An air-conditioning system includes a plurality of indoor units; a relay unit including an intermediate heat exchanger configured to exchange heat between refrigerant and a heat medium; and a heat source unit configured to supply cooling energy or heating energy to each of the plurality of indoor units via the relay unit. The heat source unit and the relay unit are connected by a heat-source connection pipe through which the refrigerant flows, and the relay unit and the plurality of indoor units are connected by a load connection pipe through which the heat medium flows. The load connection pipe comprises a main pipe connecting between the relay unit and one of the indoor units provided at an end of the load connection pipe opposite to the relay unit. The main pipe has branch parts associated with the indoor units.

Variable volume ratio compressors may be controlled using a switching parameter based on compressor speed and suction density to improve the matching of compressor volume ratio to desired discharge conditions. Delay periods may be implemented in the determination of when to change volume ratio to control the frequency of changes to the volume ratio. The switching parameter may be a product of the compressor speed and suction density. The volume ratio of the compressor may be controlled by switching valves directing pressure to a piston of a variable volume ratio system of the compressor.

In an air-conditioning system, a gaseous refrigerant remaining in a reservoir can be discharged from the reservoir even when a cooling operation has started and the reservoir is being filled with a liquid refrigerant. Therefore, the reservoir can be filled with the liquid refrigerant at a faster speed.

An air-conditioning apparatus is able to ensure an appropriate flow rate of refrigerant and an appropriate amount of oil returned to a compressor that match operation conditions regardless of an operating state of a refrigerant circuit and a change in an operation condition. The air-conditioning apparatus includes: a first detector configured to detect a refrigerant temperature within an accumulator; a storage unit configured to store information regarding a two-layer separation temperature of refrigerant and refrigerating machine oil; a determiner configured to compare the refrigerant temperature with the two-layer separation temperature and determine a two-layer separation state of the refrigerant and the refrigerating machine oil; a second detector configured to detect a state of the refrigerant sucked by the compressor; and a control unit configured to adjust an opening degree of a flow control valve on the basis of the two-layer separation state and a state of the sucked refrigerant.

Variable volume ratio compressors may be controlled using a switching parameter based on compressor speed and suction density to improve the matching of compressor volume ratio to desired discharge conditions. Delay periods may be implemented in the determination of when to change volume ratio to control the frequency of changes to the volume ratio. The switching parameter may be a product of the compressor speed and suction density. The volume ratio of the compressor may be controlled by switching valves directing pressure to a piston of a variable volume ratio system of the compressor.

Provided are an air conditioner and a mode switching control method thereof. The air conditioner comprises an outdoor unit and an indoor unit. One end of the outdoor unit is connected to one end of the indoor unit via a throttling element, and the other end of the indoor unit is connected to the other end of the outdoor unit via a liquid storage tank. The mode switching control method comprises the following steps: when the indoor unit switches to a refrigeration mode, acquiring an outlet superheat degree of the liquid storage tank, and determining whether the outlet superheat degree is less than a first preset value; and if the outlet superheat degree is less than the first preset value, controlling to turn down the throttling element until the outlet superheat degree is greater than a second preset value that is greater than the first preset value.

The various embodiments described herein include methods, devices, and systems for determining refrigerant charge level. In one aspect, a refrigeration system includes: (1) a compressor to compress a refrigerant; (2) a condenser disposed downstream of the compressor to condense the refrigerant; (3) an evaporator disposed downstream of the condenser to vaporize the refrigerant; (4) refrigerant lines fluidly connecting the compressor, the condenser and the evaporator in series to form a refrigerant circuit for circulating the refrigerant; (5) at least one sensor configured to measure temperature and pressure of the refrigerant in the refrigerant circuit; and (6) a controller communicatively coupled to the at least one sensor and configured to: (a) determine a sub-cooling level or super-heating level based on the temperature and/or pressure measured by the at least one sensor; and (b) facilitate operation of the refrigeration system based on the sub-cooling level or the super-heating level.

A heating, ventilation, and air conditioning (HVAC) system and controller therefor to operate with thermal energy reservoirs are provided to set a four-way valve to route a refrigerant through a refrigerant circuit in a first direction when the HVAC system is set to a cooling mode or in a second direction, opposite to the first direction, when the HVAC system is set to a heating mode; and set bypass valves in the refrigerant circuit based on a temperature of a temperature holding material in a thermal energy reservoir and which of the heating mode and the cooling mode the four-way valve is set to, wherein the bypass valves route the refrigerant through the thermal energy reservoir to transfer thermal energy between the refrigerant and the temperature holding material.

A passive liquid collecting device has a reservoir with an outlet and one or more rigid structures within the reservoir. The rigid structures are configured to collect a liquid and direct the liquid to the outlet. Porous capillary media are supported by the rigid structures. A thermal control loop is also disclosed.

A liquid level detector includes: a vertically-mounted accumulator that stores refrigerant; a heater that heats the accumulator; a temperature detector that detects a surface temperature of the accumulator; a pressure detector that detects a pressure of the refrigerant in the accumulator; and a controller. The controller detects a position of a liquid surface of the refrigerant in the accumulator based on a surface temperature of the accumulator detected by the temperature detector when the accumulator is heated by the heater, and a pressure of the refrigerant in the accumulator detected by the pressure detector.