Microclimate Improvement of Inner-City Urban Areas in a Mediterranean Coastal City
Abstract
:1. Introduction
- The albedo increase of roofs and paving surfaces [11,16,17]. The term albedo is defined as the hemispherical and wavelength-integrated reflectance of a material or surface [18,19]. Several studies showed that the albedo increase on a city scale contributes to lowering urban temperatures and thus to decreasing the buildings’ cooling demand and the energy consumption respectively [16,17,18,19,20,21,22,23]
- The use of cool materials at the paving surfaces, i.e., materials with high solar reflectance and high infrared emittance values [18]. Therefore, cool materials absorb less solar radiation and at the same time release the absorbed heat more easily. As a consequence, these materials develop lower surface temperatures, reducing heat convection from the surfaces to the ambient air, hence leading to lower air temperatures and a cooler environment [16]. Numerous studies focused on the positive influence of cool materials on surface and ambient temperatures [20,23,24,25,26,27]. For instance, Synnefa et al. [23] found that for a maximum solar reflectance difference of 22 between a standard and a cool material, there was a surface temperature difference of 10.2 °C during the summer. Several researchers studied cool materials’ application on urban open spaces and their positive effect on the human thermal comfort [11,17,20,28,29,30,31]. In all those cited studies, the contribution of cool materials to ambient temperature reduction was confirmed. Santamouris et al. [29] identified a reduction of the peak ambient temperature down to 1.9 °C during a typical summer day. Similarly, Gaitani et al. [11] also estimated an ambient temperature reduction down to 1.6 °C due to the use of cool materials.
- The use of surfaces with high permeability, such as vegetated surfaces and pavements made of pervious, porous, or water-retaining materials [14,27]. Asaeda et al. [32] accentuate that the evapotranspiration process at bare soil surfaces constitutes a key parameter in microclimate. The use of permeable materials should be increased in order to allow the exchange of water between the surface and the underlying soil layers, hence fostering the evaporation process [32,33]. As cited in Scholz and Grabowiecki (2007), the basic principle permeable pavement systems is to “collect, treat and infiltrate freely any surface runoff to support groundwater recharge ([34], p. 3831).” Additionally, the permeable pavements decrease the water runoff, enrich and refresh the groundwater, and contribute to pollution prevention and to water conservation due to the recycling process.
- The increase of vegetation and the use of vegetated systems (green roofs, green walls, and living walls). The vegetation, particularly trees, contributes to cooling the urban environment in three ways:In addition, vegetation contributes to the improvement of air quality [36,40], controls the air circulation and protects from cold seasonal winds [37], reduces water runoff and improves groundwater quality [36,37], controls noise [41], and reduces building cooling/heating loads (with adequate tree planting, green roofs, etc.) [21,37]. The vegetation could also be applied to buildings’ envelope as in the case of ‘green’ roofs, green ‘facades’, and ‘living’ walls. These systems primarily improve energy building performance due to enhancing building insulation and thus reducing the cooling/heating demand. Hence, these applications of vegetation contribute to the improvement of the indoor and outdoor environment [42,43,44,45,46]
- To provide efficient shading of open space surfaces. This can be achieved with vegetation (trees) or by using shading devices to control the solar radiation incidence. As cited by Santamouris (2013), “shaded surfaces present a much lower surface temperature as the absorbed direct solar radiation is seriously reduced” [16]
2. Materials and Methods
2.1. Methodology
2.2. Simulations and Models
2.3. Selection of a Typical Day
2.4. Models and Simulation Input Data
2.5. Reliability and Validation of ENVI-Met
2.6. Methodology of the Parametric Study—Bioclimatic Renewal Scenarios
- The ‘Cool Materials Scenario’ included: the use of cool, light-colored concrete tiles at the paved and impervious surfaces of the urban block (Table 6). These surfaces constitute the urban blocks’ enclosed courtyards, sidewalks, pedestrian streets, and roads. The selection of the paving materials satisfied two basic criteria: (a) present high infrared emittance (over 0.9), and (b) ensure the highest possible reflectivity, taking into consideration that the material reflectivity may gradually decrease to 0.5 due to aging [29], as well as cause glare problems or high contrast levels due to being excessively high, namely higher than 0.85 [29]. The surfaces exposed to sunlight for a longer period of the day were paved with high albedo tiles (0.77). The one-way roads were paved with cool, off-white asphalt (albedo 0.55) and the double-direction roads with light-colored asphalt (albedo up to 0.45) in order to avoid optical discomfort from high reflectivity while driving.
- The ‘Cool Materials & Albedo increase of the Building Envelope’ Scenario included: the application of cool materials on the paved surfaces as mentioned above, and additionally the albedo increase of the building walls from 0.5 to 0.65 and of the building roofs from 0.5 to 0.9. The roofs’ albedo was increased since all roofs of the study area are flat and at the same average height (≥16 m), thus not causing optical discomfort at the pedestrian level due to minimized reflections. Moreover, this albedo value was chosen in reference to the previsions of a relevant Greek building regulation (Article 8, Act no. Δ6/Β/14826 “Measures for amelioration of energy efficiency in the public and private building sector”, FEK B’ 1122/17.6.2008).
- The ‘Vegetation’ Scenario included: (a) coverage with vegetation of the UB courtyards at approximately 100% of the total area, (b) the tree planting of the courtyards with deciduous species at least 25% (the 25% refers to the minimum ground surface shaded by the trees. The minimum shade provided on the ground level by a tree is reached when the solar radiation casts vertically to the tree canopy, i.e., at the maximum solar altitude. Therefore, the shaded ground surface equals the projected canopy surface [69]) of the total area, and (c) the tree planting across the sidewalks and pedestrian streets. Primarily streets oriented towards the E–W axis and with low H/W ratios were planted, i.e., those exposed more to sunlight. Trees of already existing species in the case studies were planted. In the courtyards, the tree species chosen to be planted were Morus Alba and Cercis Siliquasirum, which can provide sufficient shade. These trees were planted according to the solar study and towards the N–S axis. In order to protect the pedestrian zones from the prevailing winter winds (NE), rows of evergreen trees were planted towards the wind direction. The same methodology in tree planting was applied to the Agios Nikolaos Square included in the selected urban neighborhood but modified a bit. Specifically, the coverage with vegetation was at least 30% of the square’s total area, and the tree coverage was at least 20% due to leaving uncovered space for the particular uses of the Agios Nikolaos Cathedral.
- The Final Scenario—‘Vegetation, cool materials and albedo increase’ (Figure A2 and Figure A3). This scenario is a combination of the abovementioned scenarios. Primarily the strategy referring to the vegetated surfaces increase and adequate tree planting was applied. Consequently, the conventional materials of the remaining hard and impervious surfaces (sidewalks, streets) were substituted with cool materials. Finally, the albedo of the building envelope was increased as proposed above.
2.7. The Case Studies
3. Results and Discussion
3.1. Urban Blocks: UB.A and UB.B
3.1.1. The Effect of Cool Materials (UB.B)
3.1.2. The Effect of Cool Materials and Albedo Increase (UB.B and UB.A)
3.1.3. The Effect of Vegetation (UB.B and UB.A)
3.1.4. The Combined Effect of Vegetation, Cool Materials, and Increased Albedo (UB.B and UB.A)
3.1.5. The Examined Thermal Comfort Index
3.2. The Urban Neighborhood
3.2.1. The Combined Effect of Vegetation and Cool Materials
3.2.2. The Combined Effect of Vegetation, Cool Materials, and Albedo Increase of the Building Envelope
4. Conclusions
Acknowledgments
Conflicts of Interest
Appendix A
Microclimatic Parameter Improvement in the CASE STUDY SITES | |||||
---|---|---|---|---|---|
Estimated Parameters at 1.80 m Height | URBAN BLOCK TYPE A (UB.A) | URBAN BLOCK TYPE B (UB.B) | Urban Neighborhood (URBAN) | ||
Street Canyons | Courtyard | Street Canyons | Courtyard | Total Surface Area | |
Maximum Air Temperature Decrease | 0.6–1.1 °C | 1.2 °C | 0.5–1.0 °C | 1.2 °C | 1.8 °C and 1.6 °C (maximum decrease of the mean hour temperature) |
Maximum Relative Humidity Increase | 1.4–3.3 | 4.2–4.3 | 0.7–3.7 | 4.8 | 4.7 |
Maximum Surface Temperature Decrease | 0.1–8.2 °C | 12.3–13.1 °C | 0.7–12.7 °C | 11.5 °C | 8.1 °C (see. Spatial Distribution Maps) |
Improved PMV Index | see. Spatial Distribution Maps of the PMV Index |
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Type of Criteria | The Criteria |
---|---|
Spatial and Urban morphology | 1. Predominance of the built environment over the unbuilt (urban void and open spaces)
2. High building density 3. The existence of a public open space in the study area 4. Urban blocks (UB), where the building stock was mainly constructed during the first three decades of the post-World War II period 5. Mix and variety of land uses |
Social | 6. Social mix (social composition of the population) |
Urban Block’s Morphology | 7. UB with the common rectangular shape as identified in the urban fabric of Greek city centers |
8. Representative shape of the UB | |
9. UB mainly realized with the predominant building system in Greek central areas, i.e., ’pavilion-courts’ (thus when buildings are constructed in a way that a courtyard is shaped in the interior of the urban block.) | |
Environmental | 10. Degradation of the selected area in terms of air quality (poor air quality) |
11. Degradation of the selected area in terms of traffic congestion and car circulation | |
12. Higher temperatures recorded in the selected central area compared to the city suburbs | |
13. Lack of green spaces | |
Other | 14. Accessibility in the study area (mainly in the Urban Blocks) |
Basic Simulation Assumptions in ENVI-Met Model |
---|
Flat terrain and simplified box-shaped buildings. |
Cubic grid resolution up to 1 m in the horizontal axis. Higher grid resolution can be reached only on the vertical axis. |
The wind profile is constant during the simulation. |
Building indoor temperature is constant. Buildings have no heat storage. |
The 1D soil model is based on the initial temperature and humidity profile of the soil and the various surfaces. |
The vegetation model takes into account the humidity and radiation on the soil and in the air. When the A-gs model is used (Jacobs et al., 1996), the photosynthesis rate, the CO2 demand, and the state of the stomata are estimated. |
Summer Period (June, July, August) | Air Temperature (°C) | Relative Humidity (%) | Wind Speed (m/s) | ||
---|---|---|---|---|---|
Year | Avg. | Avg. Max. | Avg. | Avg. | Prevalent Direction |
2009 | 26.8 | 31.7 | 59.2 | 3.8 | SE, ΝΕ |
2010 | 27.9 | 33.3 | 59.9 | 3.9 | ΝΕ |
2011 | 26.9 | 31.8 | 59.9 | 3.9 | ESE, ΝΕ |
2012 | 28.5 | 33.8 | 57.2 | 3.5 | ΝΕ |
2013 | 26.8 | 31.8 | 60.6 | 4.4 | ΝΕ |
Simulation Input Data | |||
---|---|---|---|
Simulation Model Size (in meters) | Geographic Location: (Latitude, Longitude) | Β39.29°, Α22.56° | |
Urban Block type A (UB.A) | 240 × 280 × 59 m | Simulation Date: | 20 June 2010 |
Urban Block type B (UB.B) | 200 × 220 × 59 m | ||
Urban Neighborhood (URBAN) | 428 × 588 × 59 m | Date, Start & Duration of the Simulation: | 18:00 (19 June 2010), 30 h |
Model area (number of grids) | Soil properties in 0.5 m depth | Temperature: 22 °C Relative Humidity: 50% | |
Urban Block type A (UB.A) | 120 × 140 × 30 | ||
Urban Block type B (UB.B) | 100 × 110 × 30 | ||
Urban Neighborhood (URBAN) | 107 × 147 × 30 | Soil properties in 1.0 m depth | Temperature: 20 °C Relative Humidity: 50% |
Size of grid cell | 2 m, horizontally & vertically | Boundary Initial Conditions Temperature in 2500 m height: | 27.4 °C |
Size of grid cell (Urban Neighborhood) | 4 m horizontally, 2 m vertically | Wind Speed & direction: | 4 m/s, NE |
Relative Humidity (in 2.0 m height): | 60% | ||
Building Properties: | |||
Interior temperature: | 25 °C | U-value Walls: | 3 W/(m2⋅K) |
Albedo Walls: | 0.5 | U-value Roofs: | 2 W/(m2⋅K) |
Albedo Roofs: | 0.5 |
Paving Materials 1: | Properties Values | Vegetation 2: | ||||
---|---|---|---|---|---|---|
Albedo | Emittance | Height (m) | Root Zone | Canopy Diameter ⌀ | ||
Reference Model | Reference Model | |||||
Conventional asphalt | 0.18 | 0.85 | Grass | 0.50 | 0.5 m | – |
Conventional asphalt (aged) | 0.05 | 0.85 | Ailanthus altissima | 15 m | 2 m | >5 m |
aged concrete tiles and pavement | 0.25 | 0.85 | Cedrus deodara | 4 m | 2 m | <5 m |
Cercis siliquasirum | 5 m | 2 m | >5 m | |||
concrete tiles | 0.30 | 0.90 | Citrus aurantium | 5 m, 3 m | 2 m | <5 m |
ceramic tiles | 0.40 | 0.90 | Laurus nobilis | 4 m | 2 m | <5 m |
white marble | 0.65 | 0.95 | Ligustrum | 6 m, 4 m | 2 m | <5 m |
grey marble | 0.4 | 0.95 | Pittosporum tobira | 4.5 m, 4 m | 2 m | <5 m |
soil | Tilia platyphyllos | 5 m | 2 m | >5 m | ||
Scenarios (+) | Scenarios (+) | |||||
Cool light-colored concrete tiles (light yellow grey and green) | 0.68 | 0.94 | Aesculus hippocastaneum | 10 m | 2 m | >5 m |
Cool off-white concrete tiles | 0.77 | 0.94 | Prunus cerasifera | 5 m | 2 m | <5 m |
Cool beige-yellow asphalt | 0.4–0.45 | 0.93 | Morus alba | 6 m | 2 m | <5 m |
Cool off-white asphalt | 0.55 | 0.93 |
The Examined Scenarios |
---|
‘Cool Materials’ Scenario: Cool, light-colored concrete tiles at the paved and impervious surfaces (up to 0.77 albedo, 0.90 emittance approximately) Cool asphalt at the streets (up to 0.55) |
‘Cool Materials and Albedo Increase of the Building Envelope’ Scenario: Cool, light-colored concrete tiles at the paved and impervious surfaces (up to 0.77 albedo, 0.90 emittance approximately) Cool asphalt at the streets Albedo increase of the walls from 0.5 to 0.65 Albedo increase of the roofs from 0.5 to 0.90 |
‘Vegetation’ Scenario: Coverage with vegetation of the urban block courtyards at 100% approximately of the total area Tree planting of the courtyards with deciduous species at least 25% of the total area Tree planting across the sidewalks and pedestrian streets |
‘Final Scenario—‘Vegetation’, cool materials and albedo increase of the building envelope’: The ‘Vegetation’ scenario combined with the ‘Cool materials and albedo increase of the building envelope’ Scenario |
Urban Geometry | Case Studies | ||
---|---|---|---|
UB.Α | UB.Β | URBAN | |
Total surface area | 3780 m2 | 1537 m2 | 103,800 m2 |
Surface area of the open spaces—void lots | 846 m2 | 225 m2 | 25,950 m2 |
Average building height | ~16 m | ~17 m | ~17 m |
Building height to street width ratio (H/W) 1 | 1.5 | 1.8 | 1.8 |
Building height to open space width ratio | 1.0 | 1.2 | – |
Length to width ratio of the urban blocks courtyards | 1:4 | 3:4 | – |
Urban Geometry | Aspect Ratio Height/Width H/W 1 | |||
---|---|---|---|---|
Urban Block UB.A | Urban Block UB.B | |||
Northwestern Street Canyon (NW) | 1.35 | | 1.3 | |
Northeastern Street canyon (NE) | 1.45 | 2.4 | ||
Southeastern Street canyon (SE) | 1.5 | 1.2 | ||
Southwestern Street canyon (SW) | 1.6 | 2.1 | ||
Courtyard | 1.0 | 1.2 |
© 2017 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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Makropoulou, M. Microclimate Improvement of Inner-City Urban Areas in a Mediterranean Coastal City. Sustainability 2017, 9, 882. https://doi.org/10.3390/su9060882
Makropoulou M. Microclimate Improvement of Inner-City Urban Areas in a Mediterranean Coastal City. Sustainability. 2017; 9(6):882. https://doi.org/10.3390/su9060882
Chicago/Turabian StyleMakropoulou, Maria. 2017. "Microclimate Improvement of Inner-City Urban Areas in a Mediterranean Coastal City" Sustainability 9, no. 6: 882. https://doi.org/10.3390/su9060882