Heat medium circulation device

Abstract

This heat medium circulation device circulates a heat medium between an outdoor heat source unit and indoor utilization-side equipment by means of piping and a pump. The heat medium circulation device carries out freeze prevention control to drive the pump when a detected temperature from a heat medium temperature sensor that detects the temperature of the heat medium drops below a threshold while the heat source unit is stopped, and also changes the threshold according to a detected temperature from an outdoor air temperature sensor that detects the temperature of outdoor air.

Description

Heat medium circulation device

[0001] The present invention relates to a heat medium circulator that circulates a temperature-adjusted heat medium between a heat source device and a user-side device by means of piping and a pump.

[0002] Heat transfer medium circulation systems are known that send a heat transfer medium (e.g., water) heated by an outdoor heat source unit via piping and a pump to indoor user equipment (e.g., a fan coil, a floor heating panel, a hot water tank, etc.), and then return the heat transfer medium to the heat source unit via piping. In such heat transfer medium circulation systems, the heat transfer medium can freeze when the system is shut down due to a drop in outdoor temperature. As the freezing progresses, the heat transfer medium expands, potentially damaging the piping. To prevent this freezing, the heat transfer medium circulation system is equipped with a temperature sensor attached to the piping that detects the temperature of the heat transfer medium. When the temperature detected by the temperature sensor falls below a predetermined threshold while the system is shut down, an anti-freeze control is implemented, which activates a pump to circulate the heat transfer medium.

[0003] Japanese Patent Application Laid-Open No. 2003-214700

[0004] The piping between the outdoor heat source unit and the indoor user equipment has a section exposed to the cold outside air and a section that is enclosed within the heat source unit's housing or building and does not come into contact with the outside air. If the temperature sensor is installed in a section that does not come into contact with the outside air, it will not be able to properly detect the temperature drop of the heat medium in the section exposed to the cold outside air. As a result, there is a possibility that the heat medium will freeze before the temperature detected by the temperature sensor falls below the threshold and the pump starts operating.

[0005] One possible solution would be to uniformly increase the heat medium temperature threshold for determining whether to operate the pump, but this would result in the pump being operated unnecessarily even in situations where there is no risk of freezing, which is undesirable from an energy conservation perspective. Another possible solution is to detect the outside air temperature without using the heat medium temperature and operate the pump only when the detected outside air temperature is low. However, even with this method, if the outside air temperature is low, the pump would be operated immediately if the heat source unit stops, resulting in the pump being operated unnecessarily even when the temperature of the heat medium in the piping is high enough that there is no risk of freezing. An object of an embodiment of the present invention is to provide a highly reliable heat medium circulating device that is energy-efficient and can prevent the heat medium from freezing.

[0006] The heat medium circulation device of the embodiment circulates a heat medium between an outdoor heat source unit and indoor user equipment by means of piping and a pump, and includes an outdoor air temperature sensor that detects the temperature of the outdoor air, a heat medium temperature sensor that detects the temperature of the heat medium, and a controller that executes anti-freeze control to drive the pump when the temperature detected by the heat medium temperature sensor drops below a threshold while the heat source unit is stopped, and that changes the threshold in accordance with the temperature detected by the outdoor air temperature sensor.

[0007] Figure 1 is a block diagram showing the overall configuration of one embodiment. Figure 2 is a flowchart showing control of one embodiment. Figure 3 is a flowchart continuing from Figure 2. Figure 4 is a diagram showing changes in flow rate and temperature of a heat medium in one embodiment. Figure 5 is a diagram showing the relationship between outside air temperature and the maximum change in heat medium temperature, and the relationship between outside air temperature and a correction value in one embodiment. Figure 6 is a diagram showing the relationship between outside air temperature and a threshold value in one embodiment. Figure 7 is a block diagram showing a modified example of the overall configuration of one embodiment.

[0008] A heat medium circulator according to one embodiment will be described below with reference to the drawings. As shown in Fig. 1, a heat source unit (also referred to as an outdoor unit) A installed outdoors is connected to a user-side device 9 (e.g., a fan coil, a floor heating panel, a hot water tank, etc.) via pipes 6a and 6b and an indoor unit B. A signal line C for data transmission and control is connected between the heat source unit A and the indoor unit B.

[0009] The heat source unit A includes a compressor 1 that draws in, compresses, and discharges a refrigerant; a gas-side pipe 2a that sends the gas refrigerant discharged from the discharge port of the compressor 1 to a refrigerant flow path 3a of a heat medium heat exchanger (also called a water heat exchanger) 3; a liquid-side pipe 2b that directs the liquid refrigerant condensed by heat exchange with the heat medium in the refrigerant flow path 3a to a flow control valve (pressure reducer) 4; a liquid-side pipe 2c that directs the liquid refrigerant decompressed by the flow control valve 4 to an outdoor heat exchanger 5; a gas-side pipe 2d that returns the gas refrigerant evaporated by heat exchange with outside air in the outdoor heat exchanger 5 to the suction port of the compressor 1; a portion of a heat medium pipe (water pipe) 6a that directs the heat medium returning from the user device 9 to the heat medium flow path (water flow path) 3b of the heat medium heat exchanger 3; and a portion of a heat medium pipe 6b that directs water heated by heat exchange with the refrigerant in the heat medium flow path 3b to the indoor unit B. Various refrigerants such as R410A, R32, and R290 can be used as refrigerants for the refrigeration cycle. Various fluids can also be used as the heat medium. In this embodiment, a heat medium that freezes in a low-temperature environment, such as water, is used. A plate heat exchanger or a multi-tube heat exchanger can be used as the heat medium heat exchanger 3, which exchanges heat between the refrigerant and the heat medium. An outdoor fan 30 is provided opposite the outdoor heat exchanger 5, which may be a fin-tube heat exchanger or the like. The outdoor fan 30 operates to ventilate the outdoor air, thereby promoting heat exchange between the refrigerant and the outdoor air in the outdoor heat exchanger 5.

[0010] A heat pump refrigeration cycle is configured in which a refrigerant circuit flows from the compressor 1 through the gas side pipe 2a, the refrigerant flow path 3a of the heat medium heat exchanger 3, the liquid side pipe 2b, the flow control valve 4, the liquid side pipe 2c, the outdoor heat exchanger 5, and the gas side pipe 2d, before returning to the compressor 1. The refrigerant pumped up by the heat pump refrigeration cycle is sent to the user device 9 for heating or hot water supply by the heat medium passing through the heat medium heat exchanger 3.

[0011] The heat source unit A further includes an outdoor controller 10 consisting of a microcomputer and its peripheral circuits, and an outdoor air temperature sensor 11, a heat medium temperature sensor 12, and an inverter 13 connected to the outdoor controller 10. The outdoor air temperature sensor 11 is installed on the upwind side of the outdoor heat exchanger 5 and detects the outdoor air temperature To, which is the temperature of the outdoor air flowing into the outdoor heat exchanger 5. The heat medium temperature sensor 12 is attached to a portion of the heat medium piping 6a that fits within the housing of the heat source unit A and detects the temperature of the heat medium flowing into the heat medium flow path 3b of the heat medium heat exchanger 3, i.e., the return temperature Twi, which is the temperature of the heat medium returning to the heat source unit A after releasing heat in the user-side device 9. The inverter 13 converts the AC voltage of the AC power source 14 into DC voltage, converts the DC voltage into AC voltage of a frequency commanded by the outdoor controller 10, and outputs the AC voltage as drive power for the motor 1M that drives the compression mechanism of the compressor 1. The rotation speed of the motor 1M changes in accordance with the frequency (output frequency) of the AC voltage output from the inverter 13, and the capacity of the compressor 1 changes in accordance with the change in the rotation speed.

[0012] The outdoor controller 10 includes a memory 10m for storing data, and transmits the above-mentioned outdoor air temperature To and return temperature Twi to the indoor controller 20 described below via a signal line C, and controls the operation of the compressor 1 (output frequency of the inverter 13) and the opening of the flow control valve 4 in accordance with instructions from the indoor controller 20 via the signal line C. Data on the outdoor air temperature To detected by the outdoor air temperature sensor 11 is used for normal operation control and various protection controls of the compressor 1 in the heat source unit A, as well as for anti-freeze control described below.

[0013] The indoor unit B has a housing attached to an indoor wall or the like and houses an electric heater 7, a pump 8, an indoor controller 20 consisting of a microcomputer and its peripheral circuits, and heat medium temperature sensors 21 and 22 connected to the indoor controller 20. The housing also includes a remote-controller 23 on the front surface of the housing that can be operated by the user. The electric heater 7 is installed in the heat medium piping 6b and, based on instructions from the indoor controller 20, provides auxiliary heating to the heat medium flowing in from the heat source unit A when the heat pump refrigeration cycle alone is unable to sufficiently raise the temperature of the heat medium, such as during extremely low outdoor temperatures. The pump 8 is installed in the heat medium piping 6c extending from the heat medium piping 6b to the user-side devices 9 and sends the heat medium that has passed through the electric heater 7 to the user-side devices 9. Operation of the pump 8 causes the heat medium to circulate through the heat medium piping 6c, the user-side devices 9, the heat medium piping 6a, the heat medium heat exchanger 3, the heat medium piping 6b, and the electric heater 7.

[0014] The heat medium temperature sensor 21 is attached to the heat medium piping 6b at a location that fits within the housing of the indoor unit B and is upstream of the position where the electric heater 7 is located, and detects the temperature of the heat medium that is sent out from the heat source device A and flows into the electric heater 7, which is called the supply temperature Two. The heat medium temperature sensor 22 is attached to the heat medium piping 6c at a location that fits within the housing of the indoor unit B and is upstream of the position where the pump 8 is located, and detects the temperature of the heat medium that flows through the electric heater 7 to the use-side device 9, which is called the use temperature Twh. Note that the use temperature Twh is equal to the supply temperature Two when the electric heater 7 is not operating.

[0015] The operating device 23, which is located on the front of the housing of the indoor unit B, has a display 23a and is connected by a signal line to the indoor controller 20, and sets various operating conditions such as starting and stopping the operation of the heat source unit A, the operating time of the heat source unit A, and the target temperature of the heat medium in response to user operations, and displays the settings and data sent from the outdoor controller 10 in text on the display 23a. The indoor controller 20 may also be installed separately in a different location outside the housing of the indoor unit B.

[0016] The indoor controller 20 includes a data storage memory 20m and controls the electric heater 7 and the pump 8 according to the settings of the operating device 23, the supply temperature Two which is the temperature detected by the heat medium temperature sensor 21, the utilization temperature Twh which is the temperature detected by the heat medium temperature sensor 22, and also according to data sent from the outdoor controller 10, such as the return temperature Twi which is the temperature detected by the heat medium temperature sensor 12 and the outdoor air temperature To. The indoor controller 20 functions as a parent device that controls the entire heat medium circulation apparatus including the heat source unit A via the outdoor controller 10, and the outdoor controller 10 functions as a child device that controls the heat source unit A in accordance with instructions from the indoor controller 20. In this embodiment, the indoor controller 20, the outdoor controller 10, and the operating device 23 work together to function as controllers of the heat medium circulation apparatus.

[0017] The indoor controller 20 performs normal operation control, supplying heat pumped from the outdoor air by the operation of the heat source unit A to the user-side equipment 9 by operating the pump 8. In addition, the indoor controller 20 also performs anti-freeze control, driving the pump 8 when the return temperature Twi falls below a threshold while the heat source unit A is stopped. When performing anti-freeze control, the indoor controller 20 changes the threshold according to the outdoor air temperature T. Specifically, the threshold is increased as the outdoor air temperature T drops. In normal operation control, the pump 8 of the indoor unit B is stopped either synchronously with the stop of the heat source unit A, i.e., the stop of the compressor 1, or with a slight time delay after the stop of the compressor 1. Therefore, when the compressor 1 is stopped, the pump 8 is also stopped. The operation of the heat source unit A is stopped when it no longer needs to supply heat to the user-side equipment 9 (i.e., when the so-called thermo-off state is reached), or when the user operates the operating device 23 to stop the operation of the heat medium circulator (operation stop).

[0018] When the pump 8 stops, the heat medium remaining in the heat medium pipes 6a and 6b in the exposed parts is cooled by the outside air. If the heat medium is water, the heat medium in the heat medium pipes 6a and 6b starts to freeze when the temperature of the exposed parts drops below 0°C.

[0019] As specific functions of the anti-freeze control for preventing the heat medium from freezing, the indoor controller 20 includes a first control section 20a to a fourth control section 20d. When the heat source unit A is stopped and the outdoor air temperature To is equal to or higher than a predetermined reference value Tos, the first control section 20a executes first anti-freeze control, which activates the pump 8 when the return air temperature Twi falls below a threshold value T1 (first threshold value; e.g., 4°C), and then stops the pump 8 when the return air temperature Twi exceeds the threshold value T1. The reference value Tos (e.g., 5°C) is set to a temperature higher than the freezing temperature of the heat medium, i.e., a temperature higher than 0°C, which is the freezing temperature of water in this embodiment. Note that when the outdoor air temperature To is higher than 5°C, there is no risk of freezing, and therefore the first anti-freeze control is not executed.

[0020] When the outdoor fan 30 is operating and outdoor air is flowing into the outdoor heat exchanger 5, the outdoor air temperature To can be detected with high accuracy by the outdoor air temperature sensor 11. However, when the heat source unit A is stopped, the outdoor fan 30 also stops as the compressor 1 stops. When the outdoor fan 30 stops and outdoor air no longer flows into the outdoor heat exchanger 5, the accuracy with which the outdoor air temperature sensor 11 detects the outdoor air temperature To decreases. Furthermore, when the heat source unit A is installed in a sunny location, the outdoor air temperature sensor 11 detects a temperature higher than the actual outdoor air temperature due to the influence of solar radiation. In anticipation of these situations, a temperature higher than the freezing temperature of the heat medium is set as the reference value Tos, as described above, to reliably prevent the heat medium in the heat medium pipes 6a and 6b from freezing.

[0021] When the heat source unit A is stopped and the outside air temperature To is below the reference value Tos, the second control section 20b drives the pump 8 when the return temperature Twi falls below a threshold T2 (second threshold; for example, 7°C) higher than the threshold T1, and then executes second anti-freeze control to stop the pump 8 when the return temperature Twi exceeds the threshold T2.

[0022] The threshold value T1 is set to a value that can reliably prevent freezing even when the heat transfer medium pipes 6a, 6b, and 6c are at their longest length under the specifications when the outside air temperature To is equal to or higher than the reference value Tos. Similarly, the threshold value T2 is set to a value with a margin that can reliably prevent freezing even when the heat transfer medium pipes 6a, 6b, and 6c are at their longest length under the specifications when the outside air temperature To is lower than the reference value Tos.

[0023] In this way, a threshold value T1 (e.g., 4°C) and a threshold value T2 (e.g., 7°C) higher than threshold T1 are prepared as reference values ​​for the heat medium temperature used to determine whether or not to operate pump 8 for anti-freezing purposes. By selecting and using either threshold value T1 or T2 depending on the outside air temperature To while heat source unit A is stopped, it is possible to reduce opportunities for pump 8 to be operated due to unnecessary anti-freezing control intervention and achieve anti-freezing control with excellent energy conservation. Here, threshold value T2 is set to a value higher than threshold value T1 (7°C > 4°C), and this is because the outside air temperature To is switched based on the reference value Tos. In other words, as the outside air temperature To decreases, the threshold value is changed to a higher value.

[0024] Furthermore, since the threshold value T2 is set to a high value with a sufficient margin as described above, it can be adjusted to an appropriate value depending on the installation conditions of the heat medium circulating device. In order to suppress unnecessary operation of the pump 8 by adjusting the threshold value T2 and further improve energy saving, a third control section 20c and a fourth control section 20d are further provided.

[0025] After the heat source unit A is shut down, the third control section 20c stores (updates) in the memory 20m the outside air temperature T when the pump 8 is started and the maximum downward change ΔTwi of the return temperature Twi within a certain time (e.g., 10 seconds) from the start of the pump 8 during the first (initial) second anti-freeze control and each subsequent execution of the second anti-freeze control. This data is used to set the threshold T2 (new threshold T2') for the next second anti-freeze control. Here, the maximum downward change ΔTwi refers to the difference between the return temperature Twi(s) at or immediately before the start of the pump 8 and the minimum return temperature Twi (min) within a certain time (e.g., 10 seconds) from the start of the pump 8. ΔTwi = Twi(s) - Twi(min). The maximum changes ΔTwi1 to ΔTwi4, described below, have the same meaning.

[0026] The fourth control section 20d sequentially sets a new threshold value T2' appropriate for each execution of the second anti-freeze control from the second time onward after the heat source unit A is shut down, based on the current outside air temperature To, the reference value To, and the stored threshold setting data (the outside air temperature To and the maximum change ΔTwi during the previous execution of the second anti-freeze control). Specifically, the fourth control section 20d multiplies the maximum change ΔTwi(n-1) in the return temperature Twi resulting from the previous second anti-freeze control by the ratio of the difference between the current outside air temperature To(n) and the reference value To (= To(n) - To) to the difference between the outside air temperature To(n-1) at the start of the previous second anti-freeze control and the reference value To (= To(n-1) - To) and adds the result of this multiplication to the threshold value T1 as a correction value α, thereby setting a new threshold value T2' (= T1 + α) for the second and subsequent executions of the second anti-freeze control. α = [(To(n) - Tos) / (To(n-1) - Tos)] x ΔTwi(n-1) Here, "n" means the number of times the second anti-freeze control is executed and is an integer greater than or equal to "2".

[0027] Through the processing of these first to fourth control sections 20a to 20d, the indoor controller 20 executes appropriate anti-freeze control that reflects the installation status of the heat medium circulator including the external environment in which the heat source unit A is installed, in particular the lengths and installation positions of the heat medium piping 6b between the heat source unit A and the indoor unit B, the heat medium piping 6c between the indoor unit B and the user-side equipment 9, and the heat medium piping 6a between the user-side equipment 9 and the heat source unit A.

[0028] Next, the control executed by the indoor controller 20 while the heat source unit A is stopped will be described with reference to the flowchart of FIG. 2 and the flowchart of FIG. 3 which follows FIG.

[0029] <First anti-freeze control> After the operation of heat source unit A stops, if the execution flag f of the second anti-freeze control is "0" (YES in S1), the indoor controller 20 determines that the second anti-freeze control has not yet been executed and compares the outdoor air temperature To with the reference value Tos (= 5°C) (S2).

[0030] If the outdoor air temperature To is equal to or higher than the reference value Tos (=5°C) (NO in S2), the indoor controller 20 compares the return temperature Twi with the threshold value T1 (=4°C) (S3). If the return temperature Twi is equal to or higher than the threshold value T1 (NO in S3), the indoor controller 20 determines that there is no risk of the heat medium freezing and returns to the determination in S1 above.

[0031] If the return temperature Twi is lower than the threshold value T1 (YES in S3), the indoor controller 20 determines that there is a risk of the heat medium freezing and drives the pump 8 (S4). Driving the pump 8 causes the heat medium in the heat medium pipes 6a, 6b, and 6c to circulate through the heat medium heat exchanger 3 and the use-side devices 9. This circulation prevents the heat medium from freezing, and the circulating heat medium is warmed by the residual heat of the heat medium heat exchanger 3 and the use-side devices 9, thereby enhancing the effect of preventing freezing (start of first anti-freeze control).

[0032] 4 shows by solid lines how the flow rate F of the heat medium in the heat medium pipes 6a, 6b, and 6c changes in an increasing direction as a result of the execution of this first anti-freeze control, and how the return temperature Twi and the supply temperature Two change in a decreasing direction once and then change in an increasing direction as the flow rate F increases. The phenomenon in which the return temperature Twi and the supply temperature Two change in a decreasing direction once occurs when the low-temperature heat medium that has remained in the parts of the heat medium pipes 6a, 6b, and 6c exposed to the outside air suddenly flows toward the installation positions of the heat medium temperature sensors 12 and 21, and the heat of the low-temperature heat medium is transferred to the heat medium temperature sensors 12 and 21.

[0033] After starting the operation of the pump 8, when the return temperature Twi rises to a value exceeding the threshold value T1 (T1 + hysteresis, for example, 1°C) (YES in S5), the indoor controller 20 stops the pump 8 (S6) and returns to the judgment in S1 (end of first anti-freeze control). Note that it is possible to eliminate the temperature addition of the hysteresis amount by providing a delay time in the judgment.

[0034] <Initial (first) second anti-freeze control> After the operation of heat source unit A stops, if the execution flag f of the second anti-freeze control is “0” (YES in S1), the indoor controller 20 compares the outside air temperature To with the reference value Tos (= 5°C) (S2).

[0035] If the outdoor air temperature To is less than the reference value Tos (YES in S2), the indoor controller 20 compares the return temperature Twi with a threshold value T2 (7°C) that is higher than the threshold value T1 (S7). If the return temperature Twi is equal to or higher than the threshold value T2 (NO in S7), the indoor controller 20 determines that there is no risk of the heat medium freezing and returns to the determination in S1 above.

[0036] If the return temperature Twi is lower than the threshold value T2 (YES in S7), the indoor controller 20 determines that there is a risk of the heat medium freezing and drives the pump 8 (S8). Driving the pump 8 in this way prevents the heat medium from freezing (start of the first second anti-freeze control).

[0037] When the outside air temperature To is lower than the reference value Tos, a threshold value T2 higher than the normal threshold value T1 is used as the judgment criterion, so the timing of driving the pump 8 to prevent freezing is earlier than when the threshold value T1 is used. Accordingly, as shown by the dashed line in Figure 4, the timing at which the return temperature Twi changes from a temporary drop to an increase is also earlier than when the threshold value T1 is used.

[0038] Therefore, it is possible to reliably prevent the heat medium in the heat medium pipes 6a, 6b, and 6c that are exposed to the outside air and are in a low temperature state from freezing. Moreover, since the threshold value T2 is used only when the outside air temperature To is lower than the reference value Tos, the pump 8 is not driven unnecessarily in a situation where there is no possibility of freezing.

[0039] Next, the indoor controller 20 stores the outside air temperature To when the pump 8 starts operating as "To1" in the memory 20m (S9), and detects the maximum downward change ΔTwi in the return temperature Twi within a certain time (e.g., 10 seconds) from the start of operation of the pump 8 as "ΔTwi1" (NO in S10 and S11). After the certain time has elapsed (YES in S10), the indoor controller 20 stores the stored outside air temperature To1 and the detected maximum change ΔTwi1 in the memory 20m as threshold setting data (To1, ΔTwi1) for setting a new threshold T2' for the next second antifreeze control (S12).

[0040] Then, when the return temperature Twi rises to a value exceeding the threshold value T2 (T2 +, for example, 1°C as a hysteresis amount) (YES in S13), the indoor controller 20 stops the pump 8 (S14), sets flag f to "1" to indicate that the second anti-freeze control has been executed (YES in S15), and returns to the judgment in S1 above (end of the initial second anti-freeze control). Note that the temperature addition for the hysteresis amount may be omitted by providing a delay time in the judgment.

[0041] The fixed time (10 seconds) for monitoring the maximum change ΔTwi(n) detected in the first and subsequent second antifreeze control cycles includes the response time from when the heat medium in the heat medium pipes 6a, 6b, and 6c exposed to the outside air flows to the heat medium temperature sensor 12, which detects the return temperature Twi, until the heat medium temperature sensor 12 can accurately detect the minimum temperature Twi(min) of the heat medium that has flowed in. The time is set as short as possible within this time. By shortening this time, the operating time of the pump 8 can be reduced, thereby reducing the power consumption of the pump 8.

[0042] <Second Second Anti-Freeze Control> After heat source unit A is stopped, if flag f is "1" (NO in S1), the indoor controller 20 determines that the second anti-freeze control has already been executed, and multiplies the maximum downward change ΔTwi1 in the return temperature Twi due to the previous second anti-freeze control by the ratio of [the difference between the current outdoor air temperature To2 and the reference value Tos (To2 - Tos)] to [the difference between the outdoor air temperature To1 at the start of the previous second anti-freeze control and the reference value Tos (To1 - Tos)], and obtains the result of this multiplication as a correction value α for setting an optimal threshold value T2' for the current (second) second anti-freeze control (S16). α = [(To2 - Tos) / (To1 - Tos)] × ΔTwi1

[0043] The relationship between the outside air temperature To and the maximum change amount ΔTwi, and the relationship between the outside air temperature To and the correction value α are shown in Figure 5. The maximum change amount ΔTwi (= 0) of the return temperature Twi when the outside air temperature To is the reference value To is defined as "ΔTwi0", and a linear line X1 extending from the intersection (To, ΔTwi0) of the reference value To and the change amount ΔTwi0 to the intersection (To1, ΔTwi1) of the outside air temperature To1 captured in the previous second anti-freeze control and the maximum change amount ΔTwi1 indicates the correction value α to be added to the threshold value T1 in order to find the optimum threshold value T2' for the current second anti-freeze control.

[0044] Next, the indoor controller 20 adds the calculated correction value α to the threshold value T1 to set an optimal threshold value T2' (= T1 + α) for the second second anti-freeze control, and stores this in the memory 20m (S17). The relationship between the outdoor air temperature To and the threshold values ​​T1, T2, and T2' is shown in Figure 6. The larger the maximum change ΔTwi from the outdoor air temperature To during the previous second anti-freeze control, i.e., the greater the decrease in the return temperature Twi, the larger the correction value α. Furthermore, the lower the current outdoor air temperature To, the larger the correction value α.

[0045] If the outdoor air temperature To is less than the reference value Tos (YES in S18), the indoor controller 20 compares the return temperature Twi with the threshold value T2' (S19). If the return temperature Twi is equal to or greater than the threshold value T2' (NO in S19), the indoor controller 20 determines that there is no risk of the heat medium freezing and returns to the determination in S1 above.

[0046] If the return temperature Twi is lower than the threshold value T2' (YES in S19), the indoor controller 20 determines that there is a possibility of the heat medium freezing and drives the pump 8 (S20). By driving the pump 8, the heat medium in the heat medium pipes 6a, 6b, 6c circulates through the heat medium heat exchanger 3 and the user-side devices 9, preventing the heat medium from freezing (start of the second antifreeze control for the second time).

[0047] The indoor controller 20 stores the outside air temperature To when the pump 8 starts operating as "To2" in the memory 20m (S21), and detects the maximum downward change ΔTwi in the return temperature Twi within a certain time (= 10 seconds) from the start of operation of the pump 8 as "ΔTwi2" (NO in S22 and S23). After the certain time has elapsed (YES in S22), the indoor controller 20 stores (updates) the stored outside air temperature To2 and the detected maximum change ΔTwi2 in the memory 20m as threshold setting data (To2, ΔTwi2) for setting a new threshold T2' for the next second antifreeze control (S24).

[0048] Next, when the return temperature Twi rises to a value exceeding the threshold value T2' (T2' +, for example, 1°C as a hysteresis) (YES in S25), the indoor controller 20 stops the pump 8 (S26) and returns to the judgment in S1 above (end of the second anti-freeze control for the second time).

[0049] As described above, the new threshold value T2' is set based on the current outside air temperature To, the reference value Tos, and the threshold setting data (To1, ΔTwi1) obtained in the previous second anti-freeze control, so that the temperature drop that leads to the freezing of the heat medium can be properly detected even if the heat medium temperature sensor 12 is installed inside the housing of the heat source unit A. This makes it possible to reliably prevent the heat medium from freezing, improving the reliability of the anti-freeze control.

[0050] In addition, if the judgment in S18 above shows that the outdoor air temperature To is equal to or higher than the reference value Tos (YES in S18), the indoor controller 20 executes the above-mentioned first anti-freeze control based on a comparison between the return temperature Twi and the threshold value T1 (S3 to S6).

[0051] <Third Second Anti-Freeze Control> After the second second anti-freeze control is completed, the indoor controller 20 determines that the second anti-freeze control has already been performed because the execution flag f is "1" (YES in S1). Then, the indoor controller 20 multiplies the maximum downward change ΔTwi2 in the return temperature Twi due to the previous second anti-freeze control by the ratio of the difference between the current outside air temperature To3 and the reference value Tos ("To3 - Tos") to the difference between the outside air temperature To2 at the start of the previous second anti-freeze control and the reference value Tos ("To2 - Tos"), and calculates the result of this multiplication as a correction value α for setting an optimal threshold value T2' for the current (third) second anti-freeze control (S16). α = [(To3 - Tos) / (To2 - Tos)] × ΔTwi2

[0052] As shown in Figure 5, the linear line X2 extending from the intersection (Tos, ΔTwi0) of the reference value Tos and the change amount ΔTwi0 to the intersection (To2, ΔTwi2) of the outside air temperature To2 captured in the previous second anti-freezing control and the maximum change amount ΔTwi2 indicates that it is the correction value α to be added to the threshold value T1 in order to obtain the optimal threshold value T2' in the current second second anti-freezing control.

[0053] Next, the indoor controller 20 adds the calculated correction value α to the threshold value T1 to set an optimal threshold value T2' (= T1 + α) for the third second anti-freeze control, and stores this in memory 20m (S17). Then, if the outdoor air temperature To is less than the reference value Tos (YES in S18), the indoor controller 20 compares the return temperature Twi with the threshold value T2' (S19). If the return temperature Twi is equal to or greater than the threshold value T2' (NO in S19), the indoor controller 20 determines that there is no risk of the heat medium freezing, and returns to the judgment in S1 above.

[0054] If the return temperature Twi is lower than the threshold value T2' (YES in S19), the indoor controller 20 determines that there is a risk of the heat medium freezing and drives the pump 8 (S20). By driving the pump 8, the drop in the return temperature Twi is suppressed, and the heat medium is prevented from freezing (start of the third second antifreeze control).

[0055] The indoor controller 20 stores the outdoor air temperature To when the pump 8 starts operating as "To3" in the memory 20m (S21), and detects the maximum downward change ΔTwi in the return temperature Twi within a certain time (= 10 seconds) from the start of operation of the pump 8 as "ΔTwi3" (NO in S22 and S23). After the certain time has elapsed (YES in S22), the indoor controller 20 stores (updates) the stored outdoor air temperature To3 and the detected maximum change ΔTwi3 in the memory 20m as threshold setting data (To3, ΔTwi3) for setting the next threshold T2 for the second antifreeze control (S24).

[0056] Next, when the return temperature Twi rises to a value exceeding the threshold value T2' (T2' +, for example, 1°C) (YES in S25), the indoor controller 20 stops the pump 8 (S26) and returns to the judgment in S1 above (end of the third second anti-freeze control).

[0057] As described above, a new threshold value T2' is set based on the current outside air temperature To, the reference value Tos, and the threshold setting data (To2, ΔTwi2) captured in the previous second anti-freeze control. Therefore, even if the heat medium temperature sensor 12 is installed inside the housing of the heat source unit A, it is possible to properly capture the temperature drop that leads to the freezing of the heat medium.

[0058] <Fourth Second Anti-Freeze Control> After the third second anti-freeze control is completed, the indoor controller 20 determines that the second anti-freeze control has already been performed because the execution flag f is "1" (YES in S1). Based on this determination, the indoor controller 20 multiplies the maximum downward change ΔTwi3 in the return temperature Twi resulting from the previous second anti-freeze control by the ratio of the difference between the current outside air temperature To4 and the reference value Tos ("To4 - Tos") to the difference between the outside air temperature To3 at the start of the previous second anti-freeze control and the reference value Tos ("To3 - Tos"), and calculates the result of this multiplication as a correction value α for setting an optimal threshold value T2' for the current (fourth) second anti-freeze control (S16). α = [(To4 - Tos) / (To3 - Tos)] × ΔTwi3

[0059] As shown in Figure 5, the linear line X3 extending from the intersection (Tos, ΔTwi0) of the reference value Tos and the change amount ΔTwi0 to the intersection (To3, ΔTwi3) of the outside air temperature To3 captured in the previous second anti-freezing control and the maximum change amount ΔTwi3 indicates that this is the correction value α to be added to the threshold value T1 in order to obtain the optimal threshold value T2' in the current second second anti-freezing control.

[0060] Next, the indoor controller 20 adds the calculated correction value α to the threshold value T1 to set an optimal threshold value T2' (= T1 + α) for the fourth second anti-freeze control, and stores this in memory 20m (S17). Then, if the outdoor air temperature To is less than the reference value Tos (YES in S18), the indoor controller 20 compares the return temperature Twi with the threshold value T2' (S19). If the return temperature Twi is equal to or greater than the threshold value T2' (NO in S19), the indoor controller 20 determines that there is no risk of the heat medium freezing, and returns to the judgment in S1 above.

[0061] If the return temperature Twi is less than the threshold value T2' (YES in S19), the indoor controller 20 determines that there is a risk of the heat medium freezing and drives the pump 8 (S20). By driving the pump 8, the decrease in the return temperature Twi is suppressed, and the heat medium is prevented from freezing (start of the fourth second antifreeze control).

[0062] The indoor controller 20 stores the outdoor air temperature To when the pump 8 starts operating as "To4" in the memory 20m (S21), and detects the maximum downward change ΔTwi in the return temperature Twi during a certain period of time (10 seconds) from the start of operation of the pump 8 as "ΔTwi4" (NO in S22 and S23). After the certain period of time has elapsed (YES in S22), the indoor controller 20 stores (updates) the stored outdoor air temperature To4 and the detected maximum change ΔTwi4 in the memory 20m as threshold setting data (To4, ΔTwi4) for setting the next threshold T2 for the second antifreeze control (S24).

[0063] Next, when the return temperature Twi rises to a value exceeding the threshold value T2' (T2' +, for example, 1°C) (YES in S25), the indoor controller 20 stops the pump 8 (S26) and returns to the judgment in S1 above (end of the fourth second anti-freeze control).

[0064] <Fifth and subsequent second anti-freeze control> In the fifth and subsequent second anti-freeze control, the indoor controller 20 executes the same control as the fourth second anti-freeze control. Then, in conjunction with the next start and stop of operation of the heat source unit A, the indoor controller 20 executes the first anti-freeze control and the first and second anti-freeze controls.

[0065] As described above, in the second and subsequent second anti-freeze control operations, the threshold value T2' appropriate for each second anti-freeze control is sequentially set using the maximum change ΔTwi, which is data obtained from the most recent return temperature Twi, thereby minimizing the operation time of the pump 8 required to prevent the heat transfer medium from freezing. In other words, unnecessary operation of the pump 8 is suppressed, contributing to energy conservation. This unnecessary operation refers to operation of the pump 8 in the region between the threshold value T2 and the threshold value T2' shown in FIG. 6. In other words, if a fixed value of only the threshold value T2 (e.g., 7°C) is set as the criterion for starting operation of the pump 8, the pump 8 will operate even in the above region. On the other hand, by using the new threshold value T2', the pump 8 will not operate in this region. To give a specific example, when the threshold value T2 is used, the pump 8 will operate when the outside air temperature T is -10°C and the return temperature Twi is 6°C. In contrast, when the threshold value T2' is used, the pump 8 will not operate even when the outside air temperature T is -10°C and the return temperature Twi is 6°C.

[0066] <Modification 1> In the above embodiment, the return temperature Twi is used for the anti-freeze control. However, the supply temperature Two or the utilization temperature Twh, which have substantially the same value as the return temperature Twi while the pump 8 is stopped, may be used for the anti-freeze control instead of the return temperature Twi. That is, the anti-freeze control can be performed in substantially the same way even if the "return temperature Twi" used for various determinations in the flowcharts of Figures 2 and 3 is changed to the "supply temperature Two" or the "utilization temperature Twh." Note that when the "return temperature Twi" is changed to the "supply temperature Two" or the "utilization temperature Twh," it takes time for the heat medium present in the portion of the heat medium pipes 6a, 6b, 6c exposed to the outside air to flow to the installation position of the heat medium temperature sensor after the pump 8 starts operating. Therefore, the fixed time for monitoring the change amount used in steps S10 and S22 of Figures 2 and 3 must be extended to a time longer than 10 seconds (for example, 20 seconds). Furthermore, when the "outlet temperature Two" or the "use temperature Twh" is used instead of the "return temperature Twi", the temperature of the heat medium is detected after passing through the heat medium heat exchanger 3. Therefore, the heat medium present in the portion of the heat medium pipes 6a, 6b, 6c exposed to the outside air passes through the heat medium heat exchanger 3, and temperature is exchanged within the heat medium heat exchanger 3, so the accuracy of detecting the temperature of the heat medium held in the pipes is slightly lower than that of the return temperature Twi.

[0067] <Modification 2> In the above embodiment, the heat medium temperature sensor 21 that detects the delivery temperature Two is attached to the heat medium pipe 6b in the indoor unit B. However, instead, a heat medium temperature sensor 21′ shown by the dashed line in FIG. 1 may be attached to the heat medium pipe 6b located on the outlet side of the heat medium flow path 3b of the heat medium heat exchanger 3 in the heat source unit A.

[0068] <Modification 3> In the above embodiment, the following formula (1) is used to calculate the correction value α, but the following formula (2) may be used to calculate the correction value α by multiplying the right-hand side of the following formula (1) by a coefficient β (approximately 0.5 to 1.5): α = [(To(n) - Tos) / (To(n-1) - Tos)] × ΔTwi(n) (1) α = β × [(To(n) - Tos) / (To(n-1) - Tos)] × ΔTwi(n) (2)

[0069] <Modification 4> In the above embodiment, an indoor unit B is provided between the heat source unit A and the user-side device 9, and the indoor unit B houses the electric heater 7, pump 8, indoor controller 20, heat medium temperature sensors 21 and 22, and operating device 23. However, as shown in FIG. 7 , the indoor unit B may be omitted, and the electric heater 7, pump 8, and heat medium temperature sensors 21 and 22 may be housed in the heat source unit A, with the control functions of the indoor controller 20 (first to fourth control sections 20a to 20d) being provided in the outdoor controller 10. While the operating device 23 can also be housed in the heat source unit A, it is preferable to install it indoors for ease of operation by the user. In this configuration, the heat medium piping 6a, which serves as the return pipe for the heat medium, is the same as in the embodiment of FIG. 1 , but the heat medium piping 6c, which serves as the forward pipe for flowing the heat medium from the heat source unit A to the user-side device 9, is connected directly from the heat source unit A to the user-side device 9.

[0070] Furthermore, the above-described embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments and modifications can be embodied in various other forms, and various omissions, rewritings, and modifications can be made without departing from the spirit of the invention. These embodiments and modifications are included within the spirit of the invention, and are also included in the scope of the inventions described in the claims and their equivalents.

[0071] A...heat source machine, B...indoor unit, 1...compressor, 3...heat medium heat exchanger (water heat exchanger), 5...outdoor heat exchanger, 6a, 6b, 6c...heat medium piping, 8...pump, 9...use side equipment, 10...outdoor controller, 11...outdoor air temperature sensor, 12...heat medium temperature sensor, 20...indoor controller, 20a...first control section, 20b...second control section, 20c...third control section, 20d...fourth control section, 21, 22...heat medium temperature sensors.

Claims

1. A heat medium circulation device that circulates a heat medium between an outdoor heat source unit and indoor user equipment using piping and a pump, comprising: an outdoor air temperature sensor that detects the temperature of the outdoor air; a heat medium temperature sensor that detects the temperature of the heat medium; and a controller that executes anti-freeze control to drive the pump when the temperature detected by the heat medium temperature sensor falls below a threshold while the heat source unit is stopped, and that changes the threshold in accordance with the temperature detected by the outdoor air temperature sensor.

2. The heat medium circulating device according to claim 1, wherein the controller changes the threshold value to a higher value when the temperature detected by the outside air temperature sensor drops.

3. The heat medium circulating device according to claim 1, wherein the heat medium temperature sensor is attached to a portion of the piping that fits within the heat source unit or to a portion on the indoor side, and the controller sets the threshold to a first threshold when the temperature detected by the outdoor air temperature sensor is equal to or higher than a predetermined reference value, and sets the threshold to a second threshold higher than the first threshold when the temperature detected by the outdoor air temperature sensor is less than the reference value.

4. The heat medium circulation device of claim 3, wherein the controller executes a first anti-freeze control to drive the pump when the detected temperature of the heat medium temperature sensor falls below the first threshold value while the heat source machine is stopped and the detected temperature of the heat medium temperature sensor is equal to or higher than the reference value, and executes a second anti-freeze control to drive the pump when the detected temperature of the heat medium temperature sensor falls below the second threshold value while the heat source machine is stopped and the detected temperature of the heat medium temperature sensor is below the reference value.

5. The heat medium circulating device according to claim 4, wherein the controller stops the pump when the temperature detected by the heat medium temperature sensor exceeds the first threshold value after the pump starts to be driven by executing the first anti-freeze control, and stops the pump when the temperature detected by the heat medium temperature sensor exceeds the second threshold value after the pump starts to be driven by executing the second anti-freeze control.

6. The heat medium circulating device according to claim 4 or claim 5, wherein the controller stores the detected temperature of the outside air temperature sensor when the pump starts to operate and the maximum amount of downward change in the detected temperature of the heat medium temperature sensor within a certain time from the start of the pump operation as threshold setting data for setting the second threshold of the next second anti-freeze control, for the first execution of the second anti-freeze control and for the second or subsequent executions of the second anti-freeze control after the heat source machine is stopped, and sets a new threshold suitable for each second anti-freeze control based on the current detected temperature of the outside air temperature sensor and the threshold setting data for each execution of the second anti-freeze control after the heat source machine is stopped.

7. The heat medium circulating device according to claim 6, wherein the controller sets the new threshold value to a higher value as the value of the threshold setting data increases.

8. The heat medium circulating device according to claim 1, wherein the heat source machine includes a heat pump type refrigeration cycle in which refrigerant discharged from a compressor is passed through a heat medium heat exchanger, a pressure reducer and an outdoor heat exchanger and returned to the compressor, and heat pumped up from outside air by operation of the heat pump type refrigeration cycle is provided to the heat medium via the heat medium heat exchanger; the pump is contained in an indoor unit placed in the room, and sends the heat medium that has passed through the heat medium heat exchanger to the user side equipment; the heat medium temperature sensor is attached to a portion of the piping that is contained within the heat source machine or a portion on the indoor side, and detects the temperature of the heat medium flowing into the heat medium heat exchanger or the temperature of the heat medium flowing to the user side equipment; and the controller is an indoor controller that is contained in the indoor unit and controls the pump, and an outdoor controller that is contained in the heat source machine and controls the compressor in response to instructions from the indoor controller.

9. The heat medium circulating device according to claim 1, wherein the heat source unit includes a heat pump type refrigeration cycle in which refrigerant discharged from a compressor is passed through a heat medium heat exchanger, a pressure reducer and an outdoor heat exchanger and returned to the compressor, and heat pumped up by operation of the heat pump type refrigeration cycle is provided to the heat medium via the heat medium heat exchanger; the pump is housed in the heat source unit and sends the heat medium that has passed through the heat medium heat exchanger to the user side device; the heat medium temperature sensor is attached to a portion of the piping that is housed in the heat source unit or a portion on the indoor side, and detects the temperature of the heat medium flowing into the heat medium heat exchanger or the temperature of the heat medium flowing out of the heat medium heat exchanger; and the controller is an outdoor controller that is housed in the heat source unit and controls the compressor and the pump.

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