Working medium heat exchange system and regulation method thereof

Abstract

The application provides a working medium heat exchange system and a regulating method thereof. The system comprises a gas storage tank, a liquid storage tank and a heat exchanger. The heat exchanger has a cold fluid area and a hot fluid area. The hot fluid area comprises a main flow path heat exchange area and a bypass heat exchange area which are arranged independently. The gas storage tank, the main flow path heat exchange area and the liquid storage tank are connected to form a main flow path. The gas storage tank, the bypass heat exchange area and the liquid storage tank are connected to form a bypass flow path. The hot fluid flows through the main flow path heat exchange area and the bypass heat exchange area, and exchanges heat with the cold fluid flowing through the cold fluid area. By adjusting the flow rate of the main flow path or the bypass flow path, the total flow rate of the hot fluid can be adjusted, so that the heat balance between the cold fluid and the hot fluid in the heat exchanger is maintained, and supercooling or overheating is avoided. In addition, according to the regulating method of the application, the flow rate of the hot fluid can be regulated by an electric valve or a variable frequency booster pump according to the rapid fluctuation or slow fluctuation of the flow rate of the cold fluid, so that the heat balance in the heat exchanger can be realized under various working conditions.

Description

Technical Field

[0001] This invention relates to the field of cryogenic cold energy power generation system technology, specifically to a working fluid heat exchange system and its control method. Background Technology

[0002] LNG (liquefied natural gas) cold energy power generation systems are a highly efficient energy utilization method. Their technical principle is primarily based on the large amount of cold energy released during the vaporization of LNG, cooling the working fluid to a temperature far below ambient level, thus creating a power cycle with an even lower cold-end temperature. In traditional power generation cycles, such as the Rankine cycle, the highest temperature is the gaseous temperature of water vapor, and the lowest temperature is approximately the ambient temperature after the water vapor condenses in the condenser. These two temperature limits restrict the range of work done by the working medium. The calculation of cycle efficiency follows Carnot's theorem; efficiency improvements are constrained by the highest cycle temperature and the condensation temperature. Therefore, introducing LNG cold energy can significantly increase the temperature difference between the hot and cold ends of the working fluid, improving power generation and operating efficiency. In this process, LNG itself absorbs heat and evaporates, gaining energy as its temperature rises above 0 degrees Celsius, before being introduced into the natural gas pipeline network.

[0003] However, due to the low temperature of LNG, typically around -162 degrees Celsius, current circulating media for LNG-powered cryogenic power generation primarily include organic media, carbon dioxide, and ammonia. Since some of these media have a triple point temperature above -100 degrees Celsius, during the condensation process within the heat exchanger, sudden fluctuations in LNG flow can easily cause supercooling, leading to the media temperature dropping below the triple point and directly sublimating. Sublimated media can clog heat exchanger channels, causing pressure runaway and serious safety issues. Therefore, rapidly and in real-time controlling the heat exchanger's operating conditions to eliminate this safety hazard is a major challenge in the construction of cryogenic cryogenic power generation systems. Summary of the Invention

[0004] To address the above problems, this invention provides a working fluid heat exchange system and its control method.

[0005] This invention provides a working fluid heat exchange system, comprising: a gas storage tank, a liquid storage tank, and a heat exchanger. The heat exchanger has a cold fluid zone and a hot fluid zone. Cold fluid flows inside the cold fluid zone, and hot fluid flows inside the hot fluid zone. The cold fluid and hot fluid exchange heat with each other. After flowing through the cold fluid zone, the cold fluid is heated and vaporized. The hot fluid flows out of the gas storage tank in gaseous form, and after passing through the hot fluid zone, it is cooled into a liquid and flows into the liquid storage tank in liquid form. The hot fluid zone includes a main flow heat exchange zone and a bypass heat exchange zone that are independently arranged. The gas storage tank, the main flow heat exchange zone, and the liquid storage tank are connected in sequence to form the main flow zone, and the gas storage tank, the bypass heat exchange zone, and the liquid storage tank are connected in sequence to form the bypass flow zone.

[0006] According to the above technical solution, the hot fluid flows through the main flow heat exchange zone and the bypass heat exchange zone, which are set independently, and exchanges heat with the cold fluid flowing through the cold fluid zone. By adjusting the flow rate of the main flow or bypass flow, the total flow rate of the hot fluid can be adjusted, thereby maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger and avoiding overcooling or overheating.

[0007] Optionally, the cold fluid zone is connected to an external cold source and an underground pipe network. The external cold source provides cold fluid, which enters the cold fluid zone in liquid form, absorbs heat to rise and vaporizes, and then flows out of the cold fluid zone in gaseous form before flowing into the underground pipe network.

[0008] Optionally, a flow sensor is installed between the external cold source and the cold fluid zone to monitor the flow rate of the cold fluid in real time.

[0009] According to the above technical solution, by monitoring the flow rate of the cold fluid flowing into the cold fluid zone through a flow sensor, it is possible to adjust the flow rate of the hot fluid accordingly based on the flow rate of the cold fluid, thereby maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger.

[0010] Optionally, an electrically controlled valve is also provided between the bypass heat exchange zone and the liquid storage tank. The electrically controlled valve is communicatively connected to the flow sensor. The electrically controlled valve adjusts its opening degree according to the monitoring data of the flow sensor to regulate the flow rate of the hot fluid in the bypass flow path.

[0011] According to the above technical solution, by adjusting the opening of the electric valve based on the cold fluid flow data obtained from the flow sensor, the flow rate of the hot fluid in the bypass flow path can be quickly adjusted, thereby rapidly adjusting the total flow rate of the hot fluid flowing through the hot fluid zone and maintaining the heat balance between the cold and hot fluids in the heat exchanger.

[0012] Optionally, a variable frequency booster pump is also installed between the main flow heat exchange zone and the liquid storage tank. The variable frequency booster pump is connected to the flow sensor and adjusts the pump frequency according to the monitoring data of the flow sensor to regulate the flow rate of the hot fluid in the main flow.

[0013] According to the above technical solution, by adjusting the pump frequency of the variable frequency booster pump based on the cold fluid flow data obtained from the flow sensor, the flow rate of the hot fluid in the main flow path can be adjusted, thereby regulating the total flow rate of the hot fluid flowing through the hot fluid zone and maintaining the heat balance between the cold and hot fluids in the heat exchanger.

[0014] Optionally, the temperature of the cold fluid flowing in the cold fluid region is lower than the triple point temperature of the hot fluid flowing in the hot fluid region.

[0015] Optionally, the heat fluid is an organic working fluid, carbon dioxide, or ammonia.

[0016] The present invention also provides a control method for the above-mentioned working fluid heat exchange system, comprising the following steps: a cold fluid flow monitoring step, wherein the flow rate of the cold fluid entering the cold fluid zone is monitored in real time by a flow sensor;

[0017] The hot fluid flow rate regulation step involves controlling the flow rate of the hot fluid by adjusting the electronically controlled valves or variable frequency booster pumps based on changes in the flow rate of the cold fluid.

[0018] According to the above technical solution, by monitoring the flow rate of the cold fluid entering the cold fluid zone and adjusting the flow rate of the hot fluid flowing through the hot fluid zone in real time according to the flow rate of the cold fluid, the heat balance between the cold fluid and the hot fluid in the heat exchanger can be maintained, and the situation of overcooling or overheating can be avoided.

[0019] In the control method provided by the present invention, optionally, in the hot fluid flow rate control step, when the flow rate of the cold fluid fluctuates rapidly, the hot fluid flow rate in the bypass flow path is adjusted by controlling the electronically controlled valve, including the following sub-steps:

[0020] When the flow rate of the cold fluid is stable, the electrically controlled valve maintains the preset opening, keeps the bypass flow area constant, and keeps the flow rate of the hot fluid in the bypass flow path constant.

[0021] When the flow rate of the cold fluid decreases rapidly, the opening degree of the electrically controlled valve decreases, the bypass flow area decreases, and the flow rate of the hot fluid in the bypass flow path decreases.

[0022] When the flow rate of cold fluid increases rapidly, the opening degree of the electrically controlled valve increases, the bypass flow area increases, and the flow rate of hot fluid in the bypass flow path increases.

[0023] According to the above technical solution, when the flow rate of the cold fluid entering the cold fluid zone fluctuates rapidly, the flow rate of the hot fluid in the bypass flow path can be quickly adjusted by adjusting the opening of the electric valve, thereby quickly adjusting the total flow rate of the hot fluid flowing through the hot fluid zone and maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger.

[0024] In the control method provided by the present invention, optionally, in the hot fluid flow rate control step, when the flow rate of the cold fluid fluctuates slowly, the hot fluid flow rate in the main flow path is adjusted by controlling the variable frequency booster pump, including the following sub-steps:

[0025] When the flow rate of the cold fluid is stable, the variable frequency booster pump maintains the preset pump frequency to keep the main flow rate constant;

[0026] When the flow rate of the cold fluid decreases slowly, the pump frequency of the variable frequency booster pump decreases, and the flow rate of the hot fluid in the main flow path decreases.

[0027] When the flow rate of the cold fluid increases slowly, the pump frequency of the variable frequency booster pump increases, and the flow rate of the hot fluid in the main flow path increases.

[0028] According to the above technical solution, when the flow rate of the cold fluid entering the cold fluid zone fluctuates slowly, the flow rate of the hot fluid in the main flow path can be adjusted by adjusting the pump frequency of the variable frequency booster pump. This allows the flow rate of the hot fluid flowing through the main flow path to be adjusted slowly in accordance with the flow rate of the cold fluid, thereby adjusting the total flow rate of the hot fluid flowing through the hot fluid zone and maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the working fluid heat exchange system according to the first embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the working fluid heat exchange system according to the second embodiment of the present invention.

[0031] Attached reference numerals: 1. Liquid storage tank; 2. Heat exchanger; 21. Main flow heat exchange zone; 22. Cold fluid zone; 23. Bypass heat exchange zone; 3. Gas storage tank; 4. Flow sensor; 5. Electrically controlled valve; 6. Variable frequency booster pump. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] <First Implementation Method>

[0034] Figure 1 This is a schematic diagram of the working fluid heat exchange system according to the first embodiment of the present invention.

[0035] like Figure 1 As shown, the working fluid heat exchange system of this embodiment includes a liquid storage tank 1, a heat exchanger 2, and a gas storage tank 3.

[0036] The heat exchanger 2 has a cold fluid zone 22 and a hot fluid zone. The hot fluid zone includes a main flow heat exchange zone 21 and a bypass heat exchange zone 23, which are set up independently.

[0037] Cold fluid flows inside the cold fluid zone 22, while hot fluid flows inside both the main flow heat exchange zone 21 and the bypass heat exchange zone 23. The hot fluid in the main flow heat exchange zone 21 and the bypass heat exchange zone 23 can exchange heat with the cold fluid in the cold fluid zone 22 at the same time.

[0038] Specifically, the main flow heat exchange zone 21 and the bypass heat exchange zone 23 are not connected to each other and have their own independent inlets and outlets. The gas storage tank 3, the main flow heat exchange zone 21 and the liquid storage tank 1 are connected in sequence to form the main flow, and the gas storage tank 3, the bypass heat exchange zone 23 and the liquid storage tank 1 are connected in sequence to form the bypass flow.

[0039] The heat transfer fluid is an organic working medium (organic compound), carbon dioxide, or ammonia. Gas tank 3 stores the gaseous heat transfer fluid, while liquid tank 1 stores the liquid heat transfer fluid. The heat transfer fluid flows out of gas tank 3 in gaseous form, is cooled into a liquid after heat exchange in the heat transfer fluid zone, and then flows into the liquid tank in liquid form.

[0040] The cold fluid zone 22 is connected to an external cold source (not shown in the figure) and an underground pipeline network (not shown in the figure). The external cold source provides cold fluid, such as LNG (liquefied natural gas). The cold fluid enters the cold fluid zone 22 in liquid form, is heated and vaporized after absorbing heat, and flows out of the cold fluid zone 22 in gaseous form before flowing into the underground pipeline network.

[0041] The temperature of the cold fluid flowing in the cold fluid region 22 is lower than the triple point temperature of the hot fluid flowing in the hot fluid region.

[0042] A flow sensor 4 is installed between the external cold source and the cold fluid zone 22 to monitor the flow rate of the cold fluid in real time.

[0043] An electrically controlled valve 5 is also provided between the bypass heat exchange zone 23 and the liquid storage tank 1. The electrically controlled valve 5 is connected to the flow sensor 4. The electrically controlled valve 5 adjusts its opening degree according to the monitoring data of the flow sensor 4 to regulate the flow rate of the hot fluid in the bypass flow path.

[0044] Specifically, the monitoring data of the flow sensor 4 is fed back in the form of an electrical signal. The electrically controlled valve 5 can receive the electrical signal in real time and adjust its own opening, thereby controlling the bypass flow area to regulate the flow rate of the hot fluid in the bypass flow path.

[0045] Meanwhile, the internal pressure of the gas storage tank 3 is greater than that of the liquid storage tank 1. The pressure difference between the gas storage tank 3 and the liquid storage tank 1 can drive the hot fluid from the gas storage tank 3 through the hot fluid zone into the liquid storage tank 1. When the opening of the electrically controlled valve 5 increases, the flow rate in the bypass flow path can increase rapidly due to the pressure difference between the gas storage tank 3 and the liquid storage tank 1, thus quickly adjusting the flow rate of the hot fluid.

[0046] In conventional heat exchangers, the lack of bypass and additional heat exchange area means that when the flow rate of the fluid on one side fluctuates, it is impossible to adjust the flow rate of the fluid on the other side in real time. Therefore, when cooling conditions are involved near the triple point, there are significant safety hazards, increasing the risk of system operation and the difficulty of control.

[0047] In this embodiment, by setting up a bypass flow path and an additional bypass heat exchange zone 23, and supplementing it with a flow sensor 4 and an electrically controlled valve 5 for flow regulation, the flow rate of the hot fluid can be quickly adjusted according to the change in the flow rate of the cold fluid, so as to achieve real-time tracking of the flow rate of the hot fluid, maintain the stability of the heat exchange temperature at all times, control the temperature to not deviate, and effectively eliminate potential safety hazards.

[0048] Furthermore, the control method of the working fluid heat exchange system in this embodiment includes the following steps:

[0049] The cold fluid flow monitoring step involves using flow sensor 4 to monitor the flow rate of the cold fluid entering the cold fluid zone 22 in real time.

[0050] The hot fluid flow rate regulation step involves controlling the flow rate of the hot fluid by adjusting the flow rate of the cold fluid using the electrically controlled valve 5.

[0051] In this embodiment, the hot fluid flow rate regulation step involves adjusting the hot fluid flow rate in the bypass path by controlling the electrically controlled valve 5 when the cold fluid flow rate fluctuates rapidly. This includes the following sub-steps:

[0052] When the flow rate of the cold fluid supplied by the external cold source into the cold fluid zone 22 is stable (i.e. the flow rate does not fluctuate or fluctuates very little), the electric control valve 5 is not triggered to operate. The electric control valve 5 maintains the preset opening, keeps the bypass flow area unchanged, and keeps the flow rate of the hot fluid in the bypass flow path unchanged.

[0053] Furthermore, under the condition that the flow rate of the cold fluid entering the cold fluid zone 22 is stable, and the flow rate of the hot fluid flowing through the main flow heat exchange zone 21 in the main flow is also stable, the bypass heat exchange zone 23 can be kept at a low flow heat exchange load or the flow can be directly closed by controlling the opening of the electrically controlled valve 5.

[0054] When the flow rate of cold fluid entering the cold fluid zone 22 decreases rapidly, the flow sensor 4 outputs an electrical signal, triggering the electric control valve 5 to operate. The opening degree of the electric control valve 5 decreases, the bypass flow area decreases, and the flow rate of hot fluid in the bypass flow path decreases.

[0055] When the flow rate of cold fluid entering the cold fluid zone 22 increases rapidly, the flow sensor 4 outputs an electrical signal, triggering the electric control valve 5 to operate. The opening degree of the electric control valve 5 increases, the bypass flow area increases, and the flow rate of hot fluid in the bypass flow path increases.

[0056] In this embodiment, rapid fluctuation is defined as a fluctuation of more than ±5% per second in the cold fluid flow rate. To address the rapid fluctuation in the cold fluid flow rate entering the cold fluid zone 22, the flow rate of the bypass path can be quickly adjusted by changing the opening of the electrically controlled valve 5. This allows for a rapid increase or decrease in the bypass flow rate, thereby controlling the total flow rate of the hot fluid in real time, maintaining the heat balance between the cold and hot fluids in the heat exchanger 2, and preventing overcooling or overheating.

[0057] <Second Implementation Method>

[0058] Figure 2 This is a schematic diagram of the working fluid heat exchange system according to the second embodiment of the present invention.

[0059] like Figure 2 As shown, in this embodiment, the working fluid heat exchange system, based on the first embodiment, is further equipped with a variable frequency booster pump 6 between the main flow heat exchange zone and the liquid storage tank 1.

[0060] The variable frequency booster pump 6 is communicatively connected to the flow sensor 4. The variable frequency booster pump 6 adjusts its pump frequency based on the monitoring data from the flow sensor 4 to regulate the flow rate of the hot fluid in the main flow path. The monitoring data from the flow sensor 4 is fed back in the form of an electrical signal. The variable frequency booster pump 6 can receive the electrical signal in real time and adjust its own pump frequency, thereby controlling the flow rate of the hot fluid in the main flow path.

[0061] Specifically, when the flow rate of the cold fluid changes slowly but the trend is obvious, it is no longer suitable to adjust the flow rate by quickly switching in through a bypass. By using the variable frequency booster pump 6 to control the pump frequency, the flow rate can change slowly with the adjustment of the pump frequency, thereby achieving the balance of heat under the state of slow flow rate change and maintaining the stability of the overall system parameters.

[0062] Furthermore, the control method of the working fluid heat exchange system in this embodiment includes the following steps:

[0063] The cold fluid flow monitoring step involves monitoring the flow rate of the cold fluid in real time using flow sensor 4.

[0064] The hot fluid flow rate regulation step involves controlling the flow rate of the hot fluid by adjusting the frequency converter pump based on the changes in the flow rate of the cold fluid.

[0065] In this embodiment, the hot fluid flow rate regulation step involves adjusting the hot fluid flow rate in the main flow path by controlling the variable frequency booster pump 6 when the cold fluid flow rate fluctuates slowly. This includes the following sub-steps:

[0066] When the flow rate of the cold fluid supplied by the external cold source into the cold fluid zone 22 is stable (i.e. the flow rate does not fluctuate or fluctuates very little), the variable frequency booster pump 6 is not triggered to operate. The variable frequency booster pump 6 maintains the preset pump frequency and keeps the main flow rate unchanged.

[0067] When the flow rate of cold fluid entering the cold fluid zone 22 slowly decreases, the flow sensor 4 outputs an electrical signal, triggering the variable frequency booster pump 6 to operate. The pump frequency of the variable frequency booster pump 6 decreases, and the flow rate of hot fluid in the main flow path decreases.

[0068] When the flow rate of cold fluid entering the cold fluid zone 22 slowly increases, the flow sensor 4 outputs an electrical signal, triggering the variable frequency booster pump 6 to operate. The pump frequency of the variable frequency booster pump 6 increases, and the flow rate of hot fluid in the main flow path increases.

[0069] In this embodiment, slow fluctuation is defined as a fluctuation of less than ±5% per second in the cold fluid flow rate. To address the slow fluctuation in the cold fluid flow rate entering the cold fluid zone 22, the pump frequency of the variable frequency booster pump 6 can be adjusted to slowly regulate the hot fluid flow rate in the main flow path, thereby controlling the total hot fluid flow rate in real time, maintaining the heat balance between the cold and hot fluids in the heat exchanger 2, and preventing overcooling or overheating.

[0070] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A working fluid heat exchange system, characterized in that, include: The system comprises a gas storage tank, a liquid storage tank, and a heat exchanger, wherein the heat exchanger has a cold fluid zone and a hot fluid zone. The cold fluid zone contains a cold fluid, and the hot fluid zone contains a hot fluid. The cold fluid and the hot fluid exchange heat with each other. The cold fluid heats up and vaporizes after flowing through the cold fluid zone, while the hot fluid, in gaseous form, flows out through the gas storage tank. After passing through the hot fluid zone, it is cooled into a liquid and flows into the liquid storage tank in liquid form. The hot fluid zone includes a main flow heat exchange zone and a bypass heat exchange zone that are independently set up. The gas storage tank, the main flow heat exchange zone and the liquid storage tank are connected in sequence to form the main flow, and the gas storage tank, the bypass heat exchange zone and the liquid storage tank are connected in sequence to form the bypass flow path.

2. The working fluid heat exchange system according to claim 1, characterized in that, The cold fluid zone is connected to an external cold source and an underground pipe network. The external cold source provides the cold fluid, which enters the cold fluid zone in liquid form, absorbs heat to increase temperature and vaporizes, and then flows out of the cold fluid zone in gaseous form before flowing into the underground pipe network.

3. The working fluid heat exchange system according to claim 2, characterized in that, A flow sensor is installed between the external cold source and the cold fluid zone to monitor the flow rate of the cold fluid in real time.

4. The working fluid heat exchange system according to claim 3, characterized in that, An electrically controlled valve is also provided between the bypass heat exchange zone and the liquid storage tank. The electrically controlled valve is communicatively connected to the flow sensor. The electrically controlled valve adjusts its opening degree according to the monitoring data of the flow sensor to regulate the flow rate of the hot fluid in the bypass flow path.

5. The working fluid heat exchange system according to claim 3, characterized in that, A variable frequency booster pump is also provided between the main flow heat exchange zone and the liquid storage tank. The variable frequency booster pump is communicatively connected to the flow sensor. The variable frequency booster pump adjusts the pump frequency according to the monitoring data of the flow sensor to regulate the flow rate of the hot fluid in the main flow.

6. The working fluid heat exchange system according to claim 1, characterized in that, The temperature of the cold fluid flowing in the cold fluid zone is lower than the triple point temperature of the hot fluid flowing in the hot fluid zone.

7. The working fluid heat exchange system according to claim 1, characterized in that, The heat fluid is an organic working fluid, carbon dioxide, or ammonia.

8. A control method, applied to the working fluid heat exchange system as described in claim 4 or 5, characterized in that, Includes the following steps: The cold fluid flow monitoring step involves monitoring the flow rate of the cold fluid entering the cold fluid zone in real time using the flow sensor. The hot fluid flow rate regulation step involves regulating the flow rate of the hot fluid by controlling an electronically controlled valve or a variable frequency booster pump based on the flow rate changes of the cold fluid.

9. The control method according to claim 8, characterized in that, In the hot fluid flow rate regulation step, when the flow rate of the cold fluid fluctuates rapidly, the hot fluid flow rate in the bypass flow path is adjusted by controlling the electronically controlled valve, including the following sub-steps: When the flow rate of the cold fluid is stable, the electrically controlled valve maintains a preset opening, keeps the bypass flow area constant, and keeps the flow rate of the hot fluid in the bypass flow path constant. When the flow rate of the cold fluid decreases rapidly, the opening degree of the electrically controlled valve decreases, the bypass flow area decreases, and the flow rate of the hot fluid in the bypass flow path decreases. When the flow rate of the cold fluid increases rapidly, the opening degree of the electrically controlled valve increases, the bypass flow area increases, and the flow rate of the hot fluid in the bypass flow path increases.

10. The control method according to claim 8, characterized in that, In the hot fluid flow rate regulation step, when the flow rate of the cold fluid fluctuates slowly, the hot fluid flow rate in the main flow path is adjusted by controlling the variable frequency booster pump, including the following sub-steps: When the flow rate of the cold fluid is stable, the variable frequency booster pump maintains a preset pump frequency to keep the main flow rate constant. When the flow rate of the cold fluid decreases slowly, the pump frequency of the variable frequency booster pump decreases, and the flow rate of the hot fluid in the main flow path decreases. As the flow rate of the cold fluid increases slowly, the pump frequency of the variable frequency booster pump increases, and the flow rate of the hot fluid in the main flow path increases.

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