The purpose of this work was to develop a heat pump simulation program that is capable of simulating complex heat exchanger circuits. A segment-by-segment heat exchanger model has been developed in this research. When modeling the heat exchanger circuitries, local air side and refrigerant side boundary conditions for each heat exchanger segment are necessary information to account for the heat transfer and pressure drop changes. Refrigerant flow distribution in the coil circuits are determined by the flow resistance in each circuit. A novel circuiting algorithm that relaxes the constraints of previous models has been proposed to determine the refrigerant flow distribution. As reported in the literature, air side heat transfer coefficients vary row-by-row in multi-row heat exchangers. An experimental procedure that covers a range of fin densities has been conducted to develop row-by-row heat transfer correlations for louvered fin coils. A heat pump simulation program, with the proposed circuitry algorithm and developed row-by-row correlations is presented in this book.