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Heat transfer (HT) is a major constraint in thermal system analysis. However, when discussing utilizing the flexibility provided by the heating sector, for example using thermal energy storage (TES) to increase operational flexibility of combined heat and power (CHP), the HT process is often ignored. This may mean infeasibility of the resulting schedules. In response to this, this paper proposes a general TES model which takes detailed HT analysis into account. By setting the relevant parameters, this model can be used to describe the HT process for both sensible heat (SH) and latent heat (LH) TES devices. An iteration method is proposed to deal with the nonlinearity introduced by the HT constraints, and to solve the joint nonlinear dispatch problem for CHP with TES. The simulation results show that explicitly considering the HT process is essential to realistically assess and therefore make full use of the flexibility provided by TES. Moreover, the comparison between LH and SH TES shows that LH can provide more flexibility for the system, especially when the starting energy level in the TES device is low. Index Terms-combined heat and power (CHP), flexibility, heat transfer (HT), power dispatch, thermal energy storage (TES) I. NOMENCLATURE A g/g-l/l,hs/st the equivalent heat transfer (HT) area of gas/ gasliquid/ liquid sub process for the heat station/ heat storage HT, m 2 A hs/st/rl/tes the HT area of the heat exchanger for heat station/ heat storage/ heat release/ thermal energy storage (TES), m 2 c mdm/tes/water specific heat capacity of heat conduction medium/ TES material/ water, J/(kg• K) D/U tp/chp downward/ upward ramping rate of thermal units/ combined heat and power (CHP) units, MW/h d tes density of TES material, kg/ m 3