1. Compressor:
Refrigeration compressor is one of the main equipment of cold storage. Correct selection is very important. The cooling capacity of the refrigeration compressor and the power of the matched motor are closely related to the evaporating temperature and the condensing temperature.
Condensing temperature and evaporating temperature are the main parameters of refrigeration compressors, which are called refrigeration conditions. After the cooling load of the cold storage is calculated, the compressor unit with suitable cooling capacity can be selected.
The most commonly used refrigeration compressors in cold storage refrigeration systems are piston type and screw type. Now scroll compressors have gradually become the most commonly used compressors in small cold storage systems.
General principles for selection of refrigeration compressors in cold storage
1. The refrigeration capacity of the compressor should be able to meet the highest load requirements of the cold storage peak season production, and generally do not use units.
2. The determination of the capacity and number of a single machine should be considered according to factors such as the convenience of energy adjustment and the change of the working conditions of the refrigeration object. Large-scale compressors should be selected for cold storages with a large refrigeration load to prevent the number of machines from being too large. The number of large-scale cold storage compressors is not easy to choose. In addition to two, one can be selected for the life service cold storage.
3. Select a suitable compressor according to the calculated compression ratio. For Freon compressors, use a single-stage compressor if the compression ratio is less than 10, and use a two-stage compressor if the compression ratio is greater than 10.
4. When selecting multiple compressors, the possibility of mutual backup and replacement of parts between units should be comprehensively considered. The compressor models of one unit should be of the same series or the same model.
5. The working conditions of the refrigeration compressor should meet the basic design conditions as much as possible, and the working conditions should not exceed the operating range specified by the compressor manufacturer. With the continuous maturity of refrigeration control technology, the compressor unit controlled by microcomputer is an ideal choice.
6. Due to the structural characteristics of the screw compressor, its volume ratio changes with the operating conditions, so the screw compressor can adapt to different operating conditions. The single-stage compression ratio of the screw compressor is large and has a wide operating range. Under the condition of economizer, higher operating efficiency can be obtained.
7. Due to its high operating efficiency, low noise and stable operation, scroll compressors have been paid attention to in recent years, and are more and more used in small and medium-sized cold storage projects
Heat exchange equipment: condenser
The condenser can be divided into water-cooled, air-cooled, and water-air mixed cooling according to the cooling method and condensing medium.
General principles of condenser selection
1. The vertical condenser is arranged outside the machine room and is suitable for areas with abundant water sources but poor water quality or high water temperature.
2. Bedroom water condensers are widely used in Freon systems, generally arranged in the computer room, and are suitable for areas with low water temperature and good water quality.
3. Evaporative condensers are suitable for areas with low relative air humidity or water shortage, and need to be arranged in a well-ventilated place outdoors.
4. Air-cooled condensers are suitable for areas with tight water sources, and are widely used in small and medium-sized Freon refrigeration systems.
5. All kinds of water-cooled condensers can adopt the cooling method of circulating water,
6. For water-cooled or evaporative condensers, the condensing temperature should be selected according to the national standard during design, but should not exceed 40 °C.
7. From the perspective of equipment cost, the cost of evaporative condenser is the highest. Compared with large and medium-sized cold storage, evaporative condenser and other forms of water condenser and cooling water circulation combination, the initial construction cost is similar, but the evaporative condenser is more economical in later operation. In order to save energy by water, evaporative condensers are mainly used for condensers in developed countries, but in areas with high temperature and high humidity, the effect of evaporative condensers is not ideal.
Of course, the final choice of the condenser depends on the meteorological conditions of the region and the water quality of the local water source. It is also related to the actual heat load of the cold storage and the layout requirements of the computer room.
Throttle valve:
The throttling mechanism is one of the four major components of the refrigeration system of the cold storage, and it is an indispensable component to realize the vapor refrigeration cycle. Its function is to reduce the temperature and pressure of the refrigerant in the accumulator after throttling, and at the same time adjust the flow of the refrigerant according to the change of the load.
According to the adjustment method in use, the throttle mechanism can be divided into: manual adjustment throttle valve, liquid level adjustment throttle valve, non-adjustable throttle mechanism, electronic expansion valve adjusted by electronic pulse, and steam superheat adjusted. Thermal expansion valve.
The thermal expansion valve is the most commonly used throttling device in the government cooling system. It adjusts the opening degree of the valve and adjusts the liquid supply by measuring the superheat degree of the return air on the outlet pipe of the evaporator through the temperature sensor, and realizes automatic adjustment within a certain range. The function of the liquid supply volume, the adjustment function of the solid line liquid supply volume changing with the change of the heat load.
Expansion valves can be divided into two types: internal balance type and external balance type according to their structure.
Internally balanced thermal expansion valve is suitable for refrigeration systems with relatively small evaporator power. Generally, internal balanced expansion valves are used in smaller refrigeration systems.
When the evaporator has a liquid separator or the evaporation pipeline is long and there are many branches in the refrigeration system with large pressure loss on both sides of the evaporator, the external balance expansion valve is selected.
There are many types of thermal expansion valves, and expansion valves with different specifications and models actually have different cooling capacities. The selection should be based on the size of the cooling capacity of the cold storage refrigeration system, the type of refrigerant, the pressure difference before and after the expansion valve, and the size of the evaporator. Factors such as pressure drop are selected after correcting the rated cooling capacity of the expansion valve.
Determine the type of thermal expansion valve used in the cold storage system by calculating the pressure loss and evaporation temperature. When the pressure loss is less than the specified value, the internal balance can be selected, and the external balance can be selected when the value is greater than the table.
Fourth, heat exchange equipment – evaporator
The evaporator is one of the four important parts in the refrigeration system of the cold storage. It uses the liquid refrigerant to evaporate under low pressure, absorbs the heat of the cooled medium, and achieves the purpose of reducing the temperature of the cooling medium.
Evaporators are installed in different forms of cooling medium, and are divided into two types: evaporators for cooling liquids and evaporators for cooling gases.
The evaporator used in the cold storage is the evaporator for cooling the gas.
Selection principle of evaporator form:
1. The selection of the evaporator should be comprehensively determined according to food processing and refrigeration or other technological requirements.
2. The use conditions and technical standards of the evaporator should meet the standard requirements of the current refrigeration equipment
3. Air cooler cooling equipment can be used in cooling rooms, freezing rooms, and refrigerating rooms
4. Aluminum exhaust pipes, top exhaust pipes, wall exhaust pipes or air coolers can all be used in the freezer room for frozen objects. When the food is well packaged, the cooler can be used. It is easy to use the exhaust pipe form for food without packaging.
5. Due to the different freezing processes of food, appropriate freezing equipment should be selected according to the actual situation, such as freezing tunnels or tube-type freezing racks.
6. The cooling equipment in the packaging room is suitable for the use of air coolers when the storage temperature is higher than -5 °C, and the tube type evaporator is suitable for use when the storage temperature is lower than -5 °C.
7. The freezer is suitable for the use of smooth top row pipes.
The cold storage fan has many advantages such as large heat exchange, convenient and simple installation, less space occupation, beautiful appearance, automatic control, and complete defrosting. It is favored by many small cold storage, medical cold storage, and vegetable cold storage projects.
Post time: Nov-18-2022
