Heat pump with improved defrost cycle and method of defrosting a heat exchanger

Abstract

Heat pumps with improved defrost cycles, methods of defrosting heat exchangers, and methods of improving the effectiveness of defrost cycles of heat pumps, for example, having a microchannel outdoor heat exchanger. A defrost valve in a refrigerant conduit opens during a defrost cycle to deliver hot refrigerant gas to a portion of the heat exchanger that otherwise defrosts more slowly or less completely than other portions of the heat exchanger. Particular embodiments pass hot refrigerant gas through a header of the heat exchanger, such as a bottom header. In a number of embodiments, the defrost valve is open only during a portion of the defrost cycle. Further, in some embodiments, the fan that is used to blow air through the heat exchanger is operated in a reversed direction during at least part of the defrost cycle to counteract natural convection through the heat exchanger.

1 . A heat pump having an improved defrost cycle, the heat pump comprising:
 a compressor;   at least one expansion device;   a first heat exchanger comprising:
 a first header; 
 a second header; and 
 multiple cross tubes extending from the first header to the second header, wherein:
 each of the multiple cross tubes connects to the first header; 
 each of the multiple cross tubes connects to the second header; 
 the first header is parallel to the second header; 
 the multiple cross tubes are parallel to each other; and 
 the multiple cross tubes each include multiple contiguous parallel refrigerant passageways therethrough; 
 
 multiple fins between the cross tubes wherein the fins are bonded to the cross tubes; 
 at least one first connection point to the first heat exchanger where refrigerant is delivered to the first heat exchanger from the compressor during the defrost cycle; 
 a second connection point to the first heat exchanger where refrigerant exits the first heat exchanger during the defrost cycle; and 
 a third connection point to the first heat exchanger where refrigerant is delivered from the compressor to the first heat exchanger during at least part of the defrost cycle; 
   a first refrigerant conduit connecting a discharge port on the compressor to the at least one first connection point of the first heat exchanger;   a second refrigerant conduit connecting the second connection point of the first heat exchanger to the at least one expansion device;   a third refrigerant conduit connecting the first refrigerant conduit to the third connection point of the first heat exchanger;   a defrost valve located in the third refrigerant conduit between the first refrigerant conduit and the third connection point of the first heat exchanger, wherein, when the defrost valve is closed, refrigerant flow through the third refrigerant conduit is blocked; and   a control system that controls the defrost valve and opens the defrost valve during the defrost cycle allowing refrigerant to flow through the third refrigerant conduit to the third connection point to defrost the first heat exchanger;   wherein:
 the first connection point to the first heat exchanger is at the first header; 
 the second connection point to the first heat exchanger is at the second header; 
 the third connection point to the first heat exchanger is at the second header; and 
 refrigerant that, during at least part of the defrost cycle, passes through the third refrigerant conduit, through the defrost valve, and through the third connection point to the first heat exchanger, passes through the second header, heating the second header between the third connection point to the first heat exchanger and the second connection point to the first heat exchanger without passing through any cross tubes of the first heat exchanger. 
   
     
     
         2 . The heat pump of  claim 1  wherein the first heat exchanger comprises: a top and a bottom; and wherein the first header extends across the top of the first heat exchanger; the second header extends across the bottom of the first heat exchanger; the first header is horizontal; the second header is horizontal; and each of the multiple cross tubes directly connects to the first header, and directly connects to the second header. 
     
     
         3 . The heat pump of  claim 1  wherein the first heat exchanger consists essentially of:
 the first header; 
 the second header; 
 the multiple cross tubes; 
 the multiple fins between the cross tubes, 
 wherein the fins are bonded to the cross tubes; 
 the at least one first connection point to the first heat exchanger; 
 the second connection point to the first heat exchanger; and 
 the third connection point to the first heat exchanger. 
 
     
     
         4 . The heat pump of  claim 1  further comprising an extension tube located within the second header, wherein:
 the extension tube within the second header is substantially parallel to the second header; 
 and 
 the third connection point to the first heat exchanger is at the extension tube. 
 
     
     
         5 . The heat pump of  claim 1  wherein: the first heat exchanger has only two headers, the first header and the second header. 
     
     
         6 . The heat pump of  claim 1  wherein:
 the second header has a first end and a second end; 
 each of the multiple cross tubes connects to the second header between the first end and the second end; 
 the second connection point to the first heat exchanger is at the second end of the second header; and 
 the third connection point to the first heat exchanger is at the first end of the second header. 
 
     
     
         7 . The heat pump of  claim 6  wherein:
 the first header has a third end and a fourth end; 
 each of the multiple cross tubes connects to the first header between the third end and the fourth end; and 
 the at least one first connection point to the first heat exchanger consists of a single first connection point at the third end of the first header. 
 
     
     
         8 . The heat pump of  claim 6  wherein:
 the first header has a third end and a fourth end; 
 each of the multiple cross tubes connects to the first header between the third end and the fourth end; 
 the at least one first connection point to the first heat exchanger comprises a primary first connection point to the heat exchanger at the third end of the first header and a secondary first connection point to the heat exchanger at the fourth end of the first header; and 
 the first refrigerant conduit connects the discharge port on the compressor to the primary first connection point and to the secondary first connection point. 
 
     
     
         9 . The heat pump of  claim 1  wherein the control system comprises a digital controller comprising programming instructions to open the defrost valve during the defrost cycle to defrost the first heat exchanger between the third connection point and the second connection point, and wherein the digital controller further comprises programming instructions to keep the defrost valve closed when the heat pump is not in the defrost cycle. 
     
     
         10 . The heat pump of  claim 9  wherein the digital controller further comprises programming instructions to keep the defrost valve closed during part of the defrost cycle to defrost the first heat exchanger between the at least one first connection point and the second connection point. 
     
     
         11 . The heat pump of  claim 1  further comprising a first fan positioned and configured to move air through the first heat exchanger, wherein the control system comprises a digital controller comprising programming instructions to operate the first fan in a reversed direction during at least part of the defrost cycle to reduce natural convection through the first heat exchanger during the at least part of the defrost cycle. 
     
     
         12 . The heat pump of  claim 1  further comprising a reversing valve located in the first refrigerant conduit between the discharge port on the compressor and the at least one first connection point of the first heat exchanger, wherein the third refrigerant conduit connects to the first refrigerant conduit between the reversing valve and the at least one first connection point of the first heat exchanger, the heat pump further comprising a second heat exchanger, a fourth refrigerant conduit connecting the at least one expansion device to the second heat exchanger, a fifth refrigerant conduit connecting the second heat exchanger to the reversing valve, and a sixth refrigerant conduit connecting the reversing valve to an inlet port on the compressor. 
     
     
         13 . A method of defrosting a first heat exchanger of a heat pump, the heat pump comprising the first heat exchanger, a compressor, at least one expansion device, and a second heat exchanger, the first heat exchanger comprising headers, multiple cross tubes, a first connection point to the first heat exchanger, a second connection point to the first heat exchanger, and a third connection point to the first heat exchanger,
 the method comprising, in any order except where a particular order is explicitly indicated, at least the acts of:
 operating the heat pump in a defrost mode during a defrost cycle including delivering refrigerant from the compressor to the first connection point of the first heat exchanger; 
 during the defrost cycle, passing the refrigerant through the first heat exchanger from the first connection point to the first heat exchanger, through the multiple cross tubes, to the second connection point of the first heat exchanger; 
 during the defrost cycle, passing the refrigerant from the second connection point of the first heat exchanger, through the at least one expansion device, and then to the second heat exchanger; 
 during the defrost cycle, passing the refrigerant through the second heat exchanger, and then back to the compressor; and 
 during at least part of the defrost cycle, delivering at least part of the refrigerant from the compressor to the third connection point of the first heat exchanger; and 
 passing the at least part of the refrigerant from the third connection point, through one of the headers, to the second connection point without passing the at least part of the refrigerant through any of the cross tubes of the first heat exchanger. 
   
     
     
         14 . The method of  claim 13  wherein:
 the one of the headers of the first heat exchanger comprises a first end and a second end; 
 each of the cross tubes connect to the one of the headers between the first end and the second end; 
 the second connection point of the first heat exchanger is at the second end of the one of the headers; 
 the third connection point of the first heat exchanger is at the first end of the one of the headers; and 
 the act of passing the refrigerant from the third connection point, through the one of the headers, to the second connection point comprises passing the refrigerant from the first end, through the one of the headers, to the second end. 
 
     
     
         15 . The method of  claim 13  wherein:
 each cross tube comprises multiple contiguous parallel refrigerant passageways therethrough; 
 the first heat exchanger further comprises multiple fins between the cross tubes that are bonded to the cross tubes; and 
 the act of passing the refrigerant through the first heat exchanger from the first connection point, through the multiple cross tubes, to the second connection point of the first heat exchanger comprises heating the multiple fins between the cross tubes. 
 
     
     
         16 . The method of  claim 13  wherein the act of delivering refrigerant from the compressor to the third connection point of the first heat exchanger comprises opening a solenoid valve in a bypass refrigerant line extending from a supply refrigerant line connected to the first connection point, the bypass refrigerant line extending to the third connection point. 
     
     
         17 . The method of  claim 13  comprising, during a first portion of the defrost cycle, not passing refrigerant through the third connection point, and during a second portion of the defrost cycle, passing refrigerant through the third connection point. 
     
     
         18 . (canceled) 
     
     
         19 . (canceled) 
     
     
         20 . The method of  claim 13  wherein:
 the headers consist of a first header and a second header; 
 the first connection point to the first heat exchanger is at the first header; 
 the second connection point to the first heat exchanger is at the second header; 
 the third connection point to the first heat exchanger is at the second header; and 
 the act of passing the at least part of the refrigerant from the third connection point, through one of the headers, to the second connection point comprises passing the at least part of the refrigerant through the second header without passing the at least part of the refrigerant through any of the cross tubes of the first heat exchanger. 
 
     
     
         21 . The method of  claim 20  wherein:
 the first heat exchanger is an outdoor air heat exchanger; 
 the second heat exchanger is an indoor air heat exchanger; 
 the first heat exchanger comprises a top and a bottom; 
 the first header extends across the top of the first heat exchanger; 
 the second header extends across the bottom of the first heat exchanger; 
 each cross tube of the first heat exchanger comprises multiple contiguous parallel refrigerant passageways therethrough; 
 each of the multiple cross tubes directly connects to the first header; 
 each of the multiple cross tubes directly connects to the second header; 
 the first heat exchanger further comprises multiple fins between the cross tubes that are bonded to the cross tubes; and 
 the act of passing the refrigerant through the first heat exchanger from the first connection point, through the multiple cross tubes, to the second connection point of the first heat exchanger comprises heating the multiple fins between the cross tubes; 
 the act of delivering refrigerant from the compressor to the third connection point of the first heat exchanger comprises opening a solenoid valve in a bypass refrigerant line extending from a supply refrigerant line connected to the first connection point, the bypass refrigerant line extending to the third connection point. 
 
     
     
         22 . A heat pump comprising:
 a compressor;   at least one expansion device;   a first heat exchanger comprising a top and a bottom and consisting essentially of:
 a first header extending across the top of the first heat exchanger; 
 a second header extending across the bottom of the first heat exchanger; and 
 multiple cross tubes extending from the first header to the second header, wherein:
 each of the multiple cross tubes is directly connected to the first header; 
 each of the multiple cross tubes is directly connected to the second header; and 
 the multiple cross tubes each include multiple contiguous parallel refrigerant passageways therethrough; 
 
 multiple fins between the cross tubes wherein the fins are bonded to the cross tubes; 
 at least one first connection point where refrigerant is delivered to the first heat exchanger from the compressor during the defrost cycle; 
 a second connection point where refrigerant exits the first heat exchanger during the defrost cycle; and 
 a third connection point where refrigerant is delivered from the compressor to the first heat exchanger during at least part of the defrost cycle; 
   a first fan positioned and configured to move air through the first heat exchanger;   a second heat exchanger;   a first refrigerant conduit connecting a discharge port on the compressor to the at least one first connection point of the first heat exchanger, wherein the first refrigerant conduit does not include any part of the first heat exchanger;   a reversing valve located in the first refrigerant conduit between the discharge port on the compressor and the at least one first connection point of the first heat exchanger;   a second refrigerant conduit connecting the second connection point of the first heat exchanger to the at least one expansion device, wherein the second refrigerant conduit does not include any part of the first heat exchanger;   a third refrigerant conduit connecting the first refrigerant conduit to the third connection point of the first heat exchanger;   a defrost valve located in the third refrigerant conduit between the first refrigerant conduit and the third connection point of the first heat exchanger, wherein, when the defrost valve is closed, refrigerant flow through the third refrigerant conduit is blocked; and   a fourth refrigerant conduit connecting the at least one expansion device to the second heat exchanger;   a fifth refrigerant conduit connecting the second heat exchanger to the reversing valve;   a sixth refrigerant conduit connecting the reversing valve to an inlet port on the compressor;   a control system that controls the defrost valve and opens the defrost valve during the defrost cycle allowing refrigerant to flow through the third refrigerant conduit to the third connection point;   wherein:
 the control system comprises a digital controller comprising programming instructions to open the defrost valve during the defrost cycle to defrost the first heat exchanger between the third connection point and the second connection point; 
 the digital controller further comprises programming instructions to keep the defrost valve closed when the heat pump is not in the defrost cycle; 
 the third refrigerant conduit connects to the first refrigerant conduit between the reversing valve and the at least one first connection point of the first heat exchanger; 
 the first connection point is at the first header; 
 the second connection point is at the second header; 
 the third connection point is at the second header; and 
 refrigerant that, during at least part of the defrost cycle, passes through the third refrigerant conduit, through the defrost valve, and through the third connection point, passes through the second header, heating the second header between the third connection point and the second connection point without passing through any cross tubes of the first heat exchanger. 
   
     
     
         23 . The heat pump of  claim 22  wherein:
 the second header has a first end and a second end; 
 each of the multiple cross tubes connects to the second header between the first end and the second end; 
 the second connection point to the first heat exchanger is at the second end of the second header; and 
 the third connection point to the first heat exchanger is at the first end of the second header.