This paper presents a detailed heat and mass transfer model for an energy recovery ventilator (ERV) with a porous hydrophillic membrane core. Through finite difference simulations, the temperature, and humidity fields in the unit are calculated. The coupled heat and mass transfer mechanism for the system is discussed. It is found that for the present crossflow arrangement, the membrane area is not effectively used in heat and moisture exchange. The heat and mass transfer rate is larger near the inlets of fluids. There is a ridge on the membrane in the direction of left-lower to upper-right where permeability is relatively higher.