🔍 Key Concepts

• Difference between a primary refrigerant (circulates in the compressor/evaporator/condenser) and a secondary refrigerant (carries cooling to remote spaces) • Properties needed for a good secondary refrigerant: safe, non‑toxic, non‑flammable, good heat capacity, easy to pump • Typical fluids used in chilled water air conditioning systems aboard ships

💭 Think About

• Ask yourself: which option is commonly pumped around the ship in pipes and coils to absorb heat from air handling units, after being cooled elsewhere? • Consider which substance on the list is safest and easiest to handle in large volumes in accommodation and machinery spaces. • Think about which one has high specific heat capacity and is already widely used in HVAC (heating, ventilation, air conditioning) systems ashore and afloat.

✅ Before You Answer

• Eliminate any substances that are gases at normal room temperature and pressure when used in open piping systems throughout the ship. • Check which option is commonly associated with chilled water systems used for air conditioning, rather than as a direct expansion refrigerant in the compressor. • Verify which choice is non‑flammable, non‑toxic, and simple to store and pump in large quantities.