Download design recommendations for new courtyard buildings

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 Tablada
1
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
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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 lowrise
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.
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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.
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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), westsouthwest (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
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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.
3.2. THERMAL COMFORT ANALYSIS
For cases with single-side ventilation, ground-floor rooms were always cooler than top
rooms, independently of the orientation and shape of the courtyard. The slightly higher
air speed of the top-floor SV rooms in comparison with the ground-floor SV rooms
seems to be not enough to counteract the influence of the solar radiation on the roof
and wall facade for these specific prototypes.
On the other hand, the higher air speed values provided by cross-ventilation strategies
improve thermal comfort under warm conditions even if the exterior air temperature is
quite high, i.e. in the range of 26ºC to 32ºC. For rooms that are more protected from
direct and indirect solar radiation, like ground-floor rooms, higher air speed values are
not as crucial as for the top-floor rooms if cooking activity is not considered. The best
thermal comfort on top-floor rooms is achieved by providing cross ventilation through
wider courtyards, by the use of exterior louvers and by orienting the room towards the
SSE and NNW.
Therefore, with the application of these strategies thermal conditions during the
summer improve in terms of PMV from 1.2 to 0.87 and in terms of Effective
Temperature (ET*) from 32.4°C to 31°C which is close to the upper limit of Old Havana
summer comfort conditions (ET* = 30.6°C) according to Tablada et al. (2009).
4. GENERAL DESIGN RECOMMENDATIONS FOR COURTYARD BUILDINGS
In this section a summary of the general recommendations for the design of naturallyventilated courtyard buildings in Old Havana are presented. The recommendations are
distilled from the previous studies which included field measurements and thermal
sensation survey, CFD simulations and thermal comfort analysis (Tablada et al. 2006,
2009).
Figure 3 and 4 illustrate several building layouts for each plot type out of around 200
analysed. Detailed recommendations for each of the three plot types and with several
open space ratios will be presented in a future publication.
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Sustainable Building 2013 Hong Kong Regional Conference
Urban Density & Sustainability
12 -13 September 2013
Figure 3: Schematic representation of some possible building layouts (out of 160 considered) for
plot type 1 (a, b, c) and plot type 2 (d, e, f) with open space ratio = 0.3. The modules in grey
represent the courtyard area and the modules with lines represent the rooms with cross
ventilation by direct contact with two courtyards or through an adjacent room.
Figure 4: Schematic representation of some possible building layouts (out of 32 considered) for
plot type 3 with open space ratio = 0.3. The modules in grey represent the courtyard area and
the modules with lines represent the rooms with cross ventilation by direct contact with two
courtyards or through an adjacent room.
4.1. GENERAL RECOMMENDATIONS
1. Building geometry
 Open space ratios > 0.25 are recommended.
 Two types of courtyards are recommended: (1) a wide courtyard (0.6 ≤ W/H ≤
1.0) to ensure enough daylight and ventilation inside main rooms (living rooms,
dining rooms and bedrooms), to provide some greenery, circulation and
access to apartments and (2) narrow courtyards (0.3 ≤ W/H ≤ 0.5) for services
rooms and as a secondary opening for the main rooms to ensure CV.
Ventilation shafts may also be a third option to ensure CV if space is limited.
 An interconnection between the street and the courtyards and among the main
courtyards through a circulation path on ground floor is recommended.
 For plot type 1 and 2 (Fig. 3), buildings with courtyards equivalent to two
modules should preferably have less than around 9 m height (1 to 3 floors).
 For plot type 3 (Fig. 4), buildings with a wide courtyard (W > 6 m) could have a
maximum height of 11 m (3 - 4 floors). If one or two wide courtyards (W ≥ 7 m)
are linked with the street, the maximum height of the building could be 14 m.
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Sustainable Building 2013 Hong Kong Regional Conference
Urban Density & Sustainability
12 -13 September 2013
2. Orientation
 The orientation of the courtyard’s main axis should prioritize the climatic factors
(prevailing winds, solar radiation) rather than following the actual plot
orientation (e.g. in Figure 3, case ‘c’ and ‘f’, and in Figure 4, case ‘d’).
 Windows orientation on top-floor rooms should be taken into account according
to the function of the room. Daytime rooms like living-rooms should preferably
be oriented towards the SSE-NNW. On the contrary, top-floor bedrooms
should preferably face ENE for SV cases but for CV cases they should face
SSE-NNW in order to avoid solar radiation on the WSW orientation. Kitchens
and bathrooms can be oriented to WSW.
 If oblique courtyard walls and windows are possible, then orientations ranging
clockwise from NNW to NNE and from SSE to SSW are preferable.
 For plot type 1 (Fig. 3), cases ‘a’ and ‘b’ are preferable for buildings with ENE
and WSW facade orientations. Case ‘c’ is better for NNW and SSE.
 For plot type 2 (Fig. 3), case ‘e’ is preferable for buildings with ENE and WSW
facade orientations. Case ‘f’ is better for NNW and SSE facade orientations.
 For plot type 3 (Fig. 4), the longest courtyard’s facades should preferably be
oriented towards NNW and SSE.
3. Ventilation and solar protection
 Cross ventilation is recommended for the main daytime-use rooms like the
living-room and dining-room. Cross ventilation on bedrooms is more effective
and necessary on top-floor than on ground and middle-floor bedrooms.
 A connection between SV rooms by internal openings or by sliding walls is
recommended in order to provide cross ventilation when required.
 Wider courtyards (0.6 ≤ W/H ≤ 1.0) should have proper sun shadings over
windows and courtyard walls (e.g. exterior horizontal louvers or pergolas with
wines). The use of movable louvers as part of the window system is
recommended for the main rooms on every floor.
 Sun shadings should protect, at least, the top-floor rooms facing the narrow
courtyards (0.3 ≤ W/H ≤ 0.5).
 The use of transitional spaces around courtyards like galleries and balconies
should be promoted in order to avoid direct solar radiation and brusque
changes in radiant temperature and daylight values.
5. CONCLUSIONS
In this paper, general design strategies to favour natural ventilation and thermal
comfort inside residential buildings in Old Havana have been recommended. The
design strategies are based on previous studies in which field measurements, thermal
comfort survey, CFD simulations, thermal simulations and a comfort analysis have
been conducted for different generic courtyard buildings.
The positive effect of the air movement on thermal comfort in warm and humid
conditions has been given priority for the elaboration of the recommendations. Higher
air speed values provided by cross ventilation strategies improve thermal comfort for
the rooms which are more exposed to solar radiation like top-floor rooms and rooms
oriented towards ENE and WSW. The cooling sensation of air movement is effective
even if the exterior air temperature is in the range of 26º C and 32º C.
In the context of Old Havana, three main design strategies should be promoted: (1) to
provide cross ventilation in the majority of rooms by means of a sequence of different
sizes courtyards linked to the street through a ground-floor circulation path; (2) to use a
higher open space ratio than the minimum required by the current urban regulations in
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Sustainable Building 2013 Hong Kong Regional Conference
Urban Density & Sustainability
12 -13 September 2013
the Historical Centre, preferably > 0.25 in order to allow wider inner courtyards with 0.6
≤ W/H ≤ 1.0; and (3) to provide an efficient solar protection for the wider courtyards –
including vegetation- in order to reduce the solar heat gain.
The results of this and previous studies indicate that adequate design solutions can
provide summer indoor thermal conditions within or close to the limits of the comfort
zone proposed for Old Havana. The recommendations of this study can be useful for
the extension and/or improvement of the current urban regulations of the Historical
Centre of Havana. They can also guide the decisions of practitioners working in other
compact low-rise urban areas in tropical humid regions.
Detailed recommendations for each of the three plot types with a larger number of
design options will be presented in a future publication. Further work is needed to
evaluate thermal, daylight and energy performance of optimal prototypes for each plot
and facade orientation.
6. REFERENCES
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