A thermal energy measurement system is disclosed for use as a calorimeter capable of providing sample thermal energy measurements in selectable modes including isothermal and/or adiabatic modes. In some embodiments, the thermal energy system further comprises a closed-loop servo controller. In some embodiments, the thermal energy measurement system is capable of providing thermal energy measurements in semi-adiabatic and/or custom programmed modes. In some embodiments, the servo controller may be implemented as a feedback circuit whose process variable is either heat flow, sample temperature, a combination thereof, or a preprogrammed time dependence of the heat flow and/or sample temperature. The output of the servo controller may be used to drive a temperature control device such as but not limited to a thermoelectric module (TEM). Methods of thermal energy measurement are also disclosed.