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HVAC School - For Techs, By Techs

Aug 31, 2023

Roman Baugh joins the podcast to talk about oil return and the refrigerant charge in VRV systems.

VRV systems—also known as variable refrigerant volume (or variable refrigerant flow/VRF) systems—have one outdoor unit, one or multiple compressors, and multiple indoor units. The outdoor unit modulates to meet the indoor units’ fluctuating demands. They are versatile and flexible systems.

Like parallel racks, VRV systems have long lines and a lot of piping, so oil return and refrigerant charge are especially critical. VRVs have specific control protocols, as they need refrigerant volume and velocity to move oil and keep it lubricating the compressor for its entire lifespan; oil return mode, the refrigerant charge, and the piping protocols are supposed to support that function. 

When it comes to piping protocols, line sizing is critical. Whenever there is a need to relocate the outdoor unit and change the piping configuration, the charge needs to be adjusted, and the piping may even need to be upsized to prevent restrictions from happening. Daikin has VRV WebXpress (and SplitXpress) software for equipment selection; the goal is to help installers out with the line length and charging whenever it needs to be changed. 

When trying to get the oil return and line sizing right, you ultimately need to look at the manufacturer’s literature and resources. It also helps service technicians if the installer makes the charge and line information readily available to anyone who works on their VRV install in the future.

Roman and Bryan also discuss:

  • Where and how oil can settle in VRVs

  • Consequences of improper charge in VRVs

  • Liquid lines in VRVs

  • Violating piping rules and safety protocols

  • Vertical separation in liquid line sizing

  • Suction line sizing

  • POE and PVE oil miscibility

  • Daikin’s resources


Check out to find Daikin’s literature and software programs.

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