Preparing BIM Models for Energy Analysis

To view an MEP system with reference to a complete building design is a holistic approach towards design. This is one of the central benefits of BIM. As we talk of design - specifically for MEP systems, a major contributing factor that distinguishes MEP systems as high performance systems is energy efficiency.

In order to virtually visualize, analyze and calculate energy efficiency of a building, MEP consultants need BIM models that are ready for energy analysis. Different energy analysis techniques require different types of models.

A model developed at an early stage talks about orientation, form and macro level occupancy effects. This model contains conceptual geometry, basic schedules and roughly defined spaces.  Moving on to a later stage, more detailed models need to be prepared that contain precise geometry and material properties.

What kind of input is needed to develop BIM models for energy analysis?

In order to analyze energy consumption, thermal comfort and visual comfort in buildings, modelers need information beyond just the building geometry.

Energy modeling, simulation and analysis results are based on information like:

  • Geometry, layout and wall construction of a building
  • Thermal performance of geometries
  • Building location along with climate data, interior conditions and set points
  • Building occupancy – with building zones and operation schedules information
  • Detailed information about systems for HVAC, hot water, fire and safety, renewable energy and other specialty systems.

Such input information is modeled into BIM, to replicate real world conditions and create simulations for analysis.

BIM Models for Energy Analysis

Energy analysis for a building is intended to derive actionable insights – insights that help improve building energy performance without compromising occupant comfort.

Simplifying the geometry and training focus only on the inputs that are needed for analysis and to gain actionable results is important for a modeler. A modeler will never pass on an overly detailed model to the simulation engine.

Architectural BIM contains all the details from an architect’s perspective, however for energy analysis, a modeler has to create models with only the information that is needed for analysis – for example – models that are built for energy analysis have all planar surfaces and wall thicknesses are described not in the geometry itself, but in the material parameters.

All our past experiences have taught us that modeling buildings appropriately is the most defining factor that leads to accurate energy analysis. It also happens that models are created with a different tool and analyzed in another. In such cases, after a model is exported, it is very important to validate its geometry. After this conversion, it is the best to inspect these models and validate them before being used for analysis.

Garbage In Garbage Out

That said, I would again come back to the inputs. Any type of computational analysis based on simulation, depends on one very important factor, and that is the inputs. It works on the principle of Garbage In – garbage out.

If inputs are incorrect or irrelevant you are never going to get the desired results. Under these idealistic conditions, your building may come forth as the perfect green building, but once it experiences the real world conditions – that do not match with the inputs you provided, your building is no more energy efficient. And this is exactly the reason why today, there are so many buildings that were designed to be energy efficient but have turned out to be quite the opposite.

So the thumb rule is – provide your BIM modelers with accurate inputs. This ensures that the output will be accurate, hence analysis reports will deliver exactly what you need, and this will henceforth transform your building from an energy guzzling giant into an ideal, environment friendly green building. This in-turn helps get all the necessary certifications, improve the building’s market value and earn reputation.

A green building also means reduced energy bills; hence more savings thus increased ROI.

About the Author: Gaurang Trivedi is engineering consultant at TrueCADD. Besides, donning multiple hats, as a website manager and marketing in charge, he also oversees the editorial content, coordinating and managing the website, its news sections, blogs and social media promotions as well.

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