A control method of a temperature and humidity separate control fresh air handling unit

Abstract

The application discloses a control method of a temperature and humidity separate control fresh air handling unit. The method sets the difference between the supply air temperature and the actual supply air temperature, controls the compressor operation frequency, and realizes high-precision supply air temperature control; the condenser of the refrigeration system is arranged behind the cooling coil, effectively reduces the condensing temperature, and improves the unit energy efficiency; the fresh air handling unit evaporator bears the high-temperature sensible heat load, the cooling coil bears the heat and humidity load, the supply air temperature and humidity parameters are set, the logic calculation of the parameters to be processed after the cooling is carried out, the cooling valve opening is adjusted, and the supply air absolute humidity content is satisfied. The application can couple the temperature, the absolute humidity content and the air volume in the supply air parameters with each other, determines the compressor frequency according to the supply air temperature, influences the absolute humidity content by the compressor frequency and the cooling valve opening, influences the fresh air volume by the absolute humidity content, and respectively decouples and processes the supply air temperature, the absolute humidity content and the air volume in the logic control.

Description

Technical Field

[0001] This invention relates to the field of fresh air handling unit technology, and specifically to a control method for a temperature and humidity controlled fresh air handling unit. Background Technology

[0002] With increasing societal emphasis on air quality, more and more venues are installing fresh air systems. These systems introduce fresh outdoor air into indoor spaces and expel harmful substances such as carbon dioxide, formaldehyde, benzene, xylene, and prevalent viruses from indoor environments. Through continuous indoor-outdoor air circulation, they improve indoor air quality. While the introduction of fresh air improves air quality, the temperature and humidity of the fresh air differ significantly from indoor air in summer and winter, requiring cooling and dehumidification or heating and humidification, resulting in high energy consumption for the units. Conventional air conditioning systems, in summer, cool the lower-temperature indoor spaces, releasing the condensation heat to the higher-temperature outdoor areas. This not only leads to low cooling system efficiency but also contributes to heat pollution, high operating costs, complex installation, and high construction costs. Furthermore, deeply cooled and dehumidified air requires external heat to reach a suitable temperature before being delivered indoors, resulting in a process of energy attrition. How to achieve temperature and humidity control of the air, improve the energy efficiency of the cooling system, and reduce the loss due to external energy attrition remains a technical problem for those skilled in the art. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a control method for temperature and humidity-controlled fresh air handling units.

[0004] To achieve the above objectives, the present invention provides a control method for a temperature and humidity controlled fresh air handling unit. The fresh air handling unit includes an evaporator and a condenser arranged in a fresh air duct along the airflow direction. A surface cooler is provided on the front or rear side of the evaporator, and the surface cooler is connected to a regulating valve. A first temperature and humidity sensor is provided at the air inlet of the fresh air duct. A temperature sensor is provided on the front side of the condenser, and a second temperature and humidity sensor is provided on its rear side. A fresh air fan is provided in the fresh air duct. An expansion valve is connected between the evaporator and the condenser, and the expansion valve and the condenser are respectively connected to the air inlet and air outlet of the compressor. The operating modes of the fresh air handling unit include dehumidification and reheat mode. Under dehumidification and reheat mode, the control method includes: When the supply air temperature setpoint T is less than the first temperature threshold range, the surface cooler is supplied with cooling water: When the fresh air unit is powered on, if the absolute humidity of the fresh air D1 is greater than the set value of the absolute humidity of the supply air D + the set absolute humidity fluctuation range d, or the fresh air temperature T1 is greater than the set value of the supply air temperature T + the set temperature fluctuation range t, then the control valve is powered on and opened to the set opening degree after a first set time delay. Then, the opening degree of the control valve is adjusted to control the temperature at the front of the condenser at the set temperature. The compressor is powered on and started after a second set time delay. After the compressor starts, it operates at the first set frequency. Then, the opening degree of the control valve is adjusted again to keep the temperature at the front of the condenser at the set temperature. The operating frequency of the compressor is adjusted according to the supply air temperature to keep the supply air temperature T2 at the set value T. When the supply air temperature setpoint T is greater than or equal to the first temperature threshold range, the regulating valve must not be electrically operated. If the absolute humidity of the fresh air D1 is greater than the set value of the absolute humidity of the supply air D + the set absolute humidity fluctuation range d, or the fresh air temperature T1 is less than the set value of the supply air temperature T - the set temperature fluctuation range t, then the compressor is powered on and started after a third set time delay. After the compressor starts, it operates at the second set frequency. During this period, if the absolute moisture content of the supply air D2 > the set value of the absolute moisture content of the supply air D or the supply air temperature T2 < the set value of the supply air temperature T - the set temperature fluctuation range t, the operating frequency of the compressor will be increased. When the absolute moisture content of the supply air D2 = the set value of the absolute moisture content of the supply air D, if the supply air temperature T2 < the set value of the supply air temperature T - the set temperature fluctuation range t, the operating frequency of the compressor will continue to increase. If the set value of the supply air temperature T + the set temperature fluctuation range t ≥ the supply air temperature T2 ≥ the set value of the supply air temperature T - the set temperature fluctuation range t, the compressor frequency will remain unchanged. If the absolute moisture content of the supply air D2 is within the range below the set value of the absolute moisture content of the supply air D, the compressor is already running at a high frequency, but the supply air temperature T2 < the set value of the supply air temperature T - the set temperature fluctuation range t, the air volume of the fresh air unit will be reduced. When the compressor frequency increases, the supply air temperature T2 increases. When the supply air temperature setpoint T + the set temperature fluctuation range t > supply air temperature T2 > supply air temperature setpoint T - the set temperature fluctuation range t, if the supply air absolute humidity D2 is within the range below the supply air absolute humidity setpoint D, the air volume of the fresh air unit is reduced. If the supply air absolute humidity D2 is below the range below the supply air absolute humidity setpoint D, and the air volume of the fresh air unit is at its minimum value, the compressor frequency is reduced to ensure that the supply air absolute humidity D2 is above the lower limit of the range below the supply air absolute humidity setpoint D. During compressor operation, if the absolute humidity content of fresh air D1 is less than or equal to the set value of absolute humidity content of supply air D - the set absolute humidity content fluctuation range d, the compressor will be shut down.

[0005] Furthermore, the fresh air handling unit also includes a third temperature and humidity sensor, which is used to collect indoor air temperature and humidity. The fresh air handling unit's operating mode also includes a heating and dehumidification mode. The operating prerequisites for the heating and dehumidification mode are: the supply air temperature setpoint T is higher than the second temperature threshold, and the absolute humidity of the fresh air is less than the absolute humidity setpoint D. In the heating and dehumidification mode, hot water is supplied to the surface cooler, the controller powers on the fresh air handling unit, and controls the regulating valve to open to the set opening degree after a fourth set time delay. After maintaining the opening of the regulating valve for a fifth set time, the opening of the regulating valve is adjusted again to keep the supply air temperature T2 at the set value T, and the airflow of the fresh air handling unit is adjusted as follows: During initial operation, if the absolute humidity of indoor air is greater than or equal to the set value of absolute humidity of indoor air, the fresh air unit will be controlled to operate under rated conditions; if the absolute humidity of indoor air is less than the set value of absolute humidity of indoor air, the air volume of the fresh air unit will be reduced. After the initial operation reaches the set time, if the absolute humidity of indoor air is greater than or equal to the set value of absolute humidity of indoor air, the air volume of the fresh air unit will be increased; otherwise, the air volume of the fresh air unit will be decreased.

[0006] Furthermore, the operating mode of the fresh air handling unit also includes a ventilation mode, in which the regulating valve is closed, and the control method further includes: When the fresh air unit is powered on, if the absolute humidity of the indoor air is greater than or equal to the set value of the absolute humidity of the indoor air during the initial operation, the fresh air unit will be controlled to operate under rated conditions. After the initial operation reaches the set time, if the absolute humidity of the indoor air is greater than or equal to the set value of the absolute humidity of the indoor air, the air volume of the fresh air unit will be increased; otherwise, the air volume of the fresh air unit will be reduced.

[0007] Furthermore, when the stop button is pressed during dehumidification and reheating, the compressor is first powered off and stopped running. After a delay of the sixth and seventh set times, the regulating valve and the fresh air unit are powered off and stopped running in sequence.

[0008] Furthermore, the fresh air unit is an EC fan with a rated operating air volume of 5000 m³ / h. 3 / h, minimum operating air volume set to 3125m³ / h 3 / h.

[0009] Furthermore, the fresh air unit also includes an exhaust fan and a differential pressure gauge. The exhaust fan is used to exhaust indoor air to the outside, and the differential pressure gauge is used to collect indoor and outdoor pressure difference information. The control method also includes controlling the operating frequency of the exhaust fan according to the indoor and outdoor pressure difference information so that the fresh air intake and exhaust volume are in a balanced state.

[0010] Beneficial effects: 1. In this invention, the air supply parameters of temperature, absolute humidity and air volume are coupled together. The compressor operating frequency, fan operating frequency and surface cooling valve opening are decoupled and controlled by logic control. When the fresh air conditions change or the indoor moisture dissipation changes, the room air temperature and humidity are kept constant. 2. This invention controls the compressor operating frequency by measuring the difference between the set supply air temperature and the actual supply air temperature; it adjusts the compressor operating frequency based on the reheat of the supply air temperature to achieve high-precision supply air temperature control; and it can automatically switch operating modes based on the comparison between the fresh air temperature and humidity sensor data and the set temperature and humidity. 3. In this invention, the evaporator of the fresh air handling unit bears the sensible heat load of the high-temperature part, and the surface cooler bears the heat and humidity load. By setting the supply air temperature and humidity parameters, the logic calculates the parameters that need to be processed after the surface cooler, and adjusts the opening of the surface cooler valve to meet the absolute humidity content of the supply air. 4. The fresh air unit can use a variable frequency fan or an EC fan. The space can be equipped with a variable air volume exhaust fan and an indoor-outdoor pressure difference controller. When the fresh air supply volume changes, the exhaust volume is adjusted to maintain the set indoor-outdoor pressure difference. 5. This invention places the condenser of the refrigeration system after the surface cooler, which effectively reduces the condensing temperature and improves the unit's energy efficiency. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of a temperature and humidity controlled fresh air handling unit according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a temperature and humidity controlled fresh air handling unit according to another embodiment of the present invention. Detailed Implementation

[0012] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0013] This invention provides a control method for a temperature and humidity controlled fresh air handling unit, see [link to relevant documentation]. Figure 1 and Figure 2The fresh air handling unit includes an evaporator 4 and a condenser 2 arranged along the airflow direction within a fresh air duct. A surface cooler 5 is located on the front or rear side of the evaporator 4, and the surface cooler 5 is connected to a regulating valve 6. The flow rate of the medium entering the surface cooler 5 can be controlled by adjusting the opening of the regulating valve 6. A first temperature and humidity sensor 8 is located at the air inlet of the fresh air duct, and a temperature acquisition device 9 is located on the front side of the condenser 2. The temperature acquisition device 9 can be either a temperature sensor or a temperature and humidity sensor. A second temperature and humidity sensor 10 is located on the rear side of the condenser 2. A fresh air fan 7 is located within the fresh air duct. An expansion valve 3 connects between the evaporator 4 and the condenser 2. The evaporator 4 and the condenser 2 are respectively connected to the air inlet and outlet of the compressor 1. The fresh air handling unit operates in a dehumidification and reheat mode. In the dehumidification and reheat mode, the surface cooler 5 is circulated with chilled water (the flow of chilled water in the surface cooler 5 is controlled by comparing the supply air temperature setpoint and the fresh air inlet temperature). The control method for the above-mentioned fresh air handling unit includes: When the supply air temperature setpoint T is less than the first temperature threshold range, the default setting is to dehumidify and cool the air (with cooling water flowing through the surface cooler): When the fresh air unit 7 is powered on, if the absolute humidity content of the fresh air D1 is greater than the set value of the absolute humidity content of the supply air D + the set absolute humidity content fluctuation range d, or the fresh air temperature T1 is greater than the set value of the supply air temperature T + the set temperature fluctuation range t, then the regulating valve 6 is powered on and opened to the set opening degree after a first set time delay. Then, the opening degree of the regulating valve 6 is adjusted to control the temperature in front of the condenser 2 at the set temperature. And the compressor 1 is powered on and started after a second set time delay. After the compressor 1 starts, it operates at the first set frequency. Then, the opening degree of the regulating valve 6 is adjusted again to keep the temperature in front of the condenser 2 at the set temperature. Specifically, if the temperature in front of the condenser 2 is too high, the regulating valve 6 is opened wider; if the temperature in front of the condenser 2 is too low, the regulating valve 6 is closed narrower. The operating frequency of compressor 1 is adjusted according to the supply air temperature to maintain the supply air temperature T2 at the set value T. Specifically, if the supply air temperature T2 is higher than the set value T, compressor 1 is controlled to operate at a lower frequency; if the supply air temperature T2 is lower than the set value T, compressor 1 is controlled to operate at a higher frequency. The first temperature threshold range can be a value between 18℃ and 30℃. The set value for the absolute moisture content of the supply air, D, is generally set to 11g / kg. The set fluctuation range for the absolute moisture content, d, can be 0.5g / kg, and the set fluctuation range for the temperature, t, can be 2℃. The first setting time is preferably 5 seconds, and the set opening degree of the regulating valve 6 is preferably 80% of the total opening degree. The second setting time is preferably 1 minute, the temperature on the front side of the condenser 2 is controlled at 16℃, and the first set frequency of compressor 1 is preferably 40Hz, at which point the condensing heat is approximately 10kW.

[0014] When the supply air temperature setpoint T is greater than or equal to the first temperature threshold range, the air is dehumidified and heated by default, and the control valve 6 is not powered. When the fresh air unit 7 is powered on, if the absolute humidity content of the fresh air D1 is greater than the set value of the absolute humidity content of the supply air D + the set absolute humidity content fluctuation range d, or the fresh air temperature T1 is less than the set value of the supply air temperature T + the set temperature fluctuation range t, then the compressor 1 is powered on and started after a third set time delay. After starting, the compressor 1 operates at the second set frequency. The third set time is preferably 30 seconds. The second set frequency can be set to 80Hz, but should not exceed 95Hz. The condensing heat is approximately 24kW.

[0015] During this period, if the absolute moisture content of the supplied air D2 > the set value of the absolute moisture content of the supplied air D or the supply air temperature T2 < the set value of the supply air temperature T - the set temperature fluctuation range t, the operating frequency of the compressor 1 is increased. When the absolute moisture content of the supplied air D2 = the set value of the absolute moisture content of the supplied air D, if the supply air temperature T2 < the set value of the supply air temperature T - the set temperature fluctuation range t, the operating frequency of the compressor 1 continues to increase. If the set value of the supply air temperature T + the set temperature fluctuation range t ≥ the supply air temperature T2 ≥ the set value of the supply air temperature T - the set temperature fluctuation range t, the frequency of the compressor 1 remains unchanged. If the absolute moisture content of the supplied air D2 is within the range below the set value of the absolute moisture content of the supplied air D, the compressor 1 is already running at a high frequency, but the supply air temperature T2 < the set value of the supply air temperature T - the set temperature fluctuation range t, the air volume of the fresh air unit 7 is reduced.

[0016] When the frequency of compressor 1 increases, the supply air temperature T2 increases. When the supply air temperature setpoint T + the set temperature fluctuation range t > supply air temperature T2 > supply air temperature setpoint T - the set temperature fluctuation range t, if the supply air absolute humidity D2 is within the range below the supply air absolute humidity setpoint D, the air volume of the fresh air unit is reduced, and the compressor frequency is reduced synchronously with the supply air temperature. If the supply air absolute humidity D2 is below the range below the supply air absolute humidity setpoint D, and the air volume of the fresh air unit 7 is at its minimum value, the frequency of compressor 1 is reduced to ensure that the supply air absolute humidity D2 is above the lower limit of the range below the supply air absolute humidity setpoint D. During the operation of compressor 1, if the absolute humidity content of fresh air D1 is less than the set value of absolute humidity content of supply air D - the set absolute humidity content fluctuation range d, then compressor 1 will be shut down.

[0017] When the stop button is pressed during dehumidification and reheat operation, the compressor 1 is first de-energized and stops running. Then, after a delay of the sixth and seventh set times, the regulating valve 6 and the fresh air unit 7 are de-energized and stopped running in sequence. The sixth set time is preferably 3 seconds, and the seventh set time is preferably 30 seconds.

[0018] It should be noted that the air volume of the fresh air unit 7 can be controlled by the air valve or the rotation speed of the fresh air unit 7. The rotation speed of the fresh air unit 7 can be controlled by frequency modulation or voltage regulation. The aforementioned fresh air unit 7 is an EC fan, meaning that the rotation speed of the fresh air unit 7 can be controlled by the operating voltage, thereby adjusting the air volume of the fresh air unit 7. Preferably, the rated operating air volume of the fresh air unit 7 is 5000 m³ / h. 3 / h, minimum operating air volume set to 3125m³ / h 3 / h. The airflow adjustment of the fresh air unit 7 is based on the following: Fresh air volume = 5000 * 5 / (16 - Absolute moisture content of supply air D2); The unit for fresh air volume is m³. 3 / h, the following are the voltage and air volume parameters for the preferred model of the fresh air unit 7: .

[0019] After startup, the optimal operating voltage for the fresh air unit 7 is 8.3V, which is its rated operating state and maximum airflow state, with an airflow of 5000m³ / h. 3 / h, the corresponding operating voltage is 7.3V when the air volume is at its minimum of 3125m3 / h. During the fan frequency reduction process, the moisture content and temperature of the supply air will change accordingly. The supply air temperature and moisture content are coupled with each other, and the frequency adjustment of compressor 1 and the voltage adjustment of fresh air unit 7 follow each other repeatedly.

[0020] The fresh air handling unit of this embodiment also includes a third temperature and humidity sensor 11, which is used to collect indoor air temperature and humidity. The fresh air handling unit also includes a heating and dehumidification mode. The operating conditions for the heating and dehumidification mode are: the supply air temperature setpoint T is higher than the second temperature threshold, and the absolute humidity of the fresh air is less than the absolute humidity setpoint D. In the heating and dehumidification mode, hot water is supplied to the surface cooler 5. The control method of the fresh air handling unit also includes: The fresh air unit 7 is powered on and put into operation. The regulating valve 6 is then powered on and opened to a set opening degree after a fourth set time delay. The opening degree of the regulating valve 6 is maintained for a fifth set time, and then the opening degree of the regulating valve 6 is adjusted again to keep the supply air temperature T2 at the set value T. Specifically, when the supply air temperature T2 is lower than the set value T, the opening degree of the regulating valve 6 is increased; when the supply air temperature T2 is higher than the set value T, the opening degree of the regulating valve 6 is decreased. The air volume of the fresh air unit 7 is adjusted as follows: During initial operation, if the absolute humidity of indoor air is greater than or equal to the set value of absolute humidity of indoor air, the fresh air unit 7 will be controlled to operate under rated conditions. If the absolute humidity of indoor air is less than the set value of absolute humidity of indoor air, the air volume of the fresh air unit 7 will be reduced.

[0021] After initial operation for the set time, if the absolute humidity of the indoor air is greater than or equal to the set value, the airflow of the fresh air unit 7 will be increased; otherwise, the airflow of the fresh air unit 7 will be decreased. The fourth set time is preferably 5 seconds, and the fifth set time is preferably 30 seconds. When the stop button is pressed during reheating and dehumidification, if the regulating valve 6 is also energized and open, the regulating valve 6 will preferably be de-energized after a 3-second delay, and then the supply fan will preferably be de-energized after a further 30-second delay.

[0022] The fresh air handling unit of this embodiment also includes a ventilation mode. In the ventilation mode, the regulating valve 6 is closed. The control method of the above-mentioned fresh air handling unit further includes: When the fresh air unit 7 is powered on, during initial operation, if the absolute humidity of the indoor air is greater than or equal to the set value, the fresh air unit 7 will operate under rated conditions. After the initial operation reaches the set time, if the absolute humidity of the indoor air is greater than or equal to the set value, the airflow of the fresh air unit 7 will increase; otherwise, the airflow of the fresh air unit 7 will decrease. When the stop button is pressed during ventilation operation, the fresh air unit 7 preferably de-energizes after a 30-second delay.

[0023] The aforementioned fresh air handling unit also includes an exhaust fan 12 and a differential pressure gauge 13. The exhaust fan 12 is used to exhaust indoor air to the outside, and the differential pressure gauge 13 is used to collect indoor and outdoor pressure difference information. The aforementioned control method also includes controlling the operation of the exhaust fan 12 based on the indoor and outdoor pressure difference information to keep the fresh air intake and exhaust air volume in a balanced state. The indoor air pressure can generally be set to -15 Pa.

[0024] The above description is merely a preferred embodiment of the present invention. It should be noted that for those skilled in the art, other parts not specifically described are existing technology or common knowledge. Several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A control method for a temperature and humidity controlled fresh air handling unit, characterized in that, The fresh air unit includes an evaporator and a condenser arranged in the fresh air duct along the airflow direction. A surface cooler is provided on the front or rear side of the evaporator. The surface cooler is connected to a regulating valve. A first temperature and humidity sensor is provided at the air inlet of the fresh air duct. A temperature sensor is provided on the front side of the condenser and a second temperature and humidity sensor is provided on its rear side. A fresh air fan is provided in the fresh air duct. An expansion valve is connected between the evaporator and the condenser, and the expansion valve and the condenser are respectively connected to the air inlet and air outlet of the compressor. The operating modes of the fresh air handling unit include dehumidification and reheat mode. Under dehumidification and reheat mode, the control method includes: When the supply air temperature setpoint T is less than the first temperature threshold range, the surface cooler is supplied with cooling water: When the fresh air unit is powered on, if the absolute humidity of the fresh air D1 is greater than the set value of the absolute humidity of the supply air D + the set absolute humidity fluctuation range d, or the fresh air temperature T1 is greater than the set value of the supply air temperature T + the set temperature fluctuation range t, then the control valve is powered on and opened to the set opening degree after a first set time delay. Then, the opening degree of the control valve is adjusted to control the temperature at the front of the condenser at the set temperature. The compressor is powered on and started after a second set time delay. After the compressor starts, it operates at the first set frequency. Then, the opening degree of the control valve is adjusted again to keep the temperature at the front of the condenser at the set temperature. The operating frequency of the compressor is adjusted according to the supply air temperature to keep the supply air temperature T2 at the set value T. When the supply air temperature setpoint T is greater than or equal to the first temperature threshold range, the regulating valve must not be electrically operated. If the absolute humidity of the fresh air D1 is greater than the set value of the absolute humidity of the supply air D + the set absolute humidity fluctuation range d, or the fresh air temperature T1 is less than the set value of the supply air temperature T - the set temperature fluctuation range t, then the compressor is powered on and started after a third set time delay. After the compressor starts, it operates at the second set frequency. During this period, if the absolute moisture content of the supply air D2 > the set value of the absolute moisture content of the supply air D or the supply air temperature T2 < the set value of the supply air temperature T - the set temperature fluctuation range t, the operating frequency of the compressor will be increased. When the absolute moisture content of the supply air D2 = the set value of the absolute moisture content of the supply air D, if the supply air temperature T2 < the set value of the supply air temperature T - the set temperature fluctuation range t, the operating frequency of the compressor will continue to increase. If the set value of the supply air temperature T + the set temperature fluctuation range t ≥ the supply air temperature T2 ≥ the set value of the supply air temperature T - the set temperature fluctuation range t, the compressor frequency will remain unchanged. If the absolute moisture content of the supply air D2 is within the range below the set value of the absolute moisture content of the supply air D, the compressor is already running at a high frequency, but the supply air temperature T2 < the set value of the supply air temperature T - the set temperature fluctuation range t, the air volume of the fresh air unit will be reduced. When the compressor frequency increases, the supply air temperature T2 increases. When the supply air temperature setpoint T + the set temperature fluctuation range t > supply air temperature T2 > supply air temperature setpoint T - the set temperature fluctuation range t, if the supply air absolute humidity D2 is within the range below the supply air absolute humidity setpoint D, the air volume of the fresh air unit is reduced. If the supply air absolute humidity D2 is below the range below the supply air absolute humidity setpoint D, and the air volume of the fresh air unit is at its minimum value, the compressor frequency is reduced to ensure that the supply air absolute humidity D2 is above the lower limit of the range below the supply air absolute humidity setpoint D. During compressor operation, if the absolute humidity content of fresh air D1 is less than or equal to the set value of absolute humidity content of supply air D - the set absolute humidity content fluctuation range d, the compressor will be shut down.

2. The control method for a temperature and humidity controlled fresh air handling unit according to claim 1, characterized in that, The fresh air handling unit also includes a third temperature and humidity sensor, which is used to collect indoor air temperature and humidity. The fresh air handling unit also includes a heating and dehumidification mode. The prerequisites for this mode are: the supply air temperature setpoint T is higher than the second temperature threshold, and the absolute humidity of the fresh air is less than the absolute humidity setpoint D. In this mode, hot water is supplied to the surface cooler, the fresh air handling unit is powered on, and the regulating valve is powered on and opened to the set opening degree after a fourth set time delay. The opening degree of the regulating valve is maintained for a fifth set time, and then the opening degree is adjusted again to keep the supply air temperature T2 at the set value T. The airflow of the fresh air handling unit is adjusted as follows: During initial operation, if the absolute humidity of indoor air is greater than or equal to the set value of absolute humidity of indoor air, the fresh air unit will be controlled to operate under rated conditions; if the absolute humidity of indoor air is less than the set value of absolute humidity of indoor air, the air volume of the fresh air unit will be reduced. After the initial operation reaches the set time, if the absolute humidity of indoor air is greater than or equal to the set value of absolute humidity of indoor air, the air volume of the fresh air unit will be increased; otherwise, the air volume of the fresh air unit will be decreased.

3. The control method for a temperature and humidity controlled fresh air handling unit according to claim 1, characterized in that, The operating mode of the fresh air handling unit also includes a ventilation mode, in which the regulating valve is closed, and the control method further includes: When the fresh air unit is powered on, if the absolute humidity of the indoor air is greater than or equal to the set value of the absolute humidity of the indoor air during the initial operation, the fresh air unit will be controlled to operate under rated conditions. After the initial operation reaches the set time, if the absolute humidity of the indoor air is greater than or equal to the set value of the absolute humidity of the indoor air, the air volume of the fresh air unit will be increased; otherwise, the air volume of the fresh air unit will be reduced.

4. The control method for a temperature and humidity controlled fresh air handling unit according to claim 1, characterized in that, When the stop button is pressed during dehumidification and reheating, the compressor is first powered off and stopped. After a delay of the sixth and seventh set times, the regulating valve and the fresh air unit are powered off and stopped in sequence.

5. The control method for a temperature and humidity controlled fresh air handling unit according to claim 1, characterized in that, The fresh air unit is an EC fan with a rated operating air volume of 5000 m³ / h. 3 / h, minimum operating air volume set to 3125m³ / h 3 / h.

6. The control method for a temperature and humidity controlled fresh air handling unit according to claim 1, characterized in that, The fresh air unit also includes an exhaust fan and a differential pressure gauge. The exhaust fan is used to exhaust indoor air to the outside, and the differential pressure gauge is used to collect indoor and outdoor pressure difference information. The control method also includes controlling the operating frequency of the exhaust fan according to the indoor and outdoor pressure difference information so that the fresh air intake and exhaust volume are in a balanced state.

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