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How to prepare the BIM model for the Energy Evaluation

Gabor Almasi
Archicad models have to be prepared to be able to run precise energy simulations in Energy Evaluation or in EcoDesigner Star. The more precise the model, the more precise the energy calculation you get. Geometry, Building Materials, and Priority Based Connections must be set up properly to model all the details of the building according to a real-life building. Here is a checklist of the rules you should be kept in mind to avoid errors or incorrect results:

1. Create Building Energy Model

The Building Energy Model (BEM) is a view where the enveloping building structures and openings are visible, as well as the major internal structures that represent significant heat storage mass. Here is what should be available when creating a BEM Layer Combination: 

  • Zone boundary elements should be displayed: Walls, slabs, roofs, shells, curtain walls, and openings
  • Beams, columns, etc must be on a hidden layer. Those walls or slabs must be on the hidden layers as well, which are not considered zone boundary elements. (Wall's Relation to Zones parameter can be set to „No effect on Zones”.)
  • Avoid using multiple parallel walls (or slabs or roofs) to model composite structures. If such constructions exist in the building model, make sure that only one of the parallel structures is visible in the energy model, and that the adjacent Zones touch that structure.
  • Creating a Zone only view can help us to drag zones into thermal blocks easily and it's easy to identify the unused zones in this view.
  • Set the physical properties individually or choose from the catalog

2. Rules of Zone placement

  • Use automatic Zones to provide a proper connection between the Zones and the building envelope elements.
  • Use Zone boundary lines if there is a room that is in contact with other rooms without walls between them.
  • The bottom of the zone must be in touch with the floor, and the top of the zone must be on the same level as the ceiling.

3. Create Thermal Blocks

  • A group of zones should be put into one thermal block if they have the same orientation, the same operation profile, and the same HVAC systems.
  • Once the thermal blocks are settled, choose the Operation Profiles from the list, customize them or just create new ones.
  • Assign heating, ventilation, cooling, and lighting systems either it is natural or mechanical to the thermal blocks. Use „not yet specified” systems to make demand calculations, which can be specified later.

Here are some articles to guide you on how to create thermal blocks and add zones to them: 

Creating Thermal Blocks for Energy Evaluation - Graphisoft Community

Adding Zones to a Thermal Block - Graphisoft Community

4. Space boundary geometry

  • Check Unused zones. Make sure every zone of the building is placed into a thermal block where it belongs
  • Check uncovered areas. Uncovered areas might give inaccurate results during Energy Evaluation
  • Use Area Threshold if needed. Setting an Area threshold can help to filter out small areas that are less important in the simulation
  • Use area correction if needed. Area correction should be used if the area of the listed structures must be increased or decreased.

5. Space boundary Properties

  • Check the U-values in the Structures and in the Opening list and override if necessary
  • Run Solar Analysis if the shading and all other parameters are set on the Opening tab

6. Additional Data Input

  • Additional data input, such as Location, and climate data should be given.
  • Use certified analytic weather files. If this kind of weather file is not available for the given location, check the content in the Climate Data window and run the demand calculation to make sure the given data is correct.
  • Use the Mesh tool to model the building site’s grade level, especially if it is uneven.
  • At this point fine-tune Operation profiles if necessary
  • Set the Energy Source Factors, although the default values are given
  • Add the Energy Costs based on the local standards.

7. Energy Simulation

  • Update Energy Model Review and Start Energy Simulation

I know that you recommend avoiding parallel componentsand to use composites instead. However if I wish to split the roof and ceilings into slab and roof components, how would that work with the Energy Evaluation tool?

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