Sustainable Building 2013 Hong Kong Regional Conference Urban Density & Sustainability 12 -13 September 2013 DESIGN RECOMMENDATIONS FOR NEW COURTYARD BUILDINGS IN COMPACT HISTORICAL CENTRE OF HAVANA Abel Tablada1 Department of Architecture, National University of Singapore, Singapore 4 Architecture Drive, Singapore 117 566 1 Corresponding Author E-mail: [email protected], Tel: (65) 6601 2435, Fax: (65) 6779 3078 1 Sustainable Building 2013 Hong Kong Regional Conference Urban Density & Sustainability 12 -13 September 2013 DESIGN RECOMMENDATIONS FOR NEW COURTYARD BUILDINGS IN COMPACT HISTORICAL CENTRE OF HAVANA ABSTRACT The Historical Centre of Havana in Cuba is a compact low-rise urban site declared World Cultural Heritage in 1982 by UNESCO. The Master Plan of the Historical Centre comprises the construction of residential buildings in the empty plots to allocate surplus population from overcrowded houses and from dilapidated and valuable colonial buildings. However, the new housing typologies, while increasing the gross floor area in comparison with previous colonial buildings, should also ensure proper environmental conditions and thermal comfort by maximising the potential for natural ventilation. The aim of this paper is to present preliminary design recommendations for new low-rise residential courtyard buildings inserted in the Historical Centre of Havana. The recommendations are based on previous studies on microclimatic measurements, comfort survey, Computational Fluid Dynamics simulations, thermal simulations and comfort analysis on a series of combinations of courtyard building prototypes. The recommendations aim to promote the design of thermally comfortable naturally-ventilated residential buildings in the Historical Centre of Havana in particular and in other compact low- rise urban areas in tropical-humid regions in general. Keywords: Courtyard buildings; Design recommendations; Natural ventilation; Thermal comfort; Tropical architecture. 1. INTRODUCTION The Historical Centre of Havana (Old Havana) in Cuba is a compact urban site declared World Cultural Heritage in 1982 by UNESCO. It is located on the west side of Havana’s harbour at 23.13° north and 82.35° west, very close to the Tropic of Cancer as shown in Figure 1. It has a density of 30,000 inhabitants per km2 (National Office of Statistics, 2011) plus a floating population of 37,000 per km2 in an area of 2.14 km2. Climatic conditions in the city are influenced by the sea with a combination of relatively high values of air temperature (August mean maximum: 31.4°C) and high values of relative humidity (August mean maximum: 91%). With a distinguished wet and dry season, Havana belongs to the Tropical savanna climatic zone according to Köppen’s classification. Despite the comprehensive recovering plan that has been undertaken during more than 3 decades in the Historical Centre, there is still a significant amount of buildings in disrepair and empty plots inside the boundaries of the former intramural city (Fig. 1c). The Master Plan of the Historical Centre (Office of the City’s Historian, 1998) comprises the construction of residential buildings in the empty plots to allocate surplus population from overcrowded houses and from dilapidated and valuable colonial buildings. However, the new housing typologies, while increasing the gross floor area in comparison with previous colonial buildings, should also ensure proper environmental conditions and thermal comfort by maximising the potential for natural ventilation. The application of natural ventilation strategies helps to prevent the use of air-conditioners in the new housing, contributing in this way to diminish the energy use and the effects of the urban heat island and the green-house gas emissions at local and global scales respectively. 2 Sustainable Building 2013 Hong Kong Regional Conference Urban Density & Sustainability 12 -13 September 2013 Numerous studies have proposed design strategies for buildings in tropical and humid climates. However, most of the design recommendations (e.g. Koenigsberg et al., 1973; Lippsmeier, 1980; Givoni, 1998) are based on the assumption that cities in such climates have spread-out low-density urban environments. In recent years several studies have focused on urban design guidelines for tropical high density and high-rise urban environments, especially for East Asia (e.g. Ng, 2010; Cheung and Liu, 2011; Yuan and Ng, 2012). However, nor the spread-out neither the high-rise urban environments are representative of Old Havana and other tropical cities in Latin America, Africa and Asia. Figure 1: a) Location of Havana, b) typical street in Old Havana, c) satellite view of the Historical Centre of Havana (inside doted lines is the former intramural city). At the building scale, most studies related to courtyard buildings considered hot and dry climates and focused on their thermal performance rather than on the airflow conditions. Literature related to courtyard buildings in tropical humid contexts is scarce. Bittencourt and Peixoto (2001) and Rajapaksha et al. (2003) performed CFD simulations for a building and a house with a courtyard. In addition, Murakami et al. (2004) conducted a study on a porous-type building for a compact urban area of Hanoi. However, in these studies the buildings are fully or partially isolated and have openings in their exterior envelope in contrast with the situation of the present study in which the courtyard building is located in a very compact urban environment with openings mainly in the inner courtyard walls. The purpose of this paper is, therefore, to present preliminary design recommendations for future low-rise residential courtyard buildings inserted in the Historical Centre of Havana. The recommendations are based on microclimatic measurements and a comfort survey reported in Tablada et al. (2009) and on Computational Fluid Dynamics (CFD) simulations, thermal simulations and comfort analysis (Tablada et al., 2006) on a series of combinations of courtyard building prototypes. 3 Sustainable Building 2013 Hong Kong Regional Conference Urban Density & Sustainability 12 -13 September 2013 2. MORPHOLOGY AND PLOT TYPES The urban morphology in the Historical Centre can be described as compact low-rise. The street pattern is semi-orthogonal and the parcel system shown in Figure 2a is one of shared party walls with elongated plots. The buildings occupy most of the plot area leaving only 15% to 20% of open space for inner courtyards and air/light shafts. The oldest residential buildings have one (4–5 m high) or two stories (8–10 m), while the apartment buildings have three (9–12 m) or four (12–15 m) storeys. Plot ratios vary between 1.5 and 2.5. The street canyons are about 7–10 m wide having width/height (W/H) aspect ratios from 1.2 to 0.5 (Fig. 1b). The compact nature of the urban structure and the presence of party walls for almost all buildings allowed limiting the natural ventilation and thermal comfort study to a selected number of generic building and courtyard configurations. In Tablada et al. (2009) a morphological subdivision of the Historical Centre was made and three typical plots were selected from two representative sectors. Afterwards, potential building layouts for each typical plot were explored by using a horizontal modular grid for rooms and inner courtyards (Fig. 2b). The horizontal modules are 3.5 m by 3 m and determine the room and courtyard dimensions. The width (W) of the courtyard is 3 m, 6 m or 9 m and the courtyard depth is 3.5 m, 7 m, or 10.5 m. In the selected configurations, the buildings have three floors with a total height of 9 m. Figure 2: a) Typical urban block with courtyard buildings in Old Havana, b) three representative plot types with modular subdivisions. For the CFD simulations, cases with a single or a double courtyard were considered. The aspect ratios of the courtyards were W/H = 0.33, 0.66 and 1.0. For the thermal simulations and comfort analysis, the combination of a single room with its adjacent courtyard(s) was considered. For single-side ventilated (SV) rooms, four window orientations were considered: east-northeast (ENE), south-southeast (SSE), west- southwest (WSW) and north-northwest (NNW). These orientations coincide with the actual orientation of building blocks in Old Havana. For cross-ventilated (CV) rooms, the two possible orientations were considered: ENE-WSW and SSE-NNW. 3. SUMMARY OF RESULTS FROM CFD AND THERMAL SIMULATIONS In this section the results from the natural ventilation and comfort studies in the generic buildings –three storeys with one or two consecutive courtyards- inserted in the compact urban environment of the Historical Centre of Havana are summarised. CFD 4 Sustainable Building 2013 Hong Kong Regional Conference Urban Density & Sustainability 12 -13 September 2013 simulations (by Fluent Inc, 2003) were performed to obtain the values of indoor air speed and pressure coefficients required for the thermal and comfort simulations (by EnergyPlus, 2001). Thermal comfort was analysed by using the extended Predicted Mean Vote (PMV) index adapted to regions with warm conditions (Fanger and Toftum, 2002). For a detailed description of the simulations methodology and results the reader is referred to Tablada et al. (2006). 3.1. NATURAL VENTILATION EVALUATION USING CFD SIMULATIONS The aspect ratio (W/H) of the courtyard influences the indoor air speed values, with the exception of the air speed inside the upstream rooms. A single courtyard with W/H = 0.66 provides higher indoor air speed than a narrow courtyard with W/H = 0.33. Two consecutive wider courtyards (W/H = 0.66) provide higher indoor air speed than two courtyards of W/H = 0.33 for the central CV rooms. In general the SV rooms have very low indoor air speeds (< 0.1 m/s) while the presence of more than one courtyard can provide significantly better ventilation for the central CV rooms (0.2-0.3 m/s). However, this improvement is different among the three floors and almost insignificant for the remaining SV rooms in the two-courtyard building.