A blast freezer @ Room temp. of -40*C, the evaporator if selected based on the capacity @ Evaporating temp. of -46*C it would for example 12 KW, so if am gonna select the blast cooler according to this capacity with a delta T of 6, the size of the evaporator would be very silly and small, the thing am doing that i consider the capacity @ Evaporating temp. of -35 which will be 20 KW, by this way i have a logical size of the cooler and it works efficiently and the temperature is reached, but i still wonder if i can select a smaller (Economical) evaporator lets say @-40*C with a capacity of 15 KW, and why, and what is the rule and limits??!!