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Trane Engineers Newsletter: Hydronic Variable Refrigerant Flow Systems

In this Engineers Newsletter (EN), Trane spotlights hydronic variable refrigerant flow systems; the next generation of all-electric heat pump systems that can help achieve building decarbonization goals, while satisfying upcoming demands for reduced refrigerant charge.

A hydronic variable refrigerant flow system uses the same heat-recovery outdoor unit and controls as a conventional VRF system. Refrigerant piping connects the outdoor unit to a Hybrid Branch Controller (HBC). Unlike the branch controller in a conventional VRF system, which directs refrigerant capable of heating or cooling to the various zone-level terminal units, the HBC directs hot or cold water to the terminal units. Therefore, each terminal unit includes a hydronic coil, rather than a refrigerant coil.

Hydronic variable refrigerant flow (HVRF) system
Hydronic variable refrigerant flow (HVRF) system

The HBC includes any valves necessary to direct either cold or hot water to the various zones, along with refrigerant-to-water heat exchangers and variable-speed pumps for both the cold and hot water distribution headers. A sub-HBC is available to increase the number of zones served without the use of refrigerant.

A hydronic variable refrigerant flow system provides the following benefits compared to a conventional VRF system:

  • No refrigerant piping in the occupied spaces
  • Less overall refrigerant charge (30 percent less on average)
  • Tighter temperature control
  • Reduced defrost penalty
  • Easier to install due to less copper piping
  • Less noise, especially during defrost

Download this issue of the Trane® Engineers Newsletter to read it now.

More about Trane Engineers Newsletters

Engineers Newsletters are topical, informative articles that provide engineering professionals who design HVAC systems with reliable, objective, and technologically current information in a non-commercial format. They've been published by Trane’s Applications Engineering team since 1972 and have long been a trusted technical resource throughout the industry. Subjects range from HVAC system configurations to acoustics to interpretation of ASHRAE standards.

Engineers Newsletters are provided to customers free-of-charge. Current and past issues can be viewed on, and you can even subscribe to receive e-mail notification when a new issue is published.

Kasey Boxleitner

About the author

Dustin Meredith, Lead Systems Development Engineer




Dustin has been with Trane for over 20 years, in his current role as a systems and applications engineer, he is responsible for developing integrated customer solutions for HVAC products & systems providing a link between the sales, design, and manufacturing organizations. Dustin holds multiple patents and has been instrumental in advancing cutting-edge fan and motor applications to the industry. He has authored a wide variety of technical bulletins, white papers, articles, and Trane Engineers Newsletter LIVE programs.

Dustin is a licensed professional engineer and earned his mechanical engineering and computer science degrees from the University of Kentucky. He also earned an MBA from the Gatton College of Business and Economics. He is an active member of various ASHRAE® committees.