Very low temperature refrigeration system with fast operation cycle

Abstract

Methods for shortening the cycle time in each of the defrost, standby and cool modes of operation of a very low temperature refrigeration system. These methods can be used alone or in combination with one or more of each of the other techniques, including, for example, in a single very low temperature refrigeration system, to provide a fast total cycle of one, two or all three of the defrost, standby and cool modes.

1 . A very low temperature refrigeration system, the system comprising:
 a compressor;   a plurality of heat exchangers;   an expander;   a defrost valve and   a controller comprising a processor and a memory, the controller being configured to:   (i) during startup of the compressor, control said defrost valve in a hot gas defrost circuit to open to bypass flow of a refrigerant around a high pressure side of the plurality of heat exchangers and the expander and to an evaporator inlet from which the refrigerant flows to an evaporator, thereby accommodating a volume of the refrigerant in the evaporator to limit an initial increase in pressure of the refrigerant during the startup of the compressor; and   (ii) to subsequently control the defrost valve to close so that flow of the refrigerant proceeds through the high pressure side of the plurality of heat exchangers and the expander to the evaporator.   
     
     
         2 . The very low temperature refrigeration system according to  claim 1 , wherein the refrigerant comprises a mixture of a plurality of different refrigerant components, the mixture comprising: argon, R-14, R-23, R-125 and R-245fa. 
     
     
         3 . (canceled) 
     
     
         4 . The very low temperature refrigeration system according to  claim 1 , wherein the controller is configured to subsequently control the defrost valve to close after at least about 3 seconds from the startup of the compressor and before at least about 6 seconds from the startup of the compressor. 
     
     
         5 . (canceled) 
     
     
         6 . The very low temperature refrigeration system according to  claim 1 , the controller being configured to control the system to enter a standby mode upon the subsequently closing of the defrost valve, the standby mode comprising the controller controlling a cool valve to close to prevent flow of refrigerant from the high pressure side of the plurality of heat exchangers to the evaporator, while permitting flow of refrigerant through the high pressure side of the plurality of heat exchangers and a low pressure side of the plurality of heat exchangers. 
     
     
         7 . The very low temperature refrigeration system according to  claim 1 , wherein the hot gas defrost circuit is configured to flow the refrigerant from a high pressure supply line of the compressor to the evaporator inlet from which the refrigerant flows to an evaporator. 
     
     
         8 . A method of limiting peak operating pressure during startup of a very low temperature refrigeration system having a compressor, a plurality of heat exchangers, an expander and an evaporator, the method comprising:
 during startup of the compressor, opening a defrost valve in a hot gas defrost circuit to bypass flow of a refrigerant around a high pressure side of the plurality of heat exchangers and the expander and to an evaporator inlet from which the refrigerant flows to the evaporator, thereby accommodating a volume of the refrigerant in the evaporator to limit an initial increase in pressure of the refrigerant during the startup of the compressor; and   subsequently closing the defrost valve so that flow of the refrigerant proceeds through the high pressure side of the plurality of heat exchangers and the expander to the evaporator.   
     
     
         9 . The method according to  claim 8 , wherein the refrigerant is charged into the system at a refrigerant pressure that would create a peak pressure of the refrigerant that would exceed a design pressure of the very low temperature refrigeration system during startup of the compressor absent the opening of the defrost valve; and/or
 wherein a refrigerant flow volume of the evaporator comprises greater than about 10 percent of a refrigerant system volume of the very low temperature refrigeration system; and/or   wherein the refrigerant is charged into the system such that the system has a balance pressure of between about 230 psig and about 300 psig; and/or   wherein, during the bypass flow of the refrigerant, a temperature of the refrigerant is greater than about 25° C.   
     
     
         10 - 12 . (canceled) 
     
     
         13 . A very low temperature refrigeration system, the system comprising:
 a compressor;   a plurality of heat exchangers;   an expander;   a defrost valve and   a controller comprising a processor and a memory, the controller being configured to, in a defrost mode of operation of the system,   (i) control said defrost valve in a hot gas defrost circuit to open to bypass flow of a refrigerant around a high pressure side of the plurality of heat exchangers and to an evaporator inlet from which the refrigerant flows to an evaporator, to effect warming of the evaporator, and   (ii) while controlling the defrost valve to open, control a cool valve to close so that the refrigerant does not flow from the high pressure side to the evaporator;   the controller being further configured to, (i) based on an input control signal, set a value of a stored defrost completion set point temperature of a return temperature sensor on a low pressure side of the evaporator; and (ii) during the warming of the evaporator, upon the return temperature sensor on the low pressure side of the evaporator reaching the stored defrost completion set point temperature of the return temperature sensor, control the defrost valve to close to prevent the refrigerant flowing to the evaporator.   
     
     
         14 . The very low temperature refrigeration system of  claim 13 , wherein the stored defrost completion set point temperature of the return temperature sensor is about 0° C. or lower; and/or
 wherein the return temperature sensor comprises a thermocouple on the low pressure side of the evaporator; and/or 
 said controller being configured to close the defrost valve in response to receiving a temperature control signal from the return temperature sensor that is at least as warm as the stored defrost completion set point temperature of the return temperature sensor, the controller comprising a memory for storing a defrost completion set point temperature. 
 
     
     
         15 - 16 . (canceled) 
     
     
         17 . A method of reducing time spent in a defrost mode of operation of a very low temperature refrigeration system, the method comprising:
 in a defrost mode of operation of the system, (i) opening a defrost valve in a hot gas defrost circuit to bypass flow of a refrigerant around a high pressure side of a plurality of heat exchangers and to an evaporator inlet from which the refrigerant flows to an evaporator, to effect warming of the evaporator, and (ii) while opening the defrost valve, closing a cool valve so that the refrigerant does not flow from the high pressure side to the evaporator;   based on an input control signal, setting a value of a stored defrost completion set point temperature of a return temperature sensor on a low pressure side of the evaporator; and   during the warming of the evaporator, upon the return temperature sensor on the low pressure side of the evaporator reaching the stored defrost completion set point temperature of the return temperature sensor, closing the defrost valve to prevent the refrigerant flowing to the evaporator.   
     
     
         18 . A very low temperature refrigeration system, the system comprising:
 a compressor;   a plurality of heat exchangers;   an expander;   a temperature sensor;   a plurality of valves; and   a controller comprising a processor and a memory, the controller being configured to, based on an input control signal, set a value of a stored bypass control set point temperature of a return temperature sensor on a low pressure side of an evaporator;   the controller being further configured to, upon a return temperature sensor on a low pressure side of the evaporator warming to be at or above the stored bypass control set point temperature of the return temperature sensor,   (i) control a return valve to close to prevent refrigerant flow through a low pressure side of the plurality of heat exchangers, and   (ii) control a bypass valve to open to bypass flow of the refrigerant around the low pressure side of the plurality of heat exchangers and to a suction line that enters a low pressure side of the compressor; and   the system being configured to warm the bypassed flow of the refrigerant in the suction line before it enters the low pressure side of the compressor,   wherein at least one of the plurality of heat exchangers is configured to exchange heat between the suction line and a high pressure side of the plurality of heat exchangers to warm the bypassed flow of the refrigerant in the suction line; or   wherein the refrigeration system comprises a heater for warming the bypassed flow of the refrigerant in the suction line.   
     
     
         19 - 20 . (canceled) 
     
     
         21 . The very low temperature refrigeration system of  claim 18 , wherein the stored bypass control set point temperature of the return temperature sensor is less than a rated input flow temperature of the compressor, wherein the stored bypass control set point temperature of the return temperature sensor is between about −40° C. and about −70° C. 
     
     
         22 . (canceled) 
     
     
         23 . A method of reducing recovery time after defrost of a very low temperature refrigeration system, the method comprising:
 based on an input control signal, setting a value of a stored bypass control set point temperature of a return temperature sensor on a low pressure side of the evaporator;   upon a return temperature sensor on a low pressure side of the evaporator warming to be at or above the stored bypass control set point temperature of the return temperature sensor, (i) closing a return valve to prevent refrigerant flow through a low pressure side of a plurality of heat exchangers, and (ii) opening a bypass valve to bypass flow of the refrigerant around the low pressure side of the plurality of heat exchangers and to a suction line that enters a low pressure side of a compressor; and   warming the bypassed flow of the refrigerant in the suction line before it enters the low pressure side of a compressor.)   
     
     
         24 . A very low temperature refrigeration system, the system comprising:
 a compressor;   a plurality of heat exchangers;   an expander;   a flow metering device and a cool valve with which the flow metering device is in a series flow connection to an inlet of an evaporator; and   a controller comprising a processor and a memory, the controller being configured to, upon a discharge pressure of a compressor of the system being at least as high as a stored set point of a maximum discharge pressure during the cooling mode of operation, control an unload valve to open to permit refrigerant flow to bypass around the flow metering device and to the cool valve, until the discharge pressure reduces to be less than the stored set point of the maximum discharge pressure,   wherein said controller is further configured to:
 during startup of the compressor to (i) control a defrost valve in a hot gas defrost circuit to open to bypass flow of a refrigerant around a high pressure side of the plurality of heat exchangers and the expander and to an evaporator inlet from which the refrigerant flows to an evaporator, thereby accommodating a volume of the refrigerant in the evaporator to limit an initial increase in pressure of the refrigerant during the startup of the compressor; 
 (ii) to subsequently control the defrost valve to close so that flow of the refrigerant proceeds through the high pressure side of the plurality of heat exchangers and the expander to the evaporator; and 
 during defrost to (i) control a defrost valve in a hot gas defrost circuit to open to bypass flow of a refrigerant around a high pressure side of the plurality of heat exchangers and to an evaporator inlet from which the refrigerant flows to an evaporator, to effect warming of the evaporator, and 
 (ii) while controlling the defrost valve to open, control a cool valve to close so that the refrigerant does not flow from the high pressure side to the evaporator; 
 the controller being further configured to, (i) based on an input control signal, set a value of a stored defrost completion set point temperature of a return temperature sensor on a low pressure side of the evaporator; and (ii) during the warming of the evaporator, upon the return temperature sensor on the low pressure side of the evaporator reaching the stored defrost completion set point temperature of the return temperature sensor, control the defrost valve to close to prevent the refrigerant flowing to the evaporator; and 
 following defrost upon a return temperature sensor on a low pressure side of the evaporator warming to be at or above the stored bypass control set point temperature of the return temperature sensor, 
 (i) control a return valve to close to prevent refrigerant flow through a low pressure side of the plurality of heat exchangers, and 
 (ii) control a bypass valve to open to bypass flow of the refrigerant around the low pressure side of the plurality of heat exchangers and to a suction line that enters a low pressure side of the compressor; and 
 the system being configured to warm the bypassed flow of the refrigerant in the suction line before it enters the low pressure side of the compressor. 
   
     
     
         25 . (canceled) 
     
     
         26 . A method of reducing a cool down time of a very low temperature refrigeration system, the method comprising:
 during a cooling mode of operation of the system, flowing refrigerant through a high pressure side of a plurality of heat exchangers, through a flow metering device and a cool valve with which the flow metering device is in a series flow connection to an inlet of an evaporator, through the evaporator and through a low pressure side of the plurality of heat exchangers; and   upon a discharge pressure of a compressor of the system being at least as high as a stored set point of a maximum discharge pressure during the cooling mode of operation, opening an unload valve that permits refrigerant flow to bypass around the flow metering device and to the cool valve, until the discharge pressure reduces to be less than the stored set point of the maximum discharge pressure   wherein an inlet of the evaporator or an outlet of the evaporator is at a temperature of less than about −110° C., and/or   wherein the stored set point of the maximum discharge pressure is less than an activation pressure of a buffer solenoid valve of the system.   
     
     
         27 - 28 . (canceled)