Utilizing Phase Change Materials (PCMs) in building envelopes as a measure for reducing energy use has been studied and practiced over the lastfour decades. In the context of whole building Energy simulation, building envelopes are typically modeled using a simplified one dimensional finitedifference approach. PCMs can be included in such models if the models handle property variation. Simplified models generally do not capturedetailed physical phenomena of PCMs such as hysteresis and sub-cooling. This paper presents the enhancements to the simulation model for PhaseChange Materials in a modern whole building energy simulation program, EnergyPlus. The EnergyPlus PCM model was modified to anequation based model and the new model was validated. Demonstration of construction of temperature enthalpy curve from the properties of PCMavailable from experiments and manufacturers is also presented in this paper. Wallboards with experimental property data and manufacturers'catalog data were studied. In both cases, a similar behavior of the material is observed under same simulation conditions.