🔍 Key Concepts

• Difference between primary and secondary refrigerants in marine HVAC systems • Common properties desired in a secondary refrigerant (safety, corrosion, freezing point) • Typical fluids circulated through coils in large shipboard air conditioning plants

💭 Think About

• Ask yourself which option is normally circulated in piping to carry cold from a central chiller to air-handling units, rather than being compressed and expanded in a refrigeration cycle. • Consider which of these substances would be safest and easiest to handle in large volumes throughout accommodation spaces. • Think about which choices are more likely to be the actual working refrigerant in the compressor (primary) versus the transport medium (secondary).

✅ Before You Answer

• Identify which of the four is most commonly used as a safe, non‑toxic circulating fluid in HVAC systems. • Eliminate any substances that are typically primary refrigerants or industrial solvents rather than heat‑transfer fluids. • Check which option would have reasonable cost, availability, and compatibility with shipboard piping and pumps for large circulation loops.