1. Introduction of Parallel Refrigeration Units
Parallel unit refers to a refrigeration unit that integrates more than two compressors into one rack and serves multiple evaporators. The compressors have a common evaporation pressure and condensation pressure, and the parallel unit can automatically adjust energy according to the load of the system. It can realize the uniform wear of the compressor, and the refrigeration unit occupies a small area, and it is easy to realize centralized control and remote control.
The same set of units can be composed of the same type of compressors, or different types of compressors. It can be composed of the same type of compressor (such as piston machine), or it can be composed of different types of compressors (such as piston machine + screw machine); it can load a single evaporation temperature or several different evaporation temperatures. Temperature; it can be a single-stage system or a two-stage system; it can be a single-cycle system or a cascade system, etc. Most of the common compressors are single-cycle parallel systems of the same type.
Parallel compressor units better match the dynamic cooling load of the refrigeration system. By adjusting the start and stop of the compressor in the whole system, the situation of “big horse and small cart” is avoided. For example, when the cooling capacity demand is low in winter, the compressor is turned on less, and in summer, the cooling capacity demand is large, and the compressor is turned on more. The suction pressure of the compressor unit is kept constant, which greatly improves the efficiency of the system. A comparative experiment of single unit and parallel unit has been done on the same system, and the parallel unit system can save energy by 18%.
All the controls for compressors, condensers and evaporators can be concentrated in the system electric control box, and computer controllers can be used to maximize the efficiency of the system. Basically, complete unmanned operation and remote operation can be achieved.
2. Pipeline direction and pipe diameter selection
Pipeline direction: In the Freon refrigeration system, the compressor lubricating oil circulates in the system together with the refrigerant, so in order to ensure the smooth oil return of the system, the return air pipeline (low pressure pipeline) must have a certain slope Towards the compressor, usually with a slope of 0.5%.
Pipe diameter selection: If the diameter of the copper pipe is too small, the pressure loss of the refrigerant in the liquid supply pipeline (high pressure pipeline) and the return gas pipeline (low pressure pipeline) will become too large; If the value is too large, although the resistance loss in the pipeline can be reduced, it will cause an increase in the initial investment cost, and at the same time, it will also cause insufficient oil return speed in the return air pipeline.
Suggested pipe diameter selection principle: the flow velocity of the refrigerant in the liquid supply pipeline is 0.5-1.0m/s, not exceeding 1.5m/s; in the return air pipeline, the flow velocity of the refrigerant in the horizontal pipeline is 7-10m/s , the flow velocity of the refrigerant in the ascending pipeline is 15~18m/s.
Branch type design: There are liquid supply headers and return air headers on the parallel unit, and there are multiple liquid supply branches on the liquid supply header, and one return air branch corresponding to each liquid supply branch is collected in the On the return air header, such a parallel unit refrigeration system pipeline is called a branch type. Each pair of branches, that is, a liquid supply branch and its corresponding air return branch, can have one evaporator (branch 1) or a group of evaporators (branch n). When it is a group of evaporators, usually the group of evaporators starts and stops at the same time.
The evaporator is higher than the compressor:
If the evaporator is higher than the compressor, as long as the return line has a certain slope and selects an appropriate pipe diameter, the system can ensure smooth oil return. However, if the height difference between the evaporator and the compressor is too large, the liquid refrigerant in the liquid supply pipeline will generate flash steam before reaching the throttling mechanism. of supercooling.
The evaporator is lower than the compressor:
If the evaporator is lower than the compressor, the refrigerant in the liquid supply pipeline will not produce flash steam due to the height difference between the evaporator and the compressor, but when designing the refrigeration system pipeline, the return of the system must be fully considered. Oil problem, at this time, the oil return bend should be designed and installed on the ascending section of each return air branch.
The evaporator is higher than the compressor:
If the evaporator is higher than the compressor, as long as the return line has a certain slope and selects an appropriate pipe diameter, the system can ensure smooth oil return. However, if the height difference between the evaporator and the compressor is too large, the liquid refrigerant in the liquid supply pipeline will generate flash steam before reaching the throttling mechanism. of supercooling.
The evaporator is lower than the compressor:
If the evaporator is lower than the compressor, the refrigerant in the liquid supply pipeline will not produce flash steam due to the height difference between the evaporator and the compressor, but when designing the refrigeration system pipeline, the return of the system must be fully considered. Oil problem, at this time, the oil return bend should be designed and installed on the ascending section of each return air branch.
Post time: Dec-22-2022
