The disclosed technology includes an on-demand water heater which uses a heat pump to heat the fluid. The on-demand heat pump water heater can have a low fluid capacity heating chamber which has an inlet and an outlet, a heat pump for heating the fluid, and a controller to control the heat pump and maintain the temperature of the fluid at a predetermined temperature. The on-demand heat pump water heater can include one or more temperature sensors, flow sensors, fluid mixing valves, or supplemental heat sources.

The disclosed technology includes an on-demand water heater which uses a heat pump to heat the fluid. The on-demand heat pump water heater can have a low fluid capacity heating chamber which has an inlet and an outlet, a heat pump for heating the fluid, and a controller to control the heat pump and maintain the temperature of the fluid at a predetermined temperature. The on-demand heat pump water heater can include one or more temperature sensors, flow sensors, fluid mixing valves, or supplemental heat sources.

The disclosed technology includes an on-demand water heater which uses a heat pump to heat the fluid. The on-demand heat pump water heater can have a low fluid capacity heating chamber which has an inlet and an outlet, a heat pump for heating the fluid, and a controller to control the heat pump and maintain the temperature of the fluid at a predetermined temperature. The on-demand heat pump water heater can include one or more temperature sensors, flow sensors, fluid mixing valves, or supplemental heat sources.

An air conditioning system has: an indoor fan that sends air into a room through an air-blowing flow path; a heat pump unit that air-conditions the room with a vapor compression refrigerant circuit; and a separate heat source unit that air-conditions the room with a furnace that heats air by burning fuel or an electric heater that heats air with heat generated by energization. As a refrigerant, a flammable refrigerant is sealed in the refrigerant circuit. A controller controls an operation of the indoor fan, the heat pump unit, and the separate heat source unit. When starting air conditioning in the room with the separate heat source unit, the controller brings a state where the indoor fan is in operation before causing an operation for burning fuel in the furnace.

A supplemental heating system includes an enclosure that encloses a primary heating device. The enclosure includes an inlet damper, an outlet damper, and an intermediate damper. In an idle state, the inlet damper and outlet damper are open while the intermediate damper is closed. In an active state, the inlet damper and outlet damper are closed while the intermediate damper is open, so that air is circulated within the enclosure.

A refrigeration cycle device performs a heating operation and a defrosting operation. A refrigerant circulates in opposite directions in the defrosting operation and the heating operation. The refrigeration cycle device includes a compressor, a first heat exchanger and a second heat exchanger, a decompressor, and a flow path switch. In the heating operation, the refrigerant circulates in the order of the compressor, the first heat exchanger, the decompressor, and the second heat exchanger. In the defrosting operation, the refrigerant circulates in the order of the compressor, the second heat exchanger, the decompressor, and the first heat exchanger. The defrosting operation includes a first mode and a second mode. The opening of the decompressor is greater in the first mode than in the heating operation. The opening of the decompressor is less in the second mode than in the first mode.

Air conditioner units and methods for operating air conditioner units are provided. A method includes determining a steady state speed of a blower fan of the air conditioner unit. The method further includes receiving a call for heating and activating the blower fan in response to the call for heating. The method further includes measuring a speed of the blower fan after activating the blower fan and comparing the measured speed of the blower fan to the steady state speed of the blower fan. When the measured speed of the blower fan is greater than the steady state speed of the blower fan, the method includes disabling one of a plurality of heater banks of a heating unit of the air conditioner unit.

A heating unit for a heating, ventilation and/or air conditioning (HVAC) system may have a first airflow path through the heating unit, a second airflow path through the heating unit, and a heater assembly having a first heating coil positioned within the first airflow path, a second heating coil positioned within the second airflow path, and a coil divider separating the first heating coil and the second heating coil.

Air conditioner units and methods for operating air conditioner units are provided. A method includes determining a steady state speed of a blower fan of the air conditioner unit. The method further includes receiving a call for heating and activating the blower fan in response to the call for heating. The method further includes measuring a speed of the blower fan after activating the blower fan and comparing the measured speed of the blower fan to the steady state speed of the blower fan. When the measured speed of the blower fan is greater than the steady state speed of the blower fan, the method includes disabling one of a plurality of heater banks of a heating unit of the air conditioner unit.

A refrigeration cycle device performs a heating operation and a defrosting operation. A refrigerant circulates in opposite directions in the defrosting operation and the heating operation. The refrigeration cycle device includes a compressor, a first heat exchanger and a second heat exchanger, a decompressor, and a flow path switch. In the heating operation, the refrigerant circulates in the order of the compressor, the first heat exchanger, the decompressor, and the second heat exchanger. In the defrosting operation, the refrigerant circulates in the order of the compressor, the second heat exchanger, the decompressor, and the first heat exchanger. The defrosting operation includes a first mode and a second mode. The opening of the decompressor is greater in the first mode than in the heating operation. The opening of the decompressor is less in the second mode than in the first mode.