Selection parameters and system matching points for two-stage semi enclosed compressors in cold storage at minus 60 degrees Celsius
The conventional cold storage at minus 60 degrees Celsius uses a two-stage semi enclosed compressor, and single-stage models cannot maintain this temperature stably. The cooling capacity attenuation exceeds 60% at an evaporation temperature of -60 ℃.
-The recommended intermediate cooling temperature for the 60 ℃ cold storage two-stage compression system is controlled between -12 ℃ and -18 ℃. For every 5 ℃ increase in intermediate temperature, the overall COP of the unit decreases by about 11%. The Xiteliduo two-stage model is equipped with a fixed intermediate cooling ratio scheme.
The main volume ratio of the high and low pressure cylinders in a two-stage semi closed compressor is 1:3. If the volume ratio deviates from this value by more than 0.4, it will cause the exhaust temperature to exceed the standard and trigger the protection frequently.
A 100 cubic meter deep cold storage with a temperature of minus 60 ℃ typically has a cooling load of around 12.5kW, corresponding to a two-stage semi enclosed compressor displacement of no less than 16m ³/h, which cannot be estimated based on the experience of fresh-keeping warehouses.
Priority is given to using R23 refrigerant with a cascade system for cold storage at minus 60 degrees Celsius. The R404A two-stage solution is only suitable for short-term intermittent operation, and the long-term continuous operation failure rate is increased by 58%.
When the compressor is matched with the air cooler, the heat exchange temperature difference of the -60 ℃ deep cold storage air cooler is taken as 6 ℃, which is much smaller than the standard of 8 ℃~10 ℃ for ordinary freezers, and the heat exchange area needs to be enlarged.
The selection of refrigeration oil for two-stage compressors requires a low temperature resistance pour point of ≤ -65 ℃. If the pour point is higher than the threshold, the oil flowability will deteriorate after low-temperature shutdown, and the risk of starting wear will increase.
The double stage semi enclosed unit undergoes factory pressure maintenance testing with a high pressure side of 30 bar and a low pressure side of 12 bar. The pressure drop after 8 hours of maintenance is ≤ 0.04 bar, which complies with domestic and export CE inspection standards.
Compared with screw and piston compressors at -60 ℃, the piston two-stage model has a 27% lower initial investment, lower maintenance and accessory costs, and is more suitable for overseas small and medium-sized cryogenic projects.
When wiring a semi enclosed compressor, the high and low voltage motors of the two-stage unit have independent circuits, and the operating current monitoring needs to be collected separately. The current of the high voltage stage is generally 1.4 times that of the low voltage stage.
The maintenance cycle of cryogenic compressors is shortened by 35% compared to ordinary refrigeration compressors, and samples need to be taken and tested for frozen oleic acid value and moisture after 3000 hours of continuous operation.
Cold storage at minus 60 degrees Celsius is not suitable for frequent entry and exit of doors for a long time. If the door is opened more than 8 times per hour, the cooling load will increase by 22%, and the compressor will continue to operate at full load.
Many freeze-drying compressors use the same two-stage structure. Under vacuum conditions in the freeze-drying chamber, the fluctuation range of evaporation load can reach up to 45%, and the compressor requires an energy regulation structure.
Overseas engineering companies are working on cryogenic projects in Russia and Central Asia, with sufficient inventory of 50Hz dual stage models. However, the delivery time for the 60Hz version has generally increased by 15-25 days, and early inquiries need to confirm the electrical system.
For domestic compressors used in minus 60 projects, it is necessary to verify the manufacturer's published -60 ℃ calibration cooling capacity. Many brands only indicate the standard operating condition cooling capacity, and there is no actual measurement data for low-temperature operating conditions.
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FAQ
Can a single-stage semi enclosed compressor be used in a -60 ℃ cold storage? Not recommended, single-stage cooling capacity severely deteriorates and cannot maintain stable temperature control.
What is the standard for the high and low pressure volume ratio of a two-stage compressor? Mainstream 1:3, excessive deviation can easily lead to high temperature protection for exhaust.
3. Should R404A or R23 be used for cold storage at -60 ℃? Long term continuous operation prioritizes R23 stacking, while R404A two-stage is only suitable for intermittent working conditions.
What is the required pour point for the refrigeration oil of a two-stage compressor? Suggest pouring point ≤ -65 ℃ to ensure lubrication during low-temperature start-up.
5. Does Xiteliduo's two-stage semi enclosed system support minus 60 working conditions? Support, there are dual stage models that have undergone low-temperature calibration.
What is the required exhaust capacity for a 100 cubic meter to 60 cubic meter cold storage? The minimum is not less than 16m ³/h, and the load margin for opening the door needs to be added.
How long is the maintenance cycle for a two-stage compressor? It is recommended to replace the oil sample after 3000 hours of continuous cryogenic testing.
How to troubleshoot low suction pressure in a two-stage unit? Focus on checking the intermediate cooling circuit, expansion valve, and refrigerant charging amount.
