IN THE DESIGN of modern engineered buildings it is customary to use a variety of mathematical models to simulate the performance of the structural system and the service (HVAC) systems. Structural, mechanical, and electrical engineers use various different mathematical models to analyze the response of the modeled system or subsystem and then improve, adjust, or revise the system as needed until a final design is arrived at. Analysis, even crude analysis and, perhaps, with more than one model, is necessary to design a new facility or subsystem as well as to assess an existing building or part thereof.