Engineered Systems - February 2008 - (Page 56) Variable Refrigerant Flow What About Multi-splits? Multi-splits offer some of the major advantages of VRF systems such as zoning, capacity control, ease of retrofit, low installation costs, minimizing ducting, and use of secondary fluids and associated costs and losses. On the other hand, their simpler piping results in longer total length of piping compared to VRF systems. Similarly, multi-split heat pumps do not have the opportunity for heat recovery between units that are cooling and units that are heating. As such, multi-split systems should be considered for smaller, simpler buildings where heat recovery is not a possibility and fewer numbers of zones need to be conditioned. refrigerant to indoor units (evaporators or condensers) located near or within the conditioned space. (When the indoor units are in the cooling mode, they act as evaporators; when they are in the heating mode, they act as condensers.) In contrast, conventional ducted systems transfer heat from the refrigerant to the space by circulating air (in ducted systems) or water (in chillers) throughout the building. VRF systems are enhanced versions of ductless multi-split systems, permitting more indoor units to be connected to each outdoor unit and providing additional features such as simultaneous heating and cooling and heat recovery. VRF heat pump systems permit heating in all of the indoor units, or cooling in all the units, not simultaneous heating and cooling. Heat recovery systems provide simultaneous heating and cooling as well as heat recovery to reduce energy use during the heating season. Over the past 15 years, the technology has advanced in a number of areas: • Standard compressors to VFD, inverter- driven scroll compressors • Direct-driven outdoor fans to VFD, inverter-driven fans • Direct-driven indoor coil motors to direct current or ECM-type motors FIGURE 1. Illustration of split system, multi-split system, and VRF system for a small commercial building with four zones (shown in the cooling mode). • Variable capacity indoor units • Better heat exchanger surfaces with multi- segmented coils • Improved controls and diagnostics • R-22 to R-410A • Better refrigerant charge and oil management HOW DOES VRF WORK? Multi-splits include multiple indoor units connected to a single outdoor unit. Ductless products are fundamentally different from ducted systems in that heat is transferred to or from the space directly by circulating 56 En gi neer ed S y stem s February 2008
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