Compressor and Condenser Operation

Let s say we have a centrifugal refrigeration compressor driven by a motor. The motor is tripping off because of high amperage. Should we open or close the suction throttle valve shown in Fig. 31.2 Answer—close it. Of course, both the evaporator vapor outlet temperature and the process fluid outlet temperature will increase. But that is the price we pay for having too small a motor driver on the compressor. Does this mean that when our home air conditioner gets low on freon, our electric bill drops Correct. But the price we pay is a hot home. 

How about the compressor discharge pressure What is this controlled by Answer—the condenser. The compressor discharge pressure has nothing whatsoever to do with the compressor. And this statement is true regardless of whether the compressor is a reciprocating or centrifugal machine, or fixed- or variable-speed. It is the condenser temperature that determines the compressor discharge pressure. 

Lowering the compressor discharge pressure can be achieved by providing cooler water to the refrigerant condenser. But how does this affect the horsepower load or electrical power demand on the compressor s 

For instance, suppose we are working with a reciprocating compressor. This particular machine has a very small volumetric clearance and a very high volumetric efficiency (these terms are explained in Chap. 42, Reciprocating Compressors ). With this compressor, a significant decrease in discharge pressure will result in only a tiny increase in vapor flow. Therefore, the work or amp load on the driver will decrease. 

For instance, suppose we are working with a reciprocating compressor. This particular machine has a very small volumetric clearance and a very high volumetric efficiency (these mysterious 

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