System and method for defrosting outdoor coils in reversible rooftop units

Abstract

A Heating, Ventilation, and Air Conditioning (HVAC) system to utilize heat from ambient air to defrost an outdoor coil in a defrost mode, instead of heat from a conditioned space, is disclosed. A return damper is positioned between the conditioned space and an inlet side of an indoor coil. A supply damper is positioned between an outlet side of the indoor coil and the conditioned space. A fresh air damper is positioned upstream of the inlet side of the indoor coil. An exhaust damper is positioned downstream of the outlet side of the indoor coil. In the defrost mode, the controller communicates electronic signals to the dampers to close the return damper and the supply damper, and to open the fresh air damper and the exhaust damper. The high-temperature refrigerant flows from a compressor to the outdoor coil and releases heat to defrost the outdoor coil.

Description

TECHNICAL FIELD

[0001] This disclosure relates generally to Heating, Ventilation, and Air Conditioning (HVAC) systems. More particularly, this disclosure relates to the system and method for defrosting outdoor coils in reversible rooftop units.BACKGROUND

[0002] Heating, ventilation, and air conditioning (HVAC) systems are used to regulate environmental conditions within an enclosed space. Air is cooled via heat transfer with refrigerant flowing through the HVAC system and returned to the enclosed space as conditioned air.SUMMARY OF THE DISCLOSURE

[0003] Some Heating, Ventilation, and Air Conditioning (HVAC) systems use reversible rooftop units to provide both heating and cooling for buildings or any physical space by reversing the refrigerant cycle as needed. During cold weather, such as winter, in a heating mode, the outdoor coil often operates at temperatures below freezing temperature (e.g., 32 Fahrenheit (°F) or 0 Celsius (°C)) to extract heat from the cold ambient air. However, in some cases, the low operating temperature causes moisture in the air to condense and freeze on the surface of the outdoor coil and form ice. The ice acts as a barrier and reduces the capability to absorb heat from the surrounding environment when needed.

[0004] One approach to address the issue of defrosting ice from the outdoor coils is to implement a defrost mode to melt the ice on the outdoor coil. In some conventional defrost modes to melt the ice on the outdoor coil, the HVAC system temporarily reverses the refrigerant flow to use the heat from the conditioned space to melt the ice on the outdoor coil. This results in the indoor coil to absorb heat from the conditioned space to melt the ice formed on the surface of the outdoor coil. However, this approach leads to extracting heat from the conditioned space which is the opposite of providing heat to the conditioned space during the heating mode and therefore, discomfort for people in the conditioned space. Further, this approach leads to an increased energy consumption of the HVAC system to restore the lost heat to the conditioned space This, in turn, increases the load on the HVAC system.

[0005] The disclosed system provides a solution to these and other technical problems of conventional HVAC systems. In some embodiments, the disclosed system is configured to use ambient air to facilitate defrosting of the outdoor coil while (at least partially) isolating the conditioned space during the defrost mode Therefore the heat from the conditioned space is not drawn into the indoor coil This, in turn, maintains the conditioned air within the conditioned space. Further, the additional energy that would otherwise be spent on restoring the lost heat to the conditioned space is obviated. Therefore, the load of the HVAC system is reduced compared to some conventional HVAC systems where the heat from the conditioned space is used to defrost the outdoor coil during the defrost operation.

[0006] In some embodiments, the disclosed HVAC system may include an indoor coil, an outdoor coil, a valve, a return damper, a supply damper, a fresh air damper, an exhaust damper, and a controller. The indoor coil may include an inlet side and an outlet side. The indoor coil is configured to condense refrigerant during a heating mode as the refrigerant in vapor form flows through the indoor coil, releases heat to a conditioned space, and transitions into liquid. The indoor coil is further configured to evaporate the refrigerant during a cooling mode as the refrigerant in liquid form flows through the indoor coil, absorbs heat from the conditioned space, and transitions into vapor.

[0007] The outdoor coil may include an inlet side and an outlet side. The outdoor coil is configured to evaporate the refrigerant during the heating mode as the refrigerant in liquid form flows through the outdoor coil, absorbs heat from ambient air, and transitions into vapor. The outdoor coil is further configured to condense the refrigerant during the cooling mode as the refrigerant in vapor form flows through the outdoor coil, releases heat to the ambient air, and transitions into liquid. The valve is positioned between a compressor and the outdoor coil. The valve is configured to reverse a flow of refrigerant between the indoor coil and outdoor coil during a transition between the heating mode and the defrost mode.

[0008] The return damper is positioned between a conditioned space and an inlet side of the indoor coil. The return damper is configured to allow recirculated air to flow from the conditioned space to the indoor coil during each of the heating mode and the cooling mode. The supply damper is positioned between an outlet side of the indoor coil and the conditioned space. The supply damper is configured to allow conditioned air to flow from the indoor coil to the conditioned space during each of the heating mode and the cooling mode. The fresh air damper is positioned upstream of the inlet side of the indoor coil. The fresh air damper is configured to allow ambient air to flow through the indoor coil during the defrost mode. The fresh air damper is also configured to allow ambient air to flow through indoor coil to the conditioned space during “Free Cooling” (e.g., approximately 45 °F or 7 °C when in cooling mode) and allow ambient air flow when the conditioned space CO2 concentration levels are higher. The exhaust damper is positioned downstream of the outlet side of the indoor coil. The exhaust damper is configured to allow airflow to the surrounding environment after passing through the indoor coil during a defrost mode. The exhaust damper is also used to maintain the pressure level inside the conditioned space. The controller is operably coupled with the return damper, the supply damper, the fresh air damper, and the exhaust damper. The controller comprises a processor configured to determine that a condition to operate in the defrost mode for the outdoor coil is met. In response to determining that the condition to operate in the defrost mode for the outdoor coil is met, the process is configured to communicate a first electronic signal to the return damper to close the return damper, communicate a second electronic signal to the supply damper to close the supply damper, communicate a third electronic signal to the fresh air damper to open the fresh air damper and communicate a fourth electronic signal to the exhaust damper to open the exhaust damper.

[0009] Certain embodiments of the present disclosure may include some, or none of these advantages. These advantages and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:

[0011] FIG. 1 illustrates a diagram of an embodiment of a Heating, Ventilation, and Air Conditioning (HVAC) system operating in a defrost mode, according to some embodiments of the present disclosure;

[0012] FIG. 2 illustrates a diagram of an embodiment of the HVAC system of FIG. 1 operating in a heating mode, according to some embodiments of the present disclosure; and

[0013] FIG. 3 illustrates a flowchart of an example method of operating the HVAC system of FIGS. 1-2.DETAILED DESCRIPTION

[0014] Embodiments of the present disclosure and its advantages are best understood by referring to FIGS. 1 through 3 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

[0015] Some Heating, Ventilation, and Air Conditioning (HVAC) systems use reversible rooftop units to provide both heating and cooling for buildings or any physical space by reversing the refrigerant cycle as needed. During cold weather, such as winter, in a heating mode, the outdoor coil often operates at temperatures below freezing temperature (e.g., 32 Fahrenheit (°F) or 0 Celsius (°C)) to extract heat from the cold ambient air. However, in some cases, the low operating temperature causes moisture in the air to condense and freeze on the surface of the outdoor coil and form ice. The ice acts a barrier and reduces the capability to absorb heat from the surrounding environment when needed.

[0016] One approach to address the issue of defrosting ice from the outdoor coils is to implement a defrost mode to melt the ice on the outdoor coil. In some conventional defrost modes to melt the ice on the outdoor coil, the HVAC system temporarily reverses the refrigerant flow to use the heat from the conditioned space to melt the ice on the outdoor coil. This results in the indoor coil to absorb heat from the conditioned space to melt the ice formed on the surface of the outdoor coil. However, this approach leads to extracting heat from the conditioned space which is the opposite of providing heat to the conditioned space during the heating mode and therefore, discomfort for people in the conditioned space. Further, this approach leads to an increased energy consumption of the HVAC system to restore the lost heat to the conditioned space This, in turn, increases the load on the HVAC system.

[0017] The disclosed system provides a solution to these and other technical problems of conventional HVAC systems. In some embodiments, the disclosed system is configured to use ambient air to facilitate defrosting of the outdoor coil while (at least partially) isolating the conditioned space during the defrost mode. Therefore the heat from the conditioned space is not drawn into the indoor coil. This, in turn, maintains the conditioned air within the conditioned space. Further, the additional energy that would otherwise be spent on restoring the lost heat to the conditioned space is obviated. Therefore, the load of the HVAC system is reduced compared to some conventional HVAC systems where the heat from the conditioned space is used to defrost the outdoor coil during the defrost operation.HVAC system

[0018] FIG. 1 illustrates an example Heating, Ventilation, and Air Conditioning (HVAC) system 100 according to an embodiment of the present disclosure. In general, the HVAC system 100 is configured to (at least partially) isolate a conditioned space during a defrost mode 101 for defrosting ice on the surface of an outdoor coil and instead, use heat from the ambient air to defrost the ice formed on the surface of the outdoor coil. In the present disclosure, it is understood that the term ‘isolate’ is not intended to mean complete or absolute isolation but rather refers to the HVAC system 100 and its ability to restrict airflow between the conditioned space and the rest of the HVAC system 100 during the defrost mode 101 to the extent necessary for operating the HVAC system, while allowing limited or controlled airflow in and out of the conditioned space, as required, to maintain balance and operational requirements.

[0019] In some embodiments, the HVAC system 100 comprises refrigerant conduit subsystems 102, one or more compressors 112, a valve 114, an outdoor heat exchanger 120 (which includes an outdoor coil 122, fans 124, and a temperature sensor circuit 126), a filter dryer 128, a valve 130, an indoor heat exchanger 134 (which includes an indoor coil 136), a blower 138, an accumulator 140, a valve 142, a fresh air damper 144, an exhaust damper 146, a supply damper 148, a return air damper 150, a gravity damper 152, and a controller 160.

[0020] In some embodiments, the HVAC system 100 includes a rooftop unit (RTU) that is positioned on the roof of a building, and the conditioned air is delivered into the interior of the building. In other embodiments, portion(s) of the system 100 may be located within the building and portion(s) outside the building. The HVAC system 100 may be configured as shown in FIG. 1 or in any other suitable configuration. For example, the HVAC system 100 may include additional components or may omit one or more components shown in FIG. 1.System Components

[0021] Some components of the HVAC system 100 may be located in an outdoor section 106 of the HVAC system 100 and other components may be in an indoor section 104 of the HVAC system 100. For example, the compressors 112, valve 114, outdoor heat exchanger 120, filter dryer 128, valve 130, accumulator 140, and valve 142 may be located in the outdoor section 106, and the indoor heat exchanger 134, blower 138, fresh air damper 144, exhaust damper 146, supply damper 148, return air damper 150, and gravity damper 152 may be located in the indoor section 104. The controller 160 may be on-site (e.g., in a building) where the HVAC system 100 is implemented. In some applications, the controller 160 may be incorporated within the outdoor section 106.

[0022] The refrigerant conduit subsystems 102 facilitate the movement of a refrigerant (also referred to herein as a working fluid) through a refrigerant cycle such that the working fluid flows as illustrated by arrows in FIG. 1. The refrigerant conduit subsystem 102 includes any conduit, tubing and the like that is illustrated in FIG. 1 fluidly connecting components of the HVAC system 100.

[0023] Each of the compressors 112 may be a variable speed compressor or a multiple-stage compressor and is generally configured to compress (e.g., increase the pressure of) the refrigerant. The HVAC system 100 may include any number of compressors 112 for one or more conditioning applications, such as for multiple floors and rooms in a building. The compressor 112 is fluidly coupled with the refrigerant conduit subsystem 102 and may be positioned downstream of the accumulator 140 and upstream of the valve 114. The compressor 112 may be in signal communication with the controller 160 using wired and / or wireless connections. The controller 160 may communicate electronic signals to the compressor 112 to control its operations. A variable-speed compressor is generally configured to operate at different speeds to increase the pressure of the refrigerant to keep the refrigerant moving along the fluid conduit subsystem 102. In the variable-speed compressor configuration, the speed of compressor 112 can be modified to adjust the cooling capacity and / or load of the HVAC system 100. Meanwhile, in the multi-stage compressor configuration, one or more compressors can be turned on or off to adjust the cooling capacity of the HVAC system 100.

[0024] The valve 114 may be an expansion valve, a flow control valve, a solenoid valve, a motorized valve, an electronic expansion valve (EEV), a thermal expansion valve (TXV), or any other suitable valve configured to control the flow of refrigerant. The valve 114 may be fluidly coupled with the refrigerant conduit subsystem 102 and positioned between the outdoor heat exchanger 120, the indoor heat exchanger 134, the compressor discharge lines 113, and valve 142. The valve 114 may be a four-way switch valve that changes the flow of the refrigerant depending on a mode of operation, such as in cooling mode, a heating mode, and a defrost mode 101. For example, the valve 114 may include a plunger or a sliding component inside it to switch the connections or paths between the ports 116a-d as needed. The valve 114 includes four ports 116d to port 116c or to port 116b to allow changing the flow of the refrigerant depending on the mode of operation. The port 116a may be connected to the compressors’ discharge lines 113, and each of the port 116b and the port 116d may be connected to the valve 142 depending on the operating mode. The plunger of valve 114 allows switching the port connection from the port 116d to port 116c or port 116b based on the conditioned space demand. The term ‘cooling mode’ refers to the mode of operation of the HVAC system 100 when the conditioning demand for the conditioned space 108 is a cooling demand. The term ‘heating mode’ refers to the mode of operation of the HVAC system 100 when the conditioning demand for the conditioned space 108 is a heating demand. The term ‘defrost mode’ refers to the mode of operation of the HVAC system 100 when the HVAC system 100 operates to defrost the outdoor coil 122. For example, in the cooling mode, the valve 114 directs the flow of the refrigerant from the discharge lines 113 of the compressors 112 to the outdoor heat exchanger 120 by connecting the port 116a to port 116b, and directs the flow of the refrigerant from the indoor heat exchanger 134 to the valve 142 by connecting the port 116c to port 116d.

[0025] In the heating mode, the valve 114 directs the flow of the refrigerant from the compressors’ discharge lines 113 to the indoor heat exchanger 134 by connecting the port 116a to port 116c, and directs the flow of the refrigerant from the outdoor heat exchanger 120 to the valve 142 by connecting the port 116b to port 116d. In the defrost mode 101, the valve 114 operates similarly to cooling mode, directing high-temperature refrigerant from the compressors’ discharge lines 113 to the outdoor heat exchanger 120 to facilitate defrosting ice on the outdoor coil. Therefore, the valve 114 is configured to reverse a flow of refrigerant between the indoor coil 136 and outdoor coil 122 during a transition between the heating mode and the defrost mode 101. The valve 114 may regulate the flow and pressure of the refrigerant. The controller 160 may be in signal communication with the valve 114 (e.g., via wired and / or wireless communication) to control its operations and configure the connections between the ports 116a-d for each mode of operation by sending electronic signals 174. The valve 114 is configured to adjust its opening to regulate the flow and pressure of the refrigerant as it transitions through the modes of operations.

[0026] The outdoor heat exchanger 120 may generally be a high-side heat exchanger, such as a gas cooler or a condenser, and is configured to transfer heat between the refrigerant and the surrounding outdoor environment. The outdoor heat exchanger 120 comprises an outdoor coil 122, one or more fans 124, and a temperature sensor circuit 126. The outdoor heat exchanger 120 is fluidly coupled with the refrigerant conduit subsystem 102 and positioned downstream of the valve 114 and upstream of the filter dryer 128 and valve 130 (in the defrost mode and cooling mode).

[0027] The outdoor coil 122 may include metallic components, such as fins, tubes, and microchannels. During the cooling mode, the outdoor heat exchanger 120 functions as a condenser, where the refrigerant in vapor form flows through the outdoor coil 122 and releases heat into the outdoor environment. During the heating mode, the outdoor heat exchanger 120 functions as an evaporator, where the refrigerant in liquid form flows through the outdoor coil 122, absorbs heat from the ambient air, and transitions into vapor. The refrigerant may enter through the outlet side 123 of the outdoor coil 122 and exit through its inlet side 121 In defrost mode 101, the outdoor coil 122 receives high-temperature refrigerant from the compressors 112 to melt the ice formed on the surface of the outdoor coil 122. The refrigerant may enter through the inlet side 121 of the outdoor coil 122 and exit through its outlet side 123.

[0028] The fans 124 are operably coupled to the outdoor coil 122 and configured to move air across the coil to facilitate faster heat transfer between the refrigerant and the surrounding environment. The fans 124 may be controlled by the controller 160 (e.g., via wired and / or wireless communication) to adjust the fan speed based on system conditions, such as the temperature detected by the temperature sensor circuit 126 and the cooling or heating demand. The outdoor heat exchanger 120 may allow the airflow 125 to pass through the outdoor coil 122 and exit through the fans 124 on another side of the outdoor heat exchanger 120.

[0029] The temperature sensor circuit 126 may include a temperature sensing element and circuitry. The temperature sensor circuit 126 may be implemented by a hardware circuit and configured to detect the temperature of the outdoor coil 122. The temperature sensor circuit 126 may include one or more temperature sensor circuits 126. The temperature sensor circuit 126 may include a temperature sensing element such as a thermocouple, a thermistor, a semiconductor-based temperature circuit board, or any other type of temperature sensor. In some examples, the temperature sensor circuit 126 may be positioned within the outdoor heat exchanger 120, on the surface of the outdoor coil 122, or at any other location. The temperature sensor circuit 126 may be attached to a surface using any appropriate means (e.g., threaded connections, clamps, adhesives, or the like). The temperature sensor circuit 126 is configured to detect the temperature of the outdoor coil 122 periodically (e.g., every second, every minute, etc.) and / or on demand (e.g., in response to a request from the controller 160). The temperature sensor circuit 126 is in signal communication with the controller 160 using wired and / or wireless connections. The temperature sensor circuit 126 may provide the detected temperature data 170 (which includes the detected temperature of the outdoor coil 122) to the controller 160. The controller 160 may use the temperature data 170 for evaluating whether to operate in the defrost mode 101.

[0030] The filter dryer 128 is generally a component configured to filter debris and remove moisture from the refrigerant as it flows through the HVAC system 100. The filter dryer 128 is fluidly coupled with the refrigerant conduit subsystem 102 and positioned downstream of the outdoor heat exchanger 120 and upstream of the valve 130 and the indoor heat exchanger 134 (in the cooling and defrost modes). The filter dryer 128 may include a filtering element, such as mesh screens or filter pads, to capture dirt, debris, or any other contaminants present in the refrigerant. The filter dryer 128 may be bi-directional, to allow the refrigerant to flow in either direction, depending on the mode of operation. For example, during each of the cooling and defrost modes, the refrigerant flows from the outdoor heat exchanger 120 toward the indoor heat exchanger 134 through the filter dryer 128. In the heating mode, the refrigerant flows from the indoor heat exchanger 134 to the outdoor heat exchanger 120 through the filter dryer 128.

[0031] The valve 130 may be an expansion valve, a flow control valve, a solenoid valve, a motorized valve, an EEV, a TXV, or any other suitable valve configured to control the flow of refrigerant. The valve 130 may be fluidly coupled with the refrigerant conduit subsystem 102 and positioned between the filter dryer 128 and the indoor heat exchanger 134. The valve 130 may regulate the flow and pressure of the refrigerant. In some embodiments, the valve 130 may be active. In this manner, active means that valve 130 may be controlled by the controller 160. For example, the controller 160 may be in signal communication with the valve 130 (e.g., via wired and / or wireless communication) to control its operations. In some embodiments, the valve 130 may be passive. In this manner, passive means that valve 130 may be mechanically calibrated to open and close based on preconfigured pressure differential across the valve. The valve 130 is configured to adjust its opening to regulate the flow and pressure of the refrigerant as needed.

[0032] The indoor heat exchanger 134 may generally include an indoor coil 136 and fans (e.g., blower 138) to move air across the coils. The indoor heat exchanger 134 is configured to facilitate the heat transfer between the refrigerant and the air within the conditioned space 108. The indoor heat exchanger 134 is fluidly coupled with the refrigerant conduit subsystem 102 and positioned downstream of the valve 130 and upstream of the accumulator 140 in the cooling mode (in the cooling and defrost modes). The indoor heat exchanger 134 is in signal communication with the controller 160 using wired and / or wireless connections. The controller 160 may send control signals to the indoor heat exchanger 134 to control the speed of the fans based on temperature conditions and the cooling demand.

[0033] The indoor coil 136 may include metallic components, such as fins, tubes, and microchannels. For example, in each of the cooling and defrost mode, the refrigerant cools metallic components (e.g., metallic coils, plates, and / or tubes) of the indoor heat exchanger 134 as the refrigerant passes through them. These metallic components may then cool the air around them. The cooled air may then be circulated such as, for example, by a fan to cool a space such as, for example, a room in a building. During each of the defrost and cooling modes, the indoor heat exchanger 134 functions as an evaporator, where the refrigerant in liquid form flows through the indoor coil 136, absorbs heat from the air in the conditioned space 108, and at least some amount of the refrigerant transitions into vapor. During the heating mode, the indoor heat exchanger 134 functions as a condenser, where the refrigerant in vapor form flows through the indoor coil 136, releases heat to the conditioned space, and at least some amount of the refrigerant transitions into liquid. The refrigerant may enter through the inlet side 137 of the indoor coil 136 and exit through its outlet side 135.

[0034] The blower 138 is generally a fan operably coupled to the indoor coil 136 and is configured to move air across the indoor coil 136 to facilitate heat exchange between the refrigerant flowing through the indoor coil 136 and the air in the conditioned space 108. This leads to airflow 145 flowing out of the blower 138. The blower 138 may be controlled by the controller 160 (e.g., via wired and / or wireless communication) to adjust its speed based on system conditions, such as temperature data and cooling or heating demand. In some embodiments, the blower 138 may be a component of the indoor heat exchanger 134.

[0035] The accumulator 140 may be a physical storage configured to collect and store refrigerant as it enters the compressors 112. The accumulator 140 is fluidly coupled with the refrigerant conduit subsystem 102 and positioned downstream of the valve 142 and upstream of the compressors’ suction lines 111. The accumulator 140 serves as a buffer to reduce the likelihood of liquid refrigerant from reaching the compressors. The accumulator 140 may separate any remaining liquid from the refrigerant vapor to allow vapor to flow toward the compressors 112. The liquid refrigerant is collected at the bottom of the accumulator 140 and the vapor refrigerant is collected on top of the accumulator 140. The accumulator 140 may be in signal communication with the controller 160 using wired and / or wireless connections.

[0036] The valve 142 may be an expansion valve, a flow control valve, a solenoid valve, a motorized valve, an EEV, a TXV, or any other suitable valve configured to control the flow of refrigerant. The valve 142 may be fluidly coupled with the refrigerant conduit subsystem 102 and positioned between the valve 114 and the accumulator 140. The valve 142 may regulate the flow and pressure of the refrigerant. In some embodiments, the valve 142 may be active—meaning that it may be controlled by the controller 160. For example, the controller 160 may be in signal communication with the valve 142 (e.g., via wired and / or wireless communication) to control its operations. In some embodiments, the valve 142 may be passive—meaning that it may be mechanically calibrated to open and close based on preconfigured pressure differential across the valve. The valve 142 is configured to adjust its opening to regulate the flow and pressure of the refrigerant as needed.

[0037] The fresh air damper 144 is generally a motorized damper configured to regulate the intake of fresh ambient air into the indoor section 104. In some embodiments, the fresh air damper 144 may include adjustable blades connected to an actuator that controls the position of the blades to either allow or restrict airflow 145. The actuator may include an electronic circuit that includes certain electronic components, such as a microcontroller, a motor driver, a power supply circuit, capacitors, resistors, diodes, and transistors. The actuator (e.g., controlled by the controller 160) receives electronic signals and translates the received electronic signals to generate drive signals to adjust the position of the blades. Thus, the fresh air damper 144 may open and close in response to receiving electronic signals from the controller 160.

[0038] The fresh air damper 144 is configured to introduce fresh air into the indoor heat exchanger 134 during specific operation modes, such as the heating mode, defrost mode and the cooling mode. For example, during each of the heating mode, defrost mode and cooling mode, the fresh air damper 144 may open its blades to permit the airflow 145 of ambient air into the indoor section 104. The fresh air damper 144 is positioned upstream of the inlet side of the indoor heat exchanger 134 to allow ambient air to flow through the indoor coil 136 during the defrost mode.

[0039] The exhaust damper 146 is generally a motorized damper configured to regulate the expulsion of air from the indoor section 104 to the ambient environment. In some embodiments, the exhaust damper 146 may include adjustable blades connected to an actuator that controls the position of the blades to either allow or restrict airflow 147. The actuator may include an electronic circuit that includes certain electronic components, such as a microcontroller, a motor driver, a power supply circuit, capacitors, resistors, diodes, and transistors. The actuator (e.g., controlled by the controller 160) receives electronic signals and translates the received electronic signals to generate drive signals to adjust the position of the blades. Thus, the exhaust damper 146 may open and close in response to receiving electronic signals from the controller 160. The exhaust damper 146 is configured to expel air that has passed through the indoor heat exchanger 134 (and its coil 136) during the defrost mode. For example, during the defrost mode, the exhaust damper 146 may open its blades to permit airflow 147 out of the indoor section 104 into the surrounding environment. The exhaust damper 146 is positioned downstream of the outlet side of the indoor heat exchanger 134 to allow airflow 147 to the surrounding environment after passing through the indoor coil 136 during the defrost mode.

[0040] The supply damper 148 is generally a motorized damper configured to regulate the flow of conditioned air from the indoor section 104 to the conditioned space 108. In some embodiments, the supply damper 148 may include adjustable blades connected to an actuator that controls the position of the blades to either allow or restrict airflow 147. The actuator may include an electronic circuit that includes certain electronic components, such as a microcontroller, a motor driver, a power supply circuit, capacitors, resistors, diodes, and transistors. The actuator (e.g., controlled by the controller 160) receives electronic signals and translates the received electronic signals to generate drive signals to adjust the position of the blades. Thus, the supply damper 148 may open and close in response to receiving electronic signals from the controller 160. The supply damper 148 is configured to direct conditioned air (that is conditioned by the indoor heat exchanger 134) into the conditioned space 108 during normal operation modes, such as the heating and cooling modes. For example, during each of the heating and cooling modes, the supply damper 148 may open its blades to permit airflow into the conditioned space 108. During the defrost mode 101, the supply damper 148 may remain closed to (at least partially) isolate the conditioned space 108 from the airflow in the indoor section 104. The supply damper 148 is located between the outlet side of the indoor heat exchanger 134 and the conditioned space to allow conditioned air to flow from the indoor coil 136 to the conditioned space 108 during normal operation modes (e.g., each of the heating mode and the cooling mode).

[0041] The return damper 150 is generally a motorized damper configured to regulate the flow of return air from the conditioned space to the indoor section 104. In some embodiments, the return damper 150 may include adjustable blades connected to an actuator that controls the position of the blades to either allow or restrict airflow 151. The actuator may include an electronic circuit that includes certain electronic components, such as a microcontroller, a motor driver, a power supply circuit, capacitors, resistors, diodes, and transistors. The actuator (e.g., controlled by the controller 160) receives electronic signals and translates the received electronic signals to generate drive signals to adjust the position of the blades. Thus, the return damper 150 may open and close in response to receiving electronic signals from the controller 160. The return damper 150 is configured to allow the flow of recirculated air (e.g., airflow 151) from the conditioned space 108 into the indoor heat exchanger 134 during normal operation modes, such as the heating and cooling modes. For example, during the heating and cooling modes, the return damper 150 may open its blades to permit airflow from the conditioned space 108 to the indoor section 104. During the defrost mode 101, the return damper 150 may remain closed to (at least partially) isolate the conditioned space 108 from the indoor section 104. The return damper 150 is located between the conditioned space 108 and the inlet side of the indoor heat exchanger 134 to allow recirculated air (e.g., airflow 151) to flow into the indoor coil 136 during normal operation modes (e.g., each of the heating mode and the cooling mode).

[0042] The gravity damper 152 is generally a mechanical damper configured to regulate the flow of excess air pressure within the conditioned space 108 by opening automatically in response to a preconfigured pressure differential between the conditioned space 108 and the surrounding environment. In some embodiments, the gravity damper 152 may include hinged or balanced blades that are mechanically calibrated to remain closed under normal conditions and open when the air pressure in the conditioned space 108 becomes more than the atmospheric pressure (e.g., more than 1 atmosphere (atm) or 14.696 pounds per square inch (psi)). Thus, the gravity damper 152 allows the pressure to be relieved by allowing airflow 153 from the conditioned space 108 to the surrounding environment. When the pressure normalizes, the gravity damper 152 closes automatically to maintain the desired pressure in the conditioned space 108.

[0043] The controller 160 is communicatively coupled (e.g., via wired and / or wireless connection) to other components in the HVAC system 100 and configured to control their operations. In some embodiments, controller 160 can be one or more controllers associated with one or more components of the HVAC system 100. The controller 160 includes a processor 162 in signal communication with a memory 166 and an input / output (I / O) interface 164. The processor 162 comprises one or more processors. The processor 162 is any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g., a multi-core processor), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), or digital signal processors (DSPs) that communicatively couples to memory 166 and controls the operation of HVAC system 100. The processor 162 may be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processor 162 is communicatively coupled to, and in signal communication with, the memory 166. The one or more processors are configured to process data and may be implemented in hardware or software. For example, the processor 162 may be 8-bit, 16-bit, 32-bit, 64-bit or of any other suitable architecture. The processor 162 may include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory 166 and executes them by directing the coordinated operations of the ALU, registers, and other components. The processor 162 may include other hardware and software that operates to process information, control the HVAC system 100, and perform any of the functions described herein.

[0044] The processor 162 may be configured to execute software instructions to perform operations of the controller 160. For example, the processor 162 may be configured to execute the software instructions 168 cause the HVAC system 100 to perform on or more of its operations described herein. The processor 162 may execute code / software instructions 168 to perform any of its operations. The processor 162 is not limited to a single processing device and may encompass multiple processing devices. The processor 162 may be configured to perform one or more operations of the controller 160 described in FIGS. 1-3 and one or more operations of the method 300 described in FIG. 3.

[0045] The memory 166 may be a non-transitory computer-readable medium. The memory 166 may include one or more disks, tape drives, or solid-state drives, and may be used as an overflow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 166 may be volatile or non-volatile and may comprise a read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM). The memory 166 is operable to store any suitable set of instructions, logic, rules, and / or code for executing the functions described in this disclosure. For example, the memory 166 may store and retrieve information corresponding to software instructions 168, temperature data 170, threshold temperature 178, electronic signals 172a-h, 174a-d, and / or other data, instructions, and operating parameters for components in the system 100.

[0046] The I / O interface 164 is configured to communicate data and signals with other devices. For example, the I / O interface 164 may be configured to communicate electrical signals with the other components of the HVAC systems 100. The I / O interface 164 may comprise ports and / or terminals for establishing signal communications between the controller 160 and other devices. The I / O interface 164 may be configured to enable wired and / or wireless communications. Connections between various components of the HVAC system 100 and between components of system 100 may be wired or wireless. For example, conventional cables and contacts may be used to couple the controller 160 to various components of the HVAC system 100.

[0047] In some embodiments, a wireless connection may be employed to provide at least some or all of the connections between components of the HVAC system 100. In some embodiments, a data bus may couple various components of the HVAC system 100 together such that data is communicated therebetween. In some embodiments, the data bus may include, for example, any combination of hardware, software embedded in a computer-readable medium, or encoded logic incorporated in hardware or otherwise stored (e.g., firmware) to couple components of the HVAC system 100 to each other.

[0048] As an example and not by way of limitation, the data bus may include an accelerated graphics port (AGP) or other graphics bus, a controller area network (CAN) bus, a front-side bus (FSB), a hypertransport TM (HT) interconnect, an InfiniBand ™ interconnect, a low-pin-count (LPC) bus, a memory bus, a micro channel architecture (MCA) bus, a peripheral component interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a serial advanced technology attachment (SATA) bus, a video electronics standards association local bus (VLB), or any other suitable bus or a combination of two or more of these. In various embodiments, the data bus may include any number, type, or configuration of data buses, where appropriate. In certain embodiments, one or more data buses (which may each include an address bus and a data bus) may couple the controller 160 to other components of the HVAC system 100.Operational flow for operating the HVAC system in the defrost mode

[0049] In some cases, ice may be formed on the surface of the outdoor coil 122 during the heating mode in cold weather (e.g., in winter). Thus, the defrost mode 101 may be required in such situations to melt the ice formed on the outdoor coil 122.

[0050] In operation, the controller 160 may determine whether a condition to operate the HVAC system 100 in the defrost mode 101 is met. For example, the controller 160 may determine whether a condition to operate the HVAC system 100 in the defrost mode is met based on specific criteria, such as whether a predefined time interval has elapsed since the last defrost cycle or whether the temperature at the outdoor coil 122 is less than the ambient temperature by more than a predefined threshold temperature 178 (e.g., more than 5°C, 41°F, etc.). In response to determining that the condition to operate in the defrost mode is met, the controller 160 may initiate the defrost mode to melt the ice from the outdoor coil 122.

[0051] To this end, the controller 160 may control the operation of the dampers (e.g., fresh air damper 144, exhaust damper 146, supply damper 148, and return damper 150). The controller 160 may communicate a first electronic signal 172a to the return damper 150, where the first electronic signal 172a causes the return damper 150 to close and prevent recirculated air (e.g., airflow 151) from flowing from the conditioned space 108 to the indoor heat exchanger 134. The controller 160 may communicate a second electronic signal 172bto the supply damper 148, where the second electronic signal 172b causes the supply damper 148 to close and prevent conditioned air (e.g., airflow) from flowing from the indoor heat exchanger 134 to the conditioned space 108 during the defrost mode. Thus, the conditioned space 108 is (at least partially) isolated during the defrost mode by the closed supply damper 148 and the return damper 150.

[0052] To utilize the ambient air’s heat and melt the ice on the surface of the outdoor coil 122, the controller 160 may open the fresh air damper 144 and the exhaust damper 146. To this end, the controller 160 communicates a third electronic signal 172c to the fresh air damper 144, where the third electronic signal 172c causes the fresh air damper 144 to open and allow ambient air (e.g., airflow 145) to flow from the surrounding environment into the indoor heat exchanger 134 during the defrost mode. The controller 160 may communicate a fourth electronic signal 172d to the exhaust damper 146, where the fourth electronic signal 172d causes the exhaust damper 146 to open and permit air (e.g., airflow 147) to flow from the indoor section 104 to the surrounding environment after passing through the indoor heat exchanger 134 during the defrost mode. In some embodiments, the dampers (e.g., fresh air damper 144, exhaust damper 146, supply damper 148, and return damper 150) may be configured (e.g., opened or closed) in parallel or sequentially in any suitable order.

[0053] After the dampers (e.g., fresh air damper 144, exhaust damper 146, supply damper 148, and return damper 150) are adjusted, the controller 160 may control the flow of refrigerant through the system to defrost the ice on the outdoor coil 122. To this end, the controller 160 may communicate an electronic signal 174a to the valve 114 to adjust it to reverse the refrigerant flow which was initially according to the heating mode to the defrost mode. The electronic signal 174a causes the port 116a to be connected to the port 116, and the port 116c to be connected to port 116d. In the defrost mode 101, the high-temperature refrigerant vapor that is discharged from the compressors’ discharge lines 113 flows toward the valve 114. The valve 114 (now adjusted based on the electronic signal 174a), directs the high-temperature refrigerant vapor from port 116ato port 116b. From port 116b, the high-temperature refrigerant vapor flows into the outdoor coil 122 of the outdoor heat exchanger 120.

[0054] As the high temperature refrigerant flows through the outdoor coil 122, it releases heat to the ice on the surface of the outdoor coil 122 and melts the ice. This process causes at least some amount of the refrigerant to transition from vapor to liquid. The controller 160 may receive temperature data 170 from the temperature sensor circuit 126 to monitor the defrosting process. After passing through the outdoor coil 122, the liquid refrigerant flows out of the outdoor coil 122 and is directed toward the filter dryer 128, where debris and moisture are filtered from the refrigerant. The refrigerant flows through the valve 130 (e.g., an expansion valve) to reduce its pressure and temperature before it enters the indoor heat exchanger 134. The refrigerant then flows into the indoor coil 136 of the indoor heat exchanger 134, where the refrigerant absorbs heat from the ambient air (e.g., airflow 145) introduced through the open fresh air damper 144. This heat exchange process causes the refrigerant to evaporate and transition from a liquid and vapor mixture to a vaporized refrigerant.

[0055] As the vaporized refrigerant exits the indoor coil 136, it is directed back toward the valve 114 (at the port 116c). The valve 114 (which is configured in the defrost mode 101), directs the refrigerant from port 116c to port 116d. From port 116d, the refrigerant passes through the valve 142 and flows back to the accumulator 140. The liquid and vapor refrigerant is collected in the accumulator 140 and the vapor refrigerant flows from the accumulator 140 toward the compressors 112. This completes the refrigerant cycle during the defrost mode 101. The controller 160 may monitor system conditions to determine whether to exit the defrost mode 101.Operational flow for operating the HVAC system to exit the defrost mode

[0056] FIG. 2 illustrates the HVAC system 100 when exiting the defrost mode 101, according to some embodiments. The components of the HVAC system 100 are described in the description of FIG. 1 and are not repeated in the description of FIG. 2. In operation, the controller 160 may determine whether the condition to operate in the defrost mode 101 is no longer met. For example, the controller 160 may evaluate system conditions such as temperature data 170 from the temperature sensor circuit 126 to determine if the ice on the outdoor coil 122 has melted. In this example, if the controller 160 determines that the temperature at the outdoor coil 122 is no longer less than the ambient temperature by more than the predefined threshold temperature 178 (temperature difference / range), the controller 160 may determine that the ice on the outdoor coil 122 has melted. In another example, the controller 160 may determine that a predefined duration for the defrost mode 101 has elapsed.

[0057] In response to determining that the condition to operate in the defrost mode is no longer met, the controller 160 may initiate the transition back to the normal operating mode, such as the heating mode 201 or cooling mode. For cooling mode, the refrigerant flow connection in the HVAC system 100 is the same as shown and described in FIG. 1, but the damper side air flow is similar to the configuration shown in for the heating mode 201 in FIG. 2. To this end, the controller 160 may communicate electronic signals to certain components to reconfigure the HVAC system 100 and the flow of the refrigerant. To this end, the controller 160 may communicate a fifth electronic signal 172e to the return damper 150 to open the return damper 150. This allows recirculated air (e.g., airflow 151) to flow from the conditioned space 108 to the indoor heat exchanger 134.

[0058] The controller 160 may communicate a sixth electronic signal 172f to the supply damper 148 to open the supply damper 148 to enable the conditioned air (e.g., airflow) to flow from the indoor heat exchanger 134 into the conditioned space 108. The controller 160 may communicate a seventh electronic signal 172g to the fresh air damper 144 to close the fresh air damper 144 and to prevent ambient air (e.g., airflow 145 (see FIG. 1)) from entering the indoor heat exchanger 134. The controller 160 may communicate an eighth electronic signal 172hto the exhaust damper 146 to close the exhaust damper 146 and to block airflow (e.g., airflow 147 (see FIG. 1)) from exiting the indoor section 104 to the surrounding environment. The controller 160 may communicate an electronic signal 174b to the valve 114 to reconfigure the paths between the ports 116a-d from the defrost mode back to the normal operating mode (e.g., heating or cooling mode). The electronic signal 174b may cause the port connections to be reconfigured depending on the operation demand, similar to that described in FIG. 1.

[0059] After the dampers (e.g., fresh air damper 144, exhaust damper 146, supply damper 148, and return damper 150) are adjusted and the valve 114 is reconfigured, the refrigerant cycle resumes for the normal operating mode. For example, in the heating mode, high-temperature refrigerant vapor flows from the compressors’ discharge lines 113 to the indoor coil 136, where it releases heat into the conditioned space 108. In some embodiments, the controller 160 may switch between the normal conditioning operation (e.g., heating or cooling mode) and the defrost mode as needed according to the conditions associated with the defrost mode, similar to that described in FIGS. 1 and 2.Example method for operating an HVAC system

[0060] FIG. 3 illustrates a flowchart of an example method 300 of operating the system 100 of FIG. 1. The method 300 may be performed by the controller 160 (see FIG. 1) when one or more processors (e.g., processor 162 of FIG. 1) execute software instructions (e.g., software instructions 168) stored in one or more memories (e.g., memory 166 of FIG. 1). The method 300 may include operations 302-318. Modifications, additions, or omissions may be made to method 300. Method 300 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order.

[0061] At operation 302, the method 300 begins as the controller 160 determines whether a condition to operate in a defrost mode for an outdoor coil 122 is met, similar to that described in FIG. 1. If it is determined that the condition to operate in the defrost mode for the outdoor coil 122 is met, the method 300 proceeds to operation 304. Otherwise, the method 300 proceeds to operation 312.

[0062] At operation 304, the controller 160 communicates a first electronic signal 172a to the return damper 150 to close the return damper 150, similar to that described in FIG. 1, and the method 300 proceeds to operation 306.

[0063] At operation 306, the controller 160 communicates a second electronic signal 172b to the supply damper 148 to close the supply damper 148, similar to that described in FIG. 1, and the method 300 proceeds to operation 308.

[0064] At operation 308, the controller 160 communicates a third electronic signal 172c to the fresh air damper 144 to open the fresh air damper 144, similar to that described in FIG. 1, and the method 300 proceeds to operation 310.

[0065] At operation 310, the controller 160 communicates a fourth electronic signal 172d to the exhaust damper 146 to open the exhaust damper 146, similar to that described in FIG. 1, and the method 300 ends.

[0066] The controller 160 may communicate the electronic signal 174a to the valve 114 to configure the flow paths for the refrigerant, similar to that described in FIG. 1.

[0067] At operation 312, the controller 160 communicates a fifth electronic signal 172e to the return damper 150 to open the return damper 150, similar to that described in FIG. 2, and the method 300 proceeds to operation 314.

[0068] At operation 314, the controller 160 communicates a sixth electronic signal 172f to the supply damper 148 to open the supply damper 148, similar to that described in FIG. 2, and the method 300 proceeds to operation 316.

[0069] At operation 316, the controller 160 communicates a seventh electronic signal 172g to the fresh air damper 144 to close the fresh air damper 144, similar to that described in FIG. 2, and the method 300 proceeds to operation 318.

[0070] At operation 318, the method 300 ends as the controller 160 communicates an eighth electronic signal 172h to the exhaust damper 146 to close the exhaust damper 146, similar to that described in FIG. 2. The controller 160 may communicate the electronic signal 174b to the valve 114 to reconfigure the flow paths for the refrigerant, similar to that described in FIGS. 1-3.

[0071] Although this disclosure has been described in terms of certain embodiments, alterations, and permutations, embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure.

[0072] While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated with another system or certain features may be omitted, or not implemented.

[0073] In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

[0074] To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants note that they do not intend any of the appended claims to invoke 35 U.S.C. § 112(f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.

Examples

example method

Example method for operating an HVAC system

[0060]FIG. 3 illustrates a flowchart of an example method 300 of operating the system 100 of FIG. 1. The method 300 may be performed by the controller 160 (see FIG. 1) when one or more processors (e.g., processor 162 of FIG. 1) execute software instructions (e.g., software instructions 168) stored in one or more memories (e.g., memory 166 of FIG. 1). The method 300 may include operations 302-318. Modifications, additions, or omissions may be made to method 300. Method 300 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order.

[0061]At operation 302, the method 300 begins as the controller 160 determines whether a condition to operate in a defrost mode for an outdoor coil 122 is met, similar to that described in FIG. 1. If it is determined that the condition to operate in the defrost mode for the outdoor coil 122 is met, the method 300 proceeds to operation 304. Otherwise, ...

TECHNICAL FIELD

[0001] This disclosure relates generally to Heating, Ventilation, and Air Conditioning (HVAC) systems. More particularly, this disclosure relates to the system and method for defrosting outdoor coils in reversible rooftop units.BACKGROUND

[0002] Heating, ventilation, and air conditioning (HVAC) systems are used to regulate environmental conditions within an enclosed space. Air is cooled via heat transfer with refrigerant flowing through the HVAC system and returned to the enclosed space as conditioned air.SUMMARY OF THE DISCLOSURE

[0003] Some Heating, Ventilation, and Air Conditioning (HVAC) systems use reversible rooftop units to provide both heating and cooling for buildings or any physical space by reversing the refrigerant cycle as needed. During cold weather, such as winter, in a heating mode, the outdoor coil often operates at temperatures below freezing temperature (e.g., 32 Fahrenheit (°F) or 0 Celsius (°C)) to extract heat from the cold ambient air. However, in some cases, the low operating temperature causes moisture in the air to condense and freeze on the surface of the outdoor coil and form ice. The ice acts as a barrier and reduces the capability to absorb heat from the surrounding environment when needed.

[0004] One approach to address the issue of defrosting ice from the outdoor coils is to implement a defrost mode to melt the ice on the outdoor coil. In some conventional defrost modes to melt the ice on the outdoor coil, the HVAC system temporarily reverses the refrigerant flow to use the heat from the conditioned space to melt the ice on the outdoor coil. This results in the indoor coil to absorb heat from the conditioned space to melt the ice formed on the surface of the outdoor coil. However, this approach leads to extracting heat from the conditioned space which is the opposite of providing heat to the conditioned space during the heating mode and therefore, discomfort for people in the conditioned space. Further, this approach leads to an increased energy consumption of the HVAC system to restore the lost heat to the conditioned space This, in turn, increases the load on the HVAC system.

[0005] The disclosed system provides a solution to these and other technical problems of conventional HVAC systems. In some embodiments, the disclosed system is configured to use ambient air to facilitate defrosting of the outdoor coil while (at least partially) isolating the conditioned space during the defrost mode Therefore the heat from the conditioned space is not drawn into the indoor coil This, in turn, maintains the conditioned air within the conditioned space. Further, the additional energy that would otherwise be spent on restoring the lost heat to the conditioned space is obviated. Therefore, the load of the HVAC system is reduced compared to some conventional HVAC systems where the heat from the conditioned space is used to defrost the outdoor coil during the defrost operation.

[0006] In some embodiments, the disclosed HVAC system may include an indoor coil, an outdoor coil, a valve, a return damper, a supply damper, a fresh air damper, an exhaust damper, and a controller. The indoor coil may include an inlet side and an outlet side. The indoor coil is configured to condense refrigerant during a heating mode as the refrigerant in vapor form flows through the indoor coil, releases heat to a conditioned space, and transitions into liquid. The indoor coil is further configured to evaporate the refrigerant during a cooling mode as the refrigerant in liquid form flows through the indoor coil, absorbs heat from the conditioned space, and transitions into vapor.

[0007] The outdoor coil may include an inlet side and an outlet side. The outdoor coil is configured to evaporate the refrigerant during the heating mode as the refrigerant in liquid form flows through the outdoor coil, absorbs heat from ambient air, and transitions into vapor. The outdoor coil is further configured to condense the refrigerant during the cooling mode as the refrigerant in vapor form flows through the outdoor coil, releases heat to the ambient air, and transitions into liquid. The valve is positioned between a compressor and the outdoor coil. The valve is configured to reverse a flow of refrigerant between the indoor coil and outdoor coil during a transition between the heating mode and the defrost mode.

[0008] The return damper is positioned between a conditioned space and an inlet side of the indoor coil. The return damper is configured to allow recirculated air to flow from the conditioned space to the indoor coil during each of the heating mode and the cooling mode. The supply damper is positioned between an outlet side of the indoor coil and the conditioned space. The supply damper is configured to allow conditioned air to flow from the indoor coil to the conditioned space during each of the heating mode and the cooling mode. The fresh air damper is positioned upstream of the inlet side of the indoor coil. The fresh air damper is configured to allow ambient air to flow through the indoor coil during the defrost mode. The fresh air damper is also configured to allow ambient air to flow through indoor coil to the conditioned space during “Free Cooling” (e.g., approximately 45 °F or 7 °C when in cooling mode) and allow ambient air flow when the conditioned space CO2 concentration levels are higher. The exhaust damper is positioned downstream of the outlet side of the indoor coil. The exhaust damper is configured to allow airflow to the surrounding environment after passing through the indoor coil during a defrost mode. The exhaust damper is also used to maintain the pressure level inside the conditioned space. The controller is operably coupled with the return damper, the supply damper, the fresh air damper, and the exhaust damper. The controller comprises a processor configured to determine that a condition to operate in the defrost mode for the outdoor coil is met. In response to determining that the condition to operate in the defrost mode for the outdoor coil is met, the process is configured to communicate a first electronic signal to the return damper to close the return damper, communicate a second electronic signal to the supply damper to close the supply damper, communicate a third electronic signal to the fresh air damper to open the fresh air damper and communicate a fourth electronic signal to the exhaust damper to open the exhaust damper.

[0009] Certain embodiments of the present disclosure may include some, or none of these advantages. These advantages and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:

[0011] FIG. 1 illustrates a diagram of an embodiment of a Heating, Ventilation, and Air Conditioning (HVAC) system operating in a defrost mode, according to some embodiments of the present disclosure;

[0012] FIG. 2 illustrates a diagram of an embodiment of the HVAC system of FIG. 1 operating in a heating mode, according to some embodiments of the present disclosure; and

[0013] FIG. 3 illustrates a flowchart of an example method of operating the HVAC system of FIGS. 1-2.DETAILED DESCRIPTION

[0014] Embodiments of the present disclosure and its advantages are best understood by referring to FIGS. 1 through 3 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

[0015] Some Heating, Ventilation, and Air Conditioning (HVAC) systems use reversible rooftop units to provide both heating and cooling for buildings or any physical space by reversing the refrigerant cycle as needed. During cold weather, such as winter, in a heating mode, the outdoor coil often operates at temperatures below freezing temperature (e.g., 32 Fahrenheit (°F) or 0 Celsius (°C)) to extract heat from the cold ambient air. However, in some cases, the low operating temperature causes moisture in the air to condense and freeze on the surface of the outdoor coil and form ice. The ice acts a barrier and reduces the capability to absorb heat from the surrounding environment when needed.

[0016] One approach to address the issue of defrosting ice from the outdoor coils is to implement a defrost mode to melt the ice on the outdoor coil. In some conventional defrost modes to melt the ice on the outdoor coil, the HVAC system temporarily reverses the refrigerant flow to use the heat from the conditioned space to melt the ice on the outdoor coil. This results in the indoor coil to absorb heat from the conditioned space to melt the ice formed on the surface of the outdoor coil. However, this approach leads to extracting heat from the conditioned space which is the opposite of providing heat to the conditioned space during the heating mode and therefore, discomfort for people in the conditioned space. Further, this approach leads to an increased energy consumption of the HVAC system to restore the lost heat to the conditioned space This, in turn, increases the load on the HVAC system.

[0017] The disclosed system provides a solution to these and other technical problems of conventional HVAC systems. In some embodiments, the disclosed system is configured to use ambient air to facilitate defrosting of the outdoor coil while (at least partially) isolating the conditioned space during the defrost mode. Therefore the heat from the conditioned space is not drawn into the indoor coil. This, in turn, maintains the conditioned air within the conditioned space. Further, the additional energy that would otherwise be spent on restoring the lost heat to the conditioned space is obviated. Therefore, the load of the HVAC system is reduced compared to some conventional HVAC systems where the heat from the conditioned space is used to defrost the outdoor coil during the defrost operation.HVAC system

[0018] FIG. 1 illustrates an example Heating, Ventilation, and Air Conditioning (HVAC) system 100 according to an embodiment of the present disclosure. In general, the HVAC system 100 is configured to (at least partially) isolate a conditioned space during a defrost mode 101 for defrosting ice on the surface of an outdoor coil and instead, use heat from the ambient air to defrost the ice formed on the surface of the outdoor coil. In the present disclosure, it is understood that the term ‘isolate’ is not intended to mean complete or absolute isolation but rather refers to the HVAC system 100 and its ability to restrict airflow between the conditioned space and the rest of the HVAC system 100 during the defrost mode 101 to the extent necessary for operating the HVAC system, while allowing limited or controlled airflow in and out of the conditioned space, as required, to maintain balance and operational requirements.

[0019] In some embodiments, the HVAC system 100 comprises refrigerant conduit subsystems 102, one or more compressors 112, a valve 114, an outdoor heat exchanger 120 (which includes an outdoor coil 122, fans 124, and a temperature sensor circuit 126), a filter dryer 128, a valve 130, an indoor heat exchanger 134 (which includes an indoor coil 136), a blower 138, an accumulator 140, a valve 142, a fresh air damper 144, an exhaust damper 146, a supply damper 148, a return air damper 150, a gravity damper 152, and a controller 160.

[0020] In some embodiments, the HVAC system 100 includes a rooftop unit (RTU) that is positioned on the roof of a building, and the conditioned air is delivered into the interior of the building. In other embodiments, portion(s) of the system 100 may be located within the building and portion(s) outside the building. The HVAC system 100 may be configured as shown in FIG. 1 or in any other suitable configuration. For example, the HVAC system 100 may include additional components or may omit one or more components shown in FIG. 1.System Components

[0021] Some components of the HVAC system 100 may be located in an outdoor section 106 of the HVAC system 100 and other components may be in an indoor section 104 of the HVAC system 100. For example, the compressors 112, valve 114, outdoor heat exchanger 120, filter dryer 128, valve 130, accumulator 140, and valve 142 may be located in the outdoor section 106, and the indoor heat exchanger 134, blower 138, fresh air damper 144, exhaust damper 146, supply damper 148, return air damper 150, and gravity damper 152 may be located in the indoor section 104. The controller 160 may be on-site (e.g., in a building) where the HVAC system 100 is implemented. In some applications, the controller 160 may be incorporated within the outdoor section 106.

[0022] The refrigerant conduit subsystems 102 facilitate the movement of a refrigerant (also referred to herein as a working fluid) through a refrigerant cycle such that the working fluid flows as illustrated by arrows in FIG. 1. The refrigerant conduit subsystem 102 includes any conduit, tubing and the like that is illustrated in FIG. 1 fluidly connecting components of the HVAC system 100.

[0023] Each of the compressors 112 may be a variable speed compressor or a multiple-stage compressor and is generally configured to compress (e.g., increase the pressure of) the refrigerant. The HVAC system 100 may include any number of compressors 112 for one or more conditioning applications, such as for multiple floors and rooms in a building. The compressor 112 is fluidly coupled with the refrigerant conduit subsystem 102 and may be positioned downstream of the accumulator 140 and upstream of the valve 114. The compressor 112 may be in signal communication with the controller 160 using wired and / or wireless connections. The controller 160 may communicate electronic signals to the compressor 112 to control its operations. A variable-speed compressor is generally configured to operate at different speeds to increase the pressure of the refrigerant to keep the refrigerant moving along the fluid conduit subsystem 102. In the variable-speed compressor configuration, the speed of compressor 112 can be modified to adjust the cooling capacity and / or load of the HVAC system 100. Meanwhile, in the multi-stage compressor configuration, one or more compressors can be turned on or off to adjust the cooling capacity of the HVAC system 100.

[0024] The valve 114 may be an expansion valve, a flow control valve, a solenoid valve, a motorized valve, an electronic expansion valve (EEV), a thermal expansion valve (TXV), or any other suitable valve configured to control the flow of refrigerant. The valve 114 may be fluidly coupled with the refrigerant conduit subsystem 102 and positioned between the outdoor heat exchanger 120, the indoor heat exchanger 134, the compressor discharge lines 113, and valve 142. The valve 114 may be a four-way switch valve that changes the flow of the refrigerant depending on a mode of operation, such as in cooling mode, a heating mode, and a defrost mode 101. For example, the valve 114 may include a plunger or a sliding component inside it to switch the connections or paths between the ports 116a-d as needed. The valve 114 includes four ports 116d to port 116c or to port 116b to allow changing the flow of the refrigerant depending on the mode of operation. The port 116a may be connected to the compressors’ discharge lines 113, and each of the port 116b and the port 116d may be connected to the valve 142 depending on the operating mode. The plunger of valve 114 allows switching the port connection from the port 116d to port 116c or port 116b based on the conditioned space demand. The term ‘cooling mode’ refers to the mode of operation of the HVAC system 100 when the conditioning demand for the conditioned space 108 is a cooling demand. The term ‘heating mode’ refers to the mode of operation of the HVAC system 100 when the conditioning demand for the conditioned space 108 is a heating demand. The term ‘defrost mode’ refers to the mode of operation of the HVAC system 100 when the HVAC system 100 operates to defrost the outdoor coil 122. For example, in the cooling mode, the valve 114 directs the flow of the refrigerant from the discharge lines 113 of the compressors 112 to the outdoor heat exchanger 120 by connecting the port 116a to port 116b, and directs the flow of the refrigerant from the indoor heat exchanger 134 to the valve 142 by connecting the port 116c to port 116d.

[0025] In the heating mode, the valve 114 directs the flow of the refrigerant from the compressors’ discharge lines 113 to the indoor heat exchanger 134 by connecting the port 116a to port 116c, and directs the flow of the refrigerant from the outdoor heat exchanger 120 to the valve 142 by connecting the port 116b to port 116d. In the defrost mode 101, the valve 114 operates similarly to cooling mode, directing high-temperature refrigerant from the compressors’ discharge lines 113 to the outdoor heat exchanger 120 to facilitate defrosting ice on the outdoor coil. Therefore, the valve 114 is configured to reverse a flow of refrigerant between the indoor coil 136 and outdoor coil 122 during a transition between the heating mode and the defrost mode 101. The valve 114 may regulate the flow and pressure of the refrigerant. The controller 160 may be in signal communication with the valve 114 (e.g., via wired and / or wireless communication) to control its operations and configure the connections between the ports 116a-d for each mode of operation by sending electronic signals 174. The valve 114 is configured to adjust its opening to regulate the flow and pressure of the refrigerant as it transitions through the modes of operations.

[0026] The outdoor heat exchanger 120 may generally be a high-side heat exchanger, such as a gas cooler or a condenser, and is configured to transfer heat between the refrigerant and the surrounding outdoor environment. The outdoor heat exchanger 120 comprises an outdoor coil 122, one or more fans 124, and a temperature sensor circuit 126. The outdoor heat exchanger 120 is fluidly coupled with the refrigerant conduit subsystem 102 and positioned downstream of the valve 114 and upstream of the filter dryer 128 and valve 130 (in the defrost mode and cooling mode).

[0027] The outdoor coil 122 may include metallic components, such as fins, tubes, and microchannels. During the cooling mode, the outdoor heat exchanger 120 functions as a condenser, where the refrigerant in vapor form flows through the outdoor coil 122 and releases heat into the outdoor environment. During the heating mode, the outdoor heat exchanger 120 functions as an evaporator, where the refrigerant in liquid form flows through the outdoor coil 122, absorbs heat from the ambient air, and transitions into vapor. The refrigerant may enter through the outlet side 123 of the outdoor coil 122 and exit through its inlet side 121 In defrost mode 101, the outdoor coil 122 receives high-temperature refrigerant from the compressors 112 to melt the ice formed on the surface of the outdoor coil 122. The refrigerant may enter through the inlet side 121 of the outdoor coil 122 and exit through its outlet side 123.

[0028] The fans 124 are operably coupled to the outdoor coil 122 and configured to move air across the coil to facilitate faster heat transfer between the refrigerant and the surrounding environment. The fans 124 may be controlled by the controller 160 (e.g., via wired and / or wireless communication) to adjust the fan speed based on system conditions, such as the temperature detected by the temperature sensor circuit 126 and the cooling or heating demand. The outdoor heat exchanger 120 may allow the airflow 125 to pass through the outdoor coil 122 and exit through the fans 124 on another side of the outdoor heat exchanger 120.

[0029] The temperature sensor circuit 126 may include a temperature sensing element and circuitry. The temperature sensor circuit 126 may be implemented by a hardware circuit and configured to detect the temperature of the outdoor coil 122. The temperature sensor circuit 126 may include one or more temperature sensor circuits 126. The temperature sensor circuit 126 may include a temperature sensing element such as a thermocouple, a thermistor, a semiconductor-based temperature circuit board, or any other type of temperature sensor. In some examples, the temperature sensor circuit 126 may be positioned within the outdoor heat exchanger 120, on the surface of the outdoor coil 122, or at any other location. The temperature sensor circuit 126 may be attached to a surface using any appropriate means (e.g., threaded connections, clamps, adhesives, or the like). The temperature sensor circuit 126 is configured to detect the temperature of the outdoor coil 122 periodically (e.g., every second, every minute, etc.) and / or on demand (e.g., in response to a request from the controller 160). The temperature sensor circuit 126 is in signal communication with the controller 160 using wired and / or wireless connections. The temperature sensor circuit 126 may provide the detected temperature data 170 (which includes the detected temperature of the outdoor coil 122) to the controller 160. The controller 160 may use the temperature data 170 for evaluating whether to operate in the defrost mode 101.

[0030] The filter dryer 128 is generally a component configured to filter debris and remove moisture from the refrigerant as it flows through the HVAC system 100. The filter dryer 128 is fluidly coupled with the refrigerant conduit subsystem 102 and positioned downstream of the outdoor heat exchanger 120 and upstream of the valve 130 and the indoor heat exchanger 134 (in the cooling and defrost modes). The filter dryer 128 may include a filtering element, such as mesh screens or filter pads, to capture dirt, debris, or any other contaminants present in the refrigerant. The filter dryer 128 may be bi-directional, to allow the refrigerant to flow in either direction, depending on the mode of operation. For example, during each of the cooling and defrost modes, the refrigerant flows from the outdoor heat exchanger 120 toward the indoor heat exchanger 134 through the filter dryer 128. In the heating mode, the refrigerant flows from the indoor heat exchanger 134 to the outdoor heat exchanger 120 through the filter dryer 128.

[0031] The valve 130 may be an expansion valve, a flow control valve, a solenoid valve, a motorized valve, an EEV, a TXV, or any other suitable valve configured to control the flow of refrigerant. The valve 130 may be fluidly coupled with the refrigerant conduit subsystem 102 and positioned between the filter dryer 128 and the indoor heat exchanger 134. The valve 130 may regulate the flow and pressure of the refrigerant. In some embodiments, the valve 130 may be active. In this manner, active means that valve 130 may be controlled by the controller 160. For example, the controller 160 may be in signal communication with the valve 130 (e.g., via wired and / or wireless communication) to control its operations. In some embodiments, the valve 130 may be passive. In this manner, passive means that valve 130 may be mechanically calibrated to open and close based on preconfigured pressure differential across the valve. The valve 130 is configured to adjust its opening to regulate the flow and pressure of the refrigerant as needed.

[0032] The indoor heat exchanger 134 may generally include an indoor coil 136 and fans (e.g., blower 138) to move air across the coils. The indoor heat exchanger 134 is configured to facilitate the heat transfer between the refrigerant and the air within the conditioned space 108. The indoor heat exchanger 134 is fluidly coupled with the refrigerant conduit subsystem 102 and positioned downstream of the valve 130 and upstream of the accumulator 140 in the cooling mode (in the cooling and defrost modes). The indoor heat exchanger 134 is in signal communication with the controller 160 using wired and / or wireless connections. The controller 160 may send control signals to the indoor heat exchanger 134 to control the speed of the fans based on temperature conditions and the cooling demand.

[0033] The indoor coil 136 may include metallic components, such as fins, tubes, and microchannels. For example, in each of the cooling and defrost mode, the refrigerant cools metallic components (e.g., metallic coils, plates, and / or tubes) of the indoor heat exchanger 134 as the refrigerant passes through them. These metallic components may then cool the air around them. The cooled air may then be circulated such as, for example, by a fan to cool a space such as, for example, a room in a building. During each of the defrost and cooling modes, the indoor heat exchanger 134 functions as an evaporator, where the refrigerant in liquid form flows through the indoor coil 136, absorbs heat from the air in the conditioned space 108, and at least some amount of the refrigerant transitions into vapor. During the heating mode, the indoor heat exchanger 134 functions as a condenser, where the refrigerant in vapor form flows through the indoor coil 136, releases heat to the conditioned space, and at least some amount of the refrigerant transitions into liquid. The refrigerant may enter through the inlet side 137 of the indoor coil 136 and exit through its outlet side 135.

[0034] The blower 138 is generally a fan operably coupled to the indoor coil 136 and is configured to move air across the indoor coil 136 to facilitate heat exchange between the refrigerant flowing through the indoor coil 136 and the air in the conditioned space 108. This leads to airflow 145 flowing out of the blower 138. The blower 138 may be controlled by the controller 160 (e.g., via wired and / or wireless communication) to adjust its speed based on system conditions, such as temperature data and cooling or heating demand. In some embodiments, the blower 138 may be a component of the indoor heat exchanger 134.

[0035] The accumulator 140 may be a physical storage configured to collect and store refrigerant as it enters the compressors 112. The accumulator 140 is fluidly coupled with the refrigerant conduit subsystem 102 and positioned downstream of the valve 142 and upstream of the compressors’ suction lines 111. The accumulator 140 serves as a buffer to reduce the likelihood of liquid refrigerant from reaching the compressors. The accumulator 140 may separate any remaining liquid from the refrigerant vapor to allow vapor to flow toward the compressors 112. The liquid refrigerant is collected at the bottom of the accumulator 140 and the vapor refrigerant is collected on top of the accumulator 140. The accumulator 140 may be in signal communication with the controller 160 using wired and / or wireless connections.

[0036] The valve 142 may be an expansion valve, a flow control valve, a solenoid valve, a motorized valve, an EEV, a TXV, or any other suitable valve configured to control the flow of refrigerant. The valve 142 may be fluidly coupled with the refrigerant conduit subsystem 102 and positioned between the valve 114 and the accumulator 140. The valve 142 may regulate the flow and pressure of the refrigerant. In some embodiments, the valve 142 may be active—meaning that it may be controlled by the controller 160. For example, the controller 160 may be in signal communication with the valve 142 (e.g., via wired and / or wireless communication) to control its operations. In some embodiments, the valve 142 may be passive—meaning that it may be mechanically calibrated to open and close based on preconfigured pressure differential across the valve. The valve 142 is configured to adjust its opening to regulate the flow and pressure of the refrigerant as needed.

[0037] The fresh air damper 144 is generally a motorized damper configured to regulate the intake of fresh ambient air into the indoor section 104. In some embodiments, the fresh air damper 144 may include adjustable blades connected to an actuator that controls the position of the blades to either allow or restrict airflow 145. The actuator may include an electronic circuit that includes certain electronic components, such as a microcontroller, a motor driver, a power supply circuit, capacitors, resistors, diodes, and transistors. The actuator (e.g., controlled by the controller 160) receives electronic signals and translates the received electronic signals to generate drive signals to adjust the position of the blades. Thus, the fresh air damper 144 may open and close in response to receiving electronic signals from the controller 160.

[0038] The fresh air damper 144 is configured to introduce fresh air into the indoor heat exchanger 134 during specific operation modes, such as the heating mode, defrost mode and the cooling mode. For example, during each of the heating mode, defrost mode and cooling mode, the fresh air damper 144 may open its blades to permit the airflow 145 of ambient air into the indoor section 104. The fresh air damper 144 is positioned upstream of the inlet side of the indoor heat exchanger 134 to allow ambient air to flow through the indoor coil 136 during the defrost mode.

[0039] The exhaust damper 146 is generally a motorized damper configured to regulate the expulsion of air from the indoor section 104 to the ambient environment. In some embodiments, the exhaust damper 146 may include adjustable blades connected to an actuator that controls the position of the blades to either allow or restrict airflow 147. The actuator may include an electronic circuit that includes certain electronic components, such as a microcontroller, a motor driver, a power supply circuit, capacitors, resistors, diodes, and transistors. The actuator (e.g., controlled by the controller 160) receives electronic signals and translates the received electronic signals to generate drive signals to adjust the position of the blades. Thus, the exhaust damper 146 may open and close in response to receiving electronic signals from the controller 160. The exhaust damper 146 is configured to expel air that has passed through the indoor heat exchanger 134 (and its coil 136) during the defrost mode. For example, during the defrost mode, the exhaust damper 146 may open its blades to permit airflow 147 out of the indoor section 104 into the surrounding environment. The exhaust damper 146 is positioned downstream of the outlet side of the indoor heat exchanger 134 to allow airflow 147 to the surrounding environment after passing through the indoor coil 136 during the defrost mode.

[0040] The supply damper 148 is generally a motorized damper configured to regulate the flow of conditioned air from the indoor section 104 to the conditioned space 108. In some embodiments, the supply damper 148 may include adjustable blades connected to an actuator that controls the position of the blades to either allow or restrict airflow 147. The actuator may include an electronic circuit that includes certain electronic components, such as a microcontroller, a motor driver, a power supply circuit, capacitors, resistors, diodes, and transistors. The actuator (e.g., controlled by the controller 160) receives electronic signals and translates the received electronic signals to generate drive signals to adjust the position of the blades. Thus, the supply damper 148 may open and close in response to receiving electronic signals from the controller 160. The supply damper 148 is configured to direct conditioned air (that is conditioned by the indoor heat exchanger 134) into the conditioned space 108 during normal operation modes, such as the heating and cooling modes. For example, during each of the heating and cooling modes, the supply damper 148 may open its blades to permit airflow into the conditioned space 108. During the defrost mode 101, the supply damper 148 may remain closed to (at least partially) isolate the conditioned space 108 from the airflow in the indoor section 104. The supply damper 148 is located between the outlet side of the indoor heat exchanger 134 and the conditioned space to allow conditioned air to flow from the indoor coil 136 to the conditioned space 108 during normal operation modes (e.g., each of the heating mode and the cooling mode).

[0041] The return damper 150 is generally a motorized damper configured to regulate the flow of return air from the conditioned space to the indoor section 104. In some embodiments, the return damper 150 may include adjustable blades connected to an actuator that controls the position of the blades to either allow or restrict airflow 151. The actuator may include an electronic circuit that includes certain electronic components, such as a microcontroller, a motor driver, a power supply circuit, capacitors, resistors, diodes, and transistors. The actuator (e.g., controlled by the controller 160) receives electronic signals and translates the received electronic signals to generate drive signals to adjust the position of the blades. Thus, the return damper 150 may open and close in response to receiving electronic signals from the controller 160. The return damper 150 is configured to allow the flow of recirculated air (e.g., airflow 151) from the conditioned space 108 into the indoor heat exchanger 134 during normal operation modes, such as the heating and cooling modes. For example, during the heating and cooling modes, the return damper 150 may open its blades to permit airflow from the conditioned space 108 to the indoor section 104. During the defrost mode 101, the return damper 150 may remain closed to (at least partially) isolate the conditioned space 108 from the indoor section 104. The return damper 150 is located between the conditioned space 108 and the inlet side of the indoor heat exchanger 134 to allow recirculated air (e.g., airflow 151) to flow into the indoor coil 136 during normal operation modes (e.g., each of the heating mode and the cooling mode).

[0042] The gravity damper 152 is generally a mechanical damper configured to regulate the flow of excess air pressure within the conditioned space 108 by opening automatically in response to a preconfigured pressure differential between the conditioned space 108 and the surrounding environment. In some embodiments, the gravity damper 152 may include hinged or balanced blades that are mechanically calibrated to remain closed under normal conditions and open when the air pressure in the conditioned space 108 becomes more than the atmospheric pressure (e.g., more than 1 atmosphere (atm) or 14.696 pounds per square inch (psi)). Thus, the gravity damper 152 allows the pressure to be relieved by allowing airflow 153 from the conditioned space 108 to the surrounding environment. When the pressure normalizes, the gravity damper 152 closes automatically to maintain the desired pressure in the conditioned space 108.

[0043] The controller 160 is communicatively coupled (e.g., via wired and / or wireless connection) to other components in the HVAC system 100 and configured to control their operations. In some embodiments, controller 160 can be one or more controllers associated with one or more components of the HVAC system 100. The controller 160 includes a processor 162 in signal communication with a memory 166 and an input / output (I / O) interface 164. The processor 162 comprises one or more processors. The processor 162 is any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g., a multi-core processor), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), or digital signal processors (DSPs) that communicatively couples to memory 166 and controls the operation of HVAC system 100. The processor 162 may be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processor 162 is communicatively coupled to, and in signal communication with, the memory 166. The one or more processors are configured to process data and may be implemented in hardware or software. For example, the processor 162 may be 8-bit, 16-bit, 32-bit, 64-bit or of any other suitable architecture. The processor 162 may include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory 166 and executes them by directing the coordinated operations of the ALU, registers, and other components. The processor 162 may include other hardware and software that operates to process information, control the HVAC system 100, and perform any of the functions described herein.

[0044] The processor 162 may be configured to execute software instructions to perform operations of the controller 160. For example, the processor 162 may be configured to execute the software instructions 168 cause the HVAC system 100 to perform on or more of its operations described herein. The processor 162 may execute code / software instructions 168 to perform any of its operations. The processor 162 is not limited to a single processing device and may encompass multiple processing devices. The processor 162 may be configured to perform one or more operations of the controller 160 described in FIGS. 1-3 and one or more operations of the method 300 described in FIG. 3.

[0045] The memory 166 may be a non-transitory computer-readable medium. The memory 166 may include one or more disks, tape drives, or solid-state drives, and may be used as an overflow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 166 may be volatile or non-volatile and may comprise a read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM). The memory 166 is operable to store any suitable set of instructions, logic, rules, and / or code for executing the functions described in this disclosure. For example, the memory 166 may store and retrieve information corresponding to software instructions 168, temperature data 170, threshold temperature 178, electronic signals 172a-h, 174a-d, and / or other data, instructions, and operating parameters for components in the system 100.

[0046] The I / O interface 164 is configured to communicate data and signals with other devices. For example, the I / O interface 164 may be configured to communicate electrical signals with the other components of the HVAC systems 100. The I / O interface 164 may comprise ports and / or terminals for establishing signal communications between the controller 160 and other devices. The I / O interface 164 may be configured to enable wired and / or wireless communications. Connections between various components of the HVAC system 100 and between components of system 100 may be wired or wireless. For example, conventional cables and contacts may be used to couple the controller 160 to various components of the HVAC system 100.

[0047] In some embodiments, a wireless connection may be employed to provide at least some or all of the connections between components of the HVAC system 100. In some embodiments, a data bus may couple various components of the HVAC system 100 together such that data is communicated therebetween. In some embodiments, the data bus may include, for example, any combination of hardware, software embedded in a computer-readable medium, or encoded logic incorporated in hardware or otherwise stored (e.g., firmware) to couple components of the HVAC system 100 to each other.

[0048] As an example and not by way of limitation, the data bus may include an accelerated graphics port (AGP) or other graphics bus, a controller area network (CAN) bus, a front-side bus (FSB), a hypertransport TM (HT) interconnect, an InfiniBand ™ interconnect, a low-pin-count (LPC) bus, a memory bus, a micro channel architecture (MCA) bus, a peripheral component interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a serial advanced technology attachment (SATA) bus, a video electronics standards association local bus (VLB), or any other suitable bus or a combination of two or more of these. In various embodiments, the data bus may include any number, type, or configuration of data buses, where appropriate. In certain embodiments, one or more data buses (which may each include an address bus and a data bus) may couple the controller 160 to other components of the HVAC system 100.Operational flow for operating the HVAC system in the defrost mode

[0049] In some cases, ice may be formed on the surface of the outdoor coil 122 during the heating mode in cold weather (e.g., in winter). Thus, the defrost mode 101 may be required in such situations to melt the ice formed on the outdoor coil 122.

[0050] In operation, the controller 160 may determine whether a condition to operate the HVAC system 100 in the defrost mode 101 is met. For example, the controller 160 may determine whether a condition to operate the HVAC system 100 in the defrost mode is met based on specific criteria, such as whether a predefined time interval has elapsed since the last defrost cycle or whether the temperature at the outdoor coil 122 is less than the ambient temperature by more than a predefined threshold temperature 178 (e.g., more than 5°C, 41°F, etc.). In response to determining that the condition to operate in the defrost mode is met, the controller 160 may initiate the defrost mode to melt the ice from the outdoor coil 122.

[0051] To this end, the controller 160 may control the operation of the dampers (e.g., fresh air damper 144, exhaust damper 146, supply damper 148, and return damper 150). The controller 160 may communicate a first electronic signal 172a to the return damper 150, where the first electronic signal 172a causes the return damper 150 to close and prevent recirculated air (e.g., airflow 151) from flowing from the conditioned space 108 to the indoor heat exchanger 134. The controller 160 may communicate a second electronic signal 172bto the supply damper 148, where the second electronic signal 172b causes the supply damper 148 to close and prevent conditioned air (e.g., airflow) from flowing from the indoor heat exchanger 134 to the conditioned space 108 during the defrost mode. Thus, the conditioned space 108 is (at least partially) isolated during the defrost mode by the closed supply damper 148 and the return damper 150.

[0052] To utilize the ambient air’s heat and melt the ice on the surface of the outdoor coil 122, the controller 160 may open the fresh air damper 144 and the exhaust damper 146. To this end, the controller 160 communicates a third electronic signal 172c to the fresh air damper 144, where the third electronic signal 172c causes the fresh air damper 144 to open and allow ambient air (e.g., airflow 145) to flow from the surrounding environment into the indoor heat exchanger 134 during the defrost mode. The controller 160 may communicate a fourth electronic signal 172d to the exhaust damper 146, where the fourth electronic signal 172d causes the exhaust damper 146 to open and permit air (e.g., airflow 147) to flow from the indoor section 104 to the surrounding environment after passing through the indoor heat exchanger 134 during the defrost mode. In some embodiments, the dampers (e.g., fresh air damper 144, exhaust damper 146, supply damper 148, and return damper 150) may be configured (e.g., opened or closed) in parallel or sequentially in any suitable order.

[0053] After the dampers (e.g., fresh air damper 144, exhaust damper 146, supply damper 148, and return damper 150) are adjusted, the controller 160 may control the flow of refrigerant through the system to defrost the ice on the outdoor coil 122. To this end, the controller 160 may communicate an electronic signal 174a to the valve 114 to adjust it to reverse the refrigerant flow which was initially according to the heating mode to the defrost mode. The electronic signal 174a causes the port 116a to be connected to the port 116, and the port 116c to be connected to port 116d. In the defrost mode 101, the high-temperature refrigerant vapor that is discharged from the compressors’ discharge lines 113 flows toward the valve 114. The valve 114 (now adjusted based on the electronic signal 174a), directs the high-temperature refrigerant vapor from port 116ato port 116b. From port 116b, the high-temperature refrigerant vapor flows into the outdoor coil 122 of the outdoor heat exchanger 120.

[0054] As the high temperature refrigerant flows through the outdoor coil 122, it releases heat to the ice on the surface of the outdoor coil 122 and melts the ice. This process causes at least some amount of the refrigerant to transition from vapor to liquid. The controller 160 may receive temperature data 170 from the temperature sensor circuit 126 to monitor the defrosting process. After passing through the outdoor coil 122, the liquid refrigerant flows out of the outdoor coil 122 and is directed toward the filter dryer 128, where debris and moisture are filtered from the refrigerant. The refrigerant flows through the valve 130 (e.g., an expansion valve) to reduce its pressure and temperature before it enters the indoor heat exchanger 134. The refrigerant then flows into the indoor coil 136 of the indoor heat exchanger 134, where the refrigerant absorbs heat from the ambient air (e.g., airflow 145) introduced through the open fresh air damper 144. This heat exchange process causes the refrigerant to evaporate and transition from a liquid and vapor mixture to a vaporized refrigerant.

[0055] As the vaporized refrigerant exits the indoor coil 136, it is directed back toward the valve 114 (at the port 116c). The valve 114 (which is configured in the defrost mode 101), directs the refrigerant from port 116c to port 116d. From port 116d, the refrigerant passes through the valve 142 and flows back to the accumulator 140. The liquid and vapor refrigerant is collected in the accumulator 140 and the vapor refrigerant flows from the accumulator 140 toward the compressors 112. This completes the refrigerant cycle during the defrost mode 101. The controller 160 may monitor system conditions to determine whether to exit the defrost mode 101.Operational flow for operating the HVAC system to exit the defrost mode

[0056] FIG. 2 illustrates the HVAC system 100 when exiting the defrost mode 101, according to some embodiments. The components of the HVAC system 100 are described in the description of FIG. 1 and are not repeated in the description of FIG. 2. In operation, the controller 160 may determine whether the condition to operate in the defrost mode 101 is no longer met. For example, the controller 160 may evaluate system conditions such as temperature data 170 from the temperature sensor circuit 126 to determine if the ice on the outdoor coil 122 has melted. In this example, if the controller 160 determines that the temperature at the outdoor coil 122 is no longer less than the ambient temperature by more than the predefined threshold temperature 178 (temperature difference / range), the controller 160 may determine that the ice on the outdoor coil 122 has melted. In another example, the controller 160 may determine that a predefined duration for the defrost mode 101 has elapsed.

[0057] In response to determining that the condition to operate in the defrost mode is no longer met, the controller 160 may initiate the transition back to the normal operating mode, such as the heating mode 201 or cooling mode. For cooling mode, the refrigerant flow connection in the HVAC system 100 is the same as shown and described in FIG. 1, but the damper side air flow is similar to the configuration shown in for the heating mode 201 in FIG. 2. To this end, the controller 160 may communicate electronic signals to certain components to reconfigure the HVAC system 100 and the flow of the refrigerant. To this end, the controller 160 may communicate a fifth electronic signal 172e to the return damper 150 to open the return damper 150. This allows recirculated air (e.g., airflow 151) to flow from the conditioned space 108 to the indoor heat exchanger 134.

[0058] The controller 160 may communicate a sixth electronic signal 172f to the supply damper 148 to open the supply damper 148 to enable the conditioned air (e.g., airflow) to flow from the indoor heat exchanger 134 into the conditioned space 108. The controller 160 may communicate a seventh electronic signal 172g to the fresh air damper 144 to close the fresh air damper 144 and to prevent ambient air (e.g., airflow 145 (see FIG. 1)) from entering the indoor heat exchanger 134. The controller 160 may communicate an eighth electronic signal 172hto the exhaust damper 146 to close the exhaust damper 146 and to block airflow (e.g., airflow 147 (see FIG. 1)) from exiting the indoor section 104 to the surrounding environment. The controller 160 may communicate an electronic signal 174b to the valve 114 to reconfigure the paths between the ports 116a-d from the defrost mode back to the normal operating mode (e.g., heating or cooling mode). The electronic signal 174b may cause the port connections to be reconfigured depending on the operation demand, similar to that described in FIG. 1.

[0059] After the dampers (e.g., fresh air damper 144, exhaust damper 146, supply damper 148, and return damper 150) are adjusted and the valve 114 is reconfigured, the refrigerant cycle resumes for the normal operating mode. For example, in the heating mode, high-temperature refrigerant vapor flows from the compressors’ discharge lines 113 to the indoor coil 136, where it releases heat into the conditioned space 108. In some embodiments, the controller 160 may switch between the normal conditioning operation (e.g., heating or cooling mode) and the defrost mode as needed according to the conditions associated with the defrost mode, similar to that described in FIGS. 1 and 2.Example method for operating an HVAC system

[0060] FIG. 3 illustrates a flowchart of an example method 300 of operating the system 100 of FIG. 1. The method 300 may be performed by the controller 160 (see FIG. 1) when one or more processors (e.g., processor 162 of FIG. 1) execute software instructions (e.g., software instructions 168) stored in one or more memories (e.g., memory 166 of FIG. 1). The method 300 may include operations 302-318. Modifications, additions, or omissions may be made to method 300. Method 300 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order.

[0061] At operation 302, the method 300 begins as the controller 160 determines whether a condition to operate in a defrost mode for an outdoor coil 122 is met, similar to that described in FIG. 1. If it is determined that the condition to operate in the defrost mode for the outdoor coil 122 is met, the method 300 proceeds to operation 304. Otherwise, the method 300 proceeds to operation 312.

[0062] At operation 304, the controller 160 communicates a first electronic signal 172a to the return damper 150 to close the return damper 150, similar to that described in FIG. 1, and the method 300 proceeds to operation 306.

[0063] At operation 306, the controller 160 communicates a second electronic signal 172b to the supply damper 148 to close the supply damper 148, similar to that described in FIG. 1, and the method 300 proceeds to operation 308.

[0064] At operation 308, the controller 160 communicates a third electronic signal 172c to the fresh air damper 144 to open the fresh air damper 144, similar to that described in FIG. 1, and the method 300 proceeds to operation 310.

[0065] At operation 310, the controller 160 communicates a fourth electronic signal 172d to the exhaust damper 146 to open the exhaust damper 146, similar to that described in FIG. 1, and the method 300 ends.

[0066] The controller 160 may communicate the electronic signal 174a to the valve 114 to configure the flow paths for the refrigerant, similar to that described in FIG. 1.

[0067] At operation 312, the controller 160 communicates a fifth electronic signal 172e to the return damper 150 to open the return damper 150, similar to that described in FIG. 2, and the method 300 proceeds to operation 314.

[0068] At operation 314, the controller 160 communicates a sixth electronic signal 172f to the supply damper 148 to open the supply damper 148, similar to that described in FIG. 2, and the method 300 proceeds to operation 316.

[0069] At operation 316, the controller 160 communicates a seventh electronic signal 172g to the fresh air damper 144 to close the fresh air damper 144, similar to that described in FIG. 2, and the method 300 proceeds to operation 318.

[0070] At operation 318, the method 300 ends as the controller 160 communicates an eighth electronic signal 172h to the exhaust damper 146 to close the exhaust damper 146, similar to that described in FIG. 2. The controller 160 may communicate the electronic signal 174b to the valve 114 to reconfigure the flow paths for the refrigerant, similar to that described in FIGS. 1-3.

[0071] Although this disclosure has been described in terms of certain embodiments, alterations, and permutations, embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure.

[0072] While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated with another system or certain features may be omitted, or not implemented.

[0073] In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

[0074] To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants note that they do not intend any of the appended claims to invoke 35 U.S.C. § 112(f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.

Examples

example method

Example method for operating an HVAC system

[0060]FIG. 3 illustrates a flowchart of an example method 300 of operating the system 100 of FIG. 1. The method 300 may be performed by the controller 160 (see FIG. 1) when one or more processors (e.g., processor 162 of FIG. 1) execute software instructions (e.g., software instructions 168) stored in one or more memories (e.g., memory 166 of FIG. 1). The method 300 may include operations 302-318. Modifications, additions, or omissions may be made to method 300. Method 300 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order.

[0061]At operation 302, the method 300 begins as the controller 160 determines whether a condition to operate in a defrost mode for an outdoor coil 122 is met, similar to that described in FIG. 1. If it is determined that the condition to operate in the defrost mode for the outdoor coil 122 is met, the method 300 proceeds to operation 304. Otherwise, ...

Claims

1. A Heating, Ventilation, and Air Conditioning (HVAC) system comprising:an indoor coil comprising an inlet side and an outlet side, the indoor coil configured to:condense refrigerant during a heating mode as the refrigerant in vapor form flows through the indoor coil, releases heat to a conditioned space, and transitions into liquid; andevaporate the refrigerant during a cooling mode as the refrigerant in liquid form flows through the indoor coil, absorbs heat from the conditioned space, and transitions into vapor;an outdoor coil comprising an inlet side and an outlet side, the outdoor coil configured to:evaporate the refrigerant during the heating mode as the refrigerant in liquid form flows through the outdoor coil, absorbs heat from ambient air, and transitions into vapor; andcondense the refrigerant during the cooling mode as the refrigerant in vapor form flows through the outdoor coil, releases heat to the ambient air, and transitions into liquid;a valve positioned between a compressor and the outdoor coil, the valve configured to reverse a flow of the refrigerant between the indoor coil and outdoor coil during a transition between the heating mode and a defrost mode;a return damper positioned between the conditioned space and the inlet side of the indoor coil, the return damper configured to allow recirculated air to flow from the conditioned space to the indoor coil during each of the heating mode and the cooling mode;a supply damper positioned between the outlet side of the indoor coil and the conditioned space, the supply damper configured to allow conditioned air to flow from the indoor coil to the conditioned space during each of the heating mode and the cooling mode, wherein the conditioned air is maintained within the conditioned space during the defrost mode when the return damper and the supply damper are closed;a fresh air damper positioned upstream of the inlet side of the indoor coil, the fresh air damper configured to allow ambient air to flow through the indoor coil during the defrost mode;an exhaust damper positioned downstream of the outlet side of the indoor coil, the exhaust damper configured to allow airflow to surrounding environment after passing through the indoor coil during the defrost mode; anda controller operably coupled with the return damper, the supply damper, the fresh air damper, and the exhaust damper, the controller comprising a processor configured to:determine that a condition to operate in the defrost mode for the outdoor coil is met; andin response to determining that the condition to operate in the defrost mode for the outdoor coil is met:communicate a first electronic signal to the return damper to close the return damper;communicate a second electronic signal to the supply damper to close the supply damper;communicate a third electronic signal to the fresh air damper to open the fresh air damper; andcommunicate a fourth electronic signal to the exhaust damper to open the exhaust damper.

2. The HVAC system of claim 1, wherein determining that the condition to operate in the defrost mode for the outdoor coil is met comprises determining that a predefined time interval has elapsed since a last defrost cycle.

3. The HVAC system of claim 1, wherein determining that the condition to operate in the defrost mode for the outdoor coil is met comprises determining that a temperature at an outdoor coil is less than an ambient temperature by more than a threshold difference.

4. The HVAC system of claim 1, wherein the processor is further configured to:determine that the condition to operate in the defrost mode for the outdoor coil is no longer met; andin response to determining that the condition to operate in the defrost mode is no longer met:communicate a fifth electronic signal to the return damper to open the return damper;communicate a sixth electronic signal to the supply damper to open the supply damper;communicate a seventh electronic signal to the fresh air damper to close the fresh air damper; andcommunicate an eighth electronic signal to the exhaust damper to close the exhaust damper.

5. The HVAC system of claim 1, wherein the return damper is motorized and configured to open and close in response to electronic signals.

6. The HVAC system of claim 1, wherein the supply damper is motorized and configured to open and close in response to electronic signals.

7. The HVAC system of claim 1, wherein the fresh air damper is motorized and configured to open and close in response to electronic signals.

8. A method for operating a Heating, Ventilation, and Air Conditioning (HVAC) system, comprising:condensing, by an indoor coil, refrigerant during a heating mode as the refrigerant in vapor form flows through the indoor coil, releases heat to an conditioned space, and transitions into liquid, wherein the indoor coil comprises an inlet side and an outlet side;evaporating, by the indoor coil, the refrigerant during a cooling mode as the refrigerant in liquid form flows through the indoor coil, absorbs heat from the conditioned space, and transitions into vapor;evaporating, by an outdoor coil, the refrigerant during the heating mode as the refrigerant in liquid form flows through the outdoor coil, absorbs heat from ambient air, and transitions into vapor;condensing, by the outdoor coil, the refrigerant during the cooling mode as the refrigerant in vapor form flows through the outdoor coil, releases heat to the ambient air, and transitions into liquid, wherein the outdoor coil comprises an inlet side and an outlet side;reversing, by a valve, a flow of the refrigerant between the indoor coil and the outdoor coil during a transition between the heating mode and a defrost mode, wherein the valve is positioned between a compressor and the outdoor coil;allowing, by a return damper, recirculated air to flow from the conditioned space to the indoor coil during each of the heating mode and the cooling mode, wherein the return damper is positioned between the conditioned space and the inlet side of the indoor coil;allowing, by a supply damper, conditioned air to flow from the indoor coil to the conditioned space during each of the heating mode and the cooling mode, wherein the conditioned air is maintained within the conditioned space during the defrost mode when the return damper and the supply damper are closed, wherein the supply damper is positioned between the outlet side of the indoor coil and the conditioned space;allowing, by a fresh air damper, ambient air to flow through the indoor coil during the defrost mode, wherein the fresh air damper is positioned upstream of the inlet side of the indoor coil;allowing, by an exhaust damper, airflow to surrounding environment after passing through the indoor coil during the defrost mode, wherein the exhaust damper is positioned downstream of the outlet side of the indoor coil; anddetermining, by a processor, that a condition to operate in the defrost mode for the outdoor coil is met; andin response to determining that the condition to operate in the defrost mode for the outdoor coil is met:communicating, by the processor, a first electronic signal to the return damper to close the return damper;communicating, by the processor, a second electronic signal to the supply damper to close the supply damper;communicating, by the processor, a third electronic signal to the fresh air damper to open the fresh air damper; andcommunicating, by the processor, a fourth electronic signal to the exhaust damper to open the exhaust damper.

9. The method of claim 8, wherein determining that the condition to operate in the defrost mode for the outdoor coil is met comprises determining that a predefined time interval has elapsed since a last defrost cycle.

10. The method of claim 8, wherein determining that the condition to operate in the defrost mode for the outdoor coil is met comprises determining that a temperature at an outdoor coil is less than an ambient temperature by more than a threshold difference.

11. The method of claim 8, further comprising:determining, by the processor, that the condition to operate in the defrost mode for the outdoor coil is no longer met; andin response to determining that the condition to operate in the defrost mode is no longer met:communicating, by the processor, a fifth electronic signal to the return damper to open the return damper;communicating, by the processor, a sixth electronic signal to the supply damper to open the supply damper;communicating, by the processor, a seventh electronic signal to the fresh air damper to close the fresh air damper; andcommunicating, by the processor, an eighth electronic signal to the exhaust damper to close the exhaust damper.

12. The method of claim 8, wherein the return damper is motorized and configured to open and close in response to electronic signals.

13. The method of claim 8, wherein the supply damper is motorized and configured to open and close in response to electronic signals.

14. The method of claim 8, wherein the fresh air damper is motorized and configured to open and close in response to electronic signals.

15. A controller of a Heating, Ventilation, and Air Conditioning (HVAC) system, the controller comprising:a processor communicatively coupled with a return damper, a supply damper, a fresh air damper, and a exhaust damper, the controller comprising a processor configured to:determine that a condition to operate in a defrost mode for an outdoor coil is met; andin response to determining that the condition to operate in the defrost mode for the outdoor coil is met:communicate a first electronic signal to the return damper to close the return damper, wherein:the return damper is positioned between a conditioned space and an inlet side of an indoor coil; andthe return damper is configured to allow recirculated air to flow from the conditioned space to the indoor coil during each of a heating mode and a cooling mode;communicate a second electronic signal to the supply damper to close the supply damper, wherein:the supply damper is positioned between an outlet side of the indoor coil and the conditioned space; andthe supply damper is configured to allow conditioned air to flow from the indoor coil to the conditioned space during each of the heating mode and the cooling mode;the conditioned air is maintained within the conditioned space during the defrost mode when the return damper and the supply damper are closed;communicate a third electronic signal to the fresh air damper to open the fresh air damper, wherein:the fresh air damper is positioned upstream of the inlet side of the indoor coil; andthe fresh air damper is configured to allow ambient air to flow through the indoor coil during the defrost mode; andcommunicate a fourth electronic signal to the exhaust damper to open the exhaust damper, wherein:the exhaust damper is positioned downstream of the outlet side of the indoor coil; andthe exhaust damper is configured to allow airflow to surrounding environment after passing through the indoor coil during the defrost mode.

16. The controller of claim 15, wherein determining that the condition to operate in the defrost mode for the outdoor coil is met comprises determining that a predefined time interval has elapsed since a last defrost cycle.

17. The controller of claim 15, wherein determining that the condition to operate in the defrost mode for the outdoor coil is met comprises determining that a temperature at the outdoor coil is less than an ambient temperature by more than a threshold difference.

18. The controller of claim 15, wherein the processor is further configured to:determine that the condition to operate in the defrost mode for the outdoor coil is no longer met; andin response to determining that the condition to operate in the defrost mode is no longer met:communicate a fifth electronic signal to the return damper to open the return damper;communicate a sixth electronic signal to the supply damper to open the supply damper;communicate a seventh electronic signal to the fresh air damper to close the fresh air damper; andcommunicate an eighth electronic signal to the exhaust damper to close the exhaust damper.

19. The controller of claim 15, wherein the return damper is motorized and configured to open and close in response to electronic signals.

20. The controller of claim 15, wherein the exhaust damper is motorized and configured to open and close in response to electronic signals.

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