Green Building Studio

Overview

To evaluate the capabilities of Autodesk Revit and Green Building Studio a case study methodology was used. The case study involved a proposed design project for a School in Abuja, Nigeria. It involved using Building models created in Revit and exported to GBS for analysis.

Case study

The case of study is a proposed Faculty storey office building located at Abuja, Nigeria. The Faculty building will be used for departmental offices, lecture halls, meeting rooms, organised seminars and conferences, alongside other educational activities.

The building will be a masonry (concrete and block) structure when constructed. For the purpose of this thesis, we will assume that we are still in the design stage.

The building design is basically box shaped with flat roof construction. The faculty buildings has different energy demand. Figures 5 and 6 shows the architectural rendering of the buildings.

Architectural Revit workflow

The building was modelled using Autodesk AutoCAD. It was then converted to a Revit model. The models contained parametric data and descriptions of the building elements.

The model was not intended for energy simulation. A few modifications were made to the original model to improve the expected result of the Energy model. The modifications were made in Autodesk Revit 2016.

Modifications and Data input

The Revit file contained the building. The building for analysis had to be isolated. Areas adjacent to heated spaces were covered with external wall construction. The reasons for this are as follows;

• Revit computes analytical surfaces based on Elements in the model and their construction status.
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• The energy modelling default values are size dependent; default values for small buildings are different from values for bigger buildings. Different building types also have different default values.

Using Revit, there are many ways of creating a simulation model for Energy/ sustainability analysis. First is the use of conceptual masses; which helps the designer to conduct analysis at the conceptual stage of the project. The other is by the use of building elements. Due to the availability of a building model the building elements were used.

For the thermal properties of the building elements to be used in the energy simulation, it is required that the elements in the building model contain the thermal properties as part of their parameters. Using the properties palette in Revit the thermal properties was added to the building elements before the energy simulation.

There is option of using Spaces or Rooms when using building elements. These are specific terminologies of Autodesk Revit. They are used to supply additional energy data for the simulation. The data that can be added are as follows;

• Lighting
• Equipment
• Occupancy

It can be specified when using Spaces as the export category, but the default values are used when Rooms is set as the export category. For this simulation, the Rooms category was used.

To create Rooms in Revit, objects like walls, floors, ceilings and roof elements are bounded. It is very important all walls, roofs, slabs and ceilings are well connected. If the bounding elements don’t touch, rooms don’t get created. There is a requirement for area and volume calculations the analysis model which could affect the results. The room elements were re-modified to touch the bounding elements.

Model Validation

When starting energy simulation, Revit normally display an error message if there are inconsistencies in the model that needs to be modified. This is where model validation comes in.

Model Validation in Revit is important for the energy analysis process. It is necessary due to certain limitations in the software and the modelling engine. When creating an energy analytical model (E.A.M.) based on building elements, there is need to review the following;

• Model size, complexity and quality – This affects the amount of time taken to generate the energy analytical model.
• Energy analytical model form and precision – the appearance of the model could be different from a basic closed shell type geometry. This could lead to minor difference in Area/volume values.
• Revit Room/space separation lines when present do not simulate heat transfer.

Model Validation

After the models are modified to an acceptable level, the Revit inbuilt energy analysis workflow can then be initiated. Iis connected to Green Building Studio so an Autodesk registration is required and then log in to Autodesk 360.

The first step is to open the energy settings. The most important basic input parameters using building elements are; building type, location, operation schedule and ground plane.

The Energy settings dialogue box is shown in Figure 10. The settings affect the result significantly. The level of complexity of the model and amount of detail available determines if other inputs will be needed. The remaining variables including Lighting Power Density, Equipment Power Density, etc. will be added automatically by the software when using Rooms category. It will be taken from the spaces data when Spaces category is used. Table 4 shows the Energy settings used with notes.

Exporting to gbXML

To be able to analyse the energy model, it needs to be exported to Green Building Studio. The file format for Green Building Studio is the gbXML file format. Green Building Studio can read any valid gbXML file, whether from Revit, Vasari or other comparable BIM tools. The gbXML file contains all of the heating and cooling information for a project according to the gbXML file structure which is based on a gbXML schema. The gbXML schema provides designers relevant information about the energy consumption characteristics of their building project. Figure 11 shows the energy models. It will export all the settings made in the Energy settings dialogue box to Green building Studio.

Autodesk Green Building Studio workflow

First step to be done is to create a new project in Green Building Studio. This is important especially in Nigeria because Green Building Studio is an American software and the default inputs are in American nomenclature (units, and currency). This must be done and necessary inputs are added before running the energy analysis because some settings cannot be changed once the runs have been initiated.

As of May 2020, the Utility rates were N 25.731 /kWh for Electricity and N 123.5/ litre for Natural gas (Statistics Nigeria).

The climate zone is added automatically based on the location. The code used in GBS is Zone 4A based on the U. S. standard for climates similar to the NIgerian climate. Table 5 shows the default values used in GBS for new projects depending on area, climatic zone and building type. This is the same values used for Revit model energy analysis.

Green Building Studio Base run

After a project is created in Green Building Studio, the next step is to upload the gbXML file from Revit to create a base run. When the run is successfully completed, the run displays in the Run List tab.

Green Building Studio also creates different alternative runs al0ngside the base run. The automat1cally created alternatives show the effect of changes to the building elements and application of Energy Conservative Measures to the energy simulation.

GBS base runs the defaults which are based on information gathered from the model imported from Revit and default values within the software. The values used in the base run are presented in Table 6 below.

Green Building Studio design alternatives

There is a design alternative feature in Green Building Studio that contains the capabilities to modify assumptions of the models that then runs a simulation which emulates the impact of the modification on energy efficiency.

To create the design alternatives, modifications were made to the following;

• HVAC equipment
• Roof construction
• Wall construction
•  Glazing type

These had the most impact on energy efficiency.

Other possible modifications are;

• Lighting efficiency
• Occupancy control
• Daylighting sensors and controls
• ·Аir tightness

In addition to the several design alternatives created by Green Building Studio, two additional alternatives were created with a combination of modifications which created the best possible simulation.

Green Building Studio work around

A standard approach for building elements and equipment types on Green Building Studio. There was need for a simulation workaround which helped with the creation of a model which is close to the expected real life situation. Selection of Equipment and U-value of the building envelope was important. Certain elements were chosen because of their U-value and not for their structural component. Table 8 shows the main workarounds used in the simulation. The HVAC equipment were chosen for their efficiency rating.

Green Building Studio makes it possible to modify one of the alternative runs that were created automatically and runs it as a separate alternative.