Patent Publication Number: US-2012023993-A1

Title: Evaporator with integrated heating element

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 61/367,902, file Jul. 27, 2010, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Heat exchangers serve to transfer heat between thermal masses. In one heat exchanger configuration, air circulates adjacent to heat exchanger surfaces that are cooled by a circulating coolant and the air gives up heat to the coolant. When temperature of the coolant is low enough, ice may form on the surfaces and impede heat exchange between the surfaces and the air. It is desirable to remove such ice with a minimum of added heat, since a surface that is heated must be re-cooled in order to resume heat exchange with the air. 
     Pulse heating is one method of removing ice build-up from the evaporator. Pulse heating is a method of melting a boundary layer of ice between the ice and the refrigerant conduit. In effect, pulse heating supplies a low voltage current through the wall of the refrigeration conduit, thereby utilizing the conduit as a conductor. The conduit is typically made from an inductive material such as stainless steel, which may be undesirable due to its weight and expense. 
     SUMMARY 
     The present invention provides an evaporator coil that has an integrated heating element. When ice builds up on the surfaces of the evaporator, an evaporator defrost cycle can be initiated in which heat from the integrated heating element can be used to melt the ice. Integrating the heating element with the refrigerant conduit can greatly reduce the heat required to defrost the evaporator, and can provide lower power defrosts that can be run with increased frequency and efficiency over other evaporator/heater arrangements. 
     For example, the evaporator disclosed herein may provide energy and efficiency savings over an evaporator that has a heater that is spaced from and/or that is in poor thermal contact with the refrigerant conduit and which typically requires excessive heating (overheating) to melt ice on the evaporator coil. Additionally, the evaporator may be less expensive to manufacture, maintain, and operate than pulse cooling systems. 
     According to one aspect, the present invention provides an evaporator coil having a conduit with an interior passageway that provides a pathway for a flow of refrigerant. An outer wall of the conduit forms a channel having a longitudinal opening that extends lengthwise adjacent to the interior passageway. The channel contains an electrical heating element that is in thermal contact with the conduit. The electrical heating element periodically provides heat to defrost the evaporator coil during an evaporator defrost cycle. 
     According to another aspect, the evaporator coil can include a second conduit having an interior passageway that provides a pathway for the electrical heating element. The second conduit can be at least partially contained within the channel of the first conduit. 
     According to another aspect, the evaporator coil can be part of an evaporator in a refrigeration system and the system can be controlled by a controller that alternates between a refrigeration cycle and the evaporator defrost cycle. 
     To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The appended drawings show various features of embodiments of the invention. 
         FIG. 1  is a schematic diagram of a refrigeration system in accordance with aspects of the invention; 
         FIG. 2  is an exemplary evaporator having an integrated heating element as may be used in the system of  FIG. 1 ; 
         FIG. 3A  is a perspective view of a segment of an evaporator coil in accordance with aspects of the invention; 
         FIG. 3B  is a cross-sectional view of the evaporator coil of  FIG. 3A  taken along lines A-A; 
         FIG. 4A  is a perspective view of a segment of an evaporator coil in accordance with aspects of the invention; 
         FIG. 4B  is a cross-sectional view of the evaporator coil of  FIG. 4A  taken along lines B-B; and 
         FIG. 5  is a detailed view of a transition region between the evaporator coil and a conduit of the refrigeration system. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an exemplary refrigeration system  10  is shown. A circulating refrigerant enters a compressor  12  as a vapor and is compressed such that it exits the compressor as a vapor at a higher temperature. The vapor travels through a condenser  14  which cools the vapor until it starts condensing into a liquid. The liquid refrigerant then passes through an expansion valve  16  where its pressure abruptly decreases, causing flash evaporation of some of the refrigerant. This results in a mixture of liquid and vapor at a lower temperature and pressure. The low temperature liquid-vapor mixture then travels through an evaporator  18 . In the evaporator, the liquid-vapor mixture is completely vaporized by blowing the warm air from the space to be cooled across the evaporator coil or tubes. The refrigerant cools the air by removing the heat, and the resulting vapor refrigerant then returns to the compressor  12  to complete the cycle. The various components of the refrigeration system can be connected via one or more conduits  20 . 
     The system may include a controller  22 . The controller  22  can be configured to control the various components of the system including the compressor, the expansion valve and the evaporator. For example, the evaporator can be controlled to alternate between the aforementioned refrigeration cycle and a defrost cycle for removing ice that may build up on the evaporator. The controller  22  can be coupled to a power supply  24 , and can control the flow of electricity to the evaporator during the evaporator defrost cycle. 
     The evaporator  18  can take a variety of forms. For example, the evaporator  18  may be a tube evaporator with fins, a coiled evaporator, a flat evaporator, a bottle brush evaporator, etc.  FIG. 2  shows one exemplary embodiment of an evaporator  18  having a coil  26  that has a plurality of longitudinal sections  28  and curved sections  30 . The evaporator coil  26  has an inlet portion  32  configured to interface with a conduit  20  of a refrigeration system  10 , and an outlet portion  34  configured to interface with another conduit  20  of the refrigeration system  10 . The evaporator  18  has an integrated heating element  36  for defrosting the evaporator during an evaporator defrost cycle. Further, the inlet portion  32  and outlet portion  34  may include a transition region as shown and described with respect to  FIG. 5 . 
       FIG. 3A  shows a segment of an evaporator coil  40  with an integrated heating element  41 , and  FIG. 3B  shows a cross-sectional view of the evaporator coil  40  taken along lines A-A. The evaporator coil  40  includes a conduit  42  having an inner wall  44  and an outer wall  46 . The inner wall  44  defines an interior passageway  48  that provides a pathway for a flow of refrigerant. 
     A channel  50  is formed by one or more portions  52  of the outer wall  46 . As shown in  FIG. 3A , the channel  50  extends lengthwise along the evaporator coil adjacent to the interior passageway  48  and has a longitudinal opening. The channel  50  may extend parallel to a central axis of the interior passageway  48 . Alternatively, the channel may be angled relative to the central axis of the interior passageway  48 , for example, the channel  50  may extend helically about the center axis of the interior passageway  48  as it extends along a length of the outer wall. 
     The channel  50  may consume a relatively small portion of the interior passageway  48 . In the exemplary embodiment of  FIGS. 3A and 3B , the channel  50  is in the general shape of a “V”, however, the channel may have a different shape. For example, the channel may have a “U” shape, a “C” shape, a curve shape or another shape. 
     The heating element  41  is integrated into the evaporator  18 . The heating element  41  is at least partially contained within the channel  50 . In the illustrated embodiment, the heating element  41  is completely contained within the channel  50 . The heating element  41  may be a resistive heating element and may be coupled to a low voltage power source, for example, a 120-volt or 220-volt power source. In one embodiment, the heating element  41  is an electric heating cable (e.g., an insulated wire). 
     The heating element  41  is in thermal contact with the conduit  42  via the portions  52  of the outer wall  46  that form the channel  50 . The heating element  41  can be in direct physical contact with the portions  52  of the outer wall  46  that form the channel  50 , or alternatively, the heating element  41  can be held in thermal and/or physical contact with the channel  50  by a thermally conductive material  56 , such as a thermally conductive adhesive. Alternatively, the heating element  41  may be welded directly to the channel  50  or held in place by a retaining element such as a strap or other mechanical implement. As shown in  FIGS. 4A and 4B  and described below, the heating element also can be contained in a separate conduit that is coupled to the channel. 
     The heating element  41  can be controlled (e.g., manually controlled or automatically controlled with the controller  22 ) to provide heat to defrost the surfaces of the evaporator  18 , including the outer wall  46  of the conduit  42 , during the evaporator defrost cycle. The controller  22  can be programmed or otherwise configured to periodically enter an evaporator defrost cycle in which the refrigeration cycle is stopped and electricity is provided to the heating element  41 . As used herein, periodically can mean regular or irregular time intervals. For example, the system can be configured to enter the defrost cycle on a regular basis such as hourly, twice a day, daily, or at any combination of regular or irregular time intervals. 
     Additionally or alternatively, the evaporator can be configured to enter the defrost cycle whenever a buildup of ice is detected by sensors or other feedback mechanisms in the system, such as sensor  54  that may be operatively coupled to the controller  22 . The system may include functionality to allow an operator to manually switch the system to the defrost mode. 
     Referring to  FIGS. 4A and 4B , another embodiment of an evaporator coil  70 , with an integrated heating element  90  is shown. The evaporator coil  70  includes a conduit  72  having an inner wall  74  and an outer wall  76 . The inner wall  74  defines an interior passageway  78  that provides a pathway for a flow of refrigerant. One or more portions  80  of the outer wall  76  form a channel  82  that extends longitudinally along the evaporator coil  70  adjacent to the interior passageway  78 . The channel  82  has a longitudinal opening. As noted above, the channel  82  need not be parallel to the axis of the passageway  78 . 
     A second conduit  84  is coupled to the first conduit  72  at the channel  82 . The second conduit  84  has an inner wall  86  that provides a passageway  88  for the heating element  90  as described above with respect to  FIGS. 3A and 3B . The heating element  90  is shown in the illustrated embodiment as being spaced from the inner wall  86  of the passageway  88 , however, the heating element may be in contact with the inner wall  86 , which can improve the efficiency of the heat transfer for defrosting the evaporator. Additionally or alternatively, the second conduit  84  may be filled with a medium to aid heat transfer between the conduit and the heating element. For example, the second conduit  84  may be filled with grease or another medium, such as a gas or liquid. The second conduit  84  may provide physical and environmental protection for the heating element  90 . 
     The second conduit  84  has an outer wall  92 . Portions  94  of the outer wall  92  are shaped to substantially match the contour of the channel  82  formed by portions  80  of the outer wall  76  of the first conduit  72 . The second conduit  84  is at least partially contained within the channel  82  and an interface is formed between the portions  80  of the outer wall  76  of the first conduit  72  and portions  94  of the outer wall  92  of the second conduit  84 . As shown best in  FIG. 4B , the shape of the channel  82  and the shape of the portions  94  of the outer wall  92  of the second conduit  84  can be complementary to one another, with the first conduit  72  and the second conduit  84  fitting together. As shown in  FIG. 4B , the conduits  72  and  84  can form an evaporator coil with an integrated heating element that has a substantially circular cross-sectional shape. 
     The conduits may be coupled and held together by an adhesive, weld, or other type of attachment. Alternatively, the conduits may be integrally formed with one another, for example, by coextruding the conduits. The conduits may be formed from the same or different materials. Some exemplary suitable materials include aluminum, copper, stainless steel, and the like. 
     An advantage of the evaporator coil disclosed herein is that it can be used to defrost an evaporator without using the evaporator coil as a conductor to melt the boundary layer of ice on the evaporator coil. Accordingly, the evaporator can be formed from cheaper materials, which may provide a cost and/or weight savings. Additionally, an evaporator with the evaporator coil disclosed herein can be have a defrost cycle without complicated and expensive electronics, such as transformers and the like. 
       FIG. 6  shows an exemplary embodiment of a transition region  100  between an evaporator coil  102  and a conduit  104  of a refrigeration system (e.g., refrigeration system  10 ). The conduit  104  has a channel  106  that is aligned with channel  108  in the evaporator coil  102 . The conduit channel  106  may be tapered such that the channel  106  is deeper at the end  110  that is connected to the evaporator coil  102 . The tapered channel can facilitate assembly and integration of the heating element into the evaporator coil and/or may provide an area to connect the heating element to a power supply or controller. The evaporator coil  102  and conduit  104  may be welded at the interface and may be made from different materials (e.g., the evaporator coil may be formed from aluminum and the conduit may be formed from copper). 
     Although the principles, embodiments and operation of the present invention have been described in detail herein, this is not to be construed as being limited to the particular illustrative forms disclosed. They will thus become apparent to those skilled in the art that various modifications of the embodiments herein can be made without departing from the spirit or scope of the invention.