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Autozoner: An algorithm for automatic thermal zoning of buildings with unknown interior space definitions


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In this paper, we present a general algorithm to automatically convert arbitrary building massing models into multi-zone building energy models (BEM). The algorithm follows current guidelines for thermal zone discretization of BEMs when actual interior space boundaries are yet undefined. Envisioned applications are for rapid model generation during schematic building design as well as for urban massing studies. We present an argument that current recommendations for separating core from perimeter zones effectively follow a straight-skeleton subdivision. Following a step-by-step explanation of the procedure, a number of example building shapes of varying complexity are shown to demonstrate the algorithm's robustness and suitability for automated multi-zone BEM generation. Going forward, it is recommended that the algorithm is adopted by software developers to ensure more consistent thermal model production within the building simulation community.
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Autozoner: An algorithm for automatic thermal zoning of build-
ings with unknown interior space definitions
Timur Dogan1, Christoph Reinhart1, and Panagiotis Michalatos2
1 Massachusetts Institute of Technology, Cambridge, USA
2 Harvard Graduate School of Design, Cambridge, USA
In this paper we present a general algorithm to automatically convert
arbitrary building massing models into multi-zone building energy
models (BEM). The algorithm follows current guidelines for thermal
zone discretization of BEMs when actual interior space boundaries are
yet undefined. Envisioned applications are for rapid model generation
during schematic building design as well as for urban massing studies.
We present an argument that current recommendations for separating
core from perimeter zones effectively follow a straight-skeleton sub-
division. Following a step-by-step explanation of the procedure, a
number of example building shapes of varying complexity are shown
to demonstrate the algorithm’s robustness and suitability for automat-
ed multi-zone BEM generation. Going forward, it is recommended
that the algorithm is adopted by software developers to ensure more
consistent thermal model production within the building simulation
Keywords: multi-zone energy modeling, automatic thermal zoning,
urban and schematic design.
1. Introduction
For decades modelers have implemented multi-zone thermal models to simulate ener-
gy use of buildings to inform construction and design processes. It is widely acknowledged
that the earlier such simulations are being used during design, the greater their impact on im-
portant design decisions can be [Schlueter and Thesseling, 2009]. It is therefore surprising,
that there exists very limited advice on how early design variants should actually be broken
up into discrete thermal zones. According to the literature [Bobenhausen, 1994] [Hirsch,
2010][BEMBOOK, 2014], a thermal zone should roughly correlate with the spatial subdivi-
sion of a building into rooms and spaces. To simplify the simulation and also the HVAC
(Heating ventilation and air conditioning) system layout, multiple rooms may be joined to-
gether into one zone if they share similar load profiles resulting from space use and solar
gains. However, the room layout that would provide the basis for such a subdivision is usually
unknown during the schematic design stage. ASHRAE 90.1 Appendix G hence provides a
brief guideline for this case, stating that a floor should be divided into a core and perimeter
region. The perimeter is defined as the space along the facade with a depth of five meters.
Further, perimeter spaces with more than one orientation should be subdivided proportionally.
The leftover region in the center of the floor forms the core [ANSI/ASHRAE/IESNA, 2013].
The motivation for dividing a building into thermal zones is that simulation programs
treat all zones as nodes within a thermal network with perfectly mixed air volumes attached to
them. If one falsely models a larger building as a single thermal zone, a localized heat surplus
that may occur during the winter near a south-facing façade may be absorbed by a space to
the north that is underserved by solar gains. As a consequence, the predicted energy demand
according to the one-zone thermal model will be dampened compared to a multi-zone model
of the same building since loads, solar gains and thermal mass effects may cancel each other
out. This can lead to significant load under-predictions [Smith et al. 2011], revealing the rele-
vance of a consistent zoning methodology in early design studies. Consistency also ensures
that the influence of generic thermal zoning on the simulation results remains the same when
multiple geometric variants are being explored. This consistency is especially desirable if a
building energy model is used for massing studies when interior space boundaries are neither
known nor under evaluation.
Figure 1 shows a series of increasingly complex floor plans that are divided according
to Appendix G using an algorithm that will be described in the following paragraphs. Figures
1 (a) and (b) show that complying with Appendix G is unambiguous and straightforward for
simple building shapes. These two floor plans correspond to the EnergyPlus Example File
Generator models [EERE, 2013] as well as the DOE reference buildings [DOE, 2013]. How-
ever, for more complex shapes such as (c) and (d), following Appendix G zoning rules quick-
ly evolves into a tedious and somewhat ambiguous process. Figure 1 (c') shows that subdivid-
ing perimeter spaces proportionally by façade orientation can get tricky in some regions due
to the asymmetric position of the courtyard. Finding the subdivision in a floor plan such as
(d), ceases to be practical by hand because of the number of zones one would have to draw as
shown in (d').
Figure 1: Floor plans zoned according to ASHRAE 90.1 Appendix G
To reduce the BEM setup time several researchers have implemented automatic zon-
ing algorithms into existing design tools. EQuest [Hirsch, 2010] and Bentley AECOsim
[Bentley, 2013] both come with a wizard for core-perimeter subdivision for simple geometric
shapes. Autodesk Vasari [Autodesk, 2013], a schematic design tool for architects, can auto-
matically split up a building massing into perimeter and core zones. Details of the zoning al-
gorithm and its implementation have not been publicly released. Reinhart et al. [2013] intro-
duced software with similar functionality. The software is, however, limited to simple and
strictly orthogonal shapes with a minimum floor plan depth, comparable to Figures 1(a).
Given the absence of a published, general and automatic zoning methodology, this
manuscript introduces a zoning algorithm, called the Autozoner. We propose that the propor-
tional space subdivision suggested by the Appendix G zoning guidelines can be related to a
topological skeleton of a polygon and that it is therefore possible to formulate a general and
robust algorithm to obtain Appendix G compliant space partitioning automatically. We de-
scribe a proof of concept implementation that is designed to convert an arbitrarily shaped ar-
chitectural massing model, represented by a closed poly-surface, into a multi-zone thermal
model that can be used by whole building energy modeling programs such as EnergyPlus,
TRNSYS and others [Crawley et al., 2000] [Klein, 1979] [ESRU, 2005]. After a detailed de-
scription of the algorithm, we test it on different shapes with varying complexity and examine
the automatically generated zoning subdivision. Finally, we show a proof of concept of how
the Autozoner can be integrated in current workflows.
2. Methodology
The following section is divided into three parts: Following a step by step de-
scription of the Autozoner algorithm, a testing procedure is described along with a
proof of concept implementation and simulation workflow.
Automated zoning:
Input: Based on the authorsexperience in architectural practice and education, urban
and schematic design processes mainly produce three types of input geometry. During the ear-
liest stages, the buildings are modeled as a single volume (Figure 2(a)). This form of repre-
sentation helps the designer to understand basic morphologic features such as the massing and
the proportions of a design. It usually originates from a 2D drawing that is extruded. Another
very common representation involves ‘stacking’ floor-volumes. This adds a notion of scale
since it immediately allows one to read floor-to-floor heights from the model and it facilitates
the distribution of densities during the design process (Figure 2(b)). In a later stage the
stacked volumes can be further subdivided and differentiated by program/function such as
shown in Figure 2(c). Here, more complex spatial arrangements within a building can be de-
picted. Prominent examples might be split-levels or atria spanning over multiple floors. The
Autozoner algorithm supports all three input geometries. In the case of a single volume model
like shown in Figure 2(a), the input must be given as a list of closed poly-surfaces with one
volume per building. Then the algorithm begins with a floor-to-floor subdivision of the enve-
lope based on a floor height that is specified by the user. The floor-to-floor distance can be
given as array to consider varying floor heights. For the models that already have a floor- or
programmatic subdivision (Figure 2(b) and (c)), the user must be able to group the volumes
accordingly. This can be done with a tree data structure where each branch represents a user-
defined group (Figure 3). Figure 3(c) shows a data tree representation of the geometry shown
in Figure 2(c). The entire scene is grouped into buildings where each building has sub-groups
that reflect the different programs within it. The volumes representing the floors are stored
inside of these sub-groups. The organization (the structure and depth of the branches) of such
a tree is arbitrary and thus allows the user to pick any grouping schema. The algorithm stores
the given tree structure and reflects it in the outputs. Starting point for all following steps is
hence a data tree of arbitrary depth containing closed poly surfaces representing floor vol-
umes. For convenience and clarity it makes sense to convert this purely geometric data into
objects that allow us to attach further information to them and that facilitate querying the data
later. We therefore introduce two constructs called ‘unit’and face’. A unit contains a floor
volume and its position in the input data tree. It further holds a list of all surfaces of the floor
volume in form of ourfaceconstruct. Since we will produce essential steps of our zone sub-
division based on a 2D floor plan we must be able to distinguish between the faces that define
the floor volume. This can be done by simply checking their normal orientation. If the face-
normal points downwards we found a floor plate, if it points up we found a ceiling or roof.
All other normal orientations must then be walls or facades. We store this information in form
of a type label in each face. To correctly handle sloped surfaces we allow the user to specify a
maximum tilt angle to distinguish floors and ceilings from possibly tilted facades. For each
unit we then compute the 2D floor plan by collecting its faces labeled as floor plate, project-
ing them onto the XY-Plane (to eliminate slopes) and merge them with a boolean addition.
Figure 2: Typical modeling styles of massing models.
Figure 3: Data tree structure for the three possible input cases
2D Zoning: The next step is to subdivide each unit into thermal zones. We begin with
the perimeter and core zone subdivision of the 2D floor plan, as described by the previously
mentioned ASHRAE 90.1 Appendix G guideline. In the simplest case the core region can be
found by offsetting the outer edge of the floor plan. Then a search for the closest point from
the outer polygon vertices to the inner ones can yield the desired subdivision. This is shown in
Figure 4(a). For more complicated cases, the above-mentioned approach fails. Figure 4(b)
shows a convex floor plan with a core region that retreated completely from the left part of
the polygon due to a series of collapsing edges during the offset. It subdivides parts that have
good ‘core visibility’ as intended but leaves the entire left half undivided. However, with a
certain thickness of the remaining polygon-tip it might be desirable to split the tip into single
sided zones instead of a lumped region with access to multiple cardinal directions. This would
require a partition somewhere along the medial axis [Preparata, 1977] of the polygon. A me-
dial axis approximation is shown in Figure 4(c). However, the medial axis does not consist of
straight-line segments and can instead involve parabolic curves. This is not desirable since the
final output of the algorithm is a set of 3D thermal zones that should ideally consist of as few
planar surfaces as possible. Very similar to the medial axis, but involving just straight lines, is
the ‘straight skeleton’ that was first described by Aichholzer et al. [1996; Aichholzer and Au-
renhammer, 1996; Barequet et al., 2003]. The straight skeleton of a polygon, as shown in Fig-
ure 4(d), divides the polygon into one cell per outer edge and is thus fulfilling the requirement
of proportionally splitting the perimeter region by orientation. In order to obtain a core and a
valid thermal zone subdivision, a couple of simple steps have to be added. After the skeleton-
ization (Figure 5(a)), the algorithm produces the core region by performing an offset of the
outer and hole polygons (see Figure 5(b)). In step (c) the core overlap is removed from each
skeleton cell by a 2D boolean difference operation. If the thermal zones have to be strictly
convex, such as required by the ‘detailed’ radiation distribution algorithms of EnergyPlus and
TRNSYS, the resulting perimeter and core zones have to be further subdivided if they are
concave. Various polygon-partitioning techniques exist for this task and have been described
in detail [O’Rourke, 1998]. Since the resulting perimeter regions are guaranteed to be hole-
free, a simple split at each concave vertex to the closest point on the exterior edge of the pol-
ygon delivers the desired result (Figure 5(d)). The core regions, however, can consist of poly-
gons with holes. One simple example is a donut-shape floor plate with a circular core region.
Here, a triangulation and a subsequent diagonal-removal procedure is used to obtain strictly
convex zones [Hertel & Mehlhorn, 1983]. Enforcing convexity as described before can yield
perimeter regions without facade access or zones that are unrealistically small and narrow. It
is therefore important to split non-convex spaces only virtually by placing a partition that is
permeable for air and radiation. The result of the previous steps is a set of 2D regions for the
perimeter and the core of each floor plate. As underlying data structure we use a doubly con-
nected edge list (DCEL), a planar graph that allows efficient topological manipulation of our
core and perimeter cells [De Berg et al., 2000]
Figure 4:From a simple and limited to a general cell finding method based on Straight
Figure 5: Step by step visualization of the 2D zoning procedure
From 2D to 3D zones: The 2D core and perimeter cells resulting from the previous
steps have to be further processed to obtain the final 3D volumes that represent a thermal
zone. The simplest and fastest approach is to extrude the cells by the floor height. This how-
ever, is only possible, without significantly altering the building shape, if the facades of the
initial envelope are strictly vertical. In order to overcome this limitation, the algorithm can use
the floor volumes stored in each unit as a basis to cut out a zone volume with the correct fa-
çade geometry. In addition to the floor volume we need to construct a cutting volume. The
required procedure is shown in Figure 6(e) whereas Figure 6(a) to (d) depict the initial Auto-
zoner steps discussed above. In Figure 6(e) we query our DCEL data structure from the 2D
zoning step for all edges of each perimeter cell that have a congruent neighboring edge in an
adjacent cell. This yields only the interior edges of the perimeter zones. We then extract them
in form of a poly-line and extend the endpoints outwards. If the extensions intersect, we close
the polygon at the intersection point (This may happen in the case of two following convex
corners in our floor plan shape) otherwise we draw a line between the two endpoints. The ex-
tension is necessary to span beyond any outward tapering of the facade. Then we begin to ex-
trude our cutting volume to match the height of the bounding box of our currently processed
floor volume (Figure 6(f)). A boolean intersection of the floor volume and the cutting volume
follows as shown in Figure 6(g). Since the cutting volume might intersect in multiple regions,
e.g. in convex corner regions where another facade is in close proximity, we check the foot
print of each volume that is returned by the intersection and only add it to our list of zone vol-
umes if it corresponds to the perimeter cell region that we are currently processing. This
method, unfortunately does not guarantee convex volumes as a result. An example where this
method would yield a concave space is a floor volume with a facade that zig-zags up multiple
times. For our implementation we consider this an exception and rely on the user to prevent
such a case when zone convexity is a requirement.
Figure 6: Graphic representation of the main algorithmic steps
Adjacency: In urban scenes it is quite common that buildings touch each other and
not every face with horizontal orientation is a facade. Similarly, the programmatically subdi-
vided volumes (Figure 2(c)) have interior partition walls. A simple 2D example is shown in
Figure 7(a) where adjacent regions with interior walls are represented by a thick stroke. In
such a case the algorithm presented thus far would build perimeter cells at each inter-building
and program-separating partition such as shown in Figure 7(b). In 2D, a simple trick to avoid
this is to join all neighboring floor plans into a single one before the cellular subdivisions are
computed. Following the subdivision, we can use the original floor plans to crop the comput-
ed results to obtain core and perimeter cells corresponding to the original floor plans. The
cropping operation can produce perimeter cells without any exterior edge. However, by keep-
ing track of the type of cell and it's parent floor plan in our DCEL data-structure we can detect
these cells and merge them with neighboring perimeter cells (if there is no neighboring pe-
rimeter cell we merge with the core). The result is a 2D cellular subdivision as shown in Fig-
ure 7(c). The dotted lines indicate edges that have been removed during the merging.
Figure 7: Zoning for adjacent regions.
In 3D the adjacency problem is far more complex. We must be able to detect horizon-
tal adjacencies of our units in order to selectively join only neighboring floor plans. Thus, we
have to test for a potential overlap of all unit faces with all other unit faces labeled as
wall/facade. We first check if the face pair resides in the same plane and has opposite face
orientation. If both tests are positive we compute a 2D polygon intersection. If we encounter
an intersection and the two faces overlap both parent units are adjacent. Then, we loop over
each unit, join its floor plan with all floor plans in adjacent units, compute the 2D zoning and
then crop the result back as described for the simple case in Figure 7. Figure 8 visualizes the-
se steps. For the input shown in (a) the final result (c) is computed. The core volumes are
shown separately for clarity in (b). The process is highlighted for the face f1 in (d) and its par-
ent unit u1 shown in (a). The adjacent floor plans are merged into the polygon set p1 in (e).
Figure 8(e) also shows the result of the cropped zoning as shaded surfaces. Figure 8(f) shows
the resulting 3D zones.
The user can further specify a minimum overlap area and a maximum floor plan dis-
tance in order to cull small overlaps and overly distant floor plans in the adjacency test. The
importance of both parameters is highlighted in (g)(h) and (i) where we deliberately set both
parameters so that all adjacencies are found. The face f2 has a clearly visible neighbor but its
parent unit u2 is slightly higher and thus overlaps with other unit faces from higher and lower
floors. Thus, faces f3-6 are also detected as adjacent. If the geometry is tapering (f3) or chang-
ing drastically from floor to floor (f5) the geometry of such floor plans should not be added to
the floor plan union (p2) since it widens or alters the core region at the adjacent edge and
would thus produce unexpected zoning (Figure 8 (h) and (i)).
Figure 8: 3D adjacency detection and adjacency aware zoning.
Modeling of windows: After the zone geometry is modeled, we have to further ar-
ticulate the facades. In our implementation the user can specify orientation dependent win-
dow-to-wall-ratios that are then used to model the windows. As a basis to construct the win-
dow geometry we retrieve all unit faces that are outward facing facades (labeled wall/facade
and no overlaps with other faces). We then sort them by face normal orientation and then
copy and scale its geometry by the specified window-to-wall-ratio around its center of mass
to obtain the window geometry (facade faces must be convex). We do not model shades at
this point, however, others can easily override our simple function with a custom implementa-
tion of window and shading surface modeling to accommodate for more elaborate designs
such as punched hole facades, horizontal window stripes or orientation dependent shading
devices. Manual intervention is also possible after the 3D geometry is output and before the
energy model is written out.
Testing the algorithm:
In order to test the algorithm’s capability, we computed subdivisions for various floor
plan outlines of varying complexity (Figure 9). Starting with a simple rectangle (a) we con-
tinued by adding convex (c) and non-convex holes (d) and increasing the overall edge count
of the polygons (g). The time required to compute the Zones was recorded (measured on 15"
MBP Early 2011 laptop). In a next step we wanted to understand how and when the results
from our automated procedure could be different to potential manual zoning. Therefore, we
also zoned each shape in Figure 9 by hand according to how we believe a typical energy
modeler would subdivide the shapes into core and perimeter cells. There is certainly a high
degree of subjectivity associated with this approach. To quantify the geometric difference be-
tween the automatically and the manually zoned versions we compare both based on the zone
floor area Ai normalized by the zone facade length lfi given as ωi in Formula 1a. We then
computed an area weighted Root Mean Square Error AW-RMSE as given in Formula 1b and
1c where ωAi is the normalized area for the automated zoning and ωMi is the normalized area
for the manual zoning. To understand the implications of the possible geometric difference on
a thermal simulation we then compare three different annual load calculations for the shapes
in Table 1. First we use the same material and internal gain settings as given in the DOE
Commercial Reference Buildings Small Office - New Construction’ case [DOE, 2013]. For
the second case we change the materiality to a heavy weight construction without insulation
and single glazing. For the third case we add insulation and triple glazing. Results are given
as percentage error labeled E%DOE, E%LOW and E%HIGH respectively. All simulations were
simulated in the Boston climate.
Further, we monitor the runtimes of our algorithm to compute the zone subdivision of
the shapes in Figure 9 and the runtimes of Energy Plus to run an annual energy simulation for
each zoned model.
Figure 9: Test shapes of varying complexity
Formula 1 a,b,c:
a) Facade area weight ωb) Percentage error E% c) Area weighted RMSE
Proof of concept implementation and workflow integration:
The algorithm presented in the previous sections was implemented as a proof of con-
cept plug-in for McNeel’s Rhinoceros [McNeel, 2012] and Grasshopper [McNeel, 2012] us-
ing the C# programming language. McNeel’s Rhinoceros is a CAD modeling software that
can create, edit, analyze, and translate curves, surfaces, and solids. Grasshopper is a graphical
editor for generative algorithms within the Rhinoceros ecosystem. Both where primarily cho-
sen due to their popularity among architects and urban planners and the extensive support for
plug-in development provided through the RhinoCommon SDK [McNeel, 2013]. However,
the Autozoner algorithm can be implemented in any modeling environment if the following
three geometric algorithms are available:
1. Offsetting and 2D boolean addition, subtraction and intersection are used
throughout the 2D zoning procedures. Our implementation uses the publicly available
polygon-clipping library called ‘Clipper’ by Johnson [2012], which provides this func-
2. For the cellular subdivision a straight skeleton algorithm is needed. The imple-
mentation of a robust straight skeleton algorithm that can handle complex polygons is not
a trivial task. Our algorithm uses a ported and slightly modified version of an implemen-
tation provided by Petr Felkel and has been extensively described by Felkel & Obdrzalek
[1998]. An alternative by Cacciola [2004] ships with CGAL [CGAL, 2014] an extensive
computational geometry library.
3. For the 3D zoning (Figure 7 (e-h)) 3D boolean operations are required. Our im-
plementation uses the boolean operations provided by Rhinoceros. However, CGAL of-
fers similar functionality.
For a fully automated massing model to BEM conversion the model geometry pro-
duced by the Autozoner has to be paired with further non geometric simulation inputs and
zone properties such as materiality, loads, schedules and HVAC settings, in order to obtain a
fully functional energy model. Automated pairing of geometry and non-geometric simulation
properties can be done with a tool-set published by Dogan [2013]. The tool-set provides a us-
er and programming interface for energy modeling within Grasshopper featuring a thermal
model class library containing abstract definitions for zones, faces, materials, etc. that can be
translated into a simulation engine specific syntax such as the EnergyPlus [EERE, 2013] IDF
format and the TRNSYS [Klein, 1979] BUI format. This allows us to launch a simulation and
visualize the simulation results spatially in the Rhino CAD modeling viewport. Once the ge-
ometric and non-geometric data streams are set up correctly, iterating through various geo-
metric design versions and getting simulation based feedback is only a matter of a few clicks.
The proposed workflow is depicted in Figure 10.
Figure 10: Energy modeling workflow integration
3. Results
This section shows the results of our automated zoning and compares the outcome
with manual zoning. Further, algorithm runtimes are presented.
Figure 11 shows the automatically zoned test floor plans of Figure 9. Simpler shapes
such as Figure 11(a) result in a subdivision with a zone count of 5. More complex shape out-
lines yield a higher zone count. An example is Figure 10(g) with 58 zones.
While comparing the automatic subdivision shown in Figure 11 with a manually gen-
erated subdivision we encountered significant differences is some regions of the shapes. The
most prominent cases are highlighted in Figure 12. Region 1 shows a detail from shape (c) of
Figure 11. A manual subdivision would very likely connect both exterior corner points with a
straight line with α=30°. The straight skeleton approach in our algorithm strictly follows the
bisectors of the exterior edges with α=45°. This leads to a difference in normalized area for f1
to f1 of 18%. A similar case shown in Region 3 leads to a local disagreement of 43% between
f2 to f2. We also observe higher disagreement in regions where the polygon offset that in-
scribes the core region vanished and many facade edges are in close proximity (Region 2 and
4). The geometric differences for the entire shapes are far less pronounced. The computed
AW-RMSEs range form 0%-7% and are given in Table 1.
These differences are also reflected in the load simulation comparison. Table 1 lists
the differences in the results for manually and automatically zoned shapes with the labels
E%DOE, E%LOW and E%HIGH. While, the disagreement does not exceed 1.65% for cases with
facade insulation and better glazing (E%DOE, E%HIGH), the deviation can jump up to 8% for
the E%LOW scenario. Here, the difference in floor area, where we assign all internal gains, to
facade length, where mayor losses occur, has a much bigger impact on the simulation out-
come. Due to the different orientations of zones it is also possible that the deviation levels
out, as it happened for shape d) were the geometric deviation is at 4% and the simulation
based deviation for all three scenarios is near zero. Table 1 also shows the measured runtimes
of our automated zoning algorithm and each EnergyPlus simulation. For small models the ge-
ometry is computed within milliseconds. Larger models with e.g. 184 zones require 15.5 se-
conds to compute. EnergyPlus simulation time ranges from 20 seconds to 5 minutes for the
largest model.
Figure 11: Automatic zoning results
Figure 12: Complex massing: Input, floor subdivision, inner subdivision and facade.
Autozoning [s]
E+ runtime [s]
Table 1: Algorithm runtime and difference compared to manual zoning
4. Discussion
The foregoing section demonstrated that the Autozoner algorithm provides a fast, ro-
bust and unambiguous method for automatic zoning of a building according to ASHRAE 90.1
Appendix G. The algorithm is based on standard computational geometry procedures such as
offsetting, straight skeleton and 2D/3D boolean operations and can thus easily be implement-
ed in a variety of energy modeling environments. Arguments for doing so are presented next
followed by the algorithm’s limitations as well as some thoughts about the usefulness of the
Appendix G guidelines themselves.
As mentioned before, the two main arguments for using the algorithm are speed and
reproducibility. If professional organizations such as the American Institute of Architecture
and ASHRAE along with green building rating systems such as LEED [UGBC, 2008], DGNB
[UGBC, 2014] BRREAM [BRREAM, 2004] want to promote early design phase rapid BEM
generation, then having an unambiguous procedure in place that does not provide a burden on
the design team is useful and facilitates compliance procedures.
It has further been shown that, comparing manually and automatically zoned BEMs
can yield differences in simulated EUI of up to 8%. Here, it is not the point to claim that one
or the other solution is more correct, both are only preliminary assumptions and do not repre-
sent actual floor plan subdivisions. It is more important to note that in a comparative study
with multiple variants, a deviation of 8% in the results solely due to inconsistency in the sub-
division, can dilute the analysis and thus complicate making the right design decisions. Thus,
it is desirable to employ a zoning method that can compute unvarying and reproducible zone
subdivisions for any shape.
It is further worth pointing out that having an algorithm that can reliably perform an
otherwise time consuming and inconsistent process has the potential to significantly increase
the adoption rate and quality of early stage BEMs. According to a recent survey by Samuel-
son et al. [2012], 30% of the participating AEC firms (Architecture, Engineering, and Con-
struction) who employ in-house energy modelers reported that simulation based feedback has
only ‘rarely’ or ‘occasionally’ an impact on design decisions, a fact that has been traced back
to time and resource intensive workflows that prohibit the early use of BPS tools [De Wilde,
1999][Mahdavi et al., 2003][Ianni et al., 2013]. Apart from individual building design, the
Autozoner can also be applied to urban projects that involve dozens of buildings that practi-
cally could not be modeled in a reasonable time frame [Besserud & Hussey, 2011][Dogan &
Reinhart, 2013][Dogan et al., 2012]. For very large urban models with hundreds of buildings
and thousands of zones the model setup may still require only seconds or minutes. However,
the simulation time and the amount of data may impose limits. The algorithm that we de-
scribed has not been optimized for efficiency in that regard. Many of the zones that the algo-
rithm creates could be merged since they have similar orientations (ASHRAE 90.1 recom-
mends merging if the difference in orientation is less than 45°) and many floors could be rep-
resented by multipliers to simplify and thus speed up the simulations. Despite all the previ-
ously mentioned improvements the presented algorithm has limitations in applicability that
modelers should be aware of:
To this point, a question that remains open is how the boundary conditions between
touching zones should be modeled by an algorithm such as the Autozoner. ASHRAE 90.1
Appendix G does not provide any binding guidance regarding this question. The DOE Refer-
ence Buildings as well as the Energy Plus Example Files model the zone subdivision with an
opaque surface without airflow between zones. What are the consequences of this decision?
Figure 13 compares annual heating and cooling loads for the same zoning of a square office
building but various heat and mass transfer effects at the interior zone boundaries. Beginning
with an adiabatic space boundary, conduction, solar radiation and different levels of air mix-
ing are added step by step. As one would expect, adding these different modes of inter-zone
heat flows successively, the ASHRAE solution is brought closer to the single zone solution.
Annual heating and cooling loads vary by up to 41% and 10%, respectively, compared to the
building modeled as a single zone. This suggests that an energy modeler and the design team
should be conscious of the likely building layout even during the earliest massing studies us-
ing the boundary conditions for the individual or open office scenarios form Figure 13 as they
may apply.
Ultimately, this observation leads to the larger questions which is how meaningful the
conceptual division of a floor plan into core and perimeter spaces is at any point in the design
process. An experienced architect working with a massing model necessarily has (or should
have) an intuition how the interior of this model could be divided. This knowledge should
hence be part of the thermal zoning considerations as early as possible. As an example, Figure
14 shows the same building as from Figure 13 divided into a conditioned workspace plus an
unconditioned circulation area (in gray). The different layouts change the annual conditioning
loads by up to 21%. Going forward, this suggests that it might be useful to go beyond Appen-
dix G and consider thermal zoning in a more architectural sense. In the meantime, it seems
that a version of the Autozoner algorithm along with an input parameter for the interior
boundary conditions that toggles between individual rooms or open plan provides a meaning-
ful step towards consistent BEM during schematic design.
Figure 13: Comparison of a perimeter and core subdivision with different inter-zonal
heat and mass transfer scenarios versus a single zone simulation and their correlation
with architectural floor plan typologies.
Figure 14: Comparison of different positions of an unheated circulation space
5. Conclusion
A general algorithm for creating multi-zone energy models for complex building
shapes with unknown interior space subdivision is introduced. The algorithm is compliant
with ASHRAE 90.1 Appendix G thermal zoning requirements and can easily be implemented
in any thermal modeling environment to alleviate time-consuming thermal model preparation
and to avoid modeling inconsistencies between different design variants. In practice the algo-
rithm should be combined with meaningful assumptions regarding the heat transfer through
interior boundaries in order to differentiate between single and open plan scenarios. It is im-
portant to note, that the algorithm should only be used during early massing studies when in-
terior space divisions are still undefined.
6. Acknowledgements
We would like to thank Transsolar Energietechnik GmbH Munich for productive discussions
and partial funding of the research project.
7. References
Aichholzer, O., Aurenhammer, F., Alberts, D., & Gärtner, B. (1996). A novel type of skeleton
for polygons (pp. 752-761). Springer Berlin Heidelberg.
Aichholzer, O., & Aurenhammer, F. (1996). Straight skeletons for general polygonal figures
in the plane (pp. 117-126). Springer Berlin Heidelberg.
ANSI/ASHRAE/IESNA Standard 90.1-2013 Appendix G
Autodesk. (2013). Autodesk Vasari. Retrieved November 1, 2013, from
Barequet, G., Goodrich, M. T., Levi-Steiner, A., & Steiner, D. (2003, January). Straight-
skeleton based contour interpolation. In Proceedings of the fourteenth annual ACM-
SIAM symposium on Discrete algorithms (pp. 119-127). Society for Industrial and
Applied Mathematics.
BEMBOOK (2013). Thermal Zoning Determination, Retrieved Jan 20 2014, from
Bentley (2013) AECOsim, Retrieved November 1, 2013,
Besserud, K., & Hussey, T. (2011). Urban design, urban simulation, and the need for compu-
tational tools. IBM Journal of Research and Development, 55(1.2), 2-1.
Bobenhausen, W. (1994). Simplified design of HVAC systems. New York: Wiley.
BRREAM 2004. Building research establishment environmental assessment method. Re-
trieved April 21, 2014,
Cacciola, F. (2004). A CGAL implementation of the Straight Skeleton of a Simple 2D Poly-
gon with Holes. In 2nd CGAL User Workshop, Polytechnic Univ., Brooklyn, New
York, USA.
CGAL (2014), Computational Geometry Algorithms Library, Retrieved April 21, 2014,
Crawley, D. B., Lawrie, L. K., Pedersen, C. O., & Winkelmann, F. C. (2000). Energy plus:
energy simulation program. ASHRAE journal, 42(4), 49-56.
De Berg, M., Van Kreveld, M., Overmars, M., & Schwarzkopf, O. C. (2000). Computational
geometry (pp. 29-33). Springer Berlin Heidelberg.
De Wilde, P., Augenbroe, G., & Van Der Voorden, M. (1999, September). Invocation of
building simulation tools in building design practice. In Proceedings of IBPSA ‘99
Buildings Simulation Conference (pp. 1211-1218).
DGNB, (2014). DGNB Zertifizierungssystem. Retrieved April 21, 2014, http://www.dgnb-
DOE. (2013). U.S. Department of Energy Commercial Reference Building Models. Retrieved
November 1, 2013, from
Dogan, T. (2013). Energy Modeling Tools for Grasshopper. Retrieved November 1 2013,
Dogan, T., Reinhart, C. (2013). Automated conversion of architectural massing models into
thermal ‘shoebox’models. Proceedings of BS2013.
Dogan, T., Reinhart, C., & Michalatos, P. (2012). Urban Daylight Simulation Calculating the
Daylit Area of Urban Designs. SimBuild 2012.
EERE. (2013). EnergyPlus Energy Simulation Software. EERE U.S. Department of Energy.
Retrieved November 1, 2013, from
EERE. (2013). EnergyPlus Example File Generator. Retrieved November 1, 2013, from
ESRU, ESP-r,, 2005.
Felkel, P., & Obdrzalek, S. (1998). Straight skeleton implementation. In Proceedings of
spring conference on computer graphics.
Hirsch, J. (2010). eQuest Introductory Tutorial, version 3.64.
Ianni, M., & de León, M. S. (2013). Applying Energy Performance-Based Design in Early
Design Stages.
Johnson, A. (2012). Clipper 6.0 -an open source freeware polygon clipping library.
Klein, S. A.(1979). TRNSYS, a transient system simulation program. Solar Energy Laborato-
ry, University of Wisconsin—Madison.
Mahdavi, A., Feurer, S., Redlein, A., & Suter, G. (2003, August). An inquiry into the building
performance simulation tools usage by architects in Austria. In Eighth International
IBPSA Conference.
McNeel, R. (2012). Grasshopper - Generative Modeling with Rhino, McNeel North America,
Seattle, USA. (
McNeel, R. (2012). Rhinoceros - NURBS Modeling for Windows (version 5.0), McNeel
North America, Seattle, WA, USA. (
McNeel, R. (2013). RhinoCommon Plug-in SDK. Retrieved November 1, 2013, from
Morbitzer, C., Strachan, P. A., Webster, J., Spires, B., & Cafferty, D. (2001). Integration of
building simulation into the design process of an architectural practice. Chicago
Preparata, F. P. (1977). The medial axis of a simple polygon. In Mathematical Foundations of
Computer Science 1977 (pp. 443-450). Springer Berlin Heidelberg.
Reinhart, C. F., Dogan, T., Jakubiec, J. A., Rakha, T., & Sang, A. (2013). UMI-An Urban
Simulation Environment for Building Energy Use, Daylighting and Walkability. In
Proceedings of BS2013
Samuelson, H. W., Lantz, A., & Reinhart, C. F. (2012). Non-technical barriers to energy
model sharing and reuse. Building and Environment, 54, 71-76.
Schlueter, A., & Thesseling, F. (2009). Building information model based energy/exergy per-
formance assessment in early design stages. Automation in Construction, 18(2), 153-
Smith, L., Bernhardt, K., & Jezyk, M. (2011). Automated energy model creation for concep-
tual design. In Proceedings of the 2011 Symposium on Simulation for Architecture
and Urban Design (pp. 13-20). Society for Computer Simulation International.
... Interoperability and data exchange problems between the different tools used in the design and analysis of sustainable buildings constitute the first primary limitation type (Attia et al., 2013;Jones et al., 2013;Negendahl, 2015;Choi and Park, 2016;Dogan, Reinhart and Michalatos, 2016). Fundamental differences in modeling capabilities between design, BES, and daylight simulation programs create a tool "gap" that frustrates architects in the design and optimization of energyefficient and comfortable buildings. ...
... Recent developments attempt to address to the need to translate CAD and BIM building models to BEM as a way to shorten the geometric modeling gap between design and building energy analysis tools. Several researchers developed methods to automatically or semi-automatically generate valid BEM from digital building models with different degrees of detail that range from conceptual building masses to fully detailed architectural models (Jones et al., 2013;Georgescu and Mezić, 2015;Kensek, 2015;Kim et al., 2015;Dogan, Reinhart and Michalatos, 2016;Jeong and Son, 2016;Lilis, Giannakis and Rovas, 2017). However, the literature on automated BEM inference and simplification focuses primarily on the thermal zoning of massing models according to ASHRAE guidelines (ASHRAE, 2013), such as in Dogan et al. (2016), Reinhart (2013, 2017), and Jones et al. (2013), or in sensitivity analysis of simple box-shaped buildings composed by planar surfaces (Amitrano et al., 2014;Picco and Marengo, 2015). ...
... Several researchers developed methods to automatically or semi-automatically generate valid BEM from digital building models with different degrees of detail that range from conceptual building masses to fully detailed architectural models (Jones et al., 2013;Georgescu and Mezić, 2015;Kensek, 2015;Kim et al., 2015;Dogan, Reinhart and Michalatos, 2016;Jeong and Son, 2016;Lilis, Giannakis and Rovas, 2017). However, the literature on automated BEM inference and simplification focuses primarily on the thermal zoning of massing models according to ASHRAE guidelines (ASHRAE, 2013), such as in Dogan et al. (2016), Reinhart (2013, 2017), and Jones et al. (2013), or in sensitivity analysis of simple box-shaped buildings composed by planar surfaces (Amitrano et al., 2014;Picco and Marengo, 2015). Jones et al. (2013), presents a conversion methodology of CAD building models based on extrusions of planar polygons. ...
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The resources involved in the construction and operation of buildings represent nearly 40% of the global emissions of greenhouse gases (GHG), making the building sector one of the primary contributors to global warming. This reality has led to the creation of many prescriptive regulatory and voluntary programs that aim to mitigate the environmental impact of the building sector while ensuring high standards for Indoor Environmental Quality (IEQ), particularly those regarding the thermal and visual comfort of building occupants. Thus, the design of high-performance buildings, i.e., resource- and energy-efficient buildings that yield high levels of IEQ, is a pressing need. This scenario pushes architects to simulate their projects’ environmental performance to better support design tasks in a process referred to as performance-based design. This dissertation studies the integration of daylighting and Building Energy Simulation (BES) tools into performance-based design supported by computational design (CD) methods, particularly parametric design and Building Performance Optimization (BPO). The assumption is that the early integration of parametric, BES, and daylighting simulation tools can be highly effective in the design, analysis, and optimization of high-performance buildings. However, the research argues that the current daylighting and Building Energy Simulation (BES) tools pose critical challenges to that desirable integration, thus hindering the deployment of efficient exploratory design methods such as Parametric Design and Analysis (PDA) and BPO. These challenges arise from limitations regarding (i) tool interoperability, (ii) computationally expensive simulation processes, and (iii) problem and performance goal definition in BPO. The primary objective of the dissertation is to improve the use of daylighting and BES tools in PDA and BPO. To that end, the research proposes and validates five modeling strategies that directly tackle the limitations mentioned above. The strategies are the following: (i) Strategy A: Automatically generate valid building geometry for BES; (ii) Strategy B: Automatically simplify building geometry for BES; (iii) Strategy C: Abstract Complex Fenestration Systems (CFS) for BES; (iv) Strategy D: Assess glare potential of indoor spaces using a time and spatial sampling technique; and (v) Strategy E: Painting with Light - a novel method for spatially specifying daylight goals in BPO. The research work shows that the strategies address the research problem and current limitations by (i) improving the interoperability between design and BES and daylighting simulation tools (Strategies A, B, and C); (ii) producing quick and adequate feedback on the daylight, thermal, and energy behavior of buildings (Strategies B, C, and D); and (iii) facilitating the spatial definition of performance goals in daylighting BPO workflows (Strategy E). These three important merits of the proposed strategies effectively contribute to improving the efficiency of using daylight and BES tools in the design, analysis, and optimization of high-performance buildings. Finally, the dissertation discusses the merits and limitations of each strategy, provides useful guidelines and recommendations for their use in building design, and suggests future directions for further research.
... However, the selection of a zoning strategy remains an essential aspect of energy modelling at the early stages [168]. There have been a variety of approaches to automatically generate zones such as one-zone-per-floor, perimeter depth zoning, cardinal direction zoning, core-and-perimeter-zoning [169][170][171][172]. Among these approaches, ASHRAE's core-and-perimeter-zones approach yields the most reliable results and used widely at the early stages [165,173,174]. ...
... In this approach, perimeter zones are created by offsetting each edge by a distance and a core zone in the centre. The approach represents a stateof-the-art approach as it provides the most realistic estimate of energy at the early stages [165,169,173,192]. ...
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Buildings represent one-third of energy consumption that concerns the global community. During the early design stages, designers have an opportunity to improve the energy performance of buildings efficiently. However, they need information to assess the effect of their design decisions on the energy performance. The doctoral research developed methods to support energy-related design decisions at the early stages using machine learning (ML) and building information modelling (BIM) by providing relevant information. The flexible representation of design at the early stages is a prime challenge to assess energy performance and the effect of design decisions on it. This challenge is addressed using a probabilistic approach that requires simulating several hundred models. Dynamic energy simulation tools are computationally expensive, prompting the development of quick metamodels using ML approaches. Further, a BIM integrated approach is developed to reuse the existing information and reduce the modelling efforts. The building design progresses by developing information through several levels of development (LOD). While focussing on energy efficiency, it is apt to reduce uncertainty in energy predictions through these LODs. Thus, the research identified design information in the order of its potential to cause uncertainty in the energy predictions. It has been found that geometrical parameters cause the maximum uncertainty in the energy predictions, followed by technical specifications such as U-values and window parameters such as window-to-wall ratio. These results form the basis for design information required in a multi-LOD context. The research further developed metamodels using ML for quick energy predictions, primarily, focussing on evolving building geometry, making it difficult to develop an ML model for early stage energy predictions. It extended the component based ML (CBML) approach and proposed using a convolutional neural network (CNN) approach to develop ML models. An approach of collecting diverse samples is developed to train CBML components and improve their generalisation. A CNN approach is used to capture the building geometry information from an image instead of simple parameters such as relative compactness. The developed model has improved prediction accuracy as the proposed CNN model architecture allows learning the interactions between the building’s geometry and its energy performance. There exists a prediction gap between ML predictions and dynamic simulations. A small prediction gap is allowed if it does not affect the comparative assessment of designs under the uncertain conditions of early design stages. Through a test case, the research demonstrated that the developed ML models are suitable to perform a comparative assessment of designs quickly. The aptness of ML models to provide quick comparative assessment of designs allows developing a BIM integrated solution and glean relevant information for supporting design interventions. In the final phase, a cloud based service was developed: It implements the developed ML models in a graphical user interface for practical applications. The tool provides information for design space exploration, energy analysis of options and their comparative assessment, sensitivity analysis, and tracks progress. Contrary to generic engineering knowledge, the developed tool extracts context-specific energy performance information. This information is more relevant as it captures the effect of changing design scenario on the energy-efficiency. The thesis facilitates the performance-oriented building design by providing relevant information using ML and BIM. The developed methods focus on informed design making from an energy perspective that can be extended to other performance evaluations. Besides developing ML models for energy prediction, this research integrates these models with BIM to extract useful information for supporting design interventions. The developed holistic approach provides a quick context-specific assessment of design interventions that enables the designer to make informed decisions.
... Extensive academic research has utilized physics-based building energy models (BEM) to understand how building design decisions influence cooling energy demand at both the building [19,20] and urban [21,22] scales. It is well established in academic literature that building design and the urban form heavily impact thermal comfort, well-being, and economic productivity [10,23,24]. ...
... While initially designed for building performance estimation on a single building scale, the building energy modeling research domain has since evolved to focus on larger models that assess larger neighborhoods or urban areas. While the magnitude of data inputs required to model hundreds, if not thousands, of buildings across a city often requires the urban simulation to be simplified through resistance-capacitance (RC) models [67] or representative archetypes [21,68], these urban building energy models (UBEMs) can provide detailed depictions of building energy and thermal performance on a larger geographic scale. For example, it is well established that urban building energy performance is significantly influenced by a building's urban contextfactors that may include surrounding buildings [69], microclimatic effects [70], or the broader urban form [71,72]. UBEMs, especially when combined with urban climate models such as urban canopy models or computational fluid dynamics, have been able to predict outdoor thermal comfort and assess the effects of urban heat island and radiation exchange on building energy demand [73,74]. ...
Cities are critical to meeting our sustainable energy goals. Informal settlement redevelopment programs represent an opportunity to improve living conditions and curb increasing demand for active cooling. We introduce an energy modeling framework for informal settlements to investigate how building design decisions influence the onset of heat stress and energy-intensive cooling demand. We show that occupants of tropically-located informal settlements are most vulnerable to prolonged heat stress year-round. Up to 98% of annual heat stress exposure can be mitigated by improving the building envelope. We find a universal solution (cool roofs) that reduces up to 91% of annual heat stress exposure. Finally, we show how proposed redevelopment building schemes could worsen thermal conditions of dwellers and further increase urban energy demand. Our results underscore how building design affects human well-being and highlight potential near-term and long-term pathways for reducing energy-intensive cooling demand for 800+ million informal settlement dwellers worldwide.
... In this approach, multi-use buildings are divided into up to three vertical zones where the ground, middle, or upper floors can be represented by different thermal zones. Furthermore, Wang et al. [21] and Cerezo Davila et al. [6] applied one thermal zone per each floor of the buildings while Chen et al. [17,22] and Dogan et al. [23] proposed novel auto-zoning algorithms that set multiple perimeter zones and one core zone to each floor of the buildings as specified by ASHRAE 90.1 Appendix G [15]. ...
... Moreover, a survey of the existing UBEMs shows that in most of the models, the choice of zoning configuration is done arbitrarily. Except for the study done by Chen and Hong [22] and Dogan et al. [23], there is no analytical justification or proper motivation behind the chosen zoning configurations in existing UBEMs. Thus, to decide on the proper thermal zoning configuration, it is necessary to analyze the impact of the number of thermal zones not only on the accuracy of the simulation results but also on the reliability of the modeling and simulation procedure. ...
Simplification of building energy models is one of the most common approaches for efficiently estimating the energy performance of buildings over a whole city. In city-scale models, the abstraction of a building into an information model and the division of the model into representative thermal zones cannot be building-specific but must be generic and applicable to many buildings. Considering the limited research on the performance of such methods, in this study, a comprehensive evaluation of the most relevant assumptions on zoning configurations and levels of detail is conducted in three building energy simulation tools IDA ICE, TRNSYS, and EnergyPlus. The findings from the evaluation of zoning configuration on building level and its comparison with the measured energy performance of buildings suggest that a single-zone model of a residential building gives a very similar result to a multi-zone model with one core zone and perimeter zones for every floor of the building. For the single-zone model, IDA ICE overestimates and EnergyPlus underestimates the energy demand compared to the more complex models by approximately the same amount, but EnergyPlus is preferred due to the shorter simulation time. It is also proven that higher levels of detail in building models can increase the accuracy of the results by approximately 6% annually. When extending the scope of the study from building level to district level analysis where a somewhat lesser degree of accuracy can be allowed on the individual building, the simplified models give acceptable results.
... This happens due to over-discretization of zones, where e.g. the irradiated heat of high solar gains is not correctly passed to nearby zones. (Dogan, Reinhart, and Michalatos 2016;Smith, Bernhardt, and Jezyk 2011) This paper focuses on two questions: first, in which cases using the ROM approach is suitable for simulating larger non-residential buildings, and second, how different zoning strategies affect the accuracy and computational effort. ...
... Additional to research regarding how to zone buildings and how this affects the simulation results, multiple studies were performed regarding automatic zoning. E.g. Dogan, Reinhart, and Michalatos (2016) as well as Smith, Bernhardt, and Jezyk (2011) presented automatic approaches for zoning for complex building shapes based on algorithms with in-depth analysis. How- ever, both approaches are valid only for the early concept phase of the building, where interior space divisions are still undefined. ...
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Non-residential buildings are accountable for 11 % of global energy-related CO2 emissions (United Nations Environment Programme 2018). To increase the performance in this sector, Building Energy Performance Simulation (BEPS) is one feasible approach. Therefore, there is need for reliable and fast simulation models. One feasible approach are so called Reduced Order Models (ROMs). Thus in this paper, a comparison between the results of the established BEPS tool EnergyPlus and a ROM in Model-ica with a reduced number of resistances and capacities is applied at the use case of a non-residential building. A self-developed toolchain was used to create equal models for ROM and EnergyPlus based on the same Building Information Modeling (BIM) model. The comparison shows that the reduced model deviates by ±10 % in annual heating and cooling. To increase accuracy and decrease computational effort the zoning strategy of non-residential buildings is investigated. The investigation shows that using a suitable zoning approach can reduce the computational effort by up to 97 %.
... In the literature, the concept of thermal zoning has been considered for building energy performance assessment across both design and operation phases. Dogan et al. [5] presented an algorithm for automatically generating multizone building energy models in spaces with undefined boundaries. O'Brien et al. [6] explored particular effects of thermal zoning on heat gain and energy consumption of solar buildings through a sensitivity analysis. ...
Conference Paper
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This paper examines the impact of building zoning on demand flexibility potentials. The building thermal dynamic response is modeled by using the state-space representation method. The comfort preference of the occupants is defined by statistical analysis of set-point temperature patterns. The created models are used to study energy flexibility through a coordinated energy management problem by means of the Stackelberg game strategy. The zoning influence on flexibility potentials is analyzed by applying this procedure to a set of houses in Quebec based on two specific scenarios accounting for single and multi-zones. The flexibility potential is evaluated by comparing overall demand peak reduction and heating consumption under each scenario signifying passive heating storage capacity of buildings. The single-zone scenario performs better at harvesting energy flexibility through reducing the peak load by 33%. The results demonstrate that the building zoning definition can lead to conditions under which the demand flexibility can change.
... This allows to auto-generate required basement and ground coupling model geometry for each BEM individually. Buildings of sufficient size (edge length > 10 m) were automatically and procedurally segmented into multiple zones per floor following the ASHRAE 90.1 Appendix G guideline (ASHRAE, 2013) using the Autozoner algorithm (Dogan et al., 2016). Notional windows were likewise procedurally generated on each exterior wall face, scaled based on percentage of wall coverage collected from studies conducted by the authors on representative BAs. ...
As global and local actors seek to address climate concerns, municipalities, regions, and countries are developing policies for the built environment to reach carbon neutrality. In most cases, however, current policies target new construction and operational carbon emissions only, thus omitting the significant carbon emission saving potential resulting from the reactivation of embodied carbon in existing buildings. This article describes the development of a high-resolution combined building stock model (BSM) and building energy model (BEM) on both building and urban scale using all residential buildings of Ithaca, NY, USA as a case study. The model offers a holistic, detailed and local perspective on operational and embodied carbon emissions, associated saving potentials at both the building and urban scale, and the linkages, trade-offs and synergies between buildings and energy use as a basis for decision-making. A circular economy (CE) in construction posited on the reuse and recycling of existing building materials, necessitates a detailed material inventory of the current building stock. However, the scale and nature of this endeavor preclude traditional survey methods. The modeling process described in this article instead engages a bottom-up data aggregation and analysis approach that combines detailed construction archetypes (CAs) and publicly available, higher-level municipal geospatial data with building metadata defining occupancy and systems to create an autogenerated, detailed 3D geometry. The resulting BSM and BEM can simulate both embodied carbon content and operational carbon emissions of individual buildings within a municipal study with minimal required input data and a feasible computational effort. This provides modelers with a new spatial and geometric fidelity to simulate holistic renewal efforts, and inform carbon neutrality policies and incentives towards the decarbonization of the built environment.
... Division en zonage detailed pour un bâtiment convexe avec et sans zone centrale Pour les bâtiments dont l'empreinte au sol est concave, cette division à partir d'une zone centrale peut poser des problèmes de zones étroites ou à géométrie complexe, comme présenté par Dogan et al.[53]. Dans la méthode de l'AutoZoner l'utilisation d'un squelette de polygone a été utilisé afin de préserver la cohérence géométrique des bâtiments. ...
La recherche doit répondre aux enjeux énergétiques globaux afin de réduire les consommations énergétiques et les émissions de gaz à effet de serre pour limiter l’impact du changement climatique. Cette recherche s’appuie notamment sur le développement de nouveaux outils de simulation urbaine, appelés UBEM (Urban Building Energy Modelling), afin d’aider les collectivités, les bureaux d’études et autres acteurs de la transition énergétique à réduire les consommations d’énergie du secteur du bâtiment. Ces UBEM sont composés de modèles devant intégrer les problématiques de manque de données de paramétrage et de coût de calcul liés à la simulation urbaine. De nombreux modèles existent avec des niveaux de détail différents, afin de simuler l’ensemble des phénomènes physiques liés au bâti, aux systèmes énergétiques ou encore aux sollicitations extérieures, en respectant ces contraintes. De par cette grande diversité de modèles à disposition de l’utilisateur, ce dernier peut se retrouver dans des situations où la sélection des modèles les plus adaptés à son étude peut s’avérer fastidieuse et complexe. Ainsi, une méthodologie permettant de réaliser une simulation dite « parcimonieuse » est proposée dans cette thèse. La parcimonie de simulation a pour objectif de trouver le bon niveau de modélisation en déterminant le point d’équilibre entre : le nombre de paramètres d’entrée et leurs incertitudes, le niveau de détail du modèle avec ses hypothèses simplificatrices, la précision obtenue vis-à-vis d’une référence et le temps de simulation, le tout pour une sortie et un contexte donnés. Pour cela, des KGI (Key Guidance Indicators), créés à partir des caractéristiques liées à l’échelle quartier, sont utilisés afin de déterminer des valeurs seuils permettant de choisir quel niveau de modélisation utiliser suivant le quartier. Cette contribution permet de pouvoir conseiller et guider divers utilisateurs et modélisateurs, dans leurs modélisations urbaines, afin de proposer une simulation non pas la plus précise, mais la plus adaptée au cas d’étude. Cette thèse propose ainsi une méthodologie pour le développement d’outils d’aide à la décision plus parcimonieux et donc plus efficaces, permettant passer de la logique du toujours plus à juste ce qu’il faut.
... In the conceptual design stage, the room division of a building has not been determined. The one-zone per floor zoning method requires less modeling and computational time than the widely used core and perimeter zoning method (ASHRAE, 2016;Dogan et al., 2016;Shin and Haberl, 2019). In some cases, zone multipliers can be used for buildings with many identical zones (U.S. ...
It is generally acknowledged that the decisions made in the early design stage of a building critically affect its performance. To promote sustainability, building simulations are widely used in the early design stage to calculate the building performance and optimize the design. However, the high computational burden limits the application of building simulations in daily design work. This paper proposes a hybrid metamodel-based method to facilitate the rapid assessment of a building's energy demand in the early design stage. This method (1) decomposes a complex building mass into several zones as different metamodel variants and characterizes the total energy demand by summing up the energy demands of all the metamodels; (2) uses the received solar radiation values as metamodel input parameters to describe the surrounding shading and reflection effects; (3) employs GPU acceleration technology to accelerate the radiation calculation and reduce the simulation time; and (4) implements a machine learning (ML) algorithm screening framework to enhance the accuracy of the metamodels. Case studies were conducted to demonstrate the proposed method. The results showed that this method could predict the energy demands of buildings in high-density urban environments with acceptable accuracy in a short period of time, which would allow designers to obtain feedback on the building energy demand immediately in the early design stage and opens up more possibilities for achieving low-energy buildings.
Historically, humanity has considered the control of cooling and heating an aspect related to both comfort and survival, currently being it evaluated not as a luxury, but as a fact of modern existence. In the global context, at the beginning of the 20th century, the efforts to develop cooling techniques with the aim of maintaining control climate at indoor spaces of the office and residential buildings, were evident. This initial direction that is taken to achieve comfort levels in terms of cooling and heating generates what is now called heating, ventilation, and air–conditioning (HVAC). This paper provides a general description of the zoning methods that support the structural description of the thermal zones of a building, required for the design, control and maintenance of HVAC systems. The main objective of this study is to systematically review the current research on zoning HVAC residential systems. The article conclusion is that an intelligent zoning strategy using a criterion associated with user behavior, occupancy patterns and its corresponding schedules, will promote the development of efficient optimization processes for energy consumption and thermal comfort if they are considered as a structural part of the HVAC system. Finally, in terms of modeling the advice is to start with a white box model, phenomenological, but to follow-up or support it with data-based models.
Conference Paper
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Recent advances in the field of building performance simulation (BPS) have not only expanded the quantity of available tools but also widened their audience from the engineering professions to architects and planners. As the user pool expands and team efforts become more common, issues of standardization and exchange of simulation data have become critical for modelers. Although significant efforts have been made in the development of formats for the exchange of geometry and weather data inputs for simulation, or full building energy models (gbXML, IFC), limited attention has been paid to the documentation and exchange of model inputs for building properties, such as material definitions or load profiles. The lack of a widely accepted file format for their comprehensive management becomes especially problematic in the case of rapid energy model generation during early schematic or urban design explorations, because it reduces the time available for design iterations and increases the risk of errors. Supported by a survey of 150 BPS professionals about their current energy modeling workflows, this paper outlines a vision for a new energy modeling data framework based on the use of building properties (BP) templates as a standard input format through the design stages of a project. A proof of concept implementation of a BP template file format and a BP template editor tool are presented along with an example design simulation exercise.
Conference Paper
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This paper describes the development of a new tool that allows designers to simulate and evaluate the daylight potential of urban master plan proposals. The tool is a plug-in for the Rhinoceros3D CAD modeler and follows a two-step workflow. During the initial step, hourly solar radiation levels on all facades within an urban scene are simulated based on Radiance/Daysim. During the second step, exterior radiation levels are converted into hourly interior illuminance distributions using a generalized impulse response. Climate based daylighting metrics, such as daylight autonomy, are also computed. The results yielded by the new method are carefully compared to regular and substantially more time-consuming Daysim simulations. This comparison shows that the overall daylit area in the investigated master plan matches Daysim predictions within 10%. Given its implementation into the Rhinoceros3D environment, as well as the almost instant simulation feedback, the tool may serve as a generative method for designers.
Conference Paper
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Many attempts have been made to automatically convert architectural 3D models into thermal models for building performance simulation. This paper describes a method that is capable of abstracting an arbitrary building massing into a meaningful group of thermal shoebox models. The algorithm is meant to bridge the existing gap between architectural and thermal representations of the same building and to facilitate the use of energy models during schematic design by providing instant performance feedback from the massing stage onwards. The method uses varying facade insolation levels as the key form-related parameter. Discrete facade segments are then grouped by similarity of their local “solar microclimate”. Each group is represented by a reference shoebox model, which consists of a two-zone thermal model for perimeter and core regions. Computed shoebox results are then extrapolated and mapped back to the architectural model. Thus, the relationship between the simulation output and the provided architectural geometry is strengthened and easier to communicate. Combined with a parametric modeling environment, the method may be used to identify optimized local massing solutions. It can also be applied at the urban level to break down a whole neighborhood into a representative subset of simple thermal models, allowing the estimation of urban energy use intensity in a feasible and timely manner.
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This paper reports on two case studies that explore the current use of computational tools in building design scenarios. Goal of the project is to gain insight into the role of tools in the design process and to investigate and capture the designer's viewpoint concerning building simulation. This viewpoint is essential for a successful application of simulation in the design process, but might differ from the viewpoint of the developer of simulation tools. Context of these case studies is an ongoing Ph.D.-project at Delft University of Technology that focuses on better integration of analysis tools (simulation tools in particular) in informed design strategies.
Conference Paper
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One widely recognized opportunity to reduce global carbon emissions is to make urban neighborhoods more resource efficient. Significant effort has hence gone into developing computer-based design tools to ensure that individual buildings use less energy. While these tools are increasingly used in practice, they currently do not allow design teams to model groups of dozens or hundreds of buildings effectively, which is why a growing number of research teams are working on dedicated urban modeling tools. Many of these teams concentrate on isolated sustainable performance aspects such as operational building energy use or transportation; however, limited progress has been made on integrating multiple performance aspects into one tool and/or on penetrating urban design education and practice. In this paper a new Rhinoceros-based urban modeling design tool called umi is presented which allows users to carry out operational energy, daylighting and walkability evaluations of complete neighborhoods. The underlying simulation engines are EnergyPlus, Radiance/Daysim as well as a series of Grasshopper and Python scripts. Technical details of umi along with a case study of a mixed use development in Boston are documented.
A key barrier to the acceptance of simulation within building design has been identified as the fact that it is not fully integrated into the design process. The project described in this paper attempts to address this barrier by embedding modelling as a standard component of design practice procedures within an architectural practice. Important elements of the research that are described in the paper are: • identifying the role building simulation can play at the different stages of design; • developing a model description that evolves through the design process as the building design becomes more highly specified; • simplifying the user interface at the early stage of the design where rapid feedback is required and where most impact can be made on the building’s energy and environmental performance; • customising results presentation to be appropriate for the particular stage of design; and • implementing these simulation concepts, observing their acceptability, and addressing quality assurance and training issues. Key words: Building design practice, outline design stage.
This paper deals with the fast computation of straight skeletons of planar straight-line graphs (PSLGs) at an industrial-strength level. We discuss both the theoretical foundations of our algorithm and the engineering aspects of our implementation Bone. Our investigation starts with an analysis of the triangulation-based algorithm by Aichholzer and Aurenhammer and we prove the existence of flip-event-free Steiner triangulations. This result motivates a careful generalization of motorcycle graphs such that their intimate geometric connection to straight skeletons is maintained. Based on the generalized motorcycle graph, we devise a non-procedural characterization of straight skeletons of PSLGs and we discuss how to obtain a discretized version of a straight skeleton by means of graphics rendering. Most importantly, this generalization allows us to present a fast and easy-to-implement straight-skeleton algorithm. We implemented our algorithm in C++ based on floating-point arithmetic. Extensive benchmarks with our code Bone demonstrate an [Formula: see text] time complexity and [Formula: see text] memory footprint on 22 300 datasets of diverse characteristics. This is a linear factor better than the implementation provided by CGAL 4.0, which shows an [Formula: see text] time complexity and an [Formula: see text] memory footprint; the CGAL code has been the only fully-functional straight-skeleton code so far. In particular, on datasets with ten thousand vertices, Bone requires about 0.2–0.6 seconds instead of 4–7 minutes consumed by the CGAL code, and Bone uses only 20 MB heap memory instead of several gigabytes. We conclude our paper with a discussion of the engineering aspects and principles that make Bone reliable enough to compute the straight skeleton of datasets comprising a few million vertices on a desktop computer.
An energy model generated during the design phase of a building could - in principal - be converted into a calibrated energy model and used to improve the building’s operational performance. However, this rarely happens in practice. Through a survey of 306 building professionals, this research investigates whether this model reuse is technically feasible, based on today’s design-phase models, and what non-technical barriers might stand in the way of its implementation. An important finding is that 75% of the engineers/energy modelers surveyed believed that their models could be used by a third party in building commissioning and operation. At the same time, many modelers voiced various reservations that might prevent them from sharing their energy models with the owner or design team. These reservations varied from a desire to protect their intellectual property, to liability concerns, to the fear of incurring additional unpaid work. In response to these findings, this paper provides suggestions for overcoming these non-technical challenges and includes references for contract precedents.