Designing outdoor spaces with COMFORT-EX

Transcription

1 International Workshop on Energy Performance and Environmental 1 Designing outdoor spaces with COMFORT-EX J. Ochoa and I. Marincic Department of Architecture, University of Sonora, Mexico H. Villa Department of Mathematics, University of Sonora, Mexico ABSTRACT In this paper we are introducing the first version of COMFORT-EX, a computational tool, with a friendly interface, developed in Java language and visible from any computer with an Internet browser. This tool pretends to assist architects, landscape architects and urban planners to determine the correct design strategies to follow for a project in specific climate conditions. It also helps to evaluate the thermal comfort sensation, and to make the pertinent corrections if necessary. A selected case study sited in the campus of the University of Sonora, evaluated with COMFORT-EX, is described. 1. INTRODUCTION The microclimates within a city change from one small area to another. For that reason, in order to control the microclimate conditions, it is necessary to know and determine which of these factors can be manipulated to create more pleasant spaces for human beings and get better conditions for a sustainable environment. This is also important for encouraging reductions in energy requirements and decreasing the environmental impact of buildings. Therefore, town planners, landscape architects and architects should pay attention in the climatic consequences of their projects and the solution of possible problems. However, when an outdoor space is going to be planned, the thermal comfort requirements of the users, nor the energy influence on adjacent buildings, are usually not considered in a quantitative way. Generally, the designer brings in to play his/her intuition to solve this problem. Since exterior spaces are usually not artificially cooled or heated, there is no extra energy consumption related with the outdoor thermal comfort. For this reason, developers of design tools and software have centered their efforts in thermal design and efficient use of energy in building indoors, banishing the landscape microclimatic design. Motivated for this situation, our research team has been developing, for several years, simplified evaluation tools and design guidelines, aimed to create environmentally conscious outdoor spaces (Ochoa and Serra, 1998). The proposed methodology is strongly involved with the typical design process. In this work we are introducing a computational tool called CONFORT-EX. One of the goals of CONFORT-Ex is to assist landscape designers and town planners in the process of microclimatic design of outdoor spaces, but in contrast with much thermal analysis software, the user does not have to employ most of the time learning how the program works looking into very thick user s manual. With CONFORT- EX one can center the attention on the design process, obtaining better results, due to the simplicity of its graphic interface. Another objective that we had in mind when the software was developed was that it could be seen on any operating sistem platform with the internet, with the advantage of continuous updating, instead of a stand alone software. CONFORT-EX is programmed in Java using a technology called servlets. Java is a relative new programming language developed by Sun Microsystems ( and released in 1995 initially as a language to connect heterogeneous household appliances. With the

2 2 International Workshop on Energy Performance and Environmental Internet boom, Java evolved as the natural language to connect heterogeneous computer systems and to get a "smart office". A servlet is a program that runs on a web server to provide functionality of processing data on the server. The user can access the servlet with a browser as a common HTML file, the servlet runs in the server and replies generating an HTML screen that the user s browser displays. Figure 1: Screen showing the map of Mexico that allows choosing the city for the evaluation. Figure 2: Screen showing the results from diagnosis component. 2. PROGRAM COMPONENTS COMFORT-EX has three components; each of them correspond to one stage of the design process, but the program itself does not cover all the aspects of the design process, encouraging the creativity of the designer. 2.1 Component 1: Diagnosis The analysis of the bioclimatic needs for each site is based on the well-known Olgyay s bioclimatic chart (Olgyay, 1962). There are two ways to enter the information: in the first way, one can select climatic data of a specific city (Fig. 1). Only some cities of México are available in version 1.0, however more cities and worldwide data will be supplied in upcoming versions. In the second option is possible to enter climatic monthly average data or to paste a text file, containing hourly data of an average day of each month for any location. The required parameters are: air temperature (Celsius degrees), relative humidity (%), horizontal solar global radiation (W/m 2 ), and wind speed (m/s). For the diagnosis, the designer can use the meteorological data of a city, or (if available) the microclimatic parameters measured in the specific site of the project. A timetable of climatic needs shows the diagnosis results. A color code makes it easy to identify appropriate strategies for the whole year, which becomes visible on screen when the mouse cursor is on any cell. See Figure Component 2: Design Guidelines Depending on the diagnosis, in this section it is possible to determine a design strategy aimed to control microclimatic parameters. Design guidelines are divided in four main groups: solar radiation control, terrestrial or long wave radiation, wind control, air temperature and humidity control. The goal of guidelines is to help the designers to generate specific design strategies for each case study, allowing choosing material properties, vegetal elements and spatial configuration. The information comes in graphics, tables and text form (Fig. 3). 2.3 Component 3: Evaluation This component of the program allows to evaluate the thermal comfort sensation in a selected place, when the design strategies have been applied. It will help the user to decide if the comfort conditions are acceptable or if it is necessary to correct some aspects of the project and then return to the evaluation component. The output of this component is in a standard text file, which can be plotted with any spreadsheet software. Thermal comfort evaluation is based on the COMFA method, developed by Brown & Gillespie (1995), modified by Ochoa (1999), which provides a simplified thermal comfort index.

3 International Workshop on Energy Performance and Environmental 3 a) The energy balance of the human body under specific thermal conditions can be used to determine the thermal comfort level of a person in an outdoor environment (Ochoa and Roset, 2000). The basic balance is expressed in Eqn. 1 (W/m 2 ): B = Met + Ra + Conv + Cond - E Re (1) where: B: Energy balance of a human body outdoors, M: Metabolic rate of internal heat production of human body depending on subjects activity, Ra: Absorbed net radiation (solar + long weave), Cv: Heat exchanged by convection, Cd: Heat exchanged by conduction due to contact of skin with solid surfaces, E: Evaporative heat loss, Re: Long wave radiation emitted by the body s external surface. Equation 1 is not very different from other authors models, like B. Givoni (1976) or P.O. Fanger (1970), but the translation from energy balance (B) to people s comfort sensation is quite different. The reason for this difference is that the indoor conditions normally do not include the wide range of microclimatic characteristics found outdoors. The humidity, radiation, wind, and precipitation are often strictly controlled or very stable indoors, whereas these elements are highly variable in the outdoor environment. The output from the evaluation component is in units of watt per square meter (W/m 2 ), and these can be interpreted as comfort sensation. When the balance is near zero (±50 W/m 2 ) a person can expect to be thermally comfortable. If the balance is a large positive value (>250 W/m 2 ), then the person would receive more energy than could lose, so overheating would occurs and the person would be uncomfortably hot. If the balance were a large negative value (<-250 W/m 2 ), a person would be too cold. b) c) Figure 3 a, b and c: Example of design guidelines generated by Component 2. Figure 4: Screen showing the data entries for evaluation component.

4 4 International Workshop on Energy Performance and Environmental Figure 5: West and north facades of case study building. Figure 6: South and west facades of case study building. The required parameters at this stage are: air temperature, relative humidity, horizontal solar radiation, wind speed, metabolic rate, clothing insulation and permeability, temperature, emittance and albedo of objects and surfaces surrounding the subject, shading factor of vegetation or objects located between the subject and the sun, solar azimuth and altitude and sky view factor. 3. CASE STUDY ANALISYS The selected case study is a two floor building located in the campus of the University of Sonora, in Hermosillo City, in north-west of Mexico. It serves as university offices and informatics center for the Department of Geology (Fig. 5 and 6). The building has a rectangular plan; the longest axis runs in east-west direction with a deviation of 10 degrees from north. The whole building is surrounded by concrete floor surfaces, with high albedo. That situation, in addition to the extremely hot climate of the Sonora s desert, provokes a very uncomfortably Figure 7: Graphic showing the output of evaluation component in energy units and as comfort sensation during the analyzed day (3: very hot, 2: hot, 1: warm, 0: comfortable, -1: cool, -2: cold, -3: very cold). sensation outdoors, and indoors. According to the entered climatic data, the analysis suggests in this case to obstruct solar radiation to avoid people s direct exposure and surface heating (lowering long-wave radiation emission), medium-low albedo pavements and vegetative ground cover (diminishing reflected radiation) and evaporative cooling (irrigation). In the proposed landscaping (Fig. 8), the pavements have been changed and vegetative ground cover and desert shade trees, has been strategically planted (Prosopis chilensis). Evaporative cooling has not been considered, because Hermosillo is water - scarce region. The evaluation results, in the graphic of Figure 7, shows an improvement of comfort sensation in south facade, but the comfort conditions have not been reached because of the intense solar radiation and air temperature (>800 W/m 2 and 37 ºC at noon in spring). 4. CONCLUSIONS The first version of COMFORT-EX has satisfied the initial expectations. The program could be improved in next versions, for example adding climatic data, materials and vegetation to the databases; and a 3-D interface to the evaluation module. However, the scope of the program is to maintain its simplicity with the purpose of being a useful tool for the people that have no expertise in energy issues.

5 International Workshop on Energy Performance and Environmental 5 Figure 8: Proposed landscaping plan. ACKNOWLEDGEMENTS This study was undertaken with the support of a research grant from The National Council of Science and Technology of Mexico (CONA- CYT) and the University of Sonora. REFERENCES Ochoa, J.M. and R. Serra, Microclimatic analysis of some urban scenarios, Environmentally Friendly Cities PLEA 98. Maldonado, E. and Yanas (editors), London: James & James S. Ochoa, J.M., R. Serra and J. Roset, Vegetation influences on the human thermal comfort in outdoor spaces. Energy Performance and Indoor Climate Buildings EPIC 98, Guarranchino, G. (editors). France: Ecole Nationale des Travaux de l Etat. Ochoa, J.M. and J. Roset, Influence of vegetation on the energetic balance of urban outdoor spaces, ISES Millennium Solar Forum, Estrada, C (editor), México: ANES. Olgyay, V., Design with Climate. U.S.A.: Princeton University Press. Brown, R.D. and T.J. Gillespie, Microclimatic Landscape Design. New York: John Wiley & Sons, Ochoa, J.M., Vegetation as a tool for microclimatic control, PhD Thesis, Spain: Polytechnic University of Catalonia, Barcelona. Givoni, B., Man Climate and Architecture. U.S.A.: Applied Science Publishers. Fanger, P.O., Human Thermal Comfort. U.S.A.: Mc Graw Hill.