Mumbai University > Mechanical Engineering > Sem 8 > Refrigeration and air conditioning

Marks: 05M

Year: May 2016

Variable refrigerant flow (VRF) systems, which were introduced in Japan more than 20 years ago, have become popular in many countries, yet they are relatively unknown in the United States. The technology has gradually expanded its market presence, reaching European markets in 1987, and steadily gaining market share throughout the world. In Japan, VRF systems are used in approximately 50% of medium-sized commercial buildings (up to70,000 ft2 [6500 m2]) and one-third of large commercial buildings(more than 70,000 ft2 [6500 m2]).

What is VRF?

Many HVAC professionals are familiar with ductless minisplit products. A variation of this product, often referred to as a multisplit, includes multiple indoor evaporators connected to a single condensing unit. Ductless products are fundamentally different from ducted systems in that heat is transferred to or from the space directly by circulating refrigerant to evaporators located near or within the conditioned space. In contrast, conventional systems transfer heat from the space to the refrigerant by circulating air (in ducted systems) or water (in chillers) throughout the building.

VRF systems are larger capacity, more complex versions of the ductless multisplit systems, with the additional capability of connecting ducted style fan coil units. They are inherently more sophisticated than multisplits, with multiple compressors, many evaporators, and complex oil and refrigerant management and control systems. They do not provide ventilation, so a separate ventilation system is necessary.

The term variable refrigerant flow refers to the ability of the system to control the amount of refrigerant flowing to each of the evaporators, enabling the use of many evaporators of differing capacities and configurations, individualized comfort control, simultaneous heating and cooling in different zones, and heat recovery from one zone to another. This refrigerant flow control lies at the heart of VRF systems and is the major technical challenge as well as the source of many of the system’s advantages.

fig.1 : VRF system.