Air conditioning unit utilizing return air for reheating and control method

Abstract

The invention relates to the field of air conditioning, and discloses an air conditioning unit utilizing return air to reheat and a control method.The air conditioning unit comprises an air conveying, distributing and processing system, a first return air inlet is formed in an air return pipe, and the first return air inlet is formed in an indoor space; the fresh air opening is formed outdoors and communicates with the first air mixing box through an air supply pipe. The fresh air opening and the air return pipe are connected to the first air mixing box, and the first air mixing box communicates with the surface air cooler. The surface air cooler, the direct expansion type air cooling evaporator, the second air mixing box and the air feeder are connected through an air feeding pipe; an air supply outlet is formed in the air supply pipe and is formed in an indoor space; a bypass pipe is arranged on the air supply pipe between the surface air cooler and the direct expansion type air cooling evaporator, and the bypass pipe is connected with a second air mixing box; the electric air volume adjusting valve is installed on the air return pipe and used for adjusting the proportion of air entering the first air mixing box through the fresh air opening and the first air return opening. The ratio of the return air volume passing through the return air inlet and the return air pipe to the fresh air volume passing through the fresh air inlet is kept at the set value, return air is utilized to the maximum degree on the premise that the indoor CO2 concentration requirement is met, and the energy consumption of an air conditioning system is reduced.

Description

Technical Field

[0001] This invention relates to the field of air conditioning, specifically to an integrated air conditioning unit and control method for deep dehumidification and reheating of return air in high-humidity spaces such as underground transportation buildings and underground commercial complexes. Background Technology

[0002] Humidity control in high-humidity environments typically employs surface coolers for cooling and dehumidification. In high-humidity environments such as underground spaces, surface coolers are often used to enhance their dehumidification capacity by lowering the temperature of the chilled water entering the cooler coils (e.g., cooling the air to 15°C for cooling and dehumidification). However, when the supplied air temperature is low (e.g., a supply air temperature of 15°C), condensation can occur at the air outlets. To avoid this, the low-temperature air is usually heated (e.g., to 20°C) before being introduced into the room using a thermoelectric resistor or high-temperature hot water. Clearly, this method of cooling and dehumidifying the air with chilled water before heating results in significant energy waste. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide an integrated air conditioning unit and control method with adjustable dehumidification capacity, no thermoelectric resistance or high-temperature hot water reheating, suitable for high-humidity environments such as underground spaces. This unit utilizes reheat ducts and fans to increase the supply air temperature and prevent condensation at the air outlets. The air conditioning unit employs a reheat duct and reheat fan, using a reheating method that mixes high-temperature indoor air (around 25°C) with cooled and dehumidified air. This consumes only a small amount of fan power, avoiding the significant energy waste caused by traditional thermoelectric resistance or high-temperature hot water reheating methods.

[0004] To further achieve the above objectives, the present invention adopts the following technical solution: An air conditioning unit utilizing return air reheat includes a built-in refrigeration cycle assembly, which includes a compressor, an expansion valve, an evaporator, and a condenser. The evaporator includes a direct-expansion air-cooled evaporator and a water-cooled evaporator, with the two sets of evaporators connected in series. Cooling water is supplied by an external cooling tower and a circulating pump. All components are connected via refrigerant piping. The unit also includes an air distribution and handling system and a reheat system. The air distribution and handling system includes: A return air duct is provided, on which a first return air inlet is installed, and the first return air inlet is located in the indoor space; a fresh air inlet is located outdoors and is connected to a first mixing box via a supply air duct; the fresh air inlet and the return air duct are connected to the first mixing box, and the first mixing box is connected to the surface cooler; the surface cooler, the direct expansion air-cooled evaporator, the second mixing box, and the supply fan are connected via a supply air duct; an air outlet is installed on the supply air duct and is located in the indoor space; a bypass pipe is provided on the supply air duct between the surface cooler and the direct expansion air-cooled evaporator, and the bypass pipe is connected to the second mixing box; The reheat system includes a second return air inlet, a reheat pipe, a reheat fan, a fourth electric air volume switch valve, and a fourth wind speed sensor. The second return air inlet is installed indoors and connected to the reheat pipe. The reheat fan and the fourth electric air volume switch valve are connected to the reheat pipe at both ends. The reheat pipe is connected to the second mixing box. The fourth wind speed sensor is installed on the reheat pipe.

[0005] Preferably, the electric air volume regulating valve is installed on the return air duct to regulate the air volume of the return air duct and adjust the air ratio entering the first mixing box through the fresh air inlet and the first return air inlet; the first electric air volume switching valve and the second electric air volume switching valve are installed on the supply air duct and located on both sides of the direct expansion air-cooled evaporator, and the third electric air volume switching valve is installed on the bypass pipe; when the first electric air volume switching valve and the second electric air volume switching valve are closed and the third electric air volume switching valve is open, the air is dehumidified only through the surface cooler; when the first electric air volume switching valve and the second electric air volume switching valve are open and the third electric air volume switching valve is closed, the air undergoes two stages of cooling and dehumidification through the surface cooler and the direct expansion air-cooled evaporator.

[0006] Preferably, multiple temperature and humidity sensors and wind speed sensors are installed on the air duct to monitor air temperature, humidity and air volume; the CO2 sensor is installed in the middle of the room.

[0007] Furthermore, the second wind speed sensor and the first temperature and humidity sensor are sequentially installed on the return air duct and near the first return air inlet; the first wind speed sensor and the second temperature and humidity sensor are sequentially installed on the supply air duct and near the supply air outlet; the third temperature and humidity sensor is installed at the fresh air inlet; the third wind speed sensor is installed on the supply air duct and near the supply air outlet; the fourth temperature and humidity sensor is installed on the supply air duct and near the surface cooler; and the fifth temperature and humidity sensor is installed on the supply air duct and located between the direct expansion air-cooled evaporator and the second mixing box.

[0008] Preferably, the system also includes a chilled water and cooling water distribution system, which includes a chilled water circulation pump, an electric water valve, a first water temperature sensor, and a second water temperature sensor. These components are connected by chilled water pipes. The first and second water temperature sensors are installed on the chilled water pipes between the water-cooled evaporator and the surface cooler. The cooling water is supplied by an external cooling tower and a circulation pump. The unit has a reserved cooling water interface.

[0009] Preferably, it also includes a control cabinet, which includes a power air switch, a signal acquisition module, a PLC, a chilled water circulating pump frequency converter, a blower frequency converter, a reheat fan frequency converter, and a control module, which includes an electric air volume regulation / on / off valve control module and a compressor control module.

[0010] A control method for an air conditioning unit utilizing return air reheat, employing the aforementioned air conditioning unit utilizing return air reheat, includes a control strategy for a supply fan and an electric air volume regulating valve: (1) The signal acquisition module in the control cabinet receives the indoor CO2 sensor signal. The PLC compares and analyzes the indoor CO2 concentration set value and the indoor CO2 sensor signal, and outputs a control signal to dynamically adjust the output frequency of the blower inverter and control the air volume. When the indoor CO2 concentration is consistent with the set value, the blower maintains the operation at that frequency. The operating frequency of the blower is not lower than 35 Hz. (2) The signal acquisition module in the control cabinet receives the signals from the second and third wind speed sensors. The PLC compares the set value and the measured value of the ratio of return air and fresh air volume, and outputs a control signal. The electric air volume valve control module adjusts the opening of the electric air volume regulating valve so that the ratio of return air volume through the return air inlet and return air duct to fresh air volume through the fresh air inlet is kept at the set value. Under the premise of meeting the indoor CO2 concentration requirements, the return air is utilized to the maximum extent to reduce the energy consumption of the air conditioning system.

[0011] A control method for an air conditioning unit utilizing return air reheating includes adjusting the air cooling and dehumidification operation strategy after the aforementioned supply fan and electric air volume regulating valve have stabilized, ensuring that the relative humidity of the return air monitored by the first temperature and humidity sensor is maintained at the set value: (1) The first temperature and humidity sensor compares with the relative humidity set value. When the return air relative humidity is greater than or equal to the set value, the first electric air volume switch valve and the second electric air volume switch valve are opened, and the third electric air volume switch valve is closed. The fresh air and return air mixed in the first mixing box are cooled and dehumidified by a two-stage cooling system with a chilled water supply and return water temperature of 7-12℃ and a direct expansion air-cooled evaporator. When the return air relative humidity is less than the set value, the third electric air volume switch valve is opened, and the first electric air volume switch valve and the second electric air volume switch valve are closed. The fresh air and return air mixed in the first mixing box are cooled and dehumidified by a chilled water supply and return water temperature of 7-12℃. (2) The opening and closing of the electric air volume switch valve affects the cooling and dehumidification effect of the air supply, further changing the relative humidity of the return air monitored by the first temperature and humidity sensor, and so on.

[0012] A control method for an air conditioning unit utilizing reheated return air includes simultaneously adjusting the reheat fan operation control strategy during the aforementioned air cooling and dehumidification operation strategy adjustment to ensure that the supply air temperature monitored by the second temperature and humidity sensor is maintained at the set value. (1) Initial state: The fifth temperature and humidity sensor or the fourth temperature and humidity sensor is used as the initial input value and compared with the set value. When the initial input value is greater than or equal to the set value, the reheat fan and the fourth electric air volume switch valve are turned off. When the initial input value is less than the set value, the reheat fan and the fourth electric air volume switch valve are turned on. The indoor high temperature air is mixed with the supply air in the second mixing box and then sent into the room. (2) After the initial state adjustment is completed, the supply air temperature monitored by the second temperature and humidity sensor is compared with the set value. When the supply air temperature monitored by the second temperature and humidity sensor is < the set value, the reheat fan and the fourth electric air volume switch valve are turned on, and the operating frequency of the reheat fan is cyclically adjusted. The indoor high-temperature air and the supply air are mixed and heated in the second mixing box and then sent into the room. When the supply air temperature monitored by the second temperature and humidity sensor is ≥ the set value, the reheat fan and the fourth electric air volume switch valve are turned off. (3) Changes in the start-up and operation frequency of the reheat fan affect the supply air temperature monitored by the second temperature and humidity sensor, and this cycle continues.

[0013] Preferably, the ratio of return air volume to fresh air volume is set to 9:1.

[0014] Compared with the prior art, the present invention has the following significant advantages: 1. Automatic air volume adjustment: The air conditioning unit provided by this invention utilizes reheated return air, which can automatically adjust the air supply volume according to changes in indoor CO2 concentration, so that the ratio of return air volume through return air inlet and return air duct to fresh air volume through fresh air inlet is maintained at 9:1. Under the premise of meeting indoor CO2 concentration requirements, the return air is utilized to the maximum extent, thereby reducing the energy consumption of the air conditioning system.

[0015] 2. Low-energy reheating: To avoid condensation at the air outlet caused by excessively low air temperature after cooling and dehumidification (the air temperature detected by the fourth or fifth temperature and humidity sensor is lower than the set value), this invention uses a reheating fan to increase the air supply temperature by mixing high-temperature indoor air with low-temperature supply air in a mixing box. The reheating fan enables precise adjustment of the air supply temperature, thus solving the condensation problem caused by excessively low supply air temperature. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the air conditioning unit structure utilizing return air reheat according to the present invention; Figure 2 This is a control principle diagram of the air conditioning unit utilizing return air reheating according to the present invention; Figure 3 The control logic of this invention Figure 1 ; Figure 4 The control logic of this invention Figure 2 Figure 5This is a side view of the air conditioning unit of the present invention; Figure 6 This is a top view of the air conditioning unit of the present invention.

[0017] Explanation of reference numerals in the attached figures: 1. Compressor; 2. Expansion valve; 3. Direct expansion air-cooled evaporator; 4. Water-cooled evaporator; 5. Water-cooled condenser; 6. Fresh air inlet; 7. First mixing box; 8. Second mixing box; 9. Surface cooler; 10. Supply air duct; 11. Bypass pipe; 12. Return air duct; 13. First return air inlet; 14. Supply air outlet; 15. Second return air inlet; 16. Reheat pipe; 17. Reheat fan; 18. Chilled water circulation pump; 19. Electric water valve; 20. Supply fan. 011. Electric air volume regulating valve; 01. First electric air volume switch valve; 02. Second electric air volume switch valve; 03. Third electric air volume switch valve; 04. Fourth electric air volume switch valve. 1.1 First temperature and humidity sensor; 1.2 Second temperature and humidity sensor; 1.3 Third temperature and humidity sensor; 1.4 Fourth temperature and humidity sensor; 1.5 Fifth temperature and humidity sensor; 2.1 First wind speed sensor; 2.2 Second wind speed sensor; 2.3 Third wind speed sensor; 2.4 Fourth wind speed sensor; 3.1 First water temperature sensor; 3.2 Second water temperature sensor; 21. CO2 sensor; 30. Control Cabinet: 30.1 Power Air Switch, 30.2 Signal Acquisition Module, 30.3 PLC, 30.4 Chilled Water Circulating Pump Inverter, 30.5 Blower Inverter, 30.6 Reheat Blower Inverter, 30.7 Control Module. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be understood that the terms “comprising” and “having” as used herein, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0020] Furthermore, in this application, unless otherwise expressly specified and limited, the terms "connection," "linking," "fixing," "installation," etc., should be interpreted broadly. For example, they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise expressly limited, those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0021] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. It should be understood that the term "and / or" as used herein is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone.

[0023] The air conditioning unit and control method utilizing return air reheat provided by the present invention will be described in detail below with reference to specific embodiments.

[0024] Example 1 An air conditioning unit that utilizes return air reheat, such as Figure 1As shown, its built-in refrigeration cycle components mainly include compressor 1, expansion valve 2, evaporator, condenser, etc. The evaporator includes direct expansion air-cooled evaporator 3 and water-cooled evaporator 4. The condenser adopts water-cooled condenser 5 (water-cooled condensers have advantages such as simple form, low cost, convenient integration and no need for equipment drive compared with air-cooled condensation methods). Cooling water is provided by external cooling tower and circulating pump. The device only has a reserved cooling water flange interface. All components are connected through refrigerant pipes (green and blue solid lines in the figure, and red dashed lines are refrigerant pipes). The solid green line (refrigerant pipe, containing low-temperature, high-pressure liquid refrigerant) connects the water-cooled condenser 5 and the expansion valve 2. The solid blue line (refrigerant pipe, containing low-temperature, low-pressure gas-liquid two-phase refrigerant) connects the expansion valve 2 and the direct-expansion air-cooled evaporator 3. The direct-expansion air-cooled evaporator 3, the water-cooled evaporator 4, and the compressor 1 are connected by a red dashed line (refrigerant pipe, containing high-temperature, low-pressure gaseous refrigerant). The compressor 1 and the water-cooled condenser 5 are also connected by a red dashed line (refrigerant pipe, containing high-temperature, high-pressure gaseous refrigerant). The transfer of cooling capacity is achieved through the transmission and state changes of the refrigerant in the refrigerant pipes and between the components. The detailed refrigeration cycle process is as follows: Low-temperature, low-pressure gaseous refrigerant is drawn into compressor 1 and compressed into high-temperature, high-pressure gaseous refrigerant; high-temperature, high-pressure gaseous vapor enters water-cooled condenser 5, where it is condensed into low-temperature, high-pressure liquid refrigerant by external circulating cooling water. Cooling water condensation is a common and efficient air conditioning condensation solution, which can share the cooling water circulation system with other air conditioning systems, reducing engineering costs and improving the adaptability of the air conditioning unit of this invention; the low-temperature, high-pressure liquid refrigerant flows through expansion valve 2, where its pressure and temperature decrease, becoming a low-temperature, low-pressure gas-liquid two-phase refrigerant; the low-temperature, low-pressure gas-liquid two-phase refrigerant absorbs high-temperature air and high-temperature chilled water (17°C chilled water) respectively through direct expansion air-cooled evaporator 3 and water-cooled evaporator 4, becoming a high-temperature, low-pressure gaseous refrigerant, and achieving cooling and dehumidification of the air; the high-temperature, low-pressure gaseous refrigerant is drawn into compressor 1 again and compressed into a high-temperature, high-pressure gaseous refrigerant, and the cycle repeats.

[0025] In this invention, two sets of evaporators are connected in series. Depending on the dehumidification requirements, two dehumidification modes can be selected: dehumidification via only the surface cooler 9, or two-stage dehumidification via the surface cooler 9 and the direct-expansion air-cooled evaporator 3. The cooling dehumidification mode is automatically selected based on indoor and outdoor air humidity conditions, providing diverse cooling and dehumidification options. The direct-expansion air-cooled evaporator 3 is equipped with an electric airflow switch valve and an air bypass pipe at both ends. An electric airflow switch valve is installed on the bypass pipe 11. Based on the analysis of indoor and outdoor air humidity conditions and the dehumidification requirements, the opening and closing status of the electric airflow switch valve is automatically controlled, realizing the automatic switching function between primary dehumidification via the surface cooler 9 and the two-stage dehumidification mode via the surface cooler 9 and the air-cooled evaporator.

[0026] An air conditioning unit that utilizes return air reheat, such as Figure 1As shown, the air distribution and treatment system mainly includes a fresh air inlet 6, a first mixing chamber 7, a second mixing chamber 8, a surface cooler 9, an air supply duct 10, a bypass duct 11, a return air duct 12, a blower 20, an electric air volume regulating valve 011, an electric air volume switching valve, a temperature and humidity sensor, a CO2 sensor 21, and a wind speed sensor. The fresh air inlet 6 and the return air duct 12 are connected to the first mixing chamber 7, which is connected to the surface cooler 9. The surface cooler 9, the direct expansion air-cooled evaporator 3, the second mixing chamber 8, and the blower 20 are connected through the air supply duct 10. A bypass duct 11 is installed on the air supply duct 10 between the surface cooler 9 and the direct expansion air-cooled evaporator 3, and the bypass duct 11 connects to the second mixing chamber 8. A first return air outlet 13 is installed on the return air duct 12, and the first return air outlet 13 is located in the indoor space; the specific location can be determined according to the characteristics of the indoor space. Air supply outlets 14 are installed on the air supply duct 10. The number and location of the air supply outlets 14 are determined according to the characteristics of the indoor space. The fresh air inlet 6 is located outdoors for easy access to fresh air and is connected to the first mixing box 7 through the air supply duct 10. The electric air volume regulating valve 011 is installed on the return air duct 12 (in scenarios such as underground spaces, where the air conditioning unit is installed in the underground machine room, the fresh air duct is generally longer and has greater air resistance, while the return air duct has relatively smaller air resistance; installing it on the return air duct facilitates the adjustment of the fresh air and return air ratio), and is used to regulate the return air volume. The duct airflow is adjusted to regulate the proportion of air entering the first mixing chamber 7 through the fresh air inlet 6 and the first return air inlet 13. While meeting indoor fresh air requirements and CO2 concentration requirements, it maximizes the return air ratio and reduces the fresh air ratio to lower cooling energy consumption. The first electric airflow switch valve 01 and the second electric airflow switch valve 02 are installed on the supply air duct 10 and located on both sides of the direct expansion air-cooled evaporator 3. The third electric airflow switch valve 03 is installed on the bypass pipe 11 and only has an on / off function. The dehumidification capacity is controlled by the switch; when the first electric air volume switch valve 01 and the second electric air volume switch valve 02 are closed and the third electric air volume switch valve 03 is open, the air is dehumidified only through the surface cooler 9; when the first electric air volume switch valve 01 and the second electric air volume switch valve 02 are open and the third electric air volume switch valve 03 is closed, the air undergoes two-stage cooling and dehumidification through the surface cooler 9 and the direct expansion air-cooled evaporator 3; multiple temperature and humidity sensors and multiple wind speed sensors are installed on the air duct to monitor the air temperature, humidity and air volume.Specifically, the second wind speed sensor 2.2 and the first temperature and humidity sensor 1.1 are sequentially installed on the return air duct 12 and near the first return air outlet 13 to monitor the return air velocity (the return air volume can be obtained using the wind speed and the duct area) and return air temperature and humidity data, respectively; the first wind speed sensor 2.1 and the second temperature and humidity sensor 1.2 are sequentially installed on the supply air duct 10 and near the supply air outlet 14 to monitor the supply air velocity (the supply air volume can be obtained using the wind speed and the duct area) and supply air temperature and humidity data, respectively; the third temperature and humidity sensor 1.3 is installed at the fresh air inlet 6 to monitor the fresh air temperature and humidity data; the third wind speed sensor 2.3 is installed at the supply air outlet 6... A fourth temperature and humidity sensor 1.4 is installed on the air supply duct 10 near the fresh air inlet 6 to monitor the fresh air velocity data (the fresh air volume can be obtained by using the velocity and duct area); a fifth temperature and humidity sensor 1.5 is installed on the air supply duct 10 and near the surface cooler 9 to monitor the air temperature and humidity after cooling and dehumidification by the surface cooler 9; a sixth temperature and humidity sensor 1.5 is installed on the air supply duct 10 and located between the direct expansion air-cooled evaporator 3 and the second mixing box 8 to monitor the air temperature and humidity after two stages of cooling and dehumidification by the surface cooler 9 and the direct expansion air-cooled evaporator 3; and a CO2 sensor 21 is installed in the middle of the room, preferably at a height of 2.0m, to monitor the indoor CO2 concentration.

[0027] An air conditioning unit that utilizes return air reheat, such as Figure 1 As shown, the reheat system mainly includes a second return air inlet 15, a reheat pipe 16, a reheat fan 17, a fourth electric airflow switching valve 04, and a fourth wind speed sensor 2.4. The second return air inlet 15 is installed indoors and connected to the reheat pipe 16. The reheat fan 17 and the fourth electric airflow switching valve 04 are connected to the reheat pipe 16 at both ends. The reheat pipe 16 is connected to the second mixing box 8. The fourth wind speed sensor 2.4 is installed on the reheat pipe 16. When the air temperature after cooling and dehumidification is too low (the air temperature monitored by the fourth temperature and humidity sensor 1.4 or the fifth temperature and humidity sensor 1.5 is lower than the set value), and there is a risk of condensation at the air outlet, the reheat system is activated. It uses the mixing of high-temperature indoor air and low-temperature supply air in the mixing box to increase the supply air temperature and solve the condensation problem caused by the low supply air temperature. The reheat pipe 16 and the reheat fan 17 are used to send the return air into the second mixing box 8. The fourth electric air volume switch valve 04 is linked to the reheat fan 17 for opening and closing. The fourth wind speed sensor 2.4 is used to monitor the air speed and air volume sent into the second mixing box 8 through the reheat pipe 16 and the reheat fan 17 (the air volume can be obtained by using the wind speed and the duct area).

[0028] An air conditioning unit that utilizes return air reheat, such as Figure 1As shown, its chilled water and cooling water distribution system mainly includes a chilled water circulation pump 18, an electric water valve 19, and multiple water temperature sensors. These components are connected through chilled water pipes. The first water temperature sensor 3.1 and the second water temperature sensor 3.2 are installed on the chilled water pipe between the water-cooled evaporator 4 and the surface cooler 9. The first water temperature sensor 3.1 and the second water temperature sensor 3.2 monitor the chilled water supply and return temperatures, respectively. The cooling water is supplied by an external cooling tower and a circulation pump. The unit has a reserved cooling water interface for connection to the water-cooled condenser 5, which supplies 32°C cooling water to the water-cooled condenser from the outside and discharges 37°C cooling water from the water-cooled condenser.

[0029] In this invention, when the dehumidification requirement is relatively low, only the surface cooler 9 is used for dehumidification. The air treated by the surface cooler 9 is directly sent into the room through the bypass pipe 11 and the supply fan 20. When the dehumidification requirement is relatively high, a two-stage dehumidification process is adopted, using the surface cooler 9 and the direct expansion air-cooled evaporator 3. The low-temperature air after two stages of dehumidification is mixed with the indoor air in the mixing box and heated before being sent into the room. The problem of condensation at the air outlet 14 of the low-temperature air after two stages of dehumidification can be solved with only a small amount of power consumption from the reheat fan 17. Based on meeting the minimum fresh air volume in the room, the air volume of the supply fan 20 and the return air duct 12 are automatically adjusted according to the indoor CO2 concentration to meet the indoor fresh air demand while maximizing the use of return air to reduce system energy consumption.

[0030] Example 2 A control cabinet applied to the aforementioned air conditioning unit, such as Figure 2 As shown, the control cabinet 30 includes a power air switch 30.1, a signal acquisition module 30.2, a PLC 30.3, a chilled water circulating pump frequency converter 30.4, a blower frequency converter 30.5, a reheat fan frequency converter 30.6, and a control module 30.7 (including an electric air volume regulation / on / off valve control module and a compressor control module), etc. The main functions of the power circuit breaker 30.1 are power distribution, leakage current protection, and overload protection. The signal acquisition module 30.2 is used to collect signals from sensors such as the temperature and humidity sensor, wind speed sensor, and CO2 sensor 21, monitoring the operating status of each component. The PLC 30.3 mainly receives and processes information from the signal acquisition module 30.2, and through its built-in program, adjusts the output frequencies of the chilled water circulating pump 18, the blower inverter 30.5, and the reheat fan inverter 30.6, directly controlling the opening of the electric air volume regulating valve 011, the opening and closing of the electric air volume switching valve, and the operating status of the compressor. The blower 20, reheat fan 17, and chilled water circulating pump inverter 30.4 receive control signals from the PLC 30.3 and directly control the operating frequencies of these components. All the above components are integrated and installed in the control cabinet; the specific installation method is not the core content of this invention and will not be elaborated here.

[0031] Example 3 A control method for an air conditioning unit that utilizes return air reheat, as described above, is as follows: Figures 1 to 4 As shown, it includes: When the air conditioning unit starts, after the cooling tower and cooling water circulation pump outside the unit start and operate normally, the electric water valve 19 is opened. After a 1-minute delay, the chilled water circulation pump 18 starts and operates normally, and the third electric air volume switch valve 03 opens. After the third electric air volume switch valve 03 is fully open, the blower 20 starts, and the remaining electric air volume valves remain closed. Then, the compressor 1 starts. When the unit is shut down, the reverse sequence is followed. After the air conditioning unit starts, the data acquisition frequency of all types of sensors is 15 minutes / time, using hourly average values. The control strategies for each system are as follows.

[0032] I. Combining the following descriptions and Figure 3 Control strategy for blower 20 and electric air volume regulating valve 011: (1) The signal acquisition module in the control cabinet receives the signal from the indoor CO2 sensor 21. The PLC compares and analyzes the indoor CO2 concentration set value (0.10‰) and the signal from the indoor CO2 sensor 21, and outputs a control signal to dynamically adjust the output frequency of the blower inverter and control the air volume. When the indoor CO2 concentration is consistent with the set value, the blower 20 maintains the operation at that frequency. The operating frequency of the blower is not lower than 35 Hz. When the increase or decrease of indoor personnel affects the CO2 concentration, the frequency is dynamically adjusted.

[0033] (2) The signal acquisition module in the control cabinet receives the signals from the second wind speed sensor 2.2 and the third wind speed sensor 2.3. The PLC compares the set value (preferably 9:1, to maximize the use of the return air cooling capacity, or other ratio values) with the measured value and outputs a control signal. The electric air volume valve control module adjusts the opening of the electric air volume regulating valve 011 so that the ratio of the return air volume through the return air inlet and return air duct 12 to the fresh air volume through the fresh air inlet is maintained at 9:1. Under the premise of meeting the indoor CO2 concentration requirements, the return air is utilized to the maximum extent, and the energy consumption of the air conditioning system is reduced.

[0034] II. Combining the following descriptions and Figure 4 After the blower 20 and the electric air volume regulating valve 011 are running stably, adjust the air cooling and dehumidification operation strategy to ensure that the relative humidity of the return air monitored by the first temperature and humidity sensor 1.1 is maintained at the set value. (1) The first temperature and humidity sensor 1.1 is compared with the relative humidity setting value (which can also be set to a certain range, but only the setting value of 60% is used as an example). When the return air relative humidity is ≥60%, the first electric air volume switch valve 01 and the second electric air volume switch valve 02 are opened and the third electric air volume switch valve 03 is closed. The fresh air and return air mixed in the first mixing box 7 are cooled and dehumidified by the surface cooler 9 with a chilled water supply and return water temperature of 7-12℃ and the direct expansion air-cooled evaporator 3 in two stages. When the return air relative humidity is <60%, the third electric air volume switch valve 03 is opened and the first electric air volume switch valve 01 and the second electric air volume switch valve 02 are closed. The fresh air and return air mixed in the first mixing box 7 are cooled and dehumidified by the surface cooler 9 with a chilled water supply and return water temperature of 7-12℃.

[0035] (2) The opening and closing of the electric air volume switch valve affects the cooling and dehumidification effect of the air supply, further changing the relative humidity of the return air monitored by the first temperature and humidity sensor 1.1, and so on.

[0036] III. Combining the following descriptions and Figure 4 To avoid condensation at the air outlet 14 due to excessively low air temperature after cooling and dehumidification, the reheat fan 17's operation control strategy is adjusted simultaneously when the air cooling and dehumidification operation strategy is adjusted to ensure that the air supply temperature monitored by the second temperature and humidity sensor 1.2 is maintained at the set value. (1) In the initial state, the fifth temperature and humidity sensor 1.5 or the fourth temperature and humidity sensor 1.4 is used as the initial input value and compared with the set value (which can also be set to a certain range, taking the set value of 17℃ as an example). When the initial input value is ≥17℃, the reheat fan 17 and the fourth electric air volume switch valve 04 are closed; when the initial input value is <17℃, the reheat fan 17 and the fourth electric air volume switch valve 04 are opened. The indoor high temperature air (around 25℃) and the supply air (<17℃) are mixed in the second mixing box 8 and then sent into the room.

[0037] (2) After the initial state adjustment is completed, the supply air temperature monitored by the second temperature and humidity sensor 1.2 is compared with the set value. When the supply air temperature monitored by the second temperature and humidity sensor 1.2 is <17℃, the reheat fan 17 and the fourth electric air volume switch valve 04 are turned on, and the operating frequency of the reheat fan 17 is adjusted cyclically (5 Hz for each adjustment). The indoor high temperature air and the supply air are mixed and heated in the second mixing box 8 and then sent into the room. When the supply air temperature monitored by the second temperature and humidity sensor 1.2 is ≥17℃, the reheat fan 17 and the fourth electric air volume switch valve 04 are turned off.

[0038] (3) The opening and closing and the change in the operating frequency of the reheat fan 17 affect the supply air temperature monitored by the second temperature and humidity sensor 1.2, and so on.

[0039] Example 4 An air conditioning unit, such as Figure 5 , Figure 6 As shown, the refrigeration cycle components, air distribution and handling system, and reheat system are all integrated into the same equipment. Air duct or water pipe interfaces are reserved at the fresh air inlet, return air inlet, air supply outlet, and cooling water connection points.

[0040] The above description is merely a specific embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any transformations or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An air conditioning unit utilizing reheated return air, comprising a built-in refrigeration cycle assembly, the refrigeration cycle assembly including a compressor, an expansion valve, an evaporator, and a condenser, wherein the evaporator includes a direct expansion air-cooled evaporator and a water-cooled evaporator, the two sets of evaporators being connected in series, cooling water being supplied by an external cooling tower and a circulating pump, and the components being connected via refrigerant pipes, characterized in that, It also includes an air distribution and treatment system and a reheat system, the air distribution and treatment system comprising: A return air duct is provided, on which a first return air inlet is installed, and the first return air inlet is located in the indoor space; a fresh air inlet is located outdoors and is connected to a first mixing box via a supply air duct; the fresh air inlet and the return air duct are connected to the first mixing box, and the first mixing box is connected to the surface cooler; the surface cooler, the direct expansion air-cooled evaporator, the second mixing box, and the supply fan are connected via a supply air duct; an air outlet is installed on the supply air duct and is located in the indoor space; a bypass pipe is provided on the supply air duct between the surface cooler and the direct expansion air-cooled evaporator, and the bypass pipe is connected to the second mixing box; The reheat system includes a second return air inlet, a reheat pipe, a reheat fan, a fourth electric air volume switch valve, and a fourth wind speed sensor. The second return air inlet is installed indoors and connected to the reheat pipe. The reheat fan and the fourth electric air volume switch valve are connected to the reheat pipe at both ends. The reheat pipe is connected to the second mixing box. The fourth wind speed sensor is installed on the reheat pipe.

2. The air conditioning unit utilizing return air reheat according to claim 1, characterized in that, An electric air volume regulating valve is installed on the return air duct to regulate the air volume of the return air duct and adjust the air ratio entering the first mixing box through the fresh air inlet and the first return air inlet; the first electric air volume switching valve and the second electric air volume switching valve are installed on the supply air duct and located on both sides of the direct expansion air-cooled evaporator, and the third electric air volume switching valve is installed on the bypass pipe; when the first electric air volume switching valve and the second electric air volume switching valve are closed and the third electric air volume switching valve is open, the air is dehumidified only through the surface cooler; when the first electric air volume switching valve and the second electric air volume switching valve are open and the third electric air volume switching valve is closed, the air undergoes two stages of cooling and dehumidification through the surface cooler and the direct expansion air-cooled evaporator.

3. The air conditioning unit utilizing return air reheat according to claim 1 or 2, characterized in that, Multiple temperature and humidity sensors and wind speed sensors are installed on the air duct to monitor air temperature, humidity and air volume; the CO2 sensor is installed in the middle of the room.

4. The air conditioning unit utilizing return air reheat according to claim 3, characterized in that, The second wind speed sensor and the first temperature and humidity sensor are installed sequentially on the return air duct and near the first return air inlet. The first wind speed sensor and the second temperature and humidity sensor are installed sequentially on the supply air duct and near the supply air outlet. The third temperature and humidity sensor is installed at the fresh air inlet. The third wind speed sensor is installed on the supply air duct and near the supply air outlet. The fourth temperature and humidity sensor is installed on the supply air duct and near the surface cooler. The fifth temperature and humidity sensor is installed on the supply air duct and located between the direct expansion air-cooled evaporator and the second mixing box.

5. The air conditioning unit utilizing return air reheat according to claim 4, characterized in that, It also includes a chilled water and cooling water distribution system, which includes a chilled water circulation pump, an electric water valve, a first water temperature sensor, and a second water temperature sensor. These components are connected by chilled water pipes. The first and second water temperature sensors are installed on the chilled water pipes between the water-cooled evaporator and the surface cooler. The cooling water is supplied by an external cooling tower and a circulation pump. The unit has a reserved cooling water interface.

6. The air conditioning unit utilizing return air reheat according to claim 5, characterized in that, It also includes a control cabinet, which includes a power air switch, a signal acquisition module, a PLC, a chilled water circulating pump frequency converter, a blower frequency converter, a reheat blower frequency converter, and a control module, which includes an electric air volume regulation / on / off valve control module and a compressor control module.

7. A control method for an air conditioning unit utilizing return air reheat, employing the air conditioning unit utilizing return air reheat as described in claim 6, characterized in that, Including control strategies for blowers and electric air volume regulating valves: (1) The signal acquisition module in the control cabinet receives the indoor CO2 sensor signal. The PLC compares and analyzes the indoor CO2 concentration set value and the indoor CO2 sensor signal, and outputs a control signal to dynamically adjust the output frequency of the blower inverter and control the air volume. When the indoor CO2 concentration is consistent with the set value, the blower maintains the operation at that frequency. The operating frequency of the blower is not lower than 35 Hz. (2) The signal acquisition module in the control cabinet receives the signals from the second and third wind speed sensors. The PLC compares the set value and the measured value of the ratio of return air and fresh air volume, and outputs a control signal. The electric air volume valve control module adjusts the opening of the electric air volume regulating valve so that the ratio of return air volume through the return air inlet and return air duct to fresh air volume through the fresh air inlet is kept at the set value. Under the premise of meeting the indoor CO2 concentration requirements, the return air is utilized to the maximum extent to reduce the energy consumption of the air conditioning system.

8. A control method for an air conditioning unit utilizing return air reheat, characterized in that, After the blower and electric air volume regulating valve described in claim 7 have stabilized, the air cooling and dehumidification operation strategy is adjusted to ensure that the relative humidity of the return air monitored by the first temperature and humidity sensor is maintained at the set value. (1) The first temperature and humidity sensor compares with the relative humidity set value. When the return air relative humidity is greater than or equal to the set value, the first electric air volume switch valve and the second electric air volume switch valve are opened, and the third electric air volume switch valve is closed. The fresh air and return air mixed in the first mixing box are cooled and dehumidified by a two-stage cooling system with a chilled water supply and return water temperature of 7-12℃ and a direct expansion air-cooled evaporator. When the return air relative humidity is less than the set value, the third electric air volume switch valve is opened, and the first electric air volume switch valve and the second electric air volume switch valve are closed. The fresh air and return air mixed in the first mixing box are cooled and dehumidified by a chilled water supply and return water temperature of 7-12℃. (2) The opening and closing of the electric air volume switch valve affects the cooling and dehumidification effect of the air supply, further changing the relative humidity of the return air monitored by the first temperature and humidity sensor, and so on.

9. A control method for an air conditioning unit utilizing return air reheat, characterized in that, When adjusting the air cooling and dehumidification operation strategy as described in claim 8, the reheat fan operation control strategy is simultaneously adjusted to ensure that the supply air temperature monitored by the second temperature and humidity sensor is maintained at the set value. (1) Initial state: The fifth temperature and humidity sensor or the fourth temperature and humidity sensor is used as the initial input value and compared with the set value. When the initial input value is greater than or equal to the set value, the reheat fan and the fourth electric air volume switch valve are turned off. When the initial input value is less than the set value, the reheat fan and the fourth electric air volume switch valve are turned on. The indoor high temperature air is mixed with the supply air in the second mixing box and then sent into the room. (2) After the initial state adjustment is completed, the air supply temperature monitored by the second temperature and humidity sensor is compared with the set value. When the air supply temperature monitored by the second temperature and humidity sensor is < the set value, the reheat fan and the fourth electric air volume switch valve are turned on, and the operating frequency of the reheat fan is adjusted in a cycle. The indoor high temperature air and the air supply are mixed and heated in the second mixing box and then sent into the room. When the supply air temperature monitored by the second temperature and humidity sensor is greater than or equal to the set value, the reheat fan and the fourth electric air volume switch valve are turned off. (3) Changes in the start-up and operation frequency of the reheat fan affect the supply air temperature monitored by the second temperature and humidity sensor, and this cycle continues.

10. The control method for an air conditioning unit utilizing return air reheat according to claim 7, characterized in that, The set value for the volume ratio of return air to fresh air is 9:1.

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