A two-stage throttling chiller unit with an air supply valve and its control method.

Abstract

This invention discloses a two-stage throttling chiller unit with a make-up air valve and its control method, comprising a compressor, a condenser, a primary throttling device, an economizer, a secondary throttling device, and an evaporator connected in sequence. The key feature is that a make-up air valve branch is provided between the economizer and the compressor, and both the primary and secondary throttling devices employ electric butterfly valves. This invention uses electric butterfly valves as throttling devices, resulting in lower costs and a wider adjustment range. Furthermore, the invention employs position-based adjustment during the adjustment process of the electric butterfly valve, thereby ensuring rapid and stable condenser liquid level and improving the reliability of the device. In addition, by controlling the opening degree and on / off state of the make-up air valve based on the compressor's operating stage, working state, and start-up time, combined with the pressure of the economizer and evaporator, the application range of the unit is expanded, the control accuracy of the make-up air valve is improved, and the reliability of the unit is increased.

Description

Technical Field

[0001] This invention relates to the field of heat exchange technology, and in particular to a two-stage throttling chiller unit with a make-up air valve and its control method. Background Technology

[0002] Most existing two-stage compression centrifugal chiller units on the market use a two-stage throttling system with incomplete cooling of the chilled water. The first-stage throttling mostly uses orifice plates or electronic expansion valves; the second-stage throttling is mostly regulated by controlling the opening of the float valve built into the economizer.

[0003] The advantage of using an orifice plate for primary throttling is low cost, but the adjustment range is limited, restricting the unit's operating range. Using an electronic expansion valve offers high adjustment accuracy and a wide range, but the cost is higher. Secondary throttling uses a float valve built into the economizer. This increases the difficulty of float valve assembly, leading to increased labor costs and time. Furthermore, the maintainability of the float valve must be considered, requiring the addition of flanges to the cylinder for easy removal, thus increasing the width of the economizer. For centrifugal intercoolers, the built-in float valve increases the economizer's height, making it the highest point of the unit and increasing the overall unit height, ultimately leading to increased transportation costs. For users requiring low pressure differential and high cooling capacity, the small pressure differential between the condenser and evaporator reduces the pressure difference between the intercooler and evaporator, decreasing the float valve's liquid supply capacity. This results in a rise in the economizer's liquid level, causing the evaporator to remain low on liquid even when the float valve is fully open, leading to low evaporation pressure and ultimately poor unit performance and liquid carryover during compressor replenishment.

[0004] When the unit is operating under low load, the compressor's IGV (Inlet Guide Vane Opening Percentage) is relatively small. This results in a lower inlet pressure after the compressor suction inlet is throttled by the IGV, leading to a decrease in the pressure after the first stage of compression. In extreme cases, the evaporation pressure may be higher than the pressure after the first stage compression, preventing liquid from the economizer from entering the evaporator and causing a low evaporation pressure, resulting in low unit operating efficiency. Furthermore, during the initial startup phase, the IGV opening is relatively low. After throttling by the IGV, the impeller suction pressure is significantly reduced. In extreme cases, this can cause the economizer pressure to fall below the evaporation pressure, preventing liquid from the economizer from entering the evaporator. This leads to a continuous decrease in evaporation pressure during startup, falling below the minimum evaporation pressure, ultimately causing the unit to alarm and shut down. Summary of the Invention

[0005] This invention addresses the shortcomings of the prior art by providing a two-stage throttling chiller unit with a make-up air valve that has a wide range of applications and reliable performance, as well as its control method.

[0006] The technical solution adopted in this invention is as follows: a two-stage throttling chiller unit with a gas-replenishing valve, comprising a compressor, a condenser, a primary throttling device, an economizer, a secondary throttling device, and an evaporator connected in sequence; characterized in that a gas-replenishing valve branch is provided between the economizer and the compressor, and both the primary and secondary throttling devices are electric butterfly valves.

[0007] According to the above technical solution, the opening degree of the primary throttling device... The liquid level in the condenser is regulated; when the liquid level in the condenser exceeds the set value, the opening of the primary throttling device is adjusted. Increase; when the condenser liquid level is lower than the set value, the opening degree of the primary throttling device increases. Close it.

[0008] According to the above technical solution, the opening degree of the secondary throttling device... It is determined based on the opening degree of the primary throttling device and the pressure of the condenser, economizer, and evaporator;

[0009] Opening degree of the secondary throttling device The calculation formula is as follows:

[0010] ;

[0011] This refers to the relationship between the opening degree of the secondary valve and the mass flow rate of the primary valve:

[0012] ;

[0013] K ( This refers to the mass flow rate of a primary valve at different opening degrees.

[0014] ;

[0015] in It is the real-time pressure of the economic instrument. It is the real-time pressure of the evaporator. It is the real-time pressure of the condenser. It is the opening degree of the first-stage throttling device. It is the opening degree of the secondary throttling device. as well as It is a correction factor.

[0016] According to the above technical solution, it also includes a liquid level sensor for measuring the liquid level in the condenser and economizer, and a pressure sensor for measuring the real-time pressure of the condenser, economizer and evaporator.

[0017] According to the above technical solution, the compressor includes a two-stage compressor or a multi-stage compressor.

[0018] According to the above technical solution, the method is used to control the two-stage throttling chiller unit with a make-up air valve, and includes the following steps:

[0019] Step 1: Check the compressor's IGV, economizer pressure, and evaporator pressure;

[0020] Step 2: Determine the compressor status. If the compressor is running, calculate the opening degree of the gas supply valve and set the gas supply valve to that opening degree. If the compressor is in the start-up stage, proceed to the next step.

[0021] Step 3: Determine the compressor start-up time. If the compressor start-up time reaches the predetermined value, calculate the opening degree of the gas supply valve and execute it. If the compressor start-up time does not reach the predetermined value, proceed to the next step.

[0022] Step 4: Determine the compressor's IGV. If the compressor's IGV reaches the predetermined value, calculate and execute the opening of the replenishing valve. If the predetermined value is not reached, the replenishing valve remains closed.

[0023] According to the above technical solution, the gas replenishment valve is driven by a motor, and the opening degree of the gas replenishment valve is controlled by the pressure difference between the economizer pressure and the evaporator.

[0024] According to the above technical solution, the predetermined value of the compressor start-up time is in the range of 3 to 8 minutes.

[0025] According to the above technical solution, the predetermined value of the compressor IGV is 5% to 20%.

[0026] The beneficial effects achieved by this invention are as follows:

[0027] 1. This invention uses an electric butterfly valve as a throttling device, which is less expensive than an electronic expansion valve. The electric butterfly valve itself has a wide adjustment range, meeting the operating requirements of the unit under different conditions. Furthermore, this invention employs position-based adjustment during the electric butterfly valve's regulation process, acting in real-time based on the deviation between the actual and target liquid levels in the condenser. When the deviation is large, the valve's movement is large, avoiding the influence of backlash; when the deviation is small, the valve's movement is small and fast, preventing overshoot and subsequent liquid level oscillation, thus ensuring rapid stabilization of the condenser liquid level and improving the reliability of the device. Additionally, compared to traditional units, this invention eliminates the float valve inside the economizer, thereby reducing the economizer's processing time and height, reducing the refrigerant charge within the economizer, lowering refrigerant costs, and avoiding the risk of increased transportation costs due to the increased overall unit height caused by the economizer.

[0028] 2. By controlling the compressor's operating stage, working status, and start-up time, combined with the pressure of the economizer and evaporator, the opening and closing of the make-up air valve are controlled. This ensures normal liquid supply from the economizer to the evaporator under conditions of high cooling capacity, low pressure difference, and low load, expanding the unit's application range and improving the control accuracy of the make-up air valve. In addition, the use of an electric make-up air valve ensures normal start-up of the unit under various operating conditions, increasing the unit's reliability. Attached Figure Description

[0029] Figure 1 A schematic diagram of the structure of the chiller unit is provided for an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of the economizer structure is provided for an embodiment of the present invention;

[0031] Figure 3 A schematic diagram illustrating an embodiment of the chiller unit control method of the present invention;

[0032] Figure 4 The diagram showing the variation of the gas supply valve opening with economizer pressure and evaporator differential pressure in an embodiment of the present invention is provided.

[0033] In the diagram: 1. Compressor; 2. Condenser; 3. Primary throttling device; 4. Economizer; 5. Secondary throttling device; 6. Evaporator; 7. Gas supply valve branch; 4-1. Gas outlet; 4-2. Liquid inlet; 4-3. Cylinder; 4-4. Butterfly head; 4-5. Liquid outlet; 4-6. Anti-vortex plate. Detailed Implementation

[0034] The invention will now be further described with reference to the accompanying drawings.

[0035] like Figure 1As shown, this invention provides a two-stage throttling chiller unit with a make-up air valve, comprising a compressor 1, a condenser 2, a primary throttling device 3, an economizer 4, a secondary throttling device 5, and an evaporator 6 connected in sequence; the compressor can be a two-stage compressor or a multi-stage compressor. A make-up air valve branch 7 is also provided between the economizer and the compressor. Both the primary and secondary throttling devices are electric butterfly valves. This invention employs position-based adjustment of the electric butterfly valve in the throttling device, acting in real-time based on the deviation between the actual liquid level and the target liquid level in the condenser; when the deviation is large, the electric butterfly valve's movement is large, avoiding the influence of backlash; when the deviation is small, the electric butterfly valve's movement is small and fast, preventing valve overshoot and resulting liquid level oscillation, thereby ensuring rapid stabilization of the condenser liquid level. Because this device uses position-based adjustment during the adjustment of the electric butterfly valve of the throttling device, compared with traditional units, the float valve inside the economizer of this invention is eliminated, thereby reducing the processing time and height of the economizer, reducing the amount of refrigerant charged inside the economizer, reducing refrigerant costs, and avoiding the risk of increased transportation costs due to the increase in the overall unit height caused by the economizer.

[0036] In some embodiments, a liquid level sensor is provided inside the condenser and the economizer; a first pressure sensor for measuring the real-time pressure of the condenser is provided on the compressor discharge pipe; a second pressure sensor for measuring the real-time pressure of the economizer is provided on the top of the economizer cylinder; and a third sensor for measuring the real-time pressure of the evaporator is provided on the compressor suction pipe.

[0037] In some of the above embodiments, the opening degree of the primary throttling device The control and regulation are based on the liquid level in the condenser. By controlling the liquid level in the condenser to a reasonable position, the heat exchange efficiency of the condenser is ensured. The opening degree of the first-stage throttling device... The control logic is as follows: the condenser liquid level is acquired by a liquid level sensor; the unit sets a target liquid level value, such as 50% (the selection range is 0 to 100%); when the liquid level acquired by the liquid level sensor is greater than 50%, the electric butterfly valve of the first-stage throttling device opens wide; when the liquid level acquired by the liquid level sensor is less than 50%, the electric butterfly valve of the first-stage throttling device closes narrow.

[0038] In some of the above embodiments, the opening degree of the secondary throttling device The opening degree of the primary throttling device And the pressure of the condenser, economizer and evaporator;

[0039] Opening degree of the secondary throttling device The calculation formula is as follows:

[0040] ;

[0041] This refers to the relationship between the opening degree of the secondary valve and the mass flow rate of the primary valve:

[0042] ;

[0043] K ( This refers to the mass flow rate of a primary valve at different opening degrees.

[0044] ;

[0045] in It is the real-time pressure of the economic instrument. It is the real-time pressure of the evaporator. It is the real-time pressure of the condenser. It is the opening degree of the first-stage throttling device. It refers to the opening degree of the secondary throttling device;

[0046] as well as It is a correction factor. The value range is 0 to 0.000003. The value range is -0.003 to 0. The value range is 0 to 0.6. The value range is 14 to 17; The value range is -0.00002 to 0. The value range is 0 to 0.0035. The value range is -2 to 0. The value range is 2 to 4. The value range is -24 to -28.

[0047] In some of the embodiments described above, such as Figure 4 As shown, the economizer includes a cylinder 4-3, an air outlet 4-1 located at the top of the cylinder, a liquid inlet 4-2 on the side wall of the cylinder, a butterfly end cap 4-4 at the bottom of the cylinder, a liquid outlet 4-5 in the middle of the butterfly end cap, and an anti-vortex plate 4-6 above the liquid outlet. Because the primary and secondary throttling devices use electric butterfly valves, and the opening of the electric butterfly valves is adjusted by position, there is no need to install a float valve in the economizer, simplifying the structure of the economizer and reducing its height and refrigerant consumption.

[0048] During the startup of a bistage centrifugal chiller, the main reason for the persistently low evaporation pressure is the initially small opening of the IGV (Inlet Gas Vent) during startup. An excessively large initial IGV opening during startup would lead to an excessively high starting current, posing a risk of exceeding the maximum starting current. The refrigerant output from the evaporator experiences a significant pressure reduction after throttling, resulting in low refrigerant pressure at the compressor intake. This ultimately leads to a low intermediate pressure after compression by the first-stage compressor, making it difficult for liquid refrigerant in the economizer to enter the evaporator, causing a liquid shortage in the evaporator. Therefore, if the gas supply valve is closed during initial startup, the economizer pressure will no longer be affected by intermediate gas supply from the compressor, and the economizer pressure will gradually increase to ensure normal liquid supply to the evaporator. As the compressor's IGV opening increases, the throttling effect weakens, and the compressor intake pressure slowly increases. At this point, the opening of the gas supply valve adjusts according to the pressure difference between the economizer and the evaporator.

[0049] To achieve the above functions, such as Figure 2 As shown, the present invention also provides a control method for a two-stage throttling chiller unit with a make-up air valve. This method is used to control the two-stage throttling chiller unit with a make-up air valve provided in some of the above embodiments, and includes the following steps:

[0050] Step 1: Detect the compressor's IGV, economizer pressure, and evaporator pressure; the compressor's IGV is acquired through an IGV position sensor; the economizer pressure and evaporator pressure are acquired through pressure sensors installed inside the unit.

[0051] Step 2: Determine the compressor status. If the compressor is running, calculate the opening degree of the gas supply valve and set the gas supply valve to that opening degree. If the compressor is in the startup stage, proceed to the next step.

[0052] Step 3: Determine the compressor start-up time. If the compressor start-up time reaches the predetermined value, calculate the opening degree of the gas supply valve and execute it. If the compressor start-up time does not reach the predetermined value, proceed to the next step.

[0053] Step 4: Determine the compressor's IGV. If the compressor's IGV reaches the predetermined value, calculate and execute the opening of the make-up air valve. If the compressor's IGV does not reach the predetermined value, the make-up air valve remains closed.

[0054] In some of the above embodiments, the predetermined value for the compressor start-up time ranges from 3 to 8 minutes (5 minutes is selected in this embodiment). The predetermined value for the compressor IGV is 5% to 20% (10% is selected in this embodiment). The make-up air valve is driven by a motor, and the opening degree of the make-up air valve is controlled by converting the pressure difference signal between the economizer pressure and the evaporator pressure into a control signal. Figure 3 As shown, an example is provided of how the opening of the make-up air valve varies with the economizer pressure and the evaporator differential pressure.

[0055] The above examples are merely illustrative of the design concept and features of this invention, intended to enable those skilled in the art to understand the content of this invention and implement it accordingly. The scope of protection of this invention is not limited to the above-described examples. Therefore, all equivalent changes or modifications made based on the design concepts and ideas disclosed in this invention are within the scope of protection of this invention.

Claims

1. A two-stage throttling chiller unit with a gas-replenishing valve, comprising a compressor, a condenser, a primary throttling device, an economizer, a secondary throttling device, and an evaporator connected in sequence; characterized in that, A gas supply valve branch is also provided between the economizer and the compressor, and both the primary throttling device and the secondary throttling device are electric butterfly valves. The opening degree of the first-stage throttling device The liquid level in the condenser is regulated; when the liquid level in the condenser exceeds the set value, the opening of the primary throttling device is adjusted. Increase; when the condenser liquid level is lower than the set value, the opening degree of the primary throttling device increases. Close the small; The opening degree of the secondary throttling device It is determined based on the opening degree of the primary throttling device and the pressure of the condenser, economizer, and evaporator; Opening degree of the secondary throttling device The calculation formula is as follows: ； This refers to the relationship between the opening degree of the secondary valve and the mass flow rate of the primary valve: ； K ( This refers to the mass flow rate of a primary valve at different opening degrees. ； in It is the real-time pressure of the economic instrument. It is the real-time pressure of the evaporator. It is the real-time pressure of the condenser. It is the opening degree of the first-stage throttling device. It is the opening degree of the secondary throttling device. as well as It is a correction factor.

2. The two-stage throttling chiller unit with air supply valve according to claim 1, characterized in that: It also includes level sensors for measuring the liquid level in the condenser and economizer, and pressure sensors for measuring the real-time pressure of the condenser, economizer and evaporator.

3. The two-stage throttling chiller unit with air supply valve according to claim 1, characterized in that: The compressor includes a two-stage compressor or a multi-stage compressor.

4. A control method for a two-stage throttling chiller unit with an air supply valve, characterized in that: This method is used to control a two-stage throttling chiller unit with an air supply valve as described in any one of claims 1-3, and includes the following steps: Step 1: Check the compressor's IGV, economizer pressure, and evaporator pressure; Step 2: Determine the compressor status. If the compressor is running, calculate the opening degree of the gas supply valve and set the gas supply valve to that opening degree. If the compressor is in the start-up stage, proceed to the next step. Step 3: Determine the compressor start-up time. If the compressor start-up time reaches the predetermined value, calculate the opening degree of the gas supply valve and execute it. If the compressor start-up time does not reach the predetermined value, proceed to the next step. Step 4: Determine the compressor's IGV. If the compressor's IGV reaches the predetermined value, calculate and execute the opening of the replenishing valve. If the predetermined value is not reached, the replenishing valve remains closed.

5. The control method for a two-stage throttling chiller unit with a make-up air valve according to claim 4, characterized in that: The gas replenishment valve is driven by a motor, and the opening degree of the gas replenishment valve is controlled by the pressure difference between the economizer pressure and the evaporator.

6. The control method for a two-stage throttling chiller unit with a make-up air valve according to claim 4 or 5, characterized in that: The predetermined value for the compressor start-up time is in the range of 3 to 8 minutes.

7. The control method for a two-stage throttling chiller unit with a make-up air valve according to claim 4 or 5, characterized in that: The predetermined value for the compressor's IGV is 5% to 20%.

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