Abstract

 

The goal of this research is to create a parametric prototype model which includes the most efficient combination of different typologies of vegetation and ground cover material to control the site’s thermal environment and adapt to the changing seasons. This dissertation is a design based project that compares the microclimate on the site before and after the parametric model is applied in order to study its effectiveness. The effectiveness of the model will be estimated by feel like temperature, as the model is built to create a physically comfortable outdoor environment for citizens. The research site is a park in a dense urban context in the subtropical climate of Neili District, Taoyuan City, Taiwan.

 

The development of the model will be based on a computational fluid dynamics (CFD) study. There are two sources of heat in thermal environments, shortwave radiation and longwave radiation. The energy from shortwave radiation mostly remains in the air, and longwave radiation is observed and released from the land and ocean. This CFD study includes analysis of how the different typology and layout of vegetation can cool the air temperature from shortwave radiation, as well as investigates the heat released as longwave radiation energy from different types of ground covering. This CFD study also includes the influence of wind features accompanying different layouts of vegetation, the influence of air temperature on the different specific heat capacity and thermal conductivity of various ground materials, the shade capacity of different types of vegetation, and the transpiration cooling effect of certain types of trees.

 

Introduction

 

This is a design-based research project located in Taoyuan City, Taiwan. Taoyuan is an industrial city located in northern Taiwan. Taiwan is an island located in eastern Asia that is placed from 21°53'48.5"N to 25°17'58.7"N latitude and 122°00'25.8"E to 120°02'06.1"E longitude. Taoyuan has a humid subtropical climate. The hottest month is July when there is a mean daily temperature of around 29.2°C, and the coldest month is January, when there is a mean daily temperature of around 15.6°C. Due to its high annual average humidity of 78.4%, its residents tend to sweat during summer time. People in Taiwan are normally able to adapt well to hot and humid weather. However, although the mean daily winter temperature is around 16°C, most people feel very cold during winter[7]. According to a local news report from the 18th of December 2014, 18 elderly people died as a result of myocardial infarction related to cold weather. On the 25th of January 2016, 60 people died for the same reason. Furthermore, Taiwan suffers from a number of typhoons each year. The impacts of typhoons not only include heavy rain and strong wind, but typhoons also bring foehn wind, which increases the air temperature rapidly and dramatically. For example, a foehn wind caused by a typhoon in Taoyuan in 2016 raised the air temperature to 38.7°C, which increased the number of people who suffered from hyperthermia by 53% compared to the same period in 2015. Aside from natural disasters, both rapid reductions to the greenbelt and increasing building project developments in the city contribute to the urban heat island (UHI) effect, which raises the mean daily air temperature by 3.17°C, making the summer even hotter. Due to local climate features and the UHI effect, it is essential to create an effective way to mitigate the outdoor thermal environment in the urban context.

 

Two key elements which could help in controlling the outdoor thermal environment have been mentioned in previous research: ground cover material, and vegetation typology and vegetation layouts. Ground cover material includes vegetation, waterbody and paving, and controls longwave radiation from the sun. Doulos, L’s research provides comprehensive data relating to the heat output performance of different types of paving and demonstrates that wise use of paving material could mitigate the air temperature. Mahmoud, A Indicate that environments near waterbodies and grasslands can be much cooler. Vegetation, such as in the form of trees, has great ability to control the microclimate, for example, by mitigating heat from shortwave radiation and changing wind velocity and direction. The effectiveness of the transpirational cooling effect by vegetation has been proved by Gromke, C[1]. More impacts of vegetation, such as the ‘reduction of the conductive and convective heat gain by lowering dry-bulb temperatures through evapotranspiration during summer’ and the ‘increase of latent cooling by adding moisture to the air through evapotranspiration’ (Dimoudi et al., 2003) in the urban environment have been indicated. Su, W and his associates show that using suitable types of materials, shade types or vegetation layouts can mitigate a hot environment.

 

However, there is a minimal amount of research concerning how to build a complete model for design purposes that integrates the elements mentioned above. Despite Dimoudi, A. describing simplified urban parameters for the use of vegetation which can be used irrespective of site context, their model does not include attention to vegetation layout, ground cover materials or waterbodies[2].

 

This research aims to create a parametric prototype model for landscape design use using Rhino and grasshopper. This prototype parametric model includes vegetation typology data, vegetation layouts, paving materials and some basic climate data. Once climate data has been input into the model, the program will automatically suggest suitable areas for trees, bush, paving, grassland and waterbodies, in order to help designers create a physically comfortable environment in a subtropical urban context.

 

The model is based on a computational fluid dynamics(CFD) study of how vegetation typologies and layouts can interact with different types of ground cover material that mitigate the thermal environment. The completed parametric prototype model is applied on site to demonstrate how it can help and bring benefit to the design process and the existing context of the site.

 

In terms of the software and equation settings for the CFD study, Envi-met is used as the main modelling software on which the tests are run. Envi-met includes equations like the Reynolds-averaged Navier–Stokes equations (RANS), which can help calculate turbulent. Envi-met can also generate a variety of heat indexes of ground cover material. Results will be used as input data to produce Physiologically Equivalent Temperature (PET) data, and data will be calculated by applying the RayMan equation. The PET data will be transferred into thermal perceptions classification (TPC) data to indicate what people really feel. Two sets of TPC data will be compared to show the original site thermal condition and the redesigned result.

 

The environment setting of the site consists of three main elements: the surrounding urban geometry, the local climatic features, and the existing materials on the site. The surrounding urban geometry consists of the shape and height of the nearby buildings, the road widths and locations, and the surface materials of the buildings. Climate data includes temperature, humidity, wind speed, wind direction, solar radiation and sunshine hours. Climate data were selected from the hottest and coldest days of 2016 according to the Central Weather Bureau of Taiwan. The existing materials at the site include the vegetation typology and its arrangement and the leaf AREA density. The test results of vegetation include evapotranspiration, transmission, albedo and permeability. The LAD data applies Mohd Fairuz Shahidan’s test result[9].  Finally, the heat index data of bricks, concrete and waterbodies are applied for the ground cover materials. The heat index contains the radiation reflection ability and the heat observe ability of each material.

 

Literature Review

 

The fact that vegetation has a strong influence on the microclimate has been proved by a number of Dimoudi et al.’s study in 2002 shows the ways that vegetation impacts the environment, including via the transmission effect, the evapotranspiration effect, the albedo effect and the permeability effect. This demonstrates that the impact of vegetation is strong and could influence the surrounding urban area [2]. The effectiveness of the cooling effect of trees was studied by Mohd Fairuz Shahidan et al. in Malaysia in 2004. They classified tree typologies by Leaf Area Index (LAI) and Leaf Area Density (LAD), with results showing that trees with higher densities had greater ability when it came to cooling effect. However, they also found that high density reduced the wind speed; with the LAD higher than 1.5, the reduction in the wind speed could exceed 63% [9].researches. A study by Gromke et al. in the Netherlands indicates that transpirational cooling by venue-trees can reduce the mean and maximum temperature by up to 0.43 °C and 1.6 °C respectively during a heat wave with wind speeds at 5.1 m s−1 at 10 m above ground [1]. A similar 2015 study by Bharathi Boppana and her associates has proved the effectiveness of the cooling effect of vegetation [3].

 

While vegetation has great cooling ability, the layout of vegetation matters too. A study by Weizhong Su and his associates in China in 2014 indicates that a dotted and circular pattern for the layout of trees has a greater mitigation effect on the thermal environment than other patterns, such as a circular pattern, radial pattern, wedge pattern and zonal pattern[8].

 

Doulos and his associates have tested 93 different paving materials to study the cooling effect of paving. The study shows that under the same test environment, the mean surface temperature of a smooth white surface marble was 29.7 degrees. In contrast, normal black asphalt was measured at over 46 degrees. This result indicates the importance of choosing materials in hot weather regions [14]. Furthermore, Tzu-Ping, L et al.’s research in 2006 shows that ‘The surface temperatures of the artificial pavements were 10 °C higher than those of the vegetation surface at noon during the summer’ (Tzu-Ping, L et al., 2016) [16]. Xiaoshan Yang and Lihua Zhao’s research shows that the temperature beneath a tree or near a waterbody or shrub is constantly lower than the mean air temperature during the daytime, with the temperature differing between 0.5°C and 1.5°C [11].

 

Interactions in the effects of paving, vegetation and waterbody can enhance the cooling effect and control the thermal environment. Dr. Ayman Hassaan and Ahmed Mahmoud measured a variety of environments with different combinations of these elements in a park located in Cairo, Egypt in 2011. Their study shows that more people were satisfied with the temperature near a waterbody, such as a fountain area, lake or cascade area [5]. A study by Dr. Limor Shashua-Bar et al. compared the heat index data of two different environment setups. The study showed that an environment with a tree shade and grassland was much cooler than artificial paving with shade provided by mesh [6]. A joint study between the Aristotle University of Thessaloniki and the Architectural Association Graduate School showed a similar result (Angeliki, C, Simos, Y, 2014)[13].

 

Numbers of researchers have indicated that while thermal environments can be controlled, people’s ability to adapt to different climates can be dramatically different. A study on tourism climate information undertaken by Tzu-Ping Lina and Andreas Matzarakisb in 2011 concerned how people react to the climate of south-east China and Taiwan. The study showed that people from a temperate region normally consider 4°C to be very cold, 23°C to be neutral and 35°C to be warm. In contrast, people from a (sub)tropical region normally consider 14°C to be very cold, 30°C to be neutral and 38°C to be warm [7]. This is a very important consideration in terms of creating a physically comfortable environment

 

Dissertation structure

 

Abstract

1.0 Introduction

Climate issue in Taiwan

Reason for doing this project in case of Taiwan

Short literature review

Introduction of the project

Research method

 

2.0 Research method

2.1 Software and settings

2.2 Characterising vegetation

2.3 Characterising ground cover materials

2.4 Characterising urban geometry and climate feature

2.5 RayMan model setting

 

3.0 Parametric studies

3.1 Existing situation simulation

3.2 Input vegetation typologies

3.3 Input ground cover materials

 

4.0 Result

4.1 Suitable urban context for apply vegetation cooling method

4.2 Vegetation typology and layout

4.3 Ground cover material and combination

4.4 PET comparison

 

5.0 Design process

5.1 Site issue

5.2 Design Solution

5.3 Design process

5.4 Applying parametric model

5.5 Design result

 

6.0Conclusion

 

Reference

 

[1] Gromke, C.C., Blocken, B.B., Janssen, W.W., Merema, B., Hooff, v., TAJ Twan and Timmermans, H.H. (2015) ‘CFD analysis of transpirational cooling by vegetation: case study for specific meteorological conditions during a heat wave in Arnhem, Netherlands.’ Building and Environment, (83) pp. 11-26.

 

[2] Dimoudi, A. and Nikolopoulou, M. (2003) ‘Vegetation in the urban environment: microclimatic analysis and benefits.’ Energy & Buildings, 35(1) pp. 69-76.

 

[3] Boppana, B. Liu, Y. Joo Poh, H. Roth, M. and Tiong Tan, S. (2015) Thermal stratification and vegetation effects on the urban micro-climate – a CFD case study. ICUC9 - 9th International Conference on Urban Climate jointly with 12th Symposium on the Urban Environment [Online] [Accessed on 5th February 2017] http://www.meteo.fr/icuc9/LongAbstracts/nomtm3-1-1721148_a.pdf

 

[4] Maerschalck, B. Maiheu, B. Janssen, S. and Vankerkom, J. (2010) CFD-modeling of complex plant-atmosphere interaction: direct and indirect effects on local turbulence. HARMO13 - 1-4 June 2010, Paris, France - 13th Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes [Online] [Accessed on 6th February 2017] http://www.harmo.org/Conferences/Proceedings/_Paris/publishedSections/H13-263-abst.pdf

 

[5] Mahmoud, A. H. A. (2011) ‘Analysis of the microclimatic and human comfort conditions in an urban park in hot and arid regions.’ Building and Environment, 46(12) PP. 2641-2656.

 

[6] Shashua‐Bar, L., Pearlmutter, D. and Erell, E. (2011) ‘The influence of trees and grass on outdoor thermal comfort in a hot‐arid environment.’ International Journal of Climatology, 31(10) pp. 1498-1506.

 

[7] Lin, T. and Matzarakis, A. (2011) ‘Tourism climate information based on human thermal perception in Taiwan and eastern china.’ Tourism Management, 32(3) pp. 492-500.

 

[8] Su, W., Zhang, Y., Yang, Y. and Ye, G. (2014) ‘Examining the Impact of Green space Patterns on Land Surface Temperature by Coupling LiDAR Data with a CFD Model.’ Sustainability, 6(10) pp. 6799-6814.

 

[9] Shahidan, M. (2015) ‘Potential of Individual and Cluster Tree Cooling Effect Performances Through Tree Canopy Density Model Evaluation in Improving Urban Microclimate.’ Curr World Environ, 10(2). pp. 398-413.

 

[10] Ambrosini, D., Galli, G., Mancini, B., Nardi, I. and Sfarra, S. (2014) ‘Evaluating Mitigation Effects of Urban Heat Islands in a Historical Small Center with the ENVI-Met® Climate Model.’ Sustainability, 6(10) pp. 7013-7029

 

[11] Yang, X. and Zhao, L. (2015) ‘Diurnal thermal behavior of pavements, vegetation, and water pond in a hot-humid city.’ Buildings, 6(1)

 

[12] Chang, C., Chang, S. and Li, M. (2007) ‘A preliminary study on the local cool-island intensity of Taipei city parks.’ Landscape and Urban Planning, 80(4) pp. 386-395.

 

[13] Chatzidimitriou, A. and Yannas, S. (2015) ‘Microclimate development in open urban spaces: The influence of form and materials.’ Energy & Buildings, 108 pp. 156-174.

 

[14] Doulos, L., Santamouris, M., and Livada, I. (2004) ‘Passive cooling of outdoor urban spaces. the role of materials.’ Solar Energy, 77(2) pp. 231-249.

 

[15] Lin, T., Matzarakis, A., and Hwang, R. (2010) ‘Shading effect on long-term outdoor thermal comfort.’ Building and Environment, 45(1) pp. 213-221.

 

[16] Lin, T., Ho, Y., and Huang, Y. (2007) ‘Seasonal effect of pavement on outdoor thermal environments in subtropical Taiwan.’ Building and Environment, 42(12) pp.  4124-4131.

 

Koralegedara, S. B., Lin, C., Sheng, Y., and Kuo, C. (2016) ‘Estimation of anthropogenic heat emissions in urban [17]taiwan and their spatial patterns.’ Environmental Pollution, 215 pp. 84-95.

 

[18] Fröhlich, D., & Matzarakis, A. (2013) ‘Modeling of changes in thermal bioclimate: Examples based on urban spaces in freiburg, germaany.’ Theoretical and Applied Climatology, 111(3) pp. 547-558