Coupling of whole-building energy simulation and multi-dimensional numerical optimization for minimizing the life cycle costs of office buildings

The minimization of life cycle costs for building materials and operational energy consumption of a reference commercial office building model is achieved through the optimization of envelope design parameters by the use of integrated energy simulation and multi-dimensional numerical optimization techniques. The whole-building energy simulation program EnergyPlus v6.0 is coupled with GenOpt v3.0 generic optimization tool to automatically compute the optimal values of thermal insulation thicknesses for external walls and roofs in addition to glazing unit types for vertical fenestration. A life cycle cost (LCC) model is implemented within the GenOpt program for the objective function evaluation using simulation outputs pertaining to energy consumption and associated utility costs. A stochastic population-based and multi-dimensional optimization technique of Particle Swarm Optimization (PSO) is utilized for searching the parameter space. This algorithm can result in a 36.2% reduction in the computational effort to converge to the global minimum point with a very high degree of accuracy compared to the full enumeration technique. The results indicate that the annual total site energy consumption of the optimized building model is reduced by 33.3% with respect to the initial baseline case. The optimized envelope parameters can yield 28.7% life cycle cost reduction over a 25 years life span with a simple pay-back period of 4.2 years.