Don’t forget the codes
Both ASHRAE Standards 15 and 34: Safety Standard for Refrigeration Systems and Designation and Classification of Refrigerants govern the use of refrigerant in variable refrigerant flow systems. When employing them, remember to consult the local authority having jurisdiction at the start of design to ensure parallel compliance with local codes, as every project is different.
ASHRAE Standard 15: This application-based standard establishes safe procedures for design, construction, installation and operation of refrigeration systems. It also sets limits, based on occupancy classification, for the maximum refrigerant charge by volume of occupied space. This is called the refrigerant concentration limit. Always do a check of the preliminary VRF system layout to determine if the RCL complies with these requirements.
If it exceeds the RCL levels, action is needed to reduce that number to an allowable level. Some options could include: increasing the room volume, relocating or removing refrigerant piping or dividing the refrigerant circuit to reduce the charge.
ASHRAE Standard 34: This standard names refrigerants and assigns them each a safety classification based on toxicity and flammability levels. Each refrigerant is also assigned a corresponding global warming potential and ozone depletion potential. The Environmental Protection Agency has implemented a plan (with few exceptions) to phase out the production and import of refrigerants with high GWP and ODP levels by 2020.