Vapor-compression refrigeration — COP sensitivity. If the evaporator temperature is held constant, how does the coefficient of performance (COP) change as condenser temperature increases?

Introduction / Context:
For a vapor-compression system, both the evaporating temperature and the condensing temperature strongly influence power input and capacity. Knowing the direction of COP change with condenser temperature helps evaluate the impact of condenser fouling, high ambient, or undersized heat rejection.

Given Data / Assumptions:

• Evaporator temperature fixed (constant load and setpoint).
• Condenser temperature increases due to higher ambient or reduced heat transfer.
• Same working fluid and cycle configuration.

Concept / Approach:
Increasing condenser temperature widens the temperature lift (T_cond − T_evap). This generally raises compressor discharge pressure, increases specific compression work, and reduces refrigerating effect per unit mass (due to higher throttling losses and smaller enthalpy difference across the evaporator), resulting in a lower COP.

Step-by-Step Solution:
COP_ref = Q_L / W_comp.As T_cond rises, W_comp per kg increases because the pressure ratio grows.Meanwhile, Q_L per kg tends to fall slightly for many refrigerants.Net effect: COP decreases.

Verification / Alternative check:
Refrigeration tables and p-h diagram estimates show larger compressor enthalpy rise and smaller evaporator enthalpy drop as condenser temperature climbs, validating the drop in COP.

Why Other Options Are Wrong:
(a) and (c) contradict cycle behaviour. (d) is not characteristic for simple cycles. (e) superheat affects capacity and compressor cooling but does not reverse the fundamental trend.

Common Pitfalls:
Ignoring condenser performance in energy audits; often the easiest efficiency gains come from improving heat rejection.

Final Answer:
decreases