EAC - Comunicações em actas de encontros científicos internacionais
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- Air flow exchange velocity of urban canyon cavities due to thermal spatial differencesPublication . Panão, Marta Oliveira; Goncalves, Helder; Ferrão, PauloIn this paper, the air exchange velocity between the urban canyon cavity and the air layer above roof level is quantified, using a two-dimensional k-ε model, and correlated with the air cavity mean temperature, for two cases: leeward and downward wall heating. The spatial thermal differences are evaluated by assuming a wall temperature higher than the air temperature, with this difference ranging between 0 and 16 K. The undisturbed wind velocity above the roof level is varied from 1 to 6 ms-1 and the canyon aspect ratio is 1.5, which corresponds to a skimming flow regime. The model predicts two situations, which correspond to air flow regimes where one or two eddies are formed, respectively: (a) for high wind speed, the air inside the cavity is negligible affect by the buoyancy effect and the air exchange velocity linearly increases with the increase of wind velocity; (b) for low wind speed, when the buoyancy forces are stronger than the wind induced forces, the air exchange velocity is not a linear function with the wind velocity. The transition wind velocity between (a) and (b) is a function of the wall-air temperature difference. The situation of windward heated wall and two eddies air flow regime is the most favorable to extract heat from the cavity. On the contrary, the heated air is hardly extracted from the cavity when only the wind induced eddy is predicted and windward wall is heated. In this situation an increase of 10 K on the wall temperature increases by 1 K the in-cavity air temperature.
- Eficiência energética na cidade: Estratégias para a promoção da capacidade natural de aquecimento e arrefecimento de edifíciosPublication . Panão, Marta Oliveira; Goncalves, Helder; Ferrão, P.Este estudo apresenta uma técnica para, a partir de um dado índice de construção, encontrar as formas urbanas mais favoráveis ao desempenho térmico de edifícios, com base na absorptância efectiva do edifício no Inverno e no Verão. Esse parâmetro é indicativo da exposição solar do mesmo e da capacidade natural de aquecimento de um edifício quando esse se encontra inserido numa malha urbana. A avaliação da absorptância efectiva para as duas estações do ano permitiu encontrar as formas de organização da malha que beneficiam a acessibilidade solar de Inverno, mas restrigem-na no Verão. Para o cálculo da absorptância efectiva utiliza-se o Método das Matrizes Urbanas que consiste em obter para cada geometria, uma matriz Ψ que descreve a forma como a radiação que incide em cada uma das parcelas que compõem as superfícies do bloco urbano se distribui pelas restantes superfícies. Essa matriz integra os factores de forma entre as superfícies e as respectivas propriedades de absorpção considerando, dessa forma, as reflexões múltiplas que ocorrem no interior do espaço urbano. A aplicação de uma metodologia de optimização a diversas formas urbanas, com base no conceito de algoritmo genético, permitiu concluir que, para as latitudes de 37º e 42º, as malhas urbanas mais favoráveis são os blocos de secção rectangular, com 3 a 5 pisos, dispostos segundo um eixo Este-Oeste por forma a possuirem uma maior fachada exposta a Sul. O espaçamento entre blocos é sempre maximizado na direcção Norte-Sul por forma a permitir, no Inverno, uma maior exposição solar da fachada Sul e, por outro lado, minimizando o espaçamento entre blocos na direcção Este-Oeste, prevenir os excessivos ganhos solares na estação de Verão. Para uma latitude de 37º são ainda soluções blocos de secção quadrangular com 5 a 8 pisos, que formam uma malha com ângulo de ±15º relativamente à direcção dos pontos cardeais.
- Green initiative for energy efficient eco-products in the construction industryPublication . Partidário, Paulo Jorge; Goncalves, Helder
- Solar XXI building PV systems: performance during the first two yeras of operationPublication . Rodrigues, Carlos; Viana, Susana; Joyce, A; Goncalves, Helder; Silva, António Rocha eThe purpose of this paper is to present the results obtained in the first two years of operation of the grid-connected photovoltaic (PV) systems installed in the named “Solar XXI” building. One PV system, made with multicrystalline silicon modules, has a peak power of 12 kW and was installed on the façade; another system made with amorphous silicon modules has a peak power of 6 kW and was installed in the surrounding park area near the building. From 1st February 2006 until 31 July 2008, the measured daily average, of the building electrical energy consumption, was about 75 kWh and the two PV systems produced in average about 72 % of this energy. The averaged measured Performance Ratio of the systems was about 0.84 for the PV Façade and about 0.76 for the PV in the Park.
- Energy simulation of a vernacular raw earth construction, in South Alentejo: a case studyPublication . Graça, João Mariz; Beirão, Teresa; Vinagre, Joel; Macedo, Pedro; Carneiro, Nuno
- Thermal performance of a passive solar office building in PortugalPublication . Goncalves, Helder; Silva, António Rocha e; Rodrigues, CarlosThis paper presents the thermal performance of a Passive Solar Office Building in Portugal in winter and summer 2006 and 2007. This Building, called Solar XXI, pretends to be an example of passive design both for heating and cooling. It contains a direct gain system assisted by a solar thermal system for winter conditions. In summer a ground cooling system (buried pipes) is used to cool the building, together with night cooling strategies. It also integrate in the vertical south envelope a Photovoltaic System (12 kWp) which provide around 12 MWh per year plus a 6kWp in the car parking, which correspond to around 76% of the electric energy consumption of the building. The integration of the PV system, in the building was done in such a way, that it is possible to recovery the heat production from the PV in order to be used for heating purposes
- Thermal performance of residential buildings in Lisbon with large glazing areasPublication . Tavares, Márcia; Goncalves, Helder; Bastos, JorgeThis work presents the results of an experimental study of residential buildings (multi-family apartments) with glazing areas greater than 75% of the total façade area, and for different solar exposures in Lisbon. These buildings were designed after the implementation of the first Portuguese Buildings Thermal Regulation and they are intrinsically related with the construction and architecture practiced in the last few years. The analysis includes the thermal behaviour of the apartments selected for the study during the summer (2007) and winter (2007-2008). During the monitoring process important data were obtained to assist in the understanding of the thermal performance of the observed units. The main thermal exchanges in a building generally take place through the transparent elements and these can be considered an element of great flexibility and adaptation to climatic variations. The mean of the interior temperature means in the different monitored compartments during the hot season was approximately 27ºC (some cases close to 29ºC), while in the cold season 21ºC (some cases close to 18ºC).
- Energy simulation of a vernacular house in Santana/Madeira Island: case studyPublication . Graça, João Mariz; Andrade, Susana
- Towards a strategy to zero energy buildings (ZEB) conceptPublication . Goncalves, HelderThe energy consumption in buildings and the need for its reduction has been since the late 60’s and 70ś a main question among professionals (designer, architects, and engineers), legislators and users around the word. Reduction in energy demand for heating for instance was implemented in the so called Solar Buildings (with reduction of 70 to 80% in the heating demand). The building regulation start putting targets, in the overall annual energy consumption xx kWh/m2 year, and some achieve the level of standards, imposing very low values, such as Passivhaus standard which fundamentally consists of an energy limit (net useful energy demand for heating of 15 kWh/m²/year and a total primary energy consumption of 120 kWh/m²/year). Now we are dealing for a new concept, in which those values approach zero (ZEB) or even minus, which correspond to building which produce more than what they spend (ENERGY PLUS BUILDINGS). This paper discusses some of the main issues regarding the strategy to achieve some of these goals in the future.
- From Summer cooling to sustainable Summer comfort in buiding thermal regulationPublication . Camelo, Susana; Goncalves, Helder; Richard, Mathieu; Laia, CarlosThe introduction of the “Energy Performance Building Directive” (EPBD) [1] and consequently the new National Building Regulation [2] in the Member States (MS) lead to a totally new legal situation concerning, requirements and procedures on the building sector. Under the scope of an EU project called Keep Cool, a survey was undertaken in order to review the energy efficiency criteria, in the national building codes, concerning summer comfort or mechanical cooling system in order to elaborate recommendations towards a sustainable summer comfort. This paper presents the results of this survey [3] carried out under the participate countries (7 countries), and the main goals were the following to update the information regarding the new national building regulations to have a first insight regarding the requirements and summer calculations adopted in each country and to identify the positive and the negative aspects of the different regulations and selection of the best practice examples, in order to draw up recommendations for introducing sustainable summer comfort measures into future national building codes. A comparative analysis has started with some very precise answers and had permitted to carry out a comparative analysis between some national building codes. A review was undertaken concerning envelope constructive solutions (opaque and transparent), thermal mass, ventilation rates and the corresponding values limits.