Multi-working-condition self-adaptive grade selection fresh air handling unit based on grade adaptation and control method thereof

Abstract

The invention discloses a multi-working-condition self-adaptive grade selection fresh air handling unit based on grade adaptation and a control method thereof, and relates to the field of air conditioning unit design. The multi-working-condition self-adaptive grade selection fresh air handling unit comprises a filter, a first-stage coil pipe, a second-stage coil pipe and a fan which are sequentially arranged in the direction from a fresh air inlet to a fresh air outlet; a first bypass air duct and a first electric air valve are arranged on the side of the first-stage coil pipe, and the first electric air valve is used for regulating and controlling the size of an opening of the first bypass air duct; a second bypass air duct and a second electric air valve are arranged on the side of the second-stage coil pipe, and the second electric air valve is used for regulating and controlling the size of an opening of the second bypass air duct; the device further comprises a control system, and the control system is used for adjusting and controlling opening and closing of the first electric air valve and the second electric air valve and adjusting the flow of the first-stage coil pipe and the flow of the second-stage coil pipe through the first electric water valve and the second electric water valve respectively. By the adoption of the scheme, the problems that an existing fresh air handling unit structure cannot well adapt to annual changes, and system energy consumption is high are solved.

Description

Technical Field

[0001] This invention relates to the field of air conditioning unit design, specifically to a multi-condition adaptive grade-selective fresh air handling unit based on grade matching and its control method. Background Technology

[0002] The supply of fresh air systems plays a crucial role in maintaining indoor air quality, protecting human health, and improving comfort. Because fresh air needs to be supplied year-round, outdoor meteorological parameters fluctuate significantly throughout the year, and fresh air accounts for a large proportion of the overall load, thus placing higher demands on the energy efficiency of fresh air systems. Fresh air systems not only need to handle a wide range of enthalpy differences but also undertake critical dehumidification tasks within independent temperature and humidity control systems. Therefore, the performance of fresh air units directly affects the stability of the building's internal environment and its energy efficiency.

[0003] However, traditional fresh air handling systems often employ a single channel, single coil, and single heat / cold source to process fresh air. This fixed, unadjustable approach proves inadequate in the face of year-round climate changes. For example, during transitional seasons, the fresh air unit still needs to process air through a heat exchanger, resulting in unnecessary energy consumption. Furthermore, a single coil has limited adjustment capabilities in temperature and humidity control, making it difficult to flexibly respond to the variability of indoor and outdoor environments. Simultaneously, the single-grade heat / cold source cannot achieve a flexible and optimal match between supply and demand, leading to energy waste and low main unit energy efficiency. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention aims to provide a multi-condition adaptive grade-selective fresh air handling unit and its control method based on grade matching. This solution addresses the problem that current fresh air handling unit structures cannot adapt well to year-round changes and that the system has high energy consumption.

[0005] This invention is achieved through the following technical solution:

[0006] A multi-condition adaptive air handling unit based on quality matching includes:

[0007] The primary coil, secondary coil, and fan are arranged sequentially from the fresh air inlet to the outlet.

[0008] The primary coil has a first bypass ventilation duct and a first electric air valve. The first electric air valve is used to adjust the opening size of the first bypass ventilation duct. The primary coil also has a first electric water valve for adjusting its own flow rate.

[0009] The secondary coil has a second bypass ventilation duct and a second electric air valve. The second electric air valve is used to adjust the opening size of the second bypass ventilation duct. The secondary coil also has a second electric water valve for adjusting its own flow rate.

[0010] It also includes a control system, which is used to control the opening and closing of the first electric air valve and the second electric air valve respectively, and to adjust the flow rate of the first-stage coil and the second-stage coil respectively through the first electric water valve and the second electric water valve.

[0011] Furthermore, a filter is also installed at the fresh air inlet.

[0012] Furthermore, the present invention also provides a design method for a multi-condition adaptive grade-selective fresh air handling unit based on quality adaptation, including the step of designing the duct size allocation for the first bypass ventilation duct and the second bypass ventilation duct, the step including:

[0013] S1: Adjust the fresh air volume L of the fresh air unit according to demand based on indoor meteorological parameters and indoor environmental parameters. xf ;

[0014] S2: Based on the fresh air enthalpy value h xf Enthalpy value of air supply point h s and fresh air volume L xf The fresh air load Q was calculated. xf ;

[0015] S3: Based on the size of the fresh air load, adjust the opening and closing of the first electric air valve and the second electric air valve respectively, and adjust the flow rate of the first-stage coil and the second-stage coil respectively through the first electric water valve and the second electric water valve.

[0016] A further step involves designing and allocating the duct dimensions of the first and second bypass ventilation ducts before step S1, specifically including the following steps:

[0017] The resistance of the bypass ventilation duct is calculated based on the air velocity at the bypass duct; where the air velocity is... L is the air volume, ρ is the air density; resistance ζ is the local resistance coefficient of the electric air valve;

[0018] Based on the coil size corresponding to the bypass ventilation duct and the oncoming wind speed of the coil at that location, the air resistance of the coil at that location is calculated; where the oncoming wind speed is... A represents the length of the coil at that location, and B represents the height of the coil at that location; air resistance. a and b are coefficients;

[0019] Finally, based on ΔP j =ΔH g Determine the height C of the adjacent ventilation duct.

[0020] In a further embodiment, step S1 also includes the following specific steps:

[0021] When the indoor CO2 concentration is less than the lower limit K1 of the CO2 concentration optimization range, adjust the opening of the fresh air valve and reduce the fresh air volume;

[0022] When the indoor CO2 concentration exceeds the upper limit K2 of the CO2 concentration optimization range, adjust the opening of the fresh air valve and increase the fresh air volume. In a further embodiment, the formula for calculating the fresh air load in step S2 is:

[0023] Q xf =L xf (h xf -h s ).

[0024] In a further embodiment, step S3, which involves adjusting the opening and closing of the first and second electric air valves according to the fresh air load, includes the following operating conditions:

[0025] Air valve operating condition 1: When the fresh air load Q xf When the value is 0, the first and second electric air valves are opened, and the main unit disconnects the power supply to the primary and secondary coils; at this time, fresh air flows sequentially through the first electric air valve, the second electric air valve, the fan, and the fresh air outlet.

[0026] Air valve operating condition 2: When 0 < fresh air load Q xf When the load Q1 is set, the second electric air valve is opened and the first electric air valve is closed. At this time, the main unit only supplies energy to the first-stage coil. Fresh air flows through the first-stage coil, the second electric air valve, the fan and the fresh air outlet in sequence.

[0027] Air valve operating condition 3: When the fresh air load Q xf When the load is set to Q1, the first and second electric air valves are closed. At this time, the main unit supplies energy to both the primary and secondary coils. Fresh air flows sequentially through the primary coil, the secondary coil, the fan, and the fresh air outlet.

[0028] In a further embodiment, step S3, which involves adjusting the flow rates of the primary and secondary coils using the first and second electric water valves respectively, based on the fresh air load, includes the following operating conditions:

[0029] Water valve operating condition 1: When the fresh air load Q xf When the value is 0, both the first and second electric water valves are closed simultaneously.

[0030] Water valve operating condition 2: When 0 < fresh air load Q xf When the load Q1 is set, the second electric water valve is closed, and the flow rate of the first-stage coil is adjusted through the first electric water valve if the air supply parameters meet the requirements.

[0031] Water valve operating condition 3: When the fresh air load Q xfWhen the load is set to Q1, open the first electric water valve to make the primary coil flow rate the design flow rate; and open the second electric water valve to adjust the flow rate of the secondary coil if the air supply parameters meet the requirements.

[0032] In a further embodiment, in the second operating condition of the water valve, the flow regulation of the primary coil includes the following specific steps:

[0033] During the heat and moisture exchange process of the primary coil, the state parameters of the air side and water side of the primary coil are calculated respectively.

[0034] Based on the state parameters of the air and water sides of the first-stage coil, and according to the thermal balance and the heat and moisture exchange equations, the water flow rate W is calculated.

[0035] Based on the obtained water flow rate W, the corresponding valve opening l is calculated;

[0036] Then adjust the first electric water valve to the opening degree l.

[0037] In a further proposed solution, under the third operating condition of the water valve, the flow regulation of the primary and secondary coils includes the following specific steps:

[0038] First, adjust the opening degree l1 of the first electric water valve to the maximum;

[0039] The state parameters of the primary coil outlet were then calculated based on the heat and moisture exchange equations.

[0040] Based on the state parameters of the primary coil outlet, the state parameters of the secondary coil on the air side and water side are calculated.

[0041] Based on the state parameters of the air and water sides of the secondary coil, and according to the heat and moisture exchange equations, the water flow rate W2 is calculated.

[0042] Based on the water flow rate W2, the corresponding valve opening l2 is calculated;

[0043] Then adjust the second electric water valve to the opening degree l2.

[0044] A further proposed approach is to define the heat and moisture exchange equations as follows:

[0045]

[0046] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0047] 1. This invention provides a multi-condition adaptive grade-selective fresh air handling unit and its control method based on grade matching. By adopting this solution, low-grade energy can be fully utilized as much as possible while minimizing resistance, reducing the energy consumption of the ventilation system, realizing the graded utilization of energy, optimizing energy use efficiency, and reducing the overall energy consumption throughout the year.

[0048] 2. This invention provides a multi-condition adaptive grade-selective fresh air handling unit and its control method based on grade matching. By adopting this solution, the space can be saved as much as possible while controlling the resistance through the design of the bypass ventilation duct height.

[0049] 3. This invention provides a multi-condition adaptive grade-selective fresh air handling unit and its control method based on grade matching. By adopting this solution, based on channel switching, the flow distribution of the primary and secondary coils can be adjusted to maximize the utilization of low-grade energy while meeting the requirements of the air supply status parameters. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0051] Figure 1 This is a schematic diagram of the structure of the fresh air handling unit provided by the present invention;

[0052] Figure 2 A schematic diagram illustrating the dimensional allocation of the coil and damper provided by the present invention;

[0053] Figure 3 This is a schematic diagram of the fresh air duct under the working condition of the air valve provided by the present invention;

[0054] Figure 4 This is a schematic diagram of the fresh air duct under the second working condition of the air valve provided by the present invention;

[0055] Figure 5 This is a schematic diagram of the fresh air duct under the third working condition of the air valve provided by the present invention;

[0056] Figure 6 This is a schematic diagram of the air valve adjustment process provided by the present invention;

[0057] Figure 7 This is a schematic diagram of the water valve adjustment process provided by the present invention;

[0058] Figure 8 A schematic diagram illustrating the state parameter changes of the water valve under operating condition two provided by the present invention;

[0059] Figure 9 This is a schematic diagram illustrating the changes in state parameters of the water valve under three operating conditions provided by the present invention.

[0060] The attached diagram shows the markings and corresponding component names:

[0061] 1-Filter, 2-Primary coil, 3-Secondary coil, 4-Fan, 5-First electric air valve, 6-Second electric air valve, 7-First electric water valve, 8-Second electric water valve. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0063] Example 1: This Example 1 provides a multi-condition adaptive grade-selective fresh air handling unit based on quality adaptation, such as... Figure 1 As shown, it includes:

[0064] The primary air coil 2, the secondary air coil 3, and the fan 4 are arranged sequentially from the fresh air inlet to the outlet.

[0065] The first-stage coil 2 has a first bypass ventilation duct and a first electric air valve 5 on one side. The first electric air valve 5 is used to adjust the opening size of the first bypass ventilation duct. The first-stage coil 2 also has a first electric water valve 7 for adjusting its own flow rate.

[0066] The secondary coil 3 is equipped with a second bypass ventilation duct and a second electric air valve 6. The second electric air valve 6 is used to adjust the opening size of the second bypass ventilation duct. The secondary coil 3 is also equipped with a second electric water valve 8 for adjusting its own flow rate.

[0067] It also includes a control system, which is used to control the opening and closing of the first electric air valve 5 and the second electric air valve 6 respectively, and to adjust the flow rate of the first-stage coil 2 and the second-stage coil 3 respectively through the first electric water valve 7 and the second electric water valve 8.

[0068] In this embodiment, a filter 1 is also provided at the fresh air inlet.

[0069] Example 2: This Example 2 is a further optimization based on Example 1, such as... Figure 2 As shown, this paper mainly provides a design method for a multi-condition adaptive grade-selective fresh air handling unit based on quality adaptation, including the step of designing the duct size allocation for the first bypass ventilation duct and the second bypass ventilation duct. This design step includes:

[0070] The height C of the bypass ventilation duct is calculated based on resistance balance, which saves space as much as possible while controlling resistance.

[0071] Resistance through the bypass duct Where ζ is the local resistance coefficient of the electric damper, and the air velocity at the bypass duct is... L represents air volume, and ρ represents air density.

[0072] Air resistance through the coil a and b are coefficients; the dimensions of the coil are A x B (length x height), and the oncoming wind speed through the coil is...

[0073] Finally, based on ΔP j =ΔH g The height C of the bypass ventilation duct can then be determined.

[0074] Example 3: This Example 3 further optimizes Example 1 and provides a control method for a multi-condition adaptive grade-selective fresh air handling unit based on quality matching, mainly including the following steps:

[0075] S1: Adjust the fresh air volume L of the four fresh air units according to indoor meteorological and environmental parameters and as needed. xf ;

[0076] S2: Based on the fresh air enthalpy value h xf Enthalpy value of air supply point h s and fresh air volume L xf The fresh air load Q was calculated. xf ;

[0077] S3: Based on the size of the fresh air load, adjust the opening and closing of the first electric air valve 5 and the second electric air valve 6 respectively, and adjust the flow rate of the first-stage coil 2 and the second-stage coil 3 respectively through the first electric water valve 7 and the second electric water valve 8.

[0078] The above steps mainly include the design of the bypass ventilation duct height, the control strategy of the electric air valve, and the control strategy of the electric water valve.

[0079] Example 4: This Example 4 is a further optimization based on Example 3, such as... Figures 3-6 As shown, a control strategy for electric air valves is mainly provided.

[0080] The four fan units are equipped with a built-in automatic control program, which allows them to flexibly supply fresh air volume (L) as needed based on real-time outdoor meteorological parameters and indoor environmental parameters throughout the year. xf Accurately calculate the fresh air load Q xf The automatic control program is based on the real-time fresh air load Q. xfThe system intelligently regulates the opening and closing of the first electric air valve 5 and the second electric air valve 6, thereby precisely controlling the flow direction of fresh air and guiding it through specific air ducts and coils. This maximizes the utilization of low-grade energy while minimizing resistance, reducing energy consumption in the ventilation system, achieving tiered utilization of energy grades, optimizing energy efficiency, and lowering overall annual energy consumption.

[0081] The specific channel switching control strategy is as follows:

[0082] 1. Adjust the fresh air volume (L) of the four fresh air units according to the indoor CO2 concentration. xf When the CO2 concentration is less than the lower limit K1 of the CO2 concentration optimization range, the control system issues a command to adjust the opening of the fresh air valve to reduce the fresh air volume; when the CO2 concentration is greater than the upper limit K2 of the CO2 concentration optimization range, the control system issues a command to adjust the opening of the fresh air valve to increase the fresh air volume.

[0083] 2. Based on the fresh air enthalpy h xf Enthalpy of air supply point hs and fresh air volume L xf The calculated fresh air load is Qxf = Lxf(hxf - hs).

[0084] 3. Determine the fresh air load Q xf Size:

[0085] Operating Condition 1: Fresh Air Load Q xf =0, the automatic control program opens the first electric air valve 5 and the second electric air valve 6, the main unit does not need power supply, and the fresh air does not pass through the coil. For example... Figure 3 As shown, at this time, the fresh air flows through the first electric air valve 5, the second electric air valve 6, the fan 4 and the fresh air outlet in sequence;

[0086] Operating Condition 2: 0 < Fresh Air Load Q xf Set load Q1, open the second electric air valve 6, close the first electric air valve 5, and the main unit uses low-grade energy supply. At this time, the fresh air only passes through the first-stage coil 2. Figure 4 As shown, at this time, the fresh air flows sequentially through the primary coil 2, the second electric air valve 6, the fan 4, and the fresh air outlet;

[0087] Operating Condition 3: Fresh Air Load Q xf ≥ Set load Q1, close the second electric air valve 6 and the first electric air valve 5. The main unit adopts dual-grade energy supply. At this time, the fresh air first undergoes preliminary pretreatment through the primary coil 2 supplied by the low-grade cold and heat source, and then undergoes further deep treatment through the secondary coil 3 supplied by the high-grade cold and heat source, realizing the cascade utilization of energy grade. Figure 5 As shown, at this time, the fresh air flows through the primary coil 2, the secondary coil 3, the fan 4, and the fresh air outlet in sequence.

[0088] Example 5: This Example 5 is a further optimization based on Example 4, such as... Figures 7-9 As shown, this paper mainly presents a control strategy for electric water valves. Specifically, it enables flow distribution control based on grade adaptation. By adjusting the flow distribution between primary coil 2 and secondary coil 3, and while meeting the air supply parameter requirements, it maximizes the utilization of low-grade energy. The main operating conditions include the following:

[0089] Operating Condition 1: Fresh Air Load Q xf =0, fresh air does not pass through the coil, the first electric water valve 7 and the second electric water valve 8 used for coil flow regulation are closed;

[0090] Operating Condition 2: 0 < Fresh Air Load Q xf <Set load Q1, fresh air only passes through the first-stage coil 2 connected to low-grade energy, and the air supply parameters meet the requirements by controlling the water flow of the first-stage coil 2;

[0091] Operating Condition 3: Fresh Air Load Q xf For a set load Q1, fresh air needs to pass through two coils sequentially. The overall allocation principle is: primary coil 2 is used to its fullest extent, while secondary coil 3's supply air parameters are controlled to meet indoor demand. Specifically: for the primary coil connected to low-grade energy, it is used to its limit, meaning the coil's water flow rate is the design flow rate, remaining constant. For the secondary coil 3 connected to high-grade energy, the supply air parameters are controlled to meet requirements.

[0092] In the second operating condition described above, i.e., when a single coil is used:

[0093] Single coil: 0 < fresh air load Q xf With a set load Q1, and fresh air passing only through primary coil 2 connected to low-grade energy, the changes in the air-side and water-side parameters of the coil during this heat and humidity exchange process are as follows: Figure 8 As shown.

[0094] The calculation method for the feng shui parameters of the air conditioning coil is as follows:

[0095] For the air side, Q1 = L xf (h1-h2);

[0096] For the water side, we have: Q2 = cm(t) w1 -t w2 );

[0097] For heat exchangers, we have: Q3 = KAΔt m ;

[0098] in:

[0099]

[0100] According to thermal equilibrium: Q1 = Q2 = Q3;

[0101] Therefore, the above formula can be expressed as the following set of heat and moisture exchange equations:

[0102]

[0103] The contact coefficient E can be obtained from the number of coil rows and the oncoming wind speed.

[0104] Based on the above set of equations, the required water flow rate W can be obtained, and the corresponding valve opening l can be calculated. The system issues a command to adjust the first electric water valve 7 to the opening l so that the air supply parameters meet the requirements.

[0105] In the above-mentioned operating condition three, that is, when dual coils are used:

[0106] Dual coil: Fresh air load Q xf With a set load Q1, the fresh air needs to pass through two coils sequentially. The changes in the air-side and water-side parameters of the coils are as follows: Figure 9 As shown.

[0107] According to the overall allocation principle of the two-stage coils, the primary coil 2 is used to its fullest extent. Therefore, the water flow rate W1 of the primary coil 2 should be the design flow rate, and the opening l1 of the first electric water valve 7 should be at its maximum. Under this premise, the state parameters of the outlet of the primary coil 2 can be obtained using the aforementioned heat exchanger heat and moisture exchange calculation formula. Using this as input conditions, the state parameters of the air side and water side of the secondary coil 3 can be obtained. The required water flow rate W2 can be obtained again using the heat and moisture exchange equations. The corresponding valve opening l2 is calculated, and the system issues commands to adjust the first electric water valve 7 to the opening l1 and the second electric water valve 8 to the opening l2, so that the air supply parameters meet the requirements.

[0108] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The multi-condition adaptive grade-selective fresh air unit based on grade adaptation is characterized by: include: A primary coil (2), a secondary coil (3) and a fan (4) are arranged in sequence from the fresh air inlet to the outlet; The first-stage coil (2) is provided with a first bypass air duct and a first electric air valve (5), wherein the first electric air valve (5) is used to adjust the opening size of the first bypass air duct; the first-stage coil (2) is also provided with a first electric water valve (7) for adjusting its own flow rate; The secondary coil (3) is provided with a second bypass air duct and a second electric air valve (6), wherein the second electric air valve (6) is used to adjust the opening size of the second bypass air duct; the secondary coil (3) is also provided with a second electric water valve (8) for adjusting its own flow rate; It also includes a control system, which is used to respectively control the opening and closing of the first electric air valve (5) and the second electric air valve (6), and to respectively adjust the flow of the primary coil (2) and the secondary coil (3) through the first electric water valve (7) and the second electric water valve (8).

2. According to claim 1, a multi-condition adaptive grade-selective fresh air unit based on grade adaptation is characterized in that: A filter (1) is also provided at the fresh air inlet.

3. A design method for a multi-condition adaptive grade-selective fresh air unit based on grade adaptation according to claim 1 or 2, characterized in that: The method comprises the steps of designing the air duct size distribution of the first bypass air duct and the second bypass air duct, the steps comprising: The resistance of the bypass duct is calculated based on the air flow rate at the bypass duct; where the air flow rate L is the air volume, ρ is the air density; resistance ζ is the local resistance coefficient of the electric air valve; According to the coil size corresponding to the bypass air duct and the headwind speed of the coil at that location, the air resistance of the coil at that location is calculated; among which, the headwind speed A is the length of the coil at that location, B is the height of the coil at that location; air resistance a and b are coefficients; Finally, according to ΔP j =ΔH g , determine the height C of the bypass duct.

4. A control method for a multi-condition adaptive grade-selective fresh air unit based on grade adaptation according to claim 1 or 2, characterized in that: The following steps are involved: S1: According to indoor meteorological parameters and indoor environmental parameters, adjust the fresh air volume L of the fresh air unit as needed xf ; S2: Based on the fresh air enthalpy value h xf , Enthalpy value of air supply point h s and fresh air volume L xf , calculate the fresh air load Q xf ; S3: According to the size of the fresh air load, the opening and closing of the first electric air valve (5) and the second electric air valve (6) are respectively regulated, and the flow rates of the primary coil (2) and the secondary coil (3) are respectively regulated through the first electric water valve (7) and the second electric water valve (8).

5. The control method of a multi-condition adaptive grade-selective fresh air unit based on grade adaptation according to claim 3 is characterized in that: The step S1 also includes the following specific steps: When the indoor CO2 concentration is less than the lower limit K1 of the CO2 concentration optimization range, adjust the opening of the fresh air valve and reduce the fresh air volume; When the indoor CO2 concentration is greater than the upper limit K2 of the CO2 concentration optimization range, adjust the opening of the fresh air valve and increase the fresh air volume.

6. The control method of a multi-condition adaptive grade-selective fresh air unit based on grade adaptation according to claim 3 is characterized in that: In step S3, the step of respectively regulating the opening and closing of the first electric air valve (5) and the second electric air valve (6) according to the size of the fresh air load includes the following working conditions: Air valve working condition 1: When the fresh air load Q xf =0, the first electric air valve (5) and the second electric air valve (6) are opened, and the host cuts off the energy supply to the primary coil (2) and the secondary coil (3); the fresh air flows through the first electric air valve (5), the second electric air valve (6), the fan (4) and the fresh air outlet in sequence; Air valve working condition 2: When 0 < fresh air load Q xf <When the load Q1 is set, the second electric air valve (6) is opened and the first electric air valve (5) is closed. At this time, the host only supplies energy to the primary coil (2); at this time, the fresh air flows through the primary coil (2), the second electric air valve (6), the fan (4) and the fresh air outlet in sequence; Air valve working condition three: when the fresh air load Q xf ≥When the load Q1 is set, the first electric air valve (5) and the second electric air valve (6) are closed, and the host supplies energy to the primary coil (2) and the secondary coil (3) at the same time; at this time, the fresh air flows through the primary coil (2), the secondary coil (3), the fan (4) and the fresh air outlet in sequence.

7. The control method of a multi-condition adaptive grade-selective fresh air unit based on grade adaptation according to claim 3 is characterized in that: In step S3, the step of respectively adjusting the flow rates of the primary coil (2) and the secondary coil (3) by means of the first electric water valve (7) and the second electric water valve (8) according to the size of the fresh air load includes the following working conditions: Water valve working condition 1: When the fresh air load Q xf =0, the first electric water valve (7) and the second electric water valve (8) are closed simultaneously; Water valve working condition 2: When 0 < fresh air load Q xf <When the load Q1 is set, the second electric water valve (8) is closed, and when the air supply parameters meet the requirements, the flow rate of the primary coil (2) is adjusted through the first electric water valve (7); Water valve working condition three: when the fresh air load Q xf When the load Q1 is set, the first electric water valve (7) is opened to make the primary coil (2) reach the design flow rate; and the second electric water valve (8) is opened. When the air supply parameters meet the requirements, the flow rate of the secondary coil (3) is adjusted through the second electric water valve (8).

8. The control method of a multi-condition adaptive grade-selective fresh air unit based on grade adaptation according to claim 7 is characterized in that: In the water valve working condition 2, the flow regulation of the primary coil (2) comprises the following specific steps: During the heat and moisture exchange process of the primary coil (2), respectively calculating the state parameters of the wind side and the water side of the primary coil (2); Based on the state parameters of the wind side and the water side of the primary coil (2), and according to the thermodynamic balance and heat and moisture exchange equations, the water flow rate W is calculated; According to the obtained water flow W, the corresponding valve opening l is calculated; Then, the first electric water valve (7) is adjusted to an opening degree of 1.

9. A control method for a multi-condition adaptive grade-selective fresh air unit based on grade adaptation according to claim 8, characterized in that: In the water valve working condition 3, the flow rate regulation of the primary coil (2) and the secondary coil (3) includes the following specific steps: Firstly, the opening degree l1 of the first electric water valve (7) is adjusted to the maximum; Then, the state parameters of the outlet of the primary coil (2) are calculated according to the heat and moisture exchange equations; Calculating the state parameters of the wind side and the water side of the secondary coil (3) based on the state parameters of the outlet of the primary coil (2); Based on the state parameters of the wind side and the water side of the secondary coil (3), and according to the heat and moisture exchange equations, the water flow rate W2 is calculated; According to the water flow W2, the corresponding valve opening l2 is calculated; Then, the second electric water valve (8) is adjusted to an opening degree of l2.

10. A control method for a multi-condition adaptive grade-selective fresh air unit based on grade adaptation according to claim 9, characterized in that: The heat and moisture exchange equations are:

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