The model defines energy conversion for a typical CHP operation that includes the normal mode and warm-up mode based on the time delay (CHPs with internal combustion engines). Energy conversion from fuel to the electric power and heat is modeled using system's part-load electrical and thermal efficiencies, based on the empirical data from the manufacturer. The curves are described by a fifth order polynomial, a function of the electric power, water flow rate and water inlet temperature. The air flow rate is modeled using a second order polynomial, a function of the fuel flow rate.