Question

A sales person selling refrigerators and deep freezers will guarantee a minimum coefficient of performance of 4.5 year round. How would you evaluate that? Are they all the same? 

Answer 1

Assume a high temperature of 35°C. If a freezer compartment is included T_L ~ -20°C (deep freezer) and fluid temperature is then T_L ~ -30°C

βdeep freezer ≤ T_L/(T_H - T_L) = (273.15 - 30)/[35 - (-30)] = 3.74 A hot summer day may require a higher TH to push Q_H out into the room, so even lower β.

Claim is possible for a refrigerator, but not for a deep freezer.