CN111829268A - A method for determining the defrosting time of a cold storage fan by using the fan power - Google Patents

Abstract

The invention relates to a method for determining defrosting time of an air cooler of a refrigeration house by utilizing fan power. When the actual power of the motor is obviously increased, the air volume of the air cooler is reduced, and after interference factors such as voltage fluctuation and the like are eliminated, the obvious increase of the power can be used as a judgment basis for frosting on the surface of the evaporator, and the controller starts the defrosting condition of the refrigerating system. After the defrosting condition is started, the frost is melted, the resistance of the evaporator is reduced, the air quantity is increased, the power of the fan motor is reduced, and when the power meter monitors that the actual power of the motor is reduced, the controller controls the refrigerating system to stop the defrosting condition and start the refrigerating condition.

Description

A method for determining the defrosting time of a cold storage fan by using the fan power

technical field

The patent of the invention belongs to the field of operation control of a refrigeration system of a cold storage, and relates to a method for determining the defrosting time of the evaporator by using the motor power of the cooling fan.

Background technique

Cold storage refers to a storage building with artificial cooling and cooling function, which is used for low-temperature storage of perishable foods (fruits and vegetables, meat and meat products, aquatic products, eggs and dairy products, etc.) and medicines. The refrigeration system of the cold storage is to exchange heat with the air in the warehouse through the evaporator (cooler) to reduce the temperature in the cold storage, and the evaporating temperature in the evaporator (cooler) is often lower than the dew point temperature of the air in the warehouse, which will cause Frost has formed on the evaporator surface. Frost has a large thermal resistance, and frost formation will not only reduce the heat exchange efficiency of the evaporator, reduce the heat exchange, and even lead to the failure of the refrigeration system. Therefore, frosting is one of the problems that must be solved in the operation of the cold storage refrigeration system. Each set of cold storage refrigeration systems will be set to run defrosting (defrosting) conditions. There are many methods of defrosting, such as manual frost sweeping, refrigerant Hot melt frost, water melt frost, electric heat melt frost, etc. In the setting of the defrosting condition of the refrigeration system, how to accurately determine when the defrosting condition starts and ends is the key technology to determine the defrosting efficiency. The current method is the timing method or the differential pressure method. Timing method According to engineering experience, the defrosting condition is turned on at a certain interval. This method is very inaccurate and often results in unnecessary fluctuations in the temperature of the cold storage and an unnecessary increase in the energy consumption of the refrigeration system. The differential pressure method is to estimate the frosting condition according to the change of the differential pressure of the cooling fan. When the differential pressure increases to the set value, the defrosting condition is turned on, and when the differential pressure decreases to the set value, the defrosting condition is stopped. The differential pressure method needs to add a whole set of differential pressure system, and the arrangement position of the pressure point has a great influence on the result. The patent of the present invention uses the feature that the power of the fan motor will increase after the evaporator is frosted to judge the start and stop time of the defrosting condition. Low, accurate judgment characteristics.

SUMMARY OF THE INVENTION

The schematic diagram of the structure of the cooling fan for the cold storage is shown in Figure 1. The air in the storage enters the evaporator 2 through the air inlet 1 to cool down, and the cooled air is sent back to the cold storage by the fan 3 through the air outlet 4. In the cooling condition, since the temperature of the surface of the evaporator 2 is lower than the dew point temperature of the temperature in the cold room, and is usually lower than 0°C, frost will occur on the surface of the evaporator of the cooling fan, resulting in the heat exchange efficiency and heat exchange of the cooling fan. At this time, the defrosting condition of the refrigeration system must be turned on to defrost. When the evaporator is frosted, the heat exchange surface inside the evaporator is covered with frost, and the cross-sectional area of the air flow channel is reduced, resulting in an increase in the resistance of the air passing through the evaporator, a decrease in the air volume, and a change in the power of the fan. The present invention utilizes the corresponding relationship between the fan power and the evaporator frosting to determine the defrosting time of the cold storage fan.

The Q-N (flow-power) curve of the axial flow fan commonly used in the cold storage fan is usually a steep drop type, that is, the power decreases with the increase of the air volume, as shown in Figure 2. In this kind of air cooler, the air volume and the motor power are in one-to-one correspondence. The low or high motor power can be used as the basis for judging whether the air volume of the air cooler is large or small, thereby indirectly judging the frosting condition of the evaporator of the air cooler. The invention uses a power meter to regularly monitor the power of the fan motor, and sends the power signal to the original controller of the refrigeration system, and the controller compares the changes of the fan motor power at different times. When the motor power increases significantly, it means that the air volume of the cooling fan is reduced. After eliminating the interference factors such as voltage fluctuation, the significant increase in power can be used as the basis for judging the occurrence of frost on the surface of the evaporator. The controller will turn on the defrosting condition of the refrigeration system. The form and method of specific defrosting conditions are not the content of this patent, and will not be described here. After the defrost condition is turned on, the frost melts, the resistance of the evaporator decreases, the air volume increases, and the power of the fan motor decreases. When the power meter detects that the motor power decreases, the controller controls the refrigeration system to stop the defrost condition and start the refrigeration condition.

Description of drawings:

Figure 1 is a schematic diagram of the structure of the air cooler. The names of the main components of the air cooler in Figure 1 are: 1. Air inlet, 2. Evaporator, 3. Fan and motor, 4. Air outlet, 5. Power meter, 6. Fan power supply

Figure 2 is a diagram of the air volume of the cooling fan-motor power.

Specific implementation method:

The air cooler is a commonly used form of evaporator in the refrigeration system of cold storage and is installed in the cold storage. The air in the cold storage enters the evaporator 2 through the air inlet 1. Inside and outside the heat exchange tube of the evaporator 2, the air exchanges heat with the refrigerant, and the air temperature drops and is sent back to the cold storage from the air outlet through the fan 3. When the refrigeration system of the cold storage and the cooling fan are turned on, the power meter 5 measures the fan power at regular intervals (such as 1 minute, 3 minutes, etc.) and outputs signals to the refrigeration controller (such as programmable logic controller PLC, single chip, etc.).

1. Determination of the time to start the defrosting condition of the refrigeration system

When the refrigeration system of the cold storage is operating under normal refrigeration conditions, when the refrigeration controller receives the fan motor power signal N _n , it compares the value of the power N _n with the value of the rated operating condition power N ₀ , when the power change rate ( N _n -N ₀ ) When / N ₀ ≥10%, the controller controls the refrigeration system to open the defrost mode. When the power change rate ( N _n -N ₀ )/ N ₀ <10%, the controller does not send an instruction, and the refrigeration system continues to perform the refrigeration operation.

2. Determination of defrosting time of closing refrigeration system

After starting the defrosting mode, when the refrigeration controller receives the fan motor power signal N _n , it compares the value of the power N _n with the value of the rated operating power N ₀ , when the power change rate ( N _n -N ₀ )/ N ₀ ≤- At 10%, the controller controls the refrigeration system to stop the defrosting mode and enter the normal refrigeration mode. When the power change rate ( N _n -N ₀ )/ N ₀ >-10%, the controller does not send an instruction, and the refrigeration system continues to defrost. frost condition.

Claims (4)

1. A method for determining defrosting time of an air cooler of a refrigeration house by utilizing fan power is characterized in that: the starting time and the ending time of the defrosting working condition of the air cooler are determined by measuring the change of the motor power of the air cooler of the refrigeration house.

2. The change in motor power for a cold storage air cooler of claim 1, being the real time power of the fan motor detected by a power meterN _n Power of air cooler under frostless rated working conditionN ₀ A comparison is made.

3. Air-cooler defrost initiation time as set forth in claim 1 when power rate of change: (N _n -N ₀ )/N ₀ And when the defrosting rate is more than or equal to 10 percent, the controller controls the refrigerating system to start a defrosting mode.

4. Air-cooler defrost termination time as set forth in claim 1 when power rate of change: (N _n -N ₀ )/N ₀ And when the temperature is less than or equal to-10%, the controller controls the refrigerating system to stop the defrosting mode and enter a normal refrigerating mode.

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