Refrigeration system having adjustable refrigeration capacity

Abstract

A subcooling heat exchanger and subcooling expansion valve in a refrigeration system provide subcooling of a pre-subcooled portion, for refrigerating a thermal load, of condensed refrigerant liquid by a pre-subcooling portion of the condensed refrigerant liquid. The amount of subcooling of the pre-subcooled portion is determined by measuring, with a pressure sensor, refrigerating suction pressure exerted by refrigerating compressors of the system. A controller then controls, based on the refrigerating suction pressure, modulation of mass of pre-subcooling portion, relative pre-subcooled portion, and expansion thereof in the subcooling expansion valve, which controls the amount of refrigerant heat exchanged, and therefore subcooling of pre-subcooled portion, between the pre-subcooling portion and the pre-subcooled portion in the subcooling heat exchanger. The pre-subcooling portion is then subsequently compressed by a subcooling compressor.

1 . An adjustment system for adjusting refrigeration capacity of a refrigeration system having a plurality of refrigerating compressors in fluid communication with at least one refrigerant condensing means and at least one evaporator, said adjustment system comprising:
 a subcooling heat exchanger in fluid communication with the refrigerant condensing means and the evaporator and situated therebetween, said subcooling heat exchanger receiving a pre-subcooled portion and a pre-subcooling portion of a condensed refrigerant liquid from said refrigerant condensing means, said pre-subcooling portion subcooling said pre-subcooled portion into a subcooled portion of said condensed refrigerant liquid in said subcooling heat exchanger by absorbingly exchanging refrigerant heat therewith, said pre-subcooling portion being evaporated thereby into a subcooling portion of refrigerant vapor, a subcooled refrigerating portion of said subcooled portion circulating from said subcooling heat exchanger to said evaporator for absorbing a load heat from a thermal load situated proximal the evaporator and thereby refrigerating said thermal load, said subcooled refrigerating portion being evaporated by absorbing said load heat in the evaporator into a corresponding refrigerating portion of refrigerant vapor;   a subcooling expansion valve in fluid communication with the refrigerant condensing means and said subcooling heat exchanger and disposed therebetween, said subcooling expansion valve selectively modulating mass of said pre-subcooling portion, relative said pre-subcooled portion, circulated therethrough into said subcooling heat exchanger and expansion of said pre-subcooling portion therein, said subcooling expansion valve thereby selectively adjusting said refrigerant heat absorbed from said pre-subcooled portion and thereby said load heat absorbable by said subcooled refrigerating portion from said thermal load, thereby adjusting the refrigerant capacity of the refrigeration system; and   a subcooling compressor in fluid communication with said subcooling heat exchanger and the refrigerant condensing means, said subcooling compressor exerting a subcooling suction pressure for drawing said pre-subcooled portion through said subcooling expansion valve and said subcooling heat exchanger and receiving said subcooling portion, said subcooling portion being compressed thereby.   
   
   
       2 . The adjustment system of  claim 1 , wherein said subcooling heat exchanger is a plate heat exchanger. 
   
   
       3 . The adjustment system of  claim 1 , further comprising a controller connected to a sensor and to said subcooling expansion valve, said sensor taking a measure of the thermal load and said controller controlling, based on said measure, modulation of said mass of said pre-subcooled portion and of said expansion thereof in said subcooling expansion valve. 
   
   
       4 . The adjustment system of  claim 1 , wherein said subcooling expansion valve is an electronic step expansion valve. 
   
   
       5 . The adjustment system of  claim 3 , wherein said controller is a proportional integral derivative controller. 
   
   
       6 . The adjustment system of  claim 3 , wherein the evaporator and the refrigerating compressors are connected in fluid communication by at least one refrigeration suction conduit and said sensor is a pressure sensor connected to said refrigeration suction conduit for sensing, as said measure, a refrigeration suction pressure exerted therewithin by the refrigerating compressor for drawing the refrigerating portion theretowards from said evaporator, said refrigeration suction pressure generally increasing and decreasing as said thermal load, respectively, increases and decreases. 
   
   
       7 . The adjustment system of  claim 1 , further comprising a bypass pressure regulating valve in fluid communication with said subcooling compressor and the refrigerating compressors and situated therebetween, said bypass pressure regulating valve opening and closing to respectively enable and disable circulation of compressed refrigerant vapor compressed by the refrigerating compressors to said subcooling compressor for compression thereby, along with said subcooling portion. 
   
   
       8 . The adjustment system of  claim 7 , further comprising a desuperheating expansion valve in fluid communication with said subcooling compressor and said subcooling heat exchanger and situated therebetween, said desuperheating expansion valve enabling a subcooled desuperheating portion of said subcooled portion to circulate therethrough into said subcooling compressor and expanding said subcooled desuperheating portion, thereby cooling said subcooling portion and said compressed refrigerant received by said subcooling compressor through said bypass pressure regulating valve. 
   
   
       9 . A refrigeration system having an adjustable refrigeration capacity, said refrigeration system comprising:
 a plurality of refrigerating compressors;   at least one refrigerant condensing means in fluid communication with said refrigerating compressors for condensing a refrigerant into a condensed refrigerant liquid;   at least one evaporator in fluid communication with said refrigerant condensing means and said refrigerating compressors and in which a subcooled refrigerating portion of said condensed refrigerant liquid is evaporated into a refrigerated portion of refrigerant vapor by absorption of a load heat from a thermal load situated proximal said evaporator and refrigerated by said refrigeration system, said refrigerating portion being circulated from said evaporator to at least one of said refrigerating compressors;   a subcooling heat exchanger in fluid communication with the refrigerant condensing means and said evaporator and situated therebetween, said subcooling heat exchanger receiving a pre-subcooled portion and a pre-subcooling portion of said condensed refrigerant liquid, said pre-subcooling portion subcooling said pre-subcooled portion into a subcooled portion of said condensed refrigerant liquid in said heat exchanger by absorbingly exchanging refrigerant heat therewith, said pre-subcooling portion being evaporated thereby into a subcooling portion of refrigerant vapor, said subcooled refrigerating portion being drawn from said subcooled portion and circulated to said evaporator;   a subcooling expansion valve in fluid communication with said refrigerant condensing means and said heat exchanger and disposed therebetween, said subcooling expansion valve selectively modulating mass of said pre-subcooling portion, relative said pre-subcooled portion, circulated therethrough into said subcooling heat exchanger and expansion of said pre-subcooling portion therein, said subcooling expansion valve thereby selectively adjusting said refrigerant heat absorbed from said pre-subcooled portion and thereby said load heat absorbable by said subcooled refrigerating portion from said thermal load, thereby adjusting the refrigerant capacity of said refrigeration system; and   a subcooling compressor in fluid communication with said subcooling heat exchanger and said refrigerant condensing means, said subcooling compressor exerting a subcooling suction pressure for drawing said pre-subcooled portion through said subcooling expansion valve and said subcooling heat exchanger and receiving said subcooling portion, said subcooling portion being compressed thereby.   
   
   
       10 . The refrigeration system of  claim 9 , wherein said subcooling heat exchanger is a plate heat exchanger. 
   
   
       11 . The refrigeration system of  claim 9 , further comprising a controller connected to a sensor and to said subcooling expansion valve, said sensor taking a measure of the thermal load and said controller controlling, based on said measure, modulation of said mass of said pre-subcooled portion and of said expansion thereof in said subcooling expansion valve. 
   
   
       12 . The refrigeration system of  claim 9 , wherein said subcooling expansion valve is an electronic step expansion valve. 
   
   
       13 . The refrigeration system of  claim 11 , wherein said controller is a proportional integral derivative controller. 
   
   
       14 . The refrigeration system of  claim 11 , wherein said evaporator and said refrigerating compressors are connected in fluid communication by at least one refrigeration suction conduit and said sensor is a pressure sensor connected to said refrigeration suction conduit for sensing, as said measure, a refrigeration suction pressure exerted therewithin by the refrigerating compressor for drawing the refrigerating portion theretowards from said evaporator, said refrigeration suction pressure generally increasing and decreasing as said thermal load, respectively, increases and decreases. 
   
   
       15 . The refrigeration system of  claim 9 , further comprising a bypass pressure regulating valve in fluid communication with said subcooling compressor and said refrigerating compressors and situated therebetween, said bypass pressure regulating valve opening and closing to respectively enable and disable circulation of compressed refrigerant vapor compressed by said refrigerating compressors to said subcooling compressor for compression thereby, along with said subcooling portion. 
   
   
       16 . The refrigeration system of  claim 15 , further comprising a desuperheating expansion valve in fluid communication with said subcooling compressor and said subcooling heat exchanger and situated therebetween, said desuperheating expansion valve enabling a subcooled desuperheating portion of said subcooled portion to circulate therethrough into said subcooling compressor and expanding said subcooled desuperheating portion, thereby cooling said subcooling portion and said compressed refrigerant received by said subcooling compressor through said bypass pressure regulating valve. 
   
   
       17 . The refrigeration system of  claim 16 , wherein said subcooling compressor is connected to said evaporator by a defrost conduit through which a subcooling compressor output portion of said refrigerant, said subcooling compressor output portion being compressed refrigerant vapor compressed by said subcooling compressor, is circulated into said evaporator when said evaporator is frosted, said subcooling compressor output portion melting frost situated within said evaporator and thereby defrosting said evaporator. 
   
   
       18 . The refrigeration system of  claim 16 , further comprising a heat reclaim means connected in fluid communication by at least one conduit to said subcooling compressor and to the refrigerant condensing means, a subcooling compressor output portion of said refrigerant, said subcooling compressor output portion being compressed refrigerant vapor compressed by said subcooling compressor, being circulated, during a heat reclaim cycle, through said at least one conduit from said subcooling compressor through said heat reclaim means to said refrigerant condensing means, said heat reclaim means absorbing, and thereby reclaiming, a rejected refrigerant heat from said subcooling compressor output portion. 
   
   
       19 . A method for adjusting refrigerant capacity of a refrigeration system having a plurality of refrigerating compressors in fluid communication with at least one evaporator and at least one refrigerant condensing means, at least one of the compressors compressing a refrigerating portion, as refrigerant vapor, into compressed refrigerant, the refrigerant condensing means condensing the compressed refrigerant into condensed refrigerant liquid of which a subcooled refrigerating portion is evaporated, into said refrigerating portion, in the evaporator by absorption of a load heat from a thermal load refrigerated by said refrigeration system and circulated therefrom to at least one of the refrigerating compressors, said method comprising the steps of:
 expanding a pre-subcooling portion of the condensed refrigerant liquid in a subcooling expansion valve in fluid communication with the refrigerant condensing means;   subcooling a pre-subcooled portion of said condensed refrigerant liquid into a subcooled portion thereof, said subcooled refrigerating portion being drawn from said subcooled portion, with said pre-subcooling portion after said expanding by exchanging of heat therebetween in a subcooling heat exchanger in fluid communication with said refrigerant condensing means, said evaporator, and said subcooling expansion valve, thereby adjusting a quantity of load heat absorbable by said refrigerating portion and the refrigeration capacity of said refrigeration system.   
   
   
       20 . The method of  claim 19 , further comprising the steps of:
 prior to said expanding, measuring a refrigeration suction pressure exerted by said refrigerating compressors for refrigerating said thermal load with a sensor connected to a controller for controlling said subcooling expansion valve; and   based on said measuring, modulating, with said controller, mass of said pre-subcooling portion, relative said pre-subcooled portion, circulated through said subcooling expansion valve and said expanding of said pre-subcooling portion therein.