An air conditioner has a refrigerant circuit filled with a predetermined amount of a refrigerant, the circuit being formed of an outdoor unit and an indoor unit connected to each other by refrigerant piping, the outdoor unit having a compressor, an outdoor heat exchanger, and an expansion valve, the indoor unit having an indoor heat exchanger. The conditioner has an estimation model that estimates an amount of remaining refrigerant remaining in the circuit by using at least rotation frequency of the compressor, refrigerant discharge temperature at the compressor, heat exchanger temperature, degree of opening of the expansion valve, and outside air temperature, of operation state quantities indicating operation states during operation. The indoor heat exchanger has a sensor that is provided at an indoor heat exchanger intermediate portion connecting a first indoor heat exchanger port and a second indoor heat exchanger port to each other.

A heat exchange system and a method for determining whether flow of cooling medium passing through a heat exchanger is too low. The heat exchange system includes a refrigerant flow path in which refrigerant circulates; a cooling medium flow path in which cooling medium circulates; and a heat exchanger connected to both the refrigerant flow path and the cooling medium flow path so that the refrigerant and the cooling medium exchange heat in the heat exchanger. The heat exchange system includes a first temperature sensor arranged at a cooling medium inlet of the heat exchanger, a second temperature sensor at a cooling medium outlet of the heat exchanger, and a controller in communication with the first temperature sensor and the second temperature sensor. The controller is configured to determine whether the flow of cooling medium in the heat exchanger is too low based on a temperature difference.

According to one embodiment, a motor drive unit includes a motor including a plurality of phase windings in a mutually unconnected state, a first inverter which controls application of electric power to one ends of the phase windings, a second inverter which controls application of electric power to the other ends of the phase windings, relays each of which includes a make break contact connected between the other ends of the phase windings, and a controller which switches, according to a value of a current flowing through the motor, between an open-windings mode and a star-connection mode.

An EXV (electronic expansion valve) control system includes an EXV controller for controlling an EXV within the refrigerant loop of an HVAC system. The EXV controller implements a master control algorithm that includes a plurality of sub-control algorithms and an initial series of branching decision points to determine the current mode of operation and to execute select sub-control algorithms corresponding to the current mode of operation, while not executing the sub-control algorithms corresponding to the other modes of operation. The sub-control algorithms implement various combinations of PID (Proportional Integral Derivative) control and feed-forward control, the results of which can be mapped to specific control instructions for the EXV.

An air conditioner unit includes a refrigeration loop, a variable speed compressor urging refrigerant through the refrigeration loop, a temperature sensor to detect a temperature within a room, and a controller operably coupled to the variable speed compressor. The controller is configured to initiate the compressor at a fixed speed, determine an estimated target temperature of the room, determine an actual temperature of the room, generate a target compressor speed, and initiate the compressor at the target speed.

Provided is a control method on electronic expansion valve in air conditioner comprises: obtaining a real-time running frequency of compressor, a real-time exhaust temperature and a real-time outdoor environment temperature as the compressor running; comparing the real-time running frequency of compressor with a first set frequency; if the real-time running frequency is greater than or equal to the first set frequency, obtaining an integral coefficient of the PID algorithm according to a first set rule; if the real-time running frequency is less than the first set frequency, obtaining an integral coefficient of the PID algorithm according to the comparison of the real-time outdoor environment temperature and the first set outdoor environment temperature and a second set rule, or according to the comparison of the real-time outdoor environment temperature and the first set outdoor environment temperature and a third set rule, wherein the selection is based on whether the air conditioner is working in cooling mode or in heating mode; performing a PID control on the electronic expansion valve by an error of the difference between real-time exhaust temperature and a set target exhaust temperature. The method realizes an accurate and stable control on electronic expansion valve opening amount.

An economizer control system includes a compressor including a compression area, a piston chamber, and an economizer inlet configured to receive economizer vapor into the compression area via a flow path that extends between the economizer inlet and the compression area. At least a portion of the flow path traverses the piston chamber. The economizer control system also includes a piston disposed within the piston chamber and configured to contact the economizer vapor. The piston is moveable between an open position that opens the flow path and a closed position that closes the flow path. Additionally, the economizer control system includes a biasing system configured to apply force to the piston to bias the piston toward the closed position.

An HVAC system includes an unloading device, a centrifugal compressor, a gas foil bearing, a VFD and a controller. The controller is programmed to start the centrifugal compressor from a stopped condition by operating the unloading device to remove a load from the centrifugal compressor, accelerating the motor to a first speed above a liftoff speed of the gas foil bearing and below an operating speed of the centrifugal compressor, running the motor for a period of time, operating the unloading device to apply the load to the centrifugal compressor, and accelerating the motor to the operating speed.

A motor drive device: a power conversion unit; a current detection unit that detects a phase current of the alternating-current motor; a position/speed specifying unit that specifies a magnetic pole position and a rotational speed of the alternating-current motor; a d-axis current pulsation generating unit that generates a d-axis current pulsation command based on q-axis current pulsation or a q-axis current pulsation command, which being in synchronization with the q-axis current pulsation or the q-axis current pulsation command and preventing or reducing an increase or decrease in amplitude of the voltage command; and a dq-axis current control unit that generates the voltage command for controlling the phase current on the dq rotating coordinates, which rotate in synchronization with the magnetic pole position, by using the magnetic pole position, the rotational speed, the phase current, the q-axis current pulsation or the q-axis current pulsation command, and the d-axis current pulsation command.

A refrigeration cycle apparatus includes low-pressure side pressure detecting means for detecting the pressure of a refrigerant being sucked by a compressor, suction refrigerant temperature detecting means for detecting the temperature of the refrigerant being sucked by the compressor, frequency detecting means for detecting the operation frequency of the compressor, cooling target fluid inflow temperature detecting means for detecting the temperature of a cooling target fluid flowing in an evaporator, cooling target fluid outflow temperature detecting means for detecting the temperature of the cooling target fluid flowing out of the evaporator, and flow rate calculating means (measuring unit, computing unit, and storage unit) for calculating the absolute quantity of the flow rate of the cooling target fluid flowing in the evaporator using a value detected by each detecting means.