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VRF System Design: Designing for the Ever-Changing Tenant Space

Mike Silverstein, Mitsubishi Electric Trane US Regional Sales Manager

Owning a building and filling spaces with new tenants comes with the challenge to prepare the space requirements to accommodate the operating needs of the next leaseholder within scope. To help meet the needs of your future tenants, look to streamline the operating systems, like the HVAC system, to better accommodate a wide range of users, make physical changes less cumbersome, and speed up the overall process. Trane Mitsubishi VRF systems are built for building owners to more efficiently prepare for tenant fit-outs.

The Trane Mitsubishi VRF system utilizes a two refrigerant pipe heat recovery system as opposed to the alternative three-pipe heat recovery option offered by other VRF manufacturers. The Mitsubishi offering utilizes a heat exchanger within the Branch Circuit (BC) Controller allowing for a two-pipe connection between the BC and the condensing unit, enabling the ability to provide subcooled refrigerant within the BC Controller. The Trane Mitsubishi VRF system provides a more stable platform to reduce installation time and potential downtime.

Let’s take a look at the pros throughout the design, installation, and operation of a VRF system, so you can decide if it aligns with your needs for tenant fit-outs.

Design Advantages:

  • Greater flexibility for future modifications or expansion. Three-pipe systems require the upstream pipe sizes to be modified not only on the downstream capacity but also on the location of the downstream units. With the Mitsubishi Trane system, the pipe size between the outdoor unit and BC Controller is dictated by the size of the outdoor unit allowing for easier modifications in the future.

  • Specialty refrigerant piping is NOT required. Manufacturers of three-pipe systems require special piping considerations including the use of proprietary Y-branches. The designer needs to ensure these fittings are laid out correctly with sufficient space between joints and indoor units.

  • BC Controllers with as many as 16 ports with the capability of connecting several sub-BCs with up to 8 ports. This allows one to consolidate the number of BC Controllers used for a given system to simplify the design and minimize electrical feeds.

Simplicity of Installation:

  • Fewer brazed connections. Three-pipe systems require significantly more brazed joints which take time to install and are potential leak points.

  • Less hard copper. Our systems typically utilize hard copper between the outdoor unit and BC Controller. Soft copper can be used in the rest of the system. Three-pipe systems typically utilize more hard copper.

  • Less risks of mistakes during installation. Three-pipe systems for certain capacity branch selector devices require two of the three pipes to be the same diameter. This can lead to confusion in the field and potential mistake during installation.

  • Fewer BC Controllers required result in fewer electrical feeds saving time and coordination with the electrical contractor during installation.

Ease of Operation:

  • Reliable control architecture. Limited to 50 units per controller, the controller provides a stable environment resulting in a responsive system with less risk of downtime.

  • Ease of troubleshooting and less downtime. With trace voltage on the communications network, systems can be readily investigated to resolve issues more rapidly.

  • Training. Training is available on-site or at the local training facility for the owner to have hands-on training for essential personnel.

  • Support. From the inception of the design through start-up and operation, the Mitsubishi Trane team is available with many resources to support the project thoroughly.

The Case for Water Cooled vs. Air Cooled:

  • One of the major design considerations for VRF systems is the refrigerant charge, and specifically, the max allowed refrigerant charge per system as outlined in ASHRAE 15. With a typical base building fit-out, the engineer must make assumptions on what the future tenant will use their space for. On larger high-rise buildings, the largest amount of refrigerant typically resides in the vertical pipe risers connecting the condensing unit to the branch boxes. By utilizing water-cooled VRF, the condensers can be placed on each floor, effectively easing most refrigerant charge concerns.

  • When water-cooled VRF condensers are installed on a floor-by-floor basis, concerns about max refrigerant line lengths go down since the large distance between the condenser and BCU has been reduced.

  • Water-cooled VRF offers flexibility for the building tenants. With a base-building condenser loop, the tenant can install the full VRF system to suit their need, not adapt an existing air-cooled VRF system. This approach also provides flexibility for ancillary equipment like computer room units (CRACs) that may not be on the base tenant HVAC system.

Interested in more details specific to your next project or for updating a building you own? Connect with one of our HVAC engineers via or (240) 306-3000.


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