In a cascade refrigeration system, what is the primary reason to use at least two compressors?

• A. Avoid very high compression ratio for each compressor
• B. Improve energy efficiency
• C. Reduce maintenance
• D. Increase evaporator area

Answer: (A)

In cascade refrigeration, the work of compression is split between stages so that each compressor handles a smaller pressure rise. If a single compressor had to achieve a very large pressure lift, it would run hotter, be less efficient, and endure more mechanical stress and lubrication challenges. Using at least two compressors (with intercooling between stages) keeps each compressor’s pressure ratio within a practical range, which improves energy efficiency, reduces discharge temperatures, and enhances reliability. The other options don’t address the fundamental reason—the design goal is to avoid an excessive lift per compressor.