a) The total cost of the heat exchanger and its maintenance cost
b) Interchange heat among the hot and cold fluids to conserve heat energy.
c) The capital cost of the heat exchanger unit
d) Amount of heat produced per day

Answer: b
Explanation: Heat economizing can be defined as the Interchange heat among the hot and cold fluids to conserve heat energy. The heat from the hot liquid is transferred to the cool liquid thus reducing the overall cost of the heating mechanism. This is especially achieved when the arrangement is in counter flow mechanism.