The influence of radiation induced defects on the thermodynamic properties in triglycine selenate(TGSe) crystal was studied by calorimetric experiments. The Landau phenomenological theory of ferroelectric phase transition was used to explain the thermodynamic properties and all free energy expansion coefficients were determined. The successive shift of the phase transition to the lower temperature occurred with ${gamma}$-irradiation dose. In this case the concentration of defects(dose of ${gamma}$-irradiation) can be considered as an independent thermodynamic parameter like hydrostatic pressure or deuterium contents which were used to study properties of this crystal. The phase transition shift for TGSe was -0.94 K/MR