Energy Modelling: the whole-building simulation behind code compliance and energy credits.

It is an hourly simulation of a building's energy use over a full year, built from its geometry, envelope construction, occupancy and equipment schedules, lighting and HVAC systems, and local weather data. The output is annual energy consumption, which is compared against a defined baseline to quantify savings. It is a comparative exercise by design, the value lies in the difference between two models built on the same assumptions.

The Energy Conservation Building Code, issued by the Bureau of Energy Efficiency, sets minimum energy performance requirements for commercial buildings and is enforced by states that adopt it into their building rules. Compliance can be shown through prescriptive requirements or through the whole-building performance route, and the latter is exactly what an energy model provides.

The code defines a compliant level and two higher tiers of performance above it, so a building can be certified as meeting the code or as exceeding it. Which tier is targeted matters: state incentives and green building energy credits often reference the higher tiers, and reaching them is an envelope and systems decision made in design, not a documentation choice made later.

The main code addresses commercial buildings. Residential envelope performance is addressed through a separate BEE code for residential buildings, which works on an envelope transmittance value rather than a full systems assessment. A residential project should be assessed against the residential framework, not the commercial one.

Rating systems and codes specify the capabilities a tool must have (hourly simulation over 8,760 hours, the ability to model the relevant systems and schedules), rather than naming a single product. Established engines used with a documented, reviewable set of inputs are what reviewers accept; the credibility comes from the assumptions being defensible, not from the software brand.

At concept or schematic design, when orientation, massing, window-to-wall ratio and envelope are still open. That is when a model can change the outcome. A model commissioned after design freeze can only report what the building will do, which is documentation rather than engineering.

No, and it should not be presented that way. A compliance model uses standardised schedules and assumptions so that two designs can be compared fairly, not so that operating cost can be forecast. Actual consumption depends on how the building is occupied, operated and maintained, which is why measured performance often differs from the modelled case.

Rating systems expect the model to be prepared by someone competent in building simulation and, for some credits, reviewed or signed by a qualified professional; ECBC compliance may require certification by an empanelled or accredited professional depending on how the state has adopted the code. The practical requirement is a modeller who can defend every input under review.