Patent Publication Number: US-7222496-B2

Title: Heat pump type air conditioner having an improved defrosting structure and defrosting method for the same

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a heat pump type air conditioner, and, more particularly, to a heat pump type air conditioner having an improved defrosting structure that is capable of removing frost accumulated on an outdoor heat exchanger while minimizing user discomfort when a heating operation is performed in low-temperature outdoor air. Also, the present invention relates to a defrosting method for such a heat pump type air conditioner. 
   2. Description of the Related Art 
     FIG. 1  is a block diagram illustrating the structure of a conventional heat pump type air conditioner. As shown in  FIG. 1 , the conventional heat pump type air conditioner comprises: a compressor  11  for compressing and circulating refrigerant; a four-way valve  12  for converting the flow direction of the refrigerant such that the refrigerant can flow either in the forward or reverse direction; an outdoor heat exchanger  13  configured to serve as a condenser when a cooling operation is performed and an evaporator when a heating operation is performed; an outdoor fan  14  for suctioning outdoor air; an indoor heat exchanger  15  configured to serve as an evaporator when a cooling operation is performed and a condenser when a heating operation is performed; an indoor fan  16  for suctioning indoor air; and an expansion valve  17  disposed between the outdoor heat exchanger  13  and the indoor heat exchanger  15  for changing the refrigerant into low-temperature and low-pressure gas refrigerant. 
   The condenser serves to remove heat from high-temperature and high-pressure gas refrigerant such that the high-temperature and high-pressure gas refrigerant is cooled, and therefore, is liquefied. On the other hand, the evaporator serves to lower the temperature of air coming into contact with the surface of the evaporator such that the temperature of moisture in the air falls below the dew point, and therefore, the moisture is changed into water drops, which will be removed. 
   The four-way valve  12  serves to convert the flow direction of the refrigerant such that the refrigerant discharged from the compressor  11  can flow to the outdoor heat exchanger  13  when a cooling operation is performed and to the indoor heat exchanger  15  when a heating operation is performed. 
   The operation of the conventional heat pump type air conditioner with the above-stated construction will be described below in detail. 
   When a user operates the conventional heat pump type air conditioner in cooling mode, the compressor  11  compresses refrigerant, and then supplies the compressed refrigerant to the outdoor heat exchanger  13 . The outdoor heat exchanger  13  performs heat exchange between the refrigerant introduced into the outdoor heat exchanger  13  and air suctioned by the outdoor fan  14 . As a result, the refrigerant is condensed into room-temperature and high-pressure liquid refrigerant, and the temperature of the air is increased. The increased-temperature air is discharged out of the air conditioner by the outdoor fan  14 . The refrigerant condensed by the outdoor heat exchanger  13  passes through a capillary tube, with the result that the condensed refrigerant is changed into low-temperature and low-pressure liquid refrigerant. The indoor heat exchanger  15  performs heat exchange between the refrigerant introduced into the indoor heat exchanger  15  and air suctioned by the indoor fan  16 . As a result, the refrigerant is changed into a low-temperature and low-pressure vapor refrigerant, and the temperature of the suctioned air is decreased. The low-temperature and low-pressure vapor refrigerant is delivered to the compressor through refrigerant piping, and the decreased-temperature air is discharged into the interior of a room by the indoor fan  15  to cool the interior of the room. 
   When the user operates the conventional heat pump type air conditioner in heating mode, on the other hand, the four-way valve  12  converts the flow direction of the refrigerant such that the refrigerant can flow from the compressor  11  to the indoor heat exchanger  15 . In this case, the outdoor heat exchanger  13  serves as an evaporator, and the indoor heat exchanger  15  serves as a condenser. As a result, a heating operation is performed. 
   When the outdoor temperature drops to approximately 5° C. to 6° C. (relative humidity 80%), the surface temperature of the outdoor heat exchanger  13  falls below 0° C., and therefore, moisture in the outdoor air is accumulated on the surface of the outdoor heat exchanger  13 . As a result, an air channel created by the outdoor fan  14  is interrupted. Consequently, the thermal efficiency of the outdoor heat exchanger is decreased, and the heating efficiency of the heat pump is significantly decreased. 
   In order to solve the above-mentioned problems, a defrosting operation for removing front accumulated on the surface of the outdoor heat exchanger  13  is performed. The defrosting operation will be described below in detail with reference to  FIG. 2 . After a heating operation has been performed for a predetermined period of time, for example, 30 minutes, the temperature of the indoor heat exchanger is measured by an indoor heat exchanger temperature sensor  18  (see  FIG. 1 ), the temperature of the interior of the room is measured by a room temperature sensor  19  (see  FIG. 1 ), and then it is determined whether the outdoor unit is to be defrosted based on the difference between the measured temperature of the indoor heat exchanger and the measured temperature of the interior of the room (Step S 1 ). When it is determined that the outdoor unit is to be defrosted, a pressure balancing operation is performed for approximately 3 minutes, and then a defrosting operation is initiated (Step S 2 ). The defrosting operation is performed for a predetermined period of time, for example, approximately 9 minutes (Step S 3 ). The time required to perform the defrosting operation is set based on the difference between the temperature of the indoor heat exchanger and the temperature of the interior of the room. Subsequently, another pressure balancing operation is performed for approximately 3 minutes, and then a heating operation is performed (Step S 4 ). As can be easily understood from the above description, the pressure balancing operation is performed for approximately 3 minutes, during which time the heating operation is paused. Consequently, it is not possible to perform the heating operation while the defrosting operation is performed. Furthermore, cool air is delivered to the interior of the room from the outdoor heat exchanger, and therefore, the temperature of the interior of the room is lowered, which inconveniences the user. In addition, the outdoor temperature is deduced from the difference between the temperature of the indoor heat exchanger and the temperature of the interior of the room. Consequently, it is difficult to accurately obtain a period of time for which the defrosting operation is performed, and therefore, it is difficult to smoothly perform the defrosting operation. 
   SUMMARY OF THE INVENTION 
   Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a heat pump type air conditioner having an improved defrosting structure that is capable of removing frost accumulated on an outdoor heat exchanger while minimizing user discomfort when a heating operation is performed. 
   To this end, the air conditioner according to the present invention incorporates a defrosting mechanism that is capable of removing frost from the outdoor heat exchanger without performing a cooling operation in a reverse cycle if frost is not excessively accumulated on the piping of the outdoor heat exchanger. Warm refrigerant from a compressor is intermittently supplied to the outdoor heat exchanger through the defrosting mechanism, and therefore, frost accumulated on the piping of the outdoor heat exchanger is more easily removed. 
   It is another object of the present invention to provide a defrosting method for a heat pump type air conditioner in low-temperature outdoor air that is capable of accurately obtaining a period of time for which a defrosting operation is performed using a sensor attached to piping of the outdoor heat exchanger, thereby mining a period of time for which a heating operation is paused. 
   In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a heat pump type air conditioner having an improved defrosting structure, the air conditioner comprising: a compressor for compressing refrigerant; an indoor heat exchanger for performing heat exchange with indoor air; an outdoor heat exchanger for performing heat exchange with outdoor air; and a first pipe line connecting the compressor, the indoor heat exchanger and the outdoor heat exchanger in a closed loop, wherein the improvement comprises: a heat discharging pipe line disposed in the outdoor heat exchanger; a second pipe line connected between the inlet of the heat discharging pipe line and the compressor; a third pipe line connected between the outlet of the heat discharging pipe line and the first pipe line; and a valve mounted on either the second pipe line or the third pipe line. 
   When the temperature of piping of the outdoor heat exchanger is between −15° C. and 0° C., i.e., when frost is not excessively accumulated on the piping of the outdoor heat exchanger, relatively warm refrigerant discharged from the compressor is supplied to the heat discharging pipe line only for a short period of time such that the frost accumulated on the piping of the outdoor heat exchanger is removed. In this way, the warm refrigerant intermittently flows through the heat discharging pipe line without performing a cooling operation in a reverse cycle such that the air conditioner is operated in cooling mode, not in heating mode, whereby frost is effectively prevented from being accumulated on the piping of the outdoor heat exchanger. 
   Preferably, the heat pump type air conditioner further comprises: a four-way valve mounted on the first pipe line for converting the flow direction of the refrigerant; and a check valve disposed between the indoor heat exchanger and the outdoor heat exchanger. 
   Preferably, the valve is a solenoid valve. In this case, supply of the warm refrigerant to the heat discharging pipe line is electronically controlled based on the temperature of the piping of the outdoor heat exchanger. 
   Preferably, the heat discharging pipe line is bypassed to the front surface of the outdoor heat exchanger. In this case, the frost accumulated on the piping of the outdoor heat exchanger is effectively removed. 
   In accordance with another aspect of the present invention, there is provided a defrosting method for a heat pump type air conditioner in low-temperature outdoor air, the method comprising the steps of: determining whether the temperature of the outdoor heat exchanger is above 0° C., which is Case A, the temperature of the outdoor heat exchanger is between a predetermined temperature and 0° C., which is Case B, or the temperature of the outdoor heat exchanger is below the predetermined temperature, which is Case C; and performing a heating operation without performing a defrosting operation in Case A, intermittently operating a solenoid valve to perform the defrosting operation in Case B, and operating a four-way valve and the solenoid valve in a reverse cycle to perform the defrosting operation in Case C. 
   When the heat pump type air conditioner is performed in heating mode, the amount of frost accumulated on the outdoor heat exchanger is deduced from the temperature of the piping of the outdoor heat exchanger, and then the defrosting operation is performed based on the temperature of the piping of the outdoor heat exchanger. As a result, the period of time for which the air conditioner is not operated, which is required to remove the frost, is reduced, whereby frost accumulated on the outdoor heat exchanger is effectively removed while minimizing user discomfort. 
   Preferably, the predetermined temperature is −15° C. to −10° C. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram illustrating the structure of a conventional heat pump type air conditioner; 
       FIG. 2  is a flow chart illustrating a defrosting method for the conventional heat pump type air conditioner shown in  FIG. 1 ; 
       FIG. 3  is a block diagram illustrating the structure of a heat pump type air conditioner according to a preferred embodiment of the present invention; and 
       FIG. 4  is a flow chart illustrating a defrosting method for the heat pump type air conditioner according to the preferred embodiment of the present invention shown in  FIG. 3 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Now, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 3  is a block diagram illustrating the structure of a heat pump type air conditioner according to a preferred embodiment of the present invention. As shown in  FIG. 3 , the heat pump type air conditioner according to the preferred embodiment of the present invention comprises: a compressor  110  for compressing and circulating refrigerant; a four-way valve  120  for converting the flow direction of the refrigerant such that the refrigerant can flow either in the forward or reverse direction; an outdoor heat exchanger  130  configured to serve as a condenser when a cooling operation is performed and an evaporator when a heating operation is performed; an outdoor fan  140  for suctioning outdoor air, an indoor heat exchanger  150  configured to serve as an evaporator when a cooling operation is performed and a condenser when a heating operation is performed; an indoor fan  160  for suctioning indoor air, a check valve  170  disposed between the outdoor heat exchanger  130  and the indoor heat exchanger  150  for changing the refrigerant into low-temperature and low-pressure gas refrigerant; a capillary tube  171  for changing refrigerant discharged from the outdoor heat exchanger  130  into low-temperature and low-pressure liquid refrigerant; and a defrosting mechanism for removing frost accumulated on piping of the outdoor heat exchanger  130 , which is caused when the temperature of the outdoor air is below 0° C. 
   The indoor heat exchanger  150  and the indoor fan  160  constitute an indoor unit, which is installed in the room. The compressor  110  generating a relatively large amount of noise, the four-way valve  120 , the outdoor heat exchanger  130 , the outdoor fan  140 , and the check valve  170  constitute an outdoor unit, which is installed outside the room. 
   The four-way valve  120  serves to convert the flow direction of the refrigerant such that the refrigerant discharged from the compressor  110  can flow to the outdoor heat exchanger  130  when a cooling operation is performed and to the indoor heat exchanger  150  when a heating operation is performed. 
   The outdoor heat exchanger  130  comprises an elongated pipe, which is bent several times, for example, in a serpentine shape, such that heat exchange with the outdoor air can be effectively preformed. To the outdoor heat exchanger  130  is attached a temperature sensor  134  for measuring the temperature of piping of the outdoor heat exchanger  130 . 
   The indoor heat exchanger  150  has a temperature sensor  151  for measuring the temperature (Tr) of the interior of the room and another temperature sensor  152  for measuring the temperature (Te) of the refrigerant discharged from the indoor heat exchanger  150 . 
   The check valve  170  allows the refrigerant to flow along a pipe line only in one direction. 
   The defrosting mechanism comprises: a heat discharging pipe line  131  disposed in the outdoor heat exchanger  130 ; a second pipe line  182  connected between the inlet of the heat discharging pipe line  131  and the compressor  110 ; a third pipe line  183  connected between the outlet of the heat discharging pipe line  131  and a first pipe line  181 ; and a solenoid valve  180  mounted on the third pipe line  183 . The solenoid valve  180  is a valve that performs opening and closing function according to the operation of an electromagnet. The solenoid valve  180  is used to automatically perform the opening and closing functions based on an electric signal. 
   When a user operates the heat pump type air conditioner with the above-stated construction according to the present invention in cooling mode, refrigerant flows in the direction of the arrows indicated by solid lines c 1  to c 7 . More specifically, the refrigerant is compressed by the compressor  110 , passes through the first pipe line  181  in the direction of the arrow indicated by the solid line c 1 , and then flows counterclockwise in the direction of the arrows indicated by the solid lines c 2  to c 5 . In this way, the refrigerant is circulated. While the refrigerant is circulated as described above, the refrigerant is changed into room-temperature and high-pressure liquid refrigerant by the outer heat exchanger  130 , and then the room-temperature and high-pressure liquid refrigerant is changed into low-temperature and low-pressure vapor refrigerant by the indoor heat exchanger  150 . As a result, the temperature of air is decreased. The refrigerant, which has been changed into the low-temperature and low-pressure vapor refrigerant by the indoor heat exchanger  150 , is delivered to the compressor through the first pipe line  181 , and the cooler air is discharged to the interior of the room through the indoor fan  150 . In this way, the cooling operation is accomplished. 
   When the user operates the heat pump type air conditioner according to the present invention in heating mode, on the other hand, refrigerant flows in the direction of arrows indicated by dotted lines b 1  to b 9 . More specifically, the refrigerant is compressed by the compressor  110 , flows in the direction of the arrow indicated by the dotted line b 1 , passes through the four-way valve  120 , and then flows clockwise in the direction of the arrows indicated by the solid lines b 2  to b 9 . In this way, the refrigerant is circulated. 
   When the temperature of the outdoor air is below 0° C., warm refrigerant discharged from the compressor  110  is supplied to the outdoor heat exchanger  130  through the second pipe line  182  so as to remove frost accumulated on the piping of the outdoor heat exchanger  130 . The refrigerant flows through the second pipe line  182  in the direction of arrows indicated by dotted lines a 1  and a 2 . As a result, the warm refrigerant passes through the heat discharging pipe line  131  in the outdoor heat exchanger  130 . At this time, heat exchange is performed between the warm refrigerant and the heat discharging pipe line  131 , and therefore, frost accumulated on the piping of the outdoor heat exchanger  130  is effectively removed. Of course, the temperature of the refrigerant is decreased. The decreased-temperature refrigerant passes through the third pipe line  183 , which is connected between the outlet of the heat discharging pipe line  131  and the first pipe line  181 , and then joins the refrigerant flowing through the first pipe line  181 . 
   The solenoid valve  180  may be mounted either on the second pipe line  182  or the third pipe line  183  so long as the solenoid valve  180  can allow the warm refrigerant to flow through the heat discharging pipe line  131  traversing the interior of in the outdoor heat exchanger  130  and stop the warm refrigerant from flowing through the heat discharging pipe line  131  traversing the interior of in the outdoor heat exchanger  130 . 
   As described above, the defrosting mechanism which comprises the second pipe line and the third pipe line, the solenoid valve for allowing the warm refrigerant to be supplied to the outdoor heat exchanger and stopping the warm refrigerant from being supplied to the outdoor heat exchanger, and the heat discharging pipe line traversing the interior of the outdoor heat exchanger, is incorporated in the heat pump type air conditioner according to the present invention. The solenoid valve is controlled such that the warm refrigerant from the compressor intermittently passes through the second pipe line, the heat discharging pipe line, and the third pipe line when frost is not excessively accumulated on the piping of the outdoor heat exchanger. As a result, frost accumulated on the piping of the outdoor heat exchanger is more easily removed. 
   A detailed description will be made hereinafter of a defrosting method for the heat pump type air conditioner with the above-stated construction in the condition of low-temperature outdoor air according to a preferred embodiment of the present invention. 
   The defrosting method for the heat pump type air conditioner in the condition of low-temperature outdoor air comprises a step of determining whether the temperature (Tc) of the piping of the outdoor heat exchanger is above 0° C. (Case A), the temperature (Tc) of the piping of the outdoor heat exchanger is between −15° C. and 0° C. (Case B), or the temperature (Tc) of the piping of the outdoor heat exchanger is below −15° C. (Case C), after operating the compressor for a predetermined period of time, for example, approximately 30 minutes (Step S 11 ). 
   In Case A, it is not necessary to perform a defrosting operation, and therefore, a heating operation is immediately initiated without performing the defrosting operation. 
   In Case B, the solenoid valve is intermittently operated to perform a defrosting operation (Step S 21 ). More specifically, the solenoid valve disposed at the outdoor heat exchanger  130  is operated, i.e., the solenoid valve is turned on, for a predetermined period of time, for example, 10 seconds, or until the temperature (Tc) of the piping of the outdoor heat exchanger exceeds 0° C., and then the operation of the solenoid valve is stopped,. i.e., the solenoid valve is turned off, for a predetermined period of time, for example, 10 minutes to 15 minutes. In this way, the defrosting operation is performed. The reason why the solenoid valve is turned on for 10 seconds and turned off for 10 minutes to 15 minutes is to make sure that the decrease in heating efficiency is minimized in the B case. After the defrosting operation is completed as described above, a heating operation is performed. 
   In Case C, in which the temperature (Tc) of the piping of the outdoor heat exchanger is below −15° C., i.e., the temperature (Tc) of the piping of the outdoor heat exchanger is very low, it is required to more accurately perform a defrosting operation. In other words, a cooling operation is performed in a reverse cycle for a predetermined period of time such that the outer heat exchanger  130  serves as a condenser, and therefore, frost accumulated on the piping of the outer heat exchanger  130  is thawed by the heat of condensation. 
   More specifically, the solenoid valve is turned off for a predetermined period of time, for example, 20 seconds (Step S 31 ), and the indoor fan  160  and the outdoor fan  140  are tuned off so as to prevent supply of cold wind (Step S 32 ). Subsequently, the four-way valve is turned off and the solenoid valve is turned on for a predetermined period of time, for example, 40 seconds (Step S 33 ), and the compressor is operated for a predetermined period of time, for example, 9 minutes (Step S 34 ). Thereafter, the four-way valve is turned on and the solenoid valve is turned off for a predetermined period of time, for example, 20 seconds (Step S 35 ), and the compressor and the outdoor fan are turned on to normally perform a heating operation (Step S 36 ). 
   The heat discharging pipe line  131  is connected to the lower end of the outdoor heat exchanger  130 , and therefore, the lower end of the outdoor heat exchanger  130  is thawed first, and then the whole piping of the outdoor heat exchanger  130  is thawed by a refrigerant circuit bypassed to the front surface of the outdoor heat exchanger  130 . Also, gas discharged from the compressor remains at the lower end of the outdoor heat exchanger  130  while the heating operation is performed, and therefore, the defrosting operation is effectively performed at a region where heat exchange is not completely performed due to water drops falling from the upper end of the outdoor heat exchanger  130 . 
   In Case C, two refrigerant lines where the four-way valve  120  and the solenoid valve are disposed are simultaneously opened so as to accomplish quick pressure equilibration. Consequently, a period of time for which the heating operation is paused is considerably reduced. For example, the period of time for which the heating operation is paused is 1 minute. This period of time is shorter than the period of time for which the heating operation is paused according to the prior art, which is 3 minutes. The defrosting operation is performed for 9 minutes according to the present invention. Also, the time required to perform a pressure balancing operation is considerably reduced. For example, the time required to perform the pressure balancing operation is 1 minute. This time is shorter than the time required to perform the pressure balancing operation according to the prior art, which is 3 minutes. 
   Consequently, the frost accumulated on the outdoor heat exchanger  130  is quickly removed based on the amount of frost accumulated on the outdoor heat exchanger through the defrosting process as described above. Also, the period of time for which the air conditioner is not operated, which is required to remove the frost, is reduced, and therefore, more comfortable and pleasant heating function is provided to a user. 
   Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 
   As apparent from the above description, the defrosting mechanism, which comprises the second pipe line and the third pipe line, the solenoid valve for allowing the warm refrigerant to be supplied to the outdoor heat exchanger and stopping the warm refrigerant from being supplied to the outdoor heat exchanger, and the heat discharging pipe line traversing the interior of in the outdoor heat exchanger, is incorporated in the heat pump type air conditioner according to the present invention. The solenoid valve is controlled such that the warm refrigerant from the compressor intermittently passes through the second pipe line, the heat discharging pipe line, and the third pipe line when frost is not excessively accumulated on the piping of the outdoor heat exchanger. Consequently, the present invention has the effect of more easily removing frost accumulated on the piping of the outdoor heat exchanger. 
   Furthermore, when the heat pump type air conditioner is operated in heating mode, the amount of frost accumulated on the outdoor heat exchanger is deduced from the temperature of the piping of the outdoor heat exchanger, and then the defrosting operation is performed based on the temperature of the piping of the outdoor heat exchanger. As a result, the frost accumulated on the outdoor heat exchanger is quickly removed based on the amount of frost accumulated on the outdoor heat exchanger. Also, the period of time for which the air conditioner is not operated, which is required to remove the frost, is reduced. Consequently, the present invention has the effect of providing more comfortable and pleasant heating function to a user.