Engineered Systems - February 2008 - (Page 54) What was a primarily residential technology is ready for larger commercial settings. What was primarily embraced overseas is building momentum in the U.S. This update traces VRF progress, examines some strengths and weaknesses, and spans the globe in an effort to compile some cost comparisons with other alternatives. BY AMMI AMARNATH AND MORTON BLATT ulti-split heat pump systems, using multiple indoor units connected to a single outdoor unit, have evolved from a technology suitable for residential and light commercial buildings to variable refrigerant flow (VRF) systems that can provide efficient space conditioning for large commercial buildings. VRF systems are very popular in Asia and Europe and, with increasing support from major U.S. and Asian manufacturers, the technology is worth considering for multizone commercial building applications. VRF technology uses smart integrated controls, VSDs, refrigerant piping, and heat recovery to provide products with attributes that include energy efficiency, flexible operation, ease of installation, and zone control. This article provides an overview of VRF system technology, including the market situation, technology attributes, performance information, and application recommendations. A future article will address user and utility issues as well as what is holding back the technology, including codes and standards issues, desired technology improvements, and market actions needed to increase penetration of these systems. M MARKET POSITION OF VRF SYSTEMS Ductless space conditioning products, the forerunner of multi-split and VRF systems, were first introduced in Japan and elsewhere in the 1950s as split systems with single indoor units and outdoor units. These ductless products were designed as quieter, more efficient alternatives to window units (Smith 2007). These units, also known as mini-split systems, have evolved from the earlier products using R-22 refrigerant to those using R-407C, on to current products using R-410A. The progression has been from a few indoor units operating off each outdoor unit to multi-split products with four units to eight units in the late 1980s, then to 16 units in the early 1990s, and to 32 units by 1999. 54 En gi neer ed S y stem s February 2008 Current VRF technology using electronically commutated motors, inverter-driven scroll compressors, multiple compressors, versatile configurations, and complex refrigerant and oil circuitry, returns, and controls, can permit as many as 60 or more indoor units to operate off one outdoor unit (Dyer 2006). Ductless and multi-split products are often considered factorybuilt systems, competing with traditional unitary products, whereas some VRF manufacturers position their VRF systems as engineered systems that are alternatives to traditional field-applied systems such as chillers. U.S. sales of all ductless, multi-split, and VRF products will be around 250,000 units in 2007. Sales in Japan (where the VRF concept was developed) and other parts of Asia have been strong. In Europe, where many existing buildings did not have A/C, retrofit opportunities have also created strong demand (Goetzler 2007). Ductless products entered the market in the U.S. in the early 1980s, but market penetration was minimal, with lack of Japanese manufacturer support infrastructure, and unfamiliarity with the technology holding back sales. Ozone depletion issues became an increasing concern at that time and the issue of a high refrigerant charge of multi-split systems was likely a strong negative for the system. Since that time, refrigerant developments, advances in charge management, controls, and inverter technology have transformed the technology. Asian manufacturers have re-entered the U.S. market individually or in partnership with U.S.-based manufacturers in the past few years to help promote the technology. Less than 10,000 VRF systems will be sold in the U.S. in 2007. One high-profile signpost for the increasing market acceptance of this technology is the inclusion of multi-split VRF technology with zoned inverter-driven heat pump and heat recovery VRF systems in the renovation of the ASHRAE headquarters building in Atlanta (Johnson 2007).
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