The use of Environmental Controls: Bioclimatic Performance of Baixa Pombalina s Heritage Buildings.

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1 The use of Environmental Controls: Bioclimatic Performance of Baixa Pombalina s Heritage Buildings. Pedro Nunes de Freitas, Ph.D. Manuel Correia Guedes, Ph.D. [Instituto SuperiorTécnico, Universidade de Lisboa] [Instituto SuperiorTécnico, Universidade de Lisboa] pedrocnfreitas@tecnico.ulisboa.pt mcguedes@civil.ist.utl.pt ABSTRACT Baixa Pombalina, the downtown and historic district of Lisbon is one of the most important pieces of urbanism and architecture ever built in Portugal, and is at present time a UNESCO World Heritage nominate. Those Buildings were built after the great earthquake of 1755, for housing, commercial, and services` functions. And they constitute a rational and functional approach for health and comfort to their residents, translating the state-of-the-art of architecture at the time, through the use of lighting and natural ventilation. In this research study, buildings of Baixa are observed as a scenario where residents of 21st Century live in spatial and built structures of 18th Century. This paper is about environmental controls within current thermal and lighting performance of Baixa Pombalina Buildings. It analyses the efficacy of those buildings from the passive design point of view, as well as the habits of its occupants in controlling and regulating the devices available in Baixa buildings at present time. A questionnaire model was developed to study bioclimatic performance of offices, and residences selected in Baixa. And field work involved a survey where workers of fifteen offices and residents of five houses have participated. Results demonstrate that in buildings of Baixa, controls are used less interactively during winter season and more interactively during summer season. Results indicate that in the Lisbon climate, it is mainly during the summer season that controls have a major role in thermal performance of these inheritage buildings. Keywords: Baixa Pombalina, Building Performance, Environmental Controls, Comfort and Occupancy. INTRODUCTION This Paper analyzes actions of control by current users in buildings of Baixa Pombalina, which are inheritage buildings built in the 18th Century. The goal of this study is to understand these buildings and their diversed systems in the context of current habits of usage and control. According to a current notion of Sustainability, construction shall ensure bioclimatic and global human comfort, in buildings and urban spaces; sustainable use of construction materials and environmental technologies in buildings (Pinheiro, 2006). The project and work of Baixa Pombalina fall in many contemporary concepts of sustainability. When Baixa buildings were designed, in the 18th Century, lighting, heating and cooling were essentially provided by natural light and ventilation. These buildings were built in a time before the use of mechanical lighting and HVAC systems, and are therefore Architecture with capability to ensure energy efficiency. However, during 20th Century, occupancy density was increased and HVAC mechanical devices were introduced, changing the thermal performance of buildings, and the actions and habits of its users before the available controls. Author A is a Doctor graduated by the Department of Architecture, Civil Enginneering, and Georesources of Instituto Superior Técnico of the University of Lisbon, Portugal. Author B is a professor in the Department of of Architecture, Civil Enginneering, and Georesources of Instituto Superior Técnico of the University of Lisbon, Portugal. 1

2 This Paper provides an overview of actions taken by users: with regard to the use of controls introduced in these buildings, e.g. mechanical devices, as well as actions to use the original controls of these buildings, e.g. windows to regulate natural ventilation. URBAN AND ARCHITECTURAL CONTEXT Baixa Pombalina is located in the historic city center of Lisbon, near Tejo River and between hills. After the Great Earthquake of 1755, the area was rebuilt according to the 1758 Plan. And their buildings are called Pombalino Yield Buildings ( Prédio de Rendimento Pombalino ), and have similar architectural features and are grouped into blocks. Figure 1 (a) View of Pombalino Buildings of Baixa and (b) Aerial view of Pombalino blocks and (c) View from inside the inner yards of Baixa (photos: author). The block improves buildings salubrity with wider spaces between buildings in order to ventilate and to illuminate. The use of the shape of rectangular block allowed two fronts separated by an inner yard, and also, a large perimeter of the façade. Blocks are of two types: The first are arranged longitudinally with the axis in the direction North-South, and occupy most part of the urban grid. The latter blocks are arranged transversely, with the axis in the direction East-West, in the Southern part of the Plan, interrupting the progression of secondary streets to Trade Square ( Praça do Comércio ). Directions have a torsion of 16,5º to the North axis, making the Southeast oriented façades differ in only 1º of the optimal benchmark tortion of 17,5º to the North axis, recommended by Olgyay (1963) for temperate climates. An inner yard ( saguão ) in the core of the block separates two rows of the lot. For reasons of salubrity, an inner yard was introduced in the block, three metres wide, allowing aeration by ventilation and natural lighting to the interior of buildings. The inclusion of the inner yard ( saguão ) in the block allows a larger passive area, i.e., area that allows to be lit and naturally ventilated, according to the LT Method (Baker & Steemers, 2000). 2

3 Figure 2 (a) View of example of an exterior masonry wall and (b) Open windows of different types in a Pombalino building and (c) Example of the air conditioned system in offices in Baixa (source: author). In buildings of Baixa, the main construction elements responsible for thermal inertia are the exterior walls, due to its thickness, the weight, and due to the inherent coefficient of thermal storage. Consisting of stone masonry wall with lime mortar coating, with approx. 0,60m total thickness (Mascarenhas, 2004), illustrated in Figure 2a. According to an analysis carried out from the available drawings (CML, 2005) the original windows were double-hung sash windows, which allowed a position of fixed aperture, and casement windows which had top-hung casement windows. Window types allowed to diversify the type of ventilation. These types of window are exemplified in Figure 2b. In some residences and offices of Baixa, air conditioning devices were introduced. Air conditioning systems were usually introduced in spaces of small or medium sizes, where each space division has its own device, exemplified in Figure 2c. a) b) c) Figure 3 (a) Scheme Plan of single-side ventilation that occurs with the windows open in the street façades and (b) scheme of single-side ventilation that occurs with the windows open in the inner yard ( saguão ) façades and (c) scheme of cross ventilation that occurs with open windows in the street and inner yard ( saguão ) façades (source: author). Baixa s interior units consist of a row of rooms with windows to the side of the street, and a row of rooms with windows to the side of the rear, to the inner yard ( saguão ). Thus, Baixa s buildings provide the possibility of having naturally ventilated rooms, in a varied way. Having windows on one side and the other allows various combinations: To open windows on the street side (only), on the rear side (only), or both. And it opens up possibilities of practicing various types of ventilation single-side, cross, stack effect, as well as night-time ventilation, as shown in Figure 3. The ventilation strategy is a major bioclimatic strategy currently recommended for the Lisbon climate (Gonçalves & Graça, 2004). 3

4 THERMAL ENVIRONMENT Lisbon has a unique variant of the typical Mediterranean climate due to its proximity to the Atlantic Ocean (Ribeiro, 1987). In the center of Lisbon, according to the climatic normal, the monthly average temperature in January is 11.0 ºC and in August is 22.3 C. The minimum temperature is -2.8 C in February and the maximum temperature is 39.5 C in July. In what regards to relative humidity (RH), the minimum value is 60% in August, and the maximum value is 87% in December (IM 1981). The following chart of Figure 4 shows monitoring values registered with datalogger devices during a year, of a selected building, used as office, and representative of the thermal environment of Pombalino Yield buildings. Results are presented according to the months of the year. The following chart is organized by data logger device that have registered indoor temperatures in a room with mechanical system off, simultaneously with outside temperatures. Figure 4 Chart measuring averages, minimum and maximum temperatures registered in a room with mechanical system off, and outdoor spaces of the case study building. The previous graph in Figure 4 shows that when outside temperatures vary between 5ºC and 34,5ºC, indoor temperatures vary between 14ºC and 28ºC with the system off. It can be observed that during certain months of the year from May to October - the average temperatures are within the range of 20ºC to 26ºC. - This means that during these months, average temperatures are within the limits of conventional comfort. METHODOLOGY A survey was conducted among subjects who live or work in Baixa, in Lisbon. The study was conducted in 20 fractions in 19 diverse buildings of Baixa, in housing and office spaces. Offices range from small private offices to large offices of Governmental Ministries and Institutes. 130 subjects were surveyed during the winter season, and 119 subjects were surveyed during the summer season, in a total of 249 subjects. 18 fractions were observed during each season of winter and summer of The variety of office and housing situations - in function, type of building, type of floor fraction, size, and location - is representative of the variety that exists in Baixa. The evaluation was based on a survey, whose model was specifically developed for users of Baixa buildings, in Lisbon. The survey consists of a questionnaire to be answered based on their experience while users who live or work in those selected buildings. 4

5 In order to obtain an overview of actions of control applied by users, an analysis of frequency of actions applied by subjects surveyed was conducted, in what regards to: 1. Use of existing mechanical devices. 2. Opening windows, in duration, and spatial distribution. And a comparison between the actions committed by users during the seasons of winter and summer was conducted. In this sample, there is a higher percentage of respondents in the office function (95%) than in the residential function (5%). Because there has been a greater availability from offices than by residences to participate in this study. The study is focused on the use of windows and mechanical devices because those are the most used environmental controls that were observed in this study. Furthermore, currently most of Baixa s interior units have air conditioning. Although the use of shading devices was also observed during this research, this paper is focused on analyzing the use of windows and mechanical devices, being the main environmental controls used in buildings of Baixa at present time. It was chosen to divide the study in winter and summer seasons, being the most representative of the opposite extreme situations that influence spaces during the year: Cold and dark compared to warm and bright climates. DISCUSSION OF RESULTS Heating and Cooling Mechanical Devices The following Tables 1 and 2 show the frequency of periods of use of heating and cooling devices, in winter and summer seasons, respectively. Periods described correspond to a progression in time duration of use of mechanical devices. Table 1. Frequency of Periods of Use of Heating Devices - Winter. Periods Frequency [%] Never / NA 6,6 % Punctually 9,9 % Only on the coldest days 20,7 % A few times per Winter 9,1 % A few times per week 2,5 % A few times per day 17,4 % Almost always on during most of the Winter 33,9 % Table 2. Frequency of Periods of Use of Cooling Devices - Summer. Periods Frequency [%] Never / NA 2,6 % Punctually 3,5 % Only on the hottest days 9,6 % A few times per Summer 2,6 % A few times per week 1,8 % A few times per day 25,4 % Almost always on during most of the Summer 54,4 % It can be observed in Tables 1 and 2 that most of respondents turn on heating devices in Winter in the period during most of the Winter, followed by only on the coldest days. In summer, most of respondents turn on cooling devices in the period during most of the summer, followed by a few times per day. Comparing both seasons, it can be observed that while in Winter the majority of respondents use the mechanical devices in the periods almost always on and exceptionally on ( only on the coldest days ), in Summer most of respondents use devices in periods almost always on and a few times per 5

6 day, revealing the habit of having the cooling devices on during most of the Summer. Hence, one can conclude that the use of heating devices in winter presents different periods of use, depending on the type of building s units. In a different way, in summer, the use of cooling devices is intensive, including AC devices (Air Conditioning devices, the most used), which are almost on during most of the season. Natural Ventilation through opening of Windows The following Tables 3 and 4 show the frequency of periods of opening windows, in winter and summer seasons, respectively. Periods described correspond to a progression in time duration of open windows. Table 3. Frequency of Opening Windows in the Winter Season. Period Frequency [%] Never 34,9 % Punctually 43,7% Morning / or Afternoon 13,5 % Morning + Afternoon / or during the Night 6,3 % Always 1,6 % Table 4. Frequency of Opening Windows in the Summer Season. Period Frequency [%] Never 16,4 % Punctually 35,3% Morning /or Afternoon /or Evening 21,6 % Morning + Afternoon / or during the Night 21,6 % Always 5,2 % In Table 3, it can be observed that in the winter, the majority of subjects open windows punctually (43,7%) followed by never (34,9%). In Table 4, it can be observed that in the summer, the majority of subjects open windows punctually (35,3%) followed by isolated periods during the morning, or the afternoon, or in the evening (21,6%) or during all day or all night (21,6%). There are 16,4% of subjects that never open windows and 5,2% that has windows always opened. The following tables 5 and 6 show the percentages of distribution of open windows, in winter and summer seasons, respectively. Table 5. Distribution of Open Windows in Winter Season. Distribution of Opening During the Day During the Night Street and Rear 3,1 % 0 % Only Street 44,1% 1,0% Only Rear 12,6 % 1,0 % No Opening 40,2 % 65,0 % NA 0 % 33,0 % Table 6. Distribution of Open Windows in Summer Season. Distribution of Opening During the Day During the Night Street and Rear simultaneously 13,9 % 2,9 % Street and Rear alternate 7,8 % 1,0 % Only Street 40,0 % 3,8 % Only Rear 10,4 % 3,8 % No Opening 26,1 % 45,2 % NA 1,7 % 43,3 % Table 5 shows that in the winter season, there is a large proportion of all subjects who does not open any window (40,2%). From those who open windows, most of subjects do it in the street side of their space (44,1%), followed by "only in the rear side (12,6%). And it can be observed that subjects rarely open windows in the street and rear sides simultaneously (3,1%). A possible explanation is to 6

7 prevent the drafts of cooling air and unwanted air in winter time. It is observed in Table 6 that in the summer, total of subjects open windows on street side primarily (40%), followed by "no opening" (26,1%) and "street and rear simultaneously" (13,9%). One possible explanation for the windows opening is to give rise to types of single-side ventilation or cross ventilation within the space allowing cooling and air renewal. It is observed that generally, subjects do not open windows during the night in summer, which could be a strategy to cool the building fabric. This occurrence can be explained by the sample, which is mainly focused in the office function, where it has been observed that subjects do not leave windows open during the evening, i.e., outside working time. It has been described by subjects in residences that in summer, most of subjects have windows always open, during daytime and nighttime, as opposed to subjects in offices, that generally have windows open during daytime only. These observed frequencies are partially explained by the widespread recurrence of mechanical devices, particularly during the summer season. This higher recurrence affects how windows are used. And to analyze these buildings natural performance, it makes difficult to understand how the performance of these buildings would be without the use of mechanical appliances. One question that arises is whether if there were no air conditioning devices, how would be these buildings use. And once not being able to use such devices, if there would be a more intensive use of other means that are available to regulate temperature, such as windows, shades or doors. The observed use frequencies of mechanical appliances and windows can be explained by the sample, which is mainly focused in the office function and less in the residential function. The office function has a considerable density of occupancy and equipment producing internal heat gains, to which users respond turning on the mechanical appliances. This higher recurrence affects how the windows are used. One can argue about the changing behavior of users of these buildings in the present context, where mechanical devices are available, as compared to the time when these buildings were constructed. Leads to formulate, as hypothesis, that users are not prepared to work with higher temperatures. Maybe because they are not used (anymore) to use all available controls: Users do not have a regular habit of opening windows. And in a simplified way, they are mainly restricted to the use of mechanical devices, neglecting the remaining environmental controls, such as windows or shading. This complementarity of resources (natural + mechanical) is an important issue in the relationship between the regulation of mechanical equipment and windows. One may question whether this complementarity comes from compensation - triggered by the unnaturalness of mechanical controls, and one tries to compensate the thermal environment and air quality by opening windows, bringing natural air. Or one may ask if this complementarity is a correction - triggered by any fluctuation in temperature during the day, and while using mechanical controls, one tries to fix temperature by opening windows. CONCLUSION Regarding the thermal performance, it can be observed from analysis of the survey responses that generally: 1. Users turn on mechanical appliances in a greater frequency in summer than in winter; 2. Users open windows more often in summer than in winter. 3. Users open windows with greater distribution variety in the summer season than in the winter season. 7

8 After the analysis of results, it can be concluded about how buildings are used by users in each season: 4. In winter, subjects use less frequently heating devices, as well as the remaining elements to regulate temperature They have a less interactive attitude - They use environmental controls to regulate temperature less frequently. 5. In summer, subjects use more frequently cooling devices, as well as the remaining elements to regulate temperature They have a more interactive attitude They use environmental controls to regulate temperature more frequently. In winter, buildings of Baixa, in what regards to their controls are used less interactively. In this season, users use less frequently buildings original controls. And in the event of using controls, they use more frequently heating appliances. It must be noted that once, these buildings had fireplaces, that were meanwhile removed, and are now practically nonexistent. Over the years, the fireplace was replaced by heating devices. In summer, architectural elements are used more interactively. In this season, most users use buildings original controls, such as windows. And users use more frequently cooling devices. It is observed that in summer, there is a greater effort than in winter, in using all means of temperature regulation available, such as windows. And in the event that users recur to air conditioning devices, they also use other controls to regulate temperature, such as opening windows (although it is not recommended to be used simultaneously because of conflict with AC). Architectural elements as a mean of temperature regulation are mainly used in the summer season. And it is an indication that under the climate of Lisbon, it is mostly in the summertime that controls have a greater role to play in these buildings in Baixa. ACKNOWLEDGEMENTS The authors wish to thank: To all those who generously participated in the survey conducted in Baixa, providing their offices, their homes, and their time. To FCT - Fundação para a Ciência e Tecnologia do Ministério da Ciência, Tecnologia, e Ensino Superior. REFERENCES BAKER, N. & STEEMERS, K Energy and Environment in Architecture. New York: E & FN Spon. CÂMARA MUNICIPAL DE LISBOA, (Ed.) Cartulário Pombalino Colecção de 70 Prospectos ( ). Lisboa: Câmara Municipal de Lisboa. GONÇALVES, Hélder, & GRAÇA, João Mariz Conceitos Bioclimáticos para os Edifícios em Portugal. Lisboa : INETI. INSTITUTO DE METEOROLOGIA Normas Climatológicas da Estação de Lisboa/Tapada da Ajuda Lisboa: Instituto de Meterologia. MASCARENHAS, Jorge Sistemas de Construção, Vol. V O Edifício de Rendimento da Baixa Pombalina de Lisboa. Lisboa : Livros Horizonte. OLGYAY, Victor Design with Climate: Bioclimatic Approach to Architectural Regionalism. 1st Edition. Princeton, N.J.: Princeton University Press. PINHEIRO, Manuel Duarte Ambiente e Construção Sustentável. Amadora : Instituto do Ambiente. RIBEIRO, Orlando Portugal, o Mediterrâneo e o Atlântico. 5th Edition. Lisboa: Livraria Sá da Costa Editora. 8