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. 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 first control unit sets a first predetermined time 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 is defrosted. 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] <000002<

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. 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 first control unit sets a first predetermined time 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 a defrost control method for a heat source system in a third modified 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 unit 20 is a heating device other than a heat pump that does not require defrosting, such as a boiler. The second heat source unit 20 is powered by energy such as oil or gas. A heat transfer medium passage F is installed between the second heat source unit 20 and the tank 30. The heat transfer medium circulates between the second heat source unit 20 and the tank 30. The second heat source unit 20 heats the heat transfer medium flowing through the heat transfer medium passage F.

[0013] The heat source system 1 is a hybrid heat source system that heats a heat medium by the first heat source unit 10 and the second heat source unit 20. By using the first heat source unit 10 in combination, the consumption of fossil fuel in the second heat source unit 20 is suppressed. By using the second heat source unit 20 in combination, the decrease in the load supply temperature due to the defrosting operation of the first heat source unit 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 the tank 30. In the first modification, the first heat source unit 10, the second heat source unit 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 unit 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 unit 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 unit 10. The first heat source unit 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 unit 10 heats the heat medium indirectly through 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 unit 10, a first control unit 10c, a second heat source unit 20, and a second control unit 20c.

[0017] The first heat source unit 10 includes 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 unit 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 the interior to 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 unit 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 unit 10 performs a heating operation, the refrigerant discharged from the compressor 11 flows 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 unit 10 performs a defrosting operation, the refrigerant discharged from the compressor 11 flows 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. In the evaporator, when the low-pressure gas-liquid two-phase refrigerant vaporizes, it absorbs the heat of vaporization from the surroundings.

[0022] [[ID=Z0]]When the first heat source unit 10 performs a heating operation, the water heat exchanger 13 functions as a condenser, and the refrigerant flowing through the water heat exchanger 13 dissipates heat. As a result, the refrigerant flowing through the water heat exchanger 13 heats the heat medium flowing through the heat medium flow path F (see FIG. 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 (frost formation) to the air heat exchanger 15.

[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. Note that starting 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 adjusts the output of the second heat source unit 20 so that the load supply temperature approaches the target temperature. When the second control unit 20c receives a 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 a predetermined percentage of the fixed output (maximum output) of the second heat source unit 20. The 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% by a predetermined percentage (for example, a uniform 20%) to 40%. Due to the increase in the output of the second heat source unit 20, the load supply temperature rises above the target temperature. During the defrost preparation operation, the second control unit 20c allows the load supply temperature to rise above the allowable upper limit temperature. The time from time t1 to t2 is the time U during which the load supply temperature rises (referred to as the temperature rise time). From time t2 to t4, the load supply temperature is maintained at a constant value.

[0035] The defrost control unit 18 determines whether a first predetermined time X has elapsed since transmitting the defrost preparation signal (S18). The initial value of 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. 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 predetermined percentage. The second control unit 20c returns to normal control. 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 defrost control unit 18 sets the first predetermined time X for the next defrost preparation operation based on the results of the previous defrost preparation operation shown in Figure 6. The defrost control unit 18 detects the load supply temperature based on the signal received from the temperature sensor T. The defrost control unit 18 detects the time (referred to as the temperature stabilization time) C during the previous defrost preparation operation in which the load supply temperature was maintained at approximately a constant level. In the example in Figure 6, the temperature stabilization time C is from time t2 to t4. The start of the temperature stabilization time C is determined as the start of the time in which the rate of increase of the load supply temperature was maintained at or below a predetermined value. The end of the temperature stabilization time C is determined as the start of the time in which the rate of decrease of the load supply temperature was maintained at or above a predetermined value.

[0041] The defrost control unit 18 calculates the temperature stabilization excess time d by subtracting the minimum temperature stabilization time Cmin from the temperature stabilization time C (S26). As mentioned above, the defrost preparation operation of the second heat source unit 20 suppresses the decrease in the load supply temperature due to the defrost operation of the first heat source unit 10. The minimum temperature stabilization time Cmin is the minimum time required to maintain the load supply temperature above the allowable lower limit temperature during the defrost operation of the first heat source unit 10. The minimum temperature stabilization time Cmin is set in advance based on experiments, etc. In the example in Figure 6, the minimum temperature stabilization time Cmin is from time t2 to t3.

[0042] The defrost control unit 18 determines whether the temperature stabilization excess time d is greater than 0 (S28). The temperature stabilization excess time d is wasted time in terms of maintaining the load supply temperature above the allowable lower limit temperature. The occurrence of the temperature stabilization excess time d results in the second heat source unit 20 consuming wasted energy. If the determination in S28 is YES, the defrost control unit 18 subtracts the temperature stabilization excess time d from the previous first predetermined time X to set the next first predetermined time X (S30). The next first predetermined time X is the previous temperature rise time U plus the minimum temperature stabilization time Cmin.

[0043] Following the previous defrost preparation operation shown in Figure 6, the next defrost preparation operation shown in Figure 7 is performed. The defrost control unit 18 transmits a defrost preparation signal at time t1 (S16). The defrost control unit 18 determines whether the next first predetermined time X has elapsed since transmitting the defrost preparation signal (S18). If the next temperature rise time U is the same as the previous time, the next first predetermined time X will have elapsed after the minimum temperature stabilization time Cmin has elapsed from time t2. If the determination in S18 is YES, the defrost control unit 18 starts reducing the output of the heating operation of the first heat source unit 10 in preparation for the defrost operation of the first heat source unit 10 (S19). After that, the same defrost control as the previous time is performed.

[0044] In the next defrost preparation operation, the minimum temperature stabilization time Cmin for the load supply temperature will be ensured. This will suppress the decrease in the load supply temperature due to the defrosting operation of the first heat source unit 10, and the load supply temperature will be maintained above the allowable lower limit temperature. Consequently, it will be possible to reduce the size of the tank 30 (see Figure 1). In addition, in the next defrost preparation operation, there will be no excess temperature stabilization time d. This will reduce the energy consumption of the second heat source unit 20.

[0045] Figure 8 includes another example of the previous defrosting preparation operation. The defrost control unit 18 transmits a defrost preparation signal at time t1 (S16). When the second control unit 20c receives the defrost preparation signal, it increases the output of the second heat source unit 20. In the example in Figure 8, the rate of increase in the output of the second heat source unit 20 is small. Therefore, the first predetermined time X elapses while the load supply temperature is rising. In the example in Figure 8, the temperature stabilization time C does not occur, so the minimum temperature stabilization time Cmin is not secured. As a result, the load supply temperature may fall below the allowable lower limit temperature during the defrosting operation of the first heat source unit 10.

[0046] The defrost control unit 18 sets the first predetermined time X for the next defrost preparation operation based on the results of the previous defrost preparation operation shown in Figure 8. The defrost control unit 18 calculates the temperature stabilization excess time d by subtracting the temperature stabilization minimum time Cmin from the temperature stabilization time C (S26). In the example in Figure 8, the temperature stabilization time C is 0, so the temperature stabilization excess time d is a negative value. The defrost control unit 18 determines whether the temperature stabilization excess time d is greater than 0 (S28). In the example in Figure 8, the determination in S28 is NO. The defrost control unit 18 adds a correction time (second predetermined time) a to the previous first predetermined time X to set the next first predetermined time X (S30). The correction time a is preset to be approximately the same as the temperature stabilization minimum time Cmin.

[0047] Following the previous defrost preparation operation shown in Figure 8, the next defrost preparation operation shown in Figure 9 is performed. The defrost control unit 18 transmits a defrost preparation signal at time t1 (S16). The defrost control unit 18 determines whether the next first predetermined time X has elapsed since transmitting the defrost preparation signal (S18). If the next temperature rise time U is the same as the previous first predetermined time X, the next first predetermined time X will elapse after a correction time a has elapsed from time t2. If the determination in S18 is YES, the defrost control unit 18 starts reducing the output of the heating operation of the first heat source unit 10 in preparation for the defrost operation of the first heat source unit 10 (S19). After that, the same defrost control as the previous operation is performed.

[0048] As mentioned above, the correction time a is set to be approximately the same as the minimum temperature stabilization time Cmin. Therefore, in the next defrost preparation operation, there is a high probability that the minimum temperature stabilization time Cmin for the load supply temperature will be secured. This suppresses the decrease in load supply temperature due to the defrosting operation of the first heat source unit 10, and the load supply temperature is maintained above the allowable lower limit temperature. In addition, in the next defrost preparation operation, the temperature stabilization excess time d will not occur. This reduces the energy consumption of the second heat source unit 20.

[0049] The temperature rise time U may vary with each defrost preparation operation due to factors such as the ambient temperature. Even in such cases, the defrost control of this embodiment increases the likelihood that the minimum temperature stabilization time Cmin for the load supply temperature will be ensured during the defrost preparation operation. In particular, after multiple defrost preparation operations, the temperature stabilization time C for the load supply temperature is expected to be approximately equal to the minimum temperature stabilization time Cmin.

[0050] 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. 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 defined as the load supply temperature. The first control unit 10c sets the first predetermined time X based on the load supply temperature. By setting a first predetermined time X 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.

[0051] The temperature stabilization time C is defined as the time during which the load supply temperature remains approximately constant after the defrost preparation operation has started and the load supply temperature has risen. The minimum time required for the temperature stabilization time C is defined as the minimum temperature stabilization time Cmin. The first control unit 10c calculates the temperature stabilization excess time d by subtracting the temperature stabilization excess time Cmin from the temperature stabilization time C in the previous defrost preparation operation. If the temperature stabilization excess time d is greater than 0, the first control unit 10c subtracts the temperature stabilization excess time d from the previous first predetermined time X to set the next first predetermined time X. As a result, the minimum temperature stabilization time Cmin for the load supply temperature is ensured during the next defrost preparation operation. Consequently, the decrease in the load supply temperature during the defrost operation of the first heat source unit 10 is suppressed.

[0052] The first control unit 10c sets the next first predetermined time X by adding a correction time a to the previous first predetermined time X if the temperature stabilization excess time d is 0 or less. As a result, the minimum temperature stabilization time Cmin for the load supply temperature is ensured during the next defrost preparation operation. Consequently, the decrease in the load supply temperature during the defrost operation of the first heat source unit 10 is suppressed.

[0053] Figure 10 is a timing chart of the defrost control method for the heat source system in a third modified example of the embodiment. The third 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 third modified example in relation to the same aspects as the embodiment may be omitted.

[0054] 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 a predetermined percentage of the second heat source unit 20's fixed output.

[0055] 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 the defrost control unit 18 starts the defrosting operation of the first heat source unit 10.

[0056] 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. The load supply temperature temporarily falls below the target temperature, but then rises above the target temperature. In the example in Figure 10, since the defrost preparation operation is ongoing, the load supply temperature rises above the allowable upper limit temperature.

[0057] At time t8, the first control unit 10c turns off the defrost preparation signal simultaneously with the end of the defrost 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 returns to normal control 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.

[0058] In the third 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.

[0059] In the embodiment described above, when the second control unit 20c receives a defrost preparation signal, it increases the output of the second heat source unit 20 by a predetermined percentage as a defrost preparation operation. Alternatively, when the second control unit 20c receives a defrost preparation signal, it may start operating the second heat source unit 20 as a defrost preparation operation. That is, the second heat source unit 20, which was stopped before receiving the defrost preparation signal, starts operating as a defrost preparation operation after receiving the defrost preparation signal.

[0060] In the embodiment described above, when the second control unit 20c receives a defrost preparation signal, it increases the output of the second heat source unit 20 by a predetermined percentage as a defrost preparation operation. Alternatively, when the second control unit 20c receives a defrost preparation signal, it may change the target temperature of the load supply temperature to a predetermined temperature higher as a defrost preparation operation. The predetermined temperature is set in advance based on experiments, etc. The second control unit 20c increases the output of the second heat source unit 20 in order to bring the load supply temperature closer to the high target temperature.

[0061] In the embodiment described above, a boiler was exemplified as the second heat source 20. However, the second heat source 20 may also be a heater. The output of a boiler changes gradually and continuously, while the output of a heater changes immediately and in steps.

[0062] 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).

[0063] According to at least one embodiment and its modifications described above, there is a first control unit 10c that sets a first predetermined time X 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.

[0064] 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]

[0065] a...Correction time (second predetermined time), C...Temperature stabilization time, Cmin...Minimum temperature stabilization time, d...Temperature stabilization excess time, 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. 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 first control unit sets the first predetermined time based on the load supply temperature. Heat source system.

2. The time during which the load supply temperature remains substantially constant after the defrost preparation operation has started and the load supply temperature has risen is defined as the temperature stabilization time. When the minimum time required for temperature stabilization is set as the minimum temperature stabilization time, The first control unit calculates the time exceeding temperature stability by subtracting the minimum temperature stability time from the temperature stability time in the previous defrost preparation operation. The first control unit, when the temperature stabilization excess time exceeds 0, subtracts the temperature stabilization excess time from the previous first predetermined time to set the next first predetermined time. The heat source system according to claim 1.

3. The first control unit, when the temperature stabilization excess time is 0 or less, adds the second predetermined time to the previous first predetermined time to set the next first predetermined time. The heat source system according to claim 2.

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