green walls and austin high-rise residential: a strategy ......high-rise residential: a strategy to...

csdCenter for Sustainable Development

Green Walls and Austin High-Rise Residential: A Strategy to Increase

Urban VegetationRandall B Maddox

Werner LangInstructor

UTSoA - Seminar in Sustainable Architecture

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main picture of presentation

Green Walls and Austin High-Rise Residential: A Strategy to Increase Urban Vegetation

Randall B Maddox

Downtown Austin: Past, Present, and Future

According to a 2008 study conducted by Capitol Market Research, Austin was the fifth fastest growing city in the nation in 2007, with a popula-tion increase of 4.3 percent. The 1.65-square-mile downtown area (0.6 percent of total city land area) was home to approximately 4000 residents in year 2000, and 5987 residents as of 2008 (Figure 2). At that time there were 12 residential projects under construction, seven of which were condominium de-

velopments. The report noted the surprising fact that “even after these new apartments and condos are completed and occupied, the popula-tion of downtown Austin will still be less than it was in 1940,” when there were approximately 12,500 people.1

In 2005, Mayor Will Wynn and members of the Austin City Coun-cil established the goal of having 25,000 residents in downtown Austin within 10 years.2 Furthermore, in 2007, Endeavor Real Estate an-nounced its planned development of a 28-story condominium/hotel as part

Fig. 1 Green wall on the Consorcio headquarters, Concepcion, Chile.


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of the Domain development.3 The vision is for the Domain to become a “second downtown,”4 with 50 new buildings ranging in height from two to 26 stories.5

Clearly Austin’s future includes dra-matic and intentional densification, especially in its downtown core. If this development is going to be done sustainably, then UHI factors must be taken into account in building design. “Among all cooling mea-sures, urban vegetation is the most effective way to directly cool UHI, by providing shade and, indirectly, by plant evapotranspiration.”6 One very familiar way to do this is through the construction of green roofs. How-ever, in high-rise buildings such as the condominium and apartment tow-ers recently built in Austin, the roof represents a very small percentage of the building skin area. Another potential lies in the green wall, and it is this strategy we investigate in this section.

UHIE, Plants, and Green Wall Technology

What plants do

The effects of plants on UHIE are complex and interrelated. Two important actions that plants perform are the absorption of gaseous pollut-ants (including carbon dioxide) into their internal tissues, and the filter-ing out of airborne particles as air passes over leaves and stems and the particles settle onto their surfac-es. These particles are then washed off by rain.

For our purposes here, we are more concerned with a plant’s potential for shading and evapotranspiration (ETP), and the effects these have on UHIE and energy usage. Huang concluded from DOE-2.1C models of shading and ETP that increasing the current level of urban tree cover by 25% can save 40% of the annual cooling energy use of an average house in Sacramento, and 25%

in Sacramento and Lake Charles. Furthermore, by placing these trees to optimize shading benefits, the values jump to 50% for Sacramento and 33% for the other cities.7 Givoni reports that on hot sunny late after-noon days in Miami, “the average temperature of walls shaded by trees or by a combination of trees and shrubs was reduced by 13.5–15.5 deg-C. Climbing vines reduced the surface temperatures by 10–12 deg-C.” He also refers to a study on a double-width mobile home where the introduction of landscaping reduced a summer day’s air conditioning needs from an average of 5.56 kW to 2.28 kW. During peak load periods, the drop was more dramatic: 8.65 to 3.67 kW.8

The shading benefit of vegetation is more complex than merely block-ing solar radiation from a building façade. “Vegetative surfaces reduce long-wave heat gain to the house because their surface temperatures are low compared to hard surfaces such as sidewalks, asphalt, or bare ground.”9 Thus vegetation is more effective as a shading device than an inanimate object, much of whose heat would be dissipated simply by re-radiation.

Concerning evapotranspiration, plants “reduce conductive and convective heat gain by lower-ing dry-bulb temperatures through ETP.”10 Huang notes that, “from the point of view of energy conserva-tion, a tree can be regarded as a natural ‘evaporative cooler’ using up to 100 gallons [379 L] of water each day. This rate of ETP translates into a cooling potential of 230,000 kcal [267.4kWh] per day. This cooling effect is the primary cause for the 5 deg-C differences in peak noontime

Fig. 2 Resident population of downtown Austin, past and projected.

Green Walls and High-Rise Residentiall: A Strategy to Increase Urban Vegetation

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temperatures observed between for-ests and open terrain.”11 The beauty of this fact is revealed in studies that showed consistently over a 15-year period that ETP rates are more closely related to net solar radiation than to air temperature or relative hu-midity.12 Thus in a hot, humid climate like Austin, where manmade evapo-rative coolers are an ineffective technology, plants are still capable of lowering dry bulb temperatures through ETP, even in the presence of high moisture content.

It is helpful to note that these stud-ies reporting decreased demand for cooling are due both to the effects of shading and ETP. In particular, Huang notes that shading accounts for only 6–17% of the total savings in some of the studies, and for 10–35% in the other, shading studies. The remaining savings result from the lowered temperatures due to ETP.13

Green wall technology

One well known way to incorporate plants into building design is through a green roof. Another option is the green wall, where plants are inte-grated into the building façade. The technology of green façades is much newer and less well known than that for green roofs.14

Most of the research being done to advance green façade technology centers around two types of green walls. The first strategy uses climb-ers—plants that are rooted in the ground or in pots and encouraged to grow up a structure exterior to the building (Figure 3). To encourage the growth of climbers is hardly new technology, for ivy has been used as an exterior wall covering for centu-

ries. However, more technologically advanced practices will most likely involve holding the climber plants away from the building façade. This research was pioneered primarily in the German speaking countries.15

The second technology is com-monly called a living wall, where plants grow in containers attached to structural elements at the exterior wall (Figures 1 and 4). These plants may either be rooted in soil or grown hydroponically—that is, fed by nutri-ent solutions instead of being rooted in soil.16

Of course, a green façade need not be a complex or advanced technical design achievement in order to war-rant consideration. Indeed, in what follows, we will present thumbnail calculations on a hypothetical Austin high-rise residential tower, where

we presume nothing more than integrated planter boxes contain-ing native Texas shrubs circling the entire building façade on every floor. Conceptually this is no more com-plex than imagining that residents merely grow shrubs in planter boxes on their balconies. Our goal is not to discuss the design of a green wall so much as to speculate about its value in addressing UHIE.

What green walls do

As a general principle of urban land-scaping, “the effect of open areas of vegetation is generally reduced if the area lies lower than the land around it or if it is surrounded by walls or pe-ripheral vegetation—in these cases the barriers prevent cool air draining from the site to influence adjacent areas.”17 This is an argument for

Fig. 3 Climbers on a green wall of the Swiss Re building, Munich, by Officium Design Engineering.


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the use of vegetation on a vertical surface, for “solar energy heating the side of a building will generate more powerful convection currents than it will on a horizontal surface, which climbers—through their cooling effect and the creation of complex air flows—can minimize.”18 Conse-quently, the impact of green walls on urban heat islands is significantly more complex than that of mere shade trees, for the intent is to maxi-mize the shading effect and to exploit micro-climate changes created by ETP very close to the building skin. Furthermore, green walls also act as a layer of insulation, for they slow wind and can reduce conductive and infiltration heat gains.19

The value of these apparent benefits is hardly clear cut, however. In 1988, Hoyano conducted experiments with a vine sunscreen shielding a south-western facing veranda. Dishcloth gourd, a vertical vine, was installed in front of the veranda, and its ef-fects were compared to a similar unscreened veranda. The screen was effective as a shading device, significantly reducing insolation inside the veranda; however, the leaf temperature of the vine was higher than the ambient air. The air temper-ature inside the screened veranda was higher than the ambient air, but still lower than the air inside the unscreened veranda. Hoyano’s con-clusion is that the overall effect of a such a screen in a hot, humid climate might be negative, in that airflow through the contained space can be significantly restricted. However, he reports that the surface temperature of the exposed walls averaged 10 deg-C above the ambient air without the vine cover, while with the vine cover, it averaged 1 deg-C below it.20

Finally, in studies prior to 1991, it was not clear whether the interac-tions between the shading and insulation effects of a green wall were necessarily productive. In particular, it had “been demonstrated that the average external surface temperature of white walls, even in a very sunny climate, is lower by about 2 deg-C than the average ambient air temperature.... In such a case shading the wall by plants, which may also reduce its long-wave heat loss, may be counter produc-tive.”21 However, we must note that the white wall is a local effect, which merely reflects the heat from the building, possibly onto another build-ing façade, and still contributes to the overall UHIE. Givoni notes that “this interaction between the shading and the insulation effects has not been studied at all in previous investiga-tions.”22 The 1991 date of this com-

ment suggests further investigation into the more recent literature.

Austin wall temperature data

To gain a sense of the effect on temperature that shading and plant coverage can have on exterior walls, several sites in Austin were tested using a Raytek MX4 infrared thermometer. The study included eighteen segments of exterior walls in downtown Austin, each of which was tested twice on the same sunny August day. Every tested wall seg-ment contained two spots in close proximity, one exposed and another covered with vine growth. Materi-als included limestone, light colored stucco, brick (painted or unpainted), and concrete.

Depending on the time of day, the

Fig. 4 Modular living wall system by Elevated Landscape Technologies, Brantford, ON.


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orientation of the façade, and the possible presence of an overhead awning or eave, exposed surfaces might or might not have been re-ceiving direct solar radiation at the moment of testing. Figure 5 contains basic statistics derived from the collected data. To illustrate, of all wall surfaces where a fully exposed, insolated section lay in proximity to a section overgrown with vegetation, the average temperature difference between these two test points was 9.45 deg-C.

The process of data collection and analysis in this study revealed sev-eral difficulties in drawing any mean-ingful conclusions from the results. First, exposed surfaces that were not receiving direct solar radiation at the time of testing could vary widely in temperature, based on the amount of indirect radiation they were receiv-ing or perhaps whether they had received direct radiation earlier in the day. A second caveat applies to awning or eave shaded surfaces, for these shading devices were above the wall segment and did not shield it from indirect solar radiation or re-radiation from nearby surfaces.

These results do suggest, however, that plant covering is of value in reducing temperature, if for no other

reason than that it shades com-pletely and consistently throughout the entire day. Measurement of any meaningful refinements of the effects of plant coverings would clearly require much more controlled experi-ments than the one conducted here.

Case Studies

We now consider two case studies of green walls. The first is the Institute of Physics in Berlin-Adlershof, a proj-ect by Augustin and Frank completed in 2003. The second is a purely hypothetical case study, where we investigate the feasibility of a high-rise residential tower in Austin that includes a façade greening strategy.

Case study 1: Institute of Physics

The Institute of Physics houses offices and research for Humboldt University of Berlin. It incorporates a variety of sustainable technologies, including rainwater collection and management, green roof and fa-çades, and adiabatic cooling with the help of collected rainwater (Figures 6–10). The facility has no connec-tion to any rainwater sewer, but collects and stores rainwater in five cisterns located in two courtyards.23

Fig. 5 Statistics on ivy-covered walls in downtown Austin.

Fig. 6 Roof-to-cistern rainwater transfer system, Institute of Physics, Berlin.

Fig. 7 Part of the cistern system, Institute of Physics, Berlin.

Fig. 8 Wisteria climbers, Institute of Physics, Berlin.


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The design process included exten-sive modeling of these systems in order to maximize their expected effi-cacies. For the green walls, Wisteria sinensis proved to be the best choice as a climber that can grow from a planter under extreme conditions. Also, because wisteria is deciduous, winter sunlight penetrates directly into the interior. The explicit goals of the Institute’s green walls were pre-cisely those mentioned previously: 1) to climatize the building passively

through summer shading and winter insolation, and 2) to harness ETP to improve the microclimate inside and around the building.24

Preliminary calculations for potential evapotranspiration rates (PET) were compared to actual ETP rates by monitoring the plants’ water usage (Figure 11). Once the plants had grown to adequate size, Schmidt notes that, “compared to the PET the real ETP is extremely high.”25

(See Figure 12.) He reports: “In the summer months July until September the water consumption for the quite well developed Wisteria sinensis increased up to 420 liters per day for 56 planter boxes. This represents a cooling value of 280 kWh per day. The mean evapotranspiration between July and August 2005 for the south face of the building was between 5.4 and 11.3 millimeters per day, depending on which floor of the building the planters were located.

Fig. 9 Planters on the façade, Institute of Physics, Berlin.Fig. 10 Adiabatic cooling unit, Institute of Physics, Berlin.

Fig. 11 Devices for measuring potential evaporation of wisteria, Institute of Physics, Berlin.

Fig. 12 Green wall on the Consorcio headquarters, Concepcion, Chile.


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This rate of evapotranspiration rep-resents a mean cooling value of 157 kWh per day.”26

According to the National Renewable Energy Laboratory, an average June day in Austin provides a solar radia-tion potential of 5.5–6.0 kWh for a 1m2 photo-voltaic panel.27 Assuming a panel operates at 15 percent effi-ciency, a 1m2 panel can generate ap-proximately 0.863 kWh of energy on an average June day. Thus it would require approximately 325 m2 of PV panel to produce the equivalent 280 kWh of cooling value provided by the wisteria.

Case Study 2: A hypothetical high-rise residential tower in Austin

The express goal of this study of green walls is to make a case for the effectiveness, feasibility, and desirability of incorporating a green façade into a high-rise residential

tower in Austin. In what follows, we do not argue for either climbers or living wall technology, but instead assume that plants could, for ex-ample, simply be rooted in planter boxes along the building’s façade. Furthermore, given the number of variables relevant to a green wall’s performance and the complex inter-actions between them, it would be impossible to argue for any concrete energy savings or quantifiable impact on UHIE. Any such local impact on the UHI is beyond the scope of this investigation. Instead, we choose to describe a specific design strat-egy and convey the magnitude of its impact solely by comparing it to the presence of trees in the downtown Austin landscape. Thus we may develop a sense for a green wall’s impact on the entire urban system.

Considerations

A first consideration in the design of a green wall is the NSEW orienta-

tions of the building’s façades and the insolation available to each. Figure 13 illustrates the results of an Ecotect model by Stefan Bader (Uni-versity of Texas School of Architec-ture) addressing this question for an Austin setting. Values in the graph are total insolation values (direct and diffuse) on a one-square-meter area for an entire month (kWh/m2).

For the month of December, no di-rect sunlight falls on the north façade of a building in Austin. Thus the 7844 kWh/m2 in Bader’s simulation is due solely to diffuse solar energy in the atmosphere. Naturally, the south façade receives the most solar radia-tion in winter. Note that a somewhat counterintuitive phenomenon occurs during summer. Due to the north-erly position of the June sun in early morning and late evening, as well as its very high altitude in midday, the north façade of a building receives more solar radiation than the south. However, both of these amounts are dramatically less than the radia-tion incident on the east and west façades.

A second consideration in green wall design is plant choices. Dunnett and Kingsbury note a trend in green roofs to use only locally native species. This rather obvious criterion makes sense, not only for reasons concern-ing plant growth, but as a state-ment of how the building’s design is integrated into the culture of the area. They also claim that plants for a green roof should be drought tolerant. This makes sense as well for Austin, but is likely not necessary in the green wall design we will de-scribe. Two hardy plants for possible use on a green façade are plumbago and lantana.

Fig. 13 Total monthly insolation (kWh/m2) on façades of a building in Austin.


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Plumbago (plumbago auriculata) thrives well in Austin and produces light blue flowers through most of the year. It will climb to almost 20 feet, but only by tying it onto supports, as it has no real climbing mechanism of its own.28 Figure 14 illustrates the natural shape of plumbago, so it might be ideally suited to a typi-cal planter box on the balcony of a residential tower.

Lantana (lantana camara or lantana montevidensis) is also a popular plant native to central Texas, which

produces flowers of widely varied colors (Figures 15 and 16). De-pending on the strain, a lantana will either grow upward into a bush, or trail outward along the ground. This latter form could be used to cascade down a façade to shade it. Lantana is extremely hardy and drought tolerant, and tends to attract hum-mingbirds and butterflies. It likes as much direct sun as possible, and would therefore be a good choice for façade greening on all but a north face.

Fig. 15 Lantana camara. Fig. 16 Close-up of one type of bud on lantana camara.

Fig. 17 The 360 condominiums, Austin. Fig. 18 Rendering of the Monarch condominiums, Austin. Fig. 19 Rendering of the Austonian condominiums, Austin.

Fig. 14 Plumbago auriculata.


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A third consideration in green wall design is how the plants will be watered. Even in a climate much wetter than Austin, it is not reason-able to think that rainwater collected from the roof of a high-rise building is adequate for green walls, for the façade surface area can easily be twenty times that of the roof.29 For a residential tower, however, there is a potential alternative in the gray water generated by residents, described in what follows.

Designing a tower in Austin

Of the residential towers recently built in downtown Austin, three have very similar exterior shapes in sizes—the 360, the Monarch, and the Austonian (Figures 17–19) Us-ing one of these as a template, say the Austonian, let us imagine that the entire perimeter of a single floor is surrounded by balconies that are bounded by planter boxes for native shrubs. One such design is illus-trated in Figure 20. Assume that the soil container is 0.5 meters (19.8 in) wide. We address a strategy for pro-viding adequate water for the plants.

Since the context of this study is a residential tower, we know that residents will generate significant gray water through such activities as showering. A typical American shower dispenses approximately 2 gal/min (7.6 L/min), which means that a shower of around five minutes duration will require, say, 40L (10.6 gal) of water. This volume is pre-cisely the amount needed to provide 1cm depth of water into a 0.5m wide planter that runs a length of 8m. In other words, if we assume that every 8 meters of façade along one floor of the building corresponds to one 5-minute shower every day, then this

alone will water all the plants on the building skin with 1cm of water every day.

Impact of shrubs on microclimate

Initial motivations for this study were an understanding of how the pres-ence of green façades on an Austin building can impact UHIE, and the development of some thumbnail quantification of the role that native shrubs might play. These hopes were originally a response to a state-ment in Santamouris: “Moffat and Schiller (1981) report that an aver-age tree evaporates 1460kg of water during a sunny summer day, which consumes about 860 megajoules (MJ) of energy, a cooling effect

outside a home ‘equal to five aver-age air conditioners’.”30 Many have conducted research that includes as-sumptions about an “average tree,” so it seems only reasonable that one might use this notion as a unit of measure with which to understand a variety of plant types.

If anything has become clear in the pursuit of this goal, it is that this sort of question is an extremely murky one due to all the relevant design variables, complex interrelationships between the quantities we want to measure, the potentially disparate behaviors of different plants, and the range of possible plant performances resulting from the amount of water that a plant receives.

Fig. 20 Concept of façade greening for an Austin high-rise condominium.


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Yet, even with all these complicating factors, the one question still re-mains: Given that much research on ETP has been conducted using the notion of an “average tree,” can we infer what an average tree actually is, and then approximate a conver-sion factor from an “average tree” to an “average shrub,” thereby giving us at least some sense of the impact of greening the façades of a high-rise residential tower? This is the final question for this section, and we ad-dress it in terms of total leaf area of trees and shrubs.

First, Huang assumed in his DOE-2.1C modeling that a “mature tree has a top view projection area of 50m2,” which appears reasonable and consistent with other assump-tions in the literature.31 Second, in order to relate total leaf area of a tree to that of a shrub, we need a sense of a plant’s leaf area index (LAI), which is the ratio of the total leaf area of a plant to its canopy area, that is, its top projection view.

The literature on LAI is extensive. Lalic and Mihailovic noted a range of tree LAIs between 2 and 18.32 How-ever, in Sonnentag et al extensive field measurements yielded average LAI values of 1.59 for trees and 1.57 for shrubs in their study.33 If these numbers are a basis for any relation-ship between trees and shrubs, it implies that an “average tree” and an “average shrub” with the same canopy area will likely have compa-rable total leaf areas.

Assuming this, we may then convert our residential green wall shrubs into a tree equivalent in the follow-ing way. If a planter box along the façade holds a mature shrub whose spread is 1 meter wide, then a 50-

meter length of planter holds the rough equivalent leaf area of one average tree. Rough measurements from Google models of the Austo-nian reveal that the perimeter of the residential floors is approximately 133 meters. Thus by wrapping one floor of the Austonian in a green wall of this sort, we have introduced the equivalent of 2.67 trees into down-town Austin. With 44 residential floors in the building, we have the equivalent of approximately 117.5 average trees on the façade of the Austonian. Using Santamouris’ claim that an average tree evapo-rates 1460 kg of water per day, this requires approximately 917 kWh of energy. In terms of PV panel area, 1063m2 would be required to gen-erate this amount of energy on an average June day in Austin.

Conclusion

Sustainable design practices need not be technologically complex or necessarily expensive to implement. Of particular interest is the scenario where a positive environmental im-pact in one area works in symbiotic relationship with another positive impact. The hypothetical case study of a high-rise Austin condominium tower illustrates such a relationship. By including a green façade and meeting its need for adequate water, we also manage a significant drop in the amount of gray water introduced into the sewer system.

If Austin is to meet its goal of 25,000 downtown residents by the year 2015, it is essential to find and exploit as many such symbiotic, sustainable design practices as pos-sible. Not only are such practices environmentally responsible, but

they also stand to have a dramatic impact on the infrastructure required for downtown Austin to support such a large number of residents.

Notes

1. Heimsath, Charles, President of Capitol Market Research, report to Downtown Austin Alliance, April 2, 2008, p 5.

2. Boyt, Jeb, letter to Mayor Will Wynn and Austin City Council members, August 3, 2006.

3. Austin Chamber of Commerce newsletter, February 2008, p 5.

4. Renovitch, James. “Recreating the Do-main,” Austin Chronicle, May 8, 2009.

5. Novak, Shonda. “Condo market on firm ground?” Austin American Statesman, August 26, 2007.

6. Huang, Jinlou (2009), p 67.

7. Givoni, B, p 291.

8. Ibid, p 292.

9. Huang (1987), p 1104.

10. Ibid.

11. Ibid, p 1106.

12. Ibid, p 1107.

13. Ibid, p 1113.

14. Dunnett, Nigel and Noël Kingsbury, p 192.

15. Ibid, p 2.

16. Ibid, p 239ff.

17. Ibid, p 66.

18. Ibid, p 195.

19. Givoni, p 291.

20. Ibid, p 292.

21. Ibid, p 291.

22. Ibid.

23. Schmidt, Marco, p 1.


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24. Ibid, p 3.

25. Ibid, p 8.

26. Ibid, p 6f.

27. http://www.nrel.gov/gis/solar.html

28. Dunnett, p 302.

29. Ibid, p 194.

30. Santamouris, Mat, p 111f.

31. Huang (1987), p 1105.

32. Lalic, Branislava and Dragutin T. Mi-hailovic, p 641.

33. Sonnentag, O, p 350.

Figures

Figure 1: From the website of archdaily.com, http://www.archdaily.com/10685/consorcio-building-concepcion-enrique-browne/

Figure 2: From the April 2, 2008 presentation on a downtown condominium study, Capitol Market Research, http://www.downtownaustin.com/downloads/DTAustin_CondoStudy_20080402.pdf

Figure 3: From the website of Capitol Green-roofs, http://capitolgreenroofs.groupsite.com/discussion/topic/show/146768

Figure 4: From the website of Landscape + Urbanism, http://landscapeandurbanism.blogspot.com/2008/07/living-walls-systems-approach.html

Figure 5: By the author.

Figures 6–11: From the website of the Institute of Physics in Berlin-Adlershof, http://www.gebaeudekuehlung.de/en/index.html

Figure 12: From Marco Schmidt, “Rainwater harvesting for stormwater management and building climatization,” Technical University of Berlin, (draft).

Figure 13: Data courtesy of Stefan Bader, University of Texas School of Architecture.

Figure 14: From the website of the Depart-ment of Horticultural Sciences, Texas A&M University, http://aggie-horticulture.tamu.edu/cemap/plumbago/plumbago8.html

Figure 15: From the website of Campo Verde, http://campoverde.wordpress.com/2009/04/24/

Figure 16: From the website of World of Stock, http://www.worldofstock.com/closeups/NPF5594.php

Figure 17: From the website of the 360 Con-dos, Austin, http://360-nueces.com/

Figure 18: From the website of Urban Living, http://www.urbanliving2000.com/images/mon-arch_austin.jpg

Figure 19: From the website of austintowers.net, http://www.austintowers.net/at/condos/navigator_files/carousel_image_4_1.jpg

Figure 20: By the author.

References

Austin Chamber of Commerce, “NWBC to Hear Plans for Second Phase of the Domain,” February, 2008.

Boyt, Jeb, chair. City of Austin Downtown Commission, August 3, 2006; http://www.ci.austin.tx.us/downtown/downloads/Down-town_Development.pdf

Dunnett, Nigel and Noël Kingsbury. Planting Green Roofs and Living Walls, Timber Press, Portland, 2008.

Givoni, B. “Impact of Planted Areas on Urban Environmental Quality: A Review,” Atmo-spheric Environment, Vol 25B, No 3 (1991), 289–299.

Heimsath, Charles. “Downtown Condominium Study: Report by Capitol Market Research,” April 2, 2008; http://www.cmraustin.com/

Huang, Y. J. et al (1987). “The Potential of Vegetation in Reducing Summer Cooling Loads in Residential Buildings,” Journal of Climate and Applied Meteorology, Vol 26, September 1987, 1103–1116.

Huang, Jinlou et al (2009). “Simulation of thermal effects due to different amounts of urban vegetation within the built-up area of Beijing, China,” International Journal of Sus-tainable Development & World Ecology, Vol 16 No 1, February 2009, 67–76.

Lalic, Branislava and Dragutin T. Mihailovic, “An Empirical Relation Describing Leaf-Area Density inside the Forest for Environmental

Modeling,” Journal of the Americal Meteoro-logical Society, April 2004: 641–645.

National Renewable Energy Laboratory, http://www.nrel.gov/gis/solar.html

Novak, Shonda. “Condo market on firm ground?” Austin American Statesman, August 26, 2007.

Renovitch, James. “Recreating the Domain,” Austin Chronicle, May 8, 2009; http://www.austinchronicle.com/gyrobase/Issue/story?oid=oid:777969

Santamouris, Mat (Ed). Environmental Design of Urban Buildings: An Integrated Approach, Bath Press, Bath, UK, 2006.

Schmidt, Marco. “Rainwater harvesting for stormwater management and building climati-zation,” (draft).

Sonnentag, O. et al. “Mapping tree and shrub leaf area indices in an ombrotrophic peatland through multiple endmember spectral unmix-ing,” Remote Sensing of the Environment, 109 (2007), 342–360.

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