Heating, ventilating, and air-conditioning (HVAC) system design can be markedly improved through the application of numerical optimization procedures within the design process. This paper describes a procedure for the formulation and solution of HVAC system optimization problems that has been implemented in a library of computer programs. Consideration is given to the interaction between the simulation of the systems performance and the optimized design objective and constraint functions. Conclusions are drawn from example applications, and suggestions are made for the further development of a solution algorithm.Units: Dual