Outdoor thermal comfort in a hot and humid climate of Colombia: A field study in Barranquilla

Building and Environment 75 (2014) 142e152

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Outdoor thermal comfort in a hot and humid climate of Colombia: A field study in Barranquilla Kattia Villadiego a, *, Marc André Velay-Dabat b a b

Institute for Urbanism and Regional Planning (IUAR), Aix en Provence, France ABC laboratory e National School of Architecture, Marseille, France

a r t i c l e i n f o

a b s t r a c t

Article history: Received 8 November 2013 Received in revised form 24 January 2014 Accepted 25 January 2014

We carried out a thermal comfort survey in a hot and humid climate in Barranquilla, Colombia. Measures of climatic conditions and parallel thermal sensation questionnaires were used in order to increase knowledge about thermal sensation in tropical climates. We used the ASHRAE sensorial scale of seven symmetrical points to evaluate sensation; we also asked about agreement preference. The survey was focused on pedestrians in five different zones of Barranquilla established through the Local Climate Zone System. Results show a high tolerance to high temperature and relative humidity. The mean thermal sensation votes for the whole sample was 0 ¼ neutral; people felt satisfied but they preferred cooler temperatures. Thus, expectation and memory are other factors that influence perception. Also, the survey reveals that climate conditions are not enough to explain thermal sensation. Overall, air temperature, solar radiation and wind speed are the most influential parameters on thermal sensation. The results of the study contribute to knowledge about thermal comfort in tropical climates and encourage planners to include climate considerations into urban planning in order to improve the quality of thermal ambiance. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Thermal comfort Tropical climate Local climate zones Thermal sensation Urban planning

1. Introduction Scientists around the world are interested in the phenomenon of urbanization and its impact on climatic change. This concern becomes even more important in the case of tropical cities, because demo-spatial dynamics come with environmental alterations. Yet the climate of tropical cities remains a subject insufficiently studied [1]. In a hot and dry climate, increases in temperature expose inhabitants to difficult thermal conditions. In such conditions, any passive cooling strategies are usually insufficient to bring about thermal comfort; therefore, the use of air conditioning becomes necessary, which means increases in energy demand. However, socio-economics in tropical cities are strongly unequal; poor inhabitants do not have the possibility of avoiding unsatisfactory thermal conditions with air conditioning. Planning and urban design can improve or worsen this situation. For example, wealthy neighborhoods in general include green spaces and building separation, while people from poor neighborhoods live in compact houses without enough green zones and

* Corresponding author. Ecole Nationale Supérieure d’Architecture de Marseille, 184 av. de Luminy case postale 924, 13288 Marseille cedex 09, France. Tel.: þ33 (0) 6 60 91 69 01; fax: þ33 (0) 4 91 82 71 80. E-mail addresses: [email protected], [email protected], [email protected] (K. Villadiego). 0360-1323/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.buildenv.2014.01.017

space to allow ventilation and shade. Consequently and unintentionally, urban planning may in some ways accentuate inequality. On the other hand, a better understanding of tropical climate and thermal comfort, especially in outdoor spaces, can contribute to improved quality of urban space, urban image and economic development [2]. The relationship between the use of spaces and thermal comfort has been demonstrated by several surveys [2e7]. Visitors to a site increase economic activity. Also, studies of climate as a factor in tourism decisions have shown that tourism considerations are a significant reason to include thermal comfort in urban planning in tropical cities [8,9]. Reviews of surveys on urban thermal comfort show an increasing interest in outdoor thermal comfort in tropical climates [10e12]. Nevertheless, there is still a lack of information about thermal comfort in outdoor spaces in tropical cities; this fact is especially true for Latin America. As far as we know, there have been only a few surveys of southern México, Cuba and Brazil [13e 15]. Others surveys concern indoor conditions [16]. On the other hand, many models or indices to predict thermal sensation and comfort have been developed especially for indoor conditions. Among others, the most popular include PMV e Predicted Mean Vote [17] and PET e Physiologically Equivalent Temperature [18]. They are based on physiological and microclimatic parameters. Nevertheless, studies point out that physiological parameters are not the only factors that play a role in the perception

K. Villadiego, M.A. Velay-Dabat / Building and Environment 75 (2014) 142e152

of the thermal environment (outdoor conditions); memory, adaptation and expectations all have important roles in thermal comfort [2]. To understand human thermal perception, more surveys in several contexts are necessary. That is why more extensive studies, like this one, are necessary to understand regional particularities and then to suggest some recommendations for improving urban planning by taking into account microclimate and thermal comfort in tropical climates. Also, this kind of survey helps to improve inputs and parameters in order to ameliorate the thermal comfort index. However, we should make clear that our proposal is not the validation, creation or evaluation of the thermal comfort index. In this study we present the results of an outdoor thermal comfort survey in Barranquilla, a tropical city in Colombia, a developing country in South America. Many problems can be found in this city. The city’s growth pattern shows spatial and social fragmentation; urban climate has not been a strong urban planning criterion; and the lack of comfort in outdoor spaces has become an annoyance for citizens. Data obtained from surveys can be compared with other studies in tropical cities as a way to enhance knowledge about tropical climates and outdoor thermal comfort. 2. Methods 2.1. Research area Barranquilla is one of the most important cities of Colombia; it’s a mid-sized city with an estimated 1,193,952 inhabitants [19] and 166 km2 of surface. It is strategically located at the intersection of the Caribbean Sea and the Magdalena River, in the north of the country, at 10 590 latitude north and 74 470 longitude west, with an elevation from 4 m to 120 m above sea level (Fig. 1). Barranquilla

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has a tropical savanna climate e Aw e according to Köppen climate classification [18]; its mean annual temperature is 28  C; the thermal oscillation does not exceed 10  C; the mean annual relative humidity is 80%; and annual precipitation is 900 mm. The city has only two seasons: dry and wet. Dry season is from December to March; this period is characterized by trade winds, high solar radiation, clear skies and few rainy days. Trade winds blow from the northeast with a mean wind speed of 4.0 m/s. High relative humidity and abundant rain and storms are common the rest of the year when the wet season takes place. 2.2. Classifying Barranquilla by local climate zones In order to study urban climates, scientists have developed several methods to describe and classify the studied area. A literature review showed that this heterogeneity makes it difficult to compare research on urban climates and the judgment of the real magnitude of Urban Heat Island e UHI [20]. Looking for a standardized language, Stewart & Oke [21] proposed a system to classify urban forms and to describe site measurements in a better way; this system is called Local Climate Zones e LCZ. The parameters used to describe the zones are built fraction, soil moisture, albedo, sky view factor, roughness height, and anthropogenic heat flux. The LCZ system is being tested by climatologists and other urban experts with success. This study isn’t concerned with UHI per se but rather with urban climates, so we applied the LCZ system to classify the urban form of Barranquilla (Fig. 2). We collected urban data from maps, plans, pictures and satellites images from Google EarthÒ and Bing mapsÒ. Then we did a field study to make observations and verify the information. The final map was designed using Quantum GIS softwareÒ. Among all these zones, we selected five (5) residential

Fig. 1. Location of research area.

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Fig. 2. Barranquilla LCZs and selected survey zones. Numbers represent the zones: 1) Alto Prado (LCZ 6_4), 2) Bellavista (LCZ 6), 3) Centro (LCZ 2), 4) Ciudadela (LCZ 3), 5) Cordialidad (LCZ 7B), 8) Reference zone (LCZ8).

zones to carry out a deep field study. The first zone is a neighborhood called Alto Prado. It is a combination of open high-rise (more than ten stories) and open low-rise (less than three stories) buildings (LCZ 6_4). The cover surface is mostly permeable but there is a significant quantity of trees producing shaded outdoor spaces. The second zone is Bellavista neighborhood with open, lowrise buildings, mostly individual houses (LCZ 6), with trees and vegetation spaces well represented in this zone. Downtown was the third zone (LCZ 2); it is characterized by compact midrise buildings (from three to nine stories) and little or nonexistent vegetation, high traffic, elevated pollution and commerce. In southern Barranquilla we have popular neighborhoods with an urban form more compact than in the northern neighborhoods. Ciudadela 20 de Julio (LCZ 3) was the fourth study zone; it is also a residential zone but very compact and dense. The last zone concerns the Cordialidad neighborhood, which is a neighborhood with lightweight, low rise construction combined with scattered trees (LCZ 7B). Traffic flow here is limited and the streets are not paved. We used a reference zone located at the city’s airport because the official meteorological station is located there. This zone is classed large low-rise (LCZ 8) according to the LCZ system. It is characterized by mostly paved land with one- or three-story buildings in an open arrangement.

In Colombia, cities are classified by social stratum with the aim to have a fairer distribution of tariffs for public services such as water, electricity, and sewer. These strata go from one (1) to six (6), with six being the wealthiest. We chose the zones taking into account these differences. Alto Prado represents the highest level (6); people in this zone have higher incomes and, therefore, they have the highest tariff for public services. In addition, the land value there is higher than the other zones. Bellavista is a five (5) social stratum. Downtown and Ciudadela are two (2) social strata. But downtown is a commercial business district that is deteriorated and is lightly inhabited. Meanwhile, Ciudadela is a popular residential zone, mostly of public housing with regular public services. Cordialidad has the lowest social stratum (one). People in this zone live in substandard conditions sometimes without public services. Cordialidad is perceived as a zone of violence and insecurity. This neighborhood was originally settled through illegal occupations of the land (invasions) which then became neighborhoods. For this study, we did not choose neighborhoods in strata four (4) and three (3) because the differences in urban form between four (4) and five (5) and two (2) and three (3) are not significant. (It should be noted that, despite good intentions, the system of social stratum has in fact become an instrument of

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Fig. 3. Overview of selected survey zones: 1) Alto Prado (LCZ 6_4), 2) Bellavista (LCZ 6), 3) Centro (LCZ 2), 4) Ciudadela (LCZ 3), 5) Cordialidad (LCZ 7B), 6) Reference zone (LCZ8).

segmentation and social discrimination in Colombia.) In Fig. 3 we show the different zones.

knowledge of thermal sensation perceived in outdoor conditions of a tropical climate.

2.3. Physical measurement

2.4. Questionnaire survey

Sunny days without rain are essential for measuring temperature (Ta  C), relative humidity (H %) and wind speed (V- m/s). Considering the climate conditions of Barranquilla, the dry season was the best period to carry out the field survey. We determined that January was the month with the best conditions (Table 1). The weather in January is very stable, without rain and clouds, lower thermal oscillation and small variations of relative humidity day by day; for that reason, the survey was conducted on January 18 e 21 and January 24, 2012. Only weekdays were considered. The time interval for measurements was 5 min. However, since our purpose was not to study UHC, the measurement took place from 9:00 am to 4:00 pm with a break between 12:00 am to 01:30 pm. This schedule was determined by the pedestrian behavior in the city, because we needed enough votes of thermal sensation in our research. To record microclimate conditions, we used a Kestrel 4500 datalogging weather station with high accuracy for humidity of þ/ 3%; þ/ 1  C for temperature and wind speed accuracy of 3% of reading or 0.1 m/s. The instruments were placed at 1.50 m, avoiding taking measurements in direct sunlight. Our focus was on the city’s streets instead of resting places, because there are few parks in Barranquilla, and therefore going to the park is not a sparetime activity for people; on the other hand, most residents do not have their own automobiles so they must walk, bike or use public transportation. Streets are necessities and unavoidable for pedestrians who are our subject of interest. We had hoped to measure the Mean Radiant temperature, which is an input necessary to calculate thermal comfort index, but a last-minute technical problem with a global thermometer sensor impeded us. Since our goal is not the validation or calculation of thermal comfort index, this fact does not affect our research and primary purpose, which is to expand

A survey was carried out in parallel with micro-climate measurement in order to obtain thermal sensation votes from pedestrians in the study zones. The questionnaire was designed to take into account precedent research [2,22,23] and norms like ISO 7730 [24] and the ASHRAE standard [25]. The questionnaire was simplified given the timing (5 min) between measured data. We asked about sensation, agreement and preference of temperature (TSV), relative humidity (HSV), wind speed (WSV) and solar radiation (SSV). Also, information about physiological characteristics (e.g., age, gender, height, weight and origin) of the interview subjects was collected. Some information was obtained by observation, such as type of clothing. Since the survey focused on pedestrians, we assumed they were walking and thus in a moderate physical activity (3 met ¼ 180 W/m2) using light clothes not exceeding an insulation value of 0.5 clo. These assumptions were confirmed by the results of the survey. We used the ASHRAE sensorial scale [25] of seven symmetrical points to evaluate sensation/perception, in which 3 is hot; 2 is warm; 1 is slightly warm; 0 is neutral; 1 is slightly cool; 2 is cool and 3 is cold. The same principle was used for relative humidity. Wind speed and solar radiation were measured by a four point scale from 0, any wind/solar radiation to 4, too much wind/ solar radiation. We used a five-degree scale to measure agreement (1, very unsatisfied; 2, unsatisfied; 3, neutral; 4, satisfied; 5, perfectly satisfied). The McIntyre Scale [26] was used to evaluate preference, consistent in a simple symmetrical three point scale (1, prefer cooler; 0, no change; 1 prefer warmer). The research team consisted of five survey takers, one sociologist and four architects, distributed in a diameter of less than 30 m from the weather station.

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Table 1 Monthly climate conditions in Barranquilla. January is typically a dry month with the best conditions for the survey. Months

Jan

Feb

Mars

April

Mai

June

Jul

Aug

Sep

Oct

Nov

Dec

Temperature ( C) Mean minimal Mean Mean Maximal Rains (millimeters) Rainy days Relative humidity (%) Solar brightness (hours/month)

23.3 26.6 31.3 5 0 78 282

23.4 26.6 31.4 1 0 77 245

23.7 26.9 31.9 1 0 77 240

24.4 27.5 32.7 25 3 78 207

24.8 28.1 33.3 91 9 80 188

24.6 28.1 32.9 104 9 80 195

24.4 28.0 32.7 70 7 80 215

24.4 28.0 33.1 102 10 81 207

24.0 27.8 32.8 143 13 83 164

23.8 27.4 32.3 178 14 84 166

24.0 27.4 32.0 79 9 83 191

23.7 27.0 31.5 24 2 80 253

Source: IDEAM.

3. Results and discussion 3.1. Climatic conditions Climatic conditions were recorded at intervals of 5 min. This information was compared with data from the official weather station located at the airport (reference zone: LCZ 8; large low-rise). According to official weather reports, climate conditions during the survey were typical. Mean air temperature in January 2012, over 24 h, was 26.6  C; extreme values were between 32.5  C and 22.6  C. Average air temperature registered between 9:00 ame4:00 pm was 29  C. Relative humidity ranged between 61% and 97%; thus, mean relative humidity was around 79%, which is fairly high but normal for a tropical climate. Relative humidity decreased between 9:00 ame4:00 pm; the average in that moment was around 67%. Mean Wind Speed was 4.0 m/s, blowing from north and northeast the most part of the day. In general, cloudiness was 2 okta. Relating the measured points, mean air temperature was 28.1  C, total range from 9:00 am to 4:00 pm was between 25  C and 32  C. The lowest temperature was registered the first day at Alto Prado zone (LCZ 4_6) with a minimal reading of 25.5  C and maximal of 28.8  C. The highest air temperature was recorded the last day at Cordialidad zone (LCZ 7B), where it ranged between 27.6  C and 31.8  C. The intermediate zones showed similar results with each other: air temperature kept between 26  C and 29  C. In general, during the whole survey mean temperature increased 2.6  C, which means that variation per day was only 0.3  C. The

oscillation of daily temperature was only 3  C in each zone. Mean relative humidity was 66%. Alto Prado zone (LCZ 4_6) had the highest mean relative humidity (73%) with a maximal value of 79.7% and a minimal of 66.3%. On the other hand, Bellavista (LCZ 2; day 4) had the lowest average relative humidity (60.9%) because of an atypical decrease from 68.4% to 46.7% in 5 min; this was registered at the end of the morning (11:55); air temperature was 26.7  C, one (1) degree lower than that registered at 11:50 (27.7  C), but this follows the general tendency of air temperature during the morning; wind speed passed from 2.5 m/s at 11:50 to totally calm. This is normal for wind speed, which has a wide variability. Regarding this data, neither air temperature nor wind speed can explain the anomaly in relative humidity. An involuntary sensor manipulation error could be one hypothesis. Otherwise, Ciudadela (LCZ 3; day 4) and Cordialidad zone (LCZ 7B) would have had the lowest mean relative humidity (65.5% and 65.9% respectively). Wind speed ranged between totally calm to 5.2 m/s, which was registered only one time in the Ciudadela (LCZ 3; day 4). This explains their lower mean relative humidity. Meanwhile, maximal wind speed in other zones did not exceed 3.9 m/s. Solar radiation was similar for all the zones with cloudiness around 2 okta. We observed the best conditions in Alto Prado zone (LCZ 6_4; day one) and the worst in Cordialidad zone (LCZ 7B; day 5), which is interesting given the difference in socio-economic characteristics and the urban form of each zone. But this is not a sufficient argument to suggest discrimination, given the impossibility to compare results by zone directly. So we used a reference zone.

Fig. 4. Variations in hourly air temperature a); relative humidity b) and wind speed c) between each zone and the reference zone: 1) Alto Prado (LCZ 6_4), 2) Bellavista (LCZ 6), 3) Centro (LCZ 2), 4) Ciudadela (LCZ 3), 5) Cordialidad (LCZ 7B), 8) Reference zone (LCZ8). Alto Prado and Cordialidad zones show the biggest variation in temperature and relative humidity. Meanwhile, Alto Prado had a lower variation in wind speed, Cordialidad had the biggest variation.

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Comparing hourly data from each zone with the reference zone, we observed small variations in hourly air temperature (Fig. 4a)). The biggest difference was observed between the reference zone and Alto Prado zone (LCZ 4_6) with 1.3  C; the second one was between Cordialidad zone (LCZ 7B; day 5), but this time we had a positive result. This means that air temperature in the reference zone was cooler than in the Cordialidad zone, which confirms the fact that Alto Prado Zone had the best performance compared with the reference zone, while the worst performance was the Cordialidad zone. The intermediate zones had very steady results, but it is important to note that zones with open spaces had negatives results, whereas compacts zone had positive results. The largest variation in relative humidity (7.6 percentage points) was also reported between the reference zone and the Alto Prado zone. Relative humidity in the reference zone was higher than measured zones apart from Cordialidad zone where results were negative (Fig. 4b)). The hourly mean wind speed was lower in measured points than in the reference zone. Variations were more representative than for the other parameters. Whilst mean wind speed in the reference zone was between 3.2 m/s and 4.8 m/s, in the measured zone the mean wind speed was no greater than 1.8 m/s. The most ventilated zone was also Alto Prado, and the least was the Cordialidad zone (Fig. 4c)). The results of the measured zones and the reference zone are consistent. Lower wind speed in the measured zones is explained by the effect of roughness, which is higher in the measured sites than the reference site. Alto Prado zone is located in an optimal area to receive wind: the north east. The Cordialidad zone, by comparison, is located in the southwest of the city. While the average variation between the reference zone and the Alto Prado zone was only 1.4 m/s, the variation was 3.9 m/s between the reference zone and the Cordialidad zone. The results indicate an inequality in the climatic conditions between these zones. We note that Alto Prado is a privileged, zone six social stratum, whereas the Cordialidad zone is a poor neighborhood. Concerning temperature and relative humidity, even if the variations were small but consistent, with lower thermal oscillation in Barranquilla, the variations confirm the effect of urban form on microclimate. We addressed this subject, but it is not deeply analyzed in the current study. 3.2. Climate environment perception The entire sample comprised 781 people interviewed during the survey, with an average of 156 people per day. Regarding their

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physiology, 55% were males and 45% were females; the range of ages was between 14 and 75 years old. The average Body Mass Index (BMI) was 24.7; this means than the relation between weight and height was normal and suggests a low risk of illness. The typical subject profile was a male of 39 years old, 74 kg and 1.71 m., and a female of 37 years old, weighing 62 kg and measuring 1.60 m. Atypical cases were identified in order to establish if there is any influence of physiological characters in perception. As regards origin, 66% of persons were native Barranquilleros. Thirty-four percent (34%) of those interviewed came from other cities or regions and had been living in the city for several years. A small percentage of people were in Barranquilla for business or holidays or were living there less than one month. Foreign people were very rare. 3.2.1. Air temperature e TSV We asked pedestrians about their sensation (TSV), agreement and preference regarding current temperatures in five zones of Barranquilla. The principal aim was to know how people assessed climate conditions. Results from the whole database showed that the highest percentage of people (38%) felt neutral or “neither cool nor warm” (corresponding to “0” in a seven point thermal scale). We obtained a similar percentage (15%) of votes for 1 (slightly cool; slightly warm). People feeling warm (þ2) and hot (þ3) accounted for 22% of those interviewed. People who felt cool (2) and cold (3) were around 8%. This result was unexpected, given the fact than minimal air temperature was above 25  C at all times. Most people expressed satisfaction with the temperature (64%); 22% did not specifically answer; they were neither satisfied nor unsatisfied; only 14% of those interviewed were unsatisfied or very unsatisfied with temperatures at the moment of the survey. In spite of these results, 55% preferred cooler temperatures versus 45% of people who would like to maintain the same air temperature. This is in agreement with McIntyre [26], who established that people in warm climates who feel neutral would prefer to be cooler. The results demonstrate that people are satisfied because they have adapted to the temperature, but they are not in optimal comfort because a large percentage would prefer cooler temperatures. This confirms the fact that adaptation and expectation have an important place in thermal perception, as other studies have suggested [2,3]. Also, it points out the high tolerance to high temperatures of pedestrians in tropical cities [9,27,28]. The large spectrum of answers in a very narrow range of temperature (3  C) reveals the respondent’s high degree of sensitivity to air temperature.

Table 2 Results of thermal sensation vote by zones and total. Scale

Zone LCZ 6_4

Zone LCZ6

Zone LCZ2

Zone LCZ3

Zone LCZ7

Alto Prado

Bellavista

Centro

Ciudadela

Cordialidad

Effective 3 2

cold cool

1

slightly cool neither cool nor warm slightly warm warm hot Not answer Total

%

Effective

%

Effective

%

Effective

%

Effective

Total all zones

%

Effective

%

3

1,9 6,9

1 10

0,6 6,3

2 17

1,1 9,8

7 8

4,7 5,4

3 4

2,2 2,9

16 50

2,0 6,4

25

15,6

20

12,5

26

14,9

34

22,8

9

6,5

114

14,6

67

41,9

55

34,4

77

44,3

68

45,6

33

23,9

300

38,4

26

16,3

41

25,6

18

10,3

12

8,1

24

17,4

121

15,5

23 5 0

14,4 3,1 0,0

25 8 0

15,6 5,0 0,0

23 7 4

13,2 4,0 2,3

14 5 1

9,4 3,4 0,7

39 25 1

28,3 18,1 0,7

124 50 6

15,9 6,4 0,8

160

100

160

100

174

100

149

100

138

100

781

100

11

0

1 2 3 NR

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Disaggregating the results by zones, we obtained results similar to those of general thermal sensation, except for the last zone (Cordialidad LCZ 7B) where results lean towards warm sensations (Table 2). Satisfaction was also similar to the general results: always in the upper 50% in all zones without exception. Results regarding preference were heterogeneous. In Alto Prado zone (LCZ 4_6) and Bellavista (LCZ 6), 54% and 50% respectively of respondents preferred cooler air temperatures, whereas 45% and 47% respectively voted for remaining at the same air temperatures. At Centro (LCZ 2) and Ciudadela (LCZ 3) results were the inverse of those for preceding zones. Meanwhile 72% of people at Cordialidad zone (LCZ 7B) would prefer lower temperatures. This matched measured data indicating the highest temperature registered was in this zone. We carried out ANOVA analysis and, despite the consideration above mentioned, no significant differences between zones were found. This corresponds with results obtained by Nikolopoulou and Lykuodis [3]; in their survey developed across several European countries, the actual sensation vote e ASV- was similar for all cities in spite of different climate conditions. The outcome of preferences in the Cordialidad zone is explained by the rise of air temperature the last day. At the same time, this fact confirms once more the high sensitivity to air temperature of respondents. When mean air temperature exceeded 29.7  C (2  C higher than the first days before), people clearly perceived warm thermal sensation and preference leaned significantly towards cooler temperatures. Warm thermal sensation was especially perceived in the Cordialidad Zone, which is the poorest zone of our survey. It would not be accurate to conclude that people in this zone are the most uncomfortable, since measurements were not taken at the same time across zones, making direct comparisons possible. However, the results do show that this zone is not prepared for a rise in temperature: it is clear that people felt hot, and their socio-economic conditions and the state of their urban environment do not offer them any alternative besides adaptation. 3.2.2. Relative humidity e HSV In tropical climates, high humidity values are a source of discomfort. When the human body feels warm, it turns on thermoregulation mechanisms such as sweating. High humidity values do not allow the evaporation of sweat, making people feel uncomfortable. For this reason we asked pedestrians about their relative humidity perception (HSV). The perception of relative humidity as “normal, neither dry nor humid” was the most voted sensation (46%). The number of people who felt the environment “dry” and “too dry” was in second place with 23%. Meanwhile, in third position was the number of people (11% of respondents) who felt the environment was “humid” and “too humid.” The sensations “slightly humid” and “slightly dry” had 10% of votes in both cases.

These results were relatively consistent with answers for air temperature regarding neutral votes. Regarding the other votes, warm sensations had the second highest frequency of vote, whereas for relative humidity the second frequency of vote was for dry sensation. It is well known that relative humidity and air temperature have an inverse correlation, but we did not expect the same relation for perception; we supposed that people would link feeling warm with humid or too humid conditions. In fact, objective measures showed that mean relative humidity was high e overarching 65% e and meteorological data confirm this situation (mean relative humid of 67% in January 2012 between 09:00 ame04:00 pm). On the other hand, 63% people felt satisfied with the relative humidity and, despite preferences towards cooler air temperatures, they would rather continue at the same relative humidity. Also, there are more people who would like to feel higher humidity (21%) than people who would like to feel lower humidity (17%). In other words, the inverse relationship between measured temperature and relative humidity doesn’t exist between perceived temperature and relative humidity. Even when the relative humidity is high, people don’t feel it. People surveyed distinguish clearly the role of temperature in thermal sensation (the average values are in accordance with the perception surveys), in contrast with that happens with humidity. These results indicate that survey respondents don’t clearly understand the role that humidity plays in what they perceive. In this way, they attribute everything to the temperature without regard for relative humidity. On the other hand, it could be that these people have developed a high tolerance for humidity; that would explain why they perceive humidity to be low even when measurements indicate otherwise. This is well in agreement with Makaremi et al. [28]. The results obtained by that author indicate that survey respondents from other regions perceived the relative humidity to be very high, while natives to the locale considered the weather very dry. In addition, while the locals wished for a rise in the humidity, those not from the area preferred a drop in the humidity. On the other hand, Makaremi also found that the majority of people responded that the temperature was the most uncomfortable of the parameters. This shows the negative role of high air temperature in human thermal perception. Analyzing by zones, no significant differences were found (Table 3). Results follow the general trend, with people declaring that they perceive “neutral” conditions; meanwhile the number of people considering the atmosphere “dry” occupied second place for all zones, apart from Bellavista (LCZ6 e day 2) where 50% felt “neutral” and the rest were proportionally distributed between “dry” and “humid” votes. One explanation could be that relative humidity is highest early in the morning before we started the survey and lower in the afternoon after the survey, and that memory and expectations could be affecting survey respondents perceptions [2,3].

Table 3 Results of humidity sensation vote by zone and total. Scale

3 2 1 0 1 2 3 NR

too dry dry Slightly dry normal, neither dry nor humid slightly humid Humid too humid Not answer Total

Zone LCZ 6_4

Zone LCZ6

Zone LCZ2

Zone LCZ3

Zone LCZ 7B

Alto Prado

Bellavista

Centro

Ciudadela

Cordialidad

Total all zones

Effective

%

Effective

%

Effective

%

Effective

%

Effective

%

Effective

%

4 31 14 75 20 11 5 0 160

2,5 19,4 8,8 46,9 12,5 6,9 3,1 0,0 100

1 19 17 81 21 15 6 0 160

0,6 11,9 10,6 50,6 13,1 9,4 3,8 0,0 100

4 44 16 81 13 11 3 2 174

2,3 25,3 9,2 46,6 7,5 6,3 1,7 1,1 100

5 25 17 70 16 14 1 1 149

3,4 16,8 11,4 47,0 10,7 9,4 0,7 0,7 100

8 38 15 54 6 12 5 0 138

5,8 27,5 10,9 39,1 4,3 8,7 3,6 0,0 100

22 157 79 361 76 63 20 3 781

2,8 20,1 10,1 46,2 9,7 8,1 2,6 0,4 100

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Table 4 Results of wind speed sensation vote by zone and total. Scale

0 1 2 3 NR

no wind speed at all low wind speed moderate wind speed very strong wind speed Not answer Total

Zone LCZ 6_4

Zone LCZ6

Zone LCZ2

Zone LCZ3

Zone LCZ 7B

Alto Prado

Bellavista

Centro

Ciudadela

Cordialidad

Total all zones

Effective

%

Effective

%

Effective

%

Effective

%

Effective

%

Effective

%

2 12 95 51 0 160

1,3 7,5 59,4 31,9 0,0 100

1 15 97 47 0 160

0,6 9,4 60,6 29,4 0,0 100

1 8 86 79 0 174

0,6 4,6 49,4 45,4 0,0 100

0 7 73 69 0 149

0,0 4,7 49,0 46,3 0,0 100

7 33 76 22 0 138

5,1 23,9 55,1 15,9 0,0 100

11 75 427 268 0 781

1,4 9,6 54,7 34,3 0,0 100

3.2.3. Wind speed e WSV Natural ventilation is the only passive strategy capable of making bearable the high humidity and temperatures in tropical climates. We carried out the survey at a time when the Alize Wind was blowing in Barranquilla, so as to compare perception against objective measures of Wind Speed. The survey revealed that people who perceived “moderate wind speed” (55%) were “satisfied” and “very satisfied” (73%) and no changes were desired (61%). Wind speed was considered “very strong” for 34% of those surveyed, even if maximal wind speed was only 5.2 m/s, which is considered acceptable according to the Beaufort wind force scale, and catalogued as a “gentle breeze.” A small percentage of people (11%) perceived low wind speed or no wind speed at all. Only 9% of people were unsatisfied with wind speed and 17% were neutral. Wind speed is a very fluctuating parameter; however, during the survey it stayed between totally calm (0 m/s) to 3.9 m/s for all zones; except for Ciudadela (LCZ3 e day 4) with a maximal of 5.2 m/s. Wind speed did not affect perception in Ciudadela because the pattern of votes was similar: “moderate wind speed” was the most voted (49%) followed by “strong wind speed” (46%). No significant differences were found in perception, satisfaction and preference regarding wind speed between the zones (Table 4). The only particular exception was in the Cordialidad zone (LCZ 7B) in the morning, where the second highest percentage was for “weak wind speed.” The results are conclusive: the perception of wind speed is positive, since people are satisfied and no changes are desired. These findings confirm the positive role of wind in thermal comfort in tropical climates [28]. 3.2.4. Solar radiation e SSV We assumed that pedestrians had a negative perception of solar radiation, expressed by lack of satisfaction and preference for different conditions. That motivated us to question pedestrians about solar radiation (SSV). According to the survey, 50% of respondents considered that solar radiation was “strong” and 32% considered it “very strong,” whilst 16% answered that it felt “slightly strong.” Less than 1% expressed not feeling any solar radiation. People who felt unsatisfied numbered around 23% versus

52% who expressed satisfaction. A large percentage (24%) had no particular opinion; they were neither satisfied nor unsatisfied. Concerning respondents’ preferences, the general trend remained intact: 42% would stay without changes; 27.5% would like to feel less solar radiation but 31% would rather have more solar radiation. These outcomes contradict our assumptions about the negative role of solar radiation. On the one hand, the survey results display the adaptation and tolerance of respondents to high solar radiation conditions. On the other hand, the results indicate that solar radiation is recognized as a positive parameter in human thermal comfort, at least for the pedestrians who participated in this survey. Disaggregating results by zone, we obtained similar results (Table 5). Results by time of the day show that people prefer less solar radiation in the morning and more in the afternoon. This is a similar pattern for all zones, but it could be interesting to understand the reasons for this, taking into account that solar radiation in Barranquilla attained 5.0 or 5.5 KWh/m2, which is a high value. 3.2.5. Thermal sensation by gender and origin We analyzed thermal sensation votes by sex and origin of respondents. In both cases, we carried out ANOVAS to identify statistically significant differences. The results did not show any relevant differences between samples (Fig. 5). The observed frequency of sensation votes confirms this fact. Women felt a little warmer and unsatisfied and preferred feeling cooler than men. This fits with other studies [15,29] suggesting that women felt more uncomfortable and dissatisfied under non-neutral conditions compared to men. Concerning origin, 69% of respondents came from Barranquilla; 22% came from other cities but with the same climatic conditions (warm and humid); only 9% came from other regions. No relevant differences were found in the ANOVAs analysis. However, frequency of votes showed that people from Barranquilla felt cooler than people from other regions. The most satisfied were people from Caribbean region. We did not find any particular outcome regarding preferences. But differences were very small, so the results are not conclusive.

Table 5 Results of solar radiation sensation vote by zones and total. Scale

Zone LCZ 6_4 Alto Prado

0 1 2 3 NR

any solar radiation slightly strong solar radiation strong solar radiation very strong solar radiation not answer Total

Zone LCZ6

Zone LCZ2

Bellavista

Zone LCZ3

Centro

Zone LCZ 7B

Ciudadela

Total all zones

Cordialidad

Effective

%

Effective

%

Effective

%

Effective

%

Effective

%

Effective

%

1 18 93 46 2 160

0,6 11,3 58,1 28,8 1,3 100

1 23 87 48 1 160

0,6 14,4 54,4 30,0 0,6 100

1 29 88 52 4 174

0,6 16,7 50,6 29,9 2,3 100

2 42 63 39 3 149

1,3 28,2 42,3 26,2 2,0 100

1 16 59 62 0 138

0,7 11,6 42,8 44,9 0,0 100

6 128 390 247 10 781

0,8 16,4 49,9 31,6 1,3 100

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humidity is very weak but existent. Wind speed is a very variable parameter; correlations were not evident. We found a weak correlation between perceived and measured wind speed only in the morning, but we do not have any final explanation for this fact. Regarding these results we confirm findings from others surveys [3,28] reporting weak correlations between microclimatic conditions and subjective assessments of pedestrians. This shows that perceptions of the thermal environment cannot be explained by individual climate parameters nor simply by microclimate conditions; psychological factors appear to play a key role.

Fig. 5. Frequency of sensation votes by gender.

3.3. Thermal comfort: correlation between perception and climate conditions We studied the relationship between subjective votes and objective measures of climate conditions. First of all, we ran multiple correlations between sensation, satisfaction and preference against climate parameters; results from morning and afternoon were analyzed separately. The next step was to analyze data in order to establish thermal conditions at which people felt neutral. Before running correlations with thermal sensation, we carried out correlations between climate parameters. As we expected, air temperature and relative humidity had a strong and inversely proportional correlation (r ¼ 0.8029; p-value > 0.000 at the morning and, r ¼ 0.9145; p-value ¼ 0.000 at the afternoon). The relationship between air temperature and wind speed is also negative but moderate; correlation in the morning was r ¼ 0.4093; p-value ¼ 0.000 and in the afternoon was 0.4234. Relative humidity and wind speed has a correlation weaker than the others but not less significant. This correlation in the morning was r ¼ 0.2599; p-value > 0.000 and in the afternoon was r ¼ 0.2148; p-value > 0.000. 3.3.1. Correlation between sensation votes and climate conditions We confirmed a positive correlation, weak but statistically significant, between thermal sensation (TSV) and air temperature (morning: r ¼ 0.3050; p-value ¼ 0.000; afternoon: r ¼ 0.1331; pvalue > 0.000). Thermal sensation was also correlated with relative humidity and wind speed associated with thermal sensation votes. We found a negative and weak correlation between relative humidity and thermal sensation in the morning (r ¼ 0.1167; pvalue ¼ 0.000); no significant correlation was found in the afternoon. Concerning wind speed and thermal sensation, we did not find any correlation even in the morning or afternoon. Perceived (HSV) and measured relative humidity had a weak correlation with each other (morning r ¼ 0.1060 p-value ¼ 0.0346; Afternoon: r ¼ 0.1279; p-value ¼ 0.0126). The same procedure was done with perceptions of wind speed. There is a weak correlation in the morning between wind speed and perception of wind speed (r ¼ 0.2226 p-value ¼ 0.0000). Any significant correlation was found in the afternoon. Finally, we found a correlation between perception of solar radiation and air temperature; results were weak but statistically significant in the morning (r ¼ 0.2410; pvalue ¼ 0.0000) and afternoon (r ¼ 0.1452; p-value ¼ 0.0047). In summary, there is a confirmed correlation between air temperature with thermal sensation and perception of solar radiation. The correlation between perception and measured relative

3.3.2. Correlation between sensation votes The result of correlations between thermal sensation votes (TSV), humidity sensation votes (HSV), wind speed sensation votes (WSV) and solar radiation sensation votes (SSV) reveals that thermal sensation is linked with all the other sensation votes. The relationship between humidity sensation votes (HSV) and wind speed sensation votes (WSV) is negative; meanwhile the correlation with solar radiation sensation votes (SSV) is positive and is the higher result. This means than when people feel warm, they perceive a dry environment, low wind speed and high solar radiation, and vice versa when people feel cold. In all cases, correlations are no greater than r ¼ 0.25. Yang et al. [30] obtained similar results, concluding that solar radiation votes (SSV) have the greatest influence on thermal sensation votes; whereas humidity sensation votes (HSV) seems to be less influential on thermal sensation votes (TSV). Another interesting result is the correlation between satisfaction votes. All votes (in the morning and afternoon) have a significant and positive correlation. Thus, when people feel satisfied with any sensation they are also satisfied with the other ones. The trend is different for preference votes; preferences regarding thermal sensation and preferences for wind speed are associated. When preferences for thermal comfort are for “cooler temperatures,” the preferences for wind speed are for “higher wind speed.” Preferences regarding thermal sensation are also associated with preferences for solar radiation, but the correlation is positive. That is, when people prefer “cooler temperatures” they also prefer “less solar radiation.” No correlations between preferences regarding thermal sensation and preferences regarding relative humidity were found. 3.3.3. Thermal sensation ranges We disaggregated votes by the seven categories of thermal sensation with the purpose of identifying climate conditions associated with subjective assessments. We compared statistical descriptors of the sample to find the thermal sensation intervals (Table 6; Fig. 6). This is not a simple exercise, given the small range of thermal conditions and the huge array of votes. However, Analysis of Variance (ANOVA) showed a statistically significant difference between the mean of categories of votes. Mean air

Table 6 Table of means with intervals of confidence of 95%.

T3 T2 T1 T0 Tþ1 Tþ2 Tþ3 Total

Cases

Means

Std error Grouped

Lower limit

Upper limit

16 50 114 300 121 124 50 775

27.45 27.652 27.6149 27.9233 28.1397 28.221 28.806 27.989

0.284674 0.161036 0.106649 0.0657426 0.103518 0.102258 0.161036

27.0555 27.4288 27.4671 27.8322 27.9962 28.0792 28.5828

27.8445 27.8752 27.7627 28.0144 28.2831 28.3627 29.0292

K. Villadiego, M.A. Velay-Dabat / Building and Environment 75 (2014) 142e152

Fig. 6. ANOM graphic showing thermal sensation ranges with 95% decision limits.

temperatures associated with cool thermal sensations were 27.4  C for “(3) cold thermal sensation” and 27.6  C for (2) cool and (1) slightly cool thermal sensations. Meanwhile, mean air temperatures associated with warm thermal sensations were 28.1  C for (þ1) slightly warm; 28.2  C for (þ2) warm and 28.8  C for (þ3) hot. Mean air temperature associated with “neutral” thermal sensations was 27.9  C. Standard deviation, limits and other important results are presented in Table 6 and Fig. 6. We carried out ANOVAS for relative humidity and wind speed associated with thermal sensation votes; no significant differences were found. It is important to emphasize that we are not talking about neutral temperatures because of the transversal nature of our survey; however, results are in line with those of other researchers, with neutral temperatures being around 27  Ce28  C [4,9,22,28,30]. Mean air temperature tends to increase with the thermal sensation category; differences are very small, only in decimals, but this result is logical and coherent with expectations in warm climates and given the small range of thermal conditions during the survey (25  Ce31  C). This result confirms peoples’ high sensitivity to very small variations in air temperature and the fact that thermal sensation is affected by more factors than objective climate conditions. That is why predicting thermal sensation in outdoors spaces is a very difficult goal, and the goal of defining thermal comfort is even more complicated. For example, related literature defines neutral temperature as “the temperature at which people feel comfortable”; in the present study, mean thermal sensation was “neutral,” but that does not mean that people felt comfortable. A simple inspection of the whole sample (781 votes) shows that only 0.6% (5 votes) fulfills the three conditions necessary for declaring optimal thermal comfort: feeling neither warm nor cool, being satisfied and not preferring any changes. These results are in accordance with Humphreys and Hancock [31], who have been studying the patter of variation of the desired thermal sensation and adjusted the ASHRAE scale. 4. Conclusion In this field study, through observation and statistical analysis, we can conclude that thermal comfort perception does not merely depend on microclimatic variables. Adaptation and expectation had been suggested by authors as other important factors influencing perception [2,3]. That is, context influences thermal perception. In fact, in other surveys of tropical cities, most respondents reported thermal sensations of warm or hot, in comparison with our results in Barranquilla, where mean thermal sensation votes (MTSV) were “0 ¼ neutral”. Results from Makaremi’s research showed that 77% of people felt warm or hot thermal sensation and 91% would prefer lower air temperatures [28]. Angulo [13] founded the same thermal sensation in Tabasco (Mexico). On the other hand, a mean air temperature of 27.9  C for mean thermal sensation votes (MTSV) is

151

close to neutral temperature, as indicated by other surveys which found preferences for cooler temperatures: 27.7  C for La Havana [14]; and 27.2  C for Taiwan [9]. Thus, people develop a high tolerance to climate conditions, but neutrality cannot be assumed as comfort, because people in hot climates can be satisfied feeling cooler temperatures. The results obtained in the study show the important role of temperature, solar radiation and wind speed on thermal sensation. A correlation between thermal preferences shows a link between wind speed and solar radiation preferences. Relative humidity appears as a less significant factor. Perception is linked to climatic conditions, but the relatively lower correlation shows that no single factor can explain stand-alone thermal sensation. This information can be helpful in encouraging planners to conceive of urban spaces capable of improving air flow and incorporating shaded zones. In order to establish comfort zones or comfort indices for tropical regions, it is necessary to enlarge the surveys about subjective thermal perception including thermal preferences and regional particularities; doing so can improve the performance of models of thermal comfort prediction. The present survey contributes to the achievement of this aim. However, we do not consider the possibility of comparing votes predicted by existent models with actual votes from surveys, as other studies have done, because we found some problems in the procedure to obtain globe temperatures, thus mean radiant temperature, which is an important input to calculate thermal comfort index. Since different microclimate conditions were perceived between the zones, especially between Alto Prado (LCZ 6_4), the richest, and Cordialidad (LCZ 7B), the poorest neighborhood, we consider that demo-spatial dynamics and urban planning in Barranquilla encourage inequalities in terms of climate conditions and thermal comfort. Acknowledgments The authors wish to thank the National Research Department of Colombia e Colciencias for its financial support via the PhD scholarship for Kattia Villadiego. In addition, the authors are grateful to the National School of Architectural of Marseille for its academic and financial support. The field survey would not have been possible without the voluntary help of architects Orlando Jimenez, Maria Isabel Montañez, Maria Carolina Aldana, Luz Adriana Iriarte and sociologist Leonardo Romero. Finally, we are especially thankful to Brian McWilliams and Luz Maira Peralta for their assistance with the editing of this paper. References [1] Oke T, Taesler R, Olsson L. The tropical urban climate experiment (TRUCE). Energy Build 1990;15/16:67e73. [2] Nikolopoulou M, Baker N, Steemers K. Thermal comfort in outdoor urban spaces: understanding the human parameter. Sol Energy 2001;70(3):227e35. [3] Nikolopoulou M, Lykoudis S. Thermal comfort in outdoor urban spaces: analysis across different European countries. Build Environ 2006;41:1455e70. [4] Lin TP. Thermal perception, adaptation and attendance in a public square in hot and humid regions. Build Environ 2009;44:2017e26. [5] Thorsson S, Lindqvist M, Lindqvist S. Thermal bioclimatic conditions and patterns of behaviour in an urban park in Göteborg, Sweden. Int J Biometeorol 2004;48:149e56. [6] Zacharias J, Stathopoulos T, Wu H. Spatial behavior in San Francisco’s plazas: the effects of microclimate, other people, and environmental design. Environ Behav 2004;36:638e58. [7] Knez I, Thorsson S. Influences of culture and environmental attitude on thermal, emotional and perceptual evaluations of a public square. Int J Biometeorol 2006;50:258e68. http://dx.doi.org/10.1007/s00484-006-0024-0. [8] Matzarakis A, de Freitas C, Scott D. Advances in tourism climatology; 2004. Berichte des Meteorologischen Institutes der Universität, Freiburg. [9] Lin TP, Matzarakis A. Tourism climate and thermal comfort in Sun Moon Lake, Taiwan. Int J Biometeorol 2008;2:281e90. http://dx.doi.org/10.1007/s00484007-0122-7.

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