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Are You Exceeding The RCL On Your VRF Jobs?   Publish Date: 1/1/2015

Are You Exceeding The RCL On Your VRF Jobs?

When designing VRF projects, due to having refrigerant in the occupied space, special consideration needs to be given to the Refrigerant Concentration Limit (RCL).

ASHRAE Standard 15 classifies refrigeration system types according to the potential of the refrigeration equipment to expose the occupants to refrigerant. A Low Probability System is one “…in which the basic design, or location of the components, is such that leakage of refrigerant from a failed connection, seal or component cannot enter the occupied space.” A High Probability System is defined as one “…in which the basic design, or the location of components, is such that a leakage of refrigeration from a failed connection, seal, or component will enter the occupied space.VRF systems are considered a High Probability System because they include refrigerant containing components (air handlers, refrigerant piping, refrigerant distribution boxes, etc) that are located in an occupied space, or in an airstream serving an occupied space.

ASHRAE Standard 15 uses the Refrigerant Safety Classifications from ASHRAE Standard 34 as a model for classifying the refrigerant used. ASHRAE Standard 34 classifies refrigerants according to their toxicity and flammability. R410a, the refrigerant used in most modern VRF systems, is classified as an A1 Safety Group Refrigerant (meaning it is non-flammable and non-toxic). Although R410A is Group A1, it can displace oxygen and as such can pose a serious danger to occupants if discharged in large quantities into a small occupied space.

ASHRAE Standard 34 also sets the Refrigerant Concentration Limit (RCL) used in ASHRAE Standard 15 requirements. The Refrigerant Concentration Limit (RCL) is expressed as the maximum allowable pounds of refrigerant per 1,000 cubic feet of occupied space. ASHRAE Standard 15 defines an occupied space as “…that portion of the premises accessible to or occupied by people, excluding machinery rooms.” Refrigerant concentration limits cannot be exceeded in any occupied space. To calculate the concentration for your project, take the total refrigerant in the system and divide it by the volume of the smallest occupied space where a leak could occur. If the concentration is greater than the RCL for your Occupancy Classification, you will need to consider design changes. The RCL for R410a is typically 25 lbs / 1,000 cubic feet depending on the Occupancy Classification. Consult ASHRAE Standard 34 for the RCL specific to the project occupancy.

If the RCL is exceeded, there are a number of alternatives to explore. First, consider if the length of piping can be reduced by relocating equipment. Less piping equates to less refrigerant. If multiple outdoor units are connected to one refrigeration circuit, consider splitting the units into multiple circuits to reduce the amount of refrigerant on any one circuit. Finally, determine if it is possible to increase the size of the smallest space served. One way to achieve this if you are using wall mount units or cassettes, is to consider using a single ducted unit that would serve multiple spaces, effectively increasing the size of the space.

For more information on Fujitsu, contact your local Johnson Air Products salesperson or click here.

For more information on ASHRAE Standard 15 and 34, click here.