Applying VRF? Don’t Overlook Standard 15

Variable refrigerant flow (VRF) systems have become increasingly popular as an HVAC equipment option providing high energy efficiency at reasonable initial costs with the added benefit of simultaneous heating and cooling. However, when considering VRF in potential applications, ASHRAE Standard 15 – Safety Standard for Refrigeration Systems, must be considered to prevent danger to occupants should a refrigerant leak occur. The application of Standard 15 is based on an Occupancy Classification and a System Classification. The Refrigeration Concentration Limit (RCL) set by Standard 15 for a building is based on the smallest space in the building served by an individual evaporator unit.

Options to comply with Standard 15 and still be able to install VRF HVAC are to:

  1. Remove the smallest space(s) that are not compliant with Standard 15 and condition those spaces with a different unit.
  2. Use a common ducted evaporator to condition the two smallest spaces together.
  3. Use an above ceiling evaporator unit ducted to one or more of the smaller spaces.

Ambiguities in Standard 15 also contribute to uncertainty in how it should be applied to VRF systems. Standard 15 states that if two or more rooms are joined by permanent openings, the combined volume can be used to determine RCL. However, the standard does not specify if an undercut door or transfer opening qualifies as a permanent opening, and does not specify minimum opening sizes. Designers should consider the implications of this type of application of Standard 15 for VRF systems.