Low-temperature cooling control method for pure water medium

Abstract

The present application relates to the field of refrigeration technology, and particularly relates to a low-temperature cooling control method of pure water medium, which comprises the following steps: S1, starting a cooling water circulation loop; S2, simultaneously starting a primary refrigeration water circulation driven by an inner circulation pump and a secondary refrigeration water circulation driven by an outer circulation pump, so that the pure water medium is stored in an outer circulation water storage tank after being refrigerated in an evaporator, and then flows back to an inner circulation water storage tank after terminal heat exchange; S3, after the cooling pump, the inner circulation pump and the outer circulation pump are all started, starting a compressor; S4, when the system is shut down, the system is stopped in reverse order. In operation, the frequency conversion compressor is controlled based on the temperature of the outer circulation water storage tank, and the evaporator anti-freezing protection logic is integrated. Through the start-stop sequence and the secondary circulation control based on the high / low liquid level water tank, the present application realizes stable output of low-temperature water. The food safety hidden danger caused by medium leakage is completely eliminated, the system energy efficiency is significantly improved, the operation and maintenance cost is reduced, and the operation safety under low-temperature working condition is ensured.

Description

Technical Field

[0001] This invention relates to the field of refrigeration technology, and in particular to a low-temperature cooling control method for pure water media. Background Technology

[0002] In the food industry, where hygiene and safety requirements are stringent, many production processes necessitate maintaining the cooling medium stably within a low-temperature range of 2.5°C to 7°C. Currently, the conventional low-temperature cooling solution uses antifreeze aqueous solutions such as ethylene glycol or glycerol as the cooling medium. This solution utilizes the low freezing point of the medium, cooling it through a chiller unit before providing cooling to the production equipment or end-use environment via a plate heat exchanger. However, the aforementioned existing technology has the following drawbacks in practical applications: (1) Chemical media such as ethylene glycol and glycerol have certain toxicity or irritant properties. During long-term operation, equipment such as plate heat exchangers are at risk of leakage due to corrosion, vibration, or aging of seals. Once the media leaks and contaminates the product, it will pose a serious threat to food safety, which is unacceptable to the food industry.

[0003] (2) To ensure heat exchange efficiency, the outlet water temperature of the medium in existing technologies usually needs to be more than 3°C lower than the target required temperature. For example, to obtain a process cooling effect of 5°C, the unit needs to cool the medium to 2°C or even lower. This excessively low set temperature forces the compressor to operate in the inefficient zone of high pressure ratio and low evaporation temperature for a long time. According to the refrigeration principle, the system energy efficiency can be improved by about 3% for every 1°C increase in the evaporation temperature of the chiller unit, while the excessively low set temperature results in the overall system energy efficiency generally being less than 1.8, resulting in serious waste of electrical energy.

[0004] (3) Ethylene glycol or glycerol solution is a consumable. It will be lost due to volatilization, oxidation or leakage during system operation. The concentration needs to be checked and replenished regularly, which not only increases the workload of daily operation and maintenance, but also leads to continuous material cost expenditure.

[0005] Therefore, how to provide a cooling system that can meet the requirements of low-temperature cooling processes, ensure food safety, improve system energy efficiency, and reduce operation and maintenance costs has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0007] Design a low-temperature cooling control method for pure water medium, including the following steps: S1: Start the cooling water circulation loop. The control unit controls the operation of the cooling pump to circulate the cooling water in the condenser. S2: Start the chilled water circulation loop. The control unit controls the internal circulation pump to run, so that the pure water medium circulates and cools in the evaporator, and stores the cooled pure water medium in the external circulation water tank. At the same time, the secondary chilled water circulation loop is started, and the control unit controls the operation of the external circulation pump, so that the pure water medium flows out of the external circulation storage tank, undergoes heat exchange through the terminal heat exchanger, and returns to the internal circulation storage tank. S3: Start the compressor only after the cooling pump, internal circulation pump, and external circulation pump have all started running; S4: When shutting down, first stop the compressor, then stop the secondary chilled water circulation loop and the primary chilled water circulation loop. The control unit controls the external circulation pump and the internal circulation pump to stop running, and finally stops the cooling water circulation system, that is, controls the cooling pump to stop running.

[0008] Preferably, the compressor, evaporator, and condenser are connected in a cyclical manner to form a cooling unit; The cooling pump, condenser, and cooling tower are connected in sequence to form a cooling water circulation loop. The internal circulation water tank, internal circulation pump, and evaporator are connected in sequence along the primary chilled water circulation direction to form a primary chilled water circulation loop. The evaporator, the external circulation water tank, and the external circulation pump are connected in sequence along the secondary chilled water circulation direction to form a secondary chilled water circulation loop, and the liquid level of the external circulation water tank is higher than the liquid level of the internal circulation water tank. A heat exchange device is connected between the outlet of the external circulation water tank and the inlet of the internal circulation water tank.

[0009] Preferably, during operation, the control unit controls the compressor to load or unload based on the difference between the temperature of the external circulating water tank and the target set value. When the temperature of the external circulating water tank is higher than the target set value, the compressor is loaded and running; when the temperature of the external circulating water tank is lower than the target set value, the compressor is unloaded and running.

[0010] Preferably, the cooling tower fan control steps are also included: when the cooling tower outlet water temperature is higher than the set upper limit, the cooling tower fan is started; when the cooling tower outlet water temperature is lower than the set lower limit, the cooling tower fan is stopped.

[0011] Preferably, a hot gas bypass valve is connected between the exhaust port of the compressor and the inlet of the evaporator, and a temperature sensor for detecting the evaporation temperature or a pressure sensor for detecting the evaporation pressure is provided on the evaporator. The input terminal of the control unit is connected to the temperature sensor or the pressure sensor respectively, and the output terminal is connected to the hot gas bypass valve. When the evaporation temperature is lower than the antifreeze threshold or the evaporation pressure is lower than the pressure threshold, the control unit first controls the compressor to pre-unload. If the temperature or pressure still does not rise, the control unit opens the hot gas bypass valve to introduce the high-temperature pure water medium discharged from the compressor into the evaporator, thereby implementing the antifreeze protection mode.

[0012] Preferably, a water replenishment valve is connected to the top of the internal circulation water tank via a pipeline. The inlet of the water replenishment valve is connected to a water source, and the outlet is connected to the internal circulation water tank. When the liquid level in the internal circulation water tank is lower than a preset lower limit, the control unit controls the water replenishment valve to open and replenish tap water to the internal circulation water tank. When the liquid level is higher than a preset upper limit, the control unit controls the water replenishment valve to close.

[0013] Preferably, a cooling tower bypass valve is connected in parallel between the cooling tower inlet pipe and the cooling tower outlet pipe. The inlet of the cooling tower bypass valve is connected to the outlet of the condenser, and the two outlets are respectively connected to the cooling tower inlet and outlet. When the condenser outlet water temperature is lower than the set value, the control unit controls the cooling tower bypass valve to connect to the pipeline on the cooling tower outlet side, and at the same time closes the pipeline connected to the cooling tower inlet side, so that the cooling water is directly circulated back to the condenser after passing through the cooling pump.

[0014] Preferably, the internal circulation pump includes two internal circulation pumps connected in parallel: one internal circulation pump and one internal circulation pump; the external circulation pump includes two external circulation pumps connected in parallel: one external circulation pump and one external circulation pump; and the cooling pump includes two cooling pumps connected in parallel: one cooling pump and one cooling pump. Of the two pumps connected in parallel, one serves as the main pump and the other as the standby pump. The control unit is used to control the corresponding standby pump to start operation when the main pump fails.

[0015] The beneficial effects of this invention are as follows: 1. This invention uses pure water as the sole cooling medium, completely eliminating chemical additives such as ethylene glycol or glycerol. Even in the event of a leak in extreme circumstances, the leaked substance is only pure water, causing no chemical contamination to food, pharmaceuticals, or other products, thus ensuring process safety from the source. Furthermore, using pure water as the medium is widely available, inexpensive, and has no volatility or loss issues. During system operation, only a simple water supply valve is needed to maintain the system's water level; there is no need to periodically purchase and add expensive ethylene glycol or glycerol, greatly simplifying maintenance and reducing material costs.

[0016] 2. This invention can stably output pure water that directly meets the requirements of low-temperature processes. Since it eliminates the need for further reducing the medium temperature as in traditional technologies, the chiller's settings can be increased, resulting in a corresponding increase in evaporation pressure, thus ensuring the compressor always operates within its high-efficiency range. Combined with the variable frequency compressor's load adjustment, the system's overall energy efficiency is significantly improved compared to traditional solutions, resulting in substantial savings in electricity costs over long-term operation.

[0017] 3. By setting up an internal circulation water tank and an external circulation water tank with a liquid level difference, the external circulation water tank directly supplies cooling to the terminal, and its stable water temperature ensures a constant cooling temperature. At the same time, the control system uses the temperature of the external circulation water tank as a reference and uses a variable frequency compressor to precisely load or unload, effectively suppressing load fluctuations and controlling the fluctuation of the terminal water supply temperature, thus providing a stable and reliable cold source for temperature-sensitive processes.

[0018] 4. In terms of control logic, this invention prevents the evaporator from becoming overcooled through strict start-stop sequences and predictive load reduction based on evaporation temperature or pressure. In terms of hardware, it rapidly increases the evaporation temperature under extreme conditions through a hot gas bypass valve. This combination of hardware and software effectively solves the freezing risk of pure water during low-temperature operation, ensuring the long-term safe and stable operation of the evaporator and the entire system. Attached Figure Description

[0019] Figure 1 This is a flowchart of the present invention; Figure 2 This is a diagram showing the connection relationships of the various components in this invention; Figure 3 This is a block diagram of the control principle of the present invention; The following are the labels in the diagram: 1. Heat exchange equipment, 2. Water supply valve, 3. Internal circulation water tank, 4. Internal circulation pump 1, 5. Internal circulation pump 2, 6. External circulation pump 1, 7. External circulation pump 2, 8. External circulation water tank, 9. Compressor, 10. Evaporator, 11. Condenser, 12. Cooling tower bypass valve, 13. Cooling tower, 14. Cooling pump 1, 15. Cooling pump 2. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention. Example 1

[0021] A method for controlling low-temperature cooling in pure water medium, such as Figures 1 to 3 As shown, it includes the following steps: S1: Start the cooling water circulation loop. The control unit controls the operation of the cooling pump to circulate the cooling water in the condenser. This ensures that the condenser is properly cooled before the refrigeration starts, so that the condensing pressure will not be too high after the compressor starts, thus ensuring the safe start-up of the unit.

[0022] S2: Start the chilled water circulation loop. The control unit controls the internal circulation pump to run, so that the pure water medium circulates and cools in the evaporator, and stores the cooled pure water medium in the external circulation water tank. This process is a closed-loop refrigeration process. The purpose is to continuously transfer the cold energy generated by the evaporator to the pure water medium and use the external circulation water tank as a cold energy "reservoir".

[0023] Simultaneously, the secondary chilled water circulation loop is activated. The control unit operates the external circulation pump, causing pure water to flow from the external circulation tank, undergo heat exchange in the terminal heat exchanger, and then return to the internal circulation tank. After absorbing heat and increasing in temperature at the terminal heat exchanger, the medium flows back to the lower-positioned internal circulation tank by gravity or residual pressure, completing one cooling cycle. The primary cycle is responsible for refrigeration, while the secondary cycle is responsible for supplying cooling; the two are decoupled through tanks at different elevations. This design allows the primary cycle to operate stably and efficiently, unaffected by frequent fluctuations in terminal load, thus ensuring that the secondary cycle receives a low-temperature medium with extremely stable temperature.

[0024] S3: Start the compressor only after the cooling pump, internal circulation pump and external circulation pump have all started running. The above startup logic can ensure that there is enough medium flowing in the evaporator and condenser before the compressor starts, preventing pressure abnormalities or freezing risks caused by poor heat exchange, and is a basic guarantee for the safe operation of the system.

[0025] S4: When shutting down, first stop the compressor to cut off the cooling source. Then stop the secondary chilled water circulation loop and the primary chilled water circulation loop. The control unit controls the external circulation pump and the internal circulation pump to stop running. Finally, stop the cooling water circulation system, that is, control the cooling pump to stop running. The above shutdown logic of stopping the cooling source first and then stopping the medium circulation can effectively utilize the residual cooling capacity in the circulating water to continue cooling the terminal for a period of time, while avoiding energy waste caused by the circulation pump running idle for a long time after the compressor stops.

[0026] This method uses pure water as the cooling fluid, effectively avoiding the food safety hazards caused by leaks of traditional ethylene glycol or glycerol media, and reducing operation and maintenance costs. By starting the cooling water, primary chilled water, and secondary chilled water circulation loops in stages, starting the compressor after all pumps are running stably, and shutting down in reverse order, the system's stability and safety are ensured, helping to extend the equipment's service life. The outlet water temperature in this application can achieve precise low-temperature control close to 1°C.

[0027] The compressor, evaporator, and condenser are connected in sequence to form a cooling unit, which is used to generate cooling capacity. The cooling pump, condenser, and cooling tower are connected in sequence to form a cooling water circulation loop, which is used to remove the heat from the condenser. An internal circulation water tank, an internal circulation pump, and an evaporator are connected in sequence along the primary chilled water circulation direction to form a primary chilled water circulation loop; this loop is used to circulate the cooling capacity generated by the evaporator through a pure water medium for initial cooling, and to store the cooled pure water medium in an external circulation water tank.

[0028] The evaporator, external circulation water tank, and external circulation pump are connected in sequence along the secondary chilled water circulation direction to form a secondary chilled water circulation loop. The liquid level of the external circulation water tank is higher than that of the internal circulation water tank. The liquid level difference is used to form a natural backflow force to ensure the stable operation of the system.

[0029] A heat exchange device is connected between the outlet of the external circulation water tank and the inlet of the internal circulation water tank. This device is used to transport the low-temperature pure water medium stored in the external circulation water tank to the terminal heat exchanger for heat exchange with the user side.

[0030] During operation, the control unit controls the compressor to load or unload based on the difference between the temperature of the external circulating water tank and the target setpoint. When the temperature of the external circulating water tank is higher than the target setpoint, the compressor operates under load; when the temperature of the external circulating water tank is lower than the target setpoint, the compressor operates under unload. For example, assuming the target setpoint is 1.1℃, when the temperature sensor detects that the water temperature in the external circulating water tank is higher than 1.2℃, the control unit determines that the cooling capacity needs to be increased and instructs the variable frequency compressor to increase its operating frequency, i.e., to operate under load. When the water temperature is lower than 1.0℃, it instructs the compressor to decrease its frequency, i.e., to operate under unload. Since the external circulating water tank directly supplies water to the end user, using its temperature as the control reference can most directly and accurately meet the user's cooling demand, achieving precise control of the end-user water supply temperature. The fluctuation range can be controlled within ±0.5℃, greatly improving process stability.

[0031] It also includes cooling tower fan control procedures: when the cooling tower outlet water temperature is higher than the set upper limit, the cooling tower fan is started to enhance heat dissipation through forced ventilation; when the cooling tower outlet water temperature is lower than the set lower limit, the cooling tower fan is stopped. This automatic start-stop control minimizes fan energy consumption while ensuring condensation effect.

[0032] A hot gas bypass valve is connected between the compressor's discharge port and the evaporator's inlet. A temperature sensor for detecting the evaporation temperature or a pressure sensor for detecting the evaporation pressure is installed on the evaporator. The input terminal of the control unit is connected to the temperature sensor or the pressure sensor, respectively, and the output terminal is connected to the hot gas bypass valve. During operation, if the control unit detects that the evaporating temperature is lower than the set antifreeze threshold, or the evaporating pressure is lower than the pressure threshold, it will first instruct the compressor to pre-unload, rapidly reducing the cooling capacity output. If the temperature or pressure continues to drop, the control unit will directly open the hot gas bypass valve, introducing the high-temperature gaseous refrigerant discharged from the compressor directly into the evaporator inlet, rapidly increasing the evaporating temperature and pressure, thereby implementing forced antifreeze protection. This predictive + proactive intervention protection strategy effectively prevents the evaporator from freezing and cracking due to low temperatures, ensuring long-term reliable operation of the system under ultra-low temperature conditions.

[0033] A water supply valve is connected to the top of the internal circulation water tank via a pipe. The inlet of the water supply valve is connected to the water source, and the outlet is connected to the internal circulation water tank. When the level gauge installed on the internal circulation water tank detects that the water level is lower than the preset lower limit, the control unit determines that the system is short of water and immediately opens the water supply valve to replenish the internal circulation water tank with tap water. When the water level rises to the preset upper limit, the control unit closes the water supply valve and stops replenishing water. Since the internal circulation water tank is the balance point of the entire system's water volume, maintaining a constant water level ensures the stable operation of the internal and external circulation pumps and avoids pump cavitation or dry running due to excessively low water levels.

[0034] A bypass valve is connected in parallel between the cooling tower's inlet and outlet pipes. The inlet of the bypass valve is connected to the condenser's outlet, and its two outlets are connected to the cooling tower's inlet and outlet (or directly to the cooling pump inlet). When the control unit detects that the condenser outlet temperature is lower than the set value, it determines that cooling tower cooling is unnecessary and controls the bypass valve to switch to bypass mode: opening the pipe connected to the cooling tower outlet while simultaneously closing the pipe connected to the cooling tower inlet. In this way, the cooling water flowing from the condenser no longer needs to pass through the cooling tower for heat dissipation; instead, it directly passes through the bypass valve, is pumped back into the condenser, and is recirculated. This effectively prevents excessively low condensing pressure from affecting the unit's normal operation, while also avoiding unnecessary heat dissipation and fan operation at low temperatures, thus saving energy.

[0035] The internal circulation pumps include two pumps connected in parallel: Internal Circulation Pump 1 and Internal Circulation Pump 2. The external circulation pumps also include two pumps connected in parallel: External Circulation Pump 1 and External Circulation Pump 2. The cooling pumps also include two pumps connected in parallel: Cooling Pump 1 and Cooling Pump 2. Of these two parallel pumps, one serves as the primary pump, and the other as a standby pump. The control unit is used to control the corresponding standby pump to start operation when the primary pump fails. When one of the primary pumps, Internal Circulation Pump 1, stops due to a fault, its corresponding pressure or flow signal will become abnormal. Upon receiving the fault signal, the control unit will immediately and automatically control the corresponding standby pump, such as Internal Circulation Pump 2, to start and operate. The entire process is seamlessly integrated, ensuring uninterrupted operation of the refrigeration unit, minimizing downtime caused by single-point failures, and guaranteeing the continuity of the user's production process.

[0036] By employing the above methods, this invention resolves the leakage risks associated with traditional ethylene glycol or glycerol media, eliminating food safety hazards. Simultaneously, by using pure water as the medium and employing precise temperature and load control, the system avoids increased energy consumption due to excessively low medium temperature settings, significantly improving overall energy efficiency. Furthermore, using pure water as the cooling medium eliminates the need for frequent replacements, substantially reducing operating and maintenance costs. An integrated antifreeze protection mechanism ensures the system's safety and reliability under low-temperature operating conditions.

[0037] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling low-temperature cooling of pure water medium, characterized in that: Includes the following steps: S1: Start the cooling water circulation loop. The control unit controls the operation of the cooling pump to circulate the cooling water in the condenser. S2: Start the chilled water circulation loop. The control unit controls the internal circulation pump to run, so that the pure water medium circulates and cools in the evaporator, and stores the cooled pure water medium in the external circulation water tank. At the same time, the secondary chilled water circulation loop is started, and the control unit controls the operation of the external circulation pump, so that the pure water medium flows out of the external circulation storage tank, undergoes heat exchange through the terminal heat exchanger, and returns to the internal circulation storage tank. S3: Start the compressor only after the cooling pump, internal circulation pump, and external circulation pump have all started running; S4: When shutting down, first stop the compressor, then stop the secondary chilled water circulation loop and the primary chilled water circulation loop. The control unit controls the external circulation pump and the internal circulation pump to stop running, and finally stops the cooling water circulation system, that is, controls the cooling pump to stop running.

2. The low-temperature cooling control method for pure water medium as described in claim 1, characterized in that: The compressor, evaporator, and condenser are connected in a sequential cycle to form a cooling unit; The cooling pump, condenser, and cooling tower are connected in sequence to form a cooling water circulation loop. The internal circulation water tank, internal circulation pump, and evaporator are connected in sequence along the primary chilled water circulation direction to form a primary chilled water circulation loop. The evaporator, the external circulation water tank, and the external circulation pump are connected in sequence along the secondary chilled water circulation direction to form a secondary chilled water circulation loop, and the liquid level of the external circulation water tank is higher than the liquid level of the internal circulation water tank. A heat exchange device is connected between the outlet of the external circulation water tank and the inlet of the internal circulation water tank.

3. The low-temperature cooling control method for pure water medium as described in claim 1, characterized in that: During operation, the control unit controls the compressor to load or unload based on the difference between the temperature of the external circulating water tank and the target set value. When the temperature of the external circulating water tank is higher than the target set value, the compressor loads and runs; when the temperature of the external circulating water tank is lower than the target set value, the compressor unloads and runs.

4. The low-temperature cooling control method for pure water medium as described in claim 1, characterized in that: It also includes cooling tower fan control steps: when the cooling tower outlet water temperature is higher than the set upper limit, the cooling tower fan is started; when the cooling tower outlet water temperature is lower than the set lower limit, the cooling tower fan is stopped.

5. The low-temperature cooling control method for pure water medium as described in claim 1, characterized in that: A hot gas bypass valve is connected between the exhaust port of the compressor and the inlet of the evaporator. A temperature sensor for detecting the evaporation temperature or a pressure sensor for detecting the evaporation pressure is provided on the evaporator. The input terminal of the control unit is connected to the temperature sensor or the pressure sensor respectively, and the output terminal is connected to the hot gas bypass valve. When the evaporation temperature is lower than the antifreeze threshold or the evaporation pressure is lower than the pressure threshold, the control unit first controls the compressor to pre-unload. If the temperature or pressure still does not rise, the control unit opens the hot gas bypass valve to introduce the high-temperature pure water medium discharged from the compressor into the evaporator, thereby implementing the antifreeze protection mode.

6. The low-temperature cooling control method for pure water medium as described in claim 1, characterized in that: A water supply valve is connected to the top of the internal circulation water tank via a pipeline. The inlet of the water supply valve is connected to a water source, and the outlet is connected to the internal circulation water tank. When the liquid level in the internal circulation water tank is lower than the preset lower limit, the control unit controls the water supply valve to open and replenish the internal circulation water tank with tap water. When the liquid level is higher than the preset upper limit, the control unit controls the water supply valve to close.

7. The low-temperature cooling control method for pure water medium as described in claim 1, characterized in that: A cooling tower bypass valve is connected in parallel between the cooling tower inlet pipe and the cooling tower outlet pipe. The inlet of the cooling tower bypass valve is connected to the outlet of the condenser, and the two outlets are respectively connected to the cooling tower inlet and outlet. When the condenser outlet water temperature is lower than the set value, the control unit controls the cooling tower bypass valve to connect to the pipeline on the cooling tower outlet side, and at the same time closes the pipeline connected to the cooling tower inlet side, so that the cooling water is directly circulated back to the condenser after passing through the cooling pump.

8. The low-temperature cooling control method for pure water medium as described in claim 1, characterized in that: The internal circulation pump includes two internal circulation pumps connected in parallel: one internal circulation pump and one internal circulation pump. The external circulation pump includes two external circulation pumps connected in parallel: one external circulation pump and one external circulation pump. The cooling pump includes two cooling pumps connected in parallel: one cooling pump and one cooling pump. Of the two pumps connected in parallel, one serves as the main pump and the other as the standby pump. The control unit is used to control the corresponding standby pump to start operation when the main pump fails.

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