This is one of the most comprehensible abstracts on Energy Modeling and LEED a came across so far:

Energy Modeling, ASHRAE 90.1 and LEED (By Andrew J. Kamnik)

“The most challenging prerequisite in the LEED for New Construction certification process is the Energy and Atmosphere Prerequisite 2: Minimum Energy Performance.

Any project seeking Certified, Silver, Gold or Platinum certification must demonstrate a 10 percent improvement above a building designed to comply with ASHRAE 90.1-2007 to as a prerequisite. (For major renovations, the requirement is 5 percent improvement in the building’s performance.) The most effective means of earning this credit is through an application variously called the “Energy Model,” “LEED Model,” or simply the “Model,” but officially the “Whole Building Energy Simulation Model.” Whatever it’s called, when done correctly, it can provide an extraordinary amount of information about a building’s potential for energy savings, well before the first brick is even laid.

The energy model is a computer software simulation that starts with specified materials and systems for a building, calculates the energy cost for one year, and creates a report of the anticipated energy performance of the building. The model will reveal how energy efficient the building can be, while there is still time to enhance it.

An important concept to understand is “percent improvement.” The ASHRAE standard and the LEED model compare the annual energy cost of the proposed building vs. the baseline building that just meets code. Annual energy cost is used because it is readily understood by engineers, architects, building owners, executives, accountants, and occupants. Everyone can understand how one item may cost 10 percent less, but not everyone has a frame of reference for British Thermal Unit-hours (BTUh), kilowatt-hours (kWh), tons of carbon dioxide and the like.

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