Condenser sizing in a system is typically larger than the evaporator by what percent?

Condenser sizing in a system is typically larger than the evaporator by what percent?

• A. 15%
• B. 25%
• C. 20%
• D. 30%

Answer: (B)

The key idea is that the condenser has to reject not only the heat absorbed by the evaporator but also the extra heat produced by the compressor work. In a vapor-compression cycle, Q_out (rejected by the condenser) equals Q_in (absorbed by the evaporator) plus the work input to the compressor: Q_out = Q_in + W. The work input W is related to Q_in by the cycle’s COP (cooling efficiency): W = Q_in / COP. So Q_out = Q_in (1 + 1/COP). With typical COP values around 3–4 for many refrigerant systems, the condenser must reject roughly 1.25 to 1.33 times the evaporator capacity, i.e., about 25%–33% more. Designers commonly use about a 25% margin as a standard sizing rule, which corresponds to COP near 4. Therefore condenser capacity is sized about 25% larger than the evaporator capacity. That’s why the typical answer is 25%.

The key idea is that the condenser has to reject not only the heat absorbed by the evaporator but also the extra heat produced by the compressor work. In a vapor-compression cycle, Q_out (rejected by the condenser) equals Q_in (absorbed by the evaporator) plus the work input to the compressor: Q_out = Q_in + W. The work input W is related to Q_in by the cycle’s COP (cooling efficiency): W = Q_in / COP. So Q_out = Q_in (1 + 1/COP).

With typical COP values around 3–4 for many refrigerant systems, the condenser must reject roughly 1.25 to 1.33 times the evaporator capacity, i.e., about 25%–33% more. Designers commonly use about a 25% margin as a standard sizing rule, which corresponds to COP near 4. Therefore condenser capacity is sized about 25% larger than the evaporator capacity.

That’s why the typical answer is 25%.