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Variable-refrigerant Flow (VRF) Systems: Weighing Benefits And Limitations
May 8, 2014
Affify is careful to note that a VRF system isn't an off-the-shelf solution. It generally Ramez Affify, principal at E4P consulting engineering the assistance of a design engineer, who needs to review the load profile for the building so that each outdoor section is sized based on the peak load of all the indoor sections at any given time; then the outdoor unit can be specified.
Designing a VRF by selecting the outdoor unit first, Affify says, is a sure way to end up with an oversized system.
A VRF isn't suitable for all applications. Limitations include:
There is a limitation on the indoor coil maximum and minimum dry- and wet-bulb temperatures, which makes the units unsuitable for 100 percent outside air applications, especially in hot and humid climates.
The cooling capacity available to an indoor section is reduced at lower outdoor temperatures. This limits the use of the system in cold climates to serve rooms that require year-round cooling, such as server rooms.
But in many cases, VRF systems work well. Affify references a recent VRF installation in the desert southwest where - shortly after installation - the area experienced a heat wave where ambient outdoor temperatures reached 120F, well exceeding the manufacturers recommended range.
"To our great pleasure, the system functioned and cooled the building during [those] hot times," Affify says.