Operation control method of direct expansion type refrigerating unit

Abstract

The invention discloses an operation control method for a direct expansion type refrigerating unit. The operation control method comprises the following steps that firstly, whether a compressor breaks down or not is detected; step 2, detecting whether frequency reduction protection is needed or not; 3, calculating a load according to a PID algorithm; fourthly, the direct expansion type refrigerating unit is controlled to operate according to detection and calculation results in the first step to the fourth step; by automatically adjusting the frequency of the compressor, the problems of part damage and large air outlet temperature fluctuation caused by frequent starting / stopping of the direct expansion section can be avoided, automatic operation of the direct expansion type air conditioning unit system can be achieved in the stopping state, loading or frequency reduction is carried out on the compressor by calculating the load, and the working efficiency is improved. The stability of the system and the operability of the unit system are improved; the rotating speed of the condensation fan / the evaporation fan is controlled through the condensation temperature and the evaporation temperature, the indoor temperature is accurately controlled, temperature fluctuation is reduced, meanwhile, the service life of the compressor can be prolonged, intelligent operation control is provided, and the operation process is simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of air conditioning, and in particular to an operation control method of a direct expansion refrigeration unit. Background Art

[0002] Direct expansion air conditioning units are a common type of air conditioning equipment. The units themselves have compressors. In its refrigeration system, the night-state refrigerant evaporates directly in its evaporator coil to absorb heat from the air outside the coil and cool it. Since the refrigerant directly exchanges heat with the air to be treated, there is no secondary heat exchange in the middle to absorb heat from the air outside the coil and cool it. It has high heat exchange efficiency and a wide temperature adjustment range, and is widely used in various industries.

[0003] In the process of adjusting the temperature in a constant temperature room, the indoor temperature often fluctuates due to the time delay of natural heat dissipation and air circulation. Therefore, the demand for cooling or heating will change frequently, causing the compressor to work continuously, which consumes a lot of energy and also affects the service life of the compressor.

[0004] At present, direct expansion air conditioners can only operate under specific working conditions. If the ambient temperature fluctuates greatly, instability problems are likely to occur. Moreover, the cooling capacity adjustment of direct expansion air conditioners is mainly achieved by changing the power supply voltage of the compressor, rather than changing the operating frequency of the compressor through frequency conversion technology, so its adjustment range is very limited.

[0005] Therefore, there is an urgent need for an operation control method of a direct expansion refrigeration unit that can solve the above problems. Summary of the invention

[0006] The object of the present invention is to provide an operation control method for a direct expansion refrigeration unit to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] The present invention provides an operation control method for a direct expansion refrigeration unit, comprising the following steps:

[0009] Step 1: Check whether the compressor is faulty;

[0010] Step 2: Check whether frequency reduction protection is needed;

[0011] Step 3: Calculate the load according to the PID algorithm;

[0012] Step 4: Control the operation of the direct expansion refrigeration unit according to the detection and calculation results of steps 1 to 4.

[0013] Preferably, step one is specifically:

[0014] Check whether the compressor is faulty. If so, shut down the compressor; if not, start the compressor and go to step 2.

[0015] Preferably, the starting conditions of the compressor are:

[0016] 1) Capability E demand;

[0017] 2) High and low pressure difference ≤ 3bar;

[0018] 3) Downtime>3min.

[0019] Preferably, step 2 is specifically:

[0020] Check whether frequency reduction protection is needed. If so, control the compressor to operate at reduced load. If not, proceed to step 3.

[0021] Preferably, the frequency reduction condition is:

[0022] 1) High pressure > cooling / heating frequency reduction high pressure;

[0023] 2) Current> protection setting value;

[0024] 3) Radiator temperature>75℃;

[0025] 4) Exhaust temperature > protection temperature setting value, and exhaust temperature is rising;

[0026] 5) Low pressure < cooling / heating frequency reduction low pressure.

[0027] Preferably, step three is specifically:

[0028] Calculate the temperature deviation, which is the difference between the measured target temperature and the set target temperature;

[0029] Calculate the proportional output P = Kp*temperature deviation, where Kp is a constant;

[0030] Calculate the integral output I = (Ki*temperature deviation*Ti) + It-1, where Ki is a constant and Ti is time;

[0031] Calculate the differential output D = Kd * temperature deviation change, where Kd is a constant;

[0032] Calculate the total output E=P+I+D.

[0033] Preferably, step 4 includes frequency sending and limiting, specifically:

[0034] Based on the total output E calculated by the PID control algorithm, the system performs limiting processing to ensure that the output frequency is within the safe and effective range of the compressor, and then sends the limited frequency to the compressor driver.

[0035] Preferably, step 4 includes condensing fan / evaporating fan speed control, specifically:

[0036] In cooling mode: when the condensing temperature is low, the fan speed is kept at the lowest speed. As the condensing temperature increases, the fan speed gradually increases until it reaches a certain point, after which the fan speed is kept at the highest speed.

[0037] In heating mode: When the evaporating temperature is high, the fan speed is maintained at the highest speed. As the evaporating temperature decreases, the fan speed gradually decreases until it reaches a certain point, after which the fan speed is maintained at the lowest speed.

[0038] Compared with the prior art, the present invention has achieved the following beneficial technical effects:

[0039] In view of the problem that the existing direct expansion air conditioning units are prone to instability when the ambient temperature fluctuates greatly, the present invention uses a PID control algorithm to automatically adjust the compressor frequency according to the real-time temperature deviation, thereby improving the stability of the system under different ambient temperatures.

[0040] In view of the problem that the cooling capacity of traditional direct expansion air conditioner units is mainly adjusted by changing the power supply voltage and the adjustment range is limited, the present invention adopts frequency conversion technology to increase or decrease the frequency of the compressor according to the load demand, which significantly expands the adjustment range and makes the temperature control more precise.

[0041] Aiming at the problem that the compressor is frequently started / shutdown in the prior art, resulting in high energy consumption and shortened compressor life, the present invention reduces the number of starts and stops, reduces energy consumption, and prolongs the compressor life by automatically adjusting the compressor frequency.

[0042] Aiming at the problem that the speed control of the condensing fan and the evaporating fan in the prior art is not precise enough, resulting in poor energy efficiency and temperature control effects, the present invention controls the fan speed by the condensing temperature and the evaporating temperature, thereby achieving more precise temperature control and improving energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0044] Figure 1 This is a flow chart of the operation control method of the direct expansion refrigeration unit provided in the present invention. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] The object of the present invention is to provide an operation control method for a direct expansion refrigeration unit to solve the problems existing in the prior art.

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] Embodiment 1:

[0049] This embodiment provides an operation control method for a direct expansion refrigeration unit. The principle is to monitor the state and environmental parameters of the compressor system, combine with the PID control algorithm, and intelligently adjust the operating frequency of the compressor to achieve accurate control of the indoor temperature. When the system detects that the compressor system has no faults and does not need frequency reduction protection, it will load or maintain the current frequency according to the load calculated by the PID algorithm. If the frequency needs to be reduced or the compressor needs to be shut down, the system will perform corresponding operations; the following steps are included:

[0050] Step 1: Check whether the compressor is faulty; specifically:

[0051] Check whether the compressor is faulty. If so, shut down the compressor; if not, start the compressor and go to step 2.

[0052] The starting conditions of the compressor are:

[0053] 1) Capability E demand;

[0054] 2) High and low pressure difference ≤ 3bar;

[0055] 3) Downtime> 3min;

[0056] Step 2: Check whether frequency reduction protection is needed; specifically:

[0057] Detect whether frequency reduction protection is required. If frequency reduction protection is required, control the compressor to operate at reduced load. If frequency reduction protection is not required, proceed to step 3.

[0058] The frequency reduction condition is one of the following:

[0059] 1) High pressure > cooling / heating frequency reduction high pressure;

[0060] 2) Current> protection setting value;

[0061] 3) Radiator temperature>75℃;

[0062] 4) Exhaust temperature > protection temperature setting value, and exhaust temperature is rising;

[0063] 5) Low pressure < cooling / heating frequency reduction low pressure;

[0064] Step 3: Calculate the load according to the PID algorithm; specifically:

[0065] Calculate the temperature deviation, which is the difference between the measured target temperature and the set target temperature;

[0066] Calculate the proportional output P = Kp*temperature deviation, where Kp is a constant;

[0067] Calculate the integral output I = (Ki*temperature deviation*Ti) + It-1, where Ki is a constant and Ti is time;

[0068] Calculate the differential output D = Kd * temperature deviation change, where Kd is a constant;

[0069] Calculate the total output E = P + I + D;

[0070] Step 4: Control the operation of the direct expansion refrigeration unit according to the detection and calculation results of steps 1 to 4;

[0071] Including frequency sending and limiting, specifically:

[0072] Based on the total output E calculated by the PID control algorithm, the system performs a limiting process to ensure that the output frequency is within the safe and effective range of the compressor, and then sends the limited frequency to the compressor driver;

[0073] Including condensing fan / evaporating fan speed control, specifically:

[0074] In cooling mode: when the condensing temperature is low, the fan speed is kept at the lowest speed. As the condensing temperature increases, the fan speed gradually increases until it reaches a certain point, after which the fan speed is kept at the highest speed.

[0075] In heating mode: When the evaporating temperature is high, the fan speed is maintained at the highest speed. As the evaporating temperature decreases, the fan speed gradually decreases until it reaches a certain point, after which the fan speed is maintained at the lowest speed.

[0076] The operation control method of a direct expansion refrigeration unit provided by the present invention can achieve the following functions:

[0077] 1. Accurately control indoor temperature and reduce temperature fluctuations.

[0078] 2. Improve the energy efficiency and stability of the system.

[0079] 3. Extend the service life of the compressor.

[0080] 4. Provide intelligent operation control and simplify the operation process.

[0081] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for controlling the operation of a direct expansion refrigeration unit, characterized in that: The following steps are involved: Step 1: Check whether the compressor is faulty; Step 2: Check whether frequency reduction protection is needed; Step 3: Calculate the load according to the PID algorithm; Step 4: Control the operation of the direct expansion refrigeration unit according to the detection and calculation results of steps 1 to 4.

2. The operation control method of the direct expansion refrigeration unit according to claim 1, characterized in that: Step 1 is as follows: Check whether the compressor is faulty. If so, shut down the compressor; if not, start the compressor and go to step 2.

3. The operation control method of the direct expansion refrigeration unit according to claim 2, characterized in that: The starting conditions of the compressor are: 1) Capability E demand; 2) High and low pressure difference ≤ 3bar; 3) Downtime>3min.

4. The operation control method of the direct expansion refrigeration unit according to claim 1, characterized in that: Step 2 is as follows: Check whether frequency reduction protection is needed. If so, control the compressor to operate at reduced load. If not, proceed to step 3.

5. The operation control method of the direct expansion refrigeration unit according to claim 4, characterized in that: The frequency reduction conditions are: 1) High pressure > cooling / heating frequency reduction high pressure; 2) Current> protection setting value; 3) Radiator temperature>75℃; 4) Exhaust temperature > protection temperature setting value, and exhaust temperature is rising; 5) Low pressure < cooling / heating frequency reduction low pressure.

6. The operation control method of the direct expansion refrigeration unit according to claim 1, characterized in that: Step three is as follows: Calculate the temperature deviation, which is the difference between the measured target temperature and the set target temperature; Calculate the proportional output P = Kp*temperature deviation, where Kp is a constant; Calculate the integral output I = (Ki*temperature deviation*Ti) + It-1, where Ki is a constant and Ti is time; Calculate the differential output D = Kd * temperature deviation change, where Kd is a constant; Calculate the total output E=P+I+D.

7. The operation control method of the direct expansion refrigeration unit according to claim 1, characterized in that: Step 4 includes frequency distribution and limiting, specifically: Based on the total output E calculated by the PID control algorithm, the system performs limiting processing to ensure that the output frequency is within the safe and effective range of the compressor, and then sends the limited frequency to the compressor driver.

8. The operation control method of the direct expansion refrigeration unit according to claim 1, characterized in that: Step 4 includes condensing fan / evaporating fan speed control, specifically: In cooling mode: when the condensing temperature is low, the fan speed is kept at the lowest speed. As the condensing temperature increases, the fan speed gradually increases until it reaches a certain point, after which the fan speed is kept at the highest speed. In heating mode: When the evaporating temperature is high, the fan speed is maintained at the highest speed. As the evaporating temperature decreases, the fan speed gradually decreases until it reaches a certain point, after which the fan speed is maintained at the lowest speed.

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