System and method for defrosting outdoor coils in reversible rooftop units

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;
• and
• determining, by a processor, that a condition to operate in the defrost mode for the outdoor coil is met;
• and
• in 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;
• and
• communicating, by the processor, a fourth electronic signal to the exhaust damper to open the exhaust damper.

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;
• and
• in 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;
• and
• the 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;
• and
• 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 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;
• and
• the fresh air damper is configured to allow ambient air to flow through the indoor coil during the defrost mode;
• and
• communicate 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;
• and
• the exhaust damper is configured to allow airflow to surrounding environment after passing through the indoor coil during the defrost mode.