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BIM-BASED WORKFLOWS FOR BUILDING ENERGY MODELLING –
A VARIANT STUDY
Julia Reisinger (1), Leonard Donkor (1), Stephan Loncsek (1), Iva Kovacic (1)
(1) Department for Industrial Building and Interdisciplinary Planning, Faculty of Civil
Engineering, Vienna University of Technology, Vienna, Austria
Abstract
The AEC (Architecture, Engineering & Construction) industry counts to the most wasteful
ones, thereby urgently needing improvement for achievement of sustainable built environment.
Early design stages, where project is conceptualized, are of great importance for the future
energy performance of buildings. Tools such as the Energy Performance Certificate (EPC) - a
rating scheme to express the energy efficiency of a building during operation - are used for the
rating of building performance. Building Information Modelling (BIM - as emerging digital
design tool) coupled to EPC has the potential to serve as an early decision-making tool for
building performance optimization. However, the interoperability of the software tools is still
a challenging task, causing problems with data exchange, thus resulting in information losses.
This paper presents a comparative study of different BIM to EPC workflow-variants,
generated by applying three different BIM tools (ArchiCad, Revit and Allplan) for the same
case study; thereby comparing the variation of the obtained EPC (ArchiPhysik) results. The
process design, interoperability and the validation of the EPC results of the three variants were
evaluated. Varying requirements regarding the Level of Detail between the BIM and the
Building Energy Modelling (BEM) and the discrepancies in the EPC results were identified as
main problems. Finally, through comparison of the various exchange combinations and
identification of the potentials and deficits, suggestions for improving BIM-based workflows
for energy modelling are proposed.
Keywords: Building information modelling (BIM), Building Energy modelling (BEM),
Energy performance certificate (EPC), Interoperability, Design process
1. INTRODUCTION
The building sector is one of the biggest contributors to global environmental influences and
consumes up to 40% of all raw materials extracted from the lithosphere. Furthermore, it is
responsible for about 50% of global greenhouse gas emissions [1]. The early planning phase is
crucial for defining important sustainable variables, relevant throughout a building´s lifecycle;
these variables can minimize the environmental impact of construction projects [2]. BIM can
contribute to a more consistent decision-making process and can therefore serve as a support
for sustainable assessment of building projects in early phases [3]. The BIM model itself serves
as a joint knowledge database and offers the possibility of data transfer between multiple
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models [4]. BIM has been recognized as a useful tool for collaboration of professionals to
manage complex communication and information processes, thus in practice, there are still
difficulties with the implementation and actual performance. [5] Energy simulation programs
used in the early design stage can assist the decision-making tools, progression of optimization
methods, calculating and indicate the building energy performance [6]. The EPC certificate
provides reliable information about the building’s energy performance. It gives information
about the heating and end energy demand, CO2 emissions or the energy performance factor [7].
“…architectural design tools have poor connections to thermal and environmental analysis
software, which is exacerbated by a lack of knowledge of the data requirements of other
disciplines both upstream, and downstream [8].” In order to import, export, adapt or modify
information with BIM, a continuous cooperation between all project participants over the entire
lifecycle is necessary. In practice, the planning process participants working with BIM and
BEM still need to manual re-enter numerous data, make additions and set new parameters in
the energy performance tools in addition to the input data obtained from BIM.
The main aim of this study is examining three BIM-based workflows for energy modelling
within one case study. It investigates the quality of data exchange between the discipline models
(the 3D-Models with the EPC tool) within a Variant Study. It identifies the problems of the
BIM to BEM design process and validates the EPC results. The focus is on the modelling
process and the interoperability between the BIM models and the EPC tool and provides an
assessment for the integration of energy efficiency aspects into the overall BIM workflow.
2. LITERATURE REVIEW
Interoperability has been identified as a challenging task due to the multiple heterogeneous
applications and systems applied by diverse planning process participants. In practice, the
vision of a seamless global interoperability has not turned into reality yet [9]. Gourlis and
Kovacic [4] state that the most common information exchange format from BIM to BEM is the
open non-proprietary interface IFC (Industry Foundation Class), developed and supported by
buildingSMART [10] and the gbXML (green building extensible markup language) [11] data
format. Arayici et al. [12] developed an interoperability specification for an effective and
efficient data and process integration in BIM-practice for collaboration and information
exchange for performance based design.
Currently the most common way of sustainable planning in practice is modelling the building
with traditional CAD (computer-aided design) tools first and entering the design data into an
energy simulation tool to analyze the performance afterwards. Salguerio and Ferries [13]
pointed out that there are still limitations in the interoperability capabilities, which make
iterative interventions of the designer inevitable. The problem is that although BIM has the
capability to allow designers to compare project variants and generate important quantitative
data volumes, there is still no interface or software to organize and classify this data for enabling
an easy multiple criteria assessment. Beazley et al. [8] claim that the main problem is the
integration of different tools, the multiple data entry and the data flow between BIM models
and energy analysis tools. Pinheiro et al. [14] claim that preparing BEPS (Building Energy
Performance Simulation) models require multiple manual operations and this fact is connected
with data fragmentation and poor quality of data.
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Literature review has identified numerous problems with BIM to BEM workflows such as
data exchange and iterative manual design process loops. This paper is addressing these issues
and identifies within a Variant Study remaining bottlenecks in BIM-based workflows for EPC.
3. VARIANT STUDY
In order to evaluate the potentials of BIM for EPC, a comparative study was carried out.
Based upon a design brief of a real industrial facility (dwg. and pdf. files), BIM Models of the
same production hall were created. The building is located in Völs in Tyrol, Austria. The
building envelope characteristics are displayed in Table 1 and the facility’s basic data such as
gross floor area, volume and the energy supply in Table 2.
Table 1: Construction and u-values of the building envelope
Roof
Facade and walls
Bottom Plate
30 mm OSB plate (650 kg/m³)
260mm timber (475kg/m³) with
260mm mineral wool insulation
15 mm OSB plate
30 mm plasterboard
U-value: 0,170 W/m2K
Post and beam facade
U-value: 1,30 W/m2K
Outer wall massive
60 mm aluminum sheet
200 mm thermal insulation
200mm reinforced concrete wall
U-value: 0,187 W/m2K
Outer wall lightweight
60 mm aluminum sheet
20 mm OSB plate
260 mm timber(475kg/m³)
260 mm thermal insulation
20 mm OSB plate
U-value: 0,171 W/m
2
K
200 mm XPS
300mm reinforced
concrete
60 mm cement composite
screed
U-value: 0,186 W/m2K
Table 2: Basic data and energy characteristics of the production hall
Climate
-1,4°C – 18,6°C (outside); 17°C – 20°C (inside)
Gross floor area
10.023 m²
Volume
120.648 m³
Energy supply
District heating
Electricity supply
Electricity mix Austria 85%, 15% photovoltaics
Window ventilation
1,5 1/h (with night ventilation)
HVAC (heating, ventilation,
and air conditioning)
No mechanical ventilation; no cooling
The EPC calculations were generated using ArchiPhysik, a statistical analysis software for
building physics and energy performance assessment, authorized by the Austrian regulative.
The tool is linked to baubook [15], a building material eco-data repository, including data on
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thermal conductivity, density and specific heat capacity of construction layers, which is directly
available as default data. It does not offer IFC import/export. The software provides two
proprietary interfaces; for ArchiCad, an architectural BIM CAD software by Graphisoft and for
SketchUp, a 3D modelling software by Trimble.
For the comparative Variant Study four Variants of the same case study were generated: A
Referential Variant – EPC only; Variant A – ArchiCad to EPC; Variant B – Revit to EPC,
Variant C – Allplan to EPC.
For the referential variant, a reference EPC was created manually with ArchiPhysik; based
on the dwg. and pdf. files provided by the design brief of the industrial facility.
The BIM Model for Variant A was created with ArchiCad based on the provided
documentation. For data exchange the ArchiCad - ArchiPhysik Add-On was applied.
To obtain the model for Variant B, the architectural ArchiCad Model was imported via IFC
into Autodesk Revit. Some further re-modelling steps regarding geometry adaption were
necessary to obtain the architectural model in Revit. As Revit lacks interface to ArchiPhysik,
the model was transferred via IFC into SketchUp and for the EPC the SketchUp-ArchiPhysik
Add-On was used.
Variant C was created based on the provided documentation with Allplan, a Nemetschek
software. The geometry data was exported via Excel and transferred manually into ArchiPhysik,
as there is neither available interlink to Allplan nor an IFC. Interface.
Figure 1: BIM models: Variant A in ArchiCAD; Variant B in Revit; Variant C in Allplan
4 RESULTS
4.1 Workflows
The comparative analysis of the Referential Variant and Variant A workflows are displayed
in Figure 2. Based on the original planning documentation the data entry for the EPC was
carried out manually in the Referential Variant. In the Variant A, the software used in the
modelling process included on the BIM side ArchiCad for architecture and ArchiPhysik via the
ArchiCad Add-On for BEM. However, to transfer the BIM model to the energy calculation
software without receiving error messages, it was necessary to re-model the architectural model
to a more simplified model (BEM Model) regarding geometry and setting specific layer
combinations. With the Add-On and the simplified BIM Model, it was possible to transfer
geometry, construction and the building envelope to ArchiPhysik. In ArchiPhysik, it was
necessary to apply the project data, the construction and component list and the facility
properties for HVAC manually to create the EPC. The Add-On recognized constructions
consisting of several drawing elements as a common structure from ArchiCad and grouped
them accordingly in the ArchiPhysik component list to assign the material properties such as
Variant A
Variant B
Variant C
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thermal conductivity, density and specific heat capacity. An error occurred by importing the
post and beam façade. It was imported from ArchiCad as a wall and had to be changed to a
window in ArchiPhysik. Further manual corrections were the change or delete of room stamps
(gross floor area and volume adaption).
Figure 2: Workflows with software constellations – Reference Variant and Variant A
The workflows with software constellations in the modelling process for Variant B and C
are displayed in Figure 3. In the Variant B the ArchiCad BIM Model was transferred via IFC
to Revit, with additional geometry re-modelling necessary. The Revit BIM Model was
converted via IFC in SketchUp. By making use of the SketchUp Add-On the geometry of the
building could be imported to ArchiPhysik. As SketchUp is not a BIM software, only the
geometry could be transferred. As in Variant A, the project data, component lists and HVAC
properties had to be applied manually in ArchiPhysik. The geometry from SketchUp was
interlinked with the component list in ArchiPhysik and the building envelope was defined.
Manual Corrections in ArchiPhysik were required as the change or delete of room stamps (gross
floor area and volume adaption) and the change or reproduction of the building envelope. For
Variant C the BIM Model was created with Allplan and the geometry and building envelope
data was exported into Excel. As ArchiPhysik offers no IFC. interface, the EPC in Variant C
was carried out by applying the data manually in ArchiPhysik.
Variant A
Reference Variant
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Figure 3: Workflows with software constellations – Variant B and Variant C
4.2 Validation
The results of the quantities such as gross floor area and volume obtained from the three
different Variants based on three different BIM Models are presented in Table 3 and validated
by comparison to the Reference Variant.
Variant A shows a negligible deviation of the gross floor area and volume and Variant B and
C both differ by 0,29% from the Reference Variant. The heating and final energy demand results
of the EPC differ by 12%. Variant A has a 6% higher and Variant B a 6% lower heating demand
than the Reference Variant. The ArchiCad and Revit Model display a difference of 12,38% for
the heating demand. Variant C’s heating demand is around 3% lower than the Reference. The
final energy demand ranges from +1,95% in Variant A to -1,59% for Variant B (total difference
3,5%). The final energy demand of Variant C is 0,9% lower than the referential values.
Variant B
Variant C
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Table 3: Geometry outcomes and EPC results
REFERENCE
VARIANT A
VARIANT B
VARIANT C
Gross floor area (m²)
10.023
100%
10.019
-0,045%
10.052
+0,29%
10.052
+0,29%
Volume (m³)
120.648
100%
117.547
-2,57%
121.879
+1,02%
119.213
-1,19%
Heating energy demand
(HED) (kWh/m²a)
44,01
100%
46,66
+6,02%
41,21
-6,36%
42,64
-3,11%
End energy demand
(EED) (kWh/m²a)
194,67
100%
198,46
+1,95%
191,57
-1,59%
192,92
-0,90%
5. DISCUSSION AND CONCLUSION
A comparative study of three different BIM-based workflows for energy modelling
investigated the modelling process, the interoperability and the EPC results.
Thereby, following observations of the modelling process and interoperability were
captured: The BIM Models were created for architectural purposes. Thereby, the modelling did
not consider specific modelling requirements of energy analyzing software; resulting in
displaying too many room stamps, geometrical errors and requiring re-modelling efforts on the
building physics side. In Variant A, despite the fact that the BIM model required re-modelling
to a simplified BEM Model, the inconsistencies were kept to a minimum level as ArchiCad
has a direct Add-On to ArchiPhysik. Variant B in Revit made use of the SketchUp Add-On;
which imports only geometry to ArchiPhysik, therefore requiring revisions of gross floor area
and volume. As Variant C does not have an interface with ArchiPhysik, problems with data
transfer did not occur, but the workflow resulted in more manual, time affording work, making
the process error-prone. Although all BIM models would have contained very detailed
construction and HVAC information, these had to be applied manually in ArchiPhysik.
Regarding the validation of the EPC results, following discrepancies were identified:
Variant A displays a HED of 46,66 kWh/m²a and Variant B 41,21 kWh/m²a; the difference of
12% results from the varying gross floor area and Volume data from the BIM model.
This test implies that BIM for EPC calculation is possible with a semi-automated workflow
but still requires re-modelling and adaption, which can be time consuming, disruptive and error-
prone. In AEC practice, many different stakeholders with different mindsets are involved in a
building project, using a heterogeneous software landscape. This leads to problems in data
exchange and information losses. Even though in this study the BIM and BEM modelling was
carried out by “one hand”, problems in the design process and discrepancies in the results
occurred. The architectural model is very detailed and has a large number of room stamps and
product information, whereas the energy model needs simplified information. Due to the
oversimplification of the BIM models to BEM, they are not for architectural purposes anymore.
The comparative study identified the advantages of semi-automated BIM-based workflows
for EPC calculations as time saving in order to obtain precise geometry for the purposes of
building performance analysis. In order to enable full benefits of BIM, the focus on further
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development of open interfaces between interdisciplinary software tools is needed.
Recommendations for an improved BIM-based workflow for energy modelling are:
− Establishing a modelling standard at the very beginning of the design process;
determining the required Level of Detail.
− BIM Model shows high Level of Detail - setting own layer definitions for BEM in BIM
− Setting own BEM room stamps and hiding BIM room stamps when transferring
− Seamless modelling of components is important for exchange
In our future research, we aim to develop an optimized semi-automated BIM to EPC
workflow based on the results of this study; As well as to extend the study to BIM to LCA (life-
cycle assessment) workflows, an additional early-decision making tool for sustainability.
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