Consulting-Specifying Engineer - January 2009 - (Page 13) M/E/P Roundtable PARTICIPANTS Variable-refrigerant systems Our participant’s discuss the applications, benefits, and challenges of variable-refrigerant air conditioning systems in commercial buildings. BY MICHAEL IVANOVICH, Editor-in-Chief, PATRICK LYNCH, Associate Editor CSE: What makes VR systems worth considering at the start of a project? What factors should engineers look for that scream VR? John Brantley: VR systems are primarily a zoning system that can economically provide precise individual comfort control to multiple spaces. VR systems can be applied in any situation where the client is looking to minimize energy consumption. I have performed energy models comparing many types of systems in every portion of the United States and have found that VRFZ systems are consistently 25% or more efficient than the best alternative. Lee Smith: VRV/VRF systems offer many attributes more commonly associated with chiller type systems. They offer a very high degree of comfort, have extremely quiet operation, offer the ability to serve multiple zones, have high efficiency, can be integrated to centralized control solutions, and are able to serve large capacity applications with their modular approach. Basically any application where the optimum solution would be a chiller is where VRV/VRF systems should be seriously considered. A common mistake is thinking of VRV/VRF as a “big mini-split or ductless” system, which is absolutely not this kind of system by design, application, or attributes. The original VRV/VRF system was actually invented by a Chiller engineering team. Christian Agulles: If a project requires lots of zones for individual temperature control, energy efficiencies that can equal or exceed central chilled water systems, and very good acoustical performance within the conditioned space, VR systems are worth looking at. VR systems can also solve some problems where individual zone sub-metering is required for tenant billing and in projects where there is not much room for large duct runs. We have designed VR systems for medium and large office buildings, meeting/banquet facilities, hotels, and technology room spaces that require 24/7 cooling. They neatly and efficiently address many of the typical design challenges associated with these types of projects. VR systems easily accommodate many individual temperature zones; keep noisy compressors out of the living spaces, and the packaged control systems offer sub-metering of energy usage for each zone. With the recent availability of water-cooled VR systems and vertical indoor DX fan coil units, VR systems can be used with ground loop geo-exchange systems for an incredibly efficient system. Sunondo Roy: Projects that lend themselves to VR applications include retrofits of large loft-type spaces to individual offices, office clusters within large warehouses, renovation of older buildings with natural ventilation for all offices, and open office areas. Spaces with varying loads can easily be accommodated with evaporator units sized for the space load while the condensing unit can be much smaller than the sum of the individual evaporator units due to nature conditioning load diversity. CSE: What are the safety considerations for circulating refrigerant through occupied spaces, relative to ASHRAE Standard 15? Brantley: Refrigerant safety codes, such as ASHRAE Standard 15, provide guidance on how to prevent life safety issues associated with potential refrigerant leaks by defining the refrigerant concentration limit (RCL) per Christian Agulles, LEED AP Vice President WSP Flack + Kurtz Las Vegas. John Brantley, LEED AP CITY MULTI Mechanical Engineer, Mitsubishi Electric HVAC Suwanee, Ga. Sunondo Roy, PE, LEED AP Vice President CCJM Engineers, Ltd. Chicago Lee Smith, Dir. of Product, Engineering and Applications Daikin AC Inc. Carrolton, Texas Consulting-Specifying Engineer • JANUARY 2009 13
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