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Roman Baugh gives the Kalos techs an introduction to VRV/F systems. Variable refrigerant flow (VRF) or volume (VRV, Daikin) systems are a specific type of HVAC equipment invented by Daikin. The same superheat and subcooling principles apply, though there are a few more moving parts.

VRF systems are more like VFDs that take AC voltage, convert it to DC voltage, charge capacitor banks with the DC voltage, and use pulse-width modulation to run the compressor at different hertz (at 168 different speeds). The variable-speed nature moves varying amounts of refrigerant to meet the exact demand of indoor units and run efficiently. These systems supply a specific amount of refrigerant to a given indoor unit to meet its required capacity. The indoor and outdoor units constantly communicate (via a PID loop) to make this possible.

VRF systems may use either 2-pipe or 3-pipe heat recovery. Those pipes represent refrigerant lines moving into and out of the heat recovery box, which generates the liquid needed for the indoor units. It has a branch collector box that skims refrigerant. Hot gas goes to the unit(s) calling for heating, and it condenses to a liquid in the indoor heat exchanger, which then goes to the unit(s) calling for cooling.

Capacity varies widely among VRF systems. In some cases, two outdoor units can handle a combined 40 tons of capacity. Higher-capacity systems have higher compressor and fan speeds, usually with larger compressors. Compressors and inverter boards may be refrigerant-cooled (using liquid refrigerant). VRF indoor units vary quite a bit in shape and size, coming in wide and slim, ducted and ductless varieties. Roman covers the features, advantages, and disadvantages of existing models as well as the unit nomenclature and clearances.

Roman also covers copper tubing, including REFNET kits and Y joints, as well as proper installation of those and some general brazing tips to reduce turbulence. He also discusses oil management, especially as it relates to piping consideration and refrigerant turbulence in the copper tubing, as well as oil return mode and traps. On the installation end, it is critical to remove the shipping bracket from the compressor and eliminate cross piping. Flaring, pipe lengths, pipe diameter, and proper piping support are other considerations for VRF piping and installation.

Flowing nitrogen while brazing is important in all systems to prevent the buildup of oxides and clogged screens, but the copper oxides can damage electronic expansion valve needles, which can lead to oil loss in the compressor and catastrophic failure.

Roman goes through the process of installation, including the pre-construction phase and jobsite considerations when installing VRF systems. He also explains the difference between communicating systems (including VRF/V systems) and 24v systems, and he covers control circuit terminal designations on VRF systems.

This video also covers very basic elements of service and troubleshooting, including how to think about using the correct tools for the job. The basic starting points for VRF troubleshooting include temperature in and temperature out. Temperature sensors are common fail parts, and it's important to stay on top of those, as failed temperature sensors can cause catastrophic failure in the long run. Roman also ends on a note about the importance of reading the manual to assist with troubleshooting. He also explains the importance of pulling and weighing out the refrigerant charge before adding charge to a VRF system.

Roman's tech tip about troubleshooting inverter boards:

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