Micro-climatic Measurements in the Belen Area of Old Havana and three Courtyard Buildings: Comparison with Data from the Meteorological Station

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1 September 2004 Page 1 of 6 Micro-climatic Measurements in the Belen Area of Old Havana and three Courtyard Buildings: Comparison with Data from the Meteorological Abel Tablada de la Torre 1,3, Carlos Barceló 2, Frank De Troyer 3 1 Historian Office of Havana, Faculty of Architecture, ISPJAE, Cuba. 2 National Institute of Hygiene and Epidemiology, Havana, Cuba. 3 Katholieke Universiteit Leuven, Belgium Kasteelpark Arenberg 1 B-01 Leuven (Heverlee) Belgium Tel.: / Fax: abel.tablada@asro.kuleuven.ac.be, barcelo@inhem.sld.cu, Frank.DeTroyer@asro.kuleuven.ac.be ABSTRACT: The use of climatic data from a meteorological station for thermal simulations instead of the urban site conditions might result in erroneous evaluation of comfort inside buildings. This paper briefly summarises the method and results of two measurement campaigns in the summer 2003 and winter in the Belen area of Old Havana. The study aims to obtain micro-climatic data of the site for further use in thermal simulations of courtyard buildings. A comparison between three types of buildings was made in order to have a preliminary impression on how building and courtyard characteristics affect the interior climatic conditions. The results show that the outdoor temperature in this neighbourhood is in general higher than in the station; nevertheless, each location has its own hygro-thermal behaviour. The mean reduction of the wind speed at the roof level is significantly high. The shape and size of the courtyard proved to be essential in the thermal comfort of the buildings. Conference Topic: 3 Comfort and well-being in urban spaces Keywords: urban climate, micro-climatic measurements, thermal comfort, courtyard buildings. INTRODUCTION Present-day computer programs simulate the thermal conditions of existing and new buildings generating detailed output. However, these programs also need input on the climatic conditions of the site. Usually, architects and researchers take the climatic data of the nearest meteorological station to design new buildings or to evaluate their thermal conditions. Using the climatic data of the meteorological station without taking into account the possible heat island effect and wind reduction over the studied urban site could produce erroneous results in the evaluation of the comfort conditions of the buildings. Meteorological average height of 10-15m are clustered leaving no open spaces inside the block except the inner courtyards. Despite the relatively short distance between the site and the station, their topographical and geographical conditions are different. (Fig. 1-2) Building 1 Belen Convent Roof of Building 2 Figure 2: Some of the selected measuring places. Figure 1: View of the Belen Neighbourhood and the from the Belen Convent. The urban site of this case study is located at the west side of the harbour at 2-5m above sea level and 1 km from the meteorological station which is on the east side of the harbour at 51m above sea level. Morphologically the urban site is very compact with narrow and orthogonal streets oriented NNW-SSE and ENE-WSE. Two to four-floor buildings with Several studies have been conducted in Havana in order to determinate the microclimatic conditions and the heat island effect in several urban areas [1,2,3,4,5,6]. The majority of the measurements that supported those studies were not made in the area of Old Havana and covered short periods of time. Consequently, a series of new measurements were necessary in order to obtain more accurate microclimatic data of the Belen area for further use in simulations of courtyard buildings. In addition, thermal and wind conditions in courtyards and inside buildings

2 September 2004 Page 2 of 6 of similar materials may vary from building to building as a result of differences in form, size, and orientation of courtyards. Therefore, a comparison between three types of buildings was made in order to obtain preliminary evidences on how building and courtyard characteristics affect the interior climatic conditions. 2. FIELD MEASUREMENTS: METHOD Two measurement campaigns with a duration of two weeks in summer (July 2003) and four weeks in winter (December 2003-January 2004) were carried out. Two exterior points were used in summer and three in winter in order to compare them with the meteorological station. (Fig. 3a-b) Three representative types of courtyard buildings were selected in the neighbourhood of Belen. Building 1 has a square courtyard of 10m each side and 13m height. (Fig. 3c) Building 2 has a long and narrow courtyard of 2.5mx18mxm whose main axis is oriented E-W (Fig. 3d). Building 3 has also a rectangular courtyard of 3mx15mx14m but oriented N-S. Box The winter campaign consisted of continuous measurements of air temperature and RH besides punctual measurements of air velocity. The hygrothermal conditions were recorded using four hygrothermographs with daily calibrations and three data loggers. These instruments were placed from two to four weeks in three exteriors and in the interior of two apartments. The external points were the Church tower as with the summer measurements, the roof of the Belen Convent at 20m height and the back yard of the Santa Clara Convent. Two white louvered wooden boxes were used for the convents points (1.40m above the floor) (Fig. 3a-b). The punctual measurements focused on the wind conditions at different places of the buildings 1, 2 and 3 and the streets. These measurements were made during two weeks from 9:00 to :00 hours. Four anemometers were used to measure wind speed at the top of the three buildings in parallel with the other points: the street, the main entrance and 3 courtyard spots. In every case the anemometer was placed at 1.8m above the floor. For two days the wind measurements were carried out simultaneously at three points and included the interior of ground floor apartments. 3. RESULTS a b The hourly average of the temperature and the relative humidity (RH) over the measurement period is considered in this paper for the continuous measurements. The statistical analysis was based on the limits of confidence (95% of probability) of the differences between the measured places and the meteorological station. c Figure 3a: The Belen Convent and position of the white wooden box. b: The box at Santa Clara Convent. c, d: Courtyards of Buildings 1 and 2. The summer campaign were conducted following the specifications of Class II field measurements [7] except for the use of a hot-wire anemometer. Both continuous and punctual measurements were performed. For the continuous measurements four hygro-thermographs were used (error=0.5ºc). One was placed at the top of a church tower at m height from the ground and another on a roof of a nearby building at 15m height. Both were placed at 0.5m above the floor and were well ventilated and shaded. The other two were placed in the interior of two apartments with normal occupation, one on building 1 ground floor and the other on building 2 upper floor. The punctual measurements consisted of daily recording air temperature, relative humidity (RH), globe temperature and air velocity in the courtyards simultaneously with the living rooms, which face the courtyards, of two apartments at ground and top floor. The following instruments were used: two globetemperature thermometers, four dry bulb thermometers, two psychrometers (error=0.1ºc) and four anemometers (error= m/s). The summer campaign included a questionnaire to the inhabitants of the houses in order to assess their thermal sensation. This survey is the topic of a future paper. d 3.1 Summer hygro-thermal conditions The air temperature on the top of the church tower has marked differences with respect to the meteorological station. Figure 4 shows that during the night the tower is 1.5-2ºC warmer than the station. From 9 to 12h an inverted phenomenon occur due to the thermal capacity of the stone material of the tower. In the afternoon and evening the tower is 0.5 to 1ºC warmer than the station. The average RH in both locations is almost the same. Only in the morning the RH in the tower is 6% higher than in the station when the temperature in the tower is lower. Summer Mean Temperature Tower- Tower Figure 4: Hourly average of air temperature in the church tower and the station over the summer period. The outdoor temperatures on the roof are higher all the time in comparison with the station (fig. 5). During the night the differences are of ºC and in the morning ºC. In the afternoon the differences rise again 1-1.6ºC and during the evening

3 September 2004 Page 3 of 6 the differences are smaller with respect to the being then, not statistically relevant. The RH on the roof in the afternoon is 6-9% lower than in the station when the temperatures are higher. During the rest of the day the differences are smaller and have no statistical relevance. Summer Mean Temperature Roof- Figure 5: Hourly average of air temperature in the roof and the station over the summer period. The indoor temperatures of the room on ground floor of building 1 are more stables than in the station (fig. 6). There is a clear time lag of 2-4 hours. During the evening and night indoor temperatures are 2ºC higher. The RH in the interior follows the trend of the station. In the morning, the values in the station decrease abruptly due to the sun rise while in the apartment this decline has a time lag of 2-3 hours. Roof Summer Mean Temperature Build1 ground floor- Build1 Figure 6: Hourly average of air temperature in building 1 and the station over the summer period. Summer Mean Temp Build2 upper floor- Build2 Figure 7: Hourly average of air temperature in building 2 and the station over the summer period. The indoor temperatures of building 2 upper floor are even more stables than in building 1 ground floor (fig. 7) possibly as a result of the courtyard s narrow dimensions that allow little air exchange and no sun access (fig. 3d). The main differences with the station are during the evening and night being up to 4.5ºC warmer at 6 AM. In the case of the RH the values are also almost constant during the day and do not follow the trend of the station. The interior has 15% less than the station in the night and 6% more at midday Comparison of thermal parameters between buildings. Figures 8 and 9 show a comparison of the corrected standard effective temperature (cset) that considers the value of the globe temperature, the RH and the air speed. The measured interiors of building 1 are the least warm while the warmest are from building 3. The courtyards (patio) of building 1 and 3 are warmer than their interiors. Figure 9 also represents the cset together with the dry bulb and globe temperature differences between the courtyards and the measured interiors of each building. In the case of building 1 which courtyard area is the widest, the differences between the courtyard and the interiors are the largest for the three parameters (1.8-2ºC higher globe temperature). Building 2, which courtyard is the narrowest, has the most similar values between the interiors and the courtyard and its courtyard is the less warm from the three buildings Corrected Standard Effective Temperature cset B1gf B1uf B1patio B2gf B2uf B2patio B3gf B3uf B3patio B=Building gf=ground Floor uf=upper Floor Figure 8: Values of the corrected standard effective temperature (cset) in Building 1, 2 and 3. ºC Differences Patio-Interiors (gf=ground & uf=upper floor) b1patio-gf b1patio-uf b2patio-gf b2patio-uf b3patio-gf b3patio-uf cset Differences DBTemp Differences GlobeTemp Differences Figure 9: Differences between the courtyards (patio) and the interiors in three parameters. 3.2 Winter hygro-thermal conditions In winter, the hourly average temperature is during the night ºC warmer in the tower than in the station (fig. 10). In the afternoon the station is warmer than the tower ºC but with no statistical relevance. In the evening the tower is warmer again but with a small difference of 0.6ºC. The RH at the tower is very close to the one at the station. In the back yard of the Santa Clara convent the air temperature during the night is about 0.5ºC higher than in the station but with a low statistical provability (fig. 11). In the afternoon the convent is warmer in 1-2.5ºC and in the evening the differences are insignificant. The RH in the Sta Clara convent is close to that in the station except in the afternoon when the convent is warmer and the RH is 11% less than in the station.

4 September 2004 Page 4 of 6 Temp ºc Winter Mean Temperature Church Tower - ºC Tower Figure 10: Hourly average of air temperature in the church tower and the station over the winter period. Winter Mean Temperature Sta Clara Convent - ºC StaClara Figure 11: Hourly average of air temperature in the Sta Clara convent and the station in winter. The outdoor temperatures on the roof of the Belen convent are slightly lower than the station during the night and in the afternoon the differences are of ºC. Nevertheless, due to the amplitude of the daily differences, they are statistically not relevant. The RH at the Belen convent is close to the values of the station during the night. Nevertheless, during the day, the values can be 10% less than in the station. In the case of the buildings, the indoor temperatures have almost no fluctuation due to the thermal mass of the building and the limited ventilation (fig. 12&13). Winter Mean Temp Build 1 ground floor - ºC Build 1 Figure 12: Hourly average of air temperature in building 1 and the station over the winter period. Winter Mean Temperature Build 2 upper floor - ºC Build 2 Figure 13: Hourly average of air temperature in building 2 and the station over the winter period. This condition results in warmer interiors compared with the street and the station environment during the night. In the case of the building 1 the differences are in the range of 2-2.7ºC and in the building 2 the differences of 5-6ºC are even more pronounced. The houses can be cooler during some hours of the day, but with small differences with respect to the station. Concerning the RH both apartments are less humid during the night than the station. During the day, both the buildings and the station have similar values. 3.3 Wind conditions Summer wind conditions Figure 14 shows the exterior wind conditions. The church tower (m), which has no obstructions in the surroundings, has the highest mean wind speed in comparison to the other exterior places and the smallest differences with respect to the station. The wind speed at the ground level of empty plots and at the top of adjacent buildings was also analysed. In plot 1 the wind speed at the ground level (1.8m) is higher than at the top of adjacent building (18m) and that can be the result of the presence of some obstructions over the roof and the lower height of the buildings in front and in the back of the plot that could produces the Ventury effect on the ground level. In every case the wind speed at the roofs was at least 1.5 times higher than in the interiors and courtyards of the three buildings. m/s Mean Wind Speed & Exteriors Church Tower Plot 1 Roof Plot 1 Ground Plot 2 Roof Plot 2 Ground City locations % from station Figure 14: Average of wind speed at the station and exteriors in summer. Percent of the wind speed at exteriors from the station values. m/s Mean Wind Speed & Buildings B=Building, gf=ground Floor, uf=upper Floor 0% B1 gf B1 uf B1 Patio B2 gf B2 uf B2 Patio B3 gf B3 uf B3 Patio Building's locations % from Figure 15: Average of wind speed at the station and buildings in summer. Percent from the station data. Concerning the building s locations, building 1 has the highest interior air velocity in relation to the other buildings (fig. 15). The courtyard of building 1, that is the widest, has also higher values in relation to the courtyards of the buildings 2 and 3. The air velocity in building 2 has the lowest values when it is compared with the wind speed at the station. There is a direct correlation between the proportion of the courtyards and the air velocity measured at the centre of the courtyards. 5% 80% 70% 60% 50% 40% % 20% 10% 0% % % 20% 15% 10%

5 September 2004 Page 5 of Winter wind conditions Figure 16 shows a comparison of the average wind speed at the buildings roofs with the wind speed of the station at different hours of the day. The wind speed at the roofs is from 20% at 11:00 to almost 50% at :00 with respect to the station. The differences have no direct correlation with the values from the station and that can be the result of the influence of the changing wind direction. However, it is worth to point out that in the morning and late afternoon, when the wind speed is lower at the station, in the city the wind reduction is lesser than in other hours. This could be the result of the turbulent character of the wind in the city that generates its own pattern and also one of the effects of the heat island during calm and clear nights. [8] m/s Wind Speed & Roof Buildings per hour Building Roof % from 60.00% 50.00% 40.00%.00% 20.00% 10.00% 0.00% Figure 16: Average of wind speed at the station and exteriors in winter. Percent of the roofs wind speed from the station values..00% 20.00% 15.00% 10.00% 5.00% 0.00% % of Wind Speed of each Building with respect to MainFacade Street Courtyard CourtN CourtS 2ndfloor Interior % Build-1 from % Build-2 from % Build-3 from Figure : Percent of the wind speed of each building location with respect to the station in winter. Concerning the locations of the three selected buildings, the winter measurements confirm the results of the summer campaign. The courtyard and the interiors of building 1 have the smallest differences of air velocity with respect to the station when compare them with buildings 2 and 3. (fig. ) On the other hand, building 2 has the lowest values both in the courtyard and interiors but the highest air velocity on the main façade due to its position facing the end of a perpendicular street which is an exceptional case in this urban context. 4. DISCUSSION The overall results indicate that the hygro-thermal conditions in the analysed neighbourhood of Old Havana has not a regular behaviour compared with the meteorological station. The differences between the city and the station vary from place to place and from one season to the other. These differences can be the result of several factors like diversity in the nearby constructions and materials and the different height from ground level of the measured places. Nevertheless, some general conclusions can be arisen for each particular place. In the case of the church tower the temperatures during the night are both in summer and winter higher than in the station and lower during the day. In the case of other places like the building roof in summer and the roof of the convent in winter, the difference is less pronounced and can even be reverse. The thermal mass of the stone-made tower can be the cause of these differences, even if the instrument was located in a well ventilated space. The higher temperatures during the afternoon in the Sta Clara convent might be the result of the nearby high reflective cement material of the ground even if the position of the instrument was the best possible taking into account the high density of the site. However, these high temperatures were also registered by Ortiz and Ortiz in 55 [1] and by Nieves and Prilipko in 87 [2] in which the south part of Old Havana had differences of +3ºC and +1.5 respectively in the late afternoon. As it was expected, the average relative humidity (RH) had an inverse pattern in comparison with the air temperature. Nevertheless the RH differences between the site and the station had a more unstable behaviour than the temperature differences. In the case of the interiors, both in summer and winter, the air temperature and RH are remarkably stable. In summer, the indoor temperatures can be lower than the exteriors, but during the night the heat released from the building mass can produce uncomfortable conditions. The comparison of the three buildings and locations offer evidence of how the building layouts and courtyard s shape can influence the hygro-thermal conditions inside the houses. Even if the temperature differences are not significant between the locations of the three buildings, their resultant thermal conditions are different due to the influence of the globe temperature and the wind speed. The rooms of the building 1 are cooler than the others due to the cross ventilation between the street and the courtyard. But on the other hand, the courtyard of the building 1 is the hottest due to its squared shape and larger size that permit sun rays penetrate during more hours. In building 2, where the courtyard is the most protected from solar radiation, the rooms have no other source of air than the inner courtyard. This situation leads to warmer thermal conditions than the rooms of building 1 but similar with respect of the rooms of building 3 even if the courtyards have different orientations. The protection from the exterior, assures better thermal condition for the courtyard in building 2 in comparison with the unprotected courtyards. But on the other hand, this situation instead of providing a cooler condition during the day inside the apartments what creates is stable uncomfortable conditions due to a weak net outgoing radiation during the night and limited ventilation. This founding is in contradiction with previous studies in Old Havana [3, 5] which conclude that courtyards and rooms that are physically isolated from the street can keep during the day better thermal conditions than rooms linked to the

6 September 2004 Page 6 of 6 street with cross ventilation. Further studies with larger monitoring and number of cases should be performed in order to obtain more arguments and data for the present discussion. Concerning the wind conditions, both in summer and winter, the reduction of the wind speed at the level of the building s roof can varies from 15 to 50% with respect to the wind speed at the meteorological station. Despite this wide range of difference, from the overall wind measurements, we can consider, as a first approximation, the average wind speed of 37% in summer and 35% in winter for the thermal simulations. In other words, there is a wind speed reduction of 63% in summer and 65% in winter in comparison with the station. This situation is in line with studies made in Gothenburg [9] and Lodz [10] where the wind reduction was of 60% and -40% respectively. Nevertheless, according to Landsberg [11] the annual average speed of the wind in the cities is 20- % less than that in the rural areas and under certain climatic conditions the wind speed inside the city can be higher. These results depend, in great extend, on the conditions and selection of the measurement points, thus further measurements and simulations are needed in order to obtain more accurate data about the wind behaviour in this urban site. At the street level, the differences between the city and the station are more unstable due to the orientation and profile of the streets. Inside courtyards, the air velocity can varies due to the orientation of the courtyard and the position of the main entrance with respect to the courtyard. In building 1 the courtyard has higher air velocity than the other buildings both in summer and winter. This may be the result of the direct link between the courtyard with the street through an ample entrance and also due to the presence of a second courtyard that function as inlet/outlet. The courtyards of the building 2 and 3 have similar wind reduction among them in comparison with the station; nevertheless, the courtyard of building 2 has lower mean air velocity even if at the façade there is higher wind pressure. The very narrow profile of the courtyard and the inexistence of and outlet might be the cause of these low values. CONCLUSION The hygro-thermal conditions in the Belen neighbourhood of Old Havana can vary from one exterior place to the other according to the morphological characteristics of the adjacent fabric and the ground and building materials; nevertheless, the air temperature in this neighbourhood is in general warmer than in the station. The average differences of the air temperature and relative humidity of the measured places with respect to the station will be applied for further comfort studies on new buildings inserted in this urban context. The mean reduction of the wind speed at the roof level changes according to the speed at the station and the time of the day. This reduction can be assumed for further modelling as 60-65% from the station data. Nevertheless, more complete studies are needed in order to have full year data from different places of Old Havana. Buildings with courtyards connected to the street and to a second courtyard can offer better ventilation to their apartments. Buildings with large-squared and no shaded courtyards can be affected by an increase of air temperature due to the influence of the direct and indirect solar radiation. The factor of ventilation had a more important role in thermal comfort than the protection from solar radiation in a compact urban site even if the exterior air can be warmer during few hours of the day. The apartments facing the most shaded and protected courtyard had worse thermal conditions than the apartments facing the wide less-shaded courtyard but having cross ventilation between the street and the courtyard. ACKNOWLEDGEMENT We would like to thank Tech. José López and Lic. Armando Bacallao (Institute of Hygiene and Epidemiology) for their material help and scientific cooperation. Prof. Ana M. de la Peña (ISPJAE) and Prof. Han Verschure (KULeuven) for their advice. Prof. Hans Rosenlund and Prof. Erik Johansson (Lund University). Dr. Bruno Enriquez (Cubasolar). Lic. Franz Torres. Ing. María Buajasán and personal from Heritage Architecture (Historian Office of Havana). REFERENCES [1] Ortiz, R., and Ortiz, R., "Dónde hace más calor en La Habana? 55. [2] Nieves, M., et al., "Urbanismo y Régimen Térmico", in Arquitectura y Urbanismo, No 3, pp Havana, 88. [3] Alfonso, A., Díaz, G., De la Peña, A M., La Ciudad Compacta: Arquitectura y Microclima, ISPJAE, 91. [4] Díaz, G. El régimen térmico en espacios abiertos intraurbanos de C. Habana. Doctoral thesis. Faculty of Architecture. ISPJAE. Havana. 98. [5] Alfonso. A. Transpira la ciudad compacta? in Arquitectura y Urbanismo. No 1, pp ISPJAE, Havana, 85. [6] Barceló, C et al. Estudio de los factores físicos para la valoración higiénica del medio residencial, MICONS, Havana, 89. [7] Brager, G., Dear, R. Thermal Adaptation in the built environment: a literature review, in Energy and Buildings, 98, pp [8] Givoni, B. Climate considerations in building and urban design, V N. Reinhold, NY. 98. pp [9] Holmer, B. Wind Climate in Göteborg. Published as Göteborg University, Department of Physical Geography, Report p [10] Siedlecki, M. Urban-Rural Wind Speed Differences in Lodz. University of Lodz, [11] Landsberg, H.E., World Survey of Climatology, Vol 3. Elsevier, Amsterdam, 81. pp. 3.