Most refrigeration enough cooling or cooling capacity to maintain the desired temperature, even under the heaviest loads. This temperature is maintained by motor control. She starts the motor compressor cooling (heat sink). She switches off once the desired temperature is reached.
However, if the heat load is light, it is one system that can be excess capacity for work. Operating expenses more than if the machine with the capacity of more easily meet the necessary load. The system tends to cool too quickly turn on and off too quickly. Modulating (different power) system was designed to fit the machine with the capacity to a greater extent required heat load. Sometimes this is done using two or more compressors connected in parallel. Each1 compressor is operated motor control.
If the heat load increases, and the temperature starts to rise, one compressor will still work. However, if the temperature continues to rise, the second compressor will start to work.
Additional compressors can be reduced until the capacity is obtained. Fig. 3-13 shows a typical scheme cycle modulated installation. This setup has three compressor. Pressure control, connected to the suction line, operates engines. The control contains a special switching devices. This turn of rooms of various compressors. Each compressor will use about the same amount of time. Regulation cycle maintains an even temperature and works economically.
Any normal refrigerant management can be used. However, thermostatic expansion valve is the most common tvpe. The same fluid condenser and receiver can be used by all, compressors, or each can have its own condenser and receiver. The same evaporator, connected to all the compressors. Modulation system can use several of compressor cylinders. Each cylinder has a unloader unit. Variable speed motors are also used to provide modulated cooling capacity.
Compressors 