Patent Publication Number: US-2023144675-A1

Title: Preventing icing in an hvac system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 63/276,901 filed Nov. 8, 2021, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Embodiments of the present disclosure pertain to the art of heating, ventilation, and air conditioning systems, and more particularly to a system and method for preventing the accumulation of frost at a heat exchanger of a heating, ventilation, and air conditioning system. 
     Heating, ventilation, and air conditioning systems (HVAC) systems are typically designed for use in relatively humid or moist environments such that as air flows over an evaporator, the temperature and the humidity of the air are reduced. However, when such an HVAC system is installed in a relatively dry environment, there is little humidity to absorb the cooling capacity being provided, so most of the cooling capacity is used to reduce the temperature of the air. In this scenario, the temperature reduction of the air is substantially increased. As a result of this increased cooling of the air, the temperature of the evaporator and hence the refrigerant output from the evaporator may be at or below freezing, 32° F., resulting in the accumulation of frost thereon. 
     BRIEF DESCRIPTION 
     According to an embodiment, a method of operating a heating, ventilation, and air conditioning (HVAC) system includes monitoring a parameter of the HVAC system associated with a temperature of a refrigerant at a heat exchanger, determining if the HVAC system is in an operating condition associated with frost accumulation at the heat exchanger, and adjusting a flow rate of an airflow across the heat exchanger in response to determining that the HVAC system is in the operating condition associated with frost accumulation at the heat exchanger. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments determining if the HVAC system is in the operating condition associated with frost accumulation at the heat exchanger further comprises comparing the parameter to a threshold. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments when the parameter exceeds the threshold, the HVAC system is not in the operating condition associated with frost accumulation at the heat exchanger. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments when the parameter is equal to or below the threshold, the HVAC system is in the operating condition associated with frost accumulation at the heat exchanger. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments adjusting the flow rate of the airflow across the heat exchanger further comprises increasing the flow rate of the airflow. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the flow rate of the airflow is increased by a fixed percentage. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the flow rate of the airflow is incrementally increased until the HVAC system is not in the operating condition associated with frost accumulation at the heat exchanger. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the HVAC system comprises a compressor and the parameter is a saturated suction temperature. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments monitoring the parameter of the HVAC system associated with the temperature of the refrigerant at the heat exchanger comprises sensing a temperature between an exit of an evaporator and an inlet of the compressor. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments monitoring the parameter of the HVAC system associated with the temperature of the refrigerant at the heat exchanger further comprises sensing a pressure between an exit of an evaporator and an inlet of the compressor. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the parameter is the temperature of the refrigerant within the heat exchanger. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments determining if the HVAC system having an adjusted flow rate of the airflow across the heat exchanger is in the operating condition associated with frost accumulation at the heat exchanger and adjusting the flow rate of the airflow across the heat exchanger in response to determining that the HVAC system is not in the operating condition associated with frost accumulation at the heat exchanger. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments adjusting the flow rate of the airflow across the heat exchanger in response to determining that the HVAC system is not in the operating condition associated with frost accumulation at the heat exchanger further comprises reducing the flow rate of the airflow across the heat exchanger. 
     According to another embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a closed loop circuit having refrigerant circulating therethrough. The closed loop circuit includes a compressor and a heat exchanger. The HVAC system additionally includes a movement mechanism for moving an airflow across the heat exchanger, a sensor operable to sense a parameter of the closed loop circuit, and a controller operable to adjust a flow rate of the airflow across the heat exchanger in response to the parameter to maintain a temperature of the refrigerant at the heat exchanger above freezing. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the parameter is saturated suction temperature. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the saturated suction temperature is measured between an exit of the heat exchanger and an inlet of the compressor. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the parameter is pressure between an exit of the heat exchanger and an inlet of the compressor. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the controller is operable to increase the flow rate of the airflow across the heat exchanger when the parameter is equal to below a threshold. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the controller is operable to decrease the flow rate of the airflow across the heat exchanger when the parameter is equal to or exceeds a second threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG.  1    is a schematic diagram of an exemplary heating, ventilation, and air conditioning (HVAC) system; 
         FIG.  2    is a schematic view of an exemplary heat exchanger of an HVAC system; 
         FIG.  3    is a schematic diagram of an exemplary control system of an HVAC system according to an embodiment; 
         FIG.  4    is a graph representing a standard and adjusted airflow rate relative to a demand on the HVAC system according to an embodiment; 
         FIG.  5    is a detailed schematic diagram of the control system of  FIG.  3    according to an embodiment; 
         FIG.  6    is a detailed schematic diagram of the control system of  FIG.  3    according to another embodiment; and 
         FIG.  7    is a detailed schematic diagram of the control system of  FIG.  3    according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     With reference now to  FIG.  1   , an exemplary heating, ventilation, or air conditioning (HVAC) system is schematically illustrated. Examples of such air conditioning or refrigeration systems include, but are not limited to, split, packaged, chiller, rooftop, supermarket, and transport refrigeration systems. A refrigerant or other suitable fluid R is configured to circulate through the HVAC system  20  such that the refrigerant R absorbs heat when evaporated at a low temperature and pressure and releases heat when condensed at a higher temperature and pressure. Within the illustrated HVAC system  20 , the refrigerant R flows in a counterclockwise direction as indicated by the arrows through a vapor compression cycle. A compressor  22  receives refrigerant vapor from an evaporator  24  and compresses it to a higher temperature and pressure, with the relatively hot vapor then passing to a condenser  26 . Within the condenser  26 , the refrigerant R is cooled and condensed to a liquid state via a heat exchange relationship with a cooling medium. In the illustrated, non-limiting embodiment, the cooling medium is an airflow A, such as driven by a fan or other air movement mechanism  28  for example. It should be appreciated that the HVAC system may be reversible in certain instances (e.g., where the refrigerant flows clockwise and the condenser  26  and evaporator  24  switch roles, for example, where the condenser  26  acts as an evaporator and the evaporator  24  acts as a condenser). 
     As shown in  FIG.  1   , the liquid refrigerant R output from the condenser  26  is provided to a downstream expansion device  30 , in which the refrigerant R is expanded to a low temperature and pressure two-phase liquid/vapor state before flowing to the evaporator  24 . The low pressure vapor then returns to the compressor  22 , thereby completing the cycle of the closed loop circuit. It should be understood that the HVAC system depicted in  FIG.  1    is a simplistic representation and many enhancements and features known in the art may be included that are not shown in the schematic. 
     With continued reference to  FIG.  1   , and further reference to  FIG.  2   , as a result of the heat transfer that occurs between the airflow A and the refrigerant R at one of the heat exchangers of the HVAC system  20 , such as at the evaporator  24  for example, the temperature of the refrigerant R at or within the heat exchanger  24  may be at or below freezing (32° F.) causing condensed moisture from the air A to freeze or accumulate as frost on the exterior of the heat exchanger. 
     With reference now to  FIG.  3   , in an embodiment, the HVAC system  20  includes a control system  40  configured to monitor and dynamically adjust operation of the HVAC system  20  at the heat exchanger, for example the evaporator  24 , to maintain the temperature of the refrigerant R output from the heat exchanger above freezing (32° F.) to prevent frost or ice from accumulating on the heat exchanger  24 . In an embodiment, the HVAC system  20  includes one or more sensors S associated with the compressor  22  and a controller  42  operably coupled to the at least one sensor S. The sensor S may be arranged within the portion of the HVAC system  20  located outside, commonly referred to as an “outdoor unit” (see  FIGS.  5  and  6   ). In an embodiment, the sensor S is used to measure a pressure at the inlet of the compressor  22 . However, it should be understood that the sensor S need not be arranged at the inlet of the compressor  22 . Rather, the sensor S may be arranged at any location in the suction line, for example at any location between the outlet of the evaporator  24  and the inlet of the compressor  22 . From this pressure, the saturated suction temperature at the inlet of the compressor  22  can be calculated. However, embodiments where the control system  40  includes a sensor S operable to monitor another suitable parameter of the HVAC system  20 , such as the temperature of the refrigerant R at the outlet of the evaporator  24  for example, are also within the scope of the disclosure. It should be understood that monitoring the temperature of the refrigerant R as described herein includes embodiments where the temperature of the refrigerant itself is monitored as well as embodiments where the temperature of the tube or conduit containing the refrigerant (and having a temperature substantially identical to the refrigerant) is monitored. Further, it should be understood that the at least one sensor S may be configured to continuously monitor, or alternatively, intermittently monitor the respective parameter. 
     In operation, a processor of the controller  42  is configured to analyze the information or inputs provided by the at least one sensor(s) S to determine if the current operating condition of the HVAC system  20  at the heat exchanger, for example the evaporator  24 , will result in the formation of frost or ice thereon. In an embodiment, this analysis includes comparing the saturated suction temperature with a corresponding threshold associated with the formation of frost or ice on the heat exchanger. If the saturated suction temperature is above the threshold, the HVAC system  20  is not in an operating condition associated with frost accumulation at the heat exchanger and no changes in operation of the HVAC system  20  are required. However, when the sensed saturated suction temperature is below the threshold, the HVAC system  20  is in an operating condition associated with frost accumulation at the heat exchanger. 
     Accordingly, in such an operating condition, the controller  42  is configured to implement a corrective action to prevent and/or to counteract the formation of frost at the heat exchanger. In an embodiment, the corrective action initiated by the controller  42  is an adjustment of the airflow A being provided to the evaporator  24 , implemented via the movement mechanism  28  (which may be a fan, etc.). While maintaining a constant cooling capacity at the evaporator  24 , increasing the flow rate of the airflow A provided to the evaporator  24  distributes the cooling capacity over a larger volume of air, resulting in an increased temperature of the airflow A leaving the evaporator  24 . Accordingly, the temperature of the airflow A downstream from the evaporator  24  will be warmer than if the flow rate of the airflow A had not been increased. Further, the saturated suction temperature at the compressor  22  and the temperature of the refrigerant R output from the evaporator  24  will be warmer than if the flow rate of the airflow A had not been increased. 
     With reference to the graph shown in  FIG.  4   , an HVAC system  20  typically has a standard flow rate of the airflow A corresponding to the heating and/or cooling demand of the HVAC system  20 , represented by the line labeled STD. In an embodiment, when the sensed or calculated parameter, such as the saturated suction temperature, is less than or equal to a threshold (also referred to herein as a first threshold), the controller  42  may be configured to increase the standard flow rate of the airflow A associated with the current demand by a fixed percentage, such as anywhere between 2% and 25%. Although an increase of 10% is illustrated in the  FIG.  4   , it should be understood that an increase of any amount, such as 5%, 10%, 15%, 20%, or even 25% is within the scope of the disclosure. This adjusted flow rate is represented by the line labeled ADJ on the graph. Although an HVAC system  20  having a variable capacity is illustrated in  FIG.  4   , it should be understood that the same adjustment may be implemented on a fixed or single capacity HVAC system having a variable airflow. 
     In another embodiment, the controller  42  may be configured to incrementally increase the standard flow rate of the airflow A. In such embodiments, when the sensed or calculated parameter is less than or equal to the threshold, the controller  42  will increase the standard flow rate of the airflow A associated with the current demand by an incremental percentage, such as between 2% and 10%. If the parameter is sampled again and remains below the threshold, the controller  42  will again increase the flow rate of the airflow A associated with the demand by the incremental percentage. This incremental increasing will occur until the sensed or calculated parameter exceeds the threshold. 
     In an embodiment, the controller  42  is configured to automatically revert back to the standard flow rate of the airflow A after a fixed period of time. Alternatively, the controller  42  may be configured to revert back to the standard flow rate corresponding to the demand on the HVAC system  20  after the sensed parameter, such as the saturated suction temperature for example, has exceeded the threshold for a predetermined period of time. In yet another embodiment, the controller  42  may be configured to incrementally reduce the adjusted flow rate of the airflow A towards the standard flow rate in the event that the sensed or calculated parameter remains above the threshold. 
     In an embodiment, the HVAC system  20  will continue to operate with the increased or adjusted flow rate of the airflow A at the evaporator  24  until the sensed or calculated parameter, for example the saturated suction temperature, rises and exceeds a second, higher threshold. In such embodiments, in the event that the sensed or calculated parameter equals or exceeds the second threshold, the controller  42  is configured to automatically adjust, and more specifically decrease the flow rate of the airflow A. This reduction in the flow rate from the adjusted flow towards the standard flow may occur incrementally or alternatively, may occur in a single step. 
     Although a single controller  42  is described herein as not only receiving the sensor information and performing the comparison with the threshold, but also determining an adjusted airflow, embodiments where a plurality of controllers are configured to cooperate to perform these functions are also within the scope of the disclosure. For example, as shown in  FIGS.  5  and  6   , the outdoor unit  50  containing the at least one sensor S may include a first controller  42   a  and a general system control unit  52  of the control system  40  may include a second controller  42   b  configured to communicate with the first controller  42   a.  As shown, the second controller  42   b  is also operably coupled to the blower control  54  associated with the movement mechanism or blower  28  for moving the airflow. In an embodiment, the blower control  54  and the movement mechanism  28  are located within the interior of a building having one or more areas being conditioned by the HVAC system  20 , also commonly referred to as an “indoor unit”  56 . Although the system control unit  52  is illustrated as being remote from both the outdoor unit  50  and the indoor unit  56 , it should be understood that the system control unit  52  may be arranged anywhere within the HVAC system  20  including within either the outdoor unit  50  or the indoor unit  56 . 
     In the non-limiting embodiment of  FIG.  5   , the first controller  42   a  is configured to compare the information provided from the sensor S with the threshold and determine an adjusted flow rate of the airflow A. The adjusted flow rate is communicated to the second controller  42   b  and in response, sends a respective command to the blower control  54  to implement the adjusted flow rate at the heat exchanger. In another embodiment, as shown in  FIG.  6   , the first controller  42   a  is configured to simply communicate the sensor information and the standard flow rate of the airflow A to the second controller  42   b.  In such an embodiment, the second controller  42   b  will perform the comparison, determine the adjusted flow rate, and send a command to the blower control  54  to implement the adjusted flow rate. In yet another embodiment, illustrated in  FIG.  7   , the first controller  42   a  is configured to communicate only the sensor information to the second controller  42   b.  In such embodiments, the airflow limits may be stored in the second controller  42   b  such that the second controller  42   b  is capable of performing the comparison, determining the adjusted flow rate, and sending a command to the blower control  54  to implement the adjusted flow rate as described above. 
     An HVAC system  20  having a control system  40  operable to automatically adjust the flow rate of the airflow A at a heat exchanger, such as the evaporator  24  for example, provides optimum cooling in low humidity environments, such as a desert for example, without allowing frost to accumulate on the heat exchanger. However, such an HVAC system  20  may also be suitable for use in more humid environments. 
     The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.