CN110715466A - A multi-connected air conditioning system and its control method - Google Patents

Abstract

The invention relates to a multi-connected air conditioning system and a control method thereof. The control method includes: adjusting the opening degree of the expansion valve of the indoor unit according to the difference between the indoor temperature value set by the user and the measured value of the indoor temperature; The difference between the target value of air superheat and the measured value of suction superheat is used to adjust the compressor frequency. Compared with the prior art, in the multi-connected air-conditioning system provided by the present invention, the outdoor unit does not include an outdoor expansion valve, which can reduce the complexity of the system, reduce the refrigerant charge, and reduce the manufacturing cost. The change of the cooling/heating load of the indoor unit and the set value of the indoor temperature, accurately control the opening of the expansion valve of the indoor unit and the frequency of the compressor, so that the cooling capacity/heating capacity output by the air-conditioning system completely matches the load demand of each indoor unit; The control performance of the multi-connected air conditioning system can be improved, the control algorithm is very simple, and the practicability is better.

Description

A multi-connected air conditioning system and its control method

technical field

The invention relates to the technical field of air conditioners, in particular to a multi-connected air conditioner system and a control method thereof.

Background technique

Multi-connected air conditioning system, also known as variable refrigerant flow air conditioning system, has the advantages of flexible installation, good comfort, and high energy efficiency coefficient, and has been widely used.

FIG. 1 is a schematic structural diagram of an existing multi-connected air conditioning system, see invention patents CN103486692A, CN106196495A, CN107543290A and CN103292422B. The multi-connected air-conditioning system consists of an outdoor unit and multiple indoor units connected by connecting pipes. The outdoor unit is mainly composed of a gas-liquid separator 1, a compressor 2, a four-way reversing valve 3, an outdoor heat exchanger 4, an outdoor fan 5 and an outdoor expansion valve 6. The indoor unit is mainly composed of an indoor expansion valve 7, an indoor heat exchanger 8 and an indoor fan 9.

In the operation of a multi-connected air-conditioning system, in order to meet the cooling or heating load of multiple indoor units, it is necessary to adjust the compressor frequency and the opening of the indoor and outdoor expansion valves to achieve precise control of the refrigerant flow.

In the prior art, for the control of the compressor frequency, the invention patent CN105571067A discloses a multi-line control method and system. Calculate the comprehensive temperature difference based on the set temperature of each indoor unit and the indoor ambient temperature. Correct the evaporating temperature or condensing temperature target value according to the comprehensive temperature difference. The evaporating temperature (cooling condition) or condensing temperature (heating condition) is controlled by the compressor frequency. Invention patent CN103292422B discloses a method for controlling suction pressure in cooling operation of a multi-mechanism. Change the target value of suction pressure according to the relationship between the average inlet temperature of the indoor unit and the target value of the suction saturation temperature, and then control the suction pressure by the frequency of the compressor, so that the suction pressure of the unit operation is adapted to the operation state of the indoor unit. Invention patent CN103486692A discloses a load adaptive variable frequency multi-connected heat pump system and a method for controlling the frequency of the compressor. Under the cooling condition, the compressor frequency controls the temperature of the refrigerant liquid pipe at the inlet of the indoor heat exchanger, and the control target value of the refrigerant liquid pipe temperature is determined based on the difference between the set value of the return air temperature and the measured value. In the heating condition, the discharge pressure is controlled by the compressor frequency, and the discharge pressure control target is determined based on the measured value of the suction pressure.

In the prior art, for the control of the opening degree of the indoor expansion valve, the invention patent CN106196495A discloses a multi-line air conditioner and its control device and control method. When the air conditioner operates in the cooling mode, the opening of the indoor expansion valve is controlled based on the degree of exhaust superheat and the degree of indoor superheat; when the air conditioner operates in the heating mode, the opening degree of the indoor expansion valve is based on the degree of exhaust superheat and the degree of indoor subcooling. degree of control. Invention patent CN107543290A discloses an indoor expansion valve control method. Under the heating condition, the opening degree of the indoor expansion valve is adjusted according to the comparison result between the actual subcooling degree of the indoor heat exchanger and the target subcooling degree, and the target subcooling degree is corrected by the refrigerant superheat degree at the inlet of the gas-liquid separator. . Invention patent CN103486691A discloses a refrigerant flow control method and device for a multi-line air conditioning system. Under heating conditions, the target subcooling degree is determined according to parameters such as return air temperature value, air temperature setting value, supply air temperature value, and pressure value. Adjust the opening degree of the indoor electronic expansion valve according to the difference between the target value of the subcooling degree and the measured value, so that the opening degree control of the electronic expansion valve can respond to the real-time load change of the indoor unit. Invention patent CN106052216A discloses a method for controlling the indoor expansion valve when a multi-connector is heated. The target suction superheat is set according to the ambient temperature of the outdoor unit, and each indoor expansion valve simultaneously controls the suction superheat and the subcooling at the outlet of the indoor unit to distribute the refrigerant reasonably and achieve a balanced heating effect.

The control method of the outdoor expansion valve is rarely mentioned in the prior art. The invention patent CN103486692A points out that in the multi-line refrigeration operation, the outdoor electronic expansion valve is fully opened; in the heating operation, both the outdoor and indoor electronic expansion valves play the role of throttling effect. In fact, under heating conditions, when the indoor expansion valve is used to control the indoor subcooling degree, the outdoor expansion valve needs to control the suction superheat degree of the compressor to prevent the compressor from liquid hammer.

As can be seen from the above, the existing multi-air conditioning system control technology usually controls the suction or discharge saturation temperature by the compressor frequency, wherein the suction or discharge saturation temperature (pressure) control targets are mostly empirical correlations. For example, the invention patent CN103486692A, a load-adaptive variable frequency multi-connected heat pump system and a method for controlling the frequency of the compressor, gives the target exhaust pressure Pdo=7.7Ps min+0.4 under the heating condition, where Ps min is the suction pressure . If the target value of the exhaust pressure obtained by the empirical correlation is too high, it will cause the compressor frequency to be too high and the energy consumption will increase; if the target value of the exhaust pressure is too low, it will cause insufficient heating output by the system to meet the indoor load demand. . Therefore, it is difficult for the existing compressor frequency control methods to accurately adjust the total cooling capacity or heating capacity output by the system according to the indoor load.

For indoor expansion valve control, the existing technology usually controls the degree of subcooling or degree of superheat of the indoor unit by the opening degree of the indoor expansion valve, wherein the control targets of degree of subcooling and degree of superheat are determined according to empirical values, such as the one given in the invention patent CN106052216A. The cooling control target is 6℃-10℃. The existing indoor expansion valve control method does not directly control the return air temperature of each indoor unit. Therefore, it is impossible to distribute the refrigerant reasonably according to the temperature settings and load changes of different indoor units, so that the room temperature can accurately reach the set target. For outdoor expansion valve control, both outdoor and indoor electronic expansion valves play a throttling role in heating operation. This can cause the adjustment of the outdoor expansion valve and the indoor expansion valve to interfere with each other, resulting in unstable system operation.

To sum up, it is necessary to propose a multi-connected air-conditioning system and its control method, which can precisely adjust the compressor frequency and expansion valve opening according to the load change of the indoor unit, so that the cooling capacity or heating capacity output by the system can match the indoor unit. load demand to meet the indoor temperature set target. At the same time, the problem of mutual interference in the control of the outdoor expansion valve and the indoor expansion valve under heating conditions is solved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a multi-connected air-conditioning system and a control method thereof in order to overcome the above-mentioned defects of the prior art.

The object of the present invention can be realized through the following technical solutions:

A multi-connected air-conditioning system includes an outdoor unit and a plurality of indoor units, the outdoor unit includes a gas-liquid separator, a compressor, a four-way reversing valve, and an outdoor heat exchanger, which are connected in series in sequence, and the indoor unit includes a sequence of An indoor expansion valve and an indoor heat exchanger are connected in series, the outdoor heat exchanger is matched with an outdoor fan, the indoor heat exchanger is matched with an indoor fan, and a compressor is installed between the gas-liquid separator and the compressor Intake temperature sensor and pressure sensor, the indoor heat exchanger inlet is provided with indoor temperature sensor.

In the multi-connected air conditioning system provided by the present invention, the outdoor unit part does not include an outdoor expansion valve. The problem of mutual interference between the adjustment of the indoor expansion valve and the outdoor expansion valve is fundamentally eliminated.

Further, the air conditioning system includes:

Refrigeration cycle: including sequentially connected compressor, outdoor heat exchanger, indoor expansion valve, indoor heat exchanger and gas-liquid separator, the outlet of the gas-liquid separator is connected to the inlet of the compressor to form a circulation loop;

Heating cycle: including sequentially connected compressor, indoor heat exchanger, indoor expansion valve, outdoor heat exchanger and gas-liquid separator, the outlet of the gas-liquid separator is connected to the inlet of the compressor to form a circulation loop;

In the refrigeration cycle and heating cycle, the compressor is connected to the outdoor heat exchanger or the indoor heat exchanger through a four-way reversing valve, and the outdoor heat exchanger or the indoor heat exchanger is connected to the gas-liquid separator through a four-way reversing valve. .

Further, the multiple indoor units are connected in parallel with each other and then connected to the outdoor unit.

A control method for a multi-connected air-conditioning system, the specific steps are as follows:

(a) Detecting the suction pressure _ps of the compressor, and determining the suction saturation temperature T _sat of the compressor according to the corresponding relationship between the refrigerant saturation pressure and the saturation temperature;

(b) Detecting the suction temperature T _s of the compressor, and calculating the compressor suction superheat T _ssh =T _s −T _sat ;

(c) adjusting the compressor frequency according to the comparison result between the measured value T _ssh of the suction superheat and the target value T _ssh,0 of the suction superheat;

(d) For each indoor unit, detect the inlet air temperature T _RA of the indoor heat exchanger, and obtain the set value T _RA,0 of each indoor temperature.

(e) For each indoor unit, compare the inlet air temperature T _RA of the indoor heat exchanger with the set value T _RA,0 of the indoor temperature, and adjust the opening degree of the expansion valve of the corresponding indoor unit according to the comparison result.

Further, in step (c), the target value of suction superheat T _ssh,0 is the minimum value to ensure that the compressor is free from liquid shock, and is a fixed value under different environmental parameters, with a typical value of 5°C.

Further, in step (c): when the measured value T _ssh of the suction superheat is less than the target value T _ssh,0 of the suction superheat, the compressor frequency is controlled to increase; when the measured value T _ssh of the suction superheat is greater than When the target value of suction superheat is T _ssh,0 , the compressor frequency is controlled to decrease, and the amplitude of the compressor frequency change is determined by the PID algorithm.

Further, in step (e): under cooling conditions, when the inlet air temperature T _RA of the indoor heat exchanger is less than the set value T _RA,0 of the indoor temperature, the opening degree of the indoor expansion valve is controlled to decrease; When the inlet air temperature T _RA of the heater is greater than the set value T _RA,0 of the indoor temperature, the opening degree of the indoor expansion valve is controlled to increase, and the variation range of the opening degree of the indoor expansion valve can be determined by the PID algorithm.

Further, in step (e): under the heating condition, the control of the opening of the indoor expansion valve is opposite to that in the cooling condition, when the inlet air temperature T _RA of the indoor heat exchanger is less than the set value T _RA,0 of the indoor temperature. When , the opening degree of the indoor expansion valve is controlled to increase; when the inlet air temperature T _RA of the indoor heat exchanger is greater than the set value T _RA,0 of the indoor temperature, the opening degree of the indoor expansion valve is controlled to decrease, and the opening degree of the indoor expansion valve The magnitude of change can be determined by the PID algorithm.

For each indoor unit, the opening degree of the expansion valve of the indoor unit is controlled according to the difference between the indoor temperature value set by the user and the measured indoor temperature value. For the outdoor unit, the compressor frequency is controlled according to the difference between the target value of suction superheat and the measured value of suction superheat. Through the joint control of the frequency of the compressor and the opening of the indoor expansion valve, it not only meets the cooling or heating load requirements of each indoor unit, but also ensures the safe operation of the compressor. The above control method provided by the present invention is suitable for two operating conditions of cooling and heating.

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

1. The multi-connected air-conditioning system provided by the present invention does not include an outdoor expansion valve, which fundamentally eliminates the problem of mutual interference between the adjustment of the indoor expansion valve and the outdoor expansion valve.

2. The multi-connected air-conditioning system control method provided by the present invention can accurately control the opening degree of the expansion valve of the indoor unit and the frequency of the compressor according to the change of the cooling/heating load of each indoor unit and the set value of the indoor temperature, so that the The cooling capacity/heating capacity output by the system and the distribution of refrigerant flow between indoor units precisely match the load requirements of each indoor unit.

3. Different from the need to determine evaporation temperature/condensing temperature and subcooling/superheating control targets according to complex control algorithms in the prior art, in the control method provided by the present invention, the control targets of compressor frequency and expansion valve opening are : Inhalation superheat and indoor temperature are all based on fixed value control, and the control algorithm is very simple.

4. The multi-connected air-conditioning system provided by the present invention does not include an outdoor expansion valve, which reduces the complexity and production cost of the system.

5. In the multi-connected air-conditioning system provided by the present invention, only the indoor expansion valve is throttled under the heating condition, and the two-phase refrigerant is in the refrigerant connecting pipe between the indoor expansion valve and the outdoor heat exchanger. In the prior art, both the indoor expansion valve and the outdoor expansion valve are throttled under heating conditions, and the latter plays a major role in throttling, and the refrigerant connecting pipe between the indoor expansion valve and the outdoor expansion valve is a high-density liquid refrigeration agent. Therefore, compared with the prior art, the present invention can reduce the refrigerant charge amount under the heating condition. Since the refrigerant charge in the heating condition of the multi-connected system is larger than that in the refrigeration condition, the initial charge of the system mainly depends on the optimal charge in the heating condition. Therefore, the present invention can effectively reduce the initial charging amount of the multi-line air conditioning system and reduce the cost.

Description of drawings

1 is a schematic structural diagram of an existing multi-connected air-conditioning system;

FIG. 2 is a schematic diagram of the installation of the multi-connected air-conditioning system and the sensor according to the embodiment.

FIG. 3 is a control flow chart of the multi-connected air-conditioning system.

The numbers in the figure show:

1. Gas-liquid separator, 2. Compressor, 3. Four-way reversing valve, 4. Outdoor heat exchanger, 5. Outdoor fan, 6. Outdoor expansion valve, 7. Indoor expansion valve, 8. Indoor heat exchanger , 9, indoor fan, T1, compressor suction temperature sensor, P1, pressure sensor, T2, indoor temperature sensor.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Example

A multi-connected air conditioning system, as shown in Figure 2, includes a gas-liquid separator 1, a compressor 2, a four-way reversing valve 3, an outdoor heat exchanger 4, an outdoor fan 5, an indoor expansion valve 7, and an indoor heat exchange. 8 and indoor fan 9. The air-conditioning system can realize two operating modes of cooling and heating.

When the multi-connected air-conditioning system operates in cooling mode, the discharge end of the compressor 2 is connected to the A end of the four-way reversing valve 3, and the B end of the four-way reversing valve 3 is connected to the inlet of the outdoor heat exchanger 4. , the outlet of the outdoor heat exchanger 4 is connected to the inlet of the indoor heat exchanger 8 through the indoor expansion valve 7, and the outlets of the plurality of indoor heat exchangers 8 are connected in parallel and then connected to the C end of the four-way reversing valve 3, and then through the four The D end of the reversing valve 3 is connected to the intake end of the compressor 2 through the gas-liquid separator 1 to complete a refrigeration cycle.

When the multi-connected air-conditioning system operates in the heating mode, the discharge end of the compressor 2 is connected to the A end of the four-way reversing valve 3, and is connected to a plurality of indoor heat exchangers 8 through the C end of the four-way reversing valve 3. The outlet of the indoor heat exchanger 8 is connected to the indoor expansion valve 7, the outlets of multiple indoor expansion valves 7 are confluent and connected to the inlet of the outdoor heat exchanger 4, and the outlet of the outdoor heat exchanger 4 is reversed with the four-way The B end of the valve 3 is connected, and then the D end of the four-way reversing valve 3 is connected to the intake end of the compressor 2 through the gas-liquid separator 1 to complete a heating cycle.

A control method of a multi-connected air-conditioning system. The multi-connected air-conditioning system needs to install necessary sensors, as shown in Figure 2, including a compressor suction temperature sensor T1 arranged on the compressor suction pipeline, and arranged on the compressor. The refrigerant pressure sensor P1 on the suction line, and the indoor temperature sensor T2 set at the air inlet of the indoor heat exchanger, as shown in Figure 3, the specific steps are as follows:

(a) The suction pressure _ps of the compressor 2 is detected, and the suction saturation temperature T _sat of the compressor 2 is determined according to the corresponding relationship between the refrigerant saturation pressure and the saturation temperature.

(b) Detect the suction temperature T _s of the compressor 2 , and calculate the compressor suction superheat T _ssh =T _s −T _sat .

(c) The compressor frequency is adjusted based on the result of comparison between the measured value T _ssh of the degree of suction superheat and the target value T _ssh,0 of the degree of suction superheat. The target value of suction superheat T _ssh,0 is the minimum value to ensure that the compressor is not subject to liquid shock, and the classic value is 5 °C. When the measured value of suction superheat T _ssh is less than the target value of suction superheat T _ssh,0 , the frequency of the compressor is controlled to increase; when the measured value of suction superheat T _ssh is greater than the target value of suction heat T _{ssh ,0} , the control compressor frequency decreases. The magnitude of the compressor frequency change can be determined by a PID algorithm.

(d) For each indoor unit, detect the inlet air temperature T _RA of the indoor heat exchanger, and obtain the set value T _RA,0 of each indoor temperature.

(e) For each indoor unit, compare the inlet air temperature T _RA of the indoor heat exchanger with the set value T _RA,0 of the indoor temperature, and adjust the opening degree of the expansion valve of the corresponding indoor unit according to the comparison result. Under cooling conditions, when the inlet air temperature T _RA of the indoor heat exchanger is less than the set value T _RA,0 of the indoor temperature, the opening of the indoor expansion valve is controlled to decrease; when the inlet air temperature T _RA of the indoor heat exchanger is greater than When the set value of the indoor temperature T _RA,0 , the opening degree of the indoor expansion valve is controlled to increase. The variation range of the opening degree of the indoor expansion valve can be determined by the PID algorithm. The control of the opening degree of the indoor expansion valve in the heating condition is opposite to that in the refrigeration condition. When the inlet air temperature T _RA of the indoor heat exchanger is less than the set value T _RA,0 of the indoor temperature, the opening degree of the indoor expansion valve is controlled to increase. ; When the inlet air temperature T _RA of the indoor heat exchanger is greater than the set value T _RA,0 of the indoor temperature, the opening degree of the indoor expansion valve is controlled to decrease. The variation range of the opening degree of the indoor expansion valve can be determined by the PID algorithm.

The foregoing description of the embodiments is provided to facilitate understanding and use of the invention by those of ordinary skill in the art. It will be apparent to those skilled in the art that various modifications to these embodiments can be readily made, and the generic principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above-mentioned embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention, without departing from the scope of the present invention, should all fall within the protection scope of the present invention.

Claims (8)

1. The utility model provides a multiple air conditioning system, includes off-premises station and many indoor sets, its characterized in that, the off-premises station is including gas-liquid separator (1) that establishes ties in proper order, compressor (2), four-way reversing valve (3), outdoor heat exchanger (4), indoor set is including indoor expansion valve (7) and indoor heat exchanger (8) that establish ties in proper order, outdoor heat exchanger (4) cooperation is provided with outdoor fan (5), indoor heat exchanger (8) cooperation is provided with indoor fan (9), be provided with compressor temperature sensor (T1) and pressure sensor (P1) of breathing in between gas-liquid separator (1) and compressor (2), indoor heat exchanger (8) import is provided with indoor temperature sensor (T2).

2. The multi-connected air conditioning system as claimed in claim 1, wherein the air conditioning system comprises:

refrigeration cycle: the system comprises a compressor (2), an outdoor heat exchanger (4), an indoor expansion valve (7), an indoor heat exchanger (8) and a gas-liquid separator (1) which are connected in sequence, wherein an outlet of the gas-liquid separator (1) is connected with an inlet of the compressor (2) to form a circulating loop;

heating circulation: the system comprises a compressor (2), an indoor heat exchanger (8), an indoor expansion valve (7), an outdoor heat exchanger (4) and a gas-liquid separator (1) which are connected in sequence, wherein an outlet of the gas-liquid separator (1) is connected with an inlet of the compressor (2) to form a circulating loop;

the compressor (2) in the refrigeration cycle and the heating cycle is connected with the outdoor heat exchanger (4) or the indoor heat exchanger (8) through the four-way reversing valve (3), and the outdoor heat exchanger (4) or the indoor heat exchanger (8) is connected with the gas-liquid separator (1) through the four-way reversing valve (3).

3. The multi-connected air conditioning system as claimed in claim 1, wherein the indoor units are connected to the outdoor unit in parallel.

4. The control method of the multi-connected air conditioning system according to claim 1, characterized by comprising the following specific steps:

(a) detecting the suction pressure p of a compressor (2)_sDetermining the suction saturation temperature T of the compressor (2) according to the corresponding relation between the saturation pressure and the saturation temperature of the refrigerant_sat；

(b) Detecting the suction temperature T of the compressor (2)_sCalculating the suction superheat T of the compressor (2)_ssh＝T_s-T_sat；

(c) Based on measured value T of degree of superheat of suction gas_sshWith target value T of degree of superheat of suction gas_ssh,0Adjusting the frequency of the compressor (2) as a result of the comparison;

(d) for each indoor unit, the inlet air temperature T of the indoor heat exchanger (8) is detected_RAObtainingSet value T of each indoor temperature_RA,0。

(e) For each indoor unit, the inlet air temperature T of the indoor heat exchanger (8) is adjusted_RASet value T of indoor temperature_RA,0And comparing, and adjusting the opening of the expansion valve of the corresponding indoor unit according to the comparison result.

5. The method as claimed in claim 4, wherein the target suction superheat value T in step (c) is set to_ssh,0To ensure that the compressor (2) is not subjected to liquid slugging.

6. The control method of a multi-connected air conditioning system according to claim 4, wherein in the step (c): when the measured value T of the degree of superheat of the intake air_sshLess than target value T of degree of superheat of suction gas_ssh,0When the frequency of the compressor (2) is increased, controlling the frequency of the compressor to increase; when the measured value T of the degree of superheat of the intake air_sshGreater than the target value T of the degree of superheat of the suction gas_ssh,0And meanwhile, controlling the frequency of the compressor (2) to be reduced, and determining the amplitude of the frequency change of the compressor (2) through a PID algorithm.

7. The control method of a multi-connected air conditioning system according to claim 4, wherein in the step (e): under the refrigeration working condition, when the inlet air temperature T of the indoor heat exchanger (8)_RALess than the set value T of the indoor temperature_RA,0When the temperature is higher than the set temperature, the opening degree of the indoor expansion valve (7) is controlled to be reduced; when the inlet air temperature T of the indoor heat exchanger (8)_RASet value T greater than indoor temperature_RA,0And meanwhile, the opening degree of the indoor expansion valve (7) is controlled to be increased, and the change amplitude of the opening degree of the indoor expansion valve (7) can be determined through a PID algorithm.

8. The control method of a multi-connected air conditioning system according to claim 4, wherein in the step (e): under the heating working condition, the control of the opening degree of the indoor expansion valve (7) is opposite to the refrigeration working condition, and when the inlet air temperature T of the indoor heat exchanger (8)_RALess than the set value T of the indoor temperature_RA,0While controlling the opening degree of the indoor expansion valve (7)Increasing; when the inlet air temperature T of the indoor heat exchanger (8)_RASet value T greater than indoor temperature_RA,0And meanwhile, the opening degree of the indoor expansion valve (7) is controlled to be reduced, and the change amplitude of the opening degree of the indoor expansion valve (7) can be determined through a PID algorithm.

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