What are VRV, VWV, and VAV?

　　VRV stands for Variable Refrigerant Volume system, VWV stands for Variable Water Volume system, and VAV stands for Variable Air Volume system. They are all forms of air conditioning systems. Understanding them is easier when considering the sequence of the air conditioning process.

　　The three processes of air conditioning cooling and heating are: the air conditioning main unit prepares hot and cold air; the hot and cold air is transported through pipes; and finally, the hot and cold air is transferred to the indoor space.

　　The cooling and heating process of the air conditioning main unit involves the refrigerant circulating through the "four major components," including two heat exchangers. One is the evaporator, where the refrigerant absorbs heat and vaporizes, requiring heat from the outside—essentially cooling the outside. The other is the condenser, where the refrigerant liquefies and releases heat, requiring heat to be discharged to the outside—essentially heating the outside.

　　In practical applications, the air conditioning main unit uses one heat exchanger facing the user side. By changing the flow direction of the refrigerant, it acts as an evaporator in summer, absorbing heat from the user side to cool the user; in winter, it acts as a condenser, discharging heat to the user side to provide heating.

　　If the user-side heat exchanger is placed indoors and directly used as the terminal to transfer heat to the indoor space, it's equivalent to transporting heat through refrigerant in the pipes. This is a "fluorocarbon air conditioner," and household split air conditioners work this way.

　　VRV can be understood as a "multi-split" version of a split air conditioner. One or more outdoor units drive multiple indoor unit terminals, with the refrigerant system directly cooling and heating the indoor space. To adapt to changes in indoor load, the refrigerant flow rate in the pipes needs to be constantly adjusted, hence the name VRV variable refrigerant flow air conditioning.

　　If the user-side heat exchanger of the air conditioning main unit is not directly placed indoors but instead transfers heat to water, which then transports the heat to the indoor terminal, this is a "water air conditioner." In a water air conditioner, when the indoor load changes, one method is to keep the water flow rate constant and change the water temperature to adapt to the terminal load changes; this is a constant water volume system. Another method is to keep the water temperature constant and change the water flow rate through the terminal to adapt to the indoor load changes; in this case, the water flow rate in the pipeline changes, and it is called a VWV variable flow air conditioner. The advantage is that it can save water pump power consumption. The basic forms of air conditioning terminals are fan coil units and air handling units. Fan coil units use a fan to drive indoor air to exchange heat with the water coil, transferring the heat in the water to the indoor space; this is called a "full water system." Air handling units increase power and heat exchange capacity; essentially, they are still "large fan coil units." However, they deliver the heat-exchanged air to the target area through air ducts, which can be understood as ultimately transporting heat through air; this is called a "full air system."

　　In a full air system, when the indoor load changes, one method is to keep the air volume constant and change the air temperature to adapt to the load changes; this is a CAV constant air volume system. Another method is to keep the air temperature constant and change the air volume to adapt to the load changes; in this case, the supply and return air volume changes, and it is called a VAV variable air volume air conditioner. The advantage is that it can save fan power consumption.

　　In summary, the VRV variable refrigerant system directly cools and heats the indoor space using the refrigerant system, transporting heat through refrigerant in the pipes and changing the refrigerant flow rate to adapt to load changes. The VWV variable water volume system exchanges heat between water and refrigerant in the air conditioning main unit, transporting heat through water in the pipes and changing the water flow rate to adapt to load changes. The VAV variable air volume system exchanges heat between air and water in the air handling unit, transporting heat through air in the air ducts and changing the air volume to adapt to load changes.

　　The three air conditioning systems—VRV, VWV, and VAV—correspond to the air conditioning's heat preparation process, heat transportation process, and terminal heat transfer method, respectively. Understanding them in sequence makes it easier.

　　Source: Refrigeration Encyclopedia

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