperature (S11). When the second control unit 20c receives a defrost preparation signal, it starts defrost preparation operation (S17). The second control unit 20c increases the output of the second heat source unit 20 using a control target value related to the output of the second heat source unit 20. The second control unit 20c increases the output of the second heat source unit 20 by a first predetermined percentage relative to the fixed output (maximum output) of the second heat source unit 20. The control target value in this case is the first predetermined percentage. The initial value of the first predetermined percentage is set in advance based on experiments, etc. In the example in Figure 6, from time t1 to t2, the output of the second heat source unit 20 is increased from 20% to 40%, by 20% of the first predetermined percentage. Due to the increase in the output of the second heat source unit 20, the load supply temperature rises above the target temperature. The second control unit 20c allows the load supply temperature to rise above the allowable upper limit temperature during the defrost preparation operation.

[0035] The defrost control unit 18 determines whether a first predetermined time X has elapsed since transmitting the defrost preparation signal (S18). The first predetermined time X is set in advance based on experiments, etc. In the example in Figure 6, the first predetermined time X is from time t1 to t4. If the determination in S18 is NO, the defrost control unit 18 maintains the defrost preparation signal in the ON state. If the decision in S18 is YES, the defrost control unit 18 starts reducing the output of the heating operation of the first heat source unit 10 at time t4 in preparation for the defrost operation of the first heat source unit 10 (S19). As a result, the load supply temperature decreases, as shown in Figure 6.

[0036] At time t5, when the output of the heating operation of the first heat source unit 10 becomes 0 (heating operation stops), the defrost control unit 18 turns OFF the defrost preparation signal (S20). Specifically, the defrost control unit 18 stops transmitting the defrost preparation signal or transmits a defrost preparation completion signal. As a result, the second control unit 20c terminates the defrost preparation operation of the second heat source unit 20 (S21). Then the defrost control unit 18 starts the defrost operation of the first heat source unit 10 (S20). In other words, the defrost preparation operation of the second heat source unit 20 ends at the start of the defrost operation of the first heat source unit 10. The start of the defrost operation of the first heat source unit 10 further lowers the load supply temperature.

[0037] When the defrost preparation signal is turned OFF, the second control unit 20c stops increasing the output of the second heat source unit 20 by a first predetermined percentage. The second control unit 20c resumes normal operation (S26). That is, the second control unit 20c adjusts the output of the second heat source unit 20 so that the load supply temperature approaches the target temperature. In the example in Figure 6, at time t5, the load supply temperature drops to the target temperature (70°C). Therefore, the second control unit 20c increases the output of the second heat source unit 20. Since the first heat source unit 10 is performing defrosting, the load supply temperature temporarily falls below the target temperature. However, the effect of the increase in output of the second heat source unit 20 due to the defrost preparation operation remains, and the load supply temperature returns to the target temperature in a short time.

[0038] The defrost control unit 18 determines whether defrosting of the air heat exchanger 15 is complete (S22). If the determination in S22 is NO, the defrost control unit 18 continues the defrosting operation of the first heat source unit 10. If the determination in S22 is YES, the defrost control unit 18 stops the defrosting operation of the first heat source unit 10 (S24). As shown in Figure 6, at time t7, the defrost control unit 18 reduces the output of the defrosting operation of the first heat source unit 10. As a result, the load supply temperature rises from the target temperature. The second control unit 20c reduces the output of the second heat source unit 20. As a result, the load supply temperature returns to the target temperature.

[0039] At time t8, the defrost control unit 18 restarts the heating operation of the first heat source unit 10 (S25). As shown in Figure 6, the output of the second heat source unit 20 decreases as the output of the heating operation of the first heat source unit 10 increases. This maintains the load supply temperature at the target temperature.

[0040] The second control unit 20c sets the control target value for the next defrost preparation operation based on the previous load supply temperature data shown in Figure 6. The defrost control unit 18 transmits a defrost signal during the defrosting operation of the first heat source unit 10. The second control unit 20c receives the defrost signal and understands that the first heat source unit 10 is in defrosting operation. The second control unit 20c also detects the load supply temperature based on the signal received from the temperature sensor T. The second control unit 20c then detects the load supply temperature during the defrosting operation of the first heat source unit 10 (S30). In particular, the second control unit 20c detects the lowest load supply temperature during the defrosting operation of the first heat source unit 10 and the load supply temperature at the start time of the defrosting operation.

[0041] The second control unit 20c determines whether the lowest load supply temperature during defrosting operation has fallen below the allowable lower limit temperature (S32). In the example in Figure 6, the lowest load supply temperature during defrosting operation is 65°C, which is below the allowable lower limit temperature of 68°C. If the determination in S32 is YES, it is considered that the increase in output of the second heat source unit 20 during the defrosting preparation operation was insufficient. As mentioned above, the second control unit 20c increased the output of the second heat source unit 20 by a first predetermined percentage, which is the control target value, as part of the defrosting preparation operation. If the determination in S32 is YES, the second control unit 20c adds the first predetermined value to the previous control target value to set the next control target value (S33). The first predetermined value is the amount of increase of the first predetermined percentage, and is set in advance based on experiments, etc. For example, the first predetermined value is set to 10%. At this time, 10% of the first predetermined value is added to the previous first predetermined percentage of 20%, and the next first predetermined percentage is set to 30%.

[0042] Following the previous defrost preparation operation shown in Figure 6, the next defrost preparation operation shown in Figure 7 is performed. When the second control unit 20c receives the defrost preparation signal, it starts the defrost preparation operation (S17). The second control unit 20c increases the output of the second heat source unit 20 using the newly set control target value. In the example in Figure 7, from time t1 to t2, the output of the second heat source unit 20 is increased from 20% to 30%, which is the next first predetermined percentage, to 50%.

[0043] At time t5, the second control unit 20c completes the defrost preparation operation of the second heat source unit 20 (S21). Simultaneously, the defrost control unit 18 starts the defrost operation of the first heat source unit 10 (S20). In the example in Figure 7, the load supply temperature temporarily falls below the target temperature (70°C) during the defrost operation. However, in the next defrost preparation operation shown in Figure 7, a new control target value is used to increase the output of the second heat source unit 20 compared to the previous defrost preparation operation shown in Figure 6. As a result, the decrease in load supply temperature due to the defrost operation of the first heat source unit 10 is suppressed, and the load supply temperature is maintained above the allowable lower limit temperature (68°C). Consequently, it becomes possible to reduce the size of the tank 30 (see Figure 1).

[0044] Figure 8 includes another example of the previous defrosting preparation operation. When the second control unit 20c receives a defrost preparation signal, it starts the defrost preparation operation (S17). The second control unit 20c increases the output of the second heat source unit 20 by a first predetermined percentage, which is the control target value. In the example in Figure 8, the initial value of the first predetermined percentage is set to 60%. From time t1 to t2, the second control unit 20c increases the output of the second heat source unit 20 from 20% to 80%, which is the first predetermined percentage of 60%. Due to the increase in the output of the second heat source unit 20, the load supply temperature rises above the target temperature (70°C). During the defrost preparation operation, the second control unit 20c allows the load supply temperature to rise above the allowable upper limit temperature (72°C).

[0045] At time t5, the defrost control unit 18 turns off the defrost preparation signal and starts the defrost operation of the first heat source unit 10 (S20). Accordingly, the second control unit 20c ends the defrost preparation operation of the second heat source unit 20 (S21). The second control unit 20c stops increasing the output of the second heat source unit 20 by a first predetermined percentage and resumes normal operation (S26). In other words, the second control unit 20c adjusts the output of the second heat source unit 20 so that the load supply temperature falls within an allowable temperature range centered on the target temperature (70°C).

[0046] In the example shown in Figure 8, the output increase of the second heat source unit 20 during the defrost preparation operation is large. As a result, the minimum load supply temperature during defrost operation is maintained above the allowable lower limit temperature (68°C). On the other hand, the load supply temperature at the start time t5 of the defrost operation exceeds the allowable upper limit temperature (72°C).

[0047] The second control unit 20c sets the control target value for the next defrost preparation operation based on the previous load supply temperature data shown in Figure 8. In the example shown in Figure 8, the lowest load supply temperature during defrosting operation is above the allowable lower limit temperature, so the judgment in S32 is NO. In this case, the second control unit 20c determines whether the load supply temperature at the start time t5 of the defrosting operation exceeded the allowable upper limit temperature (S35). If the judgment in S35 is YES, it is considered that the increase in output of the second heat source unit 20 during the defrosting preparation operation was excessive. As mentioned above, the second control unit 20c increased the output of the second heat source unit 20 by the first predetermined percentage, which is the control target value, as part of the defrosting preparation operation. If the judgment in S35 is YES, the second control unit 20c subtracts the second predetermined value from the previous control target value to set the next control target value (S36). The second predetermined value is the amount of decrease of the first predetermined percentage, and is set in advance based on experiments, etc. For example, the second predetermined value is set to 20%. At this time, 20% of the second predetermined value is subtracted from the previous first predetermined percentage of 60%, and the next first predetermined percentage is set to 40%.

[0048] Following the previous defrost preparation operation shown in Figure 8, the next defrost preparation operation shown in Figure 9 is performed. When the second control unit 20c receives the defrost preparation signal, it starts the defrost preparation operation (S17). The second control unit 20c increases the output of the second heat source unit 20 by a newly set control target value, which is the first predetermined percentage. In the example in Figure 9, from time t1 to t2, the output of the second heat source unit 20 is increased from 20% to 40%, which is the next first predetermined percentage, resulting in an output of 60%.

[0049] In the next defrost preparation operation, the output of the second heat source unit 20 is reduced compared to the previous defrost preparation operation. As a result, the load supply temperature at the start time t5 of the defrost operation will be below the allowable upper limit temperature (72°C). This optimizes the increase in output of the second heat source unit 20 during the defrost preparation operation, and suppresses the energy consumption of the second heat source unit 20.

[0050] If the judgments in S32 and S35 are both NO, it is considered that the increase in output of the second heat source unit 20 during the defrost preparation operation was appropriate. In this case, the second control unit 20c sets the control target value for the next defrost preparation operation without changing the previous control target value (S38). That is, in the next defrost preparation operation, the second control unit 20c increases the output of the second heat source unit 20 by the same first predetermined percentage as the previous operation. This makes it possible to prevent the load supply temperature from falling outside the allowable temperature range during the defrost operation of the first heat source unit 10.

[0051] The defrosting time of the first heat source unit 10 (the time required from the start to the end of defrosting of the air heat exchanger 15) may vary with each defrosting operation due to the influence of the outside air temperature, etc. Even in such cases, performing the defrosting preparation operation of this embodiment increases the likelihood that the load supply temperature will be maintained above the allowable temperature during the defrosting operation. In particular, it is expected that the load supply temperature will be maintained above the allowable temperature after performing multiple defrosting preparation operations.

[0052] As detailed above, the heat source system 1 of the embodiment includes a first heat source unit 10 and a second heat source unit 20, and a first control unit 10c and a second control unit 20c. The first heat source unit 10 and the second heat source unit 20 heat the heat transfer medium supplied to the load. The first control unit 10c controls the operation of the first heat source unit 10, and the second control unit 20c controls the operation of the second heat source unit 20. The first heat source unit 10 is a heat pump through which a refrigerant circulates a compressor 11, a switching valve 12, a water heat exchanger 13, an expansion valve 14, and an air heat exchanger 15. When the first control unit 10c determines that defrosting of the air heat exchanger 15 is necessary, it transmits a defrost preparation signal. When the second control unit 20c receives the defrost preparation signal, it increases the output of the second heat source unit 20 as a defrost preparation operation, using a control target value related to the output of the second heat source unit 20. The first control unit 10c starts reducing the output of the heating operation of the first heat source unit 10 in preparation for defrosting operation of the first heat source unit 10 after a first predetermined time X has elapsed since transmitting the defrost preparation signal. The temperature of the heat medium supplied to the load is set as the load supply temperature. The second control unit 20c sets the control target value based on the load supply temperature. By setting the control target value based on the load supply temperature, the decrease in load supply temperature due to the defrosting operation of the first heat source unit 10 is suppressed.

[0053] The second control unit 20c, if the load supply temperature fell below the allowable lower limit temperature during the previous defrosting operation of the first heat source unit 10, adds a first predetermined value to the previous control target value to set the next control target value. Compared to the previous defrost preparation operation, the output of the second heat source unit 20 will increase during the next defrost preparation operation. As a result, the decrease in the load supply temperature during the next defrost operation will be suppressed, and the load supply temperature will be maintained above the allowable lower limit temperature.

[0054] The second control unit 20c, if the load supply temperature exceeded the allowable upper limit temperature at the start time of the previous defrosting operation of the first heat source unit 10, subtracts a second predetermined value from the previous control target value to set the next control target value. Compared to the previous defrost preparation operation, the output of the second heat source unit 20 will be reduced in the next defrost preparation operation. This will optimize the increase in output of the second heat source unit 20 during the defrost preparation operation, thereby suppressing the energy consumption of the second heat source unit 20.

[0055] The second control unit 20c increases the output of the second heat source unit 20 by a first predetermined percentage relative to the fixed output of the second heat source unit 20 as a defrost preparation operation. In this case, the control target value is the first predetermined percentage. By setting a first predetermined percentage, which is the control target value, based on the load supply temperature, the decrease in load supply temperature due to the defrosting operation of the first heat source unit 10 is suppressed.

[0056] A third modified example of the embodiment will be described. As described above, the second control unit 20c sets a control target value for the output of the second heat source unit 20 based on the load supply temperature. In this embodiment, the second control unit 20c increases the output of the second heat source unit 20 by a first predetermined percentage as a defrost preparation operation. In this case, the control target value is the first predetermined percentage. In contrast, in the third modified embodiment, the second control unit 20c increases the output of the second heat source unit 20 by changing the target temperature of the load supply temperature to a first predetermined temperature as a defrost preparation operation. In this case, the control target value is the first predetermined temperature. The second control unit 20c adjusts the output of the second heat source unit 20 so that the load supply temperature approaches the target temperature.

[0057] The second control unit 20c determines whether the lowest load supply temperature during defrosting operation has fallen below the allowable lower limit temperature (S32). If the determination in S32 is YES, the second control unit 20c adds the first predetermined value to the previous control target value, the first predetermined temperature, to set the next control target value (S33). If the determination in S32 is NO, the second control unit 20c determines whether the load supply temperature at the start time of defrosting operation has exceeded the allowable upper limit temperature (S35). If the determination in S35 is YES, the second control unit 20c subtracts the second predetermined value from the previous control target value, the first predetermined temperature, to set the next control target value (S36). The first predetermined value and the second predetermined value are set in advance based on experiments, etc. If the determination in S35 is NO, the second control unit 20c sets the next control target value without changing the previous control target value, the first predetermined temperature (S38).

[0058] Thus, in the third modified example, the second control unit 20c increases the output of the second heat source unit 20 by changing the target temperature of the load supply temperature to a first predetermined temperature as a defrost preparation operation. In this case, the control target value is the first predetermined temperature. By setting a first predetermined temperature, which is the control target value, based on the load supply temperature, the decrease in the load supply temperature due to the defrosting operation of the first heat source unit 10 is suppressed.

[0059] A fourth modified example of the embodiment will be described. In the fourth modified example, the defrost control unit 18 transmits a first heat production amount signal corresponding to the first heat production amount of the first heat source unit 10, along with a defrost preparation signal. The first heat production amount is the amount of heat that the first heat source unit 10 produces and supplies to the heat transfer medium per unit time. The second control unit 20c receives the first heat production amount signal along with the defrost preparation signal. As a defrost preparation operation, the second control unit 20c increases the output of the second heat source unit 20 so that the heat production amount of the second heat source unit 20 becomes a second predetermined ratio of the first heat production amount. In this case, the control target value is the second predetermined ratio.

[0060] The second control unit 20c determines whether the lowest load supply temperature during defrosting operation has fallen below the allowable lower limit temperature (S32). If the determination in S32 is YES, the second control unit 20c adds the first predetermined value to the second predetermined ratio, which is the previous control target value, to set the control target value for the next operation (S33). If the determination in S32 is NO, the second control unit 20c determines whether the load supply temperature at the start time of defrosting operation has exceeded the allowable upper limit temperature (S35). If the determination in S35 is YES, the second control unit 20c subtracts the second predetermined value from the second predetermined ratio, which is the previous control target value, to set the control target value for the next defrosting preparation operation (S36). The first predetermined value and the second predetermined value are set in advance based on experiments, etc. If the determination in S35 is NO, the second control unit 20c sets the control target value for the next operation without changing the second predetermined ratio, which is the previous control target value (S38).

[0061] Thus, in the fourth modified example, the first control unit 10c transmits a first heat production signal corresponding to the first heat production amount of the first heat source unit 10, along with a defrost preparation signal. The second control unit 20c increases the output of the second heat source unit 20 as a defrost preparation operation so that the heat production amount of the second heat source unit 20 becomes a second predetermined ratio of the first heat production amount. In this case, the control target value is the second predetermined ratio. By setting a second predetermined percentage, which is the control target value, based on the load supply temperature, the decrease in the load supply temperature due to the defrosting operation of the first heat source unit 10 is suppressed.

[0062] A fifth modified example of the embodiment will be described. Figure 10 is a timing chart of the defrost control method for the heat source system in a fifth modified example of the embodiment. The fifth modified example differs from the previously described embodiment in that the defrost preparation operation continues until the end time of the defrost operation. The explanation of the fifth modified example in relation to the same aspects as the embodiment may be omitted.

[0063] The defrost control unit 18 transmits a defrost preparation signal at time t1. When the second control unit 20c receives the defrost preparation signal, it increases the output of the second heat source unit 20 as a defrost preparation operation. The second control unit 20c increases the output of the second heat source unit 20 by setting a control target value for the output of the second heat source unit 20 based on the load supply temperature during the previous defrost operation.

[0064] When a first predetermined time X has elapsed from time t1, the defrost control unit 18 reduces the output of the heating operation of the first heat source unit 10 in preparation for defrosting. This lowers the load supply temperature. Then, at time t5, the defrost control unit 18 starts the defrosting operation of the first heat source unit 10.

[0065] The load supply temperature drops to the target temperature (70°C). Therefore, the second control unit 20c increases the output of the second heat source unit 20. The second control unit 20c further increases the output of the second heat source unit 20, which has already been increased by a predetermined percentage as part of the defrost preparation operation. The load supply temperature temporarily falls below the target temperature, but then rises above the target temperature. In the example in Figure 10, because the defrost preparation operation is ongoing, the load supply temperature rises above the allowable upper limit temperature.

[0066] At time t8, the first control unit 10c turns off the defrost preparation signal at the same time as the defrost operation ends. As a result, the second control unit 20c terminates the defrost preparation operation of the second heat source unit 20. The second control unit 20c resumes normal operation and adjusts the output of the second heat source unit 20 so that the load supply temperature approaches the target temperature. Since the load supply temperature is higher than the target temperature, the second control unit 20c reduces the output of the second heat source unit 20. As a result, the load supply temperature approaches the target temperature.

[0067] In the fifth modified example described in detail above, as in the embodiment, the decrease in load supply temperature due to the defrosting operation of the first heat source unit 10 is suppressed.

[0068] A sixth modification of the embodiment will be described. Figure 11 is a timing chart of the defrost control method for the heat source system in the sixth modified embodiment. The sixth modified embodiment differs from the fifth modified embodiment described above in that the defrost preparation operation continues for a second predetermined time Y. The explanation of the sixth modified embodiment in relation to the fifth modified embodiment may be omitted.

[0069] The defrost control unit 18 turns off the defrost preparation signal at time t6, after a second predetermined time Y has elapsed since the defrost preparation signal was turned ON. In the example in Figure 11, the defrost preparation signal is turned OFF at time t6, while the first heat source unit 10 is in the middle of defrosting operation. As a result, the second control unit 20c terminates the defrost preparation operation of the second heat source unit 20. The second control unit 20c resumes normal operation and adjusts the output of the second heat source unit 20 so that the load supply temperature approaches the target temperature. Since the load supply temperature is higher than the target temperature, the second control unit 20c reduces the output of the second heat source unit 20. As a result, the load supply temperature approaches the target temperature.

[0070] In the sixth modified example described in detail above, as in the fifth modified example, the decrease in load supply temperature due to the defrosting operation of the first heat source unit 10 is suppressed.

[0071] A seventh modification of the embodiment will be described. Figure 12 is a timing chart of the defrost control method for the heat source system in the seventh modified embodiment. The seventh modified embodiment differs from the fifth modified embodiment described above in that the second heat source unit 20 starts operation as a defrost preparation operation. The explanation of the seventh modified embodiment regarding aspects that are the same as the fifth modified embodiment may be omitted.

[0072] In the seventh modified example, the second heat source unit 20 is stopped during normal operation of the heat source system. The defrost control unit 18 transmits a defrost preparation signal at time t1. When the second control unit 20c receives the defrost preparation signal, it starts the operation of the second heat source unit 20 as a defrost preparation operation. The second control unit 20c starts the operation of the second heat source unit 20 by setting a control target value for the output of the second heat source unit 20 based on the load supply temperature during the previous defrost operation.

[0073] The defrost control unit 18 turns off the defrost preparation signal at time t8, simultaneously with the end of the defrost operation (S20). The second control unit 20c stops the operation of the second heat source unit 20 and ends the defrost preparation operation. The defrost control unit 18 restarts the heating operation of the first heat source unit 10. As the first heat source unit 10 transitions from defrost operation to heating operation, the load supply temperature may temporarily fall below the target temperature. Even in this case, the heating operation of the first heat source unit 10 will restore the load supply temperature to the target temperature.

[0074] In the seventh modified example described in detail above, as in the fifth modified example, the decrease in load supply temperature due to the defrosting operation of the first heat source unit 10 is suppressed.

[0075] An eighth variant of the embodiment will be described. Figure 13 is a timing chart of the defrost control method for the heat source system in the eighth modified embodiment. The eighth modified embodiment differs from the seventh modified embodiment described above in that a heater is used as the second heat source unit 20. The explanation of the eighth modified embodiment in relation to the seventh modified embodiment may be omitted.

[0076] In the embodiments described above and its seventh modified example, a boiler was used as the second heat source 20. In contrast, the second heat source 20 in the eighth modified example is a heater. The output of the boiler changes gradually and continuously, while the output of the heater changes immediately and in steps. In the example shown in Figure 13, the output of the heater is set to three levels: 0%, 50%, and 100% of the fixed output.

[0077] When the second control unit 20c receives a defrost preparation signal at time t1, it starts operating the second heat source unit 20 as a defrost preparation operation. The second control unit 20c increases the output of the second heat source unit 20 from 0% to 50%. During the defrost operation of the first heat source unit 10, the load supply temperature falls below the target temperature. The second control unit 20c increases the output of the second heat source unit 20 from 50% to 100%. When the defrost preparation signal turns OFF at time t8, the operation of the second heat source unit 20 ends, and the defrost preparation operation ends. The second control unit 20c decreases the output of the second heat source unit 20 from 100% to 0%.

[0078] In the eighth modification described in detail above, as in the seventh modification, the decrease in the load supply temperature due to the defrosting operation of the first heat source unit 10 is suppressed.

[0079] Some of the functions of the heat source system 1 in the embodiments and modifications described above may be implemented using a computer. In this case, the functions may be implemented by recording a program for implementing these functions on a computer-readable recording medium, loading the program recorded on this recording medium into a computer system, and executing it. Here, "computer system" includes hardware such as an OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and storage devices such as hard disks built into a computer system. Moreover, "computer-readable recording medium" may also include those that dynamically hold programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or communication lines such as telephone lines, and those that hold programs for a certain period of time, such as volatile memory inside a computer system that acts as a server or client in such cases. Furthermore, the above program may be for implementing some of the functions described above, or it may be a program that can implement the above functions in combination with a program already recorded in the computer system, or it may be implemented using hardware such as a PLD (Programmable Logic Device) or FPGA (Field Programmable Gate Array).

[0080] According to at least one embodiment and its modified form described above, there is a second control unit 20c that sets a control target value based on the load supply temperature. This makes it possible to suppress the decrease in load supply temperature due to the defrosting operation of the first heat source unit 10.

[0081] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0082] X...First predetermined time, 1...Heat source system, 10...First heat source unit, 10c...First control unit, 11...Compressor, 12...Switching valve (flow direction switching device), 13...Water heat exchanger (first heat exchanger), 14...Expansion valve (expansion device), 15...Air heat exchanger, 20...Second heat source unit, 20c...Second control unit.

Claims

1. A first heat source unit and a second heat source unit that heat the heat transfer medium supplied to the load, It comprises a first control unit that controls the operation of the first heat source unit and a second control unit that controls the operation of the second heat source unit, The first heat source unit is a heat pump through which a refrigerant circulates a compressor, a flow direction switching device, a first heat exchanger, an expansion device, and an air heat exchanger. When the first control unit determines that defrosting of the air heat exchanger is necessary, it transmits a defrosting preparation signal. When the second control unit receives the defrost preparation signal, it increases the output of the second heat source unit as a defrost preparation operation, using the control target value related to the output of the second heat source unit. The first control unit, after a first predetermined time has elapsed since transmitting the defrost preparation signal, starts reducing the output of the heating operation of the first heat source unit in preparation for the defrost operation of the first heat source unit. When the temperature of the heat transfer medium supplied to the load is defined as the load supply temperature, The second control unit sets the control target value based on the load supply temperature. Heat source system.

2. The second control unit, if the load supply temperature fell below the allowable lower limit temperature during the previous defrosting operation of the first heat source unit, adds a first predetermined value to the previous control target value to set the next control target value. The heat source system according to claim 1.

3. If the load supply temperature exceeded the allowable upper limit temperature at the start time of the previous defrosting operation of the first heat source unit, the second control unit subtracts a second predetermined value from the previous control target value to set the next control target value. The heat source system according to claim 2.

4. The second control unit, as part of the defrost preparation operation, increases the output of the second heat source by a first predetermined percentage relative to the fixed output of the second heat source unit. The control target value is the first predetermined ratio. A heat source system according to any one of claims 1 to 3.

5. The second control unit increases the output of the second heat source unit by changing the target temperature of the load supply temperature to a first predetermined temperature as the defrost preparation operation. The value to be controlled is the first predetermined temperature. A heat source system according to any one of claims 1 to 3.

6. The first control unit transmits a first heat output signal corresponding to the first heat output of the first heat source unit, along with the defrost preparation signal. The second control unit, as part of the defrost preparation operation, increases the output of the second heat source unit so that the amount of heat produced by the second heat source unit becomes a second predetermined ratio of the amount of heat produced by the first heat source unit. The control target value is the second predetermined ratio. A heat source system according to any one of claims 1 to 3.

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