The existing moving-boundary models for evaporators are obtained by expanding the continuity and internal energy equations

and the error caused by the expansion results that the models are not intrinsically conservative on both mass and energy

resulting accuracy deterioration. To guarantee intrinsically conservative on both mass and energy in calculation

the mass and internal energy are selected as the state variables

and the continuity and internal energy equations are directly solved to avoid the expansion error. The equations and algorithms for refrigerant state and phase distribution in evaporator are developed when the mass and internal energy are given. The case study shows the new model is steady and intrinsically conservative on both mass and energy in the performance simulation of 48 hours

and the simulation results agree well with the experimental data.