A water outlet temperature control method for a water chiller based on a bypass valve and a compressor stagger switch

Abstract

This invention belongs to the technical field of temperature control methods for fiber laser chillers, and particularly relates to a method for controlling the low-temperature outlet water temperature of a chiller based on a bypass valve and a compressor misalignment switch. The method includes the following steps: determining the preset temperature, temperature control accuracy, and accuracy coefficient; closing the bypass valve; starting the chiller and compressor normally; continuously monitoring the actual low-temperature outlet water temperature after the chiller starts running; and combining control of the compressor and bypass valve according to different states to maintain the low-temperature outlet water temperature within a reasonable range. This application, based on the changes in the low-temperature outlet water temperature of the chiller, utilizes a combination of compressor start control and bypass valve on / off control to achieve rapid balance of high and low pressure differences, creating conditions for the next compressor start-up more efficiently and accurately, reducing the starting current, and simultaneously improving the temperature control accuracy of the chiller water. This avoids the problem of frequent laser alarms and malfunctions due to excessive water temperature fluctuations in complex environments.

Description

Technical Field

[0001] This invention belongs to the technical field of temperature control methods for fiber laser chillers, and particularly relates to a chiller outlet water temperature control method based on a bypass valve and a compressor misalignment switch. Background Technology

[0002] With the rapid development of the laser industry, fiber lasers are widely used in industrial fields such as laser cutting and welding. Because laser cutting machines and other equipment generate a large amount of heat during operation, and elevated temperatures can severely affect laser performance, high-power fiber laser equipment requires corresponding chillers to provide circulating cooling water. With advancements in laser technology, the precision of chiller temperature control is constantly improving. During operation, to maintain a constant outlet water temperature, the compressor of the chiller will periodically stop and restart for a period of time to prevent the outlet water temperature from becoming too low. The shorter the compressor's downtime, the higher the water temperature control accuracy. After stopping, the compressor needs to wait for the pressure at the intake and exhaust ports to equalize before restarting. Excessive pressure difference can cause the compressor to fail to start, and in severe cases, may even cause excessive current and burn out the circuit. Excessive downtime reduces the chiller's temperature control accuracy. Summary of the Invention

[0003] The purpose of this invention is to provide a chiller outlet water temperature control method based on the misalignment of the bypass valve and the compressor, which can better control the operating status of the chiller compressor, reduce compressor shutdown delay, improve the temperature control accuracy of the chiller's low-temperature water, and avoid large fluctuations in water temperature.

[0004] To achieve the above objectives, the present invention adopts the following technical solution.

[0005] A method for controlling the outlet water temperature of a chiller based on a bypass valve and a compressor misalignment switch includes the following steps:

[0006] Stp1, determine the preset temperature T, temperature control accuracy ±ΔT, and accuracy coefficient k;

[0007] Stp2, close the bypass valve, start the chiller and compressor normally, and continuously monitor the actual temperature T' of the low-temperature outlet water after the chiller starts running;

[0008] Stp3. If T' < T - ΔT is detected, the bypass valve is opened while the compressor continues to run, and a portion of the refrigerant flows directly from the compressor discharge port back to the suction port, increasing the suction pressure.

[0009] Continuously monitor the actual temperature T' of the low-temperature effluent. If T' < T - ΔT, proceed to step stp4. If T - ΔT ≤ T' ≤ T + ΔT, keep the bypass valve open and continue operating. If the actual temperature T' > T + ΔT, return to step stp2.

[0010] Stp4: Turn off the compressor to stop cooling. Keep the bypass valve open to balance the pressure difference before and after the compressor. Record the actual low-temperature outlet water temperature T' as it rises to... Time required Where k is the precision coefficient, a positive number greater than 1; continue waiting. Then close the bypass valve and restart the compressor, returning to step Stp1 to start the refrigeration cycle.

[0011] In a further improved or preferred embodiment of the chiller outlet water temperature control method based on bypass valve and compressor misalignment switch, the accuracy coefficient is 1.5 or 2.0.

[0012] Its beneficial effects are as follows:

[0013] The chiller outlet water temperature control method based on bypass valve and compressor misalignment switch of this application can achieve rapid balance of high and low pressure difference by combining compressor start control and bypass valve on / off control based on the low temperature change of the chiller outlet water. This creates conditions for the next compressor start more efficiently and accurately, reduces the starting current, and makes the chiller water temperature control more accurate. It also makes the fiber laser work more stably, the processing time longer, and the working efficiency higher. It avoids the problem of frequent laser alarms and failure to work properly due to excessive water temperature fluctuations in complex environments. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the pressure balance structure of a chiller based on bypass control;

[0015] Figure 2 This is a schematic diagram of an existing pressure balance control scheme for chillers based on bypass control.

[0016] Figure 3 This is a schematic diagram of a low-temperature outlet water temperature control scheme for a chiller based on a bypass valve and a compressor misalignment switch.

[0017] Figure 4 This is a schematic diagram of test data for a chiller outlet water temperature control method based on a bypass valve and a compressor misalignment switch. Detailed Implementation

[0018] The present invention will be described in detail below with reference to specific embodiments.

[0019] This application presents a chiller outlet water temperature control method based on a bypass valve and a compressor misalignment switch, targeting a chiller pressure balance structure based on bypass control. This type of circulating chiller is mainly used for cooling laser equipment such as fiber laser cutting machines and welding machines. The pressure balance structure of the chiller based on bypass control is as follows: Figure 1 As shown, its refrigeration cycle process is as follows:

[0020] The refrigerant side consists of a compressor, condenser, fan, expansion tube, and evaporator: Low-temperature, low-pressure gaseous refrigerant is compressed by the compressor into a high-temperature, high-pressure gas, which then enters the condenser through pipes. After being cooled and condensed by the fan, it becomes a high-temperature, high-pressure liquid. Following the expansion and throttling effect of the expansion tube, it becomes a superheated, low-temperature, low-pressure superheated liquid. In the evaporator, it absorbs heat from the circulating water and evaporates into a high-temperature, low-pressure gas, then enters the compressor to begin the next cycle. The circulating water side consists of a water tank, water pump, ambient temperature heating module, and evaporator: Low-temperature circulating water in the water tank flows through the water... After pumping, a small portion of the water is heated to room temperature and enters the room temperature load of the laser. After absorbing heat from the room temperature load, it flows back to the water tank through the room temperature return port. Most of the circulating water enters the low temperature load through the low temperature outlet, absorbs heat, and then flows into the evaporator through the low temperature return port. After being cooled by the refrigerant in the evaporator, it becomes low temperature circulating water and returns to the water tank to start the next cycle. The precise adjustment of the low temperature outlet temperature is achieved by the combined action of the compressor's start and stop and the water tank's cold storage. The shorter the compressor's downtime and the larger the water tank volume, the higher the temperature control precision.

[0021] For this structure, the existing control method flow is as follows: Figure 2 As shown, the specific steps are as follows:

[0022] Stp1, set temperature is T, actual low temperature outlet water temperature is T', temperature control accuracy is ±ΔT, compressor stop time is t, bypass valve delay time is X;

[0023] Stp2. When T' < T - ΔT, the bypass valve will open, and some refrigerant will flow directly from the compressor discharge port back to the suction port, increasing the suction pressure. After the compressor is turned off, the bypass valve will close after a delay of X seconds. After the compressor stops for t seconds, if the outlet water temperature T' > T + ΔT, the compressor will start again and restart the refrigeration cycle.

[0024] The above control scheme adjusts the compressor's suction and discharge pressure difference by delaying the closing of the bypass valve after the compressor is shut down. However, the time required for pressure balance is difficult to control and predict, and controlling the suction and discharge pressure difference after the bypass valve closes is challenging. Furthermore, the chiller's water temperature changes due to factors such as ambient temperature and set temperature, making it difficult for the existing control scheme to meet actual needs.

[0025] To address the aforementioned issues and provide a more flexible and efficient bypass pressure balance control technology for chillers, this application offers a chiller outlet water temperature control method based on a bypass valve and a compressor offset switch. The specific process is as follows: Figure 3 As shown, the specific steps are as follows:

[0026] Stp1, determine the preset temperature T, temperature control accuracy ±ΔT, and accuracy coefficient k;

[0027] Stp2, close the bypass valve, start the chiller and compressor normally, and continuously monitor the actual temperature T' of the low-temperature outlet water after the chiller starts running;

[0028] Stp3. If T' < T - ΔT is detected, the bypass valve is opened while the compressor continues to run, and a portion of the refrigerant flows directly from the compressor discharge port back to the suction port, increasing the suction pressure.

[0029] Continuously monitor the actual temperature T' of the low-temperature effluent. If T' < T - ΔT, proceed to step stp4. If T - ΔT ≤ T' ≤ T + ΔT, keep the bypass valve open and continue operating. If the actual temperature T' > T + ΔT, return to step stp2.

[0030] Stp4: Turn off the compressor to stop cooling. Keep the bypass valve open to balance the pressure difference before and after the compressor. Record the actual low-temperature outlet water temperature T' as it rises to... Time required Where k is the precision coefficient, a positive number greater than 1; continue waiting. Then close the bypass valve and restart the compressor, returning to step Stp1 to start the refrigeration cycle;

[0031] Unlike the conventional delayed closing control method of bypass valves, this invention adopts a control method of compressor and bypass valve staggered switching, ensuring sufficient time for pressure balance before and after the compressor; at the same time, it judges the rise in outlet water temperature after the bypass valve is opened, and closes the bypass valve if it is too high, thus improving the accuracy of temperature control; according to the rate of water temperature recovery after the compressor is turned off, the compressor shutdown time is dynamically adjusted, further improving the temperature control accuracy.

[0032] To illustrate the differences between the control scheme of this application and existing schemes, a certain type of chiller was tested based on its specific implementation steps. The test results are shown in Table 1. The measured water temperature change curves of the chiller's low-temperature outlet water under different schemes or parameters are shown in Table 1. Figure 4 As shown.

[0033] Table 1. Low-temperature outlet water temperature of chiller under different schemes or parameters

[0034]

[0035] From Table 1 and Figure 4 As can be seen, the existing control scheme adjusts the compressor's suction and discharge pressure difference by delaying the closing of the bypass valve after the compressor is turned off. The length of the delay time X (generally taken as 45~60s based on experience) has a direct impact on the pressure balance effect. Due to the large differences in the pressure difference before and after the chiller under different operating conditions, the time required for pressure balance is different. Therefore, it can be seen that the chiller's outlet water temperature fluctuates greatly. This fluctuation can lead to a situation where the suction and discharge pressure difference is still too large after the bypass valve is closed, which cannot meet the compressor's start-up conditions.

[0036] Moreover, in conventional control methods, the compressor shutdown time t is a fixed value, but the optimal shutdown time can change due to factors such as ambient temperature and set temperature, and a fixed value is difficult to adapt to complex situations.

[0037] Meanwhile, to maintain high water temperature accuracy during shutdown, the above-mentioned scheme requires a sufficiently large water tank for stable operation. If the tank volume is insufficient, the water temperature will exceed the temperature control accuracy during shutdown. Therefore, the required equipment size and cooling capacity are relatively large. Furthermore, an excessively small value for t can cause compressor startup failure, while an excessively large value will result in poor water temperature accuracy. In comparison, the scheme proposed in this application offers faster water temperature stabilization, higher control accuracy, and smaller water temperature fluctuations.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for controlling the outlet water temperature of a chiller based on a bypass valve and a compressor offset switch, characterized in that, Includes the following steps: Stp1, determine the preset temperature T, temperature control accuracy ±ΔT, and accuracy coefficient k; Stp2, close the bypass valve, start the chiller and compressor normally, and continuously monitor the actual temperature T' of the low-temperature outlet water after the chiller starts running; Stp3. If T' < T - ΔT is detected, the bypass valve is opened while the compressor continues to run, and a portion of the refrigerant flows directly from the compressor discharge port back to the suction port, increasing the suction pressure. Continuously monitor the actual temperature T' of the low-temperature effluent. If T' < T - ΔT is detected, proceed to step stp4. If T - ΔT ≤ T' ≤ T + ΔT, keep the bypass valve open and continue operating. If the actual temperature T' of the low-temperature effluent is detected > T + ΔT, return to step stp2 for execution. Stp4: Turn off the compressor to stop cooling. Keep the bypass valve open to balance the pressure difference before and after the compressor. Record the actual low-temperature outlet water temperature T' as it rises to... Time required Where k is the precision coefficient, a positive number greater than 1; continue waiting. Then close the bypass valve and restart the compressor, returning to step Stp1 to start the refrigeration cycle.

2. The chiller outlet water temperature control method based on bypass valve and compressor misalignment switch according to claim 1, characterized in that, The accuracy factor is 1.5 or 2.0.

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