CN112923594B - Magnetic suspension evaporation cold direct expansion unit and control method thereof - Google Patents

Abstract

The invention belongs to the technical field of refrigeration and aims to solve the problems of poor heat exchange effect, inconvenient maintenance, high noise, high energy consumption and unfavorable energy saving that existing direct expansion units mostly use an oil system. The invention provides a control method of a magnetic levitation evaporative cooling direct expansion unit. The magnetic levitation evaporative cooling direct expansion unit includes a magnetic levitation compressor, an evaporative condenser, a liquid storage device, a gas-liquid separator, and a plurality of indoor air coolers. The water tank includes a condensing fan and a water tank temperature sensor. The water tank temperature sensor is used to detect the water temperature in the water tank. The control method includes: obtaining the water temperature in the water tank and/or the pressure ratio of the magnetic levitation evaporative cooling direct expansion unit; according to the water temperature in the water tank/ Or the pressure ratio of the maglev evaporative cooling direct expansion unit to control the start and stop of the condensing fan. The invention can ensure the heat exchange effect of the unit, is convenient for maintenance, has low noise, can realize the dynamic adjustment of the condensing fan, realizes energy-saving control, and is beneficial to reduce the energy consumption of the direct expansion unit.

Description

Magnetic Suspension Evaporative Cooling Direct Expansion Unit and Its Control Method

technical field

The invention belongs to the technical field of refrigeration, and specifically provides a magnetic levitation evaporative cooling direct expansion unit and a control method thereof.

Background technique

In the edible fungus breeding industry, traditional air-conditioning consumes a lot of power, and small machines with oil are easy to break, and the maintenance cost is high, and chillers are often used to produce low-temperature cold water, and the mode of alternating heat exchange between the cold water at the end of the room is either one or two The direct expansion system with one room in the module machine, but these are oil-filled systems, have disadvantages such as poor heat transfer effect, inconvenient maintenance, and high noise, and high energy consumption, which is not conducive to energy saving.

Therefore, the art needs a new magnetic levitation evaporative cooling direct expansion unit and its control method to solve the above problems.

Contents of the invention

In order to solve the above-mentioned problems in the prior art, that is, in order to solve the problems of poor heat exchange effect, inconvenient maintenance, high noise, high energy consumption and unfavorable energy saving that existing direct expansion units mostly use an oil system, the present invention A control method of a magnetic levitation evaporative cooling direct expansion unit is provided. The magnetic levitation evaporative cooling direct expansion unit includes a magnetic levitation compressor, an evaporative condenser, a liquid receiver, a gas-liquid separator, and multiple indoor cooling fans. The magnetic levitation The compressor, the evaporative condenser, the liquid receiver, a plurality of the indoor cooling fans and the gas-liquid separator are sequentially connected to form a closed-loop refrigeration system, and the evaporative condenser includes a condensing fan and a A water tank temperature sensor, the water tank temperature sensor is used to detect the water temperature in the water tank of the evaporative condenser, and the control method includes: obtaining the water temperature in the water tank and/or the pressure of the magnetic levitation evaporative cooling direct expansion unit Ratio; according to the water temperature in the water tank and/or the pressure ratio of the magnetic levitation evaporative cooling direct expansion unit, the start and stop of the condensing fan is controlled.

In the preferred technical solution of the above control method, the step of "controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling and direct expansion unit" includes: When the fan is turned off, if the water temperature in the water tank rises to the first temperature threshold, the condensing fan is turned on; wherein, the specific method of determining the first temperature threshold is: obtaining the current ambient temperature, according to The current ambient temperature and the current region and/or season determine the minimum water temperature of the water tank, the first temperature threshold is determined according to the minimum water temperature of the water tank and the first temperature threshold is greater than the minimum water temperature of the water tank .

In the preferred technical solution of the above control method, the step of "controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling and direct expansion unit" includes: When the fan is turned on, if the water temperature in the water tank drops to the second temperature threshold, then turn off the condensation fan; wherein, the second temperature threshold is determined in the following manner: obtain the current ambient temperature, according to the current The ambient temperature and the current region and/or season determine the minimum water temperature of the water tank, and the second temperature threshold is determined according to the minimum water temperature of the water tank, and the second temperature threshold is greater than the minimum water temperature of the water tank.

In the preferred technical solution of the above control method, the step of "controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling and direct expansion unit" includes: When the fan is turned off, if the pressure ratio of the maglev evaporative cooling and direct expansion unit rises to the first set ratio, the condensing fan is turned on; wherein, the specific method of determining the first set ratio is: obtaining The current ambient temperature, determine the condensation saturation temperature according to the current ambient temperature and the current region and/or season, determine the corresponding condensation pressure according to the condensation saturation temperature, and determine the lowest system according to the condensation pressure and target evaporation pressure pressure ratio, the first set ratio is determined according to the lowest system pressure ratio and the first set ratio is greater than the lowest system pressure ratio.

In the preferred technical solution of the above control method, the step of "controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling and direct expansion unit" includes: When the fan is turned on, if the pressure ratio of the maglev evaporative cooling and direct expansion unit drops to the second set ratio, the condensing fan is turned off; wherein, the specific method of determining the second set ratio is: obtaining the current According to the current ambient temperature and the current region and/or season, determine the condensation saturation temperature, determine the corresponding condensation pressure according to the condensation saturation temperature, and determine the lowest system pressure according to the condensation pressure and the target evaporation pressure ratio, the second set ratio is determined according to the lowest system pressure ratio and the second set ratio is greater than the lowest system pressure ratio.

In the preferred technical solution of the above control method, the step of "controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling and direct expansion unit" includes: When the fan is turned off, if the water temperature in the water tank rises to the first temperature threshold or the pressure ratio of the maglev evaporative cooling and direct expansion unit rises to the first set ratio, the condensing fan is turned on; The specific method for determining the first temperature threshold is: obtaining the current ambient temperature, determining the minimum water temperature of the water tank according to the current ambient temperature and the current region and/or season, and determining the minimum water temperature of the water tank according to the minimum water temperature of the water tank. The first temperature threshold and the first temperature threshold is greater than the minimum water temperature of the water tank; the specific determination method of the first set ratio is: obtain the current ambient temperature, according to the current ambient temperature and the current region and /or determine the condensation saturation temperature according to the season, determine the corresponding condensation pressure according to the condensation saturation temperature, determine the lowest system pressure ratio according to the condensation pressure and the target evaporation pressure, and determine the first setting according to the lowest system pressure ratio fixed ratio and the first set ratio is greater than the lowest system pressure ratio.

In the preferred technical solution of the above control method, the step of "controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling and direct expansion unit" includes: When the fan is turned on, if the water temperature in the water tank drops to the second temperature threshold and the pressure ratio of the maglev evaporative cooling and direct expansion unit drops to the second set ratio, the condensing fan is turned off; the second The specific method of determining the temperature threshold is: obtaining the current ambient temperature, determining the minimum water temperature of the water tank according to the current ambient temperature and the current region and/or season, and determining the second temperature according to the minimum water temperature of the water tank threshold and the second temperature threshold is greater than the minimum water temperature of the water tank; the specific determination method of the second set ratio is: obtain the current ambient temperature, according to the current ambient temperature and the current region and/or season Determine the condensation saturation temperature, determine the corresponding condensation pressure according to the condensation saturation temperature, determine the lowest system pressure ratio according to the condensation pressure and the target evaporation pressure, determine the second set ratio according to the lowest system pressure ratio, and The second set ratio is greater than the lowest system pressure ratio.

In a preferred technical solution of the above control method, a one-way valve is provided between the magnetic levitation compressor and the evaporative condenser.

In a preferred technical solution of the above control method, a load balancing valve is provided between the downstream side of the one-way valve and the gas-liquid separator.

In another aspect, the present invention also provides a magnetic levitation evaporative cooling direct expansion unit, the magnetic levitation evaporative cooling direct expansion unit includes a controller configured to be able to execute the control method described above.

In the preferred technical solution of the present invention, the direct expansion unit adopts a magnetic suspension compressor, that is, an oil-free compressor, which can ensure the heat exchange effect of the unit, and is easy to maintain and low in noise. By obtaining the water temperature in the water tank of the evaporative condenser And/or the pressure ratio of the magnetic levitation evaporative cooling direct expansion unit, and then according to the water temperature in the water tank of the evaporative condenser and/or the pressure ratio of the magnetic levitation evaporative cooling direct expansion unit, the start and stop of the condensing fan can be controlled to realize the start and stop of the condensing fan Stop control, avoiding that the condensing fan is always on as long as the evaporative condenser is running, realizes the dynamic adjustment of the condensing fan, and realizes energy-saving control, which is conducive to reducing the energy consumption of the direct expansion unit.

Description of drawings

Fig. 1 is the structural representation of magnetic levitation evaporative cooling direct expansion unit of the present invention;

Fig. 2 is the flow chart of determining the water temperature in the water tank of the opening and closing condensing fan by the magnetic levitation evaporative cooling direct expansion unit of the present invention;

Fig. 3 is a flow chart of determining the pressure ratio of the unit for opening and closing the condensing fan for the magnetic levitation evaporative cooling direct expansion unit of the present invention.

Detailed ways

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention, and are not intended to limit the protection scope of the present invention.

It should be noted that, in the description of the present invention, terms such as "middle", "upper", "lower", "inner", "outer" and other indicated directions or positional relationships are based on the directions or positional relationships shown in the drawings. The positional relationship, which is just for convenience of description, does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and should not be understood as indicating or implying relative importance.

In addition, it should be noted that, in the description of the present invention, unless otherwise specified and limited, the terms "setting" and "connection" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection , or integrally connected; it can be directly connected, or indirectly connected through an intermediary, and it can be the internal communication of two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

Based on the background technology pointed out that the existing direct expansion unit mostly adopts the oil system, which has the problems of poor heat exchange effect, inconvenient maintenance, high noise, high energy consumption and unfavorable energy saving. The invention provides a magnetic levitation evaporative cooling direct The expansion unit and its control method are designed to ensure the heat exchange effect of the unit, facilitate maintenance, have low noise, realize dynamic adjustment of the condensing fan, realize energy-saving control, and help reduce energy consumption of the direct expansion unit.

As shown in Figure 1, the maglev evaporative cold direct expansion unit of the present invention comprises a maglev compressor 1, an evaporative condenser, a liquid reservoir 2, a gas-liquid separator 3 and a plurality of indoor air coolers (shown in the figure as having 5 The situation of four indoor air coolers, of course, is not limited to 5 in practical application, specifically can be determined according to the quantity of the room and the space size of each room), magnetic levitation compressor 1, evaporative condenser, liquid receiver 2, multiple The indoor cooling fan and the gas-liquid separator 3 are connected in sequence to form a closed-loop refrigeration system. The evaporative condenser includes a water tank 4, a condensation coil, a condensation fan 5, a spray pump 6, a plurality of spray nozzles 7, and a water tank temperature sensor 8 And the ambient temperature sensor 9, the spray pump 6 communicates with the bottom of the water tank 4 through the pipeline, and the spray pump 6 also communicates with the multiple spray nozzles 7 near the upper side inside the water tank 4 through the pipeline, and the multiple spray nozzles 7 Located above the condensing coil, the inlet of the condensing coil communicates with the exhaust port of the magnetic levitation compressor 1 through a pipeline, the outlet of the condensing coil communicates with the inlet of the liquid receiver 2 through a pipeline, and the condensing fan 5 is installed in the water tank 4 At the air port of the water tank, the water tank temperature sensor 8 is set in the water tank 4 near the lower side, specifically, it can be set in the water collecting pan at the bottom of the water tank 4 and below the condensation coil, and the ambient temperature sensor 9 can be set on the water tank 4 . A one-way valve 10 is arranged between the condensing coil and the exhaust port of the maglev compressor 1. The one-way valve 10 allows the refrigerant to only flow from the exhaust port of the maglev compressor 1 to the condensing coil. The downstream of the one-way valve 10 An evaporative cooling inlet pressure sensor 11 is provided on the upstream side of the inlet of the condensing coil, and a load balancing valve 12 is connected between the downstream side of the one-way valve 10 and the gas-liquid separator 3 . The discharge port of the magnetic levitation compressor 1 is provided with a discharge pressure sensor 13 , and the air intake port of the magnetic levitation compressor 1 is provided with a suction pressure sensor 14 . A pipeline communicating with the gas-liquid separator 3 is provided between the discharge pressure sensor 13 and the one-way valve 10 , and a bypass solenoid valve 15 and a bypass expansion valve 16 are provided in parallel on the pipeline. The liquid refrigerant drawn from the accumulator 2 enters two cooling circuits, one is the liquid spray cooling circuit of the magnetic levitation compressor 1 (on which an electric ball valve 17 is arranged), and the other is through the cooling expansion valve 18 to the gas-liquid separator 3 A cooling circuit to prevent excessive suction superheating of the gas fraction. Each indoor air cooler includes an indoor fan 19, an indoor heat exchanger 20, a solenoid valve 21 and a thermal expansion valve 22 (or electronic expansion valve). Taking the thermal expansion valve 22 as an example, along the flow direction of the refrigerant, the solenoid valve 21, The thermal expansion valve 22 and the indoor heat exchanger 20 are arranged sequentially, and the air outlet end of the indoor fan 19 is arranged facing the indoor heat exchanger 20 .

In the present invention, the magnetic levitation compressor 1 discharges the compressed high-temperature and high-pressure gas refrigerant into the evaporative condenser through the check valve 10, and the liquid refrigerant from the evaporative condenser enters the liquid receiver 2, and then an economizer or no Add an economizer, flow through the electric ball valve 17 into the room, divert through the branch pipe, and then go through the thermal expansion valve 22 to reduce the pressure and enter the indoor air cooler in different rooms to cool down the room. After evaporation, the gas refrigerant aggregates and enters the gas-liquid separator 3 for gas-liquid separation. The superheated low-temperature low-pressure gas refrigerant in the device 3 enters the magnetic levitation compressor 1, the bypass expansion valve 16 and the bypass solenoid valve 15 are used to reduce the pressure ratio in the system, and then assist the start and stop of the magnetic levitation compressor 1, and the load balancing valve 12 is mainly used Energy regulation and surge control of the magnetic levitation compressor 1. The magnetic levitation compressor 1 takes the set pressure on the touch screen as the target value, controls the evaporation pressure of the indoor air cooler by controlling the suction pressure of the suction port, and performs energy regulation according to the suction pressure (that is, controls the detected suction pressure to run at the target value Nearby), to achieve the purpose of cooling the room to the desired temperature. When the gas refrigerant flows into the evaporative condenser, specifically, the gas refrigerant flows into the condensing coil through the inlet of the condensing coil, and the gas refrigerant in the condensing coil exchanges heat with the water and air outside the condensing coil, so that the gas The refrigerant becomes liquid refrigerant.

The control method of the present invention includes: obtaining the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling direct expansion unit; and controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling direct expansion unit. In practical applications, the start and stop of the condensing fan can be controlled solely by the water temperature in the water tank, and the start and stop of the condensing fan can also be controlled by the pressure ratio of the unit (that is, the ratio of the discharge pressure of the compressor to the suction pressure) , and can jointly control the start and stop of the condensing fan according to the water temperature in the water tank and the pressure ratio of the unit.

When the water temperature in the water tank is used to control the start and stop of the condensing fan, the temperature of the water tank when the condensing fan is turned on (recorded as the first temperature threshold) and the temperature of the water tank when the condensing fan is turned off (referred to as the second temperature threshold), As shown in Figure 2, the specific preferred method can be: first obtain the current ambient temperature t through the ambient temperature sensor, and approximate the current wet bulb temperature by the formula t1=t-Δt1, where t1 is also the lowest temperature of the evaporative cold water tank , Δt1 can be checked according to the relative humidity in different regions or different seasons, and then determine the temperature of the water tank for turning on the condensing fan (ie, the first temperature threshold) t3=t1+Δt3, and the temperature of the water tank for turning off the condensing fan (ie, the second temperature threshold )t2=t1+△t2, among them, △t3>△t2>0, by setting the temperature t2 of the water tank for turning off the condensing fan to be greater than the minimum temperature t1 of the evaporative cold water tank, it can be ensured that the condensing fan can be turned off, avoiding that the condensing fan can only be turned on Energy saving control cannot be realized if it is not turned off. In other examples, the first temperature threshold and the second temperature threshold may also be determined according to an empirical table.

When using the pressure ratio of the unit to control the start and stop of the condensing fan, you can first determine the pressure ratio when the condensing fan is turned on (recorded as the first set ratio) and the pressure ratio when the condensing fan is turned off (recorded as the second set ratio ), as shown in Figure 3, the specific preferred method can be: first obtain the current ambient temperature t through the ambient temperature sensor, and then calculate the current wet bulb temperature approximately by the formula t1=t-Δt1, Δt1 can be determined according to different regions or different Check the table to confirm the seasonal relative humidity, and then calculate the evaporative cooling condensation saturation temperature according to the formula t4=t1+△t4, where △t4 is the evaporative cooling approach temperature, which is related to the evaporative cooling performance, and convert the condensation saturation temperature t4 through the pressure-enthalpy diagram is the condensing pressure P1, then determine the lowest system pressure ratio r=P1/P2 according to the condensing pressure P1 and the set target pressure (that is, the evaporation pressure P2), P1 and P2 are absolute pressures, and finally determine the pressure to turn on the condensing fan The ratio (that is, the first set ratio) r2=r+Δr2, the pressure ratio (that is, the second set ratio) of turning off the condensing fan r1=r+Δr1, where Δr2>Δr1>0. In other examples, the first set ratio and the second set ratio can also be determined according to empirical tables.

When using the water temperature in the water tank and the pressure ratio of the unit to jointly control the start and stop of the condensing fan, the water tank temperature when the condensing fan is turned on, the water tank temperature when the condensing fan is turned off, and the pressure when the condensing fan is turned on can also be determined according to the above method. The ratio and the pressure ratio when the condensing fan is turned off will not be repeated here.

The technical solution of the present invention will be described below in combination with three preferred embodiments.

Embodiment one

The aforementioned step of "controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling and direct expansion unit" includes: when the condensing fan is turned off, if the water temperature in the water tank rises to the first When the temperature threshold is reached, the condensing fan is turned on; when the condensing fan is turned on, if the water temperature in the water tank drops to the second temperature threshold, the condensing fan is turned off, and the first temperature threshold is greater than the second temperature threshold. That is, when the condensing fan is turned off and the water temperature in the water tank rises to the first temperature threshold, the condensing fan is turned on, and if the water temperature in the water tank does not drop to the second temperature threshold, the condensing fan is kept on. When the water temperature in the water tank drops to the second temperature threshold, the condensing fan will be turned off again; when the condensing fan is turned on and the water temperature in the water tank drops to the second temperature threshold, the condensing fan will be turned off. A temperature threshold, then keep the condensing fan in the off state all the time, when the water temperature in the water tank rises to the first temperature threshold, the condensing fan is turned on again. Through such a control method, the dynamic adjustment of the condensing fan can be realized through the water temperature in the water tank, which is beneficial to its energy-saving control.

Embodiment two

The aforementioned step of "controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling direct expansion unit" includes: when the condensing fan is closed, if the pressure ratio of the maglev evaporative cooling direct expansion unit When the condensing fan is turned on, if the pressure ratio of the maglev evaporative cooling and direct expansion unit drops to the second setting ratio, the condensing fan is turned off, and the first setting ratio greater than the second set ratio. That is, when the condensing fan is turned off and the pressure ratio of the unit rises to the first set ratio, the condensing fan is turned on, and if the pressure ratio of the unit does not drop to the second set ratio, the condensing fan is kept on. When the pressure ratio of the unit drops to the second set ratio, the condensing fan is turned off again; when the condensing fan is turned on and the pressure ratio of the unit drops to the second set ratio, the condensing fan is turned off. As high as the first set ratio, the condensing fan will always be kept in the off state, and the condensing fan will be turned on again when the pressure ratio of the unit rises to the first set ratio. Through such a control method, the dynamic adjustment of the condensing fan can be realized through the pressure ratio of the unit, which is beneficial to its energy-saving control.

Embodiment three

The aforementioned step of "controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the maglev evaporative cooling and direct expansion unit" includes: when the condensing fan is turned off, if the water temperature in the water tank rises to the first A temperature threshold or the pressure ratio of the maglev evaporative cooling direct expansion unit rises to the first set ratio, then the condensing fan is turned on; when the condensing fan is turned on, if the water temperature in the water tank drops to the second temperature threshold and the maglev evaporative cooling When the pressure ratio of the direct expansion unit drops to the second set ratio, the condensing fan is turned off. That is, when the water temperature in the water tank and the pressure ratio of the unit meet the conditions for turning off the condensing fan at the same time, the condensing fan is turned off; when the water temperature in the water tank and the pressure ratio of the unit meet the conditions for turning on the condensing fan, or One of the pressure ratios of the unit satisfies the condition of turning on the condensing fan and the other satisfies the condition of turning off the condensing fan. The maglev evaporative cooling and direct expansion unit of the present invention all perform the operation of turning on the condensing fan, ensuring the heat exchange of the unit between energy saving and heat exchange Effect. In addition, by simultaneously referring to the water temperature condition in the water tank and the pressure ratio condition of the unit, the reliability of the unit can be further improved.

So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings, but those skilled in the art will easily understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims (10)

1. The utility model provides a control method of magnetic suspension evaporation cold direct expansion unit, its characterized in that, magnetic suspension evaporation cold direct expansion unit includes magnetic suspension compressor, evaporative condenser, reservoir, gas-liquid separator and a plurality of indoor air-cooler, magnetic suspension compressor, reservoir, a plurality of indoor air-cooler and gas-liquid separator connect gradually and constitute closed-loop refrigerating system jointly, evaporative condenser includes condensing fan and water tank temperature sensor, water tank temperature sensor is used for detecting the temperature of water in the water tank of evaporative condenser, control method includes:

acquiring the water temperature in the water tank and/or the pressure ratio of the magnetic suspension evaporation cold direct expansion unit;

controlling the start and stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the magnetic suspension evaporation cold direct expansion unit;

when the water temperature in the water tank is used for controlling the start and stop of the condensing fan, firstly determining the water tank temperature when the condensing fan is started and the water tank temperature when the condensing fan is closed, acquiring the current environment temperature through an environment temperature sensor, calculating the current wet bulb temperature, determining the water tank temperature when the condensing fan is started, closing the water tank temperature of the condensing fan, and setting the water tank temperature when the condensing fan is closed to be higher than the lowest temperature of an evaporative cold water tank so as to ensure that the condensing fan is closed;

when the start-stop of the condensing fan is controlled by adopting the pressure ratio of the magnetic suspension evaporation direct expansion unit, the pressure ratio when the condensing fan is started and the pressure ratio when the condensing fan is closed are firstly determined, the current environment temperature is obtained through an environment temperature sensor, the current wet bulb temperature is calculated, table lookup confirmation is carried out according to the relative humidity in different areas or seasons, the evaporation condensation saturation temperature is calculated, the condensation saturation temperature is converted into the condensation pressure through a pressure enthalpy chart, the lowest system pressure ratio is determined to be absolute pressure according to the condensation pressure and the set target pressure, the pressure ratio when the condensing fan is started is finally determined, and the pressure ratio of the condensing fan is closed.

2. The control method according to claim 1, wherein the step of controlling the start-stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the magnetic levitation evaporation direct-expansion unit comprises:

if the water temperature in the water tank rises to a first temperature threshold value under the condition that the condensing fan is closed, the condensing fan is started;

the specific determination mode of the first temperature threshold value is as follows: the method comprises the steps of obtaining the current environment temperature, determining the lowest water temperature of the water tank according to the current environment temperature and the current region and/or season, and determining the first temperature threshold according to the lowest water temperature of the water tank, wherein the first temperature threshold is larger than the lowest water temperature of the water tank.

3. The control method according to claim 1, wherein the step of controlling the start-stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the magnetic levitation evaporation direct-expansion unit comprises:

if the water temperature in the water tank is reduced to a second temperature threshold value under the condition that the condensing fan is started, the condensing fan is closed;

the specific determination mode of the second temperature threshold value is as follows: acquiring the current ambient temperature, determining the lowest water temperature of the water tank according to the current ambient temperature and the current region and/or season, and determining the second temperature threshold according to the lowest water temperature of the water tank, wherein the second temperature threshold is larger than the lowest water temperature of the water tank.

4. The control method according to claim 1, wherein the step of controlling the start-stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the magnetic levitation evaporation direct-expansion unit comprises:

under the condition that the condensing fan is closed, if the pressure ratio of the magnetic suspension evaporation direct expansion unit is increased to a first set ratio, the condensing fan is started;

the specific determination mode of the first set ratio is as follows: acquiring a current environment temperature, determining a condensation saturation temperature according to the current environment temperature and a current region and/or season, determining a corresponding condensation pressure according to the condensation saturation temperature, determining a lowest system pressure ratio according to the condensation pressure and a target evaporation pressure, determining a first set ratio according to the lowest system pressure ratio, and enabling the first set ratio to be larger than the lowest system pressure ratio.

5. The control method according to claim 1, wherein the step of controlling the start-stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the magnetic levitation evaporation direct-expansion unit comprises:

under the condition that the condensing fan is started, if the pressure ratio of the magnetic suspension evaporation direct expansion unit is reduced to a second set ratio, the condensing fan is closed;

the specific determination mode of the second set ratio is as follows: acquiring a current environment temperature, determining a condensation saturation temperature according to the current environment temperature and a current region and/or season, determining a corresponding condensation pressure according to the condensation saturation temperature, determining a lowest system pressure ratio according to the condensation pressure and a target evaporation pressure, determining a second set ratio according to the lowest system pressure ratio, and enabling the second set ratio to be larger than the lowest system pressure ratio.

6. The control method according to claim 1, wherein the step of controlling the start-stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the magnetic levitation evaporation direct-expansion unit comprises:

under the condition that the condensing fan is closed, if the water temperature in the water tank rises to a first temperature threshold value or the pressure ratio of the magnetic suspension evaporation direct expansion unit rises to a first set ratio, the condensing fan is started;

the specific determination mode of the first temperature threshold value is as follows: acquiring a current environment temperature, determining the lowest water temperature of the water tank according to the current environment temperature and the current region and/or season, and determining the first temperature threshold according to the lowest water temperature of the water tank, wherein the first temperature threshold is larger than the lowest water temperature of the water tank;

the specific determination mode of the first setting ratio is as follows: acquiring a current environment temperature, determining a condensation saturation temperature according to the current environment temperature and a current region and/or season, determining a corresponding condensation pressure according to the condensation saturation temperature, determining a lowest system pressure ratio according to the condensation pressure and a target evaporation pressure, determining a first set ratio according to the lowest system pressure ratio, and enabling the first set ratio to be larger than the lowest system pressure ratio.

7. The control method according to claim 1, wherein the step of controlling the start-stop of the condensing fan according to the water temperature in the water tank and/or the pressure ratio of the magnetic levitation evaporation direct-expansion unit comprises:

under the condition that the condensing fan is started, if the water temperature in the water tank is reduced to a second temperature threshold value and the pressure ratio of the magnetic suspension evaporation direct-expansion unit is reduced to a second set ratio, the condensing fan is closed;

the specific determination mode of the second temperature threshold value is as follows: acquiring the current ambient temperature, determining the lowest water temperature of the water tank according to the current ambient temperature and the current region and/or season, and determining the second temperature threshold according to the lowest water temperature of the water tank, wherein the second temperature threshold is larger than the lowest water temperature of the water tank;

the specific determination mode of the second setting ratio is as follows: acquiring a current environment temperature, determining a condensation saturation temperature according to the current environment temperature and a current region and/or season, determining a corresponding condensation pressure according to the condensation saturation temperature, determining a lowest system pressure ratio according to the condensation pressure and a target evaporation pressure, determining a second set ratio according to the lowest system pressure ratio, and enabling the second set ratio to be larger than the lowest system pressure ratio.

8. The control method according to claim 1, wherein a check valve is provided between the magnetic levitation compressor and the evaporative condenser.

9. The control method according to claim 8, characterized in that a load balancing valve is provided between the downstream side of the check valve and the gas-liquid separator.

10. A magnetic levitation evaporation direct expansion unit, characterized in that it comprises a controller configured to be able to perform the control method according to any of claims 1 to 9.