On Nov. 1, 2017, the U.S. Department of Defense (DoD) issued an updated Unified Facilities Criteria (UFC) document addressing requirements and guidance in the design of heating, ventilating, and air-conditioning (HVAC) systems, together with the criteria for selecting HVAC materials and equipment. UFC documents provide planning, design, construction, sustainment, restoration, and modernization criteria for all military and defense agencies.
One significant change in this update involved enhanced guidance regarding the use of variable refrigerant flow (VRF) systems. A previous, and now superseded, version of the document, issued Jan. 25, 2017, had the following restrictions:
“1. For Air Force facilities, do not use VRF systems.
2. For Army facilities, VRF systems are strongly discouraged.
3. For Navy facilities, request for approval from the Facilities Engineering Command (FEC) for the use of VRF systems.”
The updated change revised and expanded this language with explanations regarding the reasons for its different treatment of VRF systems as compared with other HVAC system types.
1. “All HVAC control systems, including VRF systems, must meet the requirements” of Unified Facility Guide Specifications, which “require the installation of non-proprietary control networks down to the level of each individual device in the system. As of the publication date of this UFC, all known commercially-available VRF systems rely on a proprietary network” that “does not comply with the UFGS requirements.”
The practical implications of a proprietary control network are that only factory-authorized technicians are allowed to install and service VRF systems, cutting down on the ability of a building owner to shop around for better prices, and leading to higher life-cycle operating costs. In comparison, water-based hydronic systems can be installed and serviced by a wide variety of contractors.
From Appendix B-11 of the document: “Further, the facility owner remains dependent upon the original vendor for maintenance and support which also violates the Open system requirements of the specifications.”
2. “VRF systems piping/tubing must have all brazed connections” and the “list of fittings and joints that are prohibited include but are not limited to the following: push-on fittings, extruded fittings, flare fittings, press-connect fittings, mechanical joints and groove joints.”
From Appendix B-11: “VRF systems increase the risk of adverse mission impacts due to new EPA leak-rate rules on HFC [hydrofluorocarbon] refrigerant systems (if 50 lbs or greater of refrigerant) and the challenge of locating and repairing a leak in often hard to access areas …” and “Tracing and repairing a leak on a VRF system is many times more difficult with an additional access requirement of maintenance crews to the workspace environment.” Another issue with using refrigerant to move heating or cooling energy around a building is that refrigerant is heavier than air, and “puddles” on the floor of a room, displacing breathable air. It is also colorless, virtually odorless, and a potent greenhouse gas with global warming potential many times higher than carbon dioxide. According to Appendix B-11, annual refrigerant leaks are estimated to be 25 percent.
Further, given that the entire VRF system is designed around the thermodynamic properties of a specific refrigerant type, this means that when a refrigerant type is phased out in favor of a more environmentally friendly formulation, as is happening today, the price of the refrigerant increases rapidly, and the VRF system itself will likely need extensive modification or even replacement in order to function properly.
3. Finally, the US DoD is very mindful of life-cycle costing of projects it undertakes, making cost-effectiveness a continuing consideration. From the UFC document: “Life Cycle Cost analysis comparing VRF with traditional systems can be difficult given the relative newness of VRF systems, and given that many VRF systems can only be serviced by factory-trained technicians which affects the maintenance costs for the system compared to more traditional systems.”
One tool for comparing life-cycle costs for various HVAC system types in new buildings is the Building Efficiency System Tool™ (BEST), recently introduced by the Hydronics Industry Alliance – Commercial committee of the Radiant Professionals Alliance. The BEST quickly generates annual energy consumption and life-cycle cost comparisons, based on applied system performance data, for a building’s HVAC system.
Frequently, HVAC system selections are made based on packaged system efficiency ratings, without consideration of actual operating costs of as-installed systems, which nearly always exceed what is modeled in the laboratory rating tests. BEST is available at www.BestHVAC.org.