True Partners Consulting Engineers - AS / ISO 5149 Refrigerant Charge Calculator

AS/NZS 5149-1 REFRIGERANT CHARGE LIMIT CALCULATIONS

What is the maximum allowable refrigerant charge for your commercial AC application based on AS/NZS 5149?

To determine the accurate maximum refrigerant charge limit for your system, a rigorous assessment of key design and safety parameters is essential. Here’s an orderly procedure to aid you in defining the correct charge limit using the True Partners’ Refrigerant Charge Limit calculator, designed in accordance with AS/NZS 5149 (Refer Annex GG of AS/NZS 60335.2.40 for Household and similar electrical appliances):

Step 1 – Select the Occupancy Category and type for the designated space (e.g., Supermarket Public Area). Refer below for further information.

Step 2 – Define the Refrigeration System Classification and Location Class (e.g., compressor in a machinery room for a direct system classified as Location Class II). Refer below for further information.

Steps 3 & 4 – Input the Refrigerant Type and confirm its Safety Group parameters – The tool will automatically populate the corresponding Toxicity Class, Flammability Class, Practical Limit, and Lower Flammability Limit (LFL).

Step 5 – Input the key location dimensions – Record the floor area, ceiling height, and the estimated net volume ratio (the proportion of the room’s volume not occupied by stock or equipment).

Step 6 – Specify the Air Conditioning Unit location details – Select the system and mounting type, which influences certain safety factors in the calculation.

Step 8 – Enter the Actual Refrigerant Charge in kg – This allows the tool to compare the proposed charge against the calculated legal maximum.

Step 9 – Obtain your Refrigerant Charge Limit result – The tool will apply the governing clauses from standards Tables A.1 (Toxicity) and A.2 (Flammability) to calculate the maximum allowable charge. The final limit is displayed in purple. If your actual charge (input in Step 8) exceeds this limit, the cell will turn red, indicating a non-compliant design that requires modification.

True Partners’ Refrigerant Charge Limit calculator will determine the maximum compliant refrigerant charge based on the lowest applicable limit from toxicity and flammability criteria. The tool clearly states the governing formula for each criterion (e.g., "Toxicity Limit x Location Volume" or "20% x LFL x Room volume"). Ensuring your system charge is within this calculated limit is a fundamental requirement for safety compliance and risk mitigation in occupied spaces.

Example:

This example demonstrates the calculation of the maximum allowable refrigerant charge for a medium-temperature (MT) refrigeration rack system serving the public area of a large supermarket. The space has a total floor area of 3,000 m² with a ceiling height of 5 m. The system uses refrigerant R134a.

Installation Details:

• System Type: MT air-cooled refrigeration rack system

• Refrigerant: R134a

• Application: Direct expansion (DX) refrigeration for display cabinets in public supermarket area

• Space Dimensions: 75 m × 40 m × 5 m (length × width × height)

• Occupancy Factor: Stock, display cabinets, and equipment occupy 50% of the total volume

Step-by-Step Calculation Procedure:

Step 1: Determine Occupancy Category

The public area of a supermarket is classified as General Occupancy (Category a) according to Clause 5.1 of AS/NZS 5149.1.

Step 2: Determine Location Classification

The MT rack system is a direct system with compressors located in a separate machinery room, while refrigerant piping extends into the occupied public space. According to Clause 5.3.4, this configuration corresponds to Location Classification II.

Step 3: Determine Refrigerant Safety Parameters

From AS/NZS ISO 817 Table 5:

• Refrigerant: R134a

• Safety Group: A1

• Toxicity Class: A

• Flammability Class: 1 (non-flammable)

Step 4: Identify Toxicity Limit Value

From Table B.1 of AS/NZS 5149.1:

• Practical Limit for R134a: 0.25 kg/m³

• The toxicity limit is the higher of ATEL/ODL or Practical Limit

• Toxicity Limit Applied: 0.25 kg/m³ (Practical Limit)

Step 5: Calculate Room Volume

• Gross Volume: 75 m × 40 m × 5 m = 15,000 m³

• Net Volume Factor: 50% free volume (accounting for occupied space by stock and equipment)

• Net Room Volume: 15,000 m³ × 0.5 = 7,500 m³

Step 6: Calculate Toxicity-Based Charge Limit

Using Table A.1 of AS/NZS 5149.1:

• Toxicity Class: A

• Occupancy Category: a

• Location Classification: II

• Applicable Rule: "Toxicity limit × Room volume"

Calculation:

Toxicity Charge Limit = Toxicity Limit × Net Room Volume

= 0.25 kg/m³ × 7,500 m³

= 1,875 kg

Step 7: Evaluate Flammability-Based Requirements

• Flammability Class: 1 (non-flammable)

• According to Step 5 of Paragraph A.2: No requirement to consider Table A.2 for flammability Class 1 refrigerants

Step 8: Determine Final Charge Limit

• For A1 refrigerants (R134a), only the toxicity-based limit applies

• Final Maximum Allowable Charge: 1,875 kg of R134a

Tool Input Parameters:

Expected Tool Outputs

Toxicity Limit Calculation: 0.25 kg/m³ × 7,500 m³ = 1,875 kg
Flammability Limit Calculation: Not applicable for Class 1 refrigerants (NF)
Final Refrigerant Charge Limit: 1,875 kg (displayed in purple)
Concentration Limit: 0.25 kg/m³

Disclaimer- Our engineering calculators only provide guidance and estimate to help you determine your component size requirements. This guide should not be considered a replacement for an expert advice. If you have any questions regarding TPCE calculators, please feel free to CONTACT US today, one of our friendly experts will be in touch with you as soon as possible to assist you with your engineering needs.

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