Chapter 50, Problem 12RQ

Free-cooling can be accomplished if the
A. enthalpy of the return air is lower than the enthalpy of the outside air.
B. enthalpy of the outside air is lower than the enthalpy of the return air.
C. enthalpy of the return air is lower than the enthalpy of the supply air.
D. enthalpy of the return air is the same as the enthalpy of the outside air.