Method of operating a refrigeration plant and a plant for performing the method

Abstract

A refrigeration plant including an oil-injected compressor, an oil separator, a condenser and an evaporator. The plant comprises means to introduce liquid refrigerant to the compression phase of the cycle ahead of the oil separator. The plant further comprises means to adjust the amount of liquid refrigerant introduced in response to the temperature difference between the condenser and the oil separator, in order to keep the difference on a constant level of 5° C. to 15° C.

I claim: .[.1. A method of operating a refrigeration plant comprising: a refrigerant flow circuit including a compressor of the screw rotor type, a condenser and an evaporator; means for circulating oil and for injecting said oil into the compression chambers of said compressor; an oil separator provided in said circuit between the outlet of said compressor and the inlet of said condenser; and means for introducing liquid refrigerant into a circuit portion between the inlet of the compressor and the inlet of said oil separator; 
     
        higher than said liquefaction temperature..]. 3. A refrigeration plant comprising: a refrigerant flow circuit including a compressor of the screw rotor type, a condenser and an evaporator;   means for circulating oil and for injecting said oil into the compression chambers of said compressor;   an oil separator provided in said circuit between the outlet of said compressor and the inlet of said condenser;   means for introducing liquid refrigerant into a circuit portion between the inlet of the compressor and the inlet of said oil .[.seperator.]. .Iadd.separator.Iaddend.;   means responsive to at least one parameter indicative of the difference between the temperature in the oil separator and the temperature in the condenser;   adjustable means for varying the quantity of liquid refrigerant introduced into said circuit portion; .[.and.].   .Iadd.means for controlling the capacity of the compressor, said capacity controlling means being operatively connected to said adjustable means to reduce the quantity of liquid refrigerant introduced during operation at partial capacity; and .Iaddend.   means connecting said responsive means with said adjustable means to control said adjustable means such that said temperature difference is kept small but is prevented from dropping down to zero. .[.4. A plant as defined in claim 3, comprising means for controlling the capacity of the compressor, said capacity controlling means being operatively connected to said adjustable means to reduce the quantity of liquid refrigerant introduced during operation at partial capacity..]. .[.5. A plant as defined in claim 3, wherein said responsive means includes a temperature sensing device in each of the condenser and the oil separator, said sensing devices being combined to produce a signal representing said temperature difference, said connecting means controlling said adjustable means as a function of said signal to keep said difference substantially constant..]. .[.6. A plant as defined in claim 3 wherein said responsive means includes a temperature sensing device and a pressure sensing device coupled to said oil separator, said devices being connected to a computer for producing a signal representing the difference between the temperature in the oil separator and the liquefaction temperature of the refrigerant at the pressure prevailing in the oil separator..]. .[.7. A plant according to claim 3 wherein said connecting means controls said adjustable means such that said temperature in the oil separator is about 5° C. to 15° C. higher than the temperature in said condenser..]. .[.8. A plant according to claim 3 wherein said liquid refrigerant is introduced into the compression chambers of said compressor and said adjustable means comprises a valve means coupled in the path of said liquid refrigerant to said compressor, said valve means being opened to increase the quantity of said liquid refrigerant introduced into said compressor..]. .[.9. A plant according to claim 3 wherein said liquid refrigerant is introduced into a discharge conduit of said compressor and including return conduit means returning liquid refrigerant to said condenser, said adjustable means comprising a valve means in said return conduit, said valve means being closed to increase the quantity of liquid refrigerant introduced into said discharge conduit of said compressor..].   
     
     
         0. A plant according to claim .[.4.]. .Iadd.3 .Iaddend.wherein said connecting means comprises a motor coupled to said adjustable means via a gear mechanism, said capacity controlling means also being coupled to said 
     
     
        adjustable means via said gear mechanism. 11. A plant according to claim .[.4.]. .Iadd.3 .Iaddend.wherein said controlling means includes a cam 
     
     
        arrangement operatively coupled to said adjustable means. 12. A plant according to claim .[.5.]. .Iadd.3 .Iaddend.wherein said connecting means comprises a motor coupled to said adjustable means via a gear mechanism. 
     
     
          . A plant according to claim .[.6.]. .Iadd.3 .Iaddend.wherein said temperature sensing and pressure sensing devices are in said oil separator. .[.14. A method as defined in claim 1 comprising controlling the introduction of said liquid refrigerant into the compression chambers 
     
     
        of said compressor..]. 15. A .[.method.]. .Iadd.plant .Iaddend.according to claim .[.1 comprising controlling the introduction of said liquid refrigerant into.]. .Iadd.16, wherein said introducing means communicates with .Iaddend.a discharge conduit of said compressor. .Iadd. 16. A refrigeration plant comprising: a refrigerant flow circuit including a compressor of the screw rotor type, a condenser and an evaporator, said compressor having a discharge conduit;   means for circulating oil and for injecting said oil into the compression chambers of said compressor;   an oil separator provided in said circuit between the outlet of said compressor and the inlet of said condenser;   means for introducing liquid refrigerant into said discharge conduit of said compressor at a position between said compressor and the inlet of said oil separator;   return conduit means returning liquid refrigerant to said condenser;   means responsive to at least one parameter indicative of the difference between the temperature in the oil separator and the temperature in the condenser;   adjustable valve means in said return conduit means for varying the quantity of liquid refrigerant introduced into said discharge conduit of said compressor, said valve means being closed to increase the quantity of liquid refrigerant introduced into said discharge conduit of said compressor; and   means connecting said responsive means with said adjustable valve means to control said adjustable valve means such that said temperature difference is kept small but is prevented from dropping down to zero. .Iaddend.