Original drawings may differ from the equipment or operating hours in use today. Before renovation, the team needs to understand how well an energy model represents current conditions. Reviewing documents, consumption records and operational information together provides a clearer starting point for comparing improvements. Modelling turns that information into a technical assessment supporting design and investment decisions.
Defining the existing building under current conditions
In design projects, part of the inputs consists of decisions that have not yet been implemented; the model carries the intended form of the future building into calculation. In renovation, the building already exists. Its geometry, envelope components, equipment and operating patterns can be observed, and many can be verified from documents and operating records. This difference also changes the need for verification: the model must be comparable with the building's current consumption records. Our energy modelling in design article provides a general overview of new design modelling.
The as-is model and its inputs
The as-is model carries the building's current state into calculation. Inputs include architectural documents, envelope and insulation information, heating, cooling and ventilation equipment, lighting, control settings, operating hours, occupancy and the region's weather conditions. The currency of documentation matters: equipment added later or changing usage patterns may make an old document less representative of today's building. Missing information can be supported by a site survey or measurement. The U.S. Department of Energy describes building energy modelling as a versatile, multipurpose tool used across new construction and retrofit design, code compliance and further applications. U.S. Department of Energy — Building energy modelling.
Aligning the model with measured data: calibration
Calibration is the process of comparing the consumption calculated by the model with the consumption measured in the building and investigating the differences. The aim is to explain differences between calculations and measurements and improve inputs using verified building information. Where a deviation appears, inputs such as operating patterns, equipment loads or control settings are reviewed against how the building operates today.
A reliable comparison requires a consistent period and scope: which periods, meters and energy types are matched with the calculation should be explicit. Consumption, cost and emissions are formed from separate calculation inputs; these inputs are distinguished when consumption is compared. The criteria and thresholds used to evaluate alignment are checked from the current guideline edition the study relies on; the criteria used are stated in the report. ASHRAE Guideline 14 provides a framework for determining energy, demand and water savings through measurement. ASHRAE — Guideline 14-2023, Addendum a Even a calibrated model is a calculated result; it is not the same form of evidence as measured data.
Comparing improvement scenarios
A calibrated model allows improvement options to be compared under consistent conditions. Measures are modelled sometimes individually, sometimes as packages, because the effect of some measures depends on how others operate. When scenarios are run under the same weather conditions and operating assumptions, it becomes easier to separate which decision drives the difference between results.
When reading results, consumption, cost and emissions should be recognised as separate calculations: tariff structures and emission factors are different inputs, and a change in consumption may not translate proportionally into cost and emissions. Model output is decision-support information; it is not presented as an implemented and measured saving.
Relation to verification and certification
Post-implementation assessment uses measured data; this is a different form of evidence from calculated scenario results. Renovation and retrofit can be treated as an opportunity to raise the energy performance of existing buildings; the U.S. Department of Energy's resource notes that modelling helps identify the most impactful measures through simulations and that energy-use goals are followed from first planning stages through post-retrofit monitoring. U.S. Department of Energy — Existing building retrofits.
Where certification is an objective, the pathway is selected according to renovation scope and building use. Major renovations can be addressed through design and construction systems, while operational improvements may suit an appropriate operational assessment. The process and evidence conditions of pathways focused on buildings in use are planned separately; our LEED O+M recertification article covers the general process. The modelling scope is assessed together with the evidence needs of the intended pathway.
AECO's contribution
AECO's building energy modelling service can assess current conditions and improvement options. Calibration needs are established alongside available measurements and the purpose of the study. Parametric examination of options is supported by optimisation work; measurement needs for calibration and verification can be discussed through testing and measurement services. Sharing existing consumption records, system documents and planned renovations helps define the scope of the work.