Low-temperature refrigerating system for high-humidity environment and control method

Abstract

The invention discloses a low-temperature refrigerating system in a high-humidity environment and a control method. The low-temperature refrigerating system comprises a dehumidifier arranged below a refrigerating evaporator, the dehumidifier is communicated with the cascade refrigerating unit through a refrigerant pipeline, a refrigerant inlet pipeline is provided with an electromagnetic valve used for controlling refrigerant to enter, and a refrigerating discharge pipeline is provided with a temperature sensor used for monitoring the temperature of an outlet of the dehumidifier. The box body temperature sensor is arranged in the environment test box and is used for acquiring the temperature in the box body. According to the scheme, the problem that the surface of the evaporator frosts during cooling under the high-humidity working condition can be solved.

Description

Technical Field

[0001] The present invention relates to the field of environmental testing and refrigeration technology, and in particular to a low-temperature refrigeration system and a control method for a high-humidity environment. Background Art

[0002] The environmental test chamber uses two-stage cascade refrigeration, and uses the low temperature stage to control the temperature in the cabin. The lowest evaporation temperature of the evaporator is below -70℃. When the humidity in the cabin is high, the condensed water in the air will gather on the surface of the evaporator during the cooling process. As the evaporation temperature decreases, the condensed water forms a frost layer that adheres to the surface of the evaporator heat exchange fins. In severe cases, the frost layer will block the air passage, causing the evaporator to lose its cooling ability. The low-temperature liquid refrigerant in the evaporator cannot absorb heat and is still liquid at the outlet of the evaporator. The compressor is at risk of liquid hammer, which can damage the entire refrigeration system. Summary of the invention

[0003] In view of the problem of frosting on the evaporator surface when cooling under high humidity conditions pointed out in the above background technology, an object of the present invention is to provide a low-temperature refrigeration system and control method for a high humidity environment.

[0004] To achieve the purpose of the present invention, the technical solution provided by the present invention is as follows:

[0005] First aspect

[0006] The present application provides a low-temperature refrigeration system for a high-humidity environment, including a dehumidifier arranged below a refrigeration evaporator, the dehumidifier being connected to a cascade refrigeration unit through a refrigerant pipeline, and the refrigerant inlet pipeline being provided with a solenoid valve for controlling the entry of refrigerant, and the refrigeration discharge pipeline being provided with a temperature sensor for monitoring the outlet temperature of the dehumidifier; and also including a box temperature sensor arranged in an environmental test box for collecting the temperature inside the box.

[0007] Furthermore, the dehumidifier is a dehumidification coil.

[0008] Furthermore, when multiple evaporators are connected in parallel, a solenoid valve is provided at the inlet of each evaporator, and a temperature sensor is provided at the refrigerant outlet of each evaporator, and the opening and closing frequency of the solenoid valve at the inlet is controlled according to the temperature of the outlet.

[0009] Second aspect

[0010] The present application provides a method for controlling a low-temperature refrigeration system in a high-humidity environment, the method being implemented by the above-mentioned system, removing most of the water vapor in the humid air through a dehumidifier, collecting the temperature of a temperature sensor installed at the outlet of the dehumidifier and comparing it with the actual temperature in the environmental test chamber, controlling the opening frequency of the solenoid valve at the refrigerant inlet of the dehumidifier, and thus controlling the surface temperature of the dehumidifier; first, after starting the cooling operation, when the temperature in the chamber is above 0°C, by controlling the surface temperature of the dehumidifier to be lower than the dew point temperature of the air in the environmental chamber, water molecules in the air circulation process in the chamber are quickly condensed onto the dehumidifier when passing through the dehumidifier, and finally forming water droplets that fall onto the water receiving tray at the bottom of the dehumidifier and are discharged from the chamber through the drainage system. After the temperature in the chamber is lower than 0 degrees, it is possible to automatically determine whether to continue to open the dehumidifier solenoid valve according to the humidity conditions in the chamber.

[0011] Furthermore, when multiple evaporators are connected in parallel for refrigeration, a solenoid valve is installed on the liquid inlet pipe of each evaporator, and a temperature sensor is installed at the evaporator outlet. During refrigeration operation, the controller collects the temperatures of each temperature sensor installed at the outlet of the refrigeration evaporator, compares and calculates them with each other, and controls the opening frequency of each solenoid valve to achieve a uniform liquid inlet volume for each evaporator.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] First, most of the water vapor in the humid air is removed through the dehumidification coil. This can be achieved by collecting the temperature of the temperature sensor installed at the outlet of the dehumidification coil and comparing it with the actual temperature of the box, controlling the opening frequency of the solenoid valve at the refrigerant inlet of the dehumidification coil, and thus controlling the surface temperature of the dehumidification coil. After the cooling operation starts, when the temperature in the box is above 0°C, the surface temperature of the dehumidification coil can be controlled to be lower than the dew point temperature of the air in the environmental cabin, so that the water molecules in the cabin circulate quickly onto the dehumidification coil when passing through the dehumidification coil, and finally form water droplets that fall onto the water receiving pan at the bottom of the dehumidification coil and are discharged from the box through the drainage system. After the temperature in the box is lower than 0 degrees, it can automatically determine whether to continue to open the dehumidification coil solenoid valve according to the humidity conditions in the box. The above solution can solve the problem of frosting on the evaporator surface when cooling under high humidity conditions.

[0014] In addition, when multiple evaporators are connected in parallel for refrigeration, a solenoid valve is installed on the liquid inlet pipe of each evaporator, and a temperature sensor is installed at the evaporator outlet. During refrigeration operation, the controller collects the temperature of each temperature sensor installed at the outlet of the refrigeration evaporator, compares and calculates each other, and controls the opening frequency of each solenoid valve to achieve a uniform liquid inflow to each evaporator. The above solution can solve the problem of uneven refrigerant distribution when multiple evaporators are connected in parallel. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1A first schematic diagram of the system structure provided in an embodiment of the present application;

[0016] Figure 2 This is the second schematic diagram of the system structure adopted by the embodiment of the present application. DETAILED DESCRIPTION

[0017] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Example 1

[0019] like Figure 1 As shown, the present application provides a low-temperature refrigeration system for a high-humidity environment, including a dehumidifier arranged below a refrigeration evaporator, the dehumidifier being connected to a cascade refrigeration unit through a refrigerant pipeline, and the refrigerant inlet pipeline being provided with a solenoid valve for controlling the refrigerant inlet, and the refrigeration discharge pipeline being provided with a temperature sensor for monitoring the dehumidifier outlet temperature; and also including a box temperature sensor arranged in an environmental test box for collecting the box internal temperature. The dehumidifier is a dehumidifying coil.

[0020] It should be noted that the system removes most of the water vapor in the humid air through the dehumidification coil. This can be achieved by collecting the temperature of the temperature sensor installed at the outlet of the dehumidification coil and comparing it with the actual temperature of the box, controlling the opening frequency of the solenoid valve at the refrigerant inlet of the dehumidification coil, and thus controlling the surface temperature of the dehumidification coil; first, after starting the cooling operation, when the temperature in the box is above 0℃, the surface temperature of the dehumidification coil can be controlled to be lower than the dew point temperature of the air in the environmental chamber, so that the water molecules in the air circulation process in the cabin will quickly condense onto the dehumidification coil when passing through the dehumidification coil, and finally form water droplets that fall onto the water receiving tray at the bottom of the dehumidification coil and are discharged from the box through the drainage system. After the temperature in the box is lower than 0 degrees, it can automatically determine whether to continue to open the dehumidification coil solenoid valve according to the humidity in the box.

[0021] It should be noted that the maximum thickness of the frost layer on the surface area of ​​the dehumidification coil is 4mm. The total surface area of ​​the coil can meet the requirement that the frost amount under the worst working conditions is more than 90% of the water content of the air in the test chamber. The minimum temperature of the refrigerant in the coil is above -70°C. The dew point temperature of the air after dehumidification by the coil can be reduced to -70°C. Most of the water vapor in the humid air is removed by the dehumidification coil. The surface temperature of the dehumidification coil can be controlled by controlling the valve opening of the refrigerant inlet of the dehumidification coil, and the dew point temperature of the air can be reduced to -70°C at the lowest. The water content in the air after dehumidification by the coil is very low, so the frost layer on the surface of the evaporator is very thin and does not affect its refrigeration performance.

[0022] Example 2

[0023] like Figure 2 As shown in the figure, when the environmental test chamber is large, multiple evaporators are sometimes used for refrigeration. Due to the influence of factors such as pipelines and air volume, the amount of refrigerant distributed in each evaporator will be different. The refrigerant in the evaporator with more refrigerant distribution cannot be fully vaporized, and the outlet is in a liquid state. The outlet superheat of the evaporator with less refrigerant distribution is higher, which greatly reduces the refrigeration capacity of the entire system.

[0024] The control system is used to solve the problem of uneven distribution of multiple evaporators. When multiple evaporators are connected in parallel, a solenoid valve is set at the inlet of each evaporator, and a temperature sensor is set at the refrigerant outlet of each evaporator. The opening and closing frequency of the solenoid valve at the inlet is controlled according to the outlet temperature. When the refrigerant is unevenly distributed, the temperature of the refrigerant outlet of each evaporator will be different. The refrigerant with a lower temperature will be distributed too much, and the refrigerant with a higher temperature will be distributed too little. The opening and closing frequency of the solenoid valve at the inlet is controlled according to the outlet temperature to make the outlet temperature of each evaporator tend to be the same. This can effectively ensure that the refrigerant in each evaporator is evenly distributed, and the refrigeration system can achieve the best refrigeration performance.

[0025] It should be noted that this system solves the control process of cooling and frosting in high-humidity conditions and uneven liquid distribution when multiple evaporators are connected in parallel for refrigeration. All of these need to be achieved through the PID closed-loop adjustment of the solenoid valve. The system control uses Siemens 6ES7510-1DK03-0AB0PLC as the main controller, and collects temperature values ​​through the analog input module 6ES7134-6JD00-0CA1. The main PLC performs the main logic operation. Through PID operation, the dehumidification valve, refrigeration valve and other actuators are controlled to ensure that the temperature and humidity can reach and maintain the set value. PID regulation control is a traditional control method. It is suitable for almost all sites such as temperature, pressure, flow, and liquid level. Different sites only need different PID parameters. As long as the parameters are set properly, good results can be achieved. All can reach 0.1% or even higher control requirements. In the temperature control process of this cabin, the classic PID algorithm is mainly used for adjustment. The main PID formula is as follows:

[0026]

[0027] U(i) = energy output value, ranging from 0 to 100%. A negative value indicates cooling mode or dehumidification mode.

[0028] Kp = controller proportional gain, which represents the inverse of the temperature input range in the program. For example, if you want to enter proportional control when the difference between the set temperature and the current temperature is 15 degrees, then KP = 1 / 15, that is, KP = 1 / (T set - T current) = 1 / ε(i).

[0029] Ti = integral coefficient, the empirical range for temperature control is (100-300).

[0030] Td = differential coefficient, the empirical range for temperature control is (1-10).

[0031] Ts = sampling period, which is also the output period.

[0032] ε(i) = deviation (ε(i) = set temperature - current temperature).

[0033] Example 3

[0034] The present application provides a method for controlling a low-temperature refrigeration system in a high-humidity environment, the method being implemented by the above-mentioned system, removing most of the water vapor in the humid air through a dehumidifier, collecting the temperature of a temperature sensor installed at the outlet of the dehumidifier and comparing it with the actual temperature in the environmental test chamber, controlling the opening frequency of the solenoid valve at the refrigerant inlet of the dehumidifier, and thus controlling the surface temperature of the dehumidifier; first, after starting the cooling operation, when the temperature in the chamber is above 0°C, by controlling the surface temperature of the dehumidifier to be lower than the dew point temperature of the air in the environmental chamber, water molecules in the air circulation process in the chamber are quickly condensed onto the dehumidifier when passing through the dehumidifier, and finally forming water droplets that fall onto the water receiving tray at the bottom of the dehumidifier and are discharged from the chamber through the drainage system. After the temperature in the chamber is lower than 0 degrees, it is possible to automatically determine whether to continue to open the dehumidifier solenoid valve according to the humidity conditions in the chamber.

[0035] Furthermore, when multiple evaporators are connected in parallel for refrigeration, a solenoid valve is installed on the liquid inlet pipe of each evaporator, and a temperature sensor is installed at the evaporator outlet. During refrigeration operation, the controller collects the temperatures of each temperature sensor installed at the outlet of the refrigeration evaporator, compares and calculates them with each other, and controls the opening frequency of each solenoid valve to achieve a uniform liquid inlet volume for each evaporator.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate and explain the present invention, and are not intended to limit the present invention to the scope of the described embodiments. In addition, those skilled in the art can understand that the present invention is not limited to the above embodiments, and more variations and modifications can be made according to the teachings of the present invention, and these variations and modifications all fall within the scope of the protection claimed by the present invention.

Claims

1. A low temperature refrigeration system for a high humidity environment, characterized in that: It includes a dehumidifier arranged below the refrigeration evaporator, the dehumidifier is connected to the cascade refrigeration unit through a refrigerant pipeline, and the refrigerant inlet pipeline is provided with a solenoid valve for controlling the entry of refrigerant, and the refrigeration discharge pipeline is provided with a temperature sensor for monitoring the outlet temperature of the dehumidifier; it also includes a box temperature sensor arranged in the environmental test box for collecting the temperature inside the box.

2. A low temperature refrigeration system for a high humidity environment according to claim 1, characterized in that: The dehumidifier is a dehumidifying coil.

3. The low temperature refrigeration system for high humidity environment according to claim 1, characterized in that: When multiple evaporators are connected in parallel, a solenoid valve is set at the inlet of each evaporator, and a temperature sensor is set at the refrigerant outlet of each evaporator to control the opening and closing frequency of the solenoid valve at the inlet according to the outlet temperature.

4. A method for controlling a low temperature refrigeration system in a high humidity environment, characterized in that: The method is implemented by the system as claimed in claim 1, most of the water vapor in the humid air is removed by a dehumidifier, and the opening frequency of the solenoid valve at the refrigerant inlet of the dehumidifier is controlled by collecting the temperature of the temperature sensor installed at the outlet of the dehumidifier and comparing it with the actual temperature in the environmental test chamber, thereby controlling the surface temperature of the dehumidifier. After the cooling operation starts, when the temperature in the chamber is above 0°C, the surface temperature of the dehumidifier is controlled to be lower than the dew point temperature of the air in the environmental chamber, so that water molecules in the air circulation process in the chamber are quickly condensed on the dehumidifier when passing through the dehumidifier, and finally form water droplets that fall into the water receiving tray at the bottom of the dehumidifier and are discharged from the chamber through the drainage system. After the temperature in the chamber is lower than 0 degrees, it can be automatically determined whether to continue to open the dehumidifier solenoid valve according to the humidity conditions in the chamber.

5. The method for controlling a low temperature refrigeration system in a high humidity environment according to claim 1, characterized in that: When multiple evaporators are connected in parallel for refrigeration, a solenoid valve is installed on the liquid inlet pipe of each evaporator, and a temperature sensor is installed at the evaporator outlet. During refrigeration operation, the controller collects the temperatures of each temperature sensor installed at the outlet of the refrigeration evaporator, compares and calculates them with each other, and controls the opening frequency of each solenoid valve to achieve a uniform liquid inlet volume for each evaporator.

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