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whole building energy simulation can be used for:

1. Carrying out compliance studies, for example, to ensure compliance with minimum energy efficiency standards like ASHRAE 90.1 in the USA, NCC Section-J in Australia or the ECBC in India. In these instances, the analyst is comparing the performance of a "reference" building against a "proposed" design solution. This compliance energy modeling scenario may be extended to voluntary codes like LEED and GreenStar. In all these instances, the energy modeler is trying to generate results which meet or exceed certain criteria, when many of the input parameters are pre-defined or constrained (for example, geometry supplied by the architecture firm, operation schedules, minimum EERs, maximum lighting power density, etc for the reference case are prescribed by relevant codes and standards)

2. It is also possible (and much more fun) to use energy simulation as a early design tool. To do this effectively requires experience in all of the building systems that impact energy consumption. It can take up a lot of time, a lot of what-if scenarios, and all our new employees go through what we refer to as a "simulation addiction" phase. In our office we also talk about "building architecture" model studies and "systems architecture" model studies. Our experience is that there is a lot of expertise on building architecture in the industry, which may be described (with some simplification) as optimising the energy performance of the building envelope. "Systems architecture" requires significant experience and knowledge of the design philosophies of the various types of environmental control systems and their practical limitations, whether these are traditional fully air-conditioned buildings, or mixed mode hybrid solutions. We could do better in this area, and the test is to compare predicted performance against a 12 month period of "normal" occupancy and operation. A quick tip: we have found that in high performance, fully air-conditioned buildings, one may only be able to represent about 50% of the building's total energy consumption in the energy simulation model. The remainder may just as well be estimated using spreadsheet calculations.

Good luck, and have fun!