While variable refrigerant flow (VRF) systems offer great flexibility in your designs and can provide outstanding energy savings, there are some code requirements that must be considered.   In Ontario, the code of reference is CAN/CSA B52 - Mechancial Refrigeration Code.  This code outlines all of the safety requirements that must be met in order for a refrigeration system to be approved for installation. 

In this post, I want to specifically address the quantity of refrigerant allowed in any given system. 

The first order of business is to define the type of system we are dealing with.  VRF systems are classified as: direct with a high probability of leakage.  It should also be noted that all VRF systems currently available in North America use R410a refrigerant.  Applying the code for different occupancy classifications, the maximum refrigerant capacity in any system is defined as follows:

The volume is calculated based on the smallest confined space that refrigerant could discharge  into in the event of a rupture.  This would include the celing plenum in a non-ducted return application as well as any spaces interconnected by transfer openings, etc. 

A word of CAUTION!  ASHRAE Standard 15 has a very similar table outlining maximum refrigerant charges.  These values are much higher than CAN/CSA B52 and should not be used if the system is being installed in Canada.