How do you calculate the refrigerant charge in an exchanger?

Answer: (Unilab Genius) ?

  1. Define the operating conditions
    • Inlet/outlet temperature and pressure in the evaporator and condenser.
    • Type of refrigerant (es. R‑134a, R‑410A).
  2. Obtain the properties of the refrigerant
    • Liquid density ρℓ and vapour density ρg under those conditions (refrigerant tables or software).
  3. Calculate the required liquid volume
    • Determine the internal volume of the refrigerant side (evaporator or condenser) using the geometry of the pipe or section.
    • If the system is designed with a liquid level, for example f=0.6 (60% of the volume), the liquid volume is Vℓ=f Vtot
  4. Convert volume to mass

mℓ=ρℓ Vℓ

  1. Add a safety margin
    • Often 5–10% is added for leaks and temperature variations.
    • Final charge: mcharge=mℓ (1 + margin)
  2. Check with the heat balance
    • If you know the required heat flow Q and the coefficient of performance COP, you can calculate the required refrigerant flow:

R =  

where hg and hℓ are the enthalpies of vapour and liquid.

  • Compare m ̇R  with the calculated mass to ensure that the charge is sufficient.

Quick example

    • Evaporator: Vtot=0.02m³, level f=0.6.
    • R‑134a at −10°C: ρℓ=1.14kg/m3.
    • Vℓ=0.012m3 → mℓ=1.37kg.
    • Margin 10 % → mcharge≈1.51kg.

Note: For complex systems (multicompartment, variable pressures), it is recommended to use refrigerant simulation software or consult an expert.

If you have specific parameters (dimensions, refrigerant, operating conditions), I can help you make a more detailed calculation.