Object-oriented programming, equation-based submodels, and system reduction in SPANK

Collaborative efforts among building simulation researchers in Europe and the US have resulted in wide acceptance of certain features as necessary attributes of future simulation environments. As identified 'in the Energy Kernel System (EKS), the principal features are those of the object-oriented programming (OOP) paradigm, in which a hierarchy of submodels is readily defined and interconnected to form system models of widely varying purpose, solution methodology, and implementation description. The Simulation Problem Analysis Kernel (SPANK) is an early, prototypical implementation intended to exhibit at least some of the EKS features, including an OOP-like environment. Additionally, SPANK implements a solution process that is based on graph algorithms and achieves solution efficiency through a reduction in size of the iterative problem. This paper enlarges on earlier descriptions of SPANK, attempting to separate and clarify the modeling issues and the solution issues. To this end the nature of the SPANK environment is compared to established OOP environments. The SPANK equation-based objects are contrasted to the assignment-based (input/output oriented) models employed in most current simulation environments. The SPANK cut-set reduction methodology is compared to the more widely known sparse matrix technique. Finally the utility of the SPANK reduction algorithm is demonstrated on a number of example problems.