In the actual operation of refrigeration equipment and system engineering, not only should the refrigeration system be adjusted to a reasonable operating range to meet the requirements of the refrigeration process and maintain its safe and normal operation, but it should also be further adjusted to the optimal operating state to achieve the goal of efficient and energy-saving operation and improve the energy-saving level of refrigeration equipment operation.

1、 In the design of refrigeration equipment, increasing the evaporation temperature and pressure will reduce the compression ratio and power consumption of the refrigeration system, which is very beneficial for energy conservation. The problem is that the evaporation temperature depends on the object being cooled, and adjusting the evaporation temperature must be based on the premise of not affecting the refrigeration process requirements of the object being cooled. However, in the operation and regulation of refrigeration equipment, attention should be paid to observation and corresponding measures should be taken in a timely manner, such as appropriate defrosting, appropriate increase in liquid supply, oil discharge and dirt removal cleaning of the evaporator, effective energy regulation of the compressor, etc., to stabilize the evaporation temperature at the design temperature and avoid unnecessary low evaporation temperature.

From the perspective of energy conservation, appropriately increasing the evaporation temperature is economically reasonable. Calculations show that when using a storage temperature of -25 ℃ instead of -30 ℃, the increase in evaporation temperature will save up to 9.8% of electricity. Therefore, for situations with short storage periods and low quality requirements for low temperatures, the evaporation temperature can be appropriately increased to achieve energy-saving effects. In addition, refrigeration units are generally designed for full load, but in reality, the operating time at full load is not long, and most of the time it is operated under conditions below the design load. When the cooling consumption decreases at partial load, increasing the evaporation temperature can achieve the same cooling effect by reducing the heat transfer temperature difference of the evaporator.

For example, when the condensation temperature is 38 ℃, the evaporation temperature of the refrigeration system is -33 ℃; When the cooling consumption is reduced to 50% of the original design, the heat transfer temperature difference of the original evaporator is reduced from 10 ℃ to 5 ℃. The warehouse still uses the original equipment to maintain the temperature at -23 ℃, but at this time, the evaporation temperature is increased to -28 ℃. Calculations show that the energy-saving effect can reach 15%.

2、 The condensation temperature and pressure are too high. If the condensation temperature is too high, it will cause the compressor exhaust pressure to be too high and the exhaust temperature to rise, which is very unfavorable for the safe operation of the compressor and can easily cause accidents; At the same time, it reduces the efficiency of the refrigeration system and increases energy consumption. From the perspective of energy conservation, a higher condensing temperature should be appropriately selected in the design of refrigeration equipment, that is, a larger condensing heat exchange area should be configured to achieve the goal of actual energy-saving operation.

From the perspective of operational regulation, the refrigeration equipment should be controlled to operate at the lowest possible condensation temperature to improve refrigeration efficiency and reduce operating costs. The condensation temperature is determined by various factors that affect the heat transfer efficiency of the condenser, such as the temperature, flow rate, flow rate, condensation area of the cooling medium, the displacement of the compressor, and air humidity, oil pollution, scale, etc.

To minimize the condensation temperature, two main approaches should be taken:

Maintain the cleanliness of the heat exchange area and eliminate factors that affect heat exchange, such as timely descaling, oil discharge, and removal of non condensable gases; Control the flow rate and velocity of the cooling medium to ensure that it flows uniformly through the heat exchange area; Special attention should also be paid to the uniformity of the distribution of cooling water in the condenser.

When operating under partial load of system equipment, special attention should be paid to simultaneously controlling and adjusting the load of the water pump or fan in the condensing system to avoid ineffective heat exchange power consumption. Because the total energy consumption of refrigeration equipment includes the energy consumption of the compressor and the energy consumption of the heat exchanger water pump and fan.

3、 The method of subcooling the refrigerant liquid before throttling can reduce the dryness of the refrigerant after throttling and improve the refrigeration capacity of the refrigeration cycle at certain condensation and evaporation temperatures.

Under normal circumstances, assuming that the outlet temperature of the condenser is 3-5K lower than the condensing temperature, the temperature rise of the cooling water in the condenser is 3-8K. Therefore, the inlet temperature of the cooling water is 5-13K lower than the condensing temperature, which is sufficient to achieve a certain degree of subcooling at the outlet temperature of the refrigerant. In a horizontal shell and tube condenser, if the condensed liquid is not immediately discharged from the bottom of the condenser but accumulates inside the condenser, this part of the liquid will continue to transfer heat to the cooling water and surrounding medium inside the tube, and a certain degree of supercooling can be obtained when discharged. The acquisition of subcooling does not result in an increase in compressor power consumption, which means that subcooling will inevitably lead to an increase in the refrigeration coefficient of the equipment system, improving the economic efficiency of refrigeration equipment operation.

Research calculations show that under the working conditions of condensation temperature of 40 ℃ and evaporation temperature of 5 ℃, a supercooling degree of 5K will increase the refrigeration capacity of R22 refrigeration equipment by 4.27%, with no change in input power and a 4.27% increase in COP value.

The suction superheat not only effectively improves the volumetric efficiency of the compressor and the refrigeration capacity per unit mass of the system, but also inevitably increases the specific volume of the compressor suction, exhaust temperature, power consumption, and the heat load of the condenser. Although its overall impact still increases the cooling capacity with the increase of superheat, the cooling coefficient of the equipment system decreases accordingly.

Although this seems to contradict the energy-saving operation of the equipment, in refrigeration equipment, especially in low-temperature refrigeration equipment, a low suction temperature can cause severe frosting and deterioration of lubrication conditions in the compressor. During the wet stroke, the volumetric efficiency of the compressor significantly decreases, resulting in a decrease in indicator efficiency, mechanical efficiency, and electrical efficiency, leading to a greater decrease in the COP value of the compressor. Moreover, wet stroke is prone to liquid hammer, which can cause fatal mechanical damage to the compressor.

In addition, make full use of the nighttime heat load reduction caused by the temperature difference between day and night, the decrease in condensation temperature, and the low valley power grid at night, and try to make the refrigeration equipment operate at night as much as possible; Optimize the design of uniform airflow organization in a refrigeration environment; The use of multi-stage segmented refrigeration technology enables the refrigeration equipment to adopt different operating parameters in each time period, reducing the heat transfer temperature difference. By utilizing the principle of large refrigeration coefficient during continuous temperature regulation, the energy-saving of the actual refrigeration freezing process can be achieved without increasing investment, which also has significant economic benefits.