Study on Effect of Greenery in NUS Environment

BS5204 Climatology and Building Design

Aung Aung La Win, Htun Kyaw Thu,

Steve Kardinal Jusuf, To Syatia Negara, Wu Xuchao

Background

• Relationship between green distribution in cities and meteorological data (macro-level, through meteorological data and satellite imagery)

• Cooling effect of green areas (micro-level, through field measurement)

• Prediction of thermal benefits of green areas

Objectives

• To identify hot spot area in NUS environment

• To study the importance of large green areas for the microclimate of NUS environment.

• To study the energy savings of a building as the result of lowered ambient temperature and improved roof thermal properties.

Methodology

Real Data

Result Compilation

Study of Satellite Images Field Measurement

TAS Energy Simulation(Base Model and

Parametric Variation)

ENVI-met Simulation(Base Model and

Parametric Variation)

Prediction

Deliverables

• Temperature distribution of different locations in NUS mapped through field measurement.

• A good understanding of the effect of greenery on the ambient temperature.

• Energy implication of lowered ambient temperature and decreased RTTV.

NUS Environment Observation

ZONE - 4

ZONE - 1

ZONE - 2

ZONE - 3

http://www.nus.edu.sg/oed.

NUS Zoning Plan

Zone 1, 3 and 4 are the main facilities where the Faculties and their amenities(Residential hall, canteen) were built.

ZONE - 2

Covers approximately 50% of NUS’ area

Acts as climatic engine

It consists of large dense greenery area and learning support facilities, such as Library, University Cultural Centre and Sport & Recreation Centre.

The large green area in the zone 2 covers 23.5 hectares constituting 15% of the total NUS campus area

Ambient Temperature Condition

• lower than in the other areas, shading provided by the trees and

• Cooling effect due to evapotranspiration process.

Acting as “O2 generator”•colder ambient temperature which may be obtained by the other zones, •especially the building at the perimeter of zone 2.

On a broader picture, the green areas can be classified into three categories:

Dense green area

Less dense green area

Sparse green area

Classification of green areas

Dense Green Area in Zone 2

The trees can provide good shading to the environment due tocrown and average height 15-20 metersLeaf Area Index (LAI) of 6

Purple MillettiaMillettia atropurpureaLAI = 6

Pong PongCerbera odollamLAI = 6

Snake as part of the ecosystem View from Central Library Annexe (left) and View Along Kent Ridge Rd (Right)

Some types of tree in the dense green area

• It provides a different environment in the campus area. • It can act as a natural reserve.• Dense green zone provides habitat to some animals.

Less dense green area

Most of the greenery condition in NUS environment can be considered as less dense green area.

Trees plantation with a certain distance about 3-10 meters or just open grassland area. Car-park area seems to have an adequate greenery to provide shading

Sparse green area

Mostly concrete or pavements cover this area Less scope for the growth of plants and trees Plants are used mainly for aesthetic purposes

Prince George’s Park Residence

No space/soil to plant trees

Surrounded by high rise buildings making the outdoor condition very hot Shiny due to the reflectance of the building’s material.

Satellite Images &

Thermal Satellite Image

• Satellite image and Thermal satellite image of Singapore was superimposed and zoomed into the NUS campus level

• Analyzed to identify “hot” and “cool” spots in the campus area

Satellite Images & Thermal Satellite Image

Satellite Image of NUS Campus

Transparent Thermal Satellite Image Overlapping on Satellite Image of NUS Campus

Thermal Satellite Image of NUS Campus

• Mostly, reddish colour of thermal distributions are on and around the buildings.

• Car parks with sparse greenery area also create hot spots in thermal distribution.

• Most of buildings were designed with combination of pitched roof and flatted roof.

• There is a tremendous thermal distribution in reddish colour.

• This is mainly because of extensive use of concrete and other heat-absorbing surfaces, which decreases surface moisture available for evapotranspiration.

• Furthermore, more solar radiation is absorbed and reradiated because dry surfaces have higher absorptivity.

• Latent heat flux is very small compared with the sensible heat in these areas.

• At the sport area, the absence of plantation creates a large area of hot spot in tennis courts, which have a lack of evaporating surfaces.

• Less dense distribution of greenery area also reduces the value of Leaf Area Index (LAI), which plays very important role in ambient temperature of an environment.

• It puts more energy into sensible heat and less into latent heat.

• It also affects the environment nearby by reradiating the absorbed heat from the large area of concrete surfaces.

As expected, the reddish colour distribution is found in denser area of buildings,the greenish in plantation areas and the yellowish in between these area.

• It is believed that the evapotranspiration from plants and trees can reduce the ambient temperature of environment nearby.

• However, at the other side of PGP residence and King Edward VII Hall area are apparent by reddish colour in surface temperature as they are far away from plantation area.

• Around PGP area, the yellowish colour of surface temperature distribution is found on the clusters of PGP residence which is beside the dense area of plantation.

• Large greenery area is found along Kent Ridge Road and Prince George’s Park Road.

• Due to the shading provided by trees and the evapotranspiration process of the trees, the deep green colour distribution in surface temperature can be seen clearly at the central part of dense greenery area.

• The buildings surrounded by or at the perimeter of the dense greenery area have better thermal distribution than other buildings further away from it, as shown by the yellowish patches.

• Thus, it can also be concluded that a building near or surrounded by the dense greenery area has better ambient temperature than the one far from it.

Some areas can be improved by adding more trees or shrubs.

Near Techno Edge canteen

Scope for improvement

The Terrace Canteen

Field Measurement

Point of Measurement

Comparison of air temperature on a typical day (15th Sep.2005)

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ture

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egre

e C

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Water Tank

Acoustic Lab

Bioinformatics Centre

Medicine Carpark

Temasek Hall

Computer Centre

Sports Field

PGP Road

Engineering Auditorium

PGP Canteen

Time of the Day

• Maximum difference: 4.11 Degree C (12:10pm)• Difference at mid-night: 2.75 Degree C (11.50pm)• Time lag of peak temperature

Inter-relations between heat, temperature and buildings

• Separation of Daytime and Night-time Data

Daytime (7:00am-19:00pm)

Night-time (19:00pm-7:00am)

• Solar Radiation, Urban Heat Island

• Building types

Comparison of daytime temperature

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1.Wate

r Tan

k

2.Acc

ousti

cal L

ab

3.Bioi

nform

atics

Cen

tre

4.Med

ical C

arpa

rk

5.Tem

asek

Hall

6.Com

puter

Cen

tre

7.Sports

Field

8.PGP Roa

d

9.Engin

eerin

g Aud

itoriu

m

10.PGP C

antee

n

Locations

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pera

ture

(Deg

ree

C)

Minimum Average Maximum

• Average: 27.4-29.6 Degree C• Maximum: 31.1-34.4 Degree C • Location 3, what’s wrong?

Comparison of nighttime temperature

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1.Wate

r Tank

2.Accoustic

al Lab

3.Bioinform

atics

Centre

4.Medi

cal Carp

ark

5.Temase

k Hall

6.Compu

ter Cen

tre

7.Sports F

ield

8.PGP Road

9.Engineer

ing Aud

itoriu

m

10.PGP Cant

een

Locations

Tem

pera

ture

(Deg

ree

C)

Maximum Average Minimum

• Average: 25.6-27.4 Degree C

• Minimum: 21.3-22.9 Degree C

ENVI-met Simulation

ENVI-met Simulation – 4 conditionsA - Current Condition

C - Replacing Forest with Buildings

B - Removing All Greenery

D - Adding More Trees

Basic Settings

• Temperature: 303 K.

• Wind speed (at 10 m above ground): 1.6 m/s

• Wind direction: South to North

• RH: 84%

• Total simulation: 24 hours

ENVI-met Results – Day Time

A

B

C

D

A B C

D

A – Current Condition

B – Removing All Greenery

C – Replacing Forest With Buildings

D – Adding More Trees SECTION

ENVI-met Results – Night Time

SECTION

A – Current Condition

B – Removing All Greenery

C – Replacing Forest With Buildings

D – Adding More Trees

A

B

C

D

A B C

D

NUS Mean Temperature Difference in Various Conditions

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Without Greenery - Current Replace Forest with Buildings - Current Denser Greenery - Current

Effects of Greenery in NUS Environment

Findings from ENVI-met Simulation

• Importance of greenery to keep low ambient temperature in NUS– Removal of all greenery increases NUS mean temperature

by 0.45 degree Celcius– Adding more greenery decreases NUS mean temperature

by 0.2 degree Celcius

• Building density affects cooling effects of greenery– The higher the building density the less pronounced the

cooling effects– Replacing forest with buildings increases NUS mean

temperature by 0.2 degree Celcius

TAS Simulation

TAS Model

• Engineering Building (EA), 7 storey high and about 2000 m2 footprint area.

• First model is the cooling load due to the difference of ambient temperature condition in the different locations

• Second model is the cooling load due to application of different types of rooftop greenery

• In each model, there are two scenarios, without internal load and with internal load.

• Basic setting for both scenarios:– Air conditioning was on 08.00 AM – 22.00 PM (extended

office hour)– Temperature and RH were input using the field

measurement result on 15th September 2005– Thermostat setting:

• Temperature upper limit: 24 deg C & lower limit: 21 deg C• Humidity upper limit: 70% & lower limit: 60%

• In the first scenario, the internal heat load was omitted to get the energy savings by considering the ambient temperature heat load and different roof heat loads only.

• In the second scenario, some general assumptions were made in terms of internal load of the building, which are as follows:– Lighting gain 15 W/m2

– Occupant’s sensible heat and latent heat 15 W/m2

– Equipment sensible gain 20 W/m2

First model

Study of the difference in ambient temperature conditions in the different

locations

Scenario 1 - No Internal loadCOMPARISON OF COOLING LOAD ON TYPICAL DAY AMBIENT TEMPERATURE - CURRENT CONDITION

4,500.00

5,000.00

5,500.00

6,000.00

6,500.00

7,000.00

WATER TANK ACOUSTICAL LAB BIOINFORMATICS MEDICAL SCHOOLCAR PARK

TEMASEK HALLCAR PARK

COMPUTERCENTRE

SPORTS FIELD PGP RD AUDITORIUMENGINEERING

PGP CANTEEN

CO

OL

ING

LO

AD

(K

Wh

)

Scenario 2 - With Internal loadCOMPARISON OF COOLING LOAD ON TYPICAL DAY AMBIENT TEMPERATURE - CURRENT CONDITION

14,400.00

14,600.00

14,800.00

15,000.00

15,200.00

15,400.00

15,600.00

15,800.00

16,000.00

16,200.00

WATER TANK ACOUSTICAL LAB BIOINFORMATICS MEDICAL SCHOOLCAR PARK

TEMASEK HALLCAR PARK

COMPUTERCENTRE

SPORTS FIELD PGP RD AUDITORIUMENGINEERING

PGP CANTEEN

CO

OL

ING

LO

AD

(K

Wh

)

Second model

Application of different types of rooftop greenery

100% turfing – R = 0.84 m2K/W100% shrubs – R = 2.216 m2K/W 100% trees – R = 1.429 m2K/W

Scenario 1 - No Internal load (7th Fl Zone)

COMPARISON OF COOLING LOAD ON 7th FLOOR ZONE - 3 DIFFERENT ROOFTOP GREENERY WITH CURRENT CONDITION

700.00

900.00

1,100.00

1,300.00

1,500.00

1,700.00

1,900.00

2,100.00

WATER TANK ACOUSTICAL LAB BIOINFORMATICS MEDICAL SCHOOLCAR PARK

TEMASEK HALLCAR PARK

COMPUTERCENTRE

SPORTS FIELD PGP RD AUDITORIUMENGINEERING

PGP CANTEEN

CO

OL

ING

LO

AD

(K

Wh

)

Current Condition Applying 100% Turfing Applying 100% Shrubs Applying 100% Trees

Scenario 1 - No Internal load (Overall)COMPARISON OF OVERALL COOLING LOAD -

3 DIFFERENT ROOFTOP GREENERY WITH CURRENT CONDITION

4,000.00

4,500.00

5,000.00

5,500.00

6,000.00

6,500.00

7,000.00

WATER TANK ACOUSTICAL LAB BIOINFORMATICS MEDICAL SCHOOLCAR PARK

TEMASEK HALLCAR PARK

COMPUTERCENTRE

SPORTS FIELD PGP RD AUDITORIUMENGINEERING

PGP CANTEEN

CO

OL

ING

LO

AD

(K

Wh

)

Current Condition Applying 100% Turfing Applying 100% Shrubs Applying 100% Trees

Scenario 2 - With Internal load (7th Fl Zone)COMPARISON OF COOLING LOAD ON 7th FLOOR ZONE -

3 DIFFERENT ROOFTOP GREENERY WITH CURRENT CONDITION

1,600.00

1,800.00

2,000.00

2,200.00

2,400.00

2,600.00

2,800.00

3,000.00

3,200.00

3,400.00

WATER TANK ACOUSTICAL LAB BIOINFORMATICS MEDICAL SCHOOLCAR PARK

TEMASEK HALLCAR PARK

COMPUTERCENTRE

SPORTS FIELD PGP RD AUDITORIUMENGINEERING

PGP CANTEEN

CO

OL

ING

LO

AD

(K

Wh

)

Current Condition Applying 100% Turfing Applying 100% Shrubs Applying 100% Trees

Scenario 2 - With Internal load (Overall)COMPARISON OF OVERALL COOLING LOAD -

3 DIFFERENT ROOFTOP GREENERY WITH CURRENT CONDITION

12,500.00

13,000.00

13,500.00

14,000.00

14,500.00

15,000.00

15,500.00

16,000.00

WATER TANK ACOUSTICAL LAB BIOINFORMATICS MEDICAL SCHOOLCAR PARK

TEMASEK HALLCAR PARK

COMPUTERCENTRE

SPORTS FIELD PGP RD AUDITORIUMENGINEERING

PGP CANTEEN

CO

OL

ING

LO

AD

(K

Wh

)

Current Condition Applying 100% Turfing Applying 100% Shrubs Applying 100% Trees

Potential of Rooftop Garden in NUS building

Most of the NUS buildings were designed with combination of pitched roof and flatted roof.The flatted roofs were left unused

There are a lot of thermal benefits by transforming it into Rooftop Garden, Direct and Indirect effects.

Limitations and Constraints

• Limited numbers of HOBO meter for the representation of distribution greenery and buildings across the complex.

• ENVI-met simulation has maximum grid scale of 250 x 250 x 30 grids. The larger is the modelled environment, the smaller is the scale of the simulation model. NUS model has the scale 1 grid = 10.71 m.

• ENVI-met simulation on rooftop greenery to get the temperature difference as a result of indirect cooling effect is not possible due to time and hardware constraints as the simulation generally takes 10 times longer than that without rooftop greenery.

Conclusions

Thermal Satellite Image• Reddish colour of thermal distribution are on, around the buildings and in

car parks. The greenish colour appears in denser areas of plantation and the yellowish colour appears in between these areas.

• The buildings surrounded by or at the perimeter of the green area have better thermal distribution than other buildings apart from dense green area. It is apparent as a yellowish in colour.

• It can be concluded that a building near or surrounded by greenery has better ambient temperature than those far from the greenery.

Field Measurement• Maximum difference: 4.11 Degree C (12:10pm) & 2.75 Degree C

(11.50pm)• This result verifies the hypothesis that the heat accumulated in the day is

hard to dissipate during night-time due to large concentration of buildings and sparse plantation in PGP residence.

ENVI-met Simulation• Presence of dense greenery areas in NUS environment is very important

in keeping low ambient temperature.

• Cooling effects of greenery areas on surrounding environment is affected by building density. The higher is the building density the less pronounced become the cooling effects.

TAS Simulation• NUS buildings also have the potential for rooftop greenery application.

• Cooling load for the 7th floor zone has the potential reduction of 14.64-25.82% by applying turfing, of 29.96-53.67% by applying shrubs and of 31.73-56.78% by applying trees.

• Overall energy savings of cooling loads may reach 3.29-9.08% by applying turfing, 6.73-18.85% by applying shrubs and 7.16-20.01% by applying trees.

FURTHER RESEARCH

NUS Microclimatic Mapping

• Temperature profile

– More points of measurement

– Longer period of measurement

– ‘Impact zone’ of Kent Ridge dense greenery

• Wind profile– Wind flow & wind speed within the each zone

– Potential for cross & natural ventilation

• Potential of rooftop garden– Mapping the potential area (flat roof building)

– Trial project in a selected NUS building (climatic performance & energy saving)

• Potential of cool roof– Applicable for non-flat roof building

– Glare problem for the surrounding