Team 16

Task: Analyse the current state of the rooftop garden and make recommendations for the future : 

Task: Analyse the current state of the rooftop garden and make recommendations for the future Rooftop garden, a cool idea?

Aim of school rooftop garden : 

Aim of school rooftop garden Initial aim: to reduce temperature of classrooms below Also to: Provide natural insulation in the winter Absorb storm water, potentially lessening the need for complex and expensive drainage systems Improve air quality and reduce CO2 emissions Factors affecting effectiveness: Construction and size of building Location Depth of growing medium Type of plants

Current state : 

Current state Plants: Nimosa Basil Palm Avocado plant Tangerine plants Sage Kam quat Sun flowers Pac choy Umbrella plants Floor painted silver Creeping zennia Aloe vera Zukini Begonia Mari-golds Pumpkins Radishes

Problems with current state of rooftop garden : 

Problems with current state of rooftop garden Not effective in reducing temperature of classroom below Layout does not cover a large surface area Small containers allow water to evaporate quickly in hot weather No irrigation system, drains clogged by leaves under heavy rainfall Tires leach when raining, chemicals dissolved in vegetation is dangerous Environment around garden – hot air from air-conditioning

How does the rooftop garden lower temperature? : 

How does the rooftop garden lower temperature? Solar energy in solar radiation: visible and invisible light Some reflected back to space by clouds as it enters Earth’s atmosphere Remaining reaches Earth’s surface Clouds and air pollution block a portion of solar radiation Solar radiation reach rooftops, solar energy converted into heat energy Conducted to room below by vibrations of roof medium

Albedo of rooftop surfaces : 

Albedo of rooftop surfaces Solar radiation reflected so not absorbed and not converted into heat energy Albedo: surface reflectivity of sun’s radiation, percentage reflected by surface or body to incident amount on it Higher albedo, greater effect on lowering temperature Most traditional rooftops low albedo – concrete/asphalt/tar High albedo surfaces – sand, certain types of plants have greater effect on lowering temperature

Evapotranspiration : 

Evapotranspiration Transport of water into atmosphere through: soil evaporation transpiration in plants -heat energy is ‘used’ to convert moisture to water vapor therefore temperature of surrounding air is lowered

Experiment : 

Experiment Null hypothesis: The model with aluminium foil and plants will not have the greatest effect on reducing temperature. Experimental Hypothesis: The model with aluminium foil and plants will have the greatest effect on reducing temperature. Independent variable: top surface of the models (aluminium, soil, plants) Dependant variable: temperature of air in model Extraneous/confounding variables: Weather on the day UV index Relative Humidity Temperature Controlled variables: Materials of models (cardboard and bricks) Size of model Surface area of top of model covered by materials Period of the day temperature is recorded

Slide 10: 

Graph showing Relative Humidity and Temperature of Shatin on Day 1 of experiment Time period of experiment Graph showing Relative Humidity and Temperature of Shatin on Day 2 of experiment

Graph showing Wind speed of Shatin on Day 1 of experiment : 

Graph showing Wind speed of Shatin on Day 1 of experiment Graph showing Wind speed of Shatin on Day 1 of experiment Time period of experiment

Slide 12: 

Experiment: Method Apparatus: -bricks x 32 -cardboard x 4 -data logger -temperature probes x4 -potted plants x 16 -aluminium foil -timer 1) Set up one control model and three independent models with different materials covering top surface 2) Place a temperature probe in each model and connect to the data logger 3) Record temperature of air in models for a period of 2 hours from 1pm to 3pm under direct sunlight 4) Temperatures will be recorded at minute intervals and transferred onto a graph.

Slide 13: 

1 2 3 4 1. Control 2. Aluminium foil , plants and soil 3. Plants and soil 4. Aluminium foil

Slide 14: 

Results 9:30 10:00 10:30 11:00 11:30 12:00 12:30 1:00 Foil: most effective Foil and plants: least effective agree with null hypothesis reject hypothesis Temperature range: 33.49°C - 47.24°C (2 d.p.) Temperature range: 29.15°C – 35.98°C (2.d.p) Plants covered model second warmest –highest temperature of 45.7°C Foil and control very close, foil lowest Foil most effective Results show problems as results for control was not as expected

Slide 15: 

1:00 pm 1:30 pm 2:00 pm 2:30 pm 3:00 pm

How good is the actual garden? : 

How good is the actual garden? Currently: floor painted silver with plants on top Experiment show this combination is least effective in lowering temperature Which means current state of rooftop garden is at least effective Increasing albedo more effective than evapotranspiration in plants so: More surfaces with high albedo – reflective surfaces Consider only painting floor of roof silver Covering rooftop surface with sand (high albedo) Recommendations

How can the rooftop garden be improved? : 

How can the rooftop garden be improved? Other reasons for retaining rooftop garden: Community Green-visually pleasing Better air quality Raise awareness of environment to students Better plants with higher albedo: -Herbaceous plants -In combination with sand

Bibliography : 

Bibliography Hong Kong Observatory http://www.scientificamerican.com/article.cfm?id=how-exactly-does-light-tr http://www.uswaternews.com/archives/arcglobal/4worlmayx5.html http://marine.rutgers.edu/mrs/education/class/yuri/albedo.gif http://www.virtualherbarium.org/horticulture/SalePlants.php?Type=herbaceous

Next year’s question : 

Next year’s question Find out how the tires leach and whether they have an effect upon the soil and the plants Investigate the ratio between the use of plants and high albedo materials and how they affect temperature Invesitgate how the tires absorb heat and how this can be reduced