refrigerated showcase small and medium display cases ammonia refrigeration system design example (2)

(3) display cases The cooling consumption of internal ventilation and air exchange. This display cases has no display cases that need to be ventilated, so there is no cold consumption for ventilation, so Q3=O.

(4) Cold consumption for operating operations.

① No. 1 frozen storage room. display cases Cooling consumption when opening the door: Use room temperature to pass through the building. Checking the table shows that in Changsha area (close to 300 degrees latitude), the temperature inside the display cases is -20°C, and the cold energy consumption value of 500t display cases is 4489W. According to the utilization factor, the freezing room is about 638.6W, and the freezing room is about 893.2W.

(5) the motor running cold consumption. No. 4, No. 5, and No. 6 freezers have the same operating cooling capacity: there are three motors used in the air cooler, each with a power of 2.2kW, N=6.6kW, and the motor running cooling capacity is Q4=6.6kW, freezing There is no fan in the cold storage room, and the cold consumption of this item is Q4=0.

(6) Total cold consumption.

① display cases Total load of room cooling equipment.

②Total load of refrigeration equipment

3. Calculating the selection of refrigeration compressors and associated equipment After calculating the refrigeration capacity of the entire display cases, you can select refrigeration compressors and equipment according to the total load of the machine. According to the design conditions of the display cases, determine the condensation temperature, the recooling temperature after the ammonia liquid is condensed, and the number of stages of the refrigeration compressor cycle, and then calculate. Re-cooling temperature of ammonia liquid: Ammonia liquid flows from the condenser into the Gaole drip reservoir. In the display cases, the line is recooled because the condenser is outdoors and the high-pressure reservoir is indoors. When ammonia flows into the high-pressure reservoir and is supplied to the expansion valve, it will naturally cool down due to the temperature of the environment, and the condensing temperature will decrease 3 ～5℃, the ammonia liquid is cooled by the serpentine coil of the intercooler, and the recooling temperature of the ammonia liquid is 3～5℃ higher than the intermediate temperature. The number of compression stages of the refrigeration cycle: This display cases requires the temperature of the refrigerated room to be -18°C and the temperature of the freezing room to be -23°C. If the temperature difference between the evaporation temperature and the temperature of the display cases room is 10°C, the evaporation temperature is -28°C And -33°C.In the actual operation of the refrigeration compressor, the sucked gas is superheated gas instead of saturated vapor. The refrigeration capacity of the refrigeration compressor can be calculated based on the specific volume of the sucked gas, which allows the refrigerant to have a certain degree of overheating.

Refrigeration compressor selection calculation The refrigeration capacity of the two-stage compressor is calculated based on the refrigeration capacity of the low-pressure compressor. The purpose of the selection calculation is to find the required compressor displacement and the required motor power. First calculate The low pressure level is then calculated for the high pressure level. When selecting compressors ' Generally, no less than two compressors should be used, and it is necessary to consider non-stop production during maintenance: When multiple compressors are equipped, pay attention to the interchangeability of models and parts, and select according to the refrigeration compressor catalog sample. In addition, a single-stage refrigeration compressor can also be considered, and the matching group is a two-stage refrigeration compression. The capacity ratio of the high-pressure stage and low-pressure stage of the compressor can be changed.

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