The Latest Trend in High Performance Mechanical Equipment.

Working in drafting for a mechanical contractor, I see a lot of trends in commercial and industrial mechanical system designs. Typically these trends eventually fade and are replaced with whatever manufacturers are claiming to be the "greenest" at the time. Lately, I have noticed a trend from the more traditional VAV cooling system, to a simpler multi-unit refrigerant system. Usually, I pay no attention to these trends because I know it will later be replaced with a more traditional system. Typically this is due to reliability or performance issues, but these systems seem to be increasingly becoming mainstream and leading the industry in high performance mechanical applications. 

How it Works

          The most familiar name associated with these multi-unit refrigerant systems is Variable Refrigerant Flow System or VRF System. Compared to traditional refrigerant systems (also known as split or DX systems) which have only one air handling unit and one condenser, the VRF utilizes multiple air handling units with one condenser. Unlike traditional DX systems, a VRF system can heat and cool multiple zones. It works exactly like the traditional DX units with one exception, with the VRF system the condenser and multiple air handlers are connected through by a box called the branch controller. The branch controller receives information from the thermostats in each zone, and adjusts the conditions in those areas accordingly. This allows each zone to be adjusted individually, which means while one zone may be in heating mode, the zone next to it can be in cooling mode. The use of these branch controller is what make these units so efficient.

Performance and Efficiency Benefits Over Traditional Designs

          To address the benefits of the VRF systems, we must first understand where more conventional VAV systems are lacking. First and foremost, VRF systems are ductless, while VAV systems usually include very elaborate and complex duct systems. Duct is a downfall, because when there is duct, many factors come into play that you do not see with ductless systems. These factors include friction loss, space constraints, air leakage, insulation,  and heat transfer to name a few. Even with advances in VAV systems such as variable frequency drives, which allow motors to throttle back when less volume is needed, the unit is incapable of shutting down. This is one of the advantages of ductless systems. Typical VAV systems are design by the maximum expected load, which in many cases leads to a system far bigger than their intended use. The main advantage of the VRF system is the adaptability to adjust to the required load needed to heat and cool a specific space. This is ideal in commercial office space, because this will limit energy usage needed to heat and cool each zone.

Conclusion

          VRF Systems appear to be here to stay, but who knows what's just around the corner. VRF systems appear to be the driving force in high performance mechanical design. Is this the end of traditional mechanical systems, or will the VRF system fade like all of the others?

- http://www.mitsubishipro.com/media/226453/cmcatalog.pdf
- http://www.govenergy.com/2008/pdfs/technology/goetzlertechn1.pdf
- http://www.johnsoncontrols.com/content/us/en/products/building_efficiency    /integrated_hvac_systems/Industrial___Commercial_HVAC_Equipment/Variable_Refrigerant_Flow_Systems_.html