An Empirical Study on an Elevated Walkway in Shanghai China

sustainability

Article Towards a Climate-Responsive Vertical Pedestrian System: An Empirical Study on an Elevated Walkway in Shanghai China

Feng Yang 1,2,*, Feng Qian 1,2 and Wanzhu Zhao 1,2

1 College of Architecture and Urban Planning (CAUP), Tongji University, Shanghai 200092, China; [email protected] (F.Q.); [email protected] (W.Z.) 2 Key Laboratory of Ecology and Energy-Saving Study of Dense Habitat, Ministry of Education, Tongji University, Shanghai 200092, China * Correspondence: [email protected]; Tel.: +86-21-6598-0048 (ext. 105)

Academic Editors: Constantinos Cartalis and Matheos Santamouris Received: 12 June 2016; Accepted: 28 July 2016; Published: 4 August 2016

Abstract: Elevated walkways can bring pedestrian-friendly urban space back to high-density urban centers that are planned largely for vehicle traffic—for instance, the Lujiazui CBD in Shanghai. Most studies on elevated walkways have focused on transportation planning, structural safety as well as urban form and design. Few have paid attention to thermal conditions and pedestrian comfort issues on elevated levels. Considering all of the environmental factors that influence human thermal comfort, one could claim that there will be more breezes on elevated levels compared to sidewalks at the ground levels, but they can be exposed to increased solar radiation and thus higher radiant temperatures, if not properly shaded. The overall effect of the change in elevation on human thermal comfort is thus unknown. This study attempts to investigate the microclimate and human thermal comfort of a recently completed Lujiazui Elevated Walkway (LEW) system in the Lujiazui CBD, Shanghai, under a hot-humid sub-tropical climate. Micrometeorological measurements and a guided questionnaire survey were carried out on peak summer days. The data analysis indicates that the LEW is thermally more uncomfortable than its ground level counterpart. Air temperature was higher, whereas wind velocity is lower on the skywalk level than on the ground level, which is counter-intuitive. The resultant physiological equivalent temperature (PET) indicates warm conditions on the ground level (with good shading) while there are hot conditions on the skywalk. Based on the empirical findings, design strategies are proposed to improve the thermal comfort conditions on the LEW, and to better support pedestrian activities in this typical high-rise high-density urban area.

Keywords: elevated walkway; thermal comfort; ﬁeld study; microclimate; pedestrian friendly

1. Introduction Elevated walkways are an effective way to connect isolated buildings, enhance their accessibility, and vitalize commercial spaces at the elevated level. In high-density urban areas, carefully-designed skywalk systems create a relatively pedestrian-friendly environment by distancing people from vehicle pollution and noise. Therefore, it has the potential to create safe and comfortable public space for social activities amidst busy urban centers. Currently, it seems that most studies on the subject of elevated walkway have been carried out from the perspective of transportation planning, structural safety or urban form and visual impact [1–3]. Few have paid attention to thermal conditions and pedestrian comfort issues on the elevated pedestrian level. It is reasonable to acclaim that it will be likely to have more breezes on the elevated levels compared to sidewalks at the ground levels [4], but it can

Sustainability 2016, 8, 744; doi:10.3390/su8080744 www.mdpi.com/journal/sustainability Sustainability 2016, 8, 744 2 of 15 be exposed to increased solar radiation and thus higher radiant temperature, if not properly shaded. The overall effect of a change in elevation on human thermal comfort is thus unknown. This study aims to investigate the microclimate and human thermal comfort of a recently completed elevated walkway system in the Lujiazui CBD in Shanghai, a large city on the southeastern coast of China and under a hot-humid sub-tropical climate. Elevated walkways (referred to as EW, hereafter) can be defined as “networks of above-grade connections between buildings that are often enclosed and climate controlled, and which link second-level corridors within buildings and various activity hubs, such as shops and offices” [5] (p. 11). There are other terms such as pedestrian skywalks, skyway systems, etc. These generally refer to the same object. In central urban areas, an EW system can facilitate pedestrian movement, improve accessibility to isolated urban buildings, protect pedestrians from vehicle pollution and noise, and provide shelter under adverse climate conditions, all contributing to a more pedestrian-friendly urban environment. There are some debates on whether or not EW systems will ruin street life in western cities [4]. In Asian cities, where population density is much higher, EW systems can greatly relieve the burden of crowded sidewalks on the ground levels. In some cases, it can help rebuild the pedestrian network, which will otherwise not work due to vehicle-oriented urban planning, for instance, the EW system in the Lujiazui CBD of Shanghai. Famous examples of EW systems include the skyway in Minneapolis, Minnesota, USA and pedestrian skywalks in Calgary, Canada. These are both North American cities with cold climates featuring long and freezing winters [2]. EW systems can also be found in Central Hong Kong [6] and Zhujiang New District, Guangzhou, China [7], both under hot-humid sub-tropical climates. In contrary to the fully-enclosed “tube” form in cold climates, EWs in warm and hot climates normally keep railings and overhangs where necessary for the sake of safety and protection, and open other surfaces to the ambient environment as much as possible, so as to enjoy natural ventilation while protecting pedestrians from summer sun and rain. Note that the EW system in some extreme climates (e.g., tropical climates) can be completely enclosed and fully air-conditioned [8]. This paper will confine the discussion on naturally ventilated EWs that prevail in sub-tropical Asian cities. Pedestrian thermal comfort is well studied at the ground level, for instance, from the perspective of wind safety and comfort [9,10], thermal comfort and urban design in response to local climate [11,12]. However, studies focusing on thermal comfort on an elevated level seem very limited, if any. It is well known that human thermal comfort is influenced by environmental factors including air temperature and humidity, air movement and radiant temperature, and personal factors including clothing level and metabolic rate [13]. At the micro-local scale, urban geometry, fabric and surface materials can influence thermal comfort by moderating the abovementioned biometeorological parameters. For instance, a study on the thermal comfort impact of street greenery in the Netherlands indicates that 10% tree cover in a street could lower mean radiant temperature by 1 K [14]. A field study in Curitiba, Brazil found that urban geometry and street canyon orientation, quantified by sky view factor (SVF), is significantly related to daytime heat island intensity and radiant temperature [15]. A study on microclimate in urban open spaces in Greece reveals the significant impact of surface material on local temperature and thermal comfort [16]. Compared with sidewalks at ground level, elevated walkways may be able to enjoy better ventilation but may also be exposed to more solar heat gain, and the composite effect is affected by surrounding urban geometry, fabric and materials. It will be useful to investigate the relationship between variables of built environment and thermal comfort indices, so as to inform future EW design to achieve a more comfortable pedestrian environment.

2. Materials and Methods The Lujiazui Elevated Walkway (LEW) is chosen as the case of the empirical study (Figure1). LEW is located in the Small Lujiazui CBD area. The purpose of introducing walkways at such a large scale is to improve the pedestrian environment for ofﬁce commuters and tourists. The LEW comprises four parts, i.e., Oriental-Pearl Ring, Century Floating Pavilion, Century Sky Bridge and Century Sustainability 2016, 8, 744 3 of 15

Corridor. The length in total is 1373 m. The width ranges from 9.1 m to 10.1 m (excluding enlarged plazas near subwaySustainability entrance).2016, 8, 744 Elevation is 8 m above ground. Construction is reinforced3 of 15 concrete and steel. The LEWconcrete connects and steel. all The of LEW the connects entrances all of the of entrances Lujiazui of Station,Lujiazui Station, Shanghai Shanghai Metro Metro LineLine 2, 2, as well as five major largeas well buildings: as five major Super large Brand buildings: Mall Super (a retail-recreationalBrand Mall (a retail-recreational complex); complex); Century Century floating pavilion (retail and restaurant);floating pavilion Shanghai (retail and International restaurant); Shanghai Financial International Center Financial (IFC) (retail Center and(IFC) office), (retail and Jinmao Tower (retail and office),office), Jinmao and Shanghai Tower (retail World and office), Financial and Shanghai Center World (SWFC) Financial (retail Center and (SWFC) office). (retail and office).

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Figure 1. Bird-view (a) and satellite image (b) of Lujiazui (LJZ) elevated walkway. Figure 1. Bird-view (a) and satellite image (b) of Lujiazui (LJZ) elevated walkway. Micrometeorological measurement was carried out on 17, 18 and 22 July 2014. Seven pairs of measurement points were chosen, representing various scenarios of urban morphology on the Micrometeorologicalwalkway, and, on the measurement sidewalk level, wassurface carried material, out degree on of 17, space 18 andenclosure, 22 July green 2014. coverage, Seven pairs of measurementand points degree were of shading. chosen, Among representing them, four pairs various of measurement scenarios points of urban are selected morphology to compare on the the walkway, and, on the sidewalkeffect of various level, shading surface devices material, on thermal degree comfort of spacemoderation. enclosure, The two greenpoints in coverage, each pair are and degree of horizontally close to each other in order to control un-measured effects of other thermal factors. shading. AmongPoints them,with a prefix four “A-” pairs are of located measurement over the LEW, points whereas are points selected with toa prefix compare “B-” are the located effect of various shading devicesunder onthe thermal LEW. These comfort include moderation. A2 (in middle Theof the two walkway points and in un-shaded) each pair vs. are A2 horizontally′(under a close to each other insteel-glass order to constructed control un-measured canopy), A3 (center effects of an of elevated other thermalplaza near factors.subway entrance) Points withvs. A3 a′ (the preﬁx “A-” are located overseat-and-rest the LEW, whereasarea around points the plaza, with under a preﬁx a steel-glass “B-” are constructed located undercanopy), the B2 LEW.(under Thesea tree include A2 canopy) vs. B2′ (directly under the LEW), and B3 (near the subway entrance, un-shaded) vs. B3′ (a 1 (in middle ofsmall the pedestrian walkway rest and area un-shaded) under and shaded vs. by A2 the(under LEW) (Figure a steel-glass 2a). Two pedestrian constructed routes canopy), connect A3 (center of an elevatedmeasurement plaza near points subway at the elevated entrance) level and vs. at A3 the1 (theground seat-and-rest level, respectively area (Figure around 2b). the plaza, under a steel-glass constructedFour rounds canopy), of traverse B2 measurements (under a treecovering canopy) all points vs. were B2 carried1 (directly out during under four theperiods LEW), and B3 per day: 8 a.m.–9:30 a.m., 10 a.m.–11:30 a.m., 2:30 p.m.–4:00 p.m., and 4:30 p.m. to 6:00 p.m., 1 (near the subwayrecording entrance, four rounds un-shaded) of air temperature, vs. B3 relati(ave small humidity, pedestrian wind velocity rest areaand globe under temperature and shaded by the LEW) (Figureusing2a). a Twoportable pedestrian micro-weather routes station. connect A reference measurement station was set pointsup on the at open the grass elevated lawn of level LZJ and at the ground level,Central respectively Green. During (Figure 8 a.m.–62b). p.m., it continuously recorded global solar radiation and wind direction, in addition to the above-mentioned parameters (Table 1). Four roundsMean of traverseradiant temperature measurements (MRT) is coveringcalculated based all points on air weretemperature, carried relative out duringhumidity, four periods per day: 8wind a.m.–9:30 velocity a.m.,and globe 10 temperature, a.m.–11:30 according a.m., 2:30to the p.m.–4:00method givenp.m., by [17].and Globe 4:30 temperature p.m. is to 6:00 p.m., recording fourmeasured rounds by a oftemperature air temperature, sensor placed relative on the center humidity, of a 40 mm-diameter wind velocity matt-grey and table-tennis globe temperature ball [18]. The equation is as below (Equation (1)): using a portable micro-weather station. A reference station was set up on the open grass lawn of . . 1.1 × 10 LZJ Central Green. DuringMRT 8 =a.m.–6 ( + 273.15) p.m., it+ continuously×( recorded− ) global− 273.15 solar radiation(1) and wind . direction, in addition to the above-mentioned parameters (Table1). where ta is air temperature(in °C), tg is globe temperature (in °C), Va is the air velocity at the level of Mean radiant temperature (MRT) is calculated based on air temperature, relative humidity, the globe (in m/s), ε is the emissivity of the black globe (without dimension), D is the diameter of the wind velocityglobe and (in meters). globe temperature, according to the method given by [17]. Globe temperature is measured by a temperature sensor placed on the center of a 40 mm-diameter matt-grey table-tennis ball [18]. The equation is as below (Equation (1)):

0.25 8 0.6 4 1.1 ˆ 10 Va MRT “ tg ` 273.15 ` ˆ tg ´ ta ´ 273.15 (1) « εD0.4 ﬀ ` ˘ ` ˘ ˝ ˝ where ta is air temperature(in C), tg is globe temperature (in C), Va is the air velocity at the level of the globe (in m/s), ε is the emissivity of the black globe (without dimension), D is the diameter of the globe (in meters). Sustainability 2016, 8, 744 4 of 15 Sustainability 2016, 8, 744 4 of 15

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Figure 2. Field measurement on the Lujiazui Elevated Walkway (LEW): measured points (a) and Figure 2. Field measurement on the Lujiazui Elevated Walkway (LEW): measured points (a) and traverse routes (b). traverse routes (b). Sustainability 2016, 8, 744 5 of 15

Table 1. Instrument speciﬁcation.

Model Parameter Accuracy Operating Range Temperature/RH Smart Sensor: ˘0.2 ˝C (0–50 ˝C); Ta, RH ´40 ˝C–75 ˝C; RH ď 95% Hobo S-THB-M002 ˘2.5% RH (10%–90%) Wind direction smart sensors: ˘3% (17–30 m/s); 0–44 m/s WV Hobo S-WDA-M003 (on the ﬁxed WD ˘4% (30–44 m/s) WV; 0–355˝ WD station only) ˘5˝ (WD) Wind velocity sensor: Cambridge ˘5% of reading or WV 0–10 m/s Accusense sensor T-DCI-F900-S-P ˘0.05 m/s (15–35 ˝C) Temperature smart sensor: S-TMB-M002 (installed in a 40 mm Tg ˘0.2 ˝C (0–50 ˝C) ´40–100 ˝C matt-grey vinyl ball) Global radiation sensor: Hobo S-LIB-M003 (on the ﬁxed GSR ˘2% at 45˝ from vertical 0–1280 W/m2 (300–1100 nm) station only) Note: Ta-air temperature; RH-relative humidity; WD-wind direction; WV-wind velocity; Tg-globe temperature; GSR-global solar radiation.

The physiological equivalent temperature (PET) is a bio-meteorological index to measure human outdoor thermal comfort [19]. It takes into account all of the relevant environmental factors (air temperature, air velocity, humidity and mean radiant temperature) while assuming constant clothing and metabolic level. It can be calculated using the method given by Matzarakis et al. [20]. A questionnaire survey was conducted based on guided interviews with LEW users, in order to gather information on subjective evaluation and perception of the respondents on the comfort effect of the ground-level, LEW level and reference level environments. The guided interview and questionnaire survey were carried out during the period of micrometeorological measurement. Firstly, the demographical information, including age, gender, residence status, clothing level, physical activity level of the respondents at 15 min ago, etc. were recorded. Then, three meteorological parameters (air temperature, Ta, relative humidity RH and wind velocity WV) were subjectively evaluated, followed by a subjective evaluation on personal acceptability towards thermal and wind environments based on the seven-scale thermal sensation vote (TSV) and four-scale wind perception. Evaluation on thermal comfort is based on ﬁve-point scales (i.e., 0: comfortable; ´1: slightly uncomfortable; ´2: uncomfortable; ´3: very uncomfortable, and ´4: unendurable). In total, 111 respondent questionnaires were collected, among them 45 from above the LEW, 49 from below the LEW and 17 from the Lujiazui Central Green (LCG) (reference station).

3. Results Micrometeorological conditions at Lujiazui reference station, i.e., Central Green station (CGS), are brieﬂy described below. It can be seen from Table2 and Figure3 that, during the measurement period, the prevailing wind direction at the LJZ urban area is from the Southeast (90–180 degree). The hourly-mean wind velocity ranges from 0.7 to 1.0 m/s. Mean air temperature exceeded 30 ˝C even in the early morning (around 8:30 a.m.) and reached as high as 34 ˝C during the afternoon (between 3:00 to 3:30 p.m.).

Table 2. Micrometeorological conditions during the ﬁeld campaign at the Central Green Station.

Ta (˝C) RH (%) WV (m/s) GSR (W/m2) Date Max Min Mean Max Min Mean Max Mean Max Min Mean 7.17 34.3 29.2 32.0 76.4 57.4 65.3 3.78 0.77 1277 0.60 481 7.18 33.6 29.1 31.9 80.2 58.7 67.8 4.53 0.77 1169 53.1 325 7.22 36.2 30.6 33.8 74.5 49.5 59.7 4.53 1.10 956 88.1 683 Mean 34.7 29.7 32.5 77.0 55.2 64.3 4.28 0.88 1134 47.3 496 Sustainability 2016, 8, 744 6 of 15 Sustainability 2016, 8, 744 6 of 15

Sustainability 2016, 8, 744 6 of 15

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Figure 3. Meteorological data at Lujiazui Central Green Station (CGS). (a) air temperature, humidity Figure 3. Meteorological(b) data at Lujiazui Central Green Station (CGS).(c) (a) air temperature, humidity and and solar radiation; (b) wind direction; (c) wind velocity. solar radiation; (b) wind direction; (c) wind velocity. Figure 3. Meteorological data at Lujiazui Central Green Station (CGS). (a) air temperature, humidity 3.1. andComparisons solar radiation; between, (b) over,wind and direction; under (LEWc) wind velocity. 3.1. Comparisons between, over, and under LEW 3.1.3.1.1. Comparisons ITD and WVR between, Comparison over, and under LEW 3.1.1. ITD andInter-urban WVR ComparisonTemperature Differential (ITD) is the air temperature differential between 3.1.1. ITD and WVR Comparison Inter-urbanmeasurement Temperaturepoints and the DifferentialLujiazui Central (ITD) Green is Station the air(CGS). temperature Wind Velocity differential Ratio (WVR) between is measurementthe Inter-urbanratio of points wind andTemperaturevelocity the at Lujiazui measurement Differential Central points Green(ITD) to thatis Station the at the air (CGS). CGS. temperature Wind Velocity differential Ratio between (WVR)is the Not surprisingly, ITD is higher at the points over LEW than those under LEW, due to less ratiomeasurement of wind velocity points at and measurement the Lujiazui points Central to Green that at Station the CGS. (CGS). Wind Velocity Ratio (WVR) is theshading ratio of and wind thus velocity more solar at measurement heat gain. However, points to it that is counter-intuitive at the CGS. to find that WVR over LEW Not surprisingly, ITD is higher at the points over LEW than those under LEW, due to less shading is generallyNot surprisingly, lower than ITD that is under higher LEW at (Figurethe points 4). over LEW than those under LEW, due to less and thusshading more and solar thus heat more gain. solar However, heat gain. itHowever, is counter-intuitive it is counter-intuitive to ﬁnd that to find WVR that over WVR LEW over is LEW generally loweris thangenerally that lower under than LEW that (Figure under4 LEW). (Figure 4).

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Figure 4. Inter-urban Temperature Differential (ITD) (a) and Wind Velocity Ratio (WVR); (b) comparison below and above LEW. SustainabilitySustainability 2016 2016, 8, ,8 744, 744 7 7of of 15 15

Sustainability 2016, 8, 744 7 of 15 FigureFigure 4. 4. Inter-urban Inter-urban TemperatureTemperature DifferentialDifferential (ITD) ((a)) andand WindWind VelocityVelocity RatioRatio (WVR);(WVR); ( b()b ) comparisoncomparison below below and and above above LEW. LEW. 3.1.2. MRT and PET Comparison 3.1.2.3.1.2. MRT MRT and and PET PET Comparison Comparison The MRT values are all higher at the over-LEW points than their counter-points under LEW, on the TheThe MRT MRT values values are are all all higher higher atat thethe over-LEWover-LEW points than theirtheir counter-pointscounter-points under under LEW, LEW, on on order of 2–6 ˝C, as are the PET values. The differences of PET are on the order of 1–3 ˝C (Figure5). thethe order order of of 2–6 2–6 °C, °C, as as are are the the PET PET values.values. TheThe diffdifferences of PETPET areare onon the the order order of of 1–3 1–3 °C °C (Figure (Figure According to the criteria given by [17], all of the points are hot (35–41 ˝C) during the measurement 5).5). According According toto thethe criteriacriteria givengiven byby [17],[17], all of the pointspoints areare hothot (35–41(35–41 °C)°C) duringduring the the period, but clearly it was less uncomfortable under the LEW than over it. measurementmeasurement period, period, but but clearly clearly it it waswas lessless uncomfortableuncomfortable under thethe LEWLEW than than over over it. it.

(a) (b) (a) (b) FigureFigure 5. 5.Mean Mean radiantradiant temperature (MRT) (MRT) (a () aand) and physiological physiological equivalent equivalent temperature temperature (PET); (PET); (b) Figure 5. Mean radiant temperature (MRT) (a) and physiological equivalent temperature (PET); (b) (b)comparison comparison below below and and above above LEW. LEW. comparison below and above LEW. 3.2. Comparison between Shaded and Un-Shaded 3.2.3.2. Comparison Comparison betweenbetween ShadedShaded andand Un-ShadedUn-Shaded 3.2.1. ITD and WVR Comparison 3.2.1. ITD and WVR Comparison 3.2.1. ITD and WVR Comparison As shown in Figure 6, all shaded points showed lower ITD values, compared to the un-shaded As shown in Figure6, all shaded points showed lower ITD values, compared to the un-shaded counterpartAs shown points. in Figure The 6,differences all shaded range points from showed 0.2 to lower 0.5˝ °C. ITD The values, two shaded compared points to atthe the un-shaded ground counterpartcounterpartlevel (B2’ points. andpoints. B3’) The The are differences differencesmarkedly range coolerrange from thanfrom 0.2 the0.2 to reference 0.5to 0.5C. °C. The CentralThe two two shaded Green shaded points station. points at theGlass-shading at groundthe ground level (B2’leveldemonstrated and (B2’ B3’) and are markedlyB3’)a clear are effect markedly cooler on thanTa coolerreduction the reference than (A2’ the Centraland reference A3’), Green in Central the station. range Green Glass-shadingof 0.1–0.3 station. °C, Glass-shading whereas demonstrated the ˝ ademonstrated clearcooling effect effect on a Taby clear reductionthe effectLEW structure (A2’on Ta and reduction A3’),was higher in the(A2’ range(B2 and′ and ofA3’), 0.1–0.3B3’), in onthe theC, range whereas order of of 0.1–0.3 the0.3–0.5 cooling °C, °C. whereas effectThe point by the the 1 ˝ LEWcoolingunder structure effectthe LEW wasby the(B2’) higher LEW was (B2 structure clearlyand B3’), cooler was on higher thethan order the (B2 point′ of and 0.3–0.5 B3’),under onC. a Thethetree order point(B2). underofThis 0.3–0.5 is the because LEW°C. The (B2’)a pointtree was clearlyundercanopy, coolerthe depending LEW than (B2’) the on pointwas the clearly undercanopy a coolergeometry tree (B2). than and This the leaf is point because density, under a intercepts tree a tree canopy, (B2).only depending aThis portion is because of on incoming the canopya tree geometrycanopy,direct solardepending and radiation, leaf density, on thecompared interceptscanopy togeometry the only opaque aportion and structureleaf of density, incoming of LEW. intercepts direct Regarding solar only radiation, aWVR, portion similar of compared incoming to the to thedirectprevious opaque solar structuresection, radiation, shaded of compared LEW. points Regarding toenjoyed the WVR,opaque higher similar structure WVR to thethan of previous LEW.their Regardingun-shaded section, shaded WVR,counterpart pointssimilar points, enjoyedto the higherpreviousexcept WVR for section, A2/A2’. than theirshaded As un-shadeddiscussed points previously,enjoyed counterpart higher this points, canWVR be except thancaused fortheir by A2/A2’. verticalun-shaded Asthermaldiscussed counterpart buoyancy previously, points, and thisexcepthorizontal can for be causedA2/A2’. displacement byAs vertical discussed ventilation thermal previously, between buoyancy groundthis andcan surfaces be horizontal caused with by displacementdifferent vertical degrees thermal ventilation of solarbuoyancy heating. between and groundhorizontal surfaces displacement with different ventilation degrees between of solar ground heating. surfaces with different degrees of solar heating.

(a) (b)

Figure(a) 6. ITD (a) and WVR (b) comparison shaded and un-shaded.(b)

FigureFigure 6.6. ITDITD ((aa)) andand WVRWVR (b) comparison shaded shaded and and un-shaded. un-shaded. Sustainability 2016, 8, 744 8 of 15 Sustainability 2016, 8, 744 8 of 15

3.2.2.3.2.2. MRTMRT andand PETPET ComparisonComparison AsAs shownshown in Figure Figure 7,7, the the cooling cooling effect effect of ofdiffe differentrent shading shading devices devices becomes becomes even evenclearer clearer in MRT in ˝ MRTcomparison: comparison: the glass-steel the glass-steel canopy canopy showed showed limited limitedMRT reduction, MRT reduction, on the order on the of order0.5–1.5 of °C. 0.5–1.5 On theC. ˝ Oncontrary, the contrary, solid shading solid shading devices (elevated devices (elevated walkway walkwayin this case) in lowered this case) MRT lowered by nearly MRT 3 by°C nearlycompared 3 C ˝ comparedto a tree canopy to a tree shading canopy (B2), shading and by (B2), about and 6 by °C about compared 6 C comparedto un-shaded to un-shadedplaces (B3). places The PET (B3). Thecomparison PET comparison has a similar has apattern similar wi patternth MRT. with The MRT. two points The two under points the underLEW (B2’ the and LEW B3’) (B2’ are and classified B3’) are ˝ ˝ classiﬁedas “warm” as (29–35 “warm” °C in (29–35 PET) whileC in PET)all other while points all otherare classified points are“hot classiﬁed” (35–41 °C “hot” in PET), (35–41 includingC in PET), the 1 1 includingtree-shading the point tree-shading (B2) and point two points (B2) and under two the points semi-transparent under the semi-transparent canopy (A2′ and canopy A3′). (A2 and A3 ).

(a) (b)

FigureFigure 7. MRT (a) and PET ( b)) comparison comparison between between shaded shaded and and un-shaded. un-shaded.

3.3. Regression Analysis 3.3. Regression Analysis Bivariate and multiple linear regression analysis are applied to identify the causal factors Bivariate and multiple linear regression analysis are applied to identify the causal factors associated with temperature and thermal comfort indices. The significant level is set at 5%. SPSS associated with temperature and thermal comfort indices. The significant level is set at 5%. software (Version 20, IBM Corporation, Armonk, NY, USA) is used to carry out the statistical SPSS software (Version 20, IBM Corporation, Armonk, NY, USA) is used to carry out the statistical analysis on the traverse measurement data. The overall sample size including all of the traverse analysis on the traverse measurement data. The overall sample size including all of the traverse measurement points (see Figure 2 for locations of the points) is 42. The dependent variable is air measurement points (see Figure2 for locations of the points) is 42. The dependent variable is air temperature (Ta), mean radiant temperature (MRT) and physiological equivalent temperature temperature (Ta), mean radiant temperature (MRT) and physiological equivalent temperature (PET). (PET). The independent variables include two point-specific variables, i.e., sky view factor (SVF) and The independent variables include two point-specific variables, i.e., sky view factor (SVF) and green green plot ratio (GPR) [21], and one site-specific variable, i.e., background air temperature measured plot ratio (GPR) [21], and one site-specific variable, i.e., background air temperature measured at at CGS (Ta_cg). CGS (Ta_cg). Linear-fit estimates indicate that Ta is related to SVF with an R-square of 0.14, significant at the R 0.05 Linear-fitlevel. A significant estimates relationship indicate that exists Ta is between related Ta to and SVF Ta_cg with an(R2 =-square 0.53; Sig. of level: 0.14, 0.01) significant (Figure at 2 the8). Air 0.05 temperature level. A significant variation relationshipis subject to many exists factors between at different Ta and Ta_cgscales ([21],R = and 0.53; SVF Sig. alone level: cannot 0.01) (Figureexplain8 ).the Air major temperature variation variation in air temperature is subject [22]. to many Although factors SVF at different as a crucial scales micro-scale [ 21], and parameter SVF alone cannotshows explaina statistically the major significant variation relationship, in air temperature its explanatory [22]. power Although is much SVF asless a than crucial the micro-scale reference parametertemperature shows recorded a statistically at the local-scale, significant i.e., relationship, Ta_cg. Higher its explanatorySVF tends towards power increasing is much less Ta, than and thea referencehigher background temperature temperature recorded at thetends local-scale, towards i.e., increasing Ta_cg. Higher Ta as SVF well. tends Multiple towards regression increasing Ta,incorporatingand a higher SVFbackground and Ta_cg temperature yields the following tends towards equation. increasing The model Ta as well.is capable Multiple of explaining regression incorporatingabout two-thirds SVF of and the Ta_cg variability yields in the Ta following(Equation equation. (2)): The model is capable of explaining about two-thirds of the variability in Ta (Equation (2)): Ta = 0.68 × Ta_cg + 1.08 × SVF + 10.03 (R2 = 0.65, F = 35.5) (1) 2 Linear-fit estimatesTa “ 0.68 indicateˆ Ta_cg significant` 1.08 ˆrelationshipSVF ` 10.03 ofp RMRT“ with0.65, Ta_cgF “ 35.5 (R2q = 0.29; Sig. level:(2) 0.01), SVF (R2 = 0.36; Sig. level: 0.01) and GPR (R2 = 0.28; Sig. level: 0.01) (Figure 9). Higher SVF tends 2 towardsLinear-fit increasing estimates MRT, indicate and higher significant background relationship temperature of MRT with tends Ta_cg towards (R = increasing 0.29; Sig. level: MRT 0.01), as 2 2 SVFwell, ( Rwhereas= 0.36; higher Sig. level: greenery 0.01) density and GPR tends (R towards= 0.28; Sig. lowering level: 0.01)MRT. (FigureSVF shows9). Higher a relatively SVF tends low towardsR-square increasing value, due MRT, to the and fact higher that MRT background is highly temperature dependent tendsupon towardsimpinging increasing solar radiation, MRT as and well, whereassince SVF higher does greenerynot take solar density geometry tends towards into account, lowering it is MRT. not adequate SVF shows to aquantify relatively solar low radiationR-square value,received due at to the the location fact that of MRTinterest is highly [22]. Greener dependenty (trees, upon shrub impinging and grass) solar may radiation, modify andMRT since by tree SVF canopy shading (direct solar radiation) and reducing ground albedo (reflected solar radiation) [23]. Sustainability 2016, 8, x FOR PEER 9 of 15

higher background temperature tends towards increasing Ta as well. Multiple regression Sustainability 2016, 8incorporating, x FOR PEER SVF and Ta_cg yields the following equation. The model is capable of explaining 9 of 15 Sustainabilityabout two-thirds2016, 8, 744 of the variability in Ta (Equation (2)): 9 of 15

Ta = 0.68 × Ta_cg + 1.08 × SVF + 10.03 (R2 = 0.65, F = 35.5) (1) higher backgrounddoes not taketemperature solar geometry intotends account, towards it is not adequate increasing to quantify Ta solar radiationas well. received Multiple at the regression incorporating locationSVF and of interest Ta_cg [22]. yields Greenery the (trees, following shrub and grass) equation. may modify The MRT model by tree canopyis capable shading of explaining about two-thirds(direct of solarthe radiation)variability and reducing in Ta ground(Equation albedo (2)): (reﬂected solar radiation) [23]. Multiple regression incorporating SVF, GPR and Ta_cg yields the following equation. The model is capable of explaining about 70% ofTa the = variability0.68 × Ta_cg in MRT + (Equation 1.08 × (3)):SVF + 10.03 (R2 = 0.65, F = 35.5) (1) MRT “ 8.25 ˆ SVF ´ 3.40 ˆ GPR ` 3.42 ˆ Ta_cg ´ 69.02 pR2 “ 0.69, F “ 27.6q (3)

(a) (b)

Figure 8. Linear-fit estimates of air temperature (Ta) with (a) sky view factor (SVF) and (b) Ta_cg.

Linear-fit estimates indicate significant relationship of MRT with Ta_cg (R2 = 0.29; Sig. level: 0.01), SVF (R2 = 0.36; Sig. level: 0.01) and GPR (R2 = 0.28; Sig. level: 0.01) (Figure 9). Higher SVF tends towards increasing MRT, and higher background temperature tends towards increasing MRT as well, whereas higher greenery density tends towards lowering MRT. SVF shows a relatively low R-square value, due to the fact that MRT is highly dependent upon impinging solar radiation, and since SVF does not take solar geometry into account, it is not adequate to quantify solar radiation received at the location of interest [22]. Greenery (trees, shrub and grass) may modify MRT by tree canopy shading (direct solar radiation) and reducing ground albedo (reflected solar radiation) [23]. Multiple regression incorporating SVF, GPR and Ta_cg yields the following equation. The model is capable of explaining about(a) 70% of the variability in MRT (Equation (3)): ( b)

2 Figure 8. Linear-fitFigure 8.estimatesLinear-ﬁtMRT = 8.25 estimates of × airSVF temperature of− 3.40 air temperature × GPR + 3.42 (Ta) (Ta) × Ta_cg with with (a −) sky69.02(a) viewsky (R factor= view 0.69, (SVF) F factor = 27.6) and (b(SVF)) Ta_cg. and (2) (b) Ta_cg.

Linear-fit estimates indicate significant relationship of MRT with Ta_cg (R2 = 0.29; Sig. level: 0.01), SVF (R2 = 0.36; Sig. level: 0.01) and GPR (R2 = 0.28; Sig. level: 0.01) (Figure 9). Higher SVF tends towards increasing MRT, and higher background temperature tends towards increasing MRT as well, whereas higher greenery density tends towards lowering MRT. SVF shows a relatively low R-square value, due to the fact that MRT is highly dependent upon impinging solar radiation, and since SVF does not take solar geometry into account, it is not adequate to quantify solar radiation received at the location of interest [22]. Greenery (trees, shrub and grass) may modify MRT by tree canopy shading (direct solar(a) radiation) and reducing(b)( ground albedo (reflectedc) solar radiation) [23].

Multiple regressionFigureFigure incorporating 9. 9.Linear-fit Linear-fit estimates estimates SVF, of of Mean MeanGPR radiant radiant and temperature temperature Ta_cg (MRT) yields(MRT) with with (thea) ( Ta_cg;a) Ta_cg;following (b) ( SVFb) SVF and and (equation.c) Green(c) The model is Green plot ratio (GPR). capable of explainingplot ratio about (GPR). 70% of the variability in MRT (Equation (3)): 2 Linear-fitLinear-fit estimates estimates indicate indicate a significanta significant relationship relationship of PETof PET with with Ta_cg Ta_cg (R2 (R= 0.29; = 0.29;Sig. Sig. level: level: 0.01 ); 2 2 2 SVFMRT0.01); (R2 SVF== 8.25 0.42; (R = Sig. ×0.42; SVF level: Sig. level:− 0.01) 3.40 0.01) and × and GPR GPR (R +2 (R =3.42 0.28;= 0.28; × Sig. Sig.Ta_cg level: level: 0.01)−0.01) 69.02 (F (Figureigure (R 10). 10 =). Higher 0.69, Higher SVF F SVF = tends 27.6) tends (2) towards increasing PET, and higher background temperature tends towards increasing PET as well, towards increasing PET, and higher background temperature tends towards increasing PET as well, whereas higher greenery density tends towards lowering PET. whereas higher greenery density tends towards lowering PET. Multiple regression incorporating SVF, GPR and Ta_cg yields the following equation. The model is capable of explaining about 72% of the variability in PET (Equation (4)). The equation with standardized coefficients is as Equation (5). Equation (6) is deducted in a separated study, using field-measured data at ground pedestrian level at the LJZ CBD area [24]. By comparison,

(a) (b)(c)

Figure 9. Linear-fit estimates of Mean radiant temperature (MRT) with (a) Ta_cg; (b) SVF and (c) Green plot ratio (GPR).

Linear-fit estimates indicate a significant relationship of PET with Ta_cg (R2 = 0.29; Sig. level: 0.01); SVF (R2 = 0.42; Sig. level: 0.01) and GPR (R2 = 0.28; Sig. level: 0.01) (Figure 10). Higher SVF tends towards increasing PET, and higher background temperature tends towards increasing PET as well, whereas higher greenery density tends towards lowering PET. Sustainability 2016, 8, 744 10 of 15 it can be seen that Equations (5) and (6) are similar in terms of variable composition and magnitudes of coefﬁcients. Therefore, the robustness of the regression results is veriﬁed:

PET “ 4.98 ˆ SVF ´ 1.46 ˆ GPR ` 1.73 ˆ Ta_cg ´ 20.33 pR2 “ 0.72, F “ 32.4q (4)

PET “ 0.49 ˆ SVF ´ 0.23 ˆ GPR ` 0.53 ˆ Ta_cg (5)

PET “ 0.56 ˆ SVF ´ 0.31 ˆ GPR ` 0.38 ˆ Ta_cg pR2 “ 0.76, F “ 24q (6) SustainabilitySustainability 2016 2016, 8, 8744, x FOR PEER 10 of10 15of 15

(a()a ) (b(b)()(cc))

FigureFigure 10. 10. Linear-fitLinear-ﬁt Linear-fit estimates estimates ofof PET with ( (aa)) Ta_cg; Ta_cg; ( (b(bb)) )SVF SVFSVF and andand (c (()cc )GPR.) GPR.GPR.

Multiple regression incorporating SVF, GPR and Ta_cg yields the following equation. The 3.4. Questionnaire Survey model is capable of explaining about 72% of the variability in PET (Equation (4)). The equation with standardizedOverall, the coefficients respondents is as reported Equation a warm-to-hot(5). Equation environment(6) is deducted at LEWin a separated and at LCG study, (Figure using 11).11 ). Thefield-measured overall portion data of atrespondents respondents ground pedestrian reporting reporting level warm warm at the to to hotLJZ hot (+1CBD (+1 toto area+3) +3) is[24]. isabout about By 77%comparison, 77% above above LEW it LEW can and be and at atLCG, LCG,seen whereas that whereas Equations the the percentage percentage (5) and (6)is isaboutare about similar 8% 8% lowerin lower terms in in theof the variablegroup group below belowcomposition LEW. LEW. andAbout magnitudes two-thirds of of respondentscoefficients. above aboveTherefore, the the LEW theLEW robustness reported reported hot of (+3),thehot regression similar(+3), similar with results the withis LCG verified: the reference LCG station.reference In comparison,station. In aboutcomparison, 61% of about thePET respondents 61% = 4.98 of the × SVF belowrespondents − 1.46 the × LEWGPR below + reported 1.73 the × LEWTa_cg hot. reported In− 20.33 addition, (R hot.2 = 0.72, 20%–25%In addition, F = 32.4) of the20%–25% respondents (3)of the reportedrespondents neutral-to-cool reported neutral-to-cool at all three places. at all three Note plac thates. all Note these that responses all these were responses collected were during collected the PET = 0.49 × SVF − 0.23 × GPR + 0.53 × Ta_cg (4) 4thduring round the measurement 4th round measurement (4:30 p.m.–6 p.m.),(4:30 p.m.–6 when air p.m.), temperature when air and temperature solar radiation and droppedsolar radiation down considerablydropped down compared considerablyPET to = peak 0.56 compared × noon SVF time.− 0.31 to peak × GPR noon + 0.38 time. × Ta_cg (R2 = 0.76, F = 24) (5)

3.4. Questionnaire Survey Overall, the respondents reported a warm-to-hot environment at LEW and at LCG (Figure 11). The overall portion of respondents reporting warm to hot (+1 to +3) is about 77% above LEW and at LCG, whereas the percentage is about 8% lower in the group below LEW. About two-thirds of respondents above the LEW reported hot (+3), similar with the LCG reference station. In comparison, about 61% of the respondents below the LEW reported hot. In addition, 20%–25% of the respondents reported neutral-to-cool at all three places. Note that all these responses were collected during the 4th round measurement (4:30 p.m.–6 p.m.), when air temperature and solar radiation dropped down considerably compared to peak noon time.

Figure 11. Thermal sensation vote comparison.

More than than 80% 80% of ofrespondents respondents reported reported perceptibl perceptiblee winds windsat all three at allplaces three (Figure places 12). (Figure About 94%12). Aboutof respondents 94% of respondentsfrom above LEW from reported above LEW perceptible reported winds perceptible (+1 to +3, winds gentle (+1 breeze to +3, to gentlestrong breezewind), whereas about 84% from below LEW reported perceptible wind, 10% lower than that above LEW. It is not surprising to find that respondents that felt comfortable comprise only around 20% both above and below the LEW (Figure 13). More people felt comfortable at the under LEW level, but with only a marginal advantage of about 5%. About 30% reported being comfortable at the LCG.

Figure 11. Thermal sensation vote comparison. Sustainability 2016, 8, 744 11 of 15 to strong wind), whereas about 84% from below LEW reported perceptible wind, 10% lower than that above LEW. It is not surprising to ﬁnd that respondents that felt comfortable comprise only around 20% both above and below the LEW (Figure 13). More people felt comfortable at the under LEW level, but with Sustainabilityonly a marginal 2016, 8,advantage 744 of about 5%. About 30% reported being comfortable at the LCG. 11 of 15 Sustainability 2016, 8, 744 11 of 15

Figure 12. Wind velocity perception comparison. FigureFigure 12. 12.Wind Wind velocity velocity perception perception comparison. comparison.

Figure 13. Thermal comfort perception comparison. FigureFigure 13. 13.Thermal Thermal comfort comfort perception perception comparison. comparison. 4. Discussion 4.4. DiscussionDiscussion Climatically, sizable green spaces such as LCG can have a clear assimilating effect on the Climatically, sizable green spaces such as LCG can have a clear assimilating effect on the surroundingClimatically, urbanized sizable area, green and spacesresults of such the aspresen LCGt study can have indicate a clear that assimilatingthe degree of effect assimilation on the surrounding urbanized area, and results of the present study indicate that the degree of assimilation issurrounding proportional urbanized to the distance. area, and In results this study, of the presentthe locations study indicatecloser to that the the LCG degree were of measured assimilation and is is proportional to the distance. In this study, the locations closer to the LCG were measured and foundproportional to have to smaller the distance. Ta differences In this study, and the higher locations velocity closer ratios to the than LCG those were farther measured away and from found it found to have smaller Ta differences and higher velocity ratios than those farther away from it (Figureto have 4). smaller Compared Ta differences to the ground and higher level, velocityselected ratioslocations than at those the LEW farther level away were from measured it (Figure with4). (Figure 4). Compared to the ground level, selected locations at the LEW level were measured with higherCompared MRT to on the the ground order level,of 2–6 selected °C, higher locations ITD on at the LEWorder levelof 0.2–0.8 were measured°C, and lower with WVR higher on MRT the higher MRT on the˝ order of 2–6 °C, higher ITD on the ˝order of 0.2–0.8 °C, and lower WVR on the orderon the of order 0.1–0.3. of 2–6 TheC, lower higher velocity ITD on ratio the order at high of 0.2–0.8er elevationC, and seems lower counter-intuitive. WVR on the order A ofpossible 0.1–0.3. order of 0.1–0.3. The lower velocity ratio at higher elevation seems counter-intuitive. A possible reasonThe lower can velocity be that ratiothe horizontal at higher elevation convection seems on counter-intuitive.the ground level Awas possible enhanced reason due can to be thermal that the reason can be that the horizontal convection on the ground level was enhanced due to thermal buoyancyhorizontal between convection shaded on the (directly ground levelunder was LEW) enhanced and un-shaded due to thermal places, buoyancy i.e., thermal between buoyancy shaded buoyancy between shaded (directly under LEW) and un-shaded places, i.e., thermal buoyancy causes(directly uplift under of warmer LEW) and air un-shadedat sun-lit spaces, places, and i.e., they thermal were buoyancysupplied by causes cooler uplift air from of warmer surrounding air at causes uplift of warmer air at sun-lit spaces, and they were supplied by cooler air from surrounding shadedsun-lit spaces,spaces (Figure and they 14). were Under supplied hot and by calm cooler we airather from conditions, surrounding thermal shaded buoyancy spaces could (Figure be the14). shaded spaces (Figure 14). Under hot and calm weather conditions, thermal buoyancy could be the majorUnder forces hot and behind calm weathermeasured conditions, air movement thermal at the buoyancy pedestrian could level be the [25]. major However, forces behindmore data measured are to major forces behind measured air movement at the pedestrian level [25]. However, more data are to be collected before any solid conclusions can be made on this observation. be collected before any solid conclusions can be made on this observation. Increasing the height of EW could expose it to higher wind speed due to less ground friction. Increasing the height of EW could expose it to higher wind speed due to less ground friction. However, to achieve tangible improvement, the height may have to be increased by a factor of two. However, to achieve tangible improvement, the height may have to be increased by a factor of two. This will significantly increase the cost of structure and lower the accessibility from ground level. This will significantly increase the cost of structure and lower the accessibility from ground level. Overall, comfort index PET indicates a hot thermal sensation for people (35–41 °C). However, PET Overall, comfort index PET indicates a hot thermal sensation for people (35–41 °C). However, PET was higher on the LEW level, on the order of 1–3 °C, indicating an even more uncomfortable thermal was higher on the LEW level, on the order of 1–3 °C, indicating an even more uncomfortable thermal environment compared to the ground level. environment compared to the ground level. Sustainability 2016, 8, 744 12 of 15 air movement at the pedestrian level [25]. However, more data are to be collected before any solid conclusions can be made on this observation. Increasing the height of EW could expose it to higher wind speed due to less ground friction. However, to achieve tangible improvement, the height may have to be increased by a factor of two. This will signiﬁcantly increase the cost of structure and lower the accessibility from ground level. Overall, comfort index PET indicates a hot thermal sensation for people (35–41 ˝C). However, PET was higher on the LEW level, on the order of 1–3 ˝C, indicating an even more uncomfortable thermal Sustainabilityenvironment 2016 compared, 8, 744 to the ground level. 12 of 15

Figure 14. DiagramDiagram showing showing possible thermal buoyancy circulation under LEW.

Shading can be effective in reducing MRT and lowering PET, and thus can be en essential Shading can be effective in reducing MRT and lowering PET, and thus can be en essential measure to improving thermal comfort. Field study further indicates that, among various materials, measure to improving thermal comfort. Field study further indicates that, among various materials, opaque shading with high thermal mass (concrete elevated walkway in this case) showed the best opaque shading with high thermal mass (concrete elevated walkway in this case) showed the best effect effect in lowering radiant temperature, on the order of 3–6 °C, followed by porous green mass (street in lowering radiant temperature, on the order of 3–6 ˝C, followed by porous green mass (street tree tree canopy) (on the order of 1–3 °C), and semitransparent (tinted glass with steel frame) structure canopy) (on the order of 1–3 ˝C), and semitransparent (tinted glass with steel frame) structure (on the (on the order of 0.5–1.5 °C). Due to its high thermal mass, concrete surfaces maintain relatively lower order of 0.5–1.5 ˝C). Due to its high thermal mass, concrete surfaces maintain relatively lower surface surface temperature in addition to intercepting 100 percent direct solar radiation. Concrete shading temperature in addition to intercepting 100 percent direct solar radiation. Concrete shading is not new. is not new. Its application to building façades can be traced back to the Brise-soleil populated by Le Its application to building façades can be traced back to the Brise-soleil populated by Le Corbusier; Corbusier; famous examples include Chandigarh City Hall in India and Unité d′habitation in France. famous examples include Chandigarh City Hall in India and Unité d1habitation in France. However, However, aesthetically, its raw and “brutalism” look might seem incompatible with the modern aesthetically, its raw and “brutalism” look might seem incompatible with the modern glass-steel towers glass-steel towers commonly found in CBD areas. Alternatively, various shading devices that are commonly found in CBD areas. Alternatively, various shading devices that are light-weight and opaque light-weight and opaque can be applied in the EW design. Note that vegetation density is found can be applied in the EW design. Note that vegetation density is found significantly correlated with significantly correlated with mean radiant temperature and the thermal comfort index. At the LEW mean radiant temperature and the thermal comfort index. At the LEW level, planting trees would be level, planting trees would be structurally difficult and not cost-effective. The effective strategy to structurally difficult and not cost-effective. The effective strategy to increase greenery mass can be increase greenery mass can be shading canopy by climbing plants (Figures 15 and 16). shading canopy by climbing plants (Figures 15 and 16). Under the peak summer weather conditions in Shanghai, outdoor thermal comfort cannot be met even with sufficient shading. A previous study shows that when outdoor air temperature is in the range of 30–32 ˝C, shaded street space can be comfortable with wind velocity on the order of 2.2–3.6 m/s [25]. The measured WVR and reference WV indicate that, on average, this WV range was not achieved during the field measurement. To boost air movement at the pedestrian level over the LEW, electrical fans can be installed on the shading canopy. For instance, in the Clarke Quay redevelopment in Singapore, air-ducts and mechanical fans were incorporated into the canopy structure over the pedestrian area to promote air ventilation under nearly calm weather conditions [26]. Combined with water misting devices to lower sensible heat (by increasing latent heat), the LEW canopy can be upgraded into a “cool corridor” during the daytime. The installation and maintenance can be costly, but for a high-profile walkway being heavily used such as LEW, it can be worthwhile to invest.

Figure 15. Diagrams of various forms of shading form for elevated walkway (EW). (a) Adjustable shading; (b) Blind shading; (c) vegetation shading; (d) Low-e glass shading; (e) opaque shading; (f) PV panel shading; (g) ETFE shading; (h) Tree shading. Sustainability 2016, 8, 744 12 of 15

Figure 14. Diagram showing possible thermal buoyancy circulation under LEW.

Shading can be effective in reducing MRT and lowering PET, and thus can be en essential measure to improving thermal comfort. Field study further indicates that, among various materials, opaque shading with high thermal mass (concrete elevated walkway in this case) showed the best effect in lowering radiant temperature, on the order of 3–6 °C, followed by porous green mass (street tree canopy) (on the order of 1–3 °C), and semitransparent (tinted glass with steel frame) structure (on the order of 0.5–1.5 °C). Due to its high thermal mass, concrete surfaces maintain relatively lower surface temperature in addition to intercepting 100 percent direct solar radiation. Concrete shading is not new. Its application to building façades can be traced back to the Brise-soleil populated by Le Corbusier; famous examples include Chandigarh City Hall in India and Unité d′habitation in France. However, aesthetically, its raw and “brutalism” look might seem incompatible with the modern glass-steel towers commonly found in CBD areas. Alternatively, various shading devices that are light-weight and opaque can be applied in the EW design. Note that vegetation density is found significantly correlated with mean radiant temperature and the thermal comfort index. At the LEW Sustainabilitylevel, planting2016, 8 trees, 744 would be structurally difficult and not cost-effective. The effective strategy13 of 15to increase greenery mass can be shading canopy by climbing plants (Figures 15 and 16).

FigureFigure 15.15. DiagramsDiagrams ofof variousvarious formsforms ofof shadingshading formform forfor elevatedelevated walkwaywalkway (EW).(EW). (a(a)) AdjustableAdjustable shading;shading; ( b(b)) Blind Blind shading; shading; (c ()c vegetation) vegetation shading; shading; (d )(d Low-e) Low-e glass glass shading; shading; (e) opaque(e) opaque shading; shading; (f) PV (f) panelPV panel shading; shading; (g) ETFE (g) ETFE shading; shading; (h) Tree (h) Tree shading. shading. Sustainability 2016, 8, 744 13 of 15

FigureFigure 16. Examples of of shading shading devices devices for for EW. EW.

Under the peak summer weather conditions in Shanghai, outdoor thermal comfort cannot be 5. Conclusions met even with sufficient shading. A previous study shows that when outdoor air temperature is in theThis range study of 30–32 investigated °C, shaded the relationshipstreet space can between be comfortable urban morphology with wind and velocity urban on microclimate the order of and thermal2.2–3.6 comfortm/s [25]. ofThe the measured recently WVR completed and reference Lujiazui WV Elevated indicate Walkwaythat, on average, (LEW) this system WV range in Shanghai, was featuringnot achieved a hot-humid during the sub-tropical field measurement. climate. To Micrometeorologicalboost air movement at measurement the pedestrian waslevel carriedover the out inLEW, the peak electrical summer fans periodcan be forinstalled three continuouson the shading days. canopy. Seven For pairs instance, of measurement in the Clarke points Quay were chosen,redevelopment representing in Singapore, various scenarios air-ducts of and urban mechanical morphology fans on were the LEW,incorporated and, on into the sidewalkthe canopy level, surfacestructure material, over the degree pedestrian of enclosure, area to greenery promote coverage,air ventilation and degreeunder nearly of shading. calm Twoweather pedestrian conditions routes [26]. Combined with water misting devices to lower sensible heat (by increasing latent heat), the connect measurement points at the elevated levels and at the ground levels, respectively, recording air LEW canopy can be upgraded into a “cool corridor” during the daytime. The installation and temperature, relative humidity, wind velocity, and globe temperature using portable micro-weather maintenance can be costly, but for a high-profile walkway being heavily used such as LEW, it can be stations. A reference station was set up on the open grass lawn of LZJ Central Green. Guided interviews worthwhile to invest. and questionnaire surveys on thermal and wind perception were also carried out spontaneously with the5. ﬁeldConclusions measurement. The data analysis indicates that:

(1) TheThis measured study investigated locations overthe relationship the LEW are between thermally urban more morphology uncomfortable and urban than microclimate those below it. andAir thermal temperature comfort was of higher,the recently whereas completed wind velocity Lujiazui is lower Elevated on the Walkway LEW level (LEW) than onsystem the ground in Shanghai, featuring a hot-humid sub-tropical climate. Micrometeorological measurement was carried out in the peak summer period for three continuous days. Seven pairs of measurement points were chosen, representing various scenarios of urban morphology on the LEW, and, on the sidewalk level, surface material, degree of enclosure, greenery coverage, and degree of shading. Two pedestrian routes connect measurement points at the elevated levels and at the ground levels, respectively, recording air temperature, relative humidity, wind velocity, and globe temperature using portable micro-weather stations. A reference station was set up on the open grass lawn of LZJ Central Green. Guided interviews and questionnaire surveys on thermal and wind perception were also carried out spontaneously with the field measurement. The data analysis indicates that: (1). The measured locations over the LEW are thermally more uncomfortable than those below it. Air temperature was higher, whereas wind velocity is lower on the LEW level than on the ground level, which is counter-intuitive. It is possible that the horizontal convection on the ground level was enhanced due to thermal buoyancy between shaded and un-shaded places. (2). Indicated by the calculated thermal comfort index (physiological equivalent temperature, PET), it was averagely hot both over and below the LEW during the measured period, although PET was 1–3 °C lower at below the LEW. In addition, about 80% of respondents reported being uncomfortable above the LEW, whereas this was 5% lower at below the LEW. (3). Shaded locations can be warm while un-shaded places can be hot indicated by PET. Opaque concrete shading is most effective in lowering Tmrt, followed by tree canopy and glass-steel canopy. (4). To achieve a thermally comfortable LEW, passive cooling systems such as shading are vital but not enough. Active energy measures can be combined with shading devices, to increase air movement and reduce sensible heat, by a carefully integrated system design. Sustainability 2016, 8, 744 14 of 15

level, which is counter-intuitive. It is possible that the horizontal convection on the ground level was enhanced due to thermal buoyancy between shaded and un-shaded places. (2) Indicated by the calculated thermal comfort index (physiological equivalent temperature, PET), it was averagely hot both over and below the LEW during the measured period, although PET was 1–3 ˝C lower at below the LEW. In addition, about 80% of respondents reported being uncomfortable above the LEW, whereas this was 5% lower at below the LEW. (3) Shaded locations can be warm while un-shaded places can be hot indicated by PET. Opaque concrete shading is most effective in lowering Tmrt, followed by tree canopy and glass-steel canopy. (4) To achieve a thermally comfortable LEW, passive cooling systems such as shading are vital but not enough. Active energy measures can be combined with shading devices, to increase air movement and reduce sensible heat, by a carefully integrated system design.

Acknowledgments: This paper is supported by the Innovation Program of Shanghai Municipal Education Commission (Project No. 15ZZ020), the Fundamental Research Funds for the Central Universities (Project No. 0100219161) and the Shanghai Summit Program. Author Contributions: Feng Yang conceived and designed the experiments; Wanzhu Zhao participated in the experiments; Feng Yang and Wanzhu Zhao analyzed the data; Feng Qian contributed reagents/materials/analysis tools; Feng Yang wrote the paper. Conﬂicts of Interest: The authors declare no conﬂict of interest.

Abbreviations

CBD central business district CGS Central Green station EW elevated walkway GPR green plot ratio GSR global solar radiation ITD inter-urban temperature differential LCG Lujiazui Central Green LEW Lujiazui elevated walkway LJZ Lujiazui MRT mean radiant temperature PET physiological equivalent temperature RH relative humidity SVF sky view factor Ta air temperature Ta_cg background air temperature measured at CGS Tg globe temperature TSV thermal sensation vote WD wind direction WV wind velocity WVR wind velocity ratio

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