In indirect low-temperature refrigerant systems, using glycol as the intermediate cooling medium offers which main advantage?

• A. Lower cost
• B. The elimination of corrosion
• C. Higher energy efficiency
• D. More rapid heat transfer

Answer: (D)

The main thing being tested is how a secondary coolant behaves at very low temperatures in an indirect system. Glycol-water mixtures stay liquid at temperatures where pure water would freeze, so the secondary loop can be circulated down to those low temperatures without ice forming. Keeping the cooling medium in liquid form allows the heat exchanger to transfer heat consistently as the process coolant exchanges heat with the glycol loop, which effectively maintains a strong temperature difference and steady heat transfer. That reliability and ability to operate without freezing is what often yields faster, more reliable heat transfer in these systems. The other options don’t capture this practical advantage: glycol adds cost and requires inhibitors, it doesn’t completely eliminate corrosion, and energy efficiency isn’t guaranteed to be higher—preventing freezing to maintain continuous heat transfer is the key benefit.