Micro-channel evaporator with frost detection and control

Abstract

A refrigerant vapor compression system includes an evaporator having a plurality of longitudinally extending, flattened heat exchange tubes disposed in parallel, spaced relationship. Each of the heat exchange tubes has a flattened cross-section and defining a plurality of discrete, longitudinally extending refrigerant flow passages. One or more frost detection sensor(s) is/are installed in operative association with the evaporator for detecting a presence of frost/ice formation on at one of the flattened heat exchange tubes and associated heat transfer fins. A defrost system is provided and operatively associated with the evaporator heat exchanger A controller, operatively coupled to the frost detection sensor(s) and to the defrost system, selectively activates the defrost system to initiate a defrost cycle of the evaporator in response to the signal indicative of the presence of frost formation on the flattened heat exchange tubes and heat transfer fins.

1 . A refrigerant vapor compression system including a refrigerant flow circuit comprising:
 a refrigerant compressor, a heat rejection heat exchanger, an expansion device and an evaporator connected serially in the refrigerant flow circuit in refrigerant flow communication, said evaporator having a plurality of longitudinally extending, flattened heat exchange tubes disposed in parallel, spaced relationship, each of said heat exchange tubes having flattened cross-section;   at least one frost detection sensor installed in operative association with said evaporator for detecting a presence of frost or ice formation on the evaporator external surfaces and generating a signal indicative of the presence of frost or ice formation at least at one location within the evaporator;   a defrost system operatively associated with said evaporator; and   a controller operatively coupled to said at least one frost detection sensor and to said defrost system, said controller selectively activating said defrost system to initiate a defrost cycle of said evaporator in response to said signal indicative of the presence of frost or ice formation at least at one location within the evaporator.   
   
   
       2 . A refrigerant vapor compression system as recited in  claim 1  wherein each of said flattened heat exchange tubes of said evaporator defines a plurality of internal discrete, longitudinally extending refrigerant flow passages. 
   
   
       3 . A refrigerant vapor compression system as recited in  claim 1  wherein said defrost system comprises an electric heating system operatively associated with said evaporator. 
   
   
       4 . A refrigerant vapor compression system as recited in  claim 1  wherein said defrost system comprises a hot gas defrost system for selectively passing at least a portion of refrigerant vapor from said compressor through said heat exchange tubes of said evaporator. 
   
   
       5 . A refrigerant vapor compression system as recited in  claim 4  wherein said hot gas defrost system comprises:
 a hot gas defrost line having an inlet opening in refrigerant flow communication with an intermediate pressure stage of said compressor and an outlet opening in refrigerant flow communication with the refrigeration cycle circuit at a location upstream, with respect to refrigerant flow, of said evaporator and downstream, with respect to refrigerant flow, of said expansion device; and   a refrigerant flow control device disposed in said hot gas defrost line and operatively coupled to said controller, said refrigerant flow control device being selectively positionable between a closed position and an open position.   
   
   
       6 . A refrigerant vapor compression system as recited in  claim 5  wherein said refrigerant flow control device is of a modulation or pulsation type. 
   
   
       7 . A refrigerant vapor compression system as recited in  claim 4  wherein said hot gas defrost system comprises:
 a hot gas defrost line having an inlet opening in refrigerant flow communication with a discharge pressure side of said compressor and an outlet opening in refrigerant flow communication with the refrigeration cycle circuit at a location upstream, with respect to refrigerant flow, of said evaporator and downstream, with respect to refrigerant flow, of said expansion device; and   a refrigerant flow control device disposed in said hot gas defrost line and operatively coupled to said controller, said refrigerant flow control device being selectively positionable between a closed position and an open position.   
   
   
       8 . A refrigerant vapor compression system as recited in  claim 7  wherein said refrigerant flow control device is of a modulation or pulsation type. 
   
   
       9 . A refrigerant vapor compression system as recited in  claim 1  wherein said refrigerant system is a heat pump and said defrost system comprises switching between heating and cooling modes of operation. 
   
   
       10 . A refrigerant vapor compression system as recited in  claim 1  wherein said at least one frost detection sensor comprises a frost detection sensor mounted on an exterior surface of one of said flattened heat exchange tubes. 
   
   
       11 . A refrigerant vapor compression system as recited in  claim 1  wherein said at least one frost detection sensor comprises a frost detection sensor mounted on a surface of one of the heat transfer fins positioned between said heat exchange tubes and permanently attached to these heat exchange tubes. 
   
   
       12 . A refrigerant vapor compression system as recited in  claim 1  wherein said at least one frost detection sensor comprises a plurality of frost detection sensors, each of said frost detection sensors installed at a different location within said evaporator. 
   
   
       13 . A refrigerant vapor compression system as recited in  claim 1  wherein said at least one frost detection sensor comprises a plurality of frost detection sensors, each of said frost detection sensors mounted on an exterior surface of a different one of said flattened heat exchange tubes. 
   
   
       14 . A refrigerant vapor compression system as recited in  claim 1  wherein said at least one frost detection sensor comprises a plurality of frost detection sensors, each of said defrost detection sensors mounted on a surface of a different one of the heat transfer fins positioned between said heat exchange tubes and permanently attached to these heat exchange tubes. 
   
   
       15 . A refrigerant vapor compression system as recited in  claim 1  wherein said flattened heat exchange tubes have a flattened rectangular or flattened oval cross-section. 
   
   
       16 . A refrigerant vapor compression system as recited in  claim 2  wherein said plurality of internal discrete, longitudinally extending fluid flow passages have a circular cross-sectional flow area. 
   
   
       17 . A refrigerant vapor compression system as recited in  claim 2  wherein said plurality of internal discrete, longitudinally extending fluid flow passages have a non-circular cross-sectional flow area. 
   
   
       18 . A refrigerant vapor compression system as recited in  claim 1  further comprising a plurality of heat transfer fins extending between adjacent flattened heat exchange tubes of said evaporator. 
   
   
       19 . A refrigerant vapor compression system as recited in  claim 18  wherein said plurality of heat transfer fins comprises a plurality of generally vertical fins extending between adjacent heat exchange tubes. 
   
   
       20 . A refrigerant vapor compression system as recited in  claim 18  wherein said plurality of heat transfer fins comprises serpentine-like fins extending between adjacent heat exchange tubes. 
   
   
       21 . A refrigerant vapor compression system as recited in  claim 20  wherein said a serpentine-like heat transfer fins extending between adjacent heat exchange tubes form one of generally triangular, rectangular or trapezoidal airflow passages. 
   
   
       22 . A refrigerant vapor compression system as recited in  claim 18  wherein said plurality of heat transfer fins are at least one of louvered, wavy, offset strip or flat plate configurations. 
   
   
       23 . A refrigerant vapor compression system as recited in  claim 1  wherein said evaporator has a first manifold and a second manifold and said flattened heat exchange tubes extend longitudinally between sad first and second manifolds in a single-pass configuration. 
   
   
       24 . A refrigerant vapor compression system as recited in  claim 1  wherein said evaporator has a first manifold and a second manifold and said flattened heat exchange tubes extend longitudinally between sad first and second manifolds a multi-pass configuration. 
   
   
       25 . A refrigerant vapor compression system as recited in  claim 1  wherein said flattened heat exchange tubes of said evaporator have a generally horizontal orientation. 
   
   
       26 . A refrigerant vapor compression system as recited in  claim 1  wherein said flattened heat exchange tubes of said evaporator have a generally vertical orientation. 
   
   
       27 . A refrigerant vapor compression system as recited in  claim 1  wherein said flattened heat exchange tubes of said evaporator have an inclination angle between 0 and 90 degrees, with respect to the horizontal axis. 
   
   
       28 . A refrigerant vapor compression system as recited in  claim 1  wherein said evaporator has a generally vertical orientation. 
   
   
       29 . A refrigerant vapor compression system as recited in  claim 1  wherein said evaporator has an inclination angle between 0 and 90 degrees, with respect to the horizontal axis. 
   
   
       30 . A refrigerant vapor compression system as recited in  claim 1  wherein said flattened heat exchange tubes of said evaporator have a generally straight configuration.