Pulse controlled expansion valve for multiple evaporators and method of controlling same

Abstract

A pulse controlled refrigeration expansion valve for multiple evaporators and method of controlling the valve is disclosed. The refrigeration system on which this invention is typically used includes a single source of pressurized refrigerant and a plurality of .[.evaportors.]. .Iadd.evaporators.Iaddend.. Each evaporator has an expansion valve associated therewith which is preferably an on/off (open/closed) direct controlled solenoid valve. The valve is periodically energized (opened) and de-energized (closed) in response to a parameter (e.g., superheat) of its respective evaporator such that the ratio of energization time/de-energization time during each period (e.g., 4 seconds) of operation of the valve is varied in response to the system parameter(s) and such that the on/off solenoid valve functions as a modulated refrigerant flow control expansion valve. A temperature sensor is provided which senses the temperature of the space being refrigerated by a respective evaporator (e.g., the interior of a freezer cabinet in a supermarket) so that upon the temperature of the refrigerated space controlled by the respective valve being within a predetermined temperature range, the temperature sensor will override the control for the solenoid valve thus closing the valve and stopping the flow of refrigerant through the respective evaporator while refrigerant continues to flow to other evaporators.

I claim: 
     
       1. In a refrigeration system having a plurality of heat exchange means, each of said heat exchange means serving a respective space, said system further having a compressor for supplying high pressure liquid .[.refreigerant.]. .Iadd.refrigerant .Iaddend.to each of said heat exchange means, each of said heat exchange means having a length through which said .[.refreigerant.]. .Iadd.refrigerant .Iaddend.flows, wherein the improvement comprises: means associated with each of said heat exchange means for expanding said .[.refreigerant.]. .Iadd.refrigerant .Iaddend.passing therethrough, for selectively blocking the flow of .[.refreigerant.]. .Iadd.refrigerant .Iaddend.therethrough, and for effectively preventing .[.starting.]. .Iadd.starving .Iaddend.or flooding of said heat exchange means, said means comprising a solenoid valve for controlling the flow of high pressure liquid .[.refreigerant.]. .Iadd.refrigerant .Iaddend.through said respective heat exchange means so that said liquid .[.refreigerant.]. .Iadd.refrigerant .Iaddend.is in heat transfer relation with substantially the entire length of said heat exchange means and so that only vaporized .[.refreigerant.]. .Iadd.refrigerant .Iaddend.exists only in the last increment of said heat exchange means thereby to maximize the heat transfer efficiency of said heat exchange means, and sample and hold means for controlling said solenoid valve, said control means having means for sampling a control parameter on an instanteous basis and means for changing the ratio of the open time to the closed time of said solenoid valve in a selected period of time in finite steps in accordance with a predetermined programmed relationship between the instantaneous value of said control parameter and said step. .Iadd. 
     
     
       2.  In a refrigeration system having a plurality of heat exchange means, each of said heat exchange means serving a respective space, said system further having a supply of refrigerant therein, a compressor for supplying high pressure, liquid refrigerant to each of said exchange means, each of said heat exchange means having a length through which said refrigerant flows for absorbing heat from the surroundings and transforming said liquid refrigerant into a vapor, wherein the improvement comprises: means associated with each of said heat exchange means for expanding said refrigerant passing therethrough, for selectively blocking the flow of refrigerant therethrough, and for effectively preventing starving or flooding of said heat exchange means, said means comprising a modulatable valve for controlling the flow of refrigerant through said respective heat exchange means so that said liquid refrigerant is in heat transfer relation with substantially the entire length of said heat exchange means and so that only vaporized refrigerant exists only in the last increment of said heat exchange means thereby to maximize the heat transfer efficiency of said heat exchange means, sample and hold means for controlling said valve, said control means having means for sampling a control parameter on an instantaneous basis and means for changing the flow of refrigerant through said valve in finite steps in accordance with a predetermined programmed relationship between the instantaneous value of said control parameter and said step; and means associated with at least one of said heat exchange means for sensing a parameter other than said control parameter and for generating a signal in response to the operation of said at least one heat exchange means, said control means being responsive to this last said signal for overriding said sample and hold means controlling said valve when said signal is outside a predetermined limit and for effecting closing of said valve thereby to block the flow of refrigerant therethrough..Iaddend.