An Optimization Methodology for Zero Net Energy Buildings

A zero net energy building (ZNEB) is grid-tied, net metered and produces as much energy on-site as it uses in a typical year. In this paper, we describe methods to cost optimize designs for ZNEB’s. The goal is to find a constrained optimum, i.e., the minimum-cost design that achieves ZNE. Increased first costs for improved efficiency are balanced against the size of the PV system required to achieve ZNE (where the net-metered PV system is the energy source of last resort, because it is expensive but can meet the remaining load “using the grid for storage”). Discrete building component options are considered within various categories (e.g., walls, ceilings, foundations, glass types, air conditioners, furnaces, etc.). Each category is optimized by balancing the marginal cost of saved energy for efficiency options against the cost of energy from the PV system. Categories are optimized sequentially with iteration to adjust for possible interactions between categories. The process is automated with software that manipulates input files, launches DOE2 simulations, reads the results, and executes the optimization methodology.