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Preliminary Evaluation of a Daylight Performance Indicator for Urban Analysis: Facade Vertical Daylight Factor per Unit Floor Area

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Daylight potential for interior spaces has been one of the primary concerns of building performance simulation and various performance indicators have been proposed for interior daylighting quality evaluation. However, interior daylight simulation on urban scale is time consuming and might be affected by a variety of factors. There is the need for measurement on urban scale that can provide relatively efficient and precise estimation of interior daylight potential. A daylight performance indicator for urban analysis was proposed: facade Vertical Daylight Factor per unit floor area, which is calculated as area-weighted total facade Vertical Daylight Factor divided by total floor area. Numerical simulation was conducted across 20 generic forms and 4 different density scenarios. The results showed a strong and positive correlation between the proposed indicator and the reference indicator of interior daylight potential, i.e. area-weighted average horizontal Daylight Factor at work plane height. The utility of the proposed daylight performance indicator lies in its efficiency of simulation for urban scale of analysis and, therefore, the impacts of geometry, spatial arrangement and envelope material properties of urban built forms on interior daylight potential can be evaluated efficiently in the early planning stage. The limitations of this study and potential future explorations are also addressed.
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PRELIMINARY EVALUATION OF A DAYLIGHT PERFORMANCE
INDICATOR FOR URBAN ANALYSIS: FACADE VERTICAL DAYLIGHT
FACTOR PER UNIT FLOOR AREA
Ji Zhang1, Chye Kiang Heng2, Lai Choo Malone-Lee1, Yi Chun Huang3, Patrick
Janssen3, Daniel Jun Chung Hii1, Ibrahim Nazim1
1Centre for Sustainable Asian Cities, School of Design and Environment, National
University of Singapore
2School of Design and Environment, National University of Singapore
3Department of Architecture, School of Design and Environment, National University
of Singapore
ABSTRACT
Daylight potential for interior spaces has been
one of the primary concerns of building
performance simulation and various
performance indicators have been proposed for
interior daylighting quality evaluation.
However, interior daylight simulation on urban
scale is time consuming and might be affected
by a variety of factors. There is the need for
measurement on urban scale that can provide
relatively efficient and precise estimation of
interior daylight potential. A daylight
performance indicator for urban analysis was
proposed: facade Vertical Daylight Factor per
unit floor area, which is calculated as area-
weighted total facade Vertical Daylight Factor
divided by total floor area. Numerical
simulation was conducted across 20 generic
forms and 4 different density scenarios. The
results showed a strong and positive
correlation between the proposed indicator and
the reference indicator of interior daylight
potential, i.e. area-weighted average horizontal
Daylight Factor at work plane height. The
utility of the proposed daylight performance
indicator lies in its efficiency of simulation for
urban scale of analysis and, therefore, the
impacts of geometry, spatial arrangement and
envelope material properties of urban built
forms on interior daylight potential can be
evaluated efficiently in the early planning
stage. The limitations of this study and
potential future explorations are also
addressed.
1. INTRODUCTION
Urban morphology and building typology have
significant impacts on a variety of
environmental performances of urban built
forms, such as energy consumption (Ratti,
Baker, & Steemers, 2005; Salat, 2009) and
incident solar radiation (Kämpf, Montavon,
Bunyesc, & Bolliger, 2010; Robinson, 2006).
Daylight is one of the primary concerns in
architectural design and urban planning
regarding the urban sustainability agenda as it
has multifaceted implications on human
physiological and psychological well-being
and building energy consumption.
Research Question
Various performance metrics have been
proposed to evaluate interior daylighting
quality on building level (Christoph F.
Reinhart, 2006). However, these metrics are
primarily developed for interior spaces and
they are not efficient to apply in urban studies.
For example, supposing three building mass
designs are proposed under the same design
conditions. The interior daylight level of the
primary interior spaces for these designs may
depend on a variety of factors, such as the
spacing to obstruction, fenestration design,
building material properties and interior spatial
layout. Site level evaluation of the daylight
performance for all the individual interior
spaces across the three design options may
become impractical to manage. The question is
whether we can develop measurement for
urban scale comparative analysis that allows
relatively efficient and precise estimation of
interior daylight potential in the early stage of
urban planning and architectural design for
various design options so that their relative
performances can be assessed. A variety of
studies have attempted to address the issue of
daylight potential as a function of built form in
this regard.
Relevant Studies
In Ratti   (2003) study, daylight
availability, which was measured indirectly
through average Sky View Factor (SVF) on
building facade and ground surface, was
examined for different building typologies
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regarding their suitability in hot-arid climate.
The results suggested that courtyard
configuration seems to perform better than
pavilion types.
Cheng et al (2006) explored the relationships
between urban built form, density and solar
potential in a parametric study which
examined a series of generic urban forms in
different densities and spatial layouts. It was
found that built form may have significant
impacts on daylight availability as indicated by
average facade Daylight Factor, and the effect
of horizontal randomness was stronger in high
density scenario than for low density scenario
whereas the effect of vertical randomness was
significant across all density scenario. The
implications are that daylight availability
might be significantly improved by changing
the spatial layout of urban geometries without
compromising the density, and increasing built
density may not necessarily lead to the
decrease of daylight availability, depending on
how the built forms are arranged. Similar
findings have been reported in early parametric
studies by Ng (2004, 2005b).
Montavon et al (2006) examined the daylight
viability for the built forms in La Ville
Radieuse as proposed by Le Corbusier for
Paris. Using the indicator of percentage of
facade area receiving, on average, 10klux or
more daylight annually, they found that the
daylight performance for the cross-shape high-
rise building was inferior to that for the
traditional low-rise compact Parisian urban
street blocks, whereas the low-rise perimeter
      
seem to perform better than the tradition
Parisian blocks. Their findings also suggested
that built form may have significant impacts on
the effectiveness of heliothermic axis which
represents the most desirable orientation for
buildings in a given geographic location
regarding solar access.
In a series of studies on daylight quality in
high density urban environment, Ng (2003a,
2003b, 2005a, 2010; Ng & Cheng, 2004)
proposed the concept of Unobstructed Vision
Area (UVA), which is measured as the area of
a horizontal vision cone unobstructed by
buildings in from of a vertical window, as an
indicator for facade daylight level. Parametric
studies utilizing generic square blocks in
typical spatial configuration in Hong Kong
suggested that UVA is positively correlated
with Vertical Daylight Factor. Depending on
the minimum VDF required and location of
windows, minimum UVA can then be
specified for a given design scenario,
therefore, facilitating the adjustment and
regulation of the design.
An Alternative Thinking
For the studies mentioned above analysis on
urban level daylight potential seemed to focus
on comparing the overall quantity of daylight
on building facade, either through measuring
via a proxy variable such as SVF, calculating
average VDF, or percentage of facade
achieving certain level of daylight intensity for
various urban forms, or on describing the
probability of a specific point on facade to
achieve a required daylight level within a
given physical context (Ng, 2009, p. 189). An
alternative thinking might be linking the
quantity of daylight receivable on facade with
usable floor spaces associated with a given
form under a given density in that the daylight
distribution across the floor spaces at a given
height (e.g. at work plane height) is what
ultimately concerns the users.
For example,  two buildings with the
same form and same physical context. One has
only one story whereas the other has two
stories within the same built volume. They
may have the same score if average VDF or
percentage of facade with VDF above certain
threshold value is calculated for them because
they have the same facade area. However, the
amount of daylight penetrating the facade and
shared by each floor will be different for the
two buildings, assuming the fenestration
design is the same in both cases. The floor of
the one-story building may receive higher level
of light through the entire facade whereas each
floor in the two-story building may receive
lower level of daylight as a result of the light
coming from only half of the facade.
Obviously, the difference in the implication of
facade daylight level on interior daylight level
can be attributed to the difference in the
amount of usable floor spaces. Another
example is what was discussed in Montavon
(2006) study. As they pointed
out, although the overall daylight performance
of the high-rise tower proposed by Le
Corbusier was inferior to the typical Parisian
blocks according to the performance indicator
used in the study, the facade convolution
implemented in the deeply serrated design
may actually increase facade area, allowing
light coming from side to penetrate deeper into
the rooms behind the facade and thus increase
the light level at the inner part of the interior
spaces.
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The Proposed Indicator
It is argued that in urban scale analysis the
quantity of an environmental variable, be it
solar radiation or daylight, as aggregated or
averaged for building surfaces may only
capture one aspect of the story about the
overall environmental performance of urban
forms. In order to obtain the first level of
understanding on the implications of facade-
level environmental quantity to interior-level
environmental potential by taking into account
the built density, accumulated environmental
quantity on facades as shared by usable floor
spaces may need to be measured for different
urban forms.
An urban scale daylight performance indicator,
facade Vertical Daylight Factor (VDF)1 per
unit floor area which is calculated as area-
weighted total facade VDF divided by total
floor area or Gross Floor Area (GFA), is
proposed in this regard (Figure 1).
Figure 1. The proposed urban scale daylight
performance indicator
Similar to the concept of Floor Area Ratio
(FAR) or plot ratio in urban planning, which is
an indicator of built density that prescribes the
amount of usable floor spaces buildable per
unit area of the site, the proposed indicator
measures the average amount of daylight
falling on facade that may eventually affect
every unit area of usable floor space.
The basic assumption of the proposed indicator
is that interior daylight potential is primarily
dependent on the amount of daylight
receivable on building facade in the first place
(Ng, 2004; Ng & Wong, 2004), other than
been affected by factors such as obstruction,
fenestration, material properties and interior
layout. And facade daylight level is primarily
affected by geometries of building mass,
facade material properties and site-level spatial
arrangement of built forms and therefore can
be adjusted through design intervention in the
early stage of planning.
Objectives
This paper reports the methods and results of
evaluating the proposed daylight performance
indicator in relation to interior daylight
potential, which is measured by a reference
indicator -weighted average horizontal
   
assuming the respective facade is fully open
(Figure 2). This reference indicator captures
the maximum potential of daylight penetration
for a given form by opening up its facade and
calculating the average level of daylight
distributed across the entire floor space.
Figure 2. The proposed indicator and the
reference indicator (colors indicate different
Daylight Factor values as simulated)
2. METHODS
The Forms
Twenty generic forms with the same foot print
area (625m2) which capture a wide range of
planar geometric characteristics were selected
for simulation studies (Figure 3). They
represent some of the typical building forms
according to preliminary review of a pool of
real urban built forms. Each form was
positioned at the center of a square-shape site
(50x50m, site coverage = 25%). The
architectural dimensions of the forms and site
were controlled to be realistic in terms of
width and depth. The purpose was to examine
if the relationship to be tested may vary
significantly across different forms under a
given density.
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Figure 3. The 20 generic forms tested
The Context
Instead of being simulated in a fixed physical
context, each form and the site was surrounded
by two layers of replications of itself. In this
regard, a theoretically homogenous context
composed of the same form and in the same
spatial layout unique for each form was
created2. The theoretical performance for the
center block in this theoretical context was
thus simulated and compared (Figure 4).
Figure 4. An example of the theoretically
homogenous simulation context (the plot from
which data was extracted is marked in dotted
line)
The Densities
To examine the sensitivity of the relationships
to be tested to the variation of density, four
different density scenarios were tested for each
form by increasing the height of the forms
(Figure 5) from 4 stories to 12, 24 and 36
stories, resulting in densities ranging from low
(FAR=1), medium (FAR=3) to high (FAR=6
and 9).
Figure 5. The four density scenarios tested
Simulation
The simulation was performed floor by floor,
form by form and density by density in
Radiance. VDF for the facade of a given floor
was simulated by setting sensors on facade in
1x1m spacing with normal perpendicular to
facade. Interior horizontal DF for a given floor
was calculated by removing the facade surface
of the respective floor and setting upward
sensors at work plane height (0.85m) in 1x1m
spacing (Figure 6). The floor by floor data was
then aggregated for the analyses related to the
entire facade surfaces and the entire floor
spaces (Figure 7).
Figure 6. An example of the location of light
sensors on façade and that on work plane
height for a given floor
Figure 7. An example of the façade VDF and
interior horizontal DF as visualized
Analysis
The bivariate correlation analyses conducted
were illustrated in Table 1. Other than the
relationship between the proposed indicator
and the reference indicator (IV), three other
analyses were performed to examine: I) if the
average amount of light received on facade and
that of the entire floor space is correlated on a
floor-by-floor basis; II) if the average amount
of light received on the entire facade is a good
predictor of the average daylight level
calculated for all floors (the reference
indicator); III) if the total amount of light
received on the facade and that for the entire
floor space is correlated on a floor-by-floor
basis. Each of the four relationships were also
further examined to check its sensitivity to the
variation of form and density.
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Table 1. The relationships examined
Average amount of daylight
Floor by floor comparison
I ).
Entire surfaces comparison
II ).
Table 1. (Continued)
Total amount of daylight
Floor by floor comparison
III ).
Entire surfaces comparison
IV ).
(Note: Since the denominators for both variables
are the same, this analysis is actually comparing
the total amount of daylight for the entire facade
vs the total amount of daylight for all floors.)
3. RESULTS
I) Generally speaking, the average facade VDF
for a given floor was significantly correlated
with the average horizontal DF for the
respective floor (R2=0.895, p<0.0001) across
all 20 forms and all 4 density scenarios (Figure
8).
Figure 8. Average facade VDF of a given floor
vs. average horizontal DF of the floor across
all forms and densities
  t vary much across
different forms, as indicated by R2 calculated
for each form which ranged from 0.9932 for
form Q to 0.9964 for form S (Fig 9, left). The
relationship tested seemed to become stronger
as density increased, as indicated by the R2
calculated for each density scenario which
increased from .075 for FAR1 to .918 for
FAR9 (Fig 9, right).
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Figure 9. Average facade VDF of a given floor
vs. average horizontal DF of the floor by form
(left) and by density (right)
II) The average VDF calculated for the entier
facade seemed to have a significant but
relatively weaker corrlation with the average
horizontal DF for all the floors (R2=0.795,
p<0.0001) across the 20 forms and 4 density
scenarios (Fig 10). The clusters as shown in
the graph is due to the incontinuity of the
density scenarios tested here.
Figure 10. Average VDF of the entire facade
vs. average horizontal DF for all the floors
       
across different forms, with the R2 calculated
for each form ranging from 0.9985 for form Q
to 0.9996 for form A (Fig 11, left). However,
as density increased the correlation between
these two variables become weaker and
weaker and less and less significant, as
indicated by the R2 calculated for each density
scenario which dropped significantly from
.671(p<0.001) for FAR1 to .149(p=.092) for
FAR9 (Fig 11, right). The results suggested the
relationship between average VDF as
calculated for the entire facade and average DF
for all floors might be significantly affected by
density.
Figure 11. Average VDF of the entire facade
vs. average horizontal DF for all the floors by
form (left) and by density (right)
III) The total VDF for the facade of a given
floor was significantly and strongly correlated
with the total horizontal DF on work plane
height for the entire floor space of the given
floor (R2=.991, p<.0001) across all forms and
densities (Fig 12).
Figure 12. Total VDF for facade of a floor vs.
total horizontal DF for the floor across all
forms and densities
This relationship varied little across different
forms, as indicated by the R2 calculated for
each form which ranged from .9932 for form Q
to .9964 for form S (Fig 13, left). The
correlation between the two variables seemed
to become stronger as density increased, as
indicated by the R2 calculated for each density
which increased slightly from .943 for FAR1
to .995 for FAR9 (Fig 13, right).
Figure 13. Total VDF for facade of a floor vs.
total horizontal DF for the floor by form (left)
and by density (right)
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IV) The facade VDF per unit floor area was
significantly and strongly correlated with the
horizontal DF per unit floor area (R2=.997,
p<.0001) across all 20 forms and 4 densities
(Fig 14).
Figure 14. Facade VDF per unit floor area vs.
horizontal DF per unit floor area across all
forms and densities
This strong correlation only slightly varied
across different forms, as indicated by the R2
calculated for each form which ranged from
.998 for form Q to .999 for form A (Fig 15,
left). However, the correlation seemed to
decrease as density increased, as indicated by
the R2 calculated for each density which
dropped from .966 for FAR1 to .437 for FAR9
(Fig 15, right).
Figure 15. Facade VDF per unit floor area vs.
horizontal DF per unit floor area by form (left)
and by density (right)
4. CONCLUSIONS
The proposed urban scale daylight
performance indicator is intended to allow
planners and architects to do relatively quick
and precise estimation of the interior daylight
potential across various design scenarios
during the early design stage when different
spatial arrangements and geometric
characteristics of simplified building masses of
different built forms can be tested.
On a floor-by-floor basis, the results indicated
that amount of light falling on facade is highly
correlated with the amount of light distributed
across the entire floor space in terms of either
the average or the total (Fig 8, 12), and the
effect of from and density on this relationship
is quite small (Fig 9, 13).
Taking the entire facade surfaces and the
usable floor spaces as a whole, the relationship
between average VDF for facade and average
horizontal DF for all floors was relatively
weaker (Fig 10) and it may be affected by
density (Fig 11). On the other hand, the
significant and strong correlation between the
proposed indicator and the reference indicator
across different forms and densities suggested
that the floor area normalized facade daylight
quantity can be used as a relatively precise and
efficient indicator of interior daylight potential
(Fig 14). However, the percentage of
variations in horizontal daylight potential that
can be explained by the variation in the
proposed indicator seemed to decrease as
density increased (Fig 15). Therefore, cautions
may need to be taken when apply the proposed
indicator in extremely high density situation.
Limitations and Future Studies
The generic built forms tested in this study
were intended to be representative. However,

different if other generic forms are considered.
Further parametric studies may consider
covering a wider range of generic forms. In
this study the variation of density was achieved
through increasing building height solely.
Future studies may need to consider other
approaches to vary density such as varying site
coverage and their respective impacts on the
sensitivity of the proposed daylight
performance indicator. The experiment of this
study was conducted only for four typical
density levels. To further test the sensitivity of
the proposed indicator to the variation of
density, more levels of built density may need
to be considered. The impacts of other factors
such as spacing between buildings and
reflectivity of facade material on the
effectiveness of the proposed performance
indicator may also need to be further explored
in a systematic way.
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The proposed indicator is based on the
calculation of daylight factor which is a static
daylight metric. Many studies related to
interior daylight potential have addressed the
limitations of using daylight factor as an
indicator of daylight quality (C. F. Reinhart,
Mardaljevic, & Rogers, 2006) and suggested
several climate-based daylight metrics
(Architectural Energy Corporation, 2005;
Nabil & Mardaljevic, 2006; Christoph F.
Reinhart & Andersen, 2006). Further studies
may need to explore if alternative dynamic
daylight metric can be used so that the annual
variation of daylight on facade can be captured
in a precise way.
ACKNOWLEDGMENT
This paper is derived from an on-going
     
Ministry of National Development.
1. Instead of using proxy variables such as SVF,
VDF is calculated in that it is widely used in
daylight studies as indicator of facade daylight
level and it was suggested to be a more
appropriate variable for studies related to
urban and inter building daylight evaluation
(Ng, 2010, p. 67). Based on the contemporary
development of numerical simulation software
and computer hardware, precise simulation of
VDF for complex urban geometries can now
be achieved in relatively efficient ways.
2. Similar understanding can be referred to in
other studies related to environmental
performance simulation for a given piece of
urban fabric (Ratti et al., 2005; Ratti et al.,
2003; Salat, 2009), in which the hidden
assumption is that the urban fabric being
analyzed is relatively homogenous in terms
built form.
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SimBuild
2012
Fifth National Conference of IBPSA-USA
Madison, Wisconsin
August 1-3, 2012
646
... Energy: representing the needs for heating, cooling and lighting Performance criteria Evaluation metric Passive Daylight Active Energy Other 1. Geometrybased [40,28,23] [ 35,28,23] [ 23] [39] [5] (urban phenomena e.g. heat island); [40] (daylight in streets); [28] (land usage) 2. External solar-and geometrybased [1,3,33,51,12,38,6,7,28,23] [ 53,5,6,7,28,23] [ 22,18,9,16,38,5,6,7,23] [ 52,33,51,40] (outdoor thermal comfort); [19] (solar access); [40] (daylight in streets) 3. ...
... In addition to looking at the metric(s) used to quantify each performance criterion, it is of interest to examine how many and which criteria are considered. Many publications deal with a unique and specific criterion, for instance related to the daylight performance [53,35], or the photovoltaic (PV) and/or solar thermal (ST) potential [22,18,9,16]. Other studies also evaluate a unique metric, but one which is meant to represent the performance in a broader sense: Otis [33] and van Esch et al. [51] measure winter and summer solar exposure in terms of radiation, with this measure being linked to the passive performance of buildings and the thermal comfort of outdoor spaces. ...
Article
The energy performance of a building is strongly influenced by its level of solar exposure, in turn affected by the climate, built context, and building morphological characteristics. Since these are typically fixed at the early-design phase, performance assessment methods based on solar considerations at the urban scale are essential to support early decision-making. As the adaptation of the well-developed building performance simulation methods to the urban scale lead to complexity issues, it is of interest to verify whether simpler metrics can act as performance indicators, as is often done at the building level with quantities such as form factor.
... However, the last four stated studies were limited to urban canyons and did not consider other urban morphologies and architectural typologies. A paper by Zhang et al. [36] proposed a daylight performance indicator for urban analysis: facade VDF per unit of floor area. A numerical simulation was conducted across multiple generic forms and different density scenarios. ...
Article
Full-text available
The attempt at a more sustainable land use by the increase of urban density may have a negative effect on the daylighting of residential buildings. In densely built areas, obstructions generated by the surrounding buildings can substantially reduce the available amount of daylight, causing poorly daylit spaces and a less healthy indoor environment with higher electricity consumption as consequence of artificial lighting. European standard EN 17037, Daylight in Buildings, was established in 2018 to ensure appropriately daylit spaces. In this paper, a three-step methodology was developed to investigate the relationship between certain urban planning parameters and the daylighting of a typical room defined by specific (Slovenian) legislative restrictions about its geometry and minimum required window to floor area ratio, in order to establish the maximum densities of residential developments still fulfilling the minimum requirements for daylight provision defined by EN 17037. The results show that a relatively low urban density is required to fulfil the stipulations for minimum daylight provision for the deepest permissible room according to the Slovenian legislation. The impact of the development floor area ratio on the daylighting potential of buildings was identified as significant, followed by the site coverage, development layout and building typology. Furthermore, the developed methodological approach clearly demonstrates a substantial potential for application in urban planning, with indoor daylight environmental conditions being linked to the planning of residential developments in the earliest stages of the project.
... to reduce solar heat gain by 27% from an equivalent flat façade" [18] because of the proper arrangement of the opaque and light-transmitting parts of the serrated oriels. The application of serrated geometry also allows for deeper daylight penetration into the core of the building, as "(…) facade convolution implemented in the «deeply serrated» design may actually increase facade area, allowing light coming from side to penetrate deeper into the rooms behind the facade and thus increase the light level at the inner part of the interior spaces" [19]. The author of the paper currently researches the issues of the daylight management and the user's visual comfort in buildings clad with serrated facades. ...
Article
Serrated building envelopes are a very eye-catching element of contemporary architecture. This type of façade in plan resembles the edges of a serrated blade, hence the name. Serrated facades substantially influence the building’s tectonics understood as the relationship between the structural and the artistic form. They also have a major impact both on building physics (increased surface of heat exchange compared to flat facades, solar avoidance – decreased solar gains if properly designed) and on visual appeal. This paper examines façade morphology and analyses regular (repetitive) and irregular (non- repetitive) serration of façades and its influence on the aesthetic quality of the envelope. The morphological analysis also includes the direction of the serration. An exceptional feature of serrated façades is that the optical phenomena on the façade change depending on the viewing angle. The presented paper is based on case studies with special attention to morphological and qualitative analysis. Recently completed case studies serve as visual (photographs) and graphical illustrations (diagrammatic drawings). A review of technical and engineering justifications of the use of serrated facades is also included and briefly explained.
... we looked at multiple studies on the subject (Cheng et al., 2006;Sok Ling et al., 2007;Lobaccaro et al., 2012;van Esch et al., 2012;Takebayashi and Moriyama, 2012;Hachem et al., 2012;Pessenlehner and Mahdavi, 2003;Zhang et al., 2012;Martins et al., 2014;Peronato, 2014). The main parameters respecting points 1 and 2 were identified as the street width, the buildings shape, height and orientation, and the density. ...
Article
Despite recent developments, neighborhood-scale performance assessment at the early-design phase is seldom carried out in practice, notably due to high computational complexity, time requirement, and perceived need for expert knowledge, ultimately limiting the integration of such a task into the design process. In this paper, we introduce a predictive modeling approach to rapidly obtain an estimate of the performance of early-design phase neighborhood projects, from simple geometry- and irradiation-based parameters. The performance criteria considered are the passive solar and daylight potential, respectively quantified by the energy need for space heating and cooling (given certain assumptions) and the spatial daylight autonomy at the ground-floor level. Two predictive models, or metamodels, are developed following distinct techniques: a multiple linear regression function and a Gaussian Processes regression model. These are developed from a reference dataset acquired through the parametric modeling and simulation of neighborhood design variants. When tested on designs provided by professionals, the metamodels with the highest accuracy within the compared types (MLR versus GPs) portray a prediction error below 10% in 87% (respectively 60%) of the cases for the passive solar (resp. daylight) potential. Results show this approach to be a promising alternative to running detailed simulations when comparing early-design variants.
Conference Paper
This study explores the relationship between urban form and environmental performance by analyzing three representative urban street block typologies proposed for Paris through her urban history. The performances of these typologies in terms of daylight potential, annual insolation, exposure to the sky, and potential to produce urban heat islands were simulated and compared. The implications of the results in 1) the importance of appropriate performance indicators to be used in comparative studies, and 2) the relationship between urban form, density, and environmental performance were discussed.
Article
Full-text available
Daylight design for "extremely" obstructed urban environment is a relatively uncharted area of study. No city in the world has an urban density as high as Hong Kong. Designing daylight in the territory is a critical and important study. The paper attempts to develop and verify a simple method of design for architects based on theoretical formulation and results obtained using computational simulations. The Unobstructed Vision Area Method (UVA) proposed here is highly correlated to the Vertical Daylight Factor (VDF) of a building surface. This 2-dimensional plan based method is very easy to use at the early design and planning stage. The method is now under consideration by the Government for its new performance based building regulations. With small modifications to its variables, the methodology for the UVA method could also be generally used for other extreme-density cities.
Article
Daylight design for "extremely" obstructed urban environment is a relatively uncharted area of scholarship. The reason might be that the problem has not been critically important. No city in the world has an urban density as high as Hong Kong. Deisgning and providing adequate daylight into buildings is a difficult challenge. A key question designers often ask is: If there is a need to build a high density city, what should it look like? What one should or should not do? There are many design variables. This study examined one of them: building heights. It attempted to determine what one could gain by optimizing it; and to understand what is the relationship between height difference of buildings in a city and the daylight performance. The study utilized computational lighting simulation as a study tool. Simplified cityscapes of various degrees of height differences are studied. They are plotted against the Vertical Daylight Factor (VDF) available to the building envelop. It has been found that, given the same high density, better daylight availability to the lower floors of buildings could be achieved by varying buildng heights.
Article
Leslie Martin and others at Cambridge University addressed the question “What building forms make the best use of land?” in a number of influential papers published in the late 1960s. They selected six simplified urban arrays based on archetypal building forms. Then they analysed and compared the archetypes in terms of built potential and day lighting criteria, eventually reaching the conclusion that courtyards perform best. Their results, which inspired a generation of designers, are briefly reviewed here and reassessed in environmental terms using innovative computer analysis techniques. Furthermore, the implications of their question, which to date has not addressed the link with climate, are explored using a case study in a hot-arid region.
Article
Today's existing building stocks are major energy consumers and CO2 emitters, depending on various factors including urban morphology, architectural archetypes, construction technologies, energy systems, and inhabitant behaviour. A large case study based on 96 000 buildings in Paris, France, is the subject of detailed analysis of the existing residential building stock by comparing some environmental metrics of Paris's urban fabric with thermal energy consumption in buildings. The environmental metrics, such as building shape factor and passive volume (for natural ventilation and daylighting), are functions of urban morphology. This comparison of urban forms and heating energy consumption reveals some impacts of urban morphology and building typology on the energy efficiency in the different zones of Paris. The energy efficiency and CO2 emissions related to heating mode and inhabitant behaviour are separated from those linked to urban form and construction technology. Thus, a balanced view of the complex impacts of morphologies, typologies, energy systems, and inhabitant behaviour on energy loads and CO2 emissions is presented, which allows for the optimization of urban form in terms of density, building configuration, and morphology. Similar large-scale simulations can analyse urban form and the mix of building stock as well as the interaction of increased equipment efficiency, alternative energy mix, and inhabitant behaviour.
Article
This paper describes the application of a new paradigm, called useful daylight illuminance (UDI), to assess daylight in buildings. The UDI paradigm is designed to aid the interpretation of climate-based analyses of daylight illuminance levels that are founded on hourly meteorological data for a period of a full year. Unlike the conventional daylight factor approach, a climate-based analysis employs realistic, time-varying sky and sun conditions and predicts hourly levels of absolute daylight illuminance. The conventional approach produces a single number – the daylight factor as a percentage – for each evaluation point in the space. In contrast, a climate-based analysis results in an illuminance prediction for every daylight hour of the year for each point considered. The UDI paradigm offers a way to reduce the voluminous time-series data to a form that is of comparative interpretative simplicity to the daylight factor method, but which nevertheless preserves a great deal of the significant information content of the illuminance time-series. The UDI paradigm informs not only on useful levels of daylight illuminance, but also on the propensity for excessive levels of daylight that are associated with occupant discomfort and unwanted solar gain. In a conventional analysis of daylight provision and solar penetration, the two phenomena are assessed independently using methods that are idealised (daylight factor) and qualitative (shadow patterns). The UDI paradigm offers a simple methodology whereby daylight provision and levels of solar exposure are quantified using a single evaluative schema. Thus, it is also well-suited for teaching purposes. Application of the UDI paradigm is demonstrated using an analysis of design variants for a deep-plan building with a light-well. Comparison is made with the conventional daylight factor approach, the LEED daylight credit and measures of daylight autonomy.
Article
Presented at the National University of Singapore 29 January 2002 Around 20 cities in the world have 10 million inhabitants or more. In these cities, buildings are ghting each other for natural light. Finding ways optimize the natu-ral agent without compromising development density is a task for architects and engineers. This paper reports a series of research projects, commissioned by the government of Hong Kong, to understand the problem and to develop a new design and regulatory method for Hong Kong. The study rst looked into the issue in terms of existing rules and policy, and identi ed their shortcomings. It then investigated daylight performance of the existing building stock with on-site measurements. Though a territory-wide user survey, the study proceeded to relate these quantitative data to user satisfaction and requirements. A minimum performance standard based on Vertical Daylight Factor (VDF) on the surface of the window was established. Using theoretical modeling, on-site measurements and computational studies of real and hypothetical cases, a design method based on Unobstructed Vision Area (UVA) was developed. The government of Hong Kong has adopted this performance-based approach; new building regulations are currently undergoing on-site trial.
Article
This study describes the development and validation of a Radiance model for a translucent panel. Using goniophotometer data combined with integrating sphere measurements, optical properties of the panel were derived and converted into a Radiance model using the trans and transdata material types. The Radiance model was validated in a full-scale test room with a facade featuring the translucent panel material. Over 120,000 desktop and ceiling illuminances under 24,000 sky conditions were measured and compared to simulation results using the Perez sky model and a Radiance-based daylight coefficient approach. Overall mean bias errors (MBE) below 9% and root mean square errors (RMSE) below 19% demonstrate that translucent materials can be modeled in Radiance with an even higher accuracy than was demonstrated in earlier validation studies for the plastic, metal, and glass material types. Further analysis of results suggests that the accuracy of around ±20% currently reached by dynamic Radiance/Perez/daylight coefficient calculations for many material types is sufficient for practical design considerations. A procedure is described showing how goniophotometer and integrating sphere measurements can be used to accurately model arbitrary translucent materials in Radiance using transdata function files.
Article
This paper explores the effects of urban texture on building energy consumption. It is based on the analysis of digital elevation models (DEMs)—raster models of cities which have proven to be very effective in the urban context. Different algorithms are proposed and discussed, including the calculation of the urban surface-to-volume ratio and the identification of all building areas that are within 6 m from a façade (passive areas). An established computer model to calculate energy consumption in buildings, the LT model, is coupled with the analysis of DEMs, providing energy simulations over extensive urban areas. Results for the three case study cities of London, Toulouse and Berlin are presented and discussed.