BEES interim report year 5 - Christchurch urban form and energy

STUDY REPORT SR 277/7 [ 2012 ]
BEES
INTERIM REPORT
Building Energy End-Use Study - Year 5
CHRISTCHURCH URBAN FORM AND ENERGY
Tavis Creswell-Wells, Michael Donn and Shaan Cory
© BRANZ 2012
ISSN: 1179-6197
BUILDING ENERGY END-USE STUDY (BEES)
YEAR 5: CHRISTCHURCH URBAN FORM AND
ENERGY
BRANZ Study Report SR 277/7
Tavis Creswell-Wells – Victoria University of Wellington
Michael Donn – Centre for Building Performance Research (CBPR)
Shaan Cory – Victoria University of Wellington
Reference
Creswell-Wells, T., Donn, M., and Cory, S. (2012). Building Energy End-use Study (BEES) Year
5 Interim Report: Christchurch Urban Form and Energy, BRANZ Study Report 277/7, Judgeford.
Centre for
Building
Performance
Research
Reviewers
Patrick Arnold – eCubed Building Workshop Ltd
Nigel Isaacs – BRANZ Ltd
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PREFACE
Understanding how energy and water resources are used in non-residential buildings is key to improving
the energy and water efficiency of New Zealand’s building stock. More efficient buildings will help reduce
greenhouse gas emissions and enhance business competitiveness. The Building Energy End-use Study
(BEES) is taking the first step towards this by establishing where and how energy and water resources
are used in non-residential buildings and what factors drive the use of these resources.
The BEES study started in 2007 and will run for six years, gathering information on energy and water use
through carrying out surveys and monitoring non-residential buildings. By analysing the information
gathered, we aim to answer eight key research questions about resource use in buildings:
1.
What is the aggregate energy and water use of non-residential buildings in New Zealand?
2.
What is the average energy and water use per unit area per year?
3.
What characterises the buildings that use the most energy and water?
4.
What is the average energy use per unit area for different categories of building use?
5.
What are the distributions of energy and water use?
6.
What are the determinants of water and energy-use patterns e.g. structure, form, function,
occupancy, building management etc?
7.
Where are the critical intervention points to improve resource use efficiency?
8.
What are the likely future changes as the building stock type and distribution change?
Understanding the importance and interaction of users, owners and those who service non-residential
buildings is also an important component of the study.
For the BEES study, non-residential buildings have been defined using categories in the New Zealand
Building Code, but in general terms the study is mainly looking at commercial office and retail buildings.
These vary from small corner store dairies to large multi-storey office buildings. For more information on
the building types included in the study please refer to BRANZ report SR224 Building Energy End-use
Study (BEES) Years 1 & 2 (2009) available on the BEES website (www.branz.co.nz/BEES).
The study has two main methods of data collection – a high level survey of buildings and businesses, and
intensive detailed monitoring of individual premises. The high level survey initially involved collecting data
about a large number of buildings. From this large sample, a smaller survey of businesses within
buildings was carried out which included a phone survey, and collecting records of energy and water use
and data on floor areas. The information will enable a picture to be built up of the total and average
energy and water use in non-residential buildings, the intensity of this use and resources used by different
categories of building use, answering research questions one to four.
The detailed monitoring of individual premises involves energy and indoor condition monitoring, occupant
questionnaires and a number of audits, including: appliances, lighting, building, hot water, water, and
equipment.
This is a study of the BEES modelling conducted by the Centre for Building Performance Research. The
studies are distributed between three reports. The first report (Gates, Creswell-Wells and Cory)
documents the outcomes of a study identifying which aspects of energy simulation models that must be
carefully quantified to ensure accurate energy performance modelling.
The second report (Cory, Munn and Gates) explores the means by which computer modelling might be
used to determine optimum building energy performance. This third report applies the results from the
first and second reports to examine the likely energy and environmental effects of the proposed urban
form in the Christchurch central city draft plan.
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SUMMARY




Improved indoor environment is possible through natural (passive) measures provided
buildings are no wider than 17m.
Courtyards in conjunction with lanes (of 10m width) could deliver a significant reduction in
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energy (up to 47.4% per m less than the ‘deep-plan’ baseline model) as they facilitate passive
cooling and daylighting.
Opening up the city centre with courtyards and lanes also creates useful outdoor spaces.
Planned façade step-backs are not effective in saving energy or making sunnier streets during
the winter period.
This report presents the results of a systematic investigation of energy performance design options for the
Christchurch central city. It is part of the BEES study in which modelling templates were previously
developed, and have been applied to this study.
In response to the Christchurch earthquakes, the Christchurch City Council (CCC) produced the ‘draft
Central City Plan’ (CCP). Included in this plan was an outline of urban form features (i.e. building height
limits, façade step-backs, lanes and courtyards) which were envisaged to increase daylight into the city;
and create porosity for movement and pockets of community. Beyond these benefits, however, was the
potential these urban forms offered for improvement of environmental and energy performance in
buildings.
The goal of the urban form ideas was that buildings and city streets would gain greater solar and fresh air
access (refer Figure A) through breaking up city blocks with lanes and courtyards. This had the potential
benefit of creating buildings that could effectively use natural lighting/heating/cooling and ventilation and
therefore a passively comfortable environment.
Largely internal building space; in reality may be
comprised of many individual buildings; shows
total net lettable area if all the city block was
developed intensely
Open outdoor space:
sun, fresh air: public/
private; lost net lettable
area
Indoor spaces adjacent to
light, sun and fresh air;
remaining net lettable
area in individual buildings
grouped
around
the
courtyards
Figure A: Plan View of City Block with the CCP Urban Form Changes Implemented
The level of improvements likely to result from the CCP’s urban form features was estimated using
OpenStudio software and simulated in EnergyPlus. Model and simulation parameters were based on
relevant New Zealand Standards and BEES data. The performance was compared to a conventional
‘deep-plan’ model. Simulations drew on the work reported in the BRANZ BEES Modelling Optimisation
analysis (Cory, Gates and Munn). Each urban form feature (step back, lane and courtyard) was tested in
terms of daylight, heating, cooling and ventilation. This determined the amount of energy each building
form required. Energy consumption was the over-arching performance indicator.
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1,600,000
80
1,400,000
70
1,200,000
60
1,000,000
50
800,000
40
600,000
30
400,000
20
200,000
10
0
0
Baseline
Stepbacks
4m Lanes (x2)
Urban Form Situation
10m Lanes (x2)
Courtyards (x3)
(with 2 lanes)
Figure B: Overall Energy Consumption for each Urban Form Change against Baseline Model
The courtyard plan form shown in Figure A is not intended to be understood as a set of three courtyard
shaped enormous buildings. Rather it shows how the many building sites in the large city blocks might be
developed. The key feature is that, however these buildings are actually placed on the city block, they are
all 17m deep at most – from window wall to window wall, to optimise daylight access and use passive
cooling. The courtyard form is a traditional European and Middle Eastern approach to this placement
along city streets. It is by no means the only way buildings open to air and light might be arrayed in a city
grid. The critical dimension (~17m depth) brings major energy savings and more productive and
comfortable building occupants who not only have improved access to light and air but also value the
views over those from deeper plan buildings.
Where the city height limit is 29m (7 storeys), the CCP proposes to have the upper two storeys step back
o
at a 45 angle, only a marginal effect on the energy performance of buildings facing the street has been
demonstrated, (Figure B). It has also been identified that this measure has a negligible effect on the sun
experienced by pedestrians in the streets. The only observable change was experienced during summer,
with no increase in solar access to street level during the winter months.
o
If the height limit was only 17m (4 storeys) then stepping back the upper two storeys at 45 would
increase street level solar access in winter as well as summer.
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Square Metre Consumption (kWh/m 2/year)
Total Consumption (kWh/year)
Results found that step-backs had minimal effect on total building energy consumption; and lanes on their
own were marginally better (refer Figure B). However, courtyards (three per block) in conjunction with
2
lanes (two 10m wide) could deliver a significant reduction in energy (up to 47.4% per m less than the
‘deep-plan’ baseline model) as they allowed passive cooling through natural ventilation and reduction in
electric light use through daylight.
CONTENTS
1.
INTRODUCTION ................................................................................ 1
1.1
1.2
1.3
1.4
2.
CCP TESTING PARAMETERS............................................................. 4
2.1
2.2
2.3
3.
Testing Locations ............................................................................... 13
Daylight Modelling Factors.................................................................. 13
The BEES Template............................................................................ 14
Working Plane Height......................................................................... 14
Thermal Comfort Band ....................................................................... 14
MODELLING METHODOLOGY ......................................................... 15
5.1
5.2
5.3
5.4
5.5
5.6
6.
Daylight to Buildings .......................................................................... 10
Passive Thermal Performance in Buildings........................................... 10
Natural Ventilation to Buildings ........................................................... 11
Total Energy Consumption in Buildings ............................................... 11
Sunlight to the Street ......................................................................... 12
IMPORTANT MODELLING FACTORS .............................................. 13
4.1
4.2
4.3
4.4
4.5
5.
CCP Proposed Passive Urban Form Features..........................................4
Restrictive Parameters Set by the CCC ..................................................8
Major Issues Regarding the CCP’s Passive Urban Form Features ............8
BENCHMARKS OF PASSIVE PERFORMANCE ................................. 10
3.1
3.2
3.3
3.4
3.5
4.
Significance and Aim of Study...............................................................1
Overview and Scope.............................................................................1
Research Question ...............................................................................2
Scope of Study.....................................................................................2
Modelling and Simulation Computer Software Used ............................. 15
The ‘Baseline Model’ and the ‘CCP Model’ ............................................ 15
Modelling the Baseline........................................................................ 15
Modelling the CCP Step-backs............................................................. 17
Modelling CCP Lanes .......................................................................... 18
Modelling CCP Courtyards................................................................... 19
TESTING AND DISCUSSION OF RESULTS ..................................... 21
6.1
6.2
6.3
6.4
Baseline Model ................................................................................... 21
CCP Model: Façade Step-backs ........................................................... 21
CCP Model: Lanes and Alleyways ........................................................ 27
CCP Model: Internal Courtyards .......................................................... 31
7.
CONCLUSIONS AND RECOMMENDATIONS ................................... 35
8.
WORKS CITED................................................................................. 38
APPENDIX A: WINDOW-TO-WALL RATIO (WWR) CALCULATIONS ........ 40
v
APPENDIX B: VISIBLE SKY ANGLE (VSA) CALCULATIONS ...................... 42
B1 – Ground Floor ........................................................................................... 42
B2 – Fourth Floor ............................................................................................ 42
B3 – Seventh Floor .......................................................................................... 42
APPENDIX C: MODELLING AND SIMULATION PROCESS ......................... 43
C1 –
C2 –
C3 –
C4 –
C5 –
C6 –
Baseline
Baseline
Baseline
Baseline
Baseline
Baseline
Geometry for Daylighting Analysis .............................................. 43
Daylight in Buildings Analysis in Ecotect/Daysim.......................... 43
Sunlight to Street Analysis in Ecotect .......................................... 43
Geometry for Thermal and Energy Analysis ................................. 44
Thermal Performance in EnergyPlus Building Analysis.................. 44
Energy Consumption in EnergyPlus Building Analysis ................... 45
APPENDIX D: STEP-BACK ENERGY CONSUMPTION CALCULATIONS ..... 46
D1 – Baseline Energy Consumption:................................................................. 46
D2 – Step-back Energy Consumption ............................................................... 46
APPENDIX E: ENERGY CONSUMPTION RATES ......................................... 47
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FIGURES
Figure 1: 'Draft Central City Plan' map showing the 'Central Core Zone' (Christchurch City Council) ................. 3
Figure 2: Central City Planning Map 3: Regulatory Framework- illustrating intended building height
restrictions (Christchurch City Council) ............................................................................................................... 5
Figure 3: CCP Proposed Step-backs (Christchurch City Council)....................................................................... 6
Figure 4: CCP Intended Effect of Step-backs on Solar Access to the Urban Canyon......................................... 6
Figure 5: CCP Map of Existing (black) and Proposed Central City Lanes (Christchurch City Council) ............... 7
Figure 6: CCP Impression of a Lane Environment (Christchurch City Council) .................................................. 7
Figure 7: CCP Impression of the Public Environment from Courtyards (Christchurch City Council) ................... 8
Figure 8: Plot of Temperatures vs Humidities: Shading shows Cool (Blue), Hot Humid (Red) and Hot Dry
(Yellow) Climates; Human Comfort (green) & Human Comfort with Air Movement (Dotted Green) ................. 11
Figure 9: Daylighting ‘Baseline Model’ with Foundation Parameters Identified ................................................. 16
Figure 10: Thermal and Energy ‘Baseline Model’ ............................................................................................. 16
Figure 11: Perspective of CCP Step-backs – Ecotect Model Geometry............................................................ 17
Figure 12: Diagram of CCP Lanes in Context of City Block .............................................................................. 18
Figure 13: Perspective of CCP Lanes – OpenStudio 4m Model Geometry ....................................................... 19
Figure 14: CCP Courtyard – Ecotect Model Geometry ..................................................................................... 20
Figure 15: CCP Courtyard Dimensions ............................................................................................................. 20
Figure 16: ‘Perimeter’ and ‘Core’ zones in Southern Facade Step-back........................................................... 21
Figure 17: Daylight Autonomy in Level G, 4, 7 cells on north and douth facades ............................................. 22
Figure 18: Baseline Daylight Autonomy of Cell N4 ........................................................................................... 22
Figure 19: Step-back Daylight Autonomy of Cell N4 ......................................................................................... 22
Figure 20: Baseline and Step-back Temperature Tendencies in North Facing Perimeter Zones ...................... 23
Figure 21: Baseline and Step-back Energy Consumption Comparison ............................................................ 24
Figure 22: Baseline and Step-back Total Energy Consumption Comparison.................................................... 24
Figure 23: Total Baseline Sunlight Hours .......................................................................................................... 25
Figure 24: Total Sunlight Hours with Step-backs .............................................................................................. 25
Figure 25: Average Annual Sunlight Hours, Seven Storey Baseline Model ...................................................... 26
Figure 26: Average Annual Sunlight Hours, Seven Storey WITH Step-backs................................................... 26
Figure 27: Average Winter Sunlight Hours, Seven Storey Baseline Model ....................................................... 26
Figure 28: Average Winter Sunlight Hours, Seven Storey WITH Step-backs ................................................... 26
Figure 29: Average Summer Sunlight Hours, Seven Storey Baseline Model .................................................... 26
Figure 30: Average Summer Sunlight Hours, Seven Storey WITH Step-backs ................................................ 26
Figure 31: Average Winter Sunlight Hours, Four Storey Baseline Model .......................................................... 27
Figure 32: Average Winter Sunlight Hours, Four Storey WITH Step-backs ...................................................... 27
Figure 33: Average Summer Sunlight Hours, Four Storey Baseline Model....................................................... 27
Figure 34: Average Summer Sunlight Hours, Four Storey WITH Step-backs ................................................... 27
Figure 35: Daylight Autonomy Model of Cell E4 with 4m Lane Adjacent........................................................... 28
Figure 36: Daylight Autonomy Model of Cell E4 with 10m Lane Adjacent......................................................... 28
o
Figure 37: Annual Passive Temperatures ( C) in Adjacent Zones for 4m and 10m Wide Lanes ...................... 28
Figure 38: Energy End-Use Component Breakdown in Perimeter Zones Adjacent to 4m and 10m wide
Lanes ................................................................................................................................................................ 29
Figure 39: Baseline 4m Lane and 10m Lane Comparison of Overall Energy Consumption.............................. 30
Figure 40: Daylight Autonomy Mapping of Level 4 Perimeter Zones facing Courtyards ................................... 31
Figure 41: Passive Temperatures in Level 4 Perimeter Cells facing Courtyards .............................................. 32
Figure 42: Level 4 Internal Perimeter Zones facing Courtyard Energy Comparison ......................................... 33
Figure 43: Dimensions and Affected Area due to Courtyards ........................................................................... 33
Figure 44: Total Sunlight Hours for Ground Level (of Seven Storeys) in Courtyard .......................................... 34
Figure 45: Total Sunlight Hours for Ground Level (of Four Storeys) in Courtyard ............................................. 34
Figure 46: Overall Energy Consumption for each Urban Form against Baseline Model ................................... 35
Figure 47: Model of Courtyard plus Lanes and Lost NLA, against Remaining NLA .......................................... 37
Figure 48: Visible Sky Angles (VSAs) at Mid-Height of each Subject Level ...................................................... 40
vii
TABLES
Table 1: Energy Consumption Rates ................................................................................................................ 47
viii
GLOSSARY
Baseline Model
Computer model representing urban and building parameters identified
throughout the study
CCC
Christchurch City Council
CCP
Draft Central City Plan
CCP Model
Baseline Model + CCP proposed changes
Central City Grid
The orthoganal street and block layout/configuration in central city
Christchurch
CERA
Christchurch Earthquake Recovery Authority
Daylight Autonomy
Percentage of time per year that a building is occupied when target
illuminance can be maintained by daylight alone
Daysim
Computer program specialising in daylight calculations in buildings
DF
Daylight Factor (the ratio – on cloudy days only - of indoor illuminance (using
only daylight as a source) to outdoor illuminance
Ecotect
Autodesk computer program used for building environmental calculations
EnergyPlus
Computer program used for simulation of comfort and energy factors
Facade Step-back
Where a façade is stepped back away from the vertical boundary of the
building to reduce its mass and allow more sunlight into the adjacent street.
GenOpt
Computer program which optimises building components within a defined set
of parameters
NIWA
National Institute of Water and Atmospheric research
NLA
Net Lettable floor Area - floor area within a building that can be leased. NLA
extends from the inner face of external walls and does not include communal
building facilities such as bathrooms, plant rooms stairwells, lifts, etc.
OpenStudio
Energy Plus ‘plug-in’ into SketchUp
Passive
Relating to, or being of a heating, cooling, ventilating or lighting system that
uses no external mechanical power.
SketchUp
Computer modelling program used for creating building geometry
Thermal Comfort Band
Temperature range in which humans have been found to be most
comfortable
Urban Canyon
Physical gap in an urban environment created by a street cutting through
dense blocks of structures (between buildings)
VSA
Visible Sky Angle - Degree of unobstructed sky visible from the middle of the
window in the subject space. Angle is from bottom of eave/overhand at
window, to top of building opposite the window.
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W/H
Width-to-Height ratio
Working Plane
Typical office desk height (700mm above finished floor level)
WWR
Window area to Wall area Ratio
x
1.
INTRODUCTION
This report summarises the results of a systematic investigation of energy performance design options for
the urban form of the Christchurch central city. The aim is to examine the significance for energy
performance and quality of the central city built environment using the principal features of the Central
City Plan (CCP) – as were available in May 2012. Ultimately it is anticipated that this material will be of
assistance to all Christchurch citizens, whether professionally qualified or generally interested, on the
relationship between urban form and energy consumption in central city Christchurch.
There were two motivations for this project. The first motivation arose from the BEES project team’s
desire to examine how the BEES project might contribute knowledge of commercial building energy
performance to the Christchurch rebuild. The Christchurch earthquakes of December 2010 and February
2011 have resulted in 80-90% of the CBD being demolished (OPUS). As the focus of BEES draws
statistically relevant energy performance data about New Zealand commercial buildings through studying
existing buildings, Christchurch had to be left out of the survey portion of the study. The BEES modelling
team undertook this study based on models drawn up for the statistical analysis of the BEES survey data.
It therefore became a first application of the potential of the BEES modelling approach to explore how
simulation based design studies might be performed on the whole BEES dataset.
The second motivation arose from a desire to examine how modelling might examine new-build design
options in general and in particular for Christchurch. Through the ‘Share an Idea’ scheme set up to
address the rebuild, the Christchurch people indicated a strong sentiment for a highly sustainable
exemplar city – “Aim high. Develop a world-class, sustainable, modern green city. The next Malmo,
Vancouver or Reykjavik. Establish a new benchmark!” (Christchurch City Council) The Christchurch City
Council (CCC) and contributors developed the draft CCP to direct the rebuild of the city centre. On the
th
18 of April 2012, the Canterbury Earthquake Recovery Authority (CERA) Minister Gerry Brownlee gave
the CCC approval to proceed with the CCP (Christchurch City Council).
1.1
Significance and Aim of Study
The basis of this analysis is the presumption that an opportunity exists for Christchurch to recreate itself
as a world leading sustainable city. The CCC’s draft CCP reflects the general desire of the Christchurch
people to move in the ‘green’ direction. Features such as height limits and courtyards are proposed (in the
CCP) to increase accessibility to natural commodities within an otherwise energy-intensive urban
environment. However, opposition exists to the concept of surrendering profitable privately owned land
area to public courtyards and lanes. Some remain unconvinced that the benefit these urban restrictions
will provide justifies the loss in productive space (Christchurch City Council).
This study applies simple analytical tests with independently validated software to question the energy
and environmental benefit of the CCP’s proposed urban design features. The significance of these
analyses is not identification of ‘best’ or ‘optimum’ urban forms, but to demonstrate the energy and
environmental impact of urban form policy planning in the central city rebuild.
1.2
Overview and Scope
The study intends to quantify the effects of design features of the CCP for the Christchurch rebuild.
Specifically, urban building form features of the CCP are investigated for their effect on passive
performance – the intrinsic performance of the buildings themselves, reducing their reliance on installation
of energy efficient equipment such as boilers and chillers or energy supply services such as photovoltaic
electricity generation. This ‘passive’ performance is evaluated by calculating the energy required to meet
thermal and lighting comfort standards in a range of standard offices.
This study draws on another BEES Year 5 report: Building Design Optimisation (Cory, Munn and Gates,
Building Energy End-use Study (BEES) Year 5 Interim Report: Building Design Optimisation). That report
establishes parameters and methods for testing the buildings in Christchurch and indicated that passive
building features could achieve energy consumption reductions.
1
1.3
Research Question
What affect will the urban form features proposed by the CCP have on the new buildings’ energy
consumption?
1.4
Scope of Study
1.4.1
The Draft Central City Plan (CCP)
All elements investigated and tested in this study are found in and based on the CCP documents which
are available to the public on the CCC website (Christchurch City Council).
1.4.2
The Passive Urban Form Focus
Passive design is a response to a site’s conditions which form the basis of a building’s performance.
Because they are fundamental to the form and the design appearance of a building, passive design
measures can only be implemented at the beginning of a project. This is because changes in building
design form and appearance are expensive and time consuming to make late in the design process. A
passive urban form study for Christchurch is therefore only useful now during the planning stages while
significant design changes affecting the form of buildings and the form of the city itself can still be made.
For this reason, this study focuses on the passive elements of a proposed sustainable urban
Christchurch.
1.4.3
‘Central Core’ Zone in Christchurch CBD
This study is specific to the Christchurch central city. Focus is placed on central city area due to the BEES
focus on commercial buildings. This is planned as an area of higher population and building density; the
city see development of this area as “…protecting the role of the central city as the region’s primary
commercial area” (Christchurch City Council).
Figure 1 shows the ‘Central Core Zone’ (in red) as defined by the CCP. It is bound within the confines of
the Avon River on the northern and western fronts, by Lichfield Street to the south and by Manchester
Street to the east.
2
Figure 1: 'Draft Central City Plan' map showing the 'Central Core Zone' (Christchurch City Council)
3
2.
CCP TESTING PARAMETERS
2.1
CCP Proposed Passive Urban Form Features
This section introduces the proposed CCP urban form features to be tested in the study. The urban form
features manifest the CCC’s urban planning intentions - mainly permeability for pedestrian access to the
large city blocks and sunlight to the street. These urban form features also enable more building spaces to
access daylight and fresh air with the by-product being a likely improved energy performance in buildings.
Sunlight is beneficial in providing natural heat both to buildings and the street, and can be utilised to
create thermally comfortable environments passively. Daylight enhances visual capacity and comfort
naturally, at the same time reducing the need for expensive artificial lighting. Finally, building occupants
require high-quality fresh air to function properly (‘old’ or ‘used’ air in buildings typically has higher levels
of CO2 than outdoor air which can cause drowsiness). This passive approach to bringing fresh outdoor air
through windows into buildings is often described as ‘natural’ ventilation to distinguish it from the delivery
of the same fresh air by mechanical means to people in commercial buildings.
Increasing permeability through the city (lanes and courtyards), brings more building surface area into
contact with outdoor air and thus makes natural ventilation more likely to be employed. As fan energy is
often a large component of any heating, ventilation and air conditioning (HVAC), using simple openings
like windows and passive ventilation openings has the potential to save energy, while still delivering better
indoor air quality.
2.1.1
Building Height Limits
As a result of the earthquakes, people in Christchurch have become concerned about the safety of tall
buildings. For this reason, and to create a more open ‘sunny’ atmosphere, residents of Christchurch
requested smaller buildings through the ‘Share an Idea’ initiative, “keep the buildings low rise – it lets
more natural light into the city” (Christchurch City Council). Figure 2 illustrates the CCP’s proposed
maximum building height limitations for different zones. The focus central core zone, seen in red, is
subject to a 29m (seven storey) maximum limit, with a minimum of three storeys. This proposed seven
storey building height restriction will be used as a modelling ‘constant’ throughout this study. The seven
storey model will not be tested against taller city models because of the CCP limit.
The study does look at the implication of maximising profit by maximising the floor area of buildings under
this height limit. One possible result of placing a height restriction like this seven storey limit is that land
owners see the only possible means of maximising returns on their site is to develop all the floor area of
each site up to the height limit. The eventual result could be covering all the land area of the city blocks
with buildings up to a limit of 29m.
NOTE: In all situations presented in this study the ground floor height is 5.0 m; and the floors-above have
4.0 m inter-floor heights, in accordance with the CCP.
4
Figure 2: Central City Planning Map 3: Regulatory Framework- illustrating intended building height
restrictions (Christchurch City Council)
2.1.2
Façade Step-backs
The first ‘passive urban form feature’ studied is the façade step-back, shown in Figure 3. This is a method
proposed by the CCP to increase solar penetration to the urban canyon (‘urban canyon’ describes the
o
result of a road cutting through dense buildings). Applied on the southern side of buildings at a 45 angle,
the step-back intends to allow more sunlight (direct solar beam) and daylight (diffused light) deeper into
o
the city. Figure 4 demonstrates how cutting the top two (sixth and seventh) floors back to a 45 angle will
result in sunlight reaching two floors lower on the opposite side of the road (at equinox). The desired
result is more daylight to buildings and more sunlight to the street for greater pedestrian comfort.
5
a
s
d
f
s
d
a
s
d
f
Figure 3: CCP Proposed Stepbacks (Christchurch City
Council)
2.1.3
Figure 4: CCP Intended Effect of Step-backs on Solar Access
to the Urban Canyon
Lanes/Alleyways
The existing/retained CBD grid consists of rectangular blocks approximately 100m long in the north-south
direction by 200m long in the east-west direction. These are substantial distances which create difficulty
in pedestrian movement and accessibility. The CCP’s ‘Strengthening the Grid’ project (increasing
permeability through the large 200x100m city block system) proposes to add seven ‘lanes’ to the 13
existing lanes in the central core zone (Christchurch City Council). The Crown (via CERA) is prepared to,
and intends to, secure the land targeted for transformation into public access routes by purchasing
obstructing land parcels. Lanes (refer Figure 5 which shows in black the lanes that existed preearthquake but also large blocks with no lanes) are expected to increase urban canyon area and allow
more natural light and air to buildings (Christchurch City Council).
There are three types of lanes proposed in the CCP – ‘wide lanes’ (4-10m wide), ‘narrow lanes’ (2-4m)
and ‘service lanes’ (3-5m). This study tested two variations of lane. The first is 4m wide as this width
represents the distinction between narrow and wide lane types and is also the mid-range size for a service
lane. The second is 10m wide as it demonstrates the effects the largest possible lane size will have on
surrounding buildings. The goal was to bracket the range of small to large, and thus establish what effect
lane width might have on building performance rather than test a myriad of combinations of lane width,
none of which would be precisely right.
6
Despite the suggestion in the CCP of having lanes covered to provide shelter from rain, all lanes were
modelled as open to the sky to best determine their influence on daylight to those spaces.
Figure 5: CCP Map of Existing (black) and Proposed
Central City Lanes (Christchurch City Council)
2.1.4
Figure 6: CCP Impression of a Lane
Environment (Christchurch City Council)
Internal Courtyards
The intention of introducing internal courtyards is to increase proximity of internal spaces to the ambient
environmental amenity of light, sun and fresh air. Courtyards work on the theory that elimination of central
‘core’ zones of deep-plan buildings, which rely entirely on artificial heating/cooling, lighting and ventilation,
will be of benefit to a building’s performance through greater access to these natural ‘amenities’.
The BEES Year 5: Building Design Optimisation report (Cory, Munn and Gates, Building Energy End-use
Study (BEES) Year 5 Interim Report: Building Design Optimisation) demonstrated perimeter zones
possess not only better access to natural amenities in terms of energy, but also provide more desirable
working conditions due to their proximity to the outdoors (views, natural light, etc). Replacing part of the
energy-intensive core zone of the building with a courtyard, converts more of the total floor area to
‘perimeter’ zones. Because of their access to views, these lower energy use and higher environmental
quality spaces are also of greater prestige and thus potentially higher rents. Section 2.3 explains how
desirable working conditions contribute to higher productivity and better returns for businesses.
An additional benefit of courtyards is the outdoor public space they provide (refer Figure 7). Courtyards
can also be used as entertainment precincts as they provide effective shelter from all winds but still receive
useful sunlight and daylight.
7
Figure 7: CCP Impression of the Public
Environment from Courtyards (Christchurch City
Council)
2.2
Restrictive Parameters Set by the CCC
2.2.1
Retaining the Central City Grid
The existing central city grid has been retained in the CCP because:
-
-
2.2.2
There is a potentially enormous cost involved in changing grid layout and the associated legal
infrastructure.
There is little difference in passive solar performance between the existing layout and other
layouts such as the ‘Spanish Grid’ (same orthogonal form but on a diagonal orientation) (van
Esch, M. et al.).
The Christchurch people have expressed a desire to retain the heart of their city through the
‘Share an Idea’ scheme (Christchurch City Council).
And, it is feasible because geotechnical data indicates it is safe to rebuild (Tonkin & Taylor Ltd.).
Road Widths
The measurement tool in Google Earth was used to determine street widths within the central core zone
existing in 2010. Lichfield, Cashel, Hereford, Colombo, Manchester and High Streets were measured for
width, with an average of 18m calculated. If an inaccuracy of ±1m was allowed for in the measurement
(Google Earth is not a precise tool), then over a distance of 18m, this is a possible inaccuracy of only
5.6% in the final measurement. In street widths up to 20m the overall conclusions of the study would not
change.
2.3
Major Issues Regarding the CCP’s Passive Urban Form Features
8
2.3.1
Net Lettable Area (NLA) and Productivity
Opposition to the concept of sacrificing net lettable area (NLA) to make way for urban form features
(Christchurch City Council) is likely to stem from property owners who see themselves as losing NLA that
could otherwise be rented. However, the flipside of that concept is the level of quality of those remaining
spaces will be much higher.
A study by Leaman and Bordass (1999) suggests that factors of staff comfort, health and satisfaction can
contribute financial gains or losses of up to 15% of turnover in a typical office organisation. They also
state that productivity increases when staff have opportunity for personal control of their environment with
rapid changes to comfort. This is best achieved with shallow-plan building forms as they allow for simple
adjustments (like opening a window) which deliver quick results. Added benefits of shallow-plans include
views and interaction with outdoors. Productivity is increased when staff are situated in desirable locations
such as near windows. Such situations are increased with the inclusion of lanes and courtyards.
Although, some undesirable windowless space is indeed being ‘sacrificed’, this building form is
contributing to developing highly-productive, desirable spaces. These desirable ‘perimeter’ spaces offer
greater potential for productivity (and reduced energy costs) than lower quality ‘core’ spaces, and are
therefore more likely to be attractive and return higher per square metre rentals.
2.3.2
Density and Urbanisation
Density is a key issue within the urban form topic. The CCP ‘Technical Appendices’ (Christchurch City
Council) document describes how there are polarised views on the matter across the Christchurch
population. Most people agree that medium-to-high population density is required to maintain life, energy
and economic viability in the city centre. However, there is debate as to the level of building density
required to sustain the population required for socio-economic fertility in the central city. While this study
does not look at such factors, it may aid in discerning an appropriate built form density. Section 12.2.3
Policy: ‘Building Density’ of the CCP Regulatory Changes document states:
“The scale and concentration of built development will be greater in the central city than
elsewhere in the city. Development is encouraged to take full advantage of the potential
provided, having regard to an appropriate urban shape and form, within the central city to
ensure maximum environmental benefit, and value in terms of city identity.”
(Christchurch City Council).
By determining which urban form features provide benefit in terms of energy and comfort, these findings
could inform a level of building density that is environmentally sustainable.
9
3.
BENCHMARKS OF PASSIVE PERFORMANCE
In building performance simulation there is a need to be able to compare results. The means by which
performance is measured often goes well beyond the legal minima of codes and standards. This section
describes the indexes used in this study to measure building performance.
3.1
Daylight to Buildings
Daylight autonomy (DA) measures illuminance levels across a space, over the full occupied year. It shows
where in the space daylight is plentiful, and where it may be lacking. DA can be set to a required minimum
illuminance level (320 Lux in this case, according to ‘New Zealand Standard 1680: 2006 Interior Lighting’)
(Standards New Zealand) and will demonstrate which areas of that space are sufficiently lit and for what
percentage of the year. In essence, DA illustrates what percentage of the year artificial lighting can be
turned off in that space and the energy savings realised.
3.2
Passive Thermal Performance in Buildings
o
Thermal conditions are measured in degrees Celsius ( C) across the occupied year (weekdays 8amo
5pm). A comfort band of 18-25 C is used in these analyses to determine ‘comfort’ in test cells. Time spent
o
o
below 18 C is considered ‘too cold’ and time spent above 25 C is considered ‘too hot’. The more time
spent within the prescribed comfort zone, without active heating or cooling, the better the passive thermal
performance. This narrow range of comfort has been seriously questioned during the CBPR BEES
modelling team collaboration with a group of researchers in the International Energy Agency (IEA)
Research Task focused on Net Zero Energy Buildings (Net ZEBs). It is argued by several researchers and
o
practitioners in this Task that this 18-25 C range is biased towards air conditioning of fully sealed spaces
often with no contact with the outdoors. It is especially focused on cooling the building, not keeping the
occupants comfortable. The increasing use of the ‘Adaptive Comfort’ model of human comfort – rather
than the Fanger model of human comfort has been brought about by a desire to avoid energy-intensive
environmental control strategies. Which often preclude thermally variable solutions, such as many
climate-responsive and energy-conserving designs, or innovative mechanical strategies that allow for
personal control.
10
Figure 8: Plot of Temperatures vs Humidities: Shading shows Cool (Blue), Hot Humid (Red) and Hot Dry
(Yellow) Climates; Human Comfort (green) & Human Comfort with Air Movement (Dotted Green)
3.3
Natural Ventilation to Buildings
Natural ventilation is not simulated in detail in this study. The modeling of the wind, its effects on the
surrounding buildings and thus its effects on an individual window or set of windows in a building is not
attempted. Instead, a rule of thumb is used which is derived from the BEES Year 5: Building Design
Optimisation report (Cory, Munn and Gates, Building Energy End-use Study (BEES) Year 5 Interim
Report: Building Design Optimisation) that 90% of artificial cooling requirements in Christchurch can be
subtracted from the simulated figure due to the use of natural ventilation. This 90% reduction was applied
to any space that was part of the ‘core’ zone in the baseline model but which was converted into a
‘perimeter’ zone by any of the CCP form changes being tested in this study. In such a case, 90% of the
cooling load energy calculated for that perimeter zone will be deducted from the total energy consumption.
3.4
Total Energy Consumption in Buildings
Energy consumption is measured in annual kilowatt hours (kWh) for each zone within the subject building
and/or for the whole building (kWh/year); and energy intensity is measured as total annual kWh for each
2
square metre (kWh/m /year). Total building energy is useful for knowing the urban form changes’ overall
effect on the full building. Square metre energy rates are useful for comparison against the loss of NLA
associated with implementing these urban form changes. This is where a debate central to this study lies
(environmental and energy performance of the building vs. floor area and profitability of that building) and
so the relationship between NLA and energy requirements of that floor area is significant.
11
3.5
Sunlight to the Street
Christchurch people were reported as requesting more sunlight to the outdoor public areas (Christchurch
City Council). The Autodesk software Ecotect has a function called ‘Total Sunlight Hours’ which
measures exactly that. Total sunlight hours counts the time each point of an analysis grid spends in direct
sunlight over a full year. It focuses on direct solar beam referred to as ‘sunlight’ and does not take into
consideration diffuse (reflected) light referred to as ‘daylight’. Total sunlight hours are measured between
7am and 7pm (Christchurch City Council). The resulting values are between 0 hours (no time spent in
sun) and 4,380 hours (maximum possible sunlight hours). The closer the figure is to 4,380 hours, the
sunnier that point (or grid average) is.
12
4.
IMPORTANT MODELLING FACTORS
Prior to modelling, certain modelling factors need to be established. The following issues are significant (in
terms of modelling accuracy and reliability) and complex enough to warrant particular investigation. Final
values to be carried forward to the modelling/simulation stages are highlighted in bold for easy
reference.
4.1
Testing Locations
Testing every possible location in an urban study of this scale is an impossibly long and time consuming
exercise. In order to portray the range of scenarios encountered around the city, this study selected a
systematically representative set of locations for testing.
4.1.1
Heights
Simple, office scale ‘test cells’ were located on ground (G), fourth and seventh levels of sevenstorey building models. These levels are selected because:
-
4.1.2
This provides good coverage of all possible situations, with any level not tested being only one
level away from a situation that is tested (comparative information)
Horizontal Locations
The horizontal positioning within city blocks of these typical office test cells depends on which of the two
types of analysis is being undertaken.
For daylight analysis, test cells are located at the mid-point of the block in the horizontal
dimension. This is because daylight and sunlight are identical on a façade regardless of location within
that façade. Placing small test cells in the centre generates quicker simulation results which can then be
applied and averaged over the full length of the façade.
For thermal/energy analysis, the ‘test cells’ encompass the full length of the façade. This is
because it is facilitated applying the validated and tested BEES energy simulation template models (refer
Section 4.3) as full floor levels.
4.2
Daylight Modelling Factors
In order to determine useful daylight within a building space, that space needs to be designed
appropriately to gain maximum benefit from available daylight.
4.2.1
External Window Size
Window-to-wall ratio (WWR) is a pivotal component to successful daylighting. Too high a glazing ratio and
glare becomes an issue (as well as the obvious solar gains and heat losses); whereas too low a ratio will
result in insufficient daylight to the space. The following WWR’s were determined using a calculation
devised by Reinhart and LoVerso, refer Appendix A. Ground floor WWR = 0.8 (80% glazed); fourth
level WWR = 0.5 (50%); and seventh level WWR = 0.5 (50%).
13
4.2.2
Test Cell Dimensions
Ecotect software user resources suggest a rule of thumb for useful daylight design. It is generally
accepted that daylight will penetrate a space horizontally by a factor 2.5 times the height of the aperture it
is emitting from (Ecotect). With the CCP-proposed floor heights of 4m, it can be assumed glazed areas
will be 3.5m above floor level (allowing 0.5m for structural and mechanical services in the ceiling). This
equates to useful daylight penetration of 7m into the space.
Test Cell dimensions will therefore be set at 7m deep and 7m wide, to maintain a square form.
4.3
The BEES Template
A product of this study is the BEES modelling templates. These templates embody current best practise
building industry and practise data (such as material properties/schedules/building form etc). They are
accurate to within 5% of a detailed model (Cory, S., Gates, A., Donn, M.). This study will employ the large
open plan (OP5) template which represents the common four perimeter zones and one core zone office
building.
4.4
Working Plane Height
The ‘Metric Handbook Planning and Design Data’ reference guide defines the working plane height to
be 0.7m above the floor level for office situations (Adler).
4.5
Thermal Comfort Band
The earlier discussion in Section 3 on definitions of thermal comfort describes the definition of a thermal
o
comfort zone from 18-25 C with humidity ranging from 20-70%.
14
5.
MODELLING METHODOLOGY
5.1
Modelling and Simulation Computer Software Used
A range of computer packages were required to undertake the desired testing for this study. A particular
point of note is the different geometry methods required for different environmental analysis programs.
Specifically, Ecotect and Daysim (daylight analysis software) use standard SketchUp geometry; whereas
EnergyPlus (thermal/energy analysis) must use OpenStudio (SketchUp plug-in) geometry. The two
methods are very similar but do possess variations. These are outlined in Appendix C. The software
packages (and their functions) used are:




5.2
Trimble (formerly Google) SketchUp – basic universal modelling tool that will be used to create
geometries.
Ecotect in conjunction with Daysim – powerful environmental analysis tools which will be used for
examination of solar-related elements (i.e. daylight autonomy to buildings and total sunlight
hours to the street). The combination is used here because Ecotect is apt in handling external
daylighting factors and geometry but Daysim generates more accurate calculations for internal
situations. In essence, Ecotect is an interface to the more reliable calculation engine Daysim.
EnergyPlus – a complex, widely-employed simulation tool used for accurate analysis of thermal
comfort and energy consumption elements (plugs into SketchUp through OpenStudio plug-in).
OpenStudio – EnergyPlus interface to SketchUp. Geometry built for EnergyPlus needs to be
made in OpenStudio in order to translate through.
The ‘Baseline Model’ and the ‘CCP Model’
In essence, two models are tested in this study. The main intent is to measure effectiveness of the CCP
passive urban form features. To do that a baseline must be established for comparison – the first of the
two models is therefore a ‘Baseline Model’. The second model is the ‘CCP Model’ and it encompasses the
passive urban form features proposed in the CCP as identified in Section 2.1. Both models consist of
identical foundation parameters (i.e. block and street dimensions, materiality, testing methods,
measurables and outputs). The differences are the passive urban form features. When one of these CCP
features (set-backs/lanes/courtyards) is inserted into the model, it becomes a CCP model and is so
named.
5.3
Modelling the Baseline
The ‘Baseline Model’ is illustrated in Figure 9. This model embodies the CCP 29m building height limit
defined in Section 2.1 and the restrictive parameters (200m x 100m grid form and 18m street width) set
out in Section 2.2. All identified passive urban form features will be applied to this Baseline Model in turn,
and tested using the measures established in Section 3. These baseline tests will provide a datum against
which the passive urban form features can be compared. A step-by-step process description can be found
in Appendix C.
5.3.1
Baseline Core Area Zone
The baseline ‘core’ zone is important to this study as it lays the foundation for which lanes, courtyards and
overall energy effects are compared. The model simplifies the block to a single building. It is recognised
that city blocks are typically many individually owned building sites. What is explored here is the extreme if
every site owner built to the full extent of their site. Then there would only be a small 7m deep perimeter
around the edge of the city block where access to daylight and fresh air could be guaranteed. There is a
15
large central core area which is unaffected by the CCP’s proposed façade step-back change, but will be
altered by the lane and courtyard changes. As the core is bound within the four perimeter zones it
possesses no access to daylight or fresh air. As a result, all heating and lighting to that space are artificial.
The effect of the step-backs, lanes and courtyards is essentially measured by the improvement they
generate over the core zone. The perimeter zones retain the same access to fresh air and daylight.
Results from lane and courtyard changes will be compared to the 100% artificial environments of the
Baseline Model core zone.
Figure 9: Daylighting ‘Baseline Model’ with Foundation Parameters Identified
Figure 10: Thermal and Energy ‘Baseline Model’
16
5.4
Modelling the CCP Step-backs
5.4.1
CCP Step-backs Geometry
The only alteration here from the geometry methodology established in Appendix C, is adding the stepbacks. The step-backs, explained in Section 2.1, can be seen applied to the model in Figure 11.
NOTE: This alteration is identical for both the daylight and thermal/energy model geometries in their
respective ways.
Figure 11: Perspective of CCP Step-backs – Ecotect Model Geometry
5.4.2
CCP Step-backs Daylight Analysis
The methodology here is exactly the same as for the Baseline Model (refer Appendix C), but for one
difference. As the step-backs are only applied to the southern side of the blocks, differences will only be
noticed on the opposite north-facing façades (although minor effects may also be experienced on the
south-facing façade). East and west-facing façades will not be affected. Therefore, daylight testing will
only be done for north and south-facing façades.
5.4.3
CCP Step-backs Thermal and Energy Analysis
For the same reasons as with the daylight analysis, thermal and energy tests were only done for the
north-facing façade. It was too difficult to model south-facing cells with a step-back included (due to
geometric complexities within the OpenStudio software) and difficulties were not justified for such minor
effects (<6%) as seen in daylight analysis on the south façade (refer Fig 17). Differences seen in the
17
north-facing perimeter zones can then be directly compared to the Baseline Model north-facing perimeter
zones results. Additionally, those localised improvements can be added to the baseline results to
determine an overall square metre improvement. These two approaches will provide insight into how
much effect improvements in north-facing zones have across the entire block.
5.5
Modelling CCP Lanes
Figure 12: Diagram of CCP Lanes in Context of City Block
As described in Section 2.1, a 4m wide lane and a 10m wide lane, each cutting through a city block from
north to south, will be tested. Lanes will create new perimeter zones (refer grey areas of Figure 12) that
will benefit from daylight and natural ventilation, and therefore create more area with a lower energy
consumption and higher desirability over the baseline core zone.
5.5.1
CCP Lanes Geometry
Lanes are inserted into the original model, rather than into the step-backs model, to ensure all changes
are standalone and comparable to the baseline. Figure 13 displays the 4m wide lane situation. The 10m
wide model is executed in exactly the same manner but with the lane (to the right in Figure 13) now set to
10m instead of 4m.
18
Figure 13: Perspective of CCP Lanes – OpenStudio 4m Model Geometry
5.5.2
CCP Lanes Daylight Analysis
As the city blocks in Christchurch’s CBD are oriented due north, it was assumed cells facing east and
west would perform identically. Therefore, daylight analysis could be carried out in only a single cell for
lanes. This cell was situated, in both the 4m and 10m lane width models, at the fourth level to represent
an average of daylight performances across the full seven levels.
5.5.3
CCP Lanes Thermal and Energy Analysis
Zones for thermal and energy analysis encompassed the entire length of the perimeter zone adjoining the
lanes. As with the daylight analysis, this was also applied to the fourth level.
5.6
Modelling CCP Courtyards
5.6.1
CCP Courtyards Geometry
The CCP does not define sizes for their proposed courtyards. A recent study on the most effective
courtyard width-to-height (W/H) ratio for natural ventilation found that a W/H ratio of 1:1 provides the best
shelter from wind in the courtyard space while retaining sufficient air movement for natural ventilation in
internal spaces (Tablada). This would indicate a 29m wide courtyard (equal to the 29m building heights)
should be used to realise best natural ventilation.
Building spaces adjacent to the courtyard now become perimeter zones and can thus be naturally lit and
naturally ventilated (refer dark grey sections in Figure 15). Now the original perimeter zones (7m wide)
PLUS the new ‘internal’ perimeter zones (also 7m wide), PLUS a 3m wide movement route between
19
them, can all be naturally lit and cross-ventilated. Using this model (refer Figure 14), a full courtyard plus
building totals 63m width.
NOTE: The courtyard is reduced to 28m in width in order to split the full block into three courtyards, each
separated by a 4m or 10m wide lane.
Figure 14: CCP Courtyard – Ecotect Model Geometry
5.6.2
Figure 15: CCP Courtyard
Dimensions
CCP Courtyard Daylight Analysis
Analysis of daylight availability was done for all of the new ‘internal’ perimeter zones opening out onto the
courtyard to determine the overall effectiveness of this urban form feature. East and west-facing zones
were again considered to perform identically. As was done for the lanes, daylight was only assessed at
the fourth level. This was to represent an average situation of the full height.
A ‘total sunlight hour’ analysis was also done for the outdoor public courtyard space at ground level. This
was done using the same method and scale as was used for the assessment of sunlight to the street in
the step-backs model.
5.6.3
CCP Courtyard Thermal and Energy Analysis
Geometry was manipulated so shading objects represented the building sections that enclose the
courtyard. All other modelling and simulation factors were identical to the technique employed for the
analysis of lanes.
20
6.
TESTING AND DISCUSSION OF RESULTS
6.1
Baseline Model
The baseline was intended as a point of reference for results of urban form changes to be compared
against. Therefore, baseline model results will be presented against changes where required.
6.2
CCP Model: Façade Step-backs
6.2.1
Daylight Autonomy in Buildings
Daylight can only access ‘perimeter’ zones and
does not affect ‘core’ zones (refer Figure 16).
The step-back urban form change influences
daylight in only the north and south-facing
perimeter zones (east and west perimeter
zones are not affected due to orientation).
Figure 17 displays DA for test cells on levels G,
four and seven on both north and south
perimeter zones. It compares DA of each cell
between step-back and baseline models to
illustrate improvements relative to each cell. DA
is given in terms of range, which covers lowest
point of daylighting performance in the cell to
the highest; and average DA, which indicates
percentage of the year that artificial lighting can
be turned off in that cell.
Figure 16: ‘Perimeter’ and ‘Core’
Southern Facade Step-back
zones
in
This graph demonstrates a clear improvement
in DA across most cells. This was expected on
the north-facing perimeter but not to such an extent on the south. The area of greatest importance is cell
N4 the mid-level zone on the northern façade (cell codes are first letter of orientation, e.g. ‘N’ for north; and
number of level, e.g. ‘4’ for fourth floor; equals cell N4). This cell is located in the region of that façade that
was expected to be most influenced by the step-backs. Additionally, it best represents likely circumstances
of commercial offices.
21
Comparison of Daylight Autonomy (DA) Between Baseline and CCP Step-backs
100
90
80
DA (%)
70
89
74
89
85
80
79
75
69
77
69
91
72
60
50
40
30
20
10
0
Figure 17: Daylight Autonomy in Level G, 4, 7 cells on north and douth facades
Figure 18 and Figure 19 offer a visual representation of DA in cell N4. Here, DA patterns can be seen at
each specific point in the test cell. Yellow squares represent areas of high DA (80-100% of year
sufficiently lit), whereas red represents less effective daylighting (40-60% of year sufficiently lit). By
comparing DA of the Baseline Model with DA of the step-backs model, an evident improvement can be
seen by the increase of yellow squares in the step-backs map (Figure 19). This improvement can be
measured as an 11% (average DA of 69% up to 80%) increase in DA in this space. Basically, this means
artificial lighting can be completely turned off for an extra 11% (around 5 weeks) of the working year.
Figure 18: Baseline Daylight Autonomy of Cell
N4
Figure 19: Step-back Daylight Autonomy of Cell
N4
22
6.2.2
Thermal Comfort
As expected, increasing daylight to building spaces also contributes to increased temperatures. Figure 20
demonstrates how the extra solar penetration into the urban canyon improves thermal conditions (for most
levels), making northern perimeter zones passively warmer than they were in the baseline model. As was
the case with the daylighting analysis, the seventh floor was entirely unaffected by the step-backs.
NOTE: the below graph represents passive temperatures without the influence of natural ventilation.
Natural ventilation is not considered for the step-back alteration, as there has been no change in access
to fresh air, so no difference would be encountered.
Less than 18
Within Comfort Band
More than 25
Step-backs N7
10%
44%
46%
Baseline N7
10%
44%
46%
Zone
Step-backs N4
50%
Baseline N4
50%
59%
Step-backs NG
10%
Baseline NG
10%
0%
41%
68%
22%
73%
20%
40%
17%
60%
80%
100%
Percentage of Occupied Year
Figure 20: Baseline and Step-back Temperature Tendencies in North Facing Perimeter Zones
6.2.3
Total Energy Consumption
DA results indicated an improvement in daylighting for test cell N4. With a 6% reduction in energy
requirements for that zone, Figure 20 supports the daylighting influence seen in Figures 18 and 19.
However, both other north-facing perimeter zones react differently to cell N4.
Test cell NG (north-facing at ground level) experienced an increase in required space conditioning energy
despite improved daylight. This is likely to be a result of the large WWR of 80% which, as Figure 20:
Baseline and Step-back Temperature Tendencies in North Facing Perimeter Zones showed, would allow
substantial heat gains (and losses) through the low insulation glazed area.
The artificial lighting energy saved would be offset by the amount of artificial cooling and heating required
to maintain thermal comfort. Test cell N7, not surprisingly, has not been influenced in terms of daylight or
energy consumption as it is already exposed to maximum visible sky angle and therefore maximum solar
access.
23
100
Energy Consumption (kWh/m2/yr)
90
91
80
91
83
77
70
60
64
66
50
40
30
20
10
0
Baseline Step-backs
NG
NG
Baseline Step-backs
N4
N4
Baseline Step-backs
N7
N7
Zone
Figure 21: Baseline and Step-back Energy Consumption Comparison
An important consideration in determining the overall influence of the step-backs on energy consumption
over the entire building is the relationship between core and perimeter zones. As this urban form change
only affects the northern perimeter zones, core zone energy consumption will remain the same. Figure 22
demonstrates how little effect the step-backs make when applied to the entire block/building. Calculations
can be found in Appendix D.
Total Consumption (kWh/m2/year)
1,600,000
1,400,000
1,200,000
1,000,000
800,000
1,617,600
1,616,200
Baseline for Total Area
Stepbacks for Total Area
600,000
400,000
200,000
0
Figure 22: Baseline and Step-back Total Energy Consumption Comparison
24
This reduction of 1,400 kWh/year (<0.001% ) over the entire building is negligible. The step-backs change
illustrates well the purpose of this study. Despite being conceived based on logical theory, testing of the
step-backs demonstrates that they in fact do not deliver any significant improvement to the city’s
performance, at least not in terms of energy consumption.
6.2.4
Total Sunlight Hours
Another factor that the step-backs influence is sunlight to the street.
Figure 23 and Figure 24 demonstrate how stepping back the façade on just the top sixth and seventh
floors can make a considerable difference to the amount of sunlight that reaches the street. This factor is
important for pedestrian comfort and has been requested by the Christchurch people. The ‘ total sunlight
hour’ maps below for east-to-west oriented streets show that an additional 236 hours (30%) of direct
sunlight can be realised through step-backs over the year (out of a possible 4,380 total sunlight hours).
Most of this improvement would be during summer months (as the angle of the winter sun would not
reach the ground level over a seven storey building in winter).
North-to-south oriented streets experienced an improvement of 6% (738 up to 778 hours) all of which
occurred at the northern most edge of the analysis grid, meaning changes were very localised and largely
unhelpful.
Figure 23: Total Baseline Sunlight Hours
Figure 24: Total Sunlight Hours with Stepbacks
In the following set of diagrams (Figure 25 to Figure 34) the images on the left show a plan view of the
grid used for the baseline buildings with no step-back of the upper floors. The images on the right are with
the step-backs in place.
Comparing Figure 25 and Figure 26, the average annual hours of sunshine does change – there are more
red grid squares, or sunshine hours, in Figure 26 where step-backs are modelled, than in Figure 25 – the
baseline seven storey building. However, if only the winter sunshine hours are analysed, there is no
25
difference between the baseline model (Figure 27) and step-backs (Figure 28). Finally, if only summer
o
sunshine hours are analysed (Figure 29 and Figure 30) it is immediately obvious that the 45 upper level
step-backs do allow more summer sunshine hours. The major benefit in east-west streets of the stepbacks shown in Figure 30 is experienced in summer. There is no apparent improvement in street level
sunshine in winter as a result of the proposed step-backs.
It seems that most of the improvement is as a result of the marked improvement in summer sun
availability, not a year-round improvement.
Figure 25: Average Annual Sunlight
Hours, Seven Storey Baseline Model
Figure 26: Average Annual Sunlight
Hours, Seven Storey WITH Step-backs
Figure 27: Average Winter Sunlight Hours,
Seven Storey Baseline Model
Figure 28: Average Winter Sunlight Hours,
Seven Storey WITH Step-backs
Figure 29: Average Summer Sunlight
Hours, Seven Storey Baseline Model
Figure 30: Average Summer Sunlight
Hours, Seven Storey WITH Step-backs
26
The analysis looked at buildings that were four storeys as well as the proposed maximum seven storey
limit. As shown in Figure 31 to Figure 34 the step-backs of levels three and four do have an effect across
the whole year, though this change is still more obvious during the summer months. Comparing the fourth
storey and the seventh storey results, the common sense notion that the lower city would have sunnier
streets in winter is obvious.
Figure 31: Average Winter Sunlight Hours,
Four Storey Baseline Model
Figure 32: Average Winter Sunlight Hours,
Four Storey WITH Step-backs
Figure 33: Average Summer Sunlight Hours,
Four Storey Baseline Model
Figure 34: Average Summer Sunlight Hours,
Four Storey WITH Step-backs
6.3
CCP Model: Lanes and Alleyways
6.3.1
Daylight Autonomy
Daylight analyses were carried out at mid-height on the east-facing perimeter zone (cell E4). This location
was selected as it gave an average situation overview of the daylight down each of the 4m wide and 10m
wide north/south lanes. East and west oriented cells perform equally. Figure 35 display the level of DA
that could be expected in each of the lanes.
At 4m wide, the first lane model delivers very poor daylight to adjacent internal spaces, averaging only
9%, with the majority of the space not reaching adequate illuminance levels at all during the year.
Therefore the 4m wide lane proved ineffective for daylighting. The 10m wide lane, however, provides
considerably more daylight and deeper into the space. Here almost half of the space (44%) is sufficiently
lit to 320 Lux throughout the year. Although still low, this test cell demonstrates that a 10m wide lane can
provide useful daylight to adjacent spaces.
27
Figure 35: Daylight Autonomy Model of Cell E4 with
4m Lane Adjacent
6.3.2
Figure 36: Daylight Autonomy Model of Cell
E4 with 10m Lane Adjacent
Total Daylight Hours
Aligned with daylighting within buildings, is sunlight to ground level in the lanes. The 4m lane is expectedly
very dark with an average of only 93 hours of direct sunlight per year over the lane. The 10m wide lane,
as in the test cells, is subject to better sunlight with an average of 348 sunlight hours per year (out of
4,380 possible sunlight hours).
Thermal Comfort
At the fourth level this zone benefits from thermal ‘buffer zones’ above and below, stabilising temperatures
and minimising heat loss. Additionally, as the narrow urban canyons created by the lanes provide little
avenue for direct sunlight onto these façades, solar gains are limited. Figure 37 demonstrates how both
4m and 10m wide lanes would result in passively comfortable spaces in adjoining perimeter zones for
around 80% and 93% of the year respectively.
Less than 18
10m lane E4
Within Comfort Band
More than 25
80%
20%
Situation
6.3.3
4m lane E4
93%
0%
20%
40%
7%
60%
80%
100%
Percentage of Occupied Year
o
Figure 37: Annual Passive Temperatures ( C) in Adjacent Zones for 4m and 10m Wide Lanes
28
Total Energy Consumption
Figure 38 shows how natural temperatures in a zone adjacent to a 4m wide lane would be comfortable
more often than in a 10m wide lane scenario. This, however, does not include the effects of natural
ventilation. Figure 39 illustrates how implementing natural ventilation in perimeter zones can drastically
reduce overall energy consumption. The BRANZ BEES Interim Report ‘Building Design Optimisation’
(Cory, Munn and Gates) states that natural ventilation can reduce artificial cooling requirements by up to
90%. When this 90% reduction value is applied to the two lanes scenarios, the 10m lane perimeter zones
actually decrease further than the 4m wide zones, due to the higher frequency of overheating in the 10m
lane. This natural ventilation (Nat. Vent.) effect can be seen as the red ‘cooling’ component of Figure 38,
for each of the lane scenarios.
60,000
Energy Consumption (kWh/yr)
6.3.4
50,000
lighting
40,000
heating
30,000
cooling
20,000
10,000
0
4m
4m Nat. Vent.
10m
10m Nat. Vent.
Lane Type
Figure 38: Energy End-Use Component Breakdown in Perimeter Zones Adjacent to 4m and 10m
wide Lanes
Figure 39 illustrates how with natural ventilation and intelligent artificial lighting (providing only enough
light to supplement natural daylight to the required illuminance level) energy consumption can be
drastically reduced. Here zones adjoining 4m wide lanes benefit mainly from natural ventilation, but the
10m wide lane model benefits from daylighting as well. Compared to the baseline square metre energy
2
2
rate of 76 kWh/m /year, the 4m wide lane reduces energy to 67 kWh/m /year (12% reduction) and the
2
10m wide model down even further to 63 kWh/m /year (17% reduction).
29
80
1,400,000
70
1,200,000
60
1,000,000
50
800,000
40
600,000
30
400,000
20
200,000
10
0
0
Baseline Core
with Zones Adjacent to 4m
Lane
with Zones Adjacent to
10m Lane
Zone
Figure 39: Baseline 4m Lane and 10m Lane Comparison of Overall Energy Consumption
30
Square Metre Consumption (kWh/m2/year)
Total Energy Consumption (kWh/year)
1,600,000
6.4
CCP Model: Internal Courtyards
6.4.1
Daylight
Autonomy
As with the lane analysis,
the effects of courtyards
were assessed on the
fourth level.
Test cells were situated
on each ‘internal’ façade
facing the courtyard to
represent
the
new
internal perimeter zones
created
by
the
courtyard’s
insertion.
Figure 40 displays DA
results for each of the
north,
south
and
east/west
(considered
equal) facing cells.
As is evident just by
looking at the colour
rendering of these maps,
all four cells experience
very high DA. In fact, the
lowest reading at any one
point across all cells is
54%, meaning that all
artificial lighting can be
turned completely off for
over half of the occupied
year.
Even more impressive,
average DA across all
Figure 40: Daylight Autonomy Mapping of Level 4 Perimeter Zones
four cells is over 80%,
facing Courtyards
meaning the majority of
each cell’s floor area is
sufficiently lit for over 80% of the occupied year. Such DA performances are very high and can effectuate
significant energy savings through reduced artificial lighting needs. Levels above this fourth level will
experience equally or even more impressive daylighting conditions, but levels closer to ground will not
benefit so prosperously.
6.4.2
Thermal Comfort
Passive temperatures reflect the high level of solar access to level four perimeter zones seen in the
daylight analysis. Figure 41 portrays mostly comfortable temperatures in all courtyard adjoining scenarios
but with definite overheating problems. The north-facing cell, modelled here without the shading, is not
surprisingly the hottest with almost half of the occupied year experiencing temperatures above 25oC. This
would readily be controlled with appropriate shading (Cory, Munn and Gates, Building Energy End-use
Study (BEES) Year 5 Interim Report: Building Design Optimisation) and the natural ventilation that the
31
courtyard makes feasible. East and west-oriented cells are more often comfortable at only 30%
overheated; and south-facing cells manage to exceed comfortable temperatures for 19% of the occupied
year, demonstrating that the heat gains from people and equipment inside the building are a significant
contributor to the temperatures experienced indoors.
Baseline core passive temperatures were included in the graph to demonstrate a comparison between
central core temperatures and new inner perimeter zone temperatures. This shows that the baseline core
actually performs particularly well in terms of thermal comfort when compared to courtyard-facing cells,
especially the north-oriented cell. However, the issue with the core zone is that 20% overheating must be
cooled by purely artificial measures, whereas perimeter zones (even the north-facing zone) require littleto-no artificial cooling as they have access to natural ventilation.
Less than 18
East/West
Facing
Within Comfort Band
More than 25
70%
South
Facing
30%
19%
Zone
81%
North
Facing
52%
Baseline
Core
48%
80%
0%
20%
20%
40%
60%
Percentage of Occupied Year
80%
100%
Figure 41: Passive Temperatures in Level 4 Perimeter Cells facing Courtyards
6.4.3
Total Energy Consumption
The square metre energy consumption rates for each courtyard-facing cell in Figure 42 illustrate the
natural ventilation point made in the previous thermal comfort analysis section. Although the north -facing
zone was passively the hottest of the four presented scenarios, it was also the least energy intensive. Due
to natural ventilation reducing cooling requirements by 90%, and ample daylighting, the north-facing
2
2
perimeter zone square metre consumption was diminished to just 20 kWh/m /year (from 76 kWh/m /year
2
baseline core). South and east/west-facing cells were nearly as efficient at 25 and 33 kWh/m /year
respectively. A table of energy consumption values for each zone tested in this study can be found in
Appendix E.
Detailed studies would be required for each individual building designed to this open ‘courtyard’ model.
The building form here is a caricature of how individual buildings might be arrayed around a city block to
create internal sheltered courtyards. The study has demonstrated the benefit of narrow-plan buildings in
terms of energy and internal environmental quality; however it is not a design specification for individual
sites or city blocks. The basic principle is to ensure narrow plans to allow through flow of air for ventilation
32
and access to daylight. How buildings such as this are arrayed on a city block requires much broader
consideration of urban design principles and goals than this simple energy study.
Square Metre Consumption
(kWh/m2/year)
80
70
60
50
40
30
20
10
0
Baseline Core zone
North facing zone
South facing zone
East/west facing
zone
Figure 42: Level 4 Internal Perimeter Zones facing Courtyard Energy Comparison
Figure 42 and Figure 43 represent a study of solely the core zone affected by the insertion of one
courtyard. The data takes effect in the yellow and grey portions of Figure 43. This is where baseline core
has changed, either becoming internal perimeter zones or courtyard. The baseline core zone affected
2
2
(one-third of a full 100m x 200m block) was 4,128 m . This area was reduced to 2,280 m with the
courtyard, none of which is now classified as ‘core’ zone.
Figure 43: Dimensions and Affected Area due to Courtyards
Figure 42 portrays the total energy saving of 78% (average between the three new courtyard facing
perimeter zones) realised through the insertion of a courtyard. Importantly here is the relationship
between energy reduction and lost NLA, which is represented by the square metre energy rate which
33
accounts for ‘energy consumed’ against ‘area consuming’ for both models. Here, although the floor area
has been reduced by one third (34%), the overall energy use has been reduced by nearly two thirds
(61%) from the ‘baseline core’ figure to the ‘replaced by courtyard’. Clearly, the block is becoming more
energy efficient on a square meter basis.
6.4.4
Total Daylight Hours
Total sunlight hours at ground level in the courtyard are not as high in the main east-west running streets
but are on par with north-south running streets. Due to the 29m high building surrounding the courtyard,
direct sunlight struggles to penetrate to that depth. Figure 44 illustrates how the area immediately south of
the northern perimeter building is predominantly under shade, achieving only about 200 hours of sunlight
per annum (in summer months). Sunlight manages to penetrate further to the south of the courtyard for
longer periods of the year but only during midday hours. Across the entire courtyard area the average
total sunlight hours is only 570 hours per year.
Figure 44: Total Sunlight Hours for Ground Level
(of Seven Storeys) in Courtyard
Figure 45: Total Sunlight Hours for Ground
Level (of Four Storeys) in Courtyard
The effect of four storey (17m) instead of seven storey (29m) buildings can readily be understood from the
Figure 45. It shows on the same light scale as Figure 44 the daylight in rooms and the solar access to the
courtyard. The data in the picture is an exaggeration of reality. There is clearly more sun in a courtyard
formed by shorter buildings.
However, with four storey (17m tall) forms, ideal wind shelter proportions would suggest courtyards that
are more like 17m across, and therefore in the plan area shown there would be space for two smaller
courtyards with a central building spanning the courtyard shown from East to West. This would increase
the shading somewhat by comparison with that shown.
34
CONCLUSIONS AND RECOMMENDATIONS
The results from the modelling have shown a range of effects resulting from urban form features proposed
by the CCP. All three features – step-backs, lanes and courtyards – have have been shown to improve
daylighting and reduce energy consumption requirements in a standardised central city block/building.
Step-backs, due to the small area they influenced, made negligible improvments to overall performance
(although would have a greater effect in conjunction with courtyards).
4m wide lanes could not offer highly useful daylight, but the ability for new perimeter zones to now utilise
natural ventilation, which would make a considerable improvement to dominant cooling loads. 10m wide
lanes also created benefits from the ability for adjoining perimeter zones to ventilate naturally.
Additionally, zones benefit from the 10m wide lanes further than from the 4m wide lanes through the extra
daylight being introduced to the urban canyon via the extra 6m width.
Courtyards, however, made the most substantial improvement to the Baseline Model. Considerable
increases in daylight levels and ability to naturally (cross) ventilate the entire building resulted in an
outstanding 61% energy reduction from the baseline.
1,600,000
80
1,400,000
70
1,200,000
60
1,000,000
50
800,000
40
600,000
30
400,000
20
200,000
10
0
0
Baseline
Stepbacks
4m Lanes (x2) 10m Lanes (x2) Courtyards (x3)
(with 2 lanes)
Urban Form Situation
Figure 46: Overall Energy Consumption for each Urban Form against Baseline Model
35
Square Metre Consumption (kWh/m2/year)
Figure 46 presents the overall effectiveness of each CCP form feature against the baseline passive
performance. This graph clearly shows the benefit courtyards, and lanes to an extent, have on passive
performance.
Total Energy Consumption (kWh/year)
7.
Figure 46 is very useful in gauging what influence the lost NLA had on energy consumption. As was
reported, step-backs effectuate negligible improvement. Lanes had a bigger effect but the most signific ant
changes were seen through the insertion of courtyards. By breaking the large 200m x 100m
blocks/buildings into three sections with lanes, each sub-block/building containing an internal courtyard
(refer Figure 46) saw a substantial reduction in energy consumption. From the 1.54 million kWh/year
baseline model down to 519,000 kWh/year, this combination of form changes implements a reduction of
roughly two-thirds (65.6%). More tellingly and reliable however is the square metre rate.
2
Originally each square metre of floor area consumed 76 kWh/m /year; this could be minimised to just
2
40 kWh/m /year using lanes and courtyards. This is a reduction of almost one half (47.4%). The amount
2
of floor area or NLA lost to achieve these energy consumption reductions was 34.7% (20,000 m down to
2
13,056 m ), or roughly one-third. This is a very important comparison. If, by employing lanes and
courtyards, the energy used could be reduced by roughly one-half, yet only one-third of NLA is lost, then
the rate of savings outweighs the rate of losses, in terms of energy consumption per square meter. This is
a significant and substantial point for justifying the implementation of lanes and courtyards in central city
Christchurch.
This finding alone, while significant in terms of energy reduction on an urban scale, can be argued not to
offset in dollar ‘savings’ the costs in terms of lost rental. However, these figures should not be compared
to the “financial losses” through rent as the study has set up an exaggerated scenario for study: prior to
the earthquakes, the CBD of Christchurch was not built up to 100% of the whole city block to the full
height allowed under the then operational height limits. What the study has taken care to show is if that
porous and narrow plan buildings are more efficient than deep plan buildings. Thus, if the area built up
previously was to be carefully planned to allow good daylight and natural ventilation the resulting buildings
would be significantly lower in energy use per square metre.
There has not been time to examine the other aspects typically associated with well-designed naturally
ventilated and naturally lit buildings: improved employee health/satisfaction/productivity. This is not
necessarily in conflict with the property market preference for large floor plates intended to make an
organisation ‘more efficient’ because all its employees are housed on single, or a small number of floors.
Large floor plates can also provide all employees with access to natural light, to openable windows, to a
delightful and attractive environment. This study shows they will also be more energy efficient.
Figure 47 portrays the geometric potential for courtyards and lanes to be combined. It demonstrates the
floor area lost (in yellow) from the baseline model; and the zones that are now subject to daylig ht and
natural ventilation (shown in brown). If this were to be implemented, large energy savings could be
realised. The final data series in Figure 46, ‘courtyards with lanes’, illustrates the improvement that this
combination would make to energy consumption.
36
Figure 47: Model of Courtyard plus Lanes and Lost NLA, against Remaining NLA
Based on these findings it is clear that employing more open urban forms such as courtyards in
conjunction with lanes (and the seven storey building height limit) would be highly beneficial to passive
performance of Christchurch’s CBD. Not only will it improve daylight, sunlight, capacity for natural
ventilation and overall energy consumption, it would also create desirable working conditions across the
entirety of each building. This model would increase proximity to outdoor commodities for all central city
users and would contribute to the sunny, open and sustainable city the Christchurch people desire.
37
8.
WORKS CITED
Adler, D. (1999) Metric Handbook Planning and Desin Data. Auckland: Architectural Press.
Architecture NZ. (2012) "The Emergence of Christchurch." architectureNZ February 2012: 25-46.
Christchurch City Council. (2011a) Central City Plan Technical Appendices. Christchurch: Christchurch
City Council.
Christchurch City Council (2011b) Draft Central City Plan Volume 2 - Regulatory Framework.
Christchurch: Christchurch City Council.
Christchurch City Council. (2011c) "Christchurch Earthquakes: Central City- draft Central City Plan."
Christchurch
City
Council.
Assessed
May
2012
<http://resources.ccc.govt.nz/files/AllCommsStuff/(2)DraftCentralCityPlanVolume1.pdf>.
Mayor welcomes new Christchurch Central Development Unit. 18 April 2012. Assessed 18 April 2012
<http://www.ccc.govt.nz/thecouncil/newsmedia/mediareleases/2012/201204182.aspx>.
Cory, S., Gates, A. and Donn, M. (2011a) BEES Simulation Template Documentation. Research.
Wellington: Centre for Building Performance Research.
CBPR (2011b) The Creation of Generic Energy Simulation Models Which Represent Typical Commercial
Buildings and Their Calibration Against Real Energy Data. Wellington: CBPR.
Cory, S, Munn, A., Gates, A. and Donn, M. (2012) Building Energy End-use Study (BEES) Year 5 Interim
Report: Building Design Optimisation. Study Report 277/6. Judgeford: BRANZ.
Ecotect. (2012) "Daylighting: Design Strategies." Ecotect
<http://wiki.naturalfrequency.com/wiki/Daylight_Strategies>.
European Commission. (2012). What is adaptive
<http://www.buildup.eu/faq/european-countries/6642>.
Community
comfort?
2012.
Wiki.
17
June
2012
February
2012
Gates, A., Cory, S., and Donn, M. (2012). Building Energy End-use Study (BEES) Year 5 Interim Report:
Modelling Detail Analysis. BRANZ Study Report 277/5. Judgeford: BRANZ.
Givoni, Baruch. (1998) Climate Considerations in Building and Urban Design. New York: John Wiley and
Sons, 1998.
GlassTech, Metro. (2010) "Catalogue and Reference Guide 6th Edition." Metro GlassTech. June 2012
<http://www.metroglasstech.co.nz/catalogue/cata_default.aspx>.
Littlefair, Paul. (2011) Site Layout Planning for Daylight and Sunlight. Watford: Bre Press, 2011.
New Zealand Green Building Council. (2009) "Office 2009 Rating Tool." New Zealand Green Building
Council. June 2012 <http://www.nzgbc.org.nz/images/stories/downloads/public/GS%20tools/OFF.pdf>.
OPUS. (2011) "OPUS Building Structures PIN Workshop." Christchurch: OPUS, 28-29 November 2011.
Reinhart, CF and VRM LoVerso. (2010) "A rules of thumb-based design sequence for diffuse daylight."
Lighting Research and Technology 2010: 7-31.
Standards New Zealand. (2006) NZS1680: Recommended Maintained Illuminances. Wellington:
Standards New Zealand.
38
Tablada, A., Blocken, B., Carmeliet, J., De Troyer, F., Verschure, H. (2005) Geometry of Building's
Courtyards to Favour Natural Ventilation. Mixed.: Unknown, 2005.
Tonkin & Taylor Ltd. (2011) Christchurch Central City Geological Interpretative Report. Christchurch:
Tonkin & Taylor Ltd.
van Esch, M., Looman, R. and de Bruin-Hordijk, G. (2012) "The effects of urban and building design
parameters on solar access to the urban canyon and the potential for direct passive solar heating
strategies." Energy and Buildings 2012: 189-200.
39
APPENDIX A: WINDOW-TO-WALL
(WWR) CALCULATIONS
RATIO
To determine the minimum WWR for external windows to achieve suitable daylighting, Reinhart and
LoVerso (2011) have devised the following calculation:
(1)
Where:
DF = Daylight Factor
An average Daylight Factor target of 5% should be targeted according to
Reinhart and LoVerso (). DF of 5% is also prescribed in the ‘British Standard 8206-2: Code of Practice for
Daylighting’ as a minimum for a well day-lit space (Littlefair).
= Visible Transmittance
Visible Transmittance will be 0.8 (80%) based on a standard value for
a high performance, clear tint, double glazed window (GlassTech).
= Visible Sky Angle
Visible Sky Angle needs to be calculated (refer Appendix B) for each of the
three levels (G, 4 and 7) being tested as they will each be subject to different Visible Sky Angles (refer
Figure 48).
Figure 48: Visible Sky Angles (VSAs) at Mid-Height of each Subject Level
40
Ground floor WWR calculation:
(2)
According to Reinhart and LoVero’s (2011) calculation, the ground floor WWR needs to equal 2.3 or
greater. This indicates that a window of area 2.3 times greater than the available wall area is required to
provide adequate daylighting to the ground floor space. This is not possible.
Fourth floor WWR calculation:
(3)
The fourth floor WWR is also too high to achieve, at 1.3 or greater. This indicates that a 5% average DF
target is too high even in a seven storey height limit urban environment.
Seventh floor WWR calculation:
(4)
As expected, the seventh floor has a much lower minimum WWR of 0.76, which is achievable and within
Reinhart and LoVero’s 80% threshold- “only zones with a minimum WWR below 80% can be realistically
day-lit.” They then state that zones with a minimum WWR of higher than 0.8 (as ground and fourth floors
are here) should be reconsidered.
To determine a more realistic WWR the GreenStar New Zealand Office 2009 tool can be used. The
Indoor Environment Quality ‘Daylight’ credit requires (for maximum points) a DF of only 2.5% over 90% of
the subject area (New Zealand Green Building Council) rather than the more stringent 5% British
Standard. Assuming an average DF of 2.5%, Ground floor WWR would equate to 1.2, which is still larger
than possible. However, it would also determine a minimum WWR of 0.67 for the fourth floor; and 0.38 for
the seventh floor.
Ground floor spaces are shown to require a large window-to-wall ratio to maximise daylighting capacity in
a low potential daylighting situation. Reinhart and LoVerso () state that “a WWR of 84% corresponds to a
‘fully glazed façade’ i.e. a rough façade opening of 100%.” The CCP describes a preference for
‘interactive frontages’ on ground floor levels within the CBD to promote marketability in public places
(Christchurch City Council) High WWRs contribute to the ‘interactive frontage’ concept, so will provide
benefit to both daylighting and ‘distinctive city’ goals. Hence the 0.8 (rounded from 84%) WWR will be
used in Ground floor situations in this study.
Both the Fourth and seventh levels can be sufficiently daylit with WWR’s of 0.67 and 0.38 respectively.
Typical inner city building façades are uniform across their entire height (with the exception of the Ground
floor). This would suggest WWRs are equal for each level. In imitating this façade type, an average val ue
of 0.5 (rounded from 0.525) from the two calculated minimum WWR figures will be used for both fourth
and seventh levels.
Based on the above calculations and GreenStar New Zealand target DF levels, the Ground level WWR
will be 0.8 and fourth/seventh levels will be a WWR of 0.5
41
APPENDIX B: VISIBLE SKY ANGLE (VSA)
CALCULATIONS
B1 – Ground Floor
o
To find x :
Adjacent = 18m
Hypotenuse = 26.5m
Therefore x = 55.8
o
o
o
Visible Sky Angle = 90 – (55.8+10) [10 angle from the vertical allowed for window rebate into façade]
Ground floor VSA = 24
o
B2 – Fourth Floor
o
To find x :
Adjacent = 18m
Hypotenuse = 14m
Therefore x = 37.9
o
o
o
Visible Sky Angle = 90 – (57.9+10) [10 angle from the vertical allowed for window rebate into façade]
Ground floor VSA = 42
o
B3 – Seventh Floor
o
To find x :
Adjacent = 18m
Hypotenuse = 2m
Therefore x = 6.34
o
o
o
Visible Sky Angle = 90 – (6.34+10) [10 angle from the vertical allowed for window rebate into façade]
Ground floor VSA = 74
o
42
APPENDIX C: MODELLING AND SIMULATION
PROCESS
C1 – Baseline Geometry for Daylighting Analysis
Following is an outline of the process used to create the Baseline Model geometry for the daylighting
analysis only. Refer Figure 9 for visual description of the daylighting Baseline Model.
1) Central city grid (3 x 3 blocks) is laid out. Blocks are 100m in the north-south direction; and 200m in
the east–west direction. Blocks are separated by 18m wide streets in all situations.
2) All nine city blocks are extruded to the predefined height of 29m. Each block consists of a single
cuboid, which represents all individual buildings in a single entity.
3) The central block of the nine is the ‘subject block’ within which all testing will take place. All
outer/surrounding blocks are employed as shading and reflectance objects to imitate a real urban
environment.
4) On all façades of the subject block, and façades opposite subject block, each level is outlined.
Ground level is 5m high with all other/upper levels being 4m high each.
5) Based on patterns seen in Architecture NZ magazine (Architecture NZ) levels G, 2, 4 and 6 will be
glazing; and levels 1, 3 and 5 will be concrete. This is done to imitate typical surface reflectance of
façades within a central city setting.
6) ‘Test cells’ are applied at the horizontal centre of each façade (north, south, east and west), at levels
G, 4 and 7 (bottom, middle and top heights). Test cells are 7m deep (refer Section 4.2) by 7m wide
(square floor area).
7) A clear, double-glazed window is inserted into the façade sharing wall of the test cell. The window
size is the window-to-wall ratio (WWR) as defined in Appendix A.
The complete geometry is now exported to Ecotect where daylight analysis can be performed.
C2 – Baseline Daylight in Buildings Analysis in Ecotect/Daysim
Daylight Autonomy (DA) has been determined as the most appropriate measure for daylight to buildings
for this study. The following process outlines how DA values were calculated for test cells in the Baseline
Model.
1)
2)
3)
4)
Baseline Model geometry imported into Ectotect; and Christchurch *.epw weather file based on
National Institute of Water and Atmospheric research (NIWA) measured data attached.
Analysis grid of 100 data points (10 wide x 10 deep) setup in each test cell (one at a time) at
predefined working plane height of 0.7m above floor level.
Model exported to Daysim for simulation. Import process defines: Intermediate (mid-season) sky;
occupied hours of 8am-5pm; and DA minimum of 320 Lux.
Daysim calculation data analysed in Daysim and exported back into Ecotect for illuminance maps
where required.
C3 – Baseline Sunlight to Street Analysis in Ecotect
Total sunlight hours have been determined as the most effective measure for sunlight available to the
street for this study. The following process outlines how total sunlight hours values were calculated for test
cells in the Baseline Model.
43
1)
2)
3)
4)
Baseline Model geometry imported into Ectotect; and Christchurch *.epw weather file based on
National Institute of Water and Atmospheric research (NIWA) measured data attached.
Analysis Grid of 100 data points (20 wide by 5 along street) setup over street at ground level in front
of subject façade.
Because total sunlight hours are a measure which considers only direct solar beam rays, this test
can be carried out in Ecotect (Ecotects limitation is that it does not consider internally reflected ray
factors). Measured across the entire year between the hours of 7am and 7pm (Christchurch City
Council). The total sunlight hours figure is out of an assumed 4,380 total sunlight hours based on the
12 hours per day, 365 days a year model.
Results are applied to the Ecotect total sunlight hours map relative to its urban context with average
figures calculated for basic quantification and comparisons.
C4 – Baseline Geometry for Thermal and Energy Analysis
Following is an outline of the process used to create the Baseline Model geometry for the thermal and
energy (refer Figure 10 consumption analysis only). Points of major difference to the daylighting model
are underlined for easy reference.
1)
2)
3)
4)
5)
6)
7)
Central city grid (3 x 3 blocks) is laid out. Blocks are 100m in the north-south direction; and 200m in
the east–west direction. Blocks are separated by 18m wide streets in all situations.
All nine city blocks are extruded as OpenStudio shading objects to the predefined height of 29m.
Each block consists of a single cuboid, which represents all individual buildings in a single entity.
The central block of the nine is the ‘subject block’ within which all testing will take place. All
outer/surrounding blocks are employed as shading and reflectance objects to imitate a real urban
environment.
On all façades of the subject block each level is outlined. Ground level is 5m high with all
other/upper levels being 4m high each. Reflectance of opposite façades is not required for thermal
and energy analysis as they are for lighting so is not applied.
‘Test cells’ are the BEES template (‘EnergyPlus object’) identified in Section 4.3. This OP5 template
consists of four ‘perimeter’ zones and one ‘core’ zone. One of these templates will be applied at
levels G, 4 and 7 (bottom, middle and top heights) and will represent the entire level. To replicate the
daylighting analysis test cells, the perimeter zones are 7m deep, but they cover the full length of the
façade.
A clear, double-glazed window is inserted into the façade sharing wall of the test cell. The window
size is the window-to-wall ratio (WWR) as defined in Appendix A.
The complete geometry is now exported to EnergyPlus where thermal comfort and energy
consumption analyses can be performed.
C5 – Baseline Thermal Performance in EnergyPlus Building
Analysis
o
‘Percentage Time within Comfort Band’ (temperature in degrees Celsius, C) has been determined as the
method of measuring thermal performance for this study. The following process outlines how thermal
comfort values were calculated for test cells in the Baseline Model.
1)
2)
3)
Baseline geometry opened in EnergyPlus. Christchurch ‘epw’ weather file (NIWA) attached and
global position located.
Correct materials applied to test cell walls, windows etc.
‘Ideal loads’ heating ventilation and air conditioning (HVAC) system applied to model. This method
o
ensures artificial HVAC is only used when temperatures rise or fall out of the predefined 18-25
comfort band.
44
4)
5)
The ‘output’ employed to deliver useful data for the ‘percentage time within comfort band’ thermal
performance measurable is ‘zone operative temperature’. This is an hourly temperature recording for
the occupied hours (8am-5pm weekdays)
‘Zone operative temperature’ figures are exported to MS Excel where they are compiled into
readable data sets and presented for analysis.
C6 – Baseline Energy Consumption in EnergyPlus Building
Analysis
Energy Consumption, measured in kWh has been determined as the method for measuring overall
passive performance in buildings. The following process outlines how energy consumption values were
calculated for test cells in the Baseline Model.
This measurable is simulated in the same ‘run’ as the thermal comfort measurable but with a different
output. ‘Energy end uses’ (for ‘interior lighting’, ‘heating’ and ‘cooling’ only) measures how much energy
was required to supplement natural lighting and temperatures to maintain comfort in the test cells. Energy
consumption figures are also exported to MS Excel for analysis and presentation.
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APPENDIX
D:
STEP-BACK
CONSUMPTION CALCULATIONS
ENERGY
D1 – Baseline Energy Consumption:
-
2
2
core zone 16,000 m at 76 kWh/m /year (according to simulations)= 1,216,000 kWh/year
2
2
east, west and south perimeter zones total 2,600 m at 112 kWh/m /year = 291,000kWh/year
2
2
subject north perimeter zone of 1,400 m at 79 kWh/m /year = 110,600 kWh/year
Totals 1,617,600 kWh/year
D2 – Step-back Energy Consumption
-
2
2
core zone 16,000 m at 76 kWh/m /year = 1,216,000 kWh/year
2
2
east, west and south perimeter zones total 2,600 m at 112 kWh/m /year = 291,000 kWh/year
2
2
subject north perimeter zone of 1,400 m at 78 kWh/m /year (average of levels G, 4 and 7) =
109,200 kWh/year
Total 1,616,200 kWh/year
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APPENDIX E: ENERGY CONSUMPTION RATES
Table 1: Energy Consumption Rates
Scenario
Scenario and Zone
Energy
per
2
(kWh/m /year)
Core
76
North
79
East/West
83
South
58
North
78 (33 with Nat. Vent.)
10m East/West
63
4m East/West
67
North Facing
20
South Facing
25
East/West Facing
33
Baseline
Step-backs
Ventilation Mode
Artificial Cooling
Lanes
Courtyards
Zone
Naturally Ventilated
Naturally Ventilated
NOTE: Energy figures did not include equipment loads, just cooling, heating and lighting. This was done
because passive form changes do not influence equipment loads. All testing and results are consistent
with this parameter.
47