VRF stands for Variable Refrigerant Flow. It is a ductless, large-scale system for HVAC that is usually modular (meaning you can combine multiple indoor units and in some cases multiple outdoor units on a single refrigerant loop).
Which is the difference between multi-split and VRF systems?
The main difference is that VRF systems have a control box between the outdoor and indoor units that regulates the flow of refrigerant so that each individual indoor unit can receive a different amount of refrigerant according to the required cooling (or heating) capacity needed at that moment. This required capacity (or 'load') is calculated and managed in slightly different ways depending on the manufacturer.
What are the different types of VRF system?
There two main types of VRF system - the main ones being Heat Pump which can only provide heating or cooling but not both at the same time, and Heat Recovery which can provide simulatenous cooling and heating for different zones (or rooms). Other types include water-cooled VRF (which uses water instead of refrigerant) and High Ambient (for use in local climates with exceptionally high ambient temperatures).
In addition to the different types of VRF system there are different types and size of outdoor VRF units. Some outdoor units are designed to be modular so that multiple ODUs can be combined into a single refrigerant loop to provide coverage to larger spaces. Others are not modular and so can support a more limited number of indoor units. In addition Hitachi has 2 exclusive formats of outdoor unit - SideSmart - slim modular outdoor units that have almost the same capacity as large modular ODUs but have a smaller footprint, and Centrifugal VRF (where the outdoor unit can be hidden indoors and entirely from view).
Are all manufacturer's VRF technology the same?
Although the fundamental refrigerant flow method is the same, how the required refrigerant for each indoor unit is calculated varies significantly. Some manufacturers use an indirect controol method which sets a target for the evaporation temperature of the refrigerant based on the gap between set and room temperature which then switches the compressor on or off to achieve that target. By controlling the evaporation temperature of the refrigerant you can indirectly control the cooling capacity.