Evaporator coil staging and control for a multi-staged space conditioning system

Abstract

A space conditioning system comprising an evaporator subunit (ES) and control subunit (CS). The ES includes at least three evaporator stages in a pathway of air flow through the ES. First and second stages are adjacent and have major surfaces substantially parallel to each other. A third stage is located in the pathway before the first stage. A major surface of the third stage covers the major surface of the first stage in a same pathway direction. The major surfaces are substantially perpendicular to the pathway. The CS is configured to operate the evaporator subunit in at least one of two partial load cooling modes. In a first mode, the CS causes refrigerant to circulate through the first and second but not through the third stage. In a second mode, the control subunit causes the refrigerant to circulate through the first and third stage but not through the second stage.

What is claimed is: 
     
         1 . A space conditioning system for conditioning air within an enclosed space, comprising:
 an evaporator subunit, said evaporator subunit including at least three evaporator stages in a pathway of air flow through said evaporator subunit, wherein:
 first and second ones of said evaporator stages are adjacent to each other and have major surfaces that are substantially parallel to each other 
 a third one of said evaporator stages is located in said pathway before said first evaporator stage and a major surface of said third evaporator stage covers said major surface of said first evaporator stage in a same direction of said pathway, and 
 said major surfaces of each of said evaporator stages are substantially perpendicular to said airflow pathway; and 
   a control subunit configured to operate said evaporator subunit in at least one of two partial load cooling modes, wherein:
 in a first mode, said control subunit causes refrigerant to circulate through said first evaporator stage and through said second evaporator stage but not through said third evaporator stage, and 
 in a second mode, said control subunit causes said refrigerant to circulate through said first evaporator stage and through said third evaporator stage but not through said second evaporator stage. 
   
     
     
         2 . The system of  claim 1 , wherein a total effective surface area of a coil of said second evaporator stage is greater than a total effective surface area of a coil of said third evaporator stage. 
     
     
         3 . The system of  claim 1 , wherein, an evaporator saturation temperature of said refrigerant in one or more suction lines leaving said evaporator subunit is higher when said subunit is operating in said first mode as compared to said second mode. 
     
     
         4 . The system of  claim 1 , wherein an enclosed space that said system is configured to condition has a greater humidity removal capacity when said evaporator subunit is operating in said second mode than when operating in said first mode. 
     
     
         5 . The system of  claim 1 , wherein said control subunit is further configured to operate said evaporator subunit in a freeze-protection mode, wherein said control subunit causes said refrigerant to circulate through said first evaporator stages and not through other said evaporator stages. 
     
     
         6 . The system of  claim 5 , wherein said control subunit is further configured to switch said evaporator subunit from said second mode to said freeze-protection mode when said refrigerant in one or more suction lines leaving said evaporator subunit is below a target temperature or pressure. 
     
     
         7 . The system of  claim 1 , further including a reheater subunit located in said flow pathway after said evaporator subunit, said reheater subunit configured to receive said refrigerant from a compressor or a condenser of said system. 
     
     
         8 . The system of  claim 7 , wherein said control subunit is further configured to cause said refrigerant to circulate through said reheater subunit when said system is operating in said second mode. 
     
     
         9 . The system of  claim 1 , wherein said evaporator subunit further includes a fourth evaporator stage, wherein said fourth evaporator stage is adjacent to said third evaporator stage, said fourth evaporator stage has a major surface that is substantially parallel to said major surface of said third evaporator stage, and, said control module cause said refrigerant to not circulate through said fourth evaporator stage during either said first mode or said second mode. 
     
     
         10 . The system of  claim 1 , wherein said evaporator stages are part of a single unitary structure. 
     
     
         11 . The system of  claim 1 , wherein said first, second and third evaporator stages are separated from each other by gaps. 
     
     
         12 . The system of  claim 1 , wherein each of said evaporator stages are connected to a different compressor. 
     
     
         13 . The system of  claim 1 , wherein a coil of said third evaporator stage has smaller total effective surface area than a coil of said first evaporator stage. 
     
     
         14 . The system of  claim 1 , wherein said system is configured as a roof-top unit. 
     
     
         15 . A method of conditioning air within an enclosed space, comprising:
 sensing a temperature or a humidity of an enclosed space;   determining whether or not a space conditioning system coupled to said enclosed space can reduce said temperature or said humidity to a target value when using said system under partial load conditions;   when using said system under partial load conditions can achieve said target conditions, operating an evaporator subunit of said system in one of two modes, wherein:
 in a first mode, a refrigerant is circulated through a first evaporator stage and a second evaporator stage, but not through a third evaporator stage of said evaporator subunit, and 
 in a second mode, said refrigerant is circulated through said first evaporator stage and said third evaporator stage but not through said second evaporator stage, and: 
 said first evaporator stage and second evaporator stage are adjacent to each other, and have major surfaces that are substantially parallel to each other; 
 said third evaporator stage is located in an airflow pathway through said system before said first evaporator stage and a major surface of said third evaporator stage covers said major surface of said first evaporator stage, and 
 said major surfaces of each of said evaporator stages are substantially perpendicular to said airflow pathway. 
   
     
     
         16 . The method of  claim 15 , wherein said evaporator subunit is operated in said first mode when a high energy efficiency is desired. 
     
     
         17 . The method of  claim 15 , wherein said evaporator subunit is operated in said first mode when said temperature of said enclosed space is above a target value. 
     
     
         18 . The method of  claim 15 , wherein said evaporator subunit is operated in said second mode when a higher humidity removal capacity is desired. 
     
     
         19 . The method of  claim 18 , further including switching said evaporator subunit from said second mode to a freeze-protection mode when a saturation temperature or pressure of said refrigerant in one or more suction lines leaving said evaporator subunit is less than a target value, wherein operating in said freeze-protection mode includes circulating said refrigerant through said first evaporator stage but not through said other evaporator stages. 
     
     
         20 . The method of  claim 18 , further including circulating said refrigerant through a repeater subunit located in said airflow pathway after said evaporator subunit.