1. Size and Purpose of the Cold Storage

 

1. Size
   • For small cold storages (such as small fresh-keeping storages with a volume of dozens of cubic meters), small refrigeration units are usually selected. If the volume of the cold storage is around 10 - 100 cubic meters, hermetic reciprocating refrigeration units are a more appropriate choice. Their refrigeration capacity generally ranges from 1kW to 10kW and can effectively meet the refrigeration needs of small spaces.
   • For medium to large cold storages (several hundred cubic meters to thousands of cubic meters), units with higher power are required. Screw refrigeration units are widely used in such cases. Their refrigeration capacity can range from dozens of kilowatts to hundreds of kilowatts. For example, for a 500-cubic-meter refrigerated storage, a screw refrigeration unit can provide a stable refrigeration effect and ensure the even distribution of temperature throughout the cold storage.
2. Purpose
   • Fresh-keeping storages are mainly used to maintain the freshness of agricultural products, fresh flowers, etc., and the temperature is generally between 0℃ and 10℃. In this case, a higher requirement for temperature accuracy is needed, and air-cooled refrigeration units that can precisely control the temperature are usually selected because the temperature control accuracy of the air-cooled system can reach about ±1℃.
   • Freezing storages are used for freezing foods such as meat and fish, and the temperature is required to be below - 18℃. At this time, the refrigeration units need to have a strong refrigeration ability to quickly reduce the temperature. For example, ammonia refrigeration units can have an evaporation temperature as low as - 30℃ or even lower, which can meet the deep freezing needs of freezing storages.

2. Refrigeration Capacity

Accurately calculating the refrigeration capacity is the key to selecting refrigeration units. The calculation of the refrigeration capacity needs to consider various factors such as the heat transfer of the enclosure structure of the cold storage, the heat of the goods, and the heat dissipation of personnel and equipment.

1. Regarding the heat transfer of the enclosure structure, it is necessary to calculate the amount of heat entering according to the materials and thicknesses of the walls, roofs, and floors of the cold storage, as well as the ambient temperature of the cold storage. For example, for a cold storage with polyurethane insulation panels, its thermal insulation performance is relatively good, and the heat transfer coefficient is relatively low. Suppose the outer wall area of a cold storage is 100 square meters, the thickness of the insulation panel is 100mm, the outdoor temperature is 30℃, and the indoor temperature is - 18℃. Through calculation, the amount of heat transferred through the enclosure structure is about XX kilowatts (the specific calculation involves heat transfer formulas).
2. The heat of the goods is determined according to the types of goods, the incoming temperature, the storage temperature, and the quantity of goods. For example, when storing 10 tons of meat with an initial temperature of 20℃ and freezing it to - 18℃, the amount of sensible heat and latent heat released by the goods needs to be calculated to obtain the required refrigeration capacity.
3. The heat dissipation of personnel and equipment cannot be ignored. Each person working in the cold storage will emit a certain amount of heat, approximately 200 - 300W per person per hour. Meanwhile, if there are lighting, handling equipment, etc. in the storage, their heat generation also needs to be calculated.

3. Energy Efficiency

 

1. Coefficient of Performance (COP)
   • The coefficient of performance is an important indicator for measuring the energy efficiency of refrigeration units. It represents the ratio of the refrigeration capacity to the input power. For example, if the refrigeration capacity of a certain refrigeration unit is 10kW and the input power is 3kW, its COP = 10 / 3 ≈ 3.3. Selecting units with a higher COP can reduce the long-term operation cost. Generally speaking, the COP of screw refrigeration units is relatively high, which can reach about 4 - 5, while that of some old reciprocating units may only be 2 - 3.
2. Energy-saving Technologies
   • Now some advanced refrigeration units adopt frequency conversion technology. By using frequency conversion to drive the compressor, the speed of the compressor can be automatically adjusted according to the actual load of the cold storage, thus achieving energy savings. For example, when the temperature inside the cold storage approaches the set value and the load decreases, the speed of the compressor decreases, reducing power consumption.

4. Refrigerant Type

 

1. Environmental Protection
   • With the improvement of environmental protection requirements, priority should be given to refrigerants that have little damage to the ozone layer and low global warming potential (GWP). For example, R404A is a commonly used refrigerant. It has no destructive effect on the ozone layer, but its GWP value is relatively high. While the new refrigerant R290 (propane) has a lower GWP value and better environmental protection performance, propane is a flammable gas, and safety measures need to be taken during its use.
2. Refrigeration Performance
   • Different refrigerants have different refrigeration performances. Ammonia (NH₃) is a medium-temperature refrigerant with good refrigeration performance. It has a large latent heat of evaporation and a large refrigeration capacity per unit volume. It is widely used in large refrigeration and freezing systems. However, ammonia is toxic and has a certain degree of flammability, so higher requirements are placed on the sealing and safety of the system.

5. Reliability and Stability

 

1. Brand and Reputation
   • Choosing refrigeration units of well-known brands usually can obtain better reliability. For example, brands like Bitzer and Copeland have a good reputation in the refrigeration industry. Their products have undergone strict quality inspections and market verifications, and the quality of key components such as compressors is guaranteed, which can maintain stability during long-term operation.
2. Maintenance Convenience
   • Whether the maintenance of refrigeration units is convenient or not is also very important. Factors such as the ease of disassembly of components and whether there is enough maintenance space need to be considered. For example, the compressors of some refrigeration units are designed with easily removable panels, which is convenient for maintenance personnel to check and replace parts. Meanwhile, brands with a good after-sales service network are also crucial. When the units malfunction, technical support and maintenance services can be obtained in a timely manner.

6. Cost

 

1. Initial Investment Cost
   • It includes the purchase price of the refrigeration units, installation costs, etc. There are significant price differences among different types and brands of refrigeration units. Generally speaking, the price of small reciprocating refrigeration units is relatively low, which may range from several thousand yuan to tens of thousands of yuan; while the price of large screw refrigeration units is relatively high, which may range from hundreds of thousands of yuan to millions of yuan. Installation costs also vary depending on factors such as the complexity of the units and the layout of the cold storage.
2. Operation Cost
   • It mainly includes electricity costs, refrigerant replenishment costs, etc. As mentioned above, units with a high energy efficiency ratio have relatively low electricity costs during operation. Meanwhile, some refrigerants are expensive and may be lost during use, requiring regular replenishment, which will also increase the operation cost.