Methods for and systems of controlling operation of one or more chillers in a primary-secondary chiller plant system. The chillers utilize a set point temperature that is based upon measuring a temperature of water at a supply side of the load on the secondary loop.

A controller performs a first operation in which a heat source device directly or indirectly heats water in a first channel of a heat exchanger and a second operation in which the heat source device directly or indirectly cools the water in the first channel of the heat exchanger after the first operation ends.

A cooling system for cooling a machine tool having a machine temperature. The cooling system comprises gas source, refrigeration circulation, fan, and controller. The gas source is configured for providing gas. The refrigeration circulation comprises heat exchanger, compressor, condenser, and expansion valve. The heat exchanger is in fluid communication with the gas source and configured to cool the gas down to target temperature and to provide the gas to the machine tool. The compressor has operation frequency. The fan is configured to cool the condenser and has a rotation speed. The controller is connected to the compressor and the fan. When a target temperature difference that is equal to the machine temperature minus the target temperature is smaller than threshold temperature difference, the controller keeps the operation frequency at minimum frequency and sets the rotation speed to be smaller than a maximum rotation speed.

An air conditioner includes a liquid pressure adjusting expansion valve that is located in an outdoor liquid refrigerant pipe at a part thereof closer to a liquid refrigerant communication pipe than to a refrigerant cooler and configured to reduce a pressure of a refrigerant so that a refrigerant flows through the liquid refrigerant communication pipe in a gas-liquid two-phase state and so that the refrigerant flows through an outlet of a refrigerant cooler in a liquid state.

A method for cooling with a refrigerant based cooling system includes circulating a refrigerant in a main flow path of a refrigeration cycle including an accumulator, compressor, condenser and an evaporator, diverting a portion of flow to a bypass flow path from a location along the main flow path that is downstream the compressor and upstream the condenser and combining flow through the bypass flow path with flow through the main flow path downstream the condenser and upstream from the evaporator. The rate of flow through the bypass flow path may be dynamically controlled.

A cooling system drains oil from low side heat exchangers to vessels and then uses compressed refrigerant to push the oil in the vessels back towards a compressor. Generally, the cooling system operates in three different modes of operation: a normal mode, an oil drain mode, and an oil return mode. During the normal mode, a primary refrigerant is cycled to cool one or more secondary refrigerants. As the primary refrigerant is cycled, oil from a compressor may mix with the primary refrigerant and become stuck in a low side heat exchanger. During the oil drain mode, the oil in the low side heat exchanger is allowed to drain into a vessel. During the oil return mode, compressed refrigerant is directed to the vessel to push the oil in the vessel back towards a compressor.

The present disclosure provides methods and systems for heat exchange, such as cooling a heat source. A cooling system of the present disclosure may comprise a first channel that is configured to direct a liquid coolant, a second channel that is configured to direct a vapor coolant generated from the liquid coolant, and a condenser that is configured to permit the vapor coolant to undergo phase transition to the liquid coolant. The cooling system may further comprise at least one cooling interface in fluid communication with the first channel and the second channel. The cooling interface may be configured to facilitate heat exchange between the liquid coolant and a heat source.

Chiller control systems and methods for chiller control use iterative modeling of cooling towers, heat exchangers, and pumps to determine the feasibility of integrated free cooling and the ability to take advantage of free cooling. The control systems and control methods can further include selecting the parameters for operating in the free cooling or integrated free cooling mode to improve efficiency and/or reduce energy consumption when operating in these modes. The models can have inputs and outputs that feed into one another, and converge at a solution over multiple iterations. The feasibility of integrated free cooling can be based on providing cooling to a cooling load process fluid at a heat exchanger. The availability of free cooling can be based on the cooling provided at the heat exchanger achieving a target temperature for the cooling load process fluid.

In an embodiment, a method of preventing evaporator coil freeze in a heating, ventilation and air conditioning (HVAC) system is performed by a controller in the HVAC system. The method includes determining a reference saturated suction temperate (SST) via a sensor disposed in relation to an evaporator coil in the HVAC system. The method also includes determining whether the reference SST is below a minimum SST threshold. The method also includes, responsive to a determination that the reference SST is below the minimum SST threshold, increasing a discharge air temperature (DAT) setpoint.

When a state in which a driving voltage of a pump is set to an upper limit voltage and an opening degree of at least one of a plurality of flow rate control valves is set to a maximum opening degree continues for a first determination time period, an operation frequency of a compressor is raised at a first time so as to increase an amount of heat exchange by a second heat exchanger. When an operation stop request is input, or an indoor temperature reaches a set temperature, in at least one of a plurality of third heat exchangers after the first time, the operation frequency of the compressor is lowered or the driving voltage of the pump is lowered.