<p>We develop a set of numerical approximations to discretize the non-isothermal incompressible hydrodynamic model for Rayleigh-Bénard convection (RBC), which ensures the negative energy dissipation rate with respect to adiabatic boundary conditions. Using the Crank-Nicolson (CN) method, the second-order backward difference method combined with the pressure-correction method, we propose two kinds of decoupled, linear, both second-order in time energy-dissipation-rate-preserving semi-discrete projection numerical algorithms. Meanwhile, the second-order fully discrete numerical algorithms are obtained by the use of a finite difference method on staggered grids in space. These numerical approximations are proved to preserve the property of the energy dissipation rate at the fully discrete level. Moreover, the numerical approximations are also unconditionally energy stable. The fast Fourier algorithm is applied to numerical implementation to enhance experimental efficiency. Convergence rate tests are conducted to verify the accuracy of the algorithms. Our simulations showcase that both hydrodynamic and thermal effects in resolving RBC within the non-isothermal hydrodynamic model of incompressible viscous fluid flow. In general, our structure-preserving projection schemes and implementation methods accurately and efficiently simulate RBC in nature.</p>