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System and Species Selection
Vertical Greening in a Subtropical City
LM Chu, PhD School of Life Sciences, CUHK Email: [email protected]
First International Conference on Green Walls Meeting the Challenge of a Sustainable Urban Future: The Contribution of Green Walls Staffordshire University, Stoke-on-Trent, UK 4-5 September 2014
Substrate-based
Major types of VGS according to planter position and orientation
Green façade Living wall
Near-wall planting Hanging Hydroponics
Hydrophilic bags
Wire
Vertical Angled Horizontal
1.1 Classification Vertical Greenery System (VGS)
Direct Indirect
Climbing
2
1. VERTICAL GREENING
Substrate-based
Direct Indirect
Major types of VGS according to planter position and orientation
Support type Carrier type
Near-wall planting Hanging Hydroponics
Hydrophilic bags
Wire
Vertical Angled Horizontal
Vertical Greenery System (VGS)
Climbing
3
1.1 Classification
Number of SCI publications (N=49) on vertical greening from 2000 to 2014 (June) classified by greenery systems and research topics.
1.3 Research on vertical greening
4
62% 13%
7%
4% 5%
5%
2% 2% Thermal behavior / MicroclimatesBuilding energyAir purificationCost-benefit analysis / Life-cycle analysisAcousticsSystem water usagePublic perceptionPlant growth performance
02468
10121416
Support-type systems
Carrier-type systems
Both systems
Unknown systems
2. FUNCTIONS AND BENEFITS 2.1 Why do we need vertical greening? Lack of greening space
5
Area of open spaces + parks
Mumbai 1.1 m2/person
Hong Kong 3.5 m2/person
Singapore 4.0 m2/person
New York 26.4 m2/person
London 31.7 m2/person
Increase green plot ratio
Horizontal planting vs Vertical planting
6
Indoor 36% Outdoor
64%
Proportion of outdoor & indoor VG projects in Hong Kong.
0102030405060708090
Number of VG projects in Hong Kong.
7
2. FUNCTIONS AND BENEFITS 2.1 Why do we need vertical greening? • Aesthetic appeal
• Urban greening (linking buildings and landscaping) • alleviate visual barrier in urban canyon • return nature to urban habitats
8
0
20
40
60
80
鵝掌柴
吊蘭
虎尾蘭
蚌花
黄金葛
腎蕨
天冬
紅掌/粉掌
灑金榕
椒草
Fre
quen
cy
Outdoor VGS
Sche
ffler
a sp
p.
Chlo
roph
ytum
co
mos
um
Sans
evie
ria sp
p.
Trad
esca
ntia
spat
hace
a 'C
ompa
cta'
Nep
hrol
epis
spp.
Epip
rem
num
pin
natu
m
Aspa
ragu
s den
siflo
rus
Anth
uriu
m
andr
aean
um
Codi
aeum
spp.
Pepe
rom
ia sp
p.
0
20
40
60
80
鵝掌柴
富貴竹/
竹蕉
黄金葛
袖珍椰子
灑金榕
吊蘭
椒草
虎尾蘭
印度橡膠榕
腎蕨
Fre
quen
cy Indoor VGS
Sche
ffler
a sp
p.
Chlo
roph
ytum
co
mos
um
Epi
prem
num
pin
natu
m
Codi
aeum
spp.
Sans
evie
ria sp
p.
Pepe
rom
ia sp
p.
Nep
hrol
epis
spp.
Drac
aena
spp.
Cham
aedo
rea
eleg
ans
Ficu
s ela
stic
a 'B
urgu
ndy’
Epi
prem
num
pin
natu
m
Epi
prem
num
pin
natu
m
Plant species most commonly used for outdoor & indoor VGS in Hong Kong. 9
Dracaena spp.
Epipremnum pinnatum
Chamaedorea elegans
Codiaeum variegatum
Indoor
Schefflera spp.
Outdoor
Schefflera spp.
Chlorophytum
comosum
Sansevieria spp.
Tradescantia spathacea 'Compacta'
Epipremnum pinnatum
Most commonly used plant species for outdoor & indoor VGS.
10
2. FUNCTIONS AND BENEFITS 2.1 Why do we need vertical greening? • Ecosystem services
• heat mitigation • dust removal • stormwater retention • noise reduction • biodiversity support
11 Buttercups, crocuses, strawberries & geraniums on the VG in Victoria, London.
VG in Edgware Road Tube Station, London.
3. RESEARCH ON VERTICAL GREENING 3.1 Heat reduction ability of planter-on-ground type VGS
13
Experimental setup Outdoor climber system on east-facing wall 13 species on planters and metal mesh Design and installation of modular planter
Average maximum temperature reduction ability of 13 vine species under different weather conditions.
14
0
1
2
3
4
Pyro
steg
ia v
enus
ta
Boug
ainv
illea
spec
tabi
lis
Qui
squa
lis in
dica
Pand
orea
jasm
inoi
des
Ure
chite
s lut
ea
Cler
oden
drum
thom
sona
e
Clito
ria te
rnat
ea
Loni
cera
japo
nica
Pass
iflor
a ed
ulis
Man
devi
lla ×
am
abili
s
Thun
berg
ia g
rand
iflor
a
Man
soa
allia
cea
Bauh
inia
gla
uca
Tem
pera
ture
redu
ctio
n (o C
) Clear sunny
Sunny intervals
Cloudy
Mean hourly temperature behind canopy for Bauhinia glauca (top) and Pyrostegia venusta (bottom).
15
20
25
30
35
40
45
22 24 26 28 30 01 03 05 07 09 11 13 15 17 19 21 23 25 27 29 31 02 04 06 08 10 12 14 16 18 20 22 24 26 28 30
Tem
pera
ture
(o C)
Control Bauhinia glauca
20
25
30
35
40
45
22 24 26 28 30 01 03 05 07 09 11 13 15 17 19 21 23 25 27 29 31 02 04 06 08 10 12 14 16 18 20 22 24 26 28 30
Tem
pera
ture
(o C)
Control Pyrostegia venusta
Jul Aug Sep
Jul Aug Sep
Diurnal temperature changes behind canopy.
Bauhinia glauca
Pyrostegia venusta
24
26
28
30
32
34
36
38
40
00:00 04:00 08:00 12:00 16:00 20:00 00:00
Tem
pera
ture
(o C)
24
26
28
30
32
34
36
38
40
00:00 04:00 08:00 12:00 16:00 20:00 00:00
Tem
pera
ture
(o C)
16
Pearson correlation between heat reduction behind canopy and canopy characteristics on clear sunny days.
Correlation coefficient
Leaf number 0.26 Leaf density (no./cm3) 0.04 Leaf angle (o) 0.04 Effective LAI 0.42 Leaf area (cm2) -0.10 Canopy thickness (cm) 0.62* Canopy coverage (%) 0.84** LAI 0.73** Leaf thickness (cm) 0.21 Leaf color (hue) 0.11 Leaf length to width ratio 0.10 PC 1 0.16 PC 2 0.79** PC 3 -0.07 PC 4 -0.23 PC 5 0.38 * p < 0.05; ** p < 0.01 17
Canopy characteristics PC1 PC2 PC3 PC4 PC5
Leaf number -0.79 0.54 0.27 0.02 -0.10
Leaf density (no./cm3) -0.82 0.34 0.37 0.18 -0.13
Leaf angle (o) -0.73 0.04 -0.44 0.01 0.43
Effective LAI 0.80 0.45 0.31 0.07 -0.19
Leaf area (cm2) 0.77 -0.41 -0.16 -0.33 0.11
Canopy thickness (cm) -0.06 0.82 -0.46 -0.07 0.11
Canopy coverage (%) 0.18 0.84 -0.35 -0.04 -0.14
LAI 0.56 0.73 0.10 -0.04 0.26
Leaf thickness (cm) 0.31 -0.14 0.55 -0.27 0.35
Leaf color (hue) -0.44 0.17 0.34 -0.67 -0.13
Leaf length:Leaf width 0.29 0.16 -0.18 -0.56 -0.53
Variance explained (%) 35 29 11 8 6
Major PCs and their attributes of canopy characteristics of the 13 climbing species.
18
• There were difference in thermal reduction performance between the various species studied.
• Pyrostegia venusta was significantly higher than Bauhinia glauca in their temperature reduction ability in the support-type vertical greening system.
• Thermal performance was significantly related to canopy attributes such as canopy thickness, canopy coverage & LAI.
• Denser, thicker and better-covered vegetation was better in terms of microclimate modification.
Summary
3.2 Heat reduction ability of modular VGS modular carrier system outdoor east-facing wall 2 species
Ophiopogon japonicus cv Nanus Nephrolepis exaltata
on modular panels
19 Experimental setup
On substrate surface (behind canopy)
Wall
Substrate panel
On wall surface (behind panel)
12 cm
Temperature sensor
42 cm
Modular panel
Ophiopogon japonicus Nephrolepis exaltata
Plant height (cm) 6.02 16.8 Canopy thickness (cm) 4.91 14.5 Canopy coverage (%) 55.0 71.2 LAI 0.63 1.10
Canopy characteristics of Ophiopogon japonicus cv Nanus & Nephrolepis exaltata on modular VGS.
20
Mean hourly temperature on the substrate surface for Ophiopogon japonicus cv Nanus (top) & Nephrolepis exaltata (bottom).
21
20
25
30
35
40
28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Tem
pera
ture
(o C) Control Liriope spicata
20
25
30
35
40
28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Tem
pera
ture
(o C)
Control Nephrolepis exaltata
Ophiopogon japonicus
Aug Sep
Aug Sep
22
24
26
28
30
32
34
36
00:00 04:00 08:00 12:00 16:00 20:00 00:00
Tem
pera
ture
(o C)
22
24
26
28
30
32
34
36
00:00 04:00 08:00 12:00 16:00 20:00 00:00
22
24
26
28
30
32
34
36
00:00 04:00 08:00 12:00 16:00 20:00 00:00
22
24
26
28
30
32
34
36
00:00 04:00 08:00 12:00 16:00 20:00 00:00
Tem
pera
ture
(o C)
Diurnal temperature changes behind canopy (on substrate surface) & panel (on wall surface).
Nep
hrol
epis
exal
tata
O
phio
pogo
n ja
poni
cus
Substrate surface Wall surface
22
Mean temperature reduction of Nephrolepis exaltata (blue) & Ophiopogon japonicus cv Nanus (red) under different weather conditions (* p<0.05).
23
24
• Nephrolepis exaltata had significantly higher temperature reduction ability than Ophiopogon japonicus cv Nanus in carrier-type VGS.
• This was attributed to its denser coverage & taller individuals.
• Nephrolepis exaltata reduced 1.5oC behind canopy while Ophiopogon japonicus cv Nanus was ineffective.
• Temperature reduction on the wall surface was negligible with or without vegetation.
• Species selection for carrier type vertical greening in maximizing temperature reduction efficiency would not be significant when there was thick substrate (thermal mass) with high in situ water content (thermal buffer).
Summary
3.3 Performance comparison between support-type and carrier-type VGS
• Species with best temperature reduction ability - Pyrostegia venusta & Nephrolepis exaltata
• Focused on wall surface temperature reduction which affects cooling energy loads & indoor living comfort
25
Temperature sensors
Air- canopy interface
Behind canopy
Wall surface
3 cm
10 cm 3 cm
Planting mesh
Air-canopy interface
Substrate surface
Wall surface
Substrate panel
12 cm 10 cm
20
22
24
26
28
30
32
34
36
00:00 06:00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 18:00 00:00
Tem
pera
ture
(o C)
Air-canopy interfaceBehind canopyWall surface
20
22
24
26
28
30
32
34
36
00:00 06:00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 06:00 12:00 18:00 00:00
Tem
pera
ture
(o C)
Air-canopy interfaceSubstrate surfaceWall surface
Diurnal temperature changes at different locations. 26
Nephrolepis exaltata
Pyrostegia venusta
Average daily maximum temperature of bare wall surface, ambient air & different locations of the support-type system & carrier-type system.
aOne-way ANOVA followed by Tukey HSD post-hoc test to determine any significant difference between mean daily maximum wall surface temperature
Daily maximum temperature (oC) a
Wall surface temperature reduction (oC)
Bare wall surface 35.2 a
Ambient air 31.9
Support system
Air-canopy interface 34.9
Air cavity 33.9
Wall surface 31.3 b 3.8
Modular system
Air-canopy interface 34.0
Substrate surface 32.4
Wall surface 28.8 c 6.4
27
Wall surface temperature under two types of VGS & a bare wall.
28
22
24
26
28
30
32
34
36
06:00 12:00 18:00 00:00 06:00
Tem
pera
ture
(o C)
Bare
Support-type
Carrier-type
29
• Support-type VGS was less effective than carrier system in heat reduction at the wall surface.
• There was a lag in heat transfer in the wall of carrier system, which resulted in slower cooling in late afternoon & higher temperature than bare wall after sunset.
• A higher continuous inflow of heat at nighttime would likely to cause excessive air-conditioning or discomfort to residents in hot summer nights.
• Although carrier-type vertical greenery system did better in heat reduction, it should be carefully selected for its installation in residential buildings.
Summary
Floor plan of experimental flats
Window opened for natural ventilation
Window sealed
Control (no VGS)
With VGS
Sensors
GW-VG1
2 flats on 4/F & 5/F at a construction site SW facing wall GW-VG1 with Peperomia claviformis summer 2013 – spring 2014 thermal performance of naturally ventilated flats with
& without GW-VG1
30 3D view of experimental flats
3.3 VGS on human thermal comfort
Sensors and measurements • temperature sensor (DS18B20 1-wire digital thermometer,
Dallas Semiconductor, USA) • air humidity sensor (HIH-4000-003, Honeywell Sensing and
Control, USA) • air velocity transducer (8455, Trust Science Innovation (TSI),
USA) • signal convertor (Ethernet 1-wire host adapters, Embedded
Data Systems, USA) • automatically logged in a computer every 30 min
radiant, air & surface temperatures; solar & infrared radiation; heat flux & wind speeds were measured
Predicted mean vote (PMV) index PMV based on heat balance principle & experimental data (thermal variables) collected Personal factors
metabolic rate of the subject clothing insulation
Environmental factors air temperature surrounding surfaces temperature (radiant
temperature) water vapor pressure relative air velocity
Predicted percentage of dissatisfied (PPD) index • PPD predicts the percentage of a large group
of people likely to feel ‘too warm’ or ‘too cool’ • ISO 7730 • Indoor
Description Numerical value* Very hot > +3 Hot +3 Warm +2 Slightly warm +1 Neutral 0 Slightly cool -1 Cool -2 Cold -3 Very cold < -3
PMV comfort scale (ASHRAE)
* Numerical value usually ranged between - 3 to + 3. Thermal neutrality when heat generated by human metabolism is allowed to dissipate to maintain thermal equilibrium/comfort.
2 indices to show indoor thermal comfort
-8
-6
-4
-2
0
2
4
6
8PM
V
0
20
40
60
80
100
PPD
With VG Control
Rainy Hot and hazy
Hot and sunny
Summer
Standing at rest (1.2 met) Clothing insulation (0.28) • Panties ; sleeveless shirt; short sleeve shirts;
short trousers; socks; thin soled shoes 33
Control With VGS
PMV exceeded +5 at around 12:00 to 16:00 under hot & sunny days in flats without VGS
PPD reached 100 for control; PPD was 60-70 with VGS
30% more people felt discomfort after 18:00
34
• VGS was effective in producing better indoor thermal comfort for residence under summer condition as suggested by the near neutral PMV.
• VGS gave lower PPD during daytime than bare wall. • There were more dissatisfaction (30% more people felt
discomfort) in flat with VGS after 18:00 under natural ventilation.
• VGS more recommended for commercial buildings where most activities were carried out in daytime.
Summary
Floor plan of experimental flats
Window sealed
Control (no VGS)
With VGS
PMV sensors
GW-VG1
3.4 Urban C footprint of a modular VGS same 2 flats as for 3.3 LCA (GaBi Software)
35 3D view of experimental flats
y = 0.1572x - 3.3072 R² = 0.5908 P < 0.001
0.0
0.4
0.8
1.2
1.6
2.0
23 24 25 26 27 28 29 30 31
Elec
trici
ty s
avin
g (k
Wh/
day)
Temperature (oC)
Regression between daily average temperature & energy saving of GW-VG1 in August and September 2013.
36
Cooling potential of VGS (8.22 m2) Estimated energy saving = 63 kWh/y
0%
20%
40%
60%
80%
100%
Glo
bal w
arm
ing
pote
ntia
l10
0 ye
ars
Aci
dific
atio
n po
tent
ial
Eutro
phic
atio
n po
tent
ial
Ozo
ne la
yer d
eple
tion
pote
ntia
l
Abi
otic
dep
letio
nel
emen
ts
Abi
otic
dep
letio
n fo
ssil
Fres
hwat
er a
quat
icec
otox
icity
pot
entia
l
Hum
an to
xici
ty p
oten
tial
Mar
ine
aqua
ticec
otox
icity
pot
entia
l
Phot
oche
mis
try. o
zone
crea
tion
pote
ntia
l
Terr
estri
c ec
otox
icity
pote
ntia
l
Materials Transportation Usage
Relative contribution of stages on the environmental burdens of VGS over a 50 year life span.
37
Impact category Impact indicator VG environmental burdens
Environmental impacts avoided by electricity saving
Payback period (y)
Marine aquatic ecotoxicity potential
kg DCB equivalent
15600 979 15.9
Abiotic depletion fossil MJ 1510 78.6 19.3 Global warming potential 100 years
kg CO2 equivalent
144 6.73 21.5
Human toxicity potential kg DCB equivalent
4.88 1.98 2.47
Acidification potential kg SO2 equivalent
0.25 0.04 6.84
Terrestrial ecotoxicity potential
kg DCB equivalent
0.24 0.01 24.0
Freshwater aquatic ecotoxicity potential
kg DCB equivalents
0.23 0.06 3.83
Eutrophication potential kg phosphate equivalent
0.04 4.46E-3 7.85
Photochemistry - ozone creation potential
kg ethene equivalent
0.03 3.16E-3 8.86
Payback period of VGS (per m2 basis) estimated using 11 environmental impact indicators in LCA.
38
Payback time (offset C debt) = 22 y
39
• VGS on wall could save as much as 16% of electricity consumption for air-conditioning in August and September (typical hot and wet summer months), which was about 63.8 kWh.
• According to LCA, the material manufacturing stage contributed to over 60% of all the environmental impact categories.
• Based on comparison between the environmental burdens & benefits for cooling (50-y building service life), environmental burdens of VGS on marine aquatic ecotoxicity potential, abiotic depletion of fossil fuels and global warming potential could be paid back in 22 years.
Summary
40
• Plant species choice is important for VGS with respect to growth & thermal performance, esp. for support system.
• Canopy features were major attributes to heat reduction. • Carrier VGS was capable of reducing heat flux through building
wall. Hence decreasing interior cooling energy consumption. • Carrier VGS gave generally better feeling of indoor satisfaction
especially under hot & sunny days as indicated by PMV & PPD indices. This resulted in better thermal comfort for occupants staying in rooms under summer condition.
• There was a lag in heat flux through the wall, which resulted in prolonged heat after sunset. This may increase cooling energy use for residential premises.
• The payback time could be long, but the benefits of the VGSs in C sequestration & energy saving should not be overlooked.
4. CONCLUSIONS
Checklist for successful VGS Purpose Aesthetics Ecosystem services Site Location (Outdoor/Indoor) Orientation Building height Climate Loading Scale System Type Irrigation Substrate Plant Growth habit/requirement Function/Purpose Pure/Mixed culture Maintenance Pest/Weed control Fertilizer Hardware repair Plant replacement
41
Bosco Verticale, Milan (2013) Clearpoint Residencies, Sri Lanka (2015)
Vegitecture Urban Greening for the Future?
Architecture for the Future?
42
VGS for Sustainable Built Environment?
ACKNOWLEDGEMENTS • Environment and Conservation Fund
• Everplant Technology Ltd
• GreenWalls Bioengineering (HK) Ltd
• Hong Kong Greenlink Kusters Co Ltd
• Strongly International Ltd
• Poying LAI (MPhil student & research assistant)
• Sharon CHAN (Research assistant)
• Lan PAN (PhD student)
43