Provided is a multi-type air conditioner, including: an outdoor unit having a liquid pipe through which a liquid refrigerant flows, and a gas pipe through which a gas refrigerant flows; a plurality of indoor units comprising a first indoor unit and a second indoor unit each connected to the liquid pipe and the gas pipe to circulate a refrigerant; a gas pipe connecting tube connecting the gas pipe and the plurality of indoor units so that a gas refrigerant flows therethrough; and a liquid pipe connecting tube connecting the liquid pipe and the plurality of indoor units so that a liquid refrigerant flows therethrough. The first indoor unit may include: a first indoor heat exchanger comprising a first heat exchanger configured to perform heat exchange between indoor air and a refrigerant, and a second heat exchanger configured to perform heat exchange between indoor air and a refrigerant and arranged in a stacked fashion with the first heat exchanger; a first indoor fan configured to blow air to the first heat exchanger and the second heat exchanger; a first liquid branch pipe connecting the liquid pipe connecting tube and the first heat exchanger so that a refrigerant flows therethrough; a first gas branch pipe connecting the gas pipe connecting tube and the second heat exchanger so that a refrigerant flows therethrough; a first heat exchanger connecting pipe connected to the first heat exchanger so that a refrigerant flows therethrough; a second heat exchanger connecting pipe connected to the second heat exchanger so that a refrigerant flows therethrough; a return pipe having one side connected to the first gas branch pipe and the other side connected to the first heat exchanger connecting pipe and the second heat exchanger connecting pipe; a first indoor expansion valve disposed at the second heat exchanger connecting pipe, wherein an opening amount of the first indoor expansion valve is adjusted in response to an input signal from a controller to selectively expand a flowing refrigerant; and a first expansion valve disposed in the return pipe, wherein an opening amount of the first expansion valve is adjusted in response to an input signal from the controller to selectively expand a flowing refrigerant.

Since the multi-type air conditioner according to the present disclosure can operate the first heat exchanger as a condenser and the second heat exchanger as an evaporator among the indoor heat exchangers, it is possible to constantly operate the dehumidifying mode while maintaining a room temperature within a predetermined range.

A sound level control system for a heating, ventilation, and air conditioning (HVAC) system is provided. The sound level control system comprises an outdoor unit with a compressor, an outdoor fan, and an outdoor controller and a communication device located at a predefined distance from the outdoor unit. The communication device measures sound levels in response to operating the outdoor unit. The outdoor controller is configured to receive a first noise level limit for a predefined time period, receive an instruction related to selective control of the outdoor unit, selectively control both of the compressor to rotate at a first compressor speed and the outdoor fan to rotate at a first fan speed based on the noise level limit for the predefined time period, and receive information related to whether a sound pressure level at a predefined location exceeds the first noise level limit for the predefined time period.

A low ambient cooling system for a variable refrigerant flow heat pump includes an outdoor air conditioning unit and an indoor air conditioning unit. The outdoor air conditioning unit includes an outdoor heat exchanger with one or more valves that selectively control refrigerant flow through different sections of condenser coils during a low ambient cooling mode. During the low ambient cooling mode, the condenser coils of the outdoor heat exchanger include an active coil section through which refrigerant flows and an inactive coil section that is closed. An outdoor-coil restrictor plate with holes is attached to the active condenser coil in the outdoor air conditioning unit. The outdoor-coil restrictor plate restricts excessive heat release from the active coil section of the condenser coils in the outdoor heat exchanger during the low ambient cooling mode.

An air-conditioning apparatus includes a controller configured to control operations of an outdoor fan. The controller has a voltage acquisition unit configured to acquire drive voltages of the outdoor fan at set time intervals while the rotation speed of the outdoor fan is maintained at a reference rotation speed, a determination unit configured to determine whether or not an acquired drive voltage is equal to or greater than a lower limit threshold and less than an upper limit threshold, an extraction unit configured to calculate an evaluation value by extracting a drive voltage determined to be equal to or greater than the lower limit threshold and less than the upper limit threshold, and a defrosting determination unit configured to decide to defrost the outdoor heat exchanger if the calculated evaluation value is equal to or greater than an evaluation threshold.

Provided is an air conditioner configured such that the inside of an indoor unit is dried while an increase in a humidity in a room is suppressed. The air conditioner of the present invention includes an outdoor unit and an indoor unit having an indoor heat exchanger and a decompression device. The indoor heat exchanger has a first heat exchange portion and a second heat exchange portion. The decompression device is connected to the first heat exchange portion and the second heat exchange portion. This air conditioner performs cooling operation or dehumidifying operation in which the first heat exchange portion and the second heat exchange portion function as evaporators and reheat dehumidifying operation in which the first heat exchange portion functions as a condenser and the second heat exchange portion functions as the evaporator. Moreover, water repelling treatment is performed for the second heat exchange portion

When a controller performs a defrosting operation in which frost on an outdoor heat exchanger is caused to be melted, the controller is configured to perform a first defrosting control in which a switching state of a switching device is set to a first state, after the controller performs the first defrosting control, perform a second defrosting control in which the switching state of the switching device is set to a second state, and after the controller performs the second defrosting control, perform a third defrosting control in which the switching state of the switching device is set to the first state.

An air conditioner and a control method for the same, the air conditioner including an air conditioning unit including a compressor, a first heat exchanger, an expansion valve, and a second heat exchanger; and a controller configured to obtain enthalpy of a refrigerant flowing in the air conditioning unit, obtain an air conditioning capacity using a circulation amount of the refrigerant and the obtained enthalpy of the refrigerant, obtain efficiency based on the obtained air conditioning capacity and supplied power, and control the air conditioning unit according to the obtained efficiency.

A sound level control system for a heating, ventilation, and air conditioning (HVAC) system is provided. The sound level control system comprises an outdoor unit with a compressor, an outdoor fan, and an outdoor controller and a communication device located at a predefined distance from the outdoor unit. The communication device measures sound levels in response to operating the outdoor unit. The outdoor controller is configured to receive a first noise level limit for a predefined time period, receive an instruction related to selective control of the outdoor unit, selectively control both of the compressor to rotate at a first compressor speed and the outdoor fan to rotate at a first fan speed based on the noise level limit for the predefined time period, and receive information related to whether a sound pressure level at a predefined location exceeds the first noise level limit for the predefined time period.

An air conditioner and control method for reducing power consumption by controlling pressure or temperature of a refrigerant. The air conditioner includes a compressor compressing a refrigerant and discharging a high pressure refrigerant gas; an outdoor heat exchanger in which the high pressure refrigerant gas is changed to a refrigerant fluid; an outdoor fan to blow outdoor air to the outdoor heat exchanger; a decompressor decompressing the refrigerant fluid into a low pressure state; an indoor heat exchanger changing the decompressed low pressure refrigerant fluid to a refrigerant gas; and a controller configured to control pressure or temperature of the refrigerant based on an operation condition including at least two of a first condition determined based on an installation environment, a second condition determined based on an optimal compression ratio of the compressor, a third condition determined based on outdoor temperature, and a fourth condition set as a default value.

Provided is a failure diagnosis system that diagnoses the state of an air-conditioning apparatus having a refrigerant circuit in which refrigerant circulates. The failure diagnosis system has an abnormality diagnosis unit that performs normal-operation abnormality diagnosis for determining whether or not there is an abnormality in the air-conditioning apparatus by using state data and control data during normal operation of the air-conditioning apparatus. If the abnormality diagnosis unit determines that there is an abnormality in the air-conditioning apparatus, the abnormality diagnosis unit changes a control value for an actuator of the air-conditioning apparatus and acquires state data and control data. Then, the abnormality diagnosis unit performs abnormality-cause identification diagnosis for identifying the cause of the abnormality in the air-conditioning apparatus by using the state data and the control data acquired before the change of the control value and the state data and the control data acquired after the change of the control value.