The Effect of a Denser City Over the Urban Microclimate: the Case of Toronto

sustainability

Article The Effect of a Denser City over the Urban Microclimate: The Case of Toronto

Umberto Berardi 1,* and Yupeng Wang 2

1 Faculty of Engineering and Architectural Science, Ryerson University, Toronto, ON M5B 2K3, Canada 2 School of Human Settlements and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, China; [email protected] * Correspondence: [email protected]; Tel.: +1-416-979-5000 (ext. 3263)

Academic Editors: Matheos Santamouris and Constantinos Cartalis Received: 14 July 2016; Accepted: 17 August 2016; Published: 19 August 2016

Abstract: In the last decades, several studies have revealed how critical the urban heat island (UHI) effect can be in cities located in cold climates, such as the Canadian one. Meanwhile, many researchers have looked at the impact of the city design over the urban microclimate, and have raised concerns about the development of too dense cities. Under the effect of the “Places to Growth” plan, the city of Toronto is experiencing one of the highest rates of building development in North America. Over 48,000 and 33,000 new home permits were issued in 2012 and 2013 respectively, and at the beginning of 2015, almost 500 high-rise proposals across the Greater Toronto Area were released. In this context, it is important to investigate how new constructions will affect the urban microclimate, and to propose strategies to mitigate possible UHI effects. Using the software ENVI-met, microclimate simulations for the Church-Yonge corridor both in the current situation and with the new constructions are reported in this paper. The outdoor air temperature and the wind speed are the parameters used to assess the outdoor microclimate changes. The results show that the new constructions could increase the wind speed around the buildings. However, high-rise buildings will somewhat reduce the air temperature during day-time, as they will create large shadow areas, with lower average mean radiant temperature.

Keywords: urban heat island effect; urban microclimate; high-rise construction; outdoor comfort

1. Introduction In the last decades, several studies have revealed how critical the urban heat island (UHI) effect can be in cities in cold climates, such as the Canadian one. This has led many researchers to look at the impact of the city design over the urban microclimate, and in particular, to raise concerns about too dense cities [1]. This study focuses on the Greater Toronto Area (GTA), the largest and most populous metropolitan area in Canada, with over 6 million persons. Toronto population is rapidly growing with new 76,500 persons in the last year, making Toronto the sixth largest metropolitan area in North America in terms of total population with only New York, Los Angeles and Chicago being signiﬁcantly larger [2]. Moreover, the annual growth over the last year shows that Toronto is not far behind New York and Los Angeles, with a signiﬁcant dependence in the case of Toronto on immigration as the key driver of population growth. The net immigration in Toronto over the last year was equal to 66,700 persons [2]. In this context, the Toronto urban environment is undergoing huge transformations. The “Places to Growth” is the Toronto development plan originally released in 2005, and reviewed in the following years, which represents the response to the forecast that by 2025 Toronto will house additional 2.4 million persons [3]. Under the effect of this plan, Toronto is experiencing one of the highest rate of building development in the developed countries. Over 48,000 and 33,000 new home permits were issued in 2012 and 2013 respectively, with 470 high-rise proposals across the

Sustainability 2016, 8, 822; doi:10.3390/su8080822 www.mdpi.com/journal/sustainability Sustainability 2016, 8, 822 2 of 11

GTA released at the beginning of 2015 [2,3]. In this regard it is important to mention that the Canadian urbanization rate is above 80%, and as a result the urban comfort and urban energy demand represent national priorities [4]. This trend is similar to that occurring in many other countries [4,5]. Given the large transformation that Toronto is facing in its urban design, and the amendments to the Official Plan housing policies which allow high-rise buildings almost everywhere around the city, it seems important to investigate how the urban design will influence the outdoor thermal comfort in Toronto and, consequently, the building energy consumption. Akbari suggested that every 0.6 ◦C increase in air temperature resulted by the UHI effect can add 1.5% to 2% to the peak demand for cooling, with many health consequences too [6]. Moreover, in Toronto, the peak demands increase the use of electricity supplied by local coal burning power plants, and consequently they have significant environmental implications. In Toronto, days with temperatures above 30 ◦C are expected to increase from an average of 13 nights per year in the 1970s to 65 by the end of this century [7,8]. Tam et al. (2015) stressed the evidence of the UHI in Toronto in by looking at the effect on a day to day temperature change between urban and rural areas [8]. Evaluating the relationships between buildings and the surrounding outdoor environment for controlling the urban microclimate and for mitigating the UHI effect is a multidisciplinary task which requires competences in many subjects, including landscape, urban planning, architecture, and building material science [8]. In view of the negative UHI effects, many researchers have focused on UHI mitigating strategies by simulating single blocks or neighbors [1,8]. However, preliminary results have shown the importance of urban design on the microclimate of outdoor spaces and urban canopy layers [9–12]. In fact, the urban density plays an important role for the UHI effect, since a denser urban form results in multiple reflections of solar energy, and influences the air convection within the urban canyons as well as the wind “porosity” of the city [13,14]. As a result, a denser morphology influences the radiant heat loss within the urban canyons due to the lower sky view factor (SVF). In fact, tall buildings and narrow urban canyons reduce the SVF and increase the amount of shaded area at the ground level, keeping the bottom of urban canyons cooler than the surrounding area by day, but increasing its temperature at night time [15–17]. Computer models have shown that an urban form with a building height to street width around 0.5 and a building density around 0.3 should be promoted to mitigate outdoor discomfort and other UHI effects [18]. However, the height of new construction in Toronto shows trends far from these geometrical design ratios. Bosselmann et al. back in 1995, presented an extensive study of how the change in the urban from of downtown Toronto was going to affect sunlight on sidewalks and open spaces as well as the wind conditions at street level [19]. By making wind tunnel measurements, they found that wind significantly accelerates above 10 m/s among several high-rise towers, creating both wind chilling effects and mechanical forces on the pedestrians that can make unsafe to walk. Mesoscale CFD studies have demonstrated that wider streets could induce easier go-through winds. However, the higher flow rate along the main streets reduces the flow rates in parallel narrower streets, negatively affecting the ventilation efficiency [20,21]. Moreover, the design of building facades also effects the urban wind environment [22]. Long building facades which are parallel to the prevailing wind direction, can accelerate horizontal vortex airflow at the edges [23]. Similarly, deeper urban canyons increase the wind speed [24]. Therefore, although the effects of the new constructions on urban wind environment depend on the construction location and the building facade design, it is evident that the development of high-rise buildings in Toronto is creating deeper urban canopies, while narrowing the relative street widths. The researches about thermal remote sensing are based on satellite measurements (2-D data) or aircraft scanners (2-D data). In particular, land surface temperatures (LST) maps derived from satellite data are the most commonly used ways to demonstrate the extent of the UHI effect in cities [25,26]. Natural Resources Canada used air temperature and surface temperature measurements collected from satellite imagery and 30 stationary stations to characterize the microclimatology across the GTA [27]. Although the UHI was most readily detected at night and when local winds were weak [27], an element that emerged in all the satellite elaborations was that downtown Toronto showed lower Sustainability 2016, 8, 822 3 of 11 surface temperatures than more peripheral suburban area [28]. In fact, in downtown, although the high density of high-rise buildings surrounded by hard and dark surfaces would probably suggest higher surface temperatures, it has emerged that suburban areas within the GTA also experienced higher thermal admittance properties, as common in downtown city centers. Moreover, it was demonstrated a strong relationship between the gross building coverage and the mean wind velocity ratio. In this sense, it was shown that the greater density of high-rise buildings in downtown Toronto could be responsible for creating vertical thermal drafts, with more releases of heat into the air [28]. Although the advantageSustainability of using 2016, 8, 822 LST is the possibility to cover extensive spatial area and to investigate3 of 11 the

UHI in a macro-scale,suggest higher 2-Dsurface LST temperatures, data have theirit has limitationsemerged that on suburban spatial areas resolution within the and GTA the also expression of urban typologies.experienced Observed higher thermal LST admitta dependsnce properties, on spatial as common resolution, in down becausetown city of centers. the different Moreover, land cover types. Typicalit was spatialdemonstrated resolution a strong ofrela 1tionship km2 ignores between landthe gross cover building characteristics coverage and onthe amean community wind scale. Furthermore,velocity LST ratio. derived In this sense, from it thewas shown satellite that database the greater ignoresdensity of thehigh-rise contribution buildings infrom downtown the surface of Toronto could be responsible for creating vertical thermal drafts, with more releases of heat into the exterior buildingair [28]. Although walls. This the advantage is a serious of using deficiency LST is the for possibility the consideration to cover extensive of urban spatial solar area heatand to absorption and reflection.investigate This the means UHI in thata macro-scale, the satellite 2-D LST pictures data have showing their limitations UHI effectson spatial ignore resolution the and contribution from the buildingthe expression walls, of urban and calculate typologies. the Observed surface LST temperatures depends on spatial from resolution, the radiated because energy of the in a small 2 spectrumdifferent range, sufferingland cover types. thermal Typical anisotropy. spatial resolution This isof especially1 km ignores relevant land cover for characteristics metropolises on a that have community scale. Furthermore, LST derived from the satellite database ignores the contribution from many high-risethe surface buildings. of exterior Recent buildingstudies walls. This have is a serious clarified deficiency the spatial for the consideration limits of satellite of urban analyses solar of the urban environment,heat absorption and and have reflection. suggested This means a combination that the satellite of pictures satellite showing images UHI with effects detailed ignore the analyses at the scale ofcontribution single neighborhoods from the building in walls, order and to calculate capture the specific surface temperatures urban elements from the [29 radiated]. In previous energy studies, the authorsin a have small comparedspectrum range, different suffering areas thermal of anisotro Toronto,py. This and is haveespecially looked relevant at thefor metropolises effect of some UHI that have many high-rise buildings. Recent studies have clarified the spatial limits of satellite analyses mitigationof strategies the urban environment, for areas of and the have city suggested with different a combination densities of satellit bothe duringimages with summer detailed and winter time [30].analyses In particular, at the scale the of surfacesingle neighborhoods reflectance in and order green to capture areas specific were urban compared elements as [29]. potential In UHI mitigationprevious strategies studies, showing the authors appreciable have compared benefits different in bothareas of cases. Toronto, and have looked at the effect The presentof some UHI study mitigation willspecifically strategies for areas focus of onthe city the with effects different of new densities constructions both during summer during summer and winter time [30]. In particular, the surface reflectance and green areas were compared as potential time in a downtownUHI mitigation area strategies where showing several appreciable new construction benefits in both projectscases. are taking place. In particular, in the selectedThe area, present open study parking will specifically lots and focus Victoria on the buildings effects of new have constructions recently during been replacedsummer time by high-rise residentialin condos. a downtown area where several new construction projects are taking place. In particular, in the The selectedselected area, area open (in Figure parking1 )lots is knownand Victoria as “Garden buildings district”, have recently and been presents replaced a mix by high-rise of condominium residential condos. and office buildings,The selected with area variable (in Figure building 1) is known heights as “Garden from two district”, to twenty and presents floors. a Themix presenceof of the Ryersoncondominium University and and office of buildings, many other with variable city attractions building heights has led from building two to twenty developers floors. The to focus on this area.presence Figure1 of shows the Ryerson that University the investigated and of many area othe isr city currently attractions occupied has led building by parking developers lots, to with low albedo surfacefocus on (asphalt). this area. Although,Figure 1 shows the that new the buildings investigated will area include is currently some occupied green by features parking (i.e.,lots, including with low albedo surface (asphalt). Although, the new buildings will include some green features (i.e., green roofs),including the main green interestroofs), the of main this interest paper of isthis towards paper is towards the effect the effect of the of newthe new urban urbangeometry geometry over the outdoor microclimate.over the outdoor microclimate.

Figure 1. Aerial photo of the neighbor investigated in the present study with evidence of the two Figure 1. Aerial photo of the neighbor investigated in the present study with evidence of the two zones zones currently undergoing new constructions. currently undergoing new constructions. Sustainability 2016, 8, 822 4 of 11

2. MethodologySustainability 2016, 8, 822 4 of 11 ENVI-met 4.0 (ENVI-MET GmbH, Essen, Germany), a three-dimensional computer software that 2. Methodology simulates micro-scale thermal interactions within the urban environment was used for simulating the areas of analysis.ENVI-met The 4.0 program(ENVI-MET is usedGmbH, to modelEssen, surface-plant-airGermany), a three-dimensional interactions in computer urban environments, software but itthat also simulates simulates micro-scale the flows aroundthermal buildings, interactions heat within and vapor the urban transfer environment at urban surfaces, was used turbulence, for simulating the areas of analysis. The program is used to model surface-plant-air interactions in urban and exchange. ENVI-met carries out detailed calculation in regards to shortwave and longwave environments, but it also simulates the flows around buildings, heat and vapor transfer at urban radiation fluxes with respect to shading, reflection and re-radiation from building systems and surfaces, turbulence, and exchange. ENVI-met carries out detailed calculation in regards to vegetation.shortwave The and software longwave was radiation chosen since fluxes it with has been respec extensivelyt to shading, validated reflection in and recent re-radiation years [29 ,from30]. It is importantbuilding to systems mention and that vegetation. ENVI-met The has software some limits was ch suchosen assince the it lack has ofbeen assessment extensively of validated anthropogenic in heatrecent emissions years (due,[29,30]. for It is example, important to to traffic mention or that air conditioning),ENVI-met has some and limits the possibility such as the to lack establish of someassessment urban parameters of anthropogenic homogenously heat emissions to the (due, entire for modelexample, only. to traffic For example,or air conditioning), the indoor and building the temperaturepossibility is to unique establish in some all theurban points parameters of the homogenously building, it is to the the same entire formodel all only. buildings For example, and is not an outputthe indoor of the building simulations, temperature but is anis unique input data in all necessary the points to of fix the boundary building, conditions it is the same for calculating for all the cell.buildings and is not an output of the simulations, but is an input data necessary to fix boundary conditionsENVI-met for has calculating a typical the spatial cell. resolution from 0.5 m to 10 m, and a temporal resolution of 10 s. A simulationENVI-met should has typicallya typical spatial be carried resolution out for from at least0.5 m 6 to h, 10 but m, aand 24 ha temporal period is resolution often more of 10 usual. seconds. A simulation should typically be carried out for at least 6 h, but a 24 h period is often more The optimal time to start a simulation is at night, so that the simulation can follow the solar radiation usual. The optimal time to start a simulation is at night, so that the simulation can follow the solar daily increase. radiation daily increase. TheThe main main input input parameters parameters of anof ENVI-metan ENVI-met simulation simulation include include weather weather conditions, conditions, structures structures and physicaland propertiesphysical properties of urban surfacesof urban and surfaces vegetation. and Combiningvegetation. Combining Reynolds averaged Reynolds Navier–Stokes averaged equationsNavier–Stokes and the equations advection and diffusion the advection equation, diffusion ENVI-met equation, allows ENVI-met to calculate allows to the calculate air temperature, the air as welltemperature, as the mean as well radiant as the temperature mean radiant (MRT). temperat Thisure temperature(MRT). This temperature has proved has to beproved important to be for outdoorimportant comfort, for outdoor since during comfort, hot since waves, during it assumeshot waves, values it assumes that values refer betterthat refer to comfortbetter to comfort perception thanperception the air temperature than the air [ 30temperature–32]. [30–32]. BasedBased on on previous previous studies, studies, a a typical typical summersummer day (15 (15 July July 2013) 2013) was was selected selected for forthe theanalysis. analysis. TheThe recording recording of twoof two weather weather stations stations (Latitude: (Latitude: 43 43°40◦400′00″00;; Longitude: Longitude: 79°24 79◦24′000″00) were00) were used used for the for the calibrationcalibration of theof the model, model, following following a a procedure procedure alreadyalready presented presented in in other other papers papers [14,30]. [14,30 Table]. Table 1 1 reportsreports the the details details of of the the initialization initialization input input parametersparameters in in the the software, software, while while the the data data about about the the urban form before and after the new constructions are presented in Table 2. The new buildings were urban form before and after the new constructions are presented in Table2. The new buildings were modelled as boxes, using the proposed maximum height (Figure 2). modelled as boxes, using the proposed maximum height (Figure2).

(a) (b)

Figure 2. ENVI-met models before the construction (a) and after it (b) of the area object of study. The Figure 2. ENVI-met models before the construction (a) and after it (b) of the area object of study. red boxes (dotted in the North zone and dashed in the South zone) represent the areas investigated The red boxes (dotted in the North zone and dashed in the South zone) represent the areas investigated in more detail. in more detail. Sustainability 2016, 8, 822 5 of 11

Table 1. Input data for the microclimate simulation model.

Simulation Parameters Assigned Values Day of the simulation 15–17 July 2013 Starting time 21:00 Wind speed 1.5 m/s Wind direction West Temperature 301.15 K (28 ◦C) Relative humidity at 2 m 58% Building interior temperature 299.15 K (26 ◦C)

Table 2. Urban form data of the investigated models, before and after the new constructions.

North Zone South Zone Before After Before After Average building height (m) 16.0 23.7 14.2 18.2 Maximum building height (m) 57.0 99.0 48.0 81.0 Land coverage (%) 39.5 44.1 48.4 53.6 Vegetation coverage (%) 11.7 11.3 2.8 2.8

Simulations started at 21:00 and lasted two days in order to have enough microclimate data. The study conducted in this paper was less sensitive to the proper assessment of the albedo of the different surfaces in the studied area, as the main goal was to look at the impact of new buildings that are going to substitute vacant parking lots. In every numerical model, especially 3D models such as the ENVI-met ones, simulations often suffer reliability at their model borders and at the grids very close to them. Nesting grids could be added in the boundary of models for increasing the authenticity of the simulation results. However, the more nesting grids are used, the lower is the chance that numerical problems occur because one or more of the model bounder are interfering with internal model dynamics. In this research, 10 nesting grids on each side of model boundaries were added in the simulation models.

Simulation Validation Figures3 and4 show the validation of the ENVI-met model through a comparison between ﬁeld measurements and simulation results for a summer day of the air temperature (Ta) [33]. The measurements data were derived from the governmental weather station data base. The maximum Ta difference between the simulations and the measurements at the airport was around 3.8 ◦C and occurred at 04:00 of 17 July. Reversely, the maximum Ta difference between the simulation and the measurement at the city center weather station was around 3.5 ◦C, and occurred at 04:00 of 17 July. The average difference between the simulations and the measured results was 1.3 ◦C. This discrepancy could be explained by inaccuracies in the simulation input for surface materials, soil, and vegetation conditions. In fact, the univocal values for the material properties used in the simulated model represents a clear discrepancy of the simulation model. Looking at the scatter plots in Figure4, the coefﬁcient of determination (R2) between the simulation and measurements is 0.75 to 0.88 for the measurements in the city center and in the airport area respectively. Sustainability 2016, 8, 822 6 of 11 SustainabilitySustainability 2016 2016, ,8 8, ,822 822 66 of of 11 11

FigureFigureFigure 3. 3. 3.Comparison Comparison Comparison betweenbetween between the the simulation simulation (ENVI-met) (ENVI-met)(ENVI-met) results results and and the the the measurement measurement measurement data data data over over over one one one summersummersummer day. day. day.

Figure 4. Correlation between the simulation result and the measured air temperature in the city FigureFigure 4. 4.Correlation Correlation between between the the simulation simulation result result and an thed the measured measured air temperatureair temperature in the in citythe centercity centercenter ( a(a) )and and in in the the airport airport area area ( b(b) )on on 16 16 July. July. (a) and in the airport area (b) on 16 July.

3.3. Results Results 3. Results FiguresFigures 5–8 5–8 show show the the air air temperature, temperature, wind wind speed speed and and wind wind direction direction maps maps at at the the ground ground level level (1.8(1.8Figures m m height height5– 8from from show ground) ground) the air at at temperature, mid-day mid-day in in the the wind two two speed zones zones andpointed pointed wind in in directionFigure Figure 2, 2, before mapsbefore atand and the after after ground the the new new level (1.8constructions.constructions. m height from The The ground) maps maps in in atFigures Figures mid-day 5 5 and and in the6, 6, although although two zones depicted depicted pointed at at ina a time Figuretime when when2, before the the sun sun and is is afterhigh high thein in the newthe constructions.sky,sky, show show an an evident The evident maps variation variation in Figures of of the 5the and air air 6temperature temperature, although depicted after after the the atconstruction, construction, a time when with with the a suna cooler cooler is high temperature temperature in the sky, showofof almost almost an evident 1 1 °C. °C. The variationThe cooler cooler ofspots spots the aircould could temperature be be found found around afteraround the the the construction, new new buildings buildings with in in athe the cooler after-construction after-construction temperature of ◦ almostmodel.model. 1 C. The cooler spots could be found around the new buildings in the after-construction model. Meanwhile,Meanwhile,Meanwhile, in inin the thethe wind windwind speed speedspeed distribution distributiondistribution showed showedshowed in Figures inin FiguresFigures7 and 778 ,andand it emerges 8,8, itit emergesemerges that the thatthat location thethe withlocationlocation wind with with speed wind wind increases speed speed areincreases increases consistent are are consistent consistent with the locationswi withth the the locations oflocations air temperature of of air air temperature temperature decrease, decrease, decrease, and vice and versa.and Sincevicevice theversa. versa. new Since Since buildings the the new new occupy buildings buildings open spacesoccupy occupy and open open resulted spaces spaces in and and accelerated resulted resulted airin in accelerated flow,accelerated they seemed air air flow, flow, to reducetheythey theseemedseemed stagnation to to reduce reduce of hot the the air stagnation stagnation at day-time, of of hot hot while air air at thanksat day-time, day-time, to their while while shading thanks thanks effects, to to their their they shading shading also reduceeffects, effects, thethey they midday also also airreducereduce temperature. the the midday midday air air temperature. temperature. In order to analyze the simulation results in more detail, it was decided to compare the microclimate parameters both in the current urban configuration and after the new constructions in some representative points. Figure9 shows the difference between the air temperature and the mean radiant temperature in the current scenario versus the post construction one, in both the zones investigated in the present paper. The figure reports the average difference of the values obtained in nine receptors in each zone, together with the standard deviation among the values in the nine receptors. Sustainability 2016, 8, 822 7 of 11 Sustainability 2016, 8, 822 7 of 11 Sustainability 2016, 8, 822 7 of 11 Sustainability 2016, 8, 822 7 of 11

(a) (b) (a) (b) (a) (b) Figure 5. Air temperature map at ground level (1.8 m height from ground) before (a) and after (b) the Figure 5. AirAir temperature temperature map map at ground at ground level level (1.8 (1.8m height m height from fromground) ground) before before (a) and (a after) and (b after) the Figurenew constructions 5. Air temperature in the North map atzone ground at the level summer (1.8 m mid-day height from (12:00, ground) 16 July). before (a) and after (b) the (newb) the constructions new constructions in the North in the zone North at zone the summer at the summer mid-day mid-day (12:00, (12:00,16 July). 16 July). new constructions in the North zone at the summer mid-day (12:00, 16 July).

(a) (b) (a) (b) (a) (b) Figure 6. Air temperature map at ground level (1.8 m height from ground) before (a) and after (b) the Figure 6. Air temperature map at ground level (1.8 m height from ground) before (a) and after (b) the FigureFigurenew constructions 6. AirAir temperature temperature in the South map map atzone atground groundat the level summer level (1.8 (1.8m mid-day height m height from (12:00, fromground) 16 July). ground) before before (a) and (a after) and (b after) the new constructions in the South zone at the summer mid-day (12:00, 16 July). (newb) the constructions new constructions in the South in the zone South at zone the summer at the summer mid-day mid-day (12:00, (12:00,16 July). 16 July).

(a) (b) (a) (b) (a) (b) Figure 7. Wind speed and direction map at ground level (1.8 m height from ground) before (a) and Figure 7. Wind speed and direction map at ground level (1.8 m height from ground) before (a) and afterFigure (b )7. the Wind new speed constructions and direction in the map North at zoneground at the level summer (1.8 m mid-dayheight from (12:00, ground) 16 July). before (a) and Figureafter (b 7.) theWind new speed constructions and direction in the map North at zone ground at the level summer (1.8 m mid-day height from (12:00, ground) 16 July). before (a) and afterafter ((bb)) thethe newnew constructionsconstructions inin thethe NorthNorth zonezone atat thethe summersummer mid-daymid-day (12:00,(12:00, 1616 July).July). Sustainability 2016, 8, 822 8 of 11

Sustainability 2016, 8, 822 8 of 11 Sustainability 2016, 8, 822 8 of 11

(a) (b)

Figure 8. Wind speed and direction map at ground level (1.8 m height from ground) before (a) and after (b) the new constructions in the South zone at the summer mid-day (12:00, 16 July).

In order to analyze the simulation results in more detail, it was decided to compare the microclimate parameters both in the current urban configuration and after the new constructions in some representative points. Figure 9 shows the difference between the air temperature and the mean radiant temperature in( athe) current scenario versus the post construction (bone,) in both the zones investigated in the present paper. The figure reports the average difference of the values obtained in Figure 8. Wind speed and direction map at ground level (1.8 m height from ground) before (a) and nineFigure receptors 8. Wind in speedeach andzone, direction together map with at groundthe standard level (1.8 deviation m height among from ground) the values before in (thea) and nine after (b) the new constructions in the South zone at the summer mid-day (12:00, 16 July). receptors.after (b) the new constructions in the South zone at the summer mid-day (12:00, 16 July).

In1.1 order to analyze the simulation results in more50 detail, it was decided to compare the microclimate0.9 parameters both in the current urban configuration and after the new constructions in 40 some representative0.7 points. Figure 9 shows the difference between the air temperature and the mean 30 radiant0.5 temperature in the current scenario versus the post construction one, in both the zones investigated in the present paper. The figure reports the average difference of the values obtained in 0.3 20 nine receptors in each zone, together with the standard deviation among the values in the nine 0.1 receptors. 10 Temperature-0.1 [C] 35791113151719212313 0 1.1-0.3 50 35791113151719212313

Mean Radiant Temperature [C] Mean Radiant Temperature -10 0.9-0.5 Hour of the day 40 Hour of the day 0.7 (a) (b) 30 0.51.1 50 0.9 0.3 4020 0.10.7 3010 0.5 Temperature-0.1 [C] 35791113151719212313 0.3 200 -0.3 35791113151719212313 0.1 Mean Radiant Temperature [C] Mean Radiant Temperature 10-10 -0.5 Hour of the day Temperature [C] Temperature -0.1 Hour of the day 0 -0.3 (a) (b) 1.1 50

-0.5 [C] Mean Radiant Temperature -10 0.9 3 5 7 9 11 13 15 17 19 21 23 1 3 3 5 7 9 11 13 15 17 19 21 23 1 3 40 Hour of the day Hour of the day 0.7 (c) 30 (d) 0.5 Figure 9. Difference between the air temperature and the mean radiant temperature in the current 0.3Figure 9. Difference between the air temperature and the20 mean radiant temperature in the current scenario and in the post construction one, in the North zone (a,b), and in the South zone (c,d). 0.1scenario and in the post construction one, in the North zone (a,b), and in the South zone (c,d). 10

Temperature [C] Temperature -0.1 0 -0.3The air temperature in the North zone shows a small reduction in the ﬁrst hours of the night and then averaged air temperature values of almost 0.9 ◦C, with a reduction that becomes almost negligible

-0.5 [C] Mean Radiant Temperature -10 during the3 following 5 7 9 11 night 13 hours. 15 17 19 21 23 1 3 3 5 7 9 11 13 15 17 19 21 23 1 3 In the South zone,Hour the same of the behaviorday appears, although it is generallyHour more of mitigatedthe day and delayed. This means that the new(c constructions) will result in a slightly cooler air temperature(d) especially during the centralFigure hours 9. Difference of the day, between thanks the to air the temperature shading that and the th newe mean constructions radiant temperature will provide. in the The current standard scenario and in the post construction one, in the North zone (a,b), and in the South zone (c,d). Sustainability 2016, 8, 822 9 of 11

The air temperature in the North zone shows a small reduction in the first hours of the night and then averaged air temperature values of almost 0.9 °C, with a reduction that becomes almost negligible during the following night hours. In the South zone, the same behavior appears, although it is generally more mitigated and Sustainabilitydelayed. This2016 , means8, 822 that the new constructions will result in a slightly cooler air temperature9 of 11 especially during the central hours of the day, thanks to the shading that the new constructions will deviationprovide. The of the standard air temperature deviation is generallyof the air constanttemperature through is generally the day, andconstant assumes through values the up day, to 0.2 and◦C, showingassumes values a reasonably up to 0.2 homogenous °C, showing value a reasonably among the homogenous several receptors. value among the several receptors. The differences in the values of the mean radiantradiant temperature before and after the construction are significant.significant. In particular, during the hottest day hours, the average difference reaches values of almost 30 °C◦C and 25 °C◦C in in the the North North and and South South areas areas of of analysis analysis respectively. respectively. Conversely, Conversely, overnight, the differencedifference ofof thethe mean mean radiant radiant temperature temperature in in the th currente current scenario scenario and and in thein the post post construction construction one tendsone tends to almost to almost disappear. disappear. This This means means that that the the new new constructions constructions will will have have a significant a significant impact impact in termsin terms of shadingof shading the the streets streets and and creating creating lower lower mean mean radiant radiant temperature. temperature. The assessment of the change in the human thermalthermal comfort before and after the constructions requires some some preliminary preliminary discussion. discussion. In fact, In fact, although although several several studies studies have haverecently recently appeared, appeared, a lack aof lack a general of a general framework framework for assessing for assessing the theoutdoor outdoor thermal thermal comfort comfort exists. exists. In In fact, fact, a a number number of biometeorological indices have been developed to describe human thermal comfort by aligning local microclimate conditions and human thermalthermal sensationsensation [[34].34]. Human thermal perception depends on air temper temperature,ature, air humidity, wind speed and radiation fluxes,fluxes, asas well well as as the the personal personal body body energy energy balance, balance, and their and variability. their variability. The Physiologically The Physiologically Equivalent TemperatureEquivalent Temperature (PET), a human (PET), thermal a human comfort thermal index comfort based index on the based Munich on the energy-balance Munich energy-balance model for individualsmodel for individuals (MEMI) was (MEMI) assessed was in assessed this study in this [35]. study PET is[35]. defined PET is as defined the air temperatureas the air temperature at which, inat which, a typical in a indoor typical setting, indoor thesetting, human the human energy ener budgetgy budget is maintained is maintained by the by skin the temperature,skin temperature, core temperature,core temperature, and sweatand sweat rate equal rate toequal those to under thos thee under conditions the conditions to be assessed. to be PET assessed. is particularly PET is suitableparticularly for outdoorsuitable for thermal outdoor comfort thermal analysis comfort as analysis it translates as it translates the evaluation the evaluation of a complex of a complex outdoor climaticoutdoor environmentclimatic environment to a simple to a indoor simple scenarioindoor sc onenario a physiologically on a physiologically equivalent equivalent basis that basis can that be easilycan be understood.easily understood. PET is PET a steady is a steady state indexstate in (thatdex assumes(that assumes thermal thermal equilibrium) equilibrium) and hasand the has unit the degreeunit degree Celsius, Celsius, being being easily easily interpreted interpreted by urban by urban planners planners and notand requiring not requiring an expert. an expert. The softwaresoftware “RayMan”“RayMan” was was used used for for the the assessment assessmen oft of PET PET using using the the output output data data from from ENVI-met ENVI- simulation.met simulation. Figure Figure 10 shows 10 theshows Physiologically the Physiologically Equivalent Equivalent Temperature Temperature (PET) in the (PET) two investigatedin the two areasinvestigated through areas the summer through day. the summer The results day. show The that resu thelts developmentshow that thewith development the higher with density the higher would reducedensity thewould PET reduce in the urbanthe PET canopy in the during urban the canopy summer during time. the The summer maximum time. PET The reduction maximum will PET be aroundreduction 17.5 will◦C be at around 10:00 in 17.5 the °C north at 10:00 zone, in andthe north around zone, 14.1 and◦C ataround 14:00 14.1 in the °C southat 14:00 zone. in the Overall, south throughzone. Overall, the investigated through the summer investigated day, the summer average day, PET the reduction average is PET 3.4 ◦reductionC in the north is 3.4 zone °C in and the 2.4north◦C inzone the and south 2.4 zone. °C in the south zone.

Figure 10. Physiologically equivalent temperature in the current scenario and in the post construction one, inin thethe NorthNorth zone zone and and in in the the South South zone zone over ov oneer one summer summer day day (from (from 04:00 04:00 16 July 16 toJuly 04:00 to 04:00 17 July). 17 July). 4. Conclusions The urban climate in downtown Toronto before and after new constructions are simulated and compared. The results show that the new constructions may increase the wind speed and decrease the surrounding air temperature by up to almost 1 ◦C during the day, with negligible effects during the Sustainability 2016, 8, 822 10 of 11 night. It is also clear that the fact that the wind speed changed after the new constructions is strongly related to the air temperature changes. Moreover, the mean radiant temperature will be significantly reduced after the new towers are completed. Overall, it seems that the new high-rise constructions could somewhat reduce the UHI effect in summer mid-days. The verification of the result of this research using measurement campaigns of the outdoor microclimate for the city of Toronto before and after new tower-type buildings, is the object of current studies. Finally, further studies should be carried out to focus on more detailed scales of analysis, in order to investigate in detail the effect of the final building forms for both the outdoor comfort and the urban walkability.

Acknowledgments: This research was funded by the Centre for Urban Research of Ryerson University. The author would express their deep gratitude to NSERC for also supporting their research studies on outdoor microclimate and sustainable building technologies. Author Contributions: Umberto Berardi and Yupeng Wang contributed equally to this paper. They performed the experiments, analyzed the data, and wrote the paper together. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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