A refrigeration cycle apparatus includes a compressor, first and second heat exchangers, an expansion valve, a four-way valve, and a controller. The four-way valve is configured to switch a direction of flow of the refrigerant between a first direction and a second direction. The controller is configured to control the four-way valve to switch an operation from a defrosting operation in which the refrigerant flows in the second direction, to a heating operation in which the refrigerant flows in the first direction, to perform a heating preparation control for increasing a degree of superheat of the refrigerant output to the compressor from the second heat exchanger, and thereafter to start the heating operation.

A refrigeration cycle apparatus includes: a refrigerant circuit including a compressor, a condenser, an expansion device, and an evaporator; a first detector provided to the compressor, and configured to detect a temperature of the compressor; a second detector provided between the compressor and the expansion device in the refrigerant circuit, and configured to detect one of a temperature of refrigerant and a pressure of the refrigerant; and a controller configured to control at least one of frequency of the compressor and an opening degree of the expansion device based on the temperature detected by the first detector and one of the temperature and the pressure detected by the second detector so as to maintain a concentration of a refrigerating machine oil dissolved in the refrigerant in the compressor and an oil level of the refrigerating machine oil in the compressor within respective predetermined ranges.

An air-conditioning apparatus includes a refrigerant circuit connecting a compressor, a first heat exchanger, a first expansion device, and a second heat exchanger. The compressor and the first heat exchanger are housed in a heat source unit, the heat source unit, houses a second expansion device provided at a location on a downstream side with respect to the first heat exchanger and on an upstream side with respect to the first expansion device, and the second expansion device and the first expansion device are connected via an extension pipe. The second expansion device reduces a pressure of refrigerant flowing into the extension pipe in cooling operation to cause the refrigerant to turn into refrigerant having a medium pressure and in a two-phase state, and the medium pressure is lower than a refrigerant pressure in a condenser and higher than a refrigerant pressure in an evaporator.

A method of defrosting an indoor coil in a refrigeration system including, while the system is operating in the refrigeration mode, with a controller of the refrigeration system, determining a defrost commencement time at which the refrigeration system is to commence operating in the defrost mode. With the controller, one or more defrost energy conservation processes are initiated prior to the defrost commencement time, to decrease a rate at which thermal energy is transferred from the refrigerant in the outdoor coil to ambient air around the outdoor coil. The defrost energy conservation process continues until a defrost energy conservation termination criterion is satisfied, at which time the defrost energy conservation process is terminated. Upon termination of the defrost energy conservation process, operation of the refrigeration system in the defrost mode is commenced.

An air-conditioning apparatus includes an outdoor unit with a compressor, an outdoor heat exchange, a four-way valve for switching a refrigerant flow passage, and an outdoor flow control valve which controls the flow rate of a liquid refrigerant; and an indoor unit that includes an indoor heat exchanger, and an indoor flow control valve which reduces refrigerant pressure. A refrigerant circuit is formed by connecting the outdoor unit and at least one indoor unit by a pipe. A controller controls a component of the refrigerant circuit, based on the relationship between a first target set temperature used for temperature control of air to be conditioned and a preset second target set temperature.

An air-conditioning apparatus includes a heat medium system configured to control a flow rate of the heat medium supplied to the heat source unit side heat exchanger that exchanges heat between refrigerant and the heat medium, the heat medium system having at least one system of a heat medium conveyor, a heat medium flow rate adjuster, and a heat medium flow rate control device. In the air-conditioning apparatus, the operation of each of use-side heat exchangers is changed to a cooling operation or a heating operation in accordance with a control command, and a cooling and heating concurrent operation is performed. The refrigerant is caused to flow through the heat source unit side heat exchanger in accordance with the ratio of the total cooling capacity of the use-side heat exchangers to the total heating capacity of the use-side heat exchangers. The heat medium flow rate control device controls the flow rate of the heat medium supplied to the heat source unit side heat exchanger, using the temperature of the heat medium flowing into the heat source unit side heat exchanger and the temperature of the heat medium flowing from the heat source unit side heat exchanger.

A system and method are described that help to alleviate pressure and strain spikes in and around dead tubes or frontiers between stages in a multi-stage condenser coil. Instead of cycling a fan off and on, fans associated with the condenser are kept running at a low speed instead of being turned off. Preventing the fans from turning off completely helps to even out the pressure and strain spikes. The present teachings can be especially beneficial in aluminum-based coils. The present teachings include both a unit controller that carries out the teachings, and a system based on temperature and/or pressure switches connected to a fan controller.

A method for monitoring gas pressure in a heat rejecting heat exchanger in a cooling circuit is disclosed. The present capacity of one or more compressors in the cooling circuit compared to a maximum capacity of the one or more compressors is established. If the present capacity of the one or more compressors is at least at a level corresponding to a pre-set percentage of the maximum capacity, a period of time elapsed from a point in time where the compressor capacity reached said level is established. If the established period of time has a duration which is longer than a pre-set period of time, then it is concluding that the cooling medium is in a gas loop operational mode, allowing an operator or a controller to adjust operation of the cooling plant such that the cooling medium is brought out of the gas loop operational mode.

A refrigeration cycle apparatus includes: a refrigerant circuit including a compressor, a condenser, an expansion device, and an evaporator; a first detector provided to the compressor, and configured to detect a temperature of the compressor; a second detector provided between the compressor and the expansion device in the refrigerant circuit, and configured to detect one of a temperature of refrigerant and a pressure of the refrigerant; and a controller configured to control at least one of frequency of the compressor and an opening degree of the expansion device based on the temperature detected by the first detector and one of the temperature and the pressure detected by the second detector so as to maintain a concentration of a refrigerating machine oil dissolved in the refrigerant in the compressor and an oil level of the refrigerating machine oil in the compressor within respective predetermined ranges.

A compressor unit includes a first case, a compressor, a connecting port, and a shutoff valve. The connecting port includes a first connecting port and a second connecting port. The shutoff valve includes a first shutoff valve and a second shutoff valve. A heat source heat exchanger is accommodated in a second case. A utilization heat exchanger is accommodated in a third case. The compressor unit is disposed inside a building. The first connecting port is connected to the heat source heat exchanger via a first connection piping. The second connecting port is connected to the utilization heat exchanger via a second connection piping. The first shutoff valve shuts off flow of a refrigerant between the first connecting port and the heat source heat exchanger. The second shutoff valve shuts off flow of the refrigerant between the second connecting port and the utilization heat exchanger.