As Variable Refrigerant Flow (VRF) systems are applied to more buildings in the United
States, many designers have asked for recommendations to apply VRF systems in compliance
with ASHRAE Standards 15 & 34.
ASHRAE Standards 15 & 34 are refrigerant safety standards recognized by many state and
local building codes. Local codes may vary from ASHRAE Standards 15 & 34 and it is
recommended that the designer review these local codes for differences from ASHRAE
Standards 15 & 34.
Frequently Asked Questions:
Q: I thought ASHRAE Standards 15 & 34 only apply to chiller systems. Do VRF systems need
to comply with ASHRAE Standards 15 & 34?
A: Chiller systems were popular when ASHRAE Standard 15 was originally introduced in 1930.
However, ASHRAE Standard 15 applies to all air conditioning systems that use refrigerant including VRF systems, packaged rooftop units, split systems, and chiller systems
Q: Can the ceiling space (plenum) be calculated as part of the occupied volume?
A: According to ASHRAE 15: “The space above a suspended ceiling shall not be included in
calculating the refrigerant quantity limit in the system unless such space is part of the air
supply or return system”
Q: When using a ducted indoor unit serving multiple offices, what volume is used for
A: Multiple offices connected by ductwork can combine the volume of the offices in the
occupied volume calculation.
Q: Where can I find the total system charge for the VRF system?
A: The LATS selection software generates an output report shows the product charge and
Additional Ref. Amount. These (2) values can be added to obtain the total system refrigerant
Q: What size should the permanent opening be to connect occupied spaces?
A: The size of a permanent opening is not listed in ASHRAE 15 and is subject to engineering
judgment. Locating the permanent opening low on the wall is recommended since R410A
refrigerant is heavier than air. It is also recommended that you consult with your local code