US20230168013A1

US20230168013A1 - Heat pump system with flash defrosting mode

Info

Publication number: US20230168013A1
Application number: US17/475,999
Authority: US
Inventors: Joseph Paul Bush
Original assignee: Mitsubishi Electric US Inc
Current assignee: Mitsubishi Electric US Inc
Priority date: 2021-09-15
Filing date: 2021-09-15
Publication date: 2023-06-01

Abstract

A heat pump system is provided, comprising: a cooling and heating coil having first and second refrigerant ports; a reheat coil having third and fourth refrigerant ports; first and second refrigerant pipes connected to the first and second refrigerant ports, respectively; a first solenoid valve between the third refrigerant port and the second refrigerant pipe; a second solenoid valve between the fourth refrigerant port and the second refrigerant line; an expansion valve between the fourth refrigeration port and the second refrigerant port; a first check valve between the fourth refrigerant port and the expansion valve; a second check valve between the expansion valve and a condensing circuit; a third check valve between the first check valve and the expansion valve; a fan circuit for blowing air across the cooling and heating coil and the reheat coil in order; and a controller for controlling the heat pump system.

Description

TECHNICAL FIELD

The disclosed devices and methods relate generally to a heating, ventilation, and air-conditioning (HVAC) system. More particularly, the disclosed devices and methods relate to a HVAC system which quickly defrosts a condenser by directing warm refrigerant from a reheat coil to a cooling and heating coil to speed up the defrosting of a condenser.

BACKGROUND

An HVAC system may have a condensing circuit and a heating and cooling unit to perform heating and cooling of an indoor area. A condenser located in the condensing circuit may collect frost on it during a heating operation in cold weather. When this occurs, it is necessary to temporarily suspend the heating operation to defrost the condenser.
In general, to defrost an outdoor condenser, an HVAC system will switch from a heating mode to a defrosting mode. In the defrosting mode, the HVAC system operates in similar fashion to a cooling mode, but fans do not blow air over the condenser or the cooling and heating coil. In a conventional defrosting mode, the heat to melt the frost on the outdoor condenser comes from the heat of compression produced by the compression of the refrigerant in the compressor of the heat pump, the heat in the refrigerant piping that has been warmed from operating in heating mode, and the heat from the cooling and heating coil that was warm from operating in the heating mode.
As a result, it is necessary to provide an HVAC system with a larger capacity than would otherwise be required to account for this temporary pause in the heating operation during the defrosting time and ensure that he system can maintain a desired level of heating. It is therefore desirable to minimize the time needed to defrost the condenser so that an HVAC system with a smaller capacity may be selected.

SUMMARY OF THE INVENTION

According to one or more embodiments, a heat pump system is provided, comprising: a cooling and heating coil having a first refrigerant port and a second refrigerant port and configured to circulate refrigerant; a reheat coil having a third refrigerant port and a fourth refrigerant port and configured to circulate the refrigerant; a plurality of refrigerant pipes configured to circulate the refrigerant, the plurality of refrigerant pipes including a first refrigerant pipe connected between the first refrigerant port and a condensing circuit, a second refrigerant pipe connected between the second refrigerant port and the condensing circuit, a third refrigerant pipe connected between the third refrigerant port and a first node on the second refrigerant pipe, a fourth refrigerant pipe connected between the fourth refrigerant port and a second node on the third refrigerant pipe, and a fifth refrigerant pipe connected between a third node on the fourth refrigerant pipe and a fourth node on the second refrigerant pipe; a first solenoid valve formed on the third refrigerant pipe between the third refrigerant port and the second node; a second solenoid valve formed on the fourth refrigerant pipe between the second node and the third node; an expansion valve connected between the second refrigerant port and the fourth node; a first check valve connected between the fourth refrigerant port and the third node and configured to prevent flow of the refrigerant from the third node to the fourth refrigerant port; a second check valve connected between the first node and the fourth node and configured to prevent flow of the refrigerant from the first node to the fourth node; a third check valve connected between the third node and the fourth node and configured to prevent flow of the refrigerant from the fourth node to the third node; a fan circuit configured to blow input air across the cooling and heating coil to generate discharge air and to blow the discharge air over the reheat coil to generate supply air; and a controller configured to control the heat pump system.
The expansion valve may be an electronically controlled expansion valve.
The first solenoid valve may be a positive off solenoid valve.
The second solenoid valve may be a positive off solenoid valve.
According to one or more embodiments, a method for operating a heat pump system to defrost a condenser is provided, the method comprising: maintaining refrigerant in a reheat coil without circulating the refrigerant through the reheat coil during a heating mode; circulating refrigerant through a cooling and heating coil during the heating mode; blowing input air across the cooling and heating coil during the heating mode to generate discharge air, the discharge air in the heating mode being warmer than the input air; blowing the discharge air over the reheat coil during the heating mode to generate supply air; circulating refrigerant from the reheat coil to the cooling and heating coil after entering a defrost mode; and circulating refrigerant from the cooling and heating coil to the condenser coil during the defrost mode.
The method may further comprise stopping blowing the input air across the cooling and heating coil and stopping blowing the discharge air over the reheat coil after entering a defrost mode.
The method may further comprise stopping blowing the input air across the cooling and heating coil and stopping blowing the discharge air over the reheat coil in response to entering the defrost mode, wherein the circulating of the refrigerant from the reheat coil to the cooling and heating coil is performed after the stopping of blowing the input air across the cooling and heating coil and the stopping of blowing the discharge air over the reheat coil, and the circulating of the refrigerant from the cooling and heating coil to the condenser coil is performed after the stopping of blowing the input air across the heating and cooling coil and the stopping of blowing the discharge air over the reheat coil.
The circulating of the refrigerant from the reheat coil to the cooling and heating coil may be achieved by opening a first solenoid valve and closing a second solenoid valve.
The method may further comprise receiving from a controller a signal indicating a start of a defrosting mode prior to entering the defrost mode.
The method may further comprise receiving a signal from a controller indicating an end of a defrosting mode and a resumption of the heating mode; and stopping circulating refrigerant from the reheat coil to the cooling and heating coil after the defrosting mode has ended and the heating mode has resumed.
The circulating of the refrigerant from the reheat coil to the cooling and heating coil may be achieved by opening a first solenoid valve and closing a second solenoid valve; and the stopping of the circulating of the refrigerant from the reheat coil to the cooling and heating coil may be achieved by closing the first solenoid valve and opening the second solenoid valve.
The method may further comprise resuming blowing input air across the cooling and heating coil to generate discharge air after the defrosting mode has ended and the heating mode has resumed; and resuming blowing the discharge air over the reheat coil to generate supply air after the defrosting mode has ended and the heating mode has resumed.
According to one or more embodiments, a non-transitory computer-readable medium comprising instructions for execution by a computer, the instructions including a computer-implemented method for controlling a heat pump system to defrost a condenser coil, the instructions for implementing: maintaining refrigerant in a reheat coil without circulating the refrigerant through the reheat coil during a heating mode; circulating refrigerant through a cooling and heating coil during the heating mode; blowing input air across the cooling and heating coil during the heating mode to generate discharge air, the discharge air in the heating mode being warmer than the input air; blowing the discharge air over the reheat coil during the heating mode to generate supply air; circulating refrigerant from the reheat coil to the cooling and heating coil after entering a defrost mode; and circulating refrigerant from the cooling and heating coil to the condenser coil during the defrost mode.
The instructions may be for further implementing stopping blowing the input air across the cooling and heating coil and stopping blowing the discharge air over the reheat coil after entering a defrost mode.
The instructions may be for further implementing stopping blowing the input air across the cooling and heating coil and stopping blowing the discharge air over the reheat coil in response to entering the defrost mode, wherein the circulating of the refrigerant from the reheat coil to the cooling and heating coil is performed after the stopping of blowing the input air across the cooling and heating coil and the stopping of blowing the discharge air over the reheat coil, and the circulating of the refrigerant from the cooling and heating coil to the condenser coil is performed after the stopping of blowing the input air across the cooling and heating coil and the stopping of blowing the discharge air over the reheat coil.
The circulating of the refrigerant from the reheat coil to the cooling and heating coil may be achieved by opening a first solenoid valve and closing a second solenoid valve.
The instructions may be for further implementing exiting the defrosting mode and resuming the heating mode; and stopping circulating refrigerant from the reheat coil to the cooling and heating coil after the defrosting mode has ended and the heating mode has resumed.
The circulating of the refrigerant from the reheat coil to the cooling and heating coil may be achieved by opening a first solenoid valve and closing a second solenoid valve; and the stopping of the circulating of the refrigerant from the reheat coil to the cooling and heating coil may be achieved by closing the first solenoid valve and opening the second solenoid valve.
The instructions may be for further implementing resuming blowing input air across the cooling and heating coil to generate discharge air after the defrosting mode has ended and the heating mode has resumed; resuming blowing the discharge air over the reheat coil to generate supply air after the defrosting mode has ended and the heating mode has resumed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer to identical or functionally similar elements and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate an exemplary embodiment and to explain various principles and advantages in accordance with the present disclosure.

FIG. 1 is a diagram of a heat pump system according to disclosed embodiments;

FIG. 2 is a diagram of a heat pump system operating in a cooling mode according to disclosed embodiments;

FIG. 3 is a diagram of a heat pump system operating in a cooling with reheat mode according to disclosed embodiments;

FIG. 4 is a diagram of a heat pump system operating in a heating mode according to disclosed embodiments;

FIG. 5 is a diagram of a heat pump system operating in a flash defrost mode according to disclosed embodiments; and

FIG. 6 is a flow chart showing the operation of a heat pump system operating in a defrost mode according to disclosed embodiments.

DETAILED DESCRIPTION

Heat Pump System

FIG. 1 is a diagram of a heat pump system 100 according to disclosed embodiments. As shown in FIG. 1 , the heat pump system 100 includes a condensing circuit 103, a heating and cooling unit 106, first and second refrigerant pipes 180, 182 that connect the condensing circuit 103 and the heating and cooling unit 106. The condensing circuit 103 includes a compressor 110, a suction accumulator 113, a reversing valve 116, a condenser 118, a condenser fan 119, a first expansion valve 120, a second expansion valve 123, and a liquid heat exchanger 126. The heating and cooling unit 106 includes a cooling and heating coil 140 having a first refrigerant port 143 and a second refrigerant port 146, a reheat coil 150 having a third refrigerant port 153 and a fourth refrigerant port 156, a cooling and heating coil fan 160, a first solenoid valve 164, a second solenoid valve 166, a third expansion valve 168, a first check valve 170, a second check valve 173, a third check valve 176, a third refrigerant pipe 184, a fourth refrigerant pipe 186, a fifth refrigerant pipe 188, a first node 190, a second node 192, a third node 194, a fourth node 196, and a controller 135. The controller 135 includes a processor 137 and a memory 139.
The compressor 110 is configured to circulate refrigerant through the heat pump system 100. The compressor 110 receives refrigerant at a low pressure from the suction accumulator 113, compresses the refrigerant to a higher pressure, thereby heating the refrigerant, and provides the relatively hot, high-pressure refrigerant to the reversing valve 116.
The suction accumulator 113 is disposed at the inlet of the compressor 110. The suction accumulator 113 operates as a refrigerant reservoir to prevent liquid refrigerant from entering the compressor 110.
The reversing valve 116 is configured to allow the system to switch the direction in which refrigerant flows, thereby permitting the heat pump system 100 to perform both heating and cooling operations. The reversing valve has at least two states in which the outlet of the compressor 110, the condenser 118, the first refrigerant port 143 of the cooling and heating coil 140, and the suction accumulator 113 are selectively connected. In a first state, the reversing valve 116 connects the outlet of the compressor 110 with the condenser 118 and connects the inlet of the compressor 110 with the first refrigerant port 143 of the cooling and heating coil 140. In a second state, the reversing valve connects the inlet of the compressor 110 and the condenser 118 and connects the outlet of the compressor 110 to the first refrigerant port 143 of the cooling and heating coil 140. The reversing valve 116 may be a four-way valve.
The condenser 118 is a heat exchanger that may be located either indoors or outdoors. The condenser 118 operates to exchange heat between refrigerant flowing through its pipes and air moving past the pipes. In a heating mode, refrigerant in the condenser 118 will absorb heat from passing air. In a cooling mode, heat will be transferred from the refrigerant circulated in the condenser 118 to the passing air. When the heat pump system 100 is in a heating mode, the condenser 118 may become cold enough that frost forms on the pipes of the condenser 118 through which the refrigerant flows.
The condenser fan 119 operates to blow condenser input air (240 in FIGS. 2-4 ) through the condenser 118 and past the refrigerant pipes in the condenser 118. The condenser fan 119 may be located and operated such that it draws air through the condenser 118 or blows air through condenser 118.
The first expansion valve 120 may be disposed on the second refrigerant pipe 182 between the condenser 118 and the liquid heat exchanger 126. The first expansion valve 120 may be an electronically controlled expansion valve. The first expansion valve 120 operates to selectively lower the pressure of the refrigerant passing through it. This drop in pressure will result in a drop in the temperature of the refrigerant. The first expansion valve 120 can be set to be: (a) controlling flow, reducing the pressure of the refrigerant that flows through it; or (b) entirely open, allowing refrigerant to freely flow through it.
The liquid heat exchanger 126 may be a subcooling heat exchanger that cools liquid refrigerant flowing through the second refrigerant pipe 182.
The second expansion valve 123 may be disposed between the second refrigerant pipe 182 and a coil of the liquid heat exchanger 126. The second expansion valve 123 may be an electronically controlled expansion valve. The second expansion valve 123 operates to selectively lower the pressure of the refrigerant passing through it. This drop in pressure will result in a drop in the temperature of the refrigerant. The second expansion valve 123 can be set to be: (a) controlling flow, reducing the pressure of the refrigerant that flows through it; or (b) entirely open, allowing refrigerant to freely flow through it.
The cooling and heating coil 140 is a heat exchanger that may be located either indoors or outdoors. The cooling and heating coil 140 operates to exchange heat between refrigerant flowing through its pipes and air moving past the pipes. In a heating mode, heat will be transferred from the refrigerant circulated in the cooling and heating coil 140 to the passing air. In a cooling mode, refrigerant in the cooling and heating coil 140 will absorb heat from passing air.
The first refrigerant port 143 may act as a refrigerant inlet or a refrigerant outlet for the cooling and heating coil 140 depending upon the direction of refrigerant flow in the heat pump system 100. The second refrigerant port 146 may act as a refrigerant inlet or a refrigerant outlet for the cooling and heating coil 140 depending upon the direction of refrigerant flow in the heat pump system 100.
The cooling and heating coil fan 160 blows cooling and heating input air (210 in FIGS. , 2-4 ) through the cooling and heating coil 140 and past the refrigerant pipes in the cooling and heating coil 140. The cooling and heating coil 140 exchanges heat with the input air to generate discharge air (220 in FIGS. 2-4 ), which is output from the cooling and heating coil 140. The cooling and heating input air 210 may be outdoor air, return air drawn from inside of a building, or a mixture of outdoor air and return air. The cooling and heating coil fan 160 may be located and operated such that it draws the cooling and heating input air 210 through the cooling and heating coil 140 or blows the cooling and heating input air 210 through cooling and heating coil 140.
The reheat coil 150 is a heat exchanger. The reheat coil 150 operates to exchange heat between refrigerant flowing through its pipes and air moving past the pipes. Specifically, the discharge air 220 will absorb heat from the refrigerant circulating in the reheat coil 150. The reheat coil 150 may be located adjacent to the cooling and heating coil 140 such that air passing through the cooling and heating coil 140 subsequently passes through the reheat coil 150.
The third refrigerant port 153 acts as a refrigerant inlet for the reheat coil 150. The fourth refrigerant port 156 may act as a refrigerant outlet for the reheat coil 150.
The cooling and heating coil fan 160 blows the discharge air 220 from the cooling and heating coil 140 through the reheat coil 150 and past the refrigerant pipes in the reheat could 150 to generate supply air (230 in FIGS. 2-4 ), which can be supplied to an indoor space that is being heated or cooled. The cooling and heating coil fan 160 may be located and operated so that it draws air through the cooling and heating coil 140 and the reheat coil 150 or such that it blows air through the cooling and heating coil 140 and the reheat coil 150.
The third refrigerant pipe 184 is a pipe for circulating refrigerant. The third refrigerant pipe 184 extends from the third refrigerant port 153 to the first node 190. The third refrigerant pipe 184 connects to the fourth refrigerant pipe 186 at the second node 192. The third refrigerant pipe connects to the second refrigerant pipe 182 at the first node 190.
The fourth refrigerant pipe 186 is a pipe for circulating refrigerant. The fourth refrigerant pipe 186 extends from the fourth refrigerant port 156 to the second node 192. The fourth refrigerant pipe 186 connects to the fifth refrigerant pipe 188 at the third node 194. The fourth refrigerant pipe 186 connects to the third refrigerant pipe 184 at the second node 192.
The fifth refrigerant pipe 188 is a pipe for circulating refrigerant. The fifth refrigerant pipe 188 extends from the third node 194 to the fourth node 196. The fifth refrigerant pipe 188 connects to the fourth refrigerant pipe 186 at the third node 194 and connects to the second refrigerant pipe 182 at the fourth node 196.
The first node 190 is an intersection of the third refrigerant pipe 184 and the second refrigerant pipe 182. The second node 192 is an intersection of the third refrigerant pipe 184 and the fourth refrigerant pipe 186. The third node 194 is an intersection of the fourth refrigerant pipe 186 and the fifth refrigerant pipe 188. The fourth node 196 is an intersection of the second refrigerant pipe 182 and the fifth refrigerant pipe 188.
The first solenoid valve 164 is disposed on the third refrigerant pipe 184 between the second node 192 and the third refrigerant port 153 of the reheat coil 150. In a fully closed state, the first solenoid valve 164 prevents flow of refrigerant through the reheat coil 150. The first solenoid valve 164 is a positive off solenoid valve in the embodiment of FIG. 1 , though it may be a positive on solenoid valve in alternate embodiments.
In alternate embodiments, an expansion valve or other type of valve may be used in place of a solenoid valve. Solenoid valves are used in the embodiment of FIG. 1 because solenoid valves can only be placed in a fully closed state or a fully open state. Other valves, such as electronic expansion valves, may not close tightly in a “fully closed” state, leading to undesired bleeding of refrigerant through the valve. Using solenoid valves simplifies the controls and reduces incidences of refrigerant leaking through valves because solenoid valves can only be fully open or fully closed.
The second solenoid valve 166 is disposed on the fourth refrigerant pipe 186 between the second node 192 and the third node 194. The second solenoid valve 166 is a positive off solenoid valve in the embodiment of FIG. 1 , though it may be a positive on solenoid valve in alternate embodiments. In alternative embodiments, an expansion valve or other type of valve may be used in place of a solenoid valve. Solenoid valves are used because they simplify the controls and reduce incidences of refrigerant leaking through valves because solenoid valves can only be fully open or fully closed.
The third expansion valve 168 is disposed on the second refrigerant pipe 182 between the fourth node 196 and the second refrigerant port 146. The third expansion valve 168 may be an electronically controlled expansion valve. The third expansion valve 168 operates to selectively reduce the pressure of the refrigerant passing through it. This drop in pressure will result in a drop in the temperature of the refrigerant. The third expansion valve 168 will be set to be controlling flow, reducing the pressure of the refrigerant that flows through it.
The first check valve 170 is disposed on the fourth refrigerant pipe 186 between the fourth refrigerant port 156 and the third node 194. The first check valve 170 allows refrigerant to flow in one direction but prevents refrigerant from flowing in the other direction. In the heat pump system 100 of FIG. 1 , the first check valve 170 is arranged to allow the flow of refrigerant from the fourth refrigerant port 156 to the third node 194 and to prevent the flow of refrigerant from the third node 194 to the fourth refrigerant port 156 and back into the reheat coil 150.
The second check valve 173 is disposed on the second refrigerant pipe 182 between the first node 190 and the fourth node 196. The second check valve 173 allows refrigerant to flow in one direction but prevents refrigerant from flowing in the other direction. In the heat pump system 100 of FIG. 1 , the second check valve 173 is arranged to allow the flow of refrigerant from the fourth node 196 to the first node 190 and to prevent the flow of refrigerant from the first node 190 towards the fourth node 196. This allows for the routing of the flow of refrigerant from the condensing circuit 103 through the second solenoid valve 166 or the first solenoid valve 164 when refrigerant is flowing from the condensing circuit 103 to the heating and cooling unit 106 via the second refrigerant pipe 182 (i.e., during a cooling mode or a defrost mode).
The third check valve 176 is disposed on the fifth refrigerant pipe 188 between the third node 194 and the fourth node 196. The third check valve 176 allows refrigerant to flow in one direction but prevents refrigerant from flowing in the other direction. In the heat pump system 100 of FIG. 1 , the third check valve 176 is arranged to allow the flow of refrigerant from the third node 194 to the fourth node 196 and to prevent the flow of refrigerant from the fourth node 196 to the third node 194.
The controller 135 operates to control the various components in the heat pump system 100. The controller 135 may be located in either of the condensing circuit 103 and the heating and cooling unit 106. In an alternate embodiment, the controller 135 may be located remotely from the heat pump system 100. The controller 135 may comprise one or more controllers. The controller 135 may comprise one or more processors, one or more transmitters, one or more receivers, one or more digital signal processors, and one or more memory structures. The controller 135 may be programmable via a user interface. Although not shown in the drawings, the controller 135 can also have the necessary interface circuitry and connections to control the operation of various elements in the heat pump system 100. This can include wired and wireless interfaces and connections.
The controller 135 may, for example, control the operation of the compressor 110, select the state of the reversing valve 116, set the expansion amount of the first, second, and third expansion valves 120, 123, and 168, open or close the first and second solenoid valves 164 and 166, and control the operation of the cooling and heating coil fan 160 and the condenser fan 119.
The processor 137 generates signals to perform the control of the controller 135. It can store information in the memory 139 and run instructions stored in the memory 137. The processor can be a microprocessor (e.g., a central processing unit), an application-specific integrated circuit (ASIC), or any suitable device for controlling the operation of all or part of the heat pump system 100.
The memory 139 can include a read-only memory (ROM), a random-access memory (RAM), an electronically programmable read-only memory (EPROM), an electrically erasable programmable read only memory (EEPROM), flash memory, or any suitable memory device.
Although not shown, the condensing circuit 103 or the heating and cooling unit 106 may include one or more sensors used to determine whether frost has formed on the condenser 118. These one or more sensors could include a temperature sensor on or proximate to the condenser 118 configured to measure an ambient temperature or a temperature of the condenser 118, a pressure sensor to monitor the pressure of the refrigerant exiting the condenser 118, a temperature sensor to monitor the temperature of the refrigerant exiting the condenser 118, or any other sensor that could provide information that may be used by the controller 135 to estimate when frost has formed on the coils of the condenser 118.

Cooling Operation

FIG. 2 is a diagram of a heat pump system 100 operating in a cooling mode according to disclosed embodiments. During the cooling mode, the first solenoid valve 164 is closed (as indicated by it being shown as black) and the second solenoid valve 166 and the second expansion valve 123 are open (as indicated by them being shown as white). As shown in FIG. 2 , the first and second check valves 170, 173 operate to prevent the flow of refrigerant (as indicated by them being shown as being partially black) and the third check valve 176 passes refrigerant (as indicated by it being shown as white).
In a cooling mode of the heat pump system 100, hot refrigerant gas leaves the outlet of the compressor 110 and enters the condenser 118. Condenser input air 240 is blown over the condenser 118 by the condenser fan 119. The refrigerant transfers heat to the condenser input air 240 and leaves the condenser 118 as a liquid. The liquid refrigerant is subsequently subcooled in a first coil of the liquid heat exchanger 126. A portion of the subcooled refrigerant is diverted through the second expansion valve 123 and into a second coil of the liquid heat exchanger 126 to absorb heat from the refrigerant that is flowing through the first coil of the liquid heat exchanger 126. The remainder of the subcooled refrigerant flows to first node 190.
The second check valve 173 prevents refrigerant flow from the first node 190 to the fourth node 196, and the first solenoid valve 164, which is set to a fully closed state, prevents refrigerant flow to the third refrigerant port 153 and through the reheat coil 150. The subcooled refrigerant flows through the second solenoid valve 166, which is set in a fully open state, to the third node 194. The first check valve 170 prevents flow to the fourth refrigerant port 156 and through the reheat coil 150.
The refrigerant flows through the third check valve 176 and the third expansion valve 168 and enters the second refrigerant port 146 of the cooling and heating coil 140. The cooling and heating coil fan 160 blows cooling and heating input air 210 over the cooling and heating coil 140, allowing the refrigerant in the cooling and heating coil 140 to absorb heat from the cooling and heating input air 210. As it absorbs heat from the input air 210, the refrigerant boils to become a gas. The gaseous refrigerant exits the cooling and heating coil 140 at the first refrigerant port 143 and flows down the first refrigerant pipe 180 and through the reversing valve 116. The refrigerant flows to the suction accumulator 113 and gaseous refrigerant from the suction accumulator 113 enters the inlet of the compressor 110.
In the cooling mode of the heat pump system 100, the controller 135 varies the cooling capacity of the air conditioner 100 by varying the speed of the compressor 110. Changing the speed of the compressor 110 changes the temperature of the cooling and heating coil 140.

Cooling With Reheat Operation

FIG. 3 is a diagram of a heat pump system 100 operating in a cooling with reheat mode. Cooling with reheat mode is used in situations when humidity is high, but the outdoor temperature is not high enough for the heat pump system 100 to provide dehumidification of the air without cooling it excessively. In this mode, the air is cooled for dehumidification and is reheated before it enters the air-conditioned space to ensure the comfort of the occupants. During the cooling mode, the first solenoid valve 164 is open (as indicated by it being shown as white) and the second solenoid valve 166 and the second expansion valve are closed (as indicated by them being shown in black). As shown in FIG. 3 , the second check valve 173 operates to prevent the flow of refrigerant (as indicated by it being shown as being partially black) and the first and third check valves 170, 176 pass refrigerant (as indicated by them being shown as white).
In a cooling with reheat mode of the heat pump system 100, hot gaseous refrigerant leaves the outlet of the compressor 110 and enters the condenser 118 via the reversing valve 116. The reversing valve 116 is in a state such that the refrigerant pipe 180 is connected to the suction accumulator 113 at the inlet of the compressor 110 and the outlet of the compressor 110 is connected to the condenser 118. Condenser input air 240 is blown over the condenser 118 by the condenser fan 119. The refrigerant transfers heat to the condenser input air 240 while it is in the condenser 118 and leaves the condenser 118 as a liquid at a high temperature. The controller 135 may control the amount of heat transferred from the refrigerant in the condenser 118 by controlling the speed of the condenser fan 119.
The liquid refrigerant flows through the first expansion valve 120 to the first node 190. The second check valve 173 prevents flow of refrigerant from the first node 190 to the fourth node 196 and the second solenoid valve 166 is closed to prevent flow of refrigerant from the second node 192 to the third node 194. The hot liquid refrigerant flows through the first solenoid valve 164, which is disposed in an open position. The refrigerant flows through the third refrigerant pipe 184 and enters the reheat coil 150 at the third refrigerant port 153. When it enters the reheat coil 150, the refrigerant may be a hot liquid or a mixture of liquid and gas. The cooling and heating coil fan 160 is operated to blow discharge air 220 that has been cooled by the cooling and heating coil 140 over the reheat coil 150. The discharge air 220 absorbs heat from the refrigerant that is flowing through the reheat coil 150 to be reheated to an appropriate temperature and becomes supply air 230 that is provided to an area being cooled.
The refrigerant exits the reheat coil 150 via the fourth refrigerant port 156 and flows through the first check valve 170 to the third node 194. The refrigerant flows through the fifth refrigerant pipe 188 via the third check valve 176 to the fourth node 196 where it then enters the second refrigerant pipe 182 and travels through the third expansion valve 168. The third expansion valve is set to lower the pressure of the refrigerant passing through it to thereby lower the temperature of the coolant.
The relatively lower-temperature refrigerant then enters the cooling and heating coil 140 through the second refrigerant port 146. The cooling and heating coil fan 160 is operated to blow cooling and heating input air 210 over the cooling and heating coil 140. The refrigerant that is flowing through the cooling and heating coil 140 absorbs heat from the cooling and heating input air 210. This cools the cooling and heating input air 210, which becomes discharge air 220.
The refrigerant exits the cooling and heating coil 140 via the first refrigerant port 143 after absorbing heat from the cooling and heating input air 210 and flows through the first refrigerant pipe 180. The refrigerant then enters the suction accumulator 113 via the reversing valve 116. Gaseous refrigerant from the suction accumulator 113 enters the inlet of the compressor 110, which continues the process. The controller 135 may control the speed of the compressor 110 to vary the amount of cooling provided by the heat pump system.
In the cooling with reheat operation, the cooling and heating coil 140 cools the input air 210 below a desired cooling temperature, resulting in discharge air 220 that is colder than is desired for the supply air 230. In some embodiments this may be done to dehumidify the input air 210. However, the reheat coil 150 heats the discharge air 220 such that the supply air 230 is the desired temperature.

Heating Operation

FIG. 4 is a diagram of a heat pump system 100 operating in a heating mode according to disclosed embodiments. In a heating mode of the heat pump system 100, hot gas refrigerant is discharged from an outlet of the compressor 110. The reversing valve 116 is disposed such that the outlet of the compressor 110 is connected to the first refrigerant pipe 180 and the condenser 118 is connected to the inlet of the compressor 110. During the cooling mode, the second expansion valve 123 is controlling (as indicated by it being shown as white) and both the first solenoid valve 164 and the second solenoid valve 166 are closed (as indicated by them being shown as black). As shown in FIG. 4 , the first and third check valves 170, 176 operate to prevent the flow of refrigerant (as indicated by them being shown as being partially black) and the second check valve 173 passes refrigerant (as indicated by it being shown as white).
In the heating mode of the heat pump system 100, hot gaseous refrigerant leaves the outlet of the compressor 110 and enters the cooling and heating coil 140 via the reversing valve 116. The reversing valve 116 is in a state such that the refrigerant pipe 180 is connected to the outlet of the compressor 110 and the inlet of the suction accumulator 113 is connected to the condenser 118. The relatively hot refrigerant flows through the first refrigerant pipe 180 to the first refrigerant port 143 of the cooling and heating coil 140 and into the cooling and heating coil 140. The cooling and heating coil fan 160 blows cooling and heating input air 210 over the cooling and heating coil 140. The cooling and heating input air 210 absorbs heat from the refrigerant flowing through the cooling and heating coil 140 and becomes discharge air 220. The cooling and heating coil fan 160 blows the discharge air 220 over the reheat coil 150.
The refrigerant is a subcooled liquid when it exits the cooling and heating coil 140 at the second refrigerant port 146. The subcooled refrigerant flows through the third expansion valve 168, which is controlled by the controller 135 to vary the amount of flow allowed through the cooling and heating coil 140. The refrigerant flows through the second check valve 173. A first portion of the refrigerant flows through a coil of the liquid heat exchanger 126 and is further subcooled. A second portion of refrigerant travels through the second expansion valve 123 and through the second coil of the liquid heat exchanger 126, where it absorbs heat from the first portion of the refrigerant. The second portion of the refrigerant then flows to the suction accumulator 113.
The first portion of the refrigerant flows through the first expansion valve 120 and into the condenser 118. Condenser input air 240 is blown across the condenser 118 by the condenser fan 119, and the refrigerant within the condenser 118 absorbs heat from the condenser input air 240 and becomes a vapor. The refrigerant vapor exits the condenser 118 and flows to the suction accumulator 113. Refrigerant vapor flows from the suction accumulator 113 to the inlet of the compressor 110. During heating mode, refrigerant does not flow through the reheat coil 150 because the first solenoid valve 164 is closed.
The reheat coil 150 does not circulate any refrigerant during the heating mode, so it does not perform any ongoing heat exchange with the discharge air 220. During most of the heating mode, the reheat coil simple passes the discharge air 220 as supply air 230. However, at the beginning of the heating mode, the refrigerant in the reheat coil 150 may be at a lower temperature than the discharge air 220. If this is the case, the refrigerant in the reheat coil 150 will absorb heat from the discharge air 220 until it is at a temperature at which heat exchange between the discharge air 220 and the refrigerant in the reheat coil 150 is negligible. Since the refrigerant in the reheat coil 150 is not circulating, no little heat is required to maintain the refrigerant in the reheat coil 150 at this relatively higher temperature throughout the heating mode.

Defrost Mode

FIG. 5 is a diagram of a heat pump system operating in a defrost mode according to disclosed embodiments. During the defrost mode, the first solenoid valve 164 is open (as indicated by it being shown as white) and the second solenoid valve 166 and the second expansion valve 123 are closed (as indicated by them being shown as black). As shown in FIG. 4 , the second check valve 173 operate to prevent the flow of refrigerant (as indicated by it being shown as being partially black) and the first and third check valves 170, 176 pass refrigerant (as indicated by them being shown as white).
In a defrost mode of the heat pump system 100, the reversing valve 116 is disposed such that the outlet of the compressor 110 is connected to the condenser 118 and the inlet of the suction accumulator 113 is connected to the first refrigerant pipe 180. Hot gas refrigerant exits the compressor 110 and enters the condenser 118 via the reversing valve 116.
During the defrost mode, the condenser fan 119 is set to stop the flow of air across the condenser 118 (represented by the stopped condenser input air 540 in FIG. 5 ). As a result there is no condenser input air 240 for the refrigerant to exchange heat with as it passes over the condenser 118, However, there will generally be frost formed on the condenser 118, which will be colder than the refrigerant flowing through condenser 118. Any frost that has accumulated on the condenser 118 therefore absorbs heat from the refrigerant and melts off the condenser 118. Having given up heat to melt the frost off the condenser 118, the refrigerant in the condenser 118 condenses to become a liquid.
The refrigerant then flows from the condenser 118 through the first expansion valve 120 and the liquid heat exchanger 126, where the liquid refrigerant may be cooled further. The liquid refrigerant flows from the liquid heat exchanger 126, through the first node 190 and through the first solenoid valve 164, which is in a fully open state, to the third refrigerant port 153. The second solenoid valve 166, which is in a fully closed state, prevents the refrigerant from flowing from the first node 190 to the third node 194 and the second check valve 173 prevents refrigerant flow from flowing from the first node 190 to the fourth node 196. In some embodiments the temperature of the refrigerant flowing between the condenser 118 and the reheat coil 150 during the defrost mode may be 10° F. to 60° F. However, this is just by way of example. The refrigerant flowing between the condenser 118 and the reheat coil 150 during the defrost mode may be different temperatures in some alternate embodiments.
Since the defrost mode is always entered into during a temporary break in the heating mode, the reheat coil 150 will typically be filled with warm liquid refrigerant that was heated by discharge air 220 blowing over the reheat coil 150 during the heating mode. The warm liquid refrigerant flows out of the reheat coil 150 via the fourth refrigerant port 156. The temperature of the refrigerant exiting the reheat coil 150 will be relatively high compared to the refrigerant being provided along the second refrigerant line from the condensing circuit 103 (e.g., 70° F. to 105° F.).
This relatively high-temperature refrigerant flows out of the reheat coil 150 via the fourth refrigerant port 156, through the first check valve 170, the third check valve 176, and to the third expansion valve 168. As it passes through the third expansion valve 168, the refrigerant flashes, or begins to boil, due to the drop in pressure. Because the refrigerant has been warmed while inside the reheat coil 150, a larger proportion of the refrigerant boils than it otherwise would if cold refrigerant was used. The refrigerant that is a mixture of gas and liquid enters the cooling and heating coil 140 through the second refrigerant port 146. The cooling and heating coil 140 is warm from operating in the heating mode. The refrigerant absorbs heat from the warm cooling and heating coil 140 and the remainder of the liquid refrigerant boils to become a vapor. The refrigerant evaporating temperature inside the cooling and heating coil 140 during the defrosting mode may be -10° F. to 40° F. Feeding the cooling and heating coil 140 with refrigerant that is already warm and that has already become partially gaseous adds to the total heat available in the cooling and heating coil 140 to defrost the condenser 118 and greatly shortens the necessary defrost time.
The refrigerant vapor exits the cooling and heating coil 140 through the first refrigerant port 143. The refrigerant vapor flows through the first refrigerant pipe 180 to the reversing valve 116 and the suction accumulator 113 and enters the compressor 110.
During the defrost mode, the cooling and heating fan coil 160 is set to stop the flow of air across the cooling and heating coil 140 (represented by the stopped heating and cooling input air 510, stopped discharge air 520, and stopped supply air 530 in FIG. 5 ). As a result, there is no heating and cooling input air 240 for the refrigerant to exchange heat with as it passes over the cooling and heating coil 140.

Method of Operation of a Heat Pump System in a Defrost Mode

FIG. 6 is a flow chart 600 showing the method of operation of a heat pump system in a defrost mode according to disclosed embodiments. The method begins with the heat pump system 100 entering a heating mode in step 605. In a heating mode of the heat pump system 100, refrigerant is maintained in a reheat coil 150, but refrigerant is not circulated through the reheat coil 150. (Step 610) This can be achieved in various embodiments by having valves (e.g., solenoid valves 164, 166) at the refrigerant ports 153, 156 of the reheat coil 150 and setting those valves to be fully closed during the heating mode, which can prevent the circulation of refrigerant through the reheat coil 150.
Refrigerant is then circulated through the cooling and heating coil 140 during the heating mode.(Step 615) This refrigerant will generally be warmer than the cooling and heating air 210 that will be passed over the heating and cooling coil 140 during the heating mode.
Cooling and heating input air 210 is blown across the cooling and heating coil 140 during the heating mode to generate discharge air 220. (Step 620) In an exemplary embodiment, this is accomplished by operating the cooling and heating coil fan 160. During this operation heat is exchanged between the refrigerant in the cooling and heating coil 140 and the cooling and heating input air 210 such that the discharge air 220 is warmer than the cooling and heating input air 210.
The discharge air 220 is blown over the reheat coil 150 during a heating mode to generate supply air 230. (Step 625) In an exemplary embodiment, this is accomplished by operating the cooling and heating coil fan 160. Since the refrigerant in the reheat coil 150 is not circulated, the temperature of the supply air 230 will be essentially the same as the temperature of the discharge air 220, except at the very beginning of the heating mode when the refrigerant in the reheat coil 150 may need to be initially heated to a temperature at which it will no longer exchange any significant heat with the discharge air 220 passing through the reheat coil 150.
The heat pump system 100 then moves from a heating mode to a defrost mode. (Step 630) In an exemplary embodiment, this may occur when the heat pump system 100 receives a signal from the controller 135 indicating a start of a defrost mode. This may be in response to one or more sensors signals indicative of frost having formed on coils of a condenser, a timer, or any other triggering signal.
Upon entering the defrost mode, the cooling and heating input air 210 stops blowing across the cooling and heating coil 140. In an exemplary embodiment, this is accomplished by stopping the operation of the cooling and heating coil fan 160. (Step 635)
Likewise, upon entering the defrost mode, the discharge air 220 stops blowing over the reheat coil 150. In an exemplary embodiment, this is accomplished by stopping the operation of the cooling and heating coil fan 160. (Step 640)
In many embodiments a single cooling and heating fan 160 will be used to both blow the cooling and heating input air 210 across the cooling and heating coil 140 and to blow the discharge air 220 over the reheat coil 150. In this case, steps 635 and 640 can be performed simultaneously by stopping operation of the cooling and heating fan 160.
Refrigerant from the reheat coil 150 is circulated to the cooling and heating coil 140 during the defrost mode. (645) In some embodiments, the temperature of the refrigerant exiting the reheat coil 150 may be 70° F. to 105° F. (though this can vary in alternate embodiments based on the temperature of the discharge air 220 in the heating mode). In contrast, the evaporating temperature in the cooling and heating coil 140 may be -10° F. to 40° F.
Circulating the refrigerant from the reheat coil 150 to the cooling and heating coil 140 may be achieved by operating valves that were used to isolate the reheat coil 150 during the heating mode (e.g., by opening the first solenoid valve 164 and closing the second solenoid valve 166 in the embodiment of FIGS. 1-5 ).
Refrigerant from the cooling and heating coil 140 is also circulated to the condenser 118 in the defrost mode. (Step 650) The refrigerant from the cooling and heating coil 140 is initially warm in the defrost mode because the heat pump system 100 was operating in heating mode immediately prior to entering the defrost mode. The warm refrigerant circulated to the condenser 118 warms the condenser 118 and causes frost that has formed on the condenser 118 to begin melting.
The refrigerant that was maintained in the reheat coil 150 without being circulated during the heating mode was also heated by the warm discharge air 220 blown over the reheat coil 150 by the cooling and heating coil fan 160 during the heating mode. As this relatively warm refrigerant is provided to the cooling and heating coil 140 during the defrost mode, it will increase the amount of heat available to the cooling and heating coil 140 relative to what would have been available if the cooling and heating coil 140 received only refrigerant from the condensing circuit 103. This will allow the cooling and heating coil 140 to provide heat to the condenser 118 more quickly and can reduce the length of a defrost mode necessary to remove frost from the coils of the condenser 118.
For example, the refrigerant that was warmed in the reheat coil 150 could pass through an expansion valve (e.g., third expansion valve 168 in FIGS. 1-5 ). As it passes through the expansion valve, the refrigerant flashes, or begins boiling, to become a mixture of gas and liquid. The refrigerant enters the cooling and heating coil 140, which is warm from operating in a heating mode, and the remainder of the liquid refrigerant absorbs heat from the cooling and heating coil 140 and boils off. Because the refrigerant was already warm when it began boiling, less heat is absorbed by the refrigerant from the cooling and heating coil 140 than would otherwise be absorbed by refrigerant that was cold prior to passing though the third expansion valve 168. This maximizes the amount of heat available in the cooling and heating coil 140 to be used to defrost the condenser 118 and reduces the defrosting time.
Although the operation of circulating refrigerant from the cooling and heating coil 140 to the condenser 118 (step 645) is listed before the operation of circulating refrigerant from the reheat coil 150 to the cooling and heating coil 140 (Step 650), these processes are typically performed at the same time and continually.
After a time, the heat pump system 100 moves from the defrost mode back to the heating mode. (Step 655) This may occur after a set period of time or in response to sensor signals similar to those that triggered the defrost mode to begin with. In an exemplary embodiment, the heat pump system 100 may receive a signal from a controller 135 indicating an end of the defrosting mode and a resumption of the heating mode. Once in the heating mode the system will again stop circulating refrigerant from the reheat coil 150 to the cooling and heating coil 140 (Step 610), resuming circulating refrigerant through the heating and cooling coil 140 (Step 615), resuming blowing cooling and heating input air 210 across the cooling and heating coil 140 to generate discharge air 220 (Step 620), and resuming blowing discharge air 220 over the reheat coil 150 to generate supply air 230 (625).
The various embodiments which demonstrate a method for controlling a heat pump system have been discussed in detail above. It should be further noted that the above-described processes can be stored as instructions in computer-readable storage medium. When the instructions are executed by a computer (e.g., a processor 137 in a controller 135), for example after being loaded from a computer-readable storage medium (e.g., a memory 139 in a controller 135), the process(es) are performed. In one or more embodiments, a non-transitory computer readable medium may be provided which comprises instructions for execution by a computer, the instructions including a computer-implemented method for controlling an air-conditioning system to defrost a condenser coil, as described above. The non-transitory computer readable medium may comprise, for example, a read-only memory (ROM), a random-access memory (RAM), a programmable ROM (PROM), and/or an electrically erasable read-only memory (EEPROM).

Conclusion

This disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention rather than to limit the true, intended, and fair scope and spirit thereof. The foregoing description is not intended to be exhaustive or to limit the invention to the preci se form disclosed. Modifications or variations are possible in light of the above teachings. The embodiment(s) was chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled. The various circuits described above can be implemented in discrete circuits or integrated circuits, as desired by implementation.

Claims

1. A heat pump system comprising:

a cooling and heating coil having a first refrigerant port and a second refrigerant port and configured to circulate refrigerant;

a reheat coil having a third refrigerant port and a fourth refrigerant port and configured to circulate the refrigerant;

a plurality of refrigerant pipes configured to circulate the refrigerant, the plurality of refrigerant pipes including

a first refrigerant pipe connected between the first refrigerant port and a condensing circuit,

a second refrigerant pipe connected between the second refrigerant port and the condensing circuit,

a third refrigerant pipe connected between the third refrigerant port and a first node on the second refrigerant pipe,

a fourth refrigerant pipe connected between the fourth refrigerant port and a second node on the third refrigerant pipe, and

a fifth refrigerant pipe connected between a third node on the fourth refrigerant pipe and a fourth node on the second refrigerant pipe;

a first solenoid valve formed on the third refrigerant pipe between the third refrigerant port and the second node;

a second solenoid valve formed on the fourth refrigerant pipe between the second node and the third node;

an expansion valve connected between the second refrigerant port and the fourth node;

a first check valve connected between the fourth refrigerant port and the third node and configured to prevent flow of the refrigerant from the third node to the fourth refrigerant port;

a second check valve connected between the first node and the fourth node and configured to prevent flow of the refrigerant from the first node to the fourth node;

a third check valve connected between the third node and the fourth node and configured to prevent flow of the refrigerant from the fourth node to the third node;

a fan circuit configured to blow input air across the cooling and heating coil to generate discharge air and to blow the discharge air over the reheat coil to generate supply air; and

a controller configured to control the heat pump system.

2. The heat pump system of claim 1, wherein the expansion valve is an electronically controlled expansion valve.

3. The heat pump system of claim 1, wherein the first solenoid valve is a positive off solenoid valve.

4. The heat pump system of claim 1, wherein the second solenoid valve is a positive off solenoid valve.

5. A method for operating a heat pump system to defrost a condenser coil, the method comprising:

maintaining refrigerant in a reheat coil without circulating the refrigerant through the reheat coil during a heating mode;

circulating refrigerant through a cooling and heating coil during the heating mode;

blowing input air across the cooling and heating coil during the heating mode to generate discharge air, the discharge air in the heating mode being warmer than the input air;

blowing the discharge air over the reheat coil during the heating mode to generate supply air;

circulating refrigerant from the reheat coil to the cooling and heating coil after entering a defrost mode; and

circulating refrigerant from the cooling and heating coil to the condenser coil during the defrost mode.

6. The method of claim 5, further comprising:

stopping blowing the input air across the cooling and heating coil and stopping blowing the discharge air over the reheat coil after entering a defrost mode.

7. The method of claim 5, further comprising

stopping blowing the input air across the cooling and heating coil and stopping blowing the discharge air over the reheat coil in response to entering the defrost mode, wherein

the circulating of the refrigerant from the reheat coil to the cooling and heating coil is performed after the stopping of blowing the input air across the cooling and heating coil and the stopping of blowing the discharge air over the reheat coil, and

the circulating of the refrigerant from the cooling and heating coil to the condenser coil is performed after the stopping of blowing the input air across the heating and cooling coil and the stopping of blowing the discharge air over the reheat coil.

8. The method of claim 5, wherein the circulating of the refrigerant from the reheat coil to the cooling and heating coil is achieved by opening a first solenoid valve and closing a second solenoid valve.

9. The method of claim 5, further comprising

receiving from a controller a signal indicating a start of a defrosting mode prior to entering the defrost mode.

10. The method of claim 5, further comprising:

receiving a signal from a controller indicating an end of a defrosting mode and a resumption of the heating mode; and

stopping circulating refrigerant from the reheat coil to the cooling and heating coil after the defrosting mode has ended and the heating mode has resumed.

11. The method of claim 10, wherein

the circulating of the refrigerant from the reheat coil to the cooling and heating coil is achieved by opening a first solenoid valve and closing a second solenoid valve; and

the stopping of the circulating of the refrigerant from the reheat coil to the cooling and heating coil is achieved by closing the first solenoid valve and opening the second solenoid valve.

12. The method of claim 10, further comprising:

resuming blowing input air across the cooling and heating coil to generate discharge air after the defrosting mode has ended and the heating mode has resumed;

resuming blowing the discharge air over the reheat coil to generate supply air after the defrosting mode has ended and the heating mode has resumed.

13. A non-transitory computer-readable medium comprising instructions for execution by a computer, the instructions including a computer-implemented method for controlling a heat pump system to defrost a condenser coil, the instructions for implementing:

14. The non-transitory computer-readable medium, as recited in claim 13, the instructions for further implementing:

15. The non-transitory computer-readable medium, as recited in claim 13, the instructions for further implementing:

the circulating of the refrigerant from the cooling and heating coil to the condenser coil is performed after the stopping of blowing the input air across the cooling and heating coil and the stopping of blowing the discharge air over the reheat coil.

16. The non-transitory computer-readable medium, as recited in claim 13, wherein the circulating of the refrigerant from the reheat coil to the cooling and heating coil is achieved by opening a first solenoid valve and closing a second solenoid valve.

17. The non-transitory computer-readable medium, as recited in claim 13, the instructions for further implementing:

exiting the defrosting mode and resuming the heating mode; and

18. The non-transitory computer-readable medium, as recited in claim 17, wherein

19. The non-transitory computer-readable medium, as recited in claim 17, the instructions for further implementing:

resuming blowing input air across the cooling and heating coil to generate discharge air after the defrosting mode has ended and the heating mode has resumed; and