By Marta Lozano, architect at AGi architects, Polytechnic University of Madrid.
Existing since Antiquity, passive architecture is that which adapts to the climatic conditions of its environment. Throughout the 20th century the focus placed on the energetic component in the architectural project was diluted due to the disassociation from local conditions proclaimed by the International Style. Currently, energy consumption caused by the use of buildings occupies first place in the construction field. This is higher than the energy consumed during the manufacture of materials and in the construction process. As a result, the energy efficiency of buildings has become one of the concerns that the industry has had to face. Passive architecture has recovered its relevance in both new developments and in the rehabilitation of existing buildings.
Currently, energy consumption caused by the use of buildings occupies first place in the construction field.
In recent years, European regulations have established a series of requirements regarding the energy efficiency of buildings. However, these specifications do not indicate exactly the way to achieve the goal of almost zero energy consumption in buildings. Therefore, the different countries must customize their own definition, depending on their climate. Thus, in the European Union a series of passive construction standards are emerging, through which these near-zero energy buildings will be reached.
The Passivhaus standard is one of the best known. The main target of passive houses is to obtain high levels of indoor comfort, maintaining a very low energy consumption. This standard is focused on controlling the heating and cooling demand, providing solutions for execution and design of passive components, always with the support of energy efficient active systems.
Passivhaus is a construction standard, based on sustainable architecture, that is to say, it pursues the goal of a building that is energy efficient, has a high level of interior comfort, is economically affordable and is environmentally friendly.
The importance of the local climate should be noted when establishing both project and construction strategies. While the energy demands will have to be the same regardless of location, the design and construction responses will have to be completely different depending on the climatic conditions of the context.
Therefore, when making a consideration concerning the application of the Passivhaus standard in the Mediterranean climate, local climatic demands must be taken into account, in order to give adequate solutions. It will be necessary to reconsider the basic principles on which the standard works so as to adapt them to this climate.
Compactness and orientation must address the production of shade in summer and the optimization of openings, being the buildings in the Mediterranean climate less compact than in continental climates, considering their orientation and size. With a correct orientation and compactness, solar gains will be maximized in winter and minimized in summer, by means of fixed or mobile solar protection.
The presence of thermal insulation will be essential, but in smaller proportions than those used in continental climates. The thickness of thermal insulation can be optimized, depending on the climate, to the point where the increase in thickness is of little relevance to improving energy efficiency. Insulation in floors will be meaningless, since they act as a heat-absorbing well. This is how the concept of thermal inertia in terms of the use of materials emerges. The walls will absorb the heat from the air, keeping the rooms cool in summer, and retaining heat in winter, to keep the building warm.
Openings are characterized by being the enclosure’s weakest point, in thermal terms, so the Passivhaus standard places special emphasis on their location during the project design and on their correct installation during construction. In the Mediterranean climate, triple glazing will not be so necessary, but a good arrangement of them. It is convenient to make a distinction between north and south windows, being necessary triple glazing to north, in order to isolate in winter and double glazing to south, to allow the entrance of solar radiation and therefore heat gains in the interior.
Ventilation plays a fundamental role in the Mediterranean climate. Mechanical ventilation with heat recovery will be used as an alternative to heating, so that the heat recovered from internal loads or radiation alone will be sufficient for comfort in winter. There is also the cold-heat recovery system, which in summer will serve to cool the interior environment.
It is also important to consider the importance of natural ventilation in summer, since it significantly reduces cooling loads. Strategies such as cross ventilation, which is based on a difference in wind pressure, or stratification ventilation, based on a difference in vertical temperatures, are both interesting in the form of night ventilation. These techniques will be carried out by designing openings on opposite sides of the building, patios, and by tempering the air prior to entering the building through buried ducts.
The absence of thermal bridges will have to be taken into account. However, as the thickness of the thermal insulation is lower than in colder climates, and therefore the enclosure has higher transmittance, the air tightness will not be as important as in the case of continental or cold weather. Wooden structures will not be necessary to avoid thermal bridges, since wood in the Mediterranean climate is less efficient, from the point of view of the summer.
The strategy of solar reflectivity will also be important. This is a strategy to minimize the impact of solar radiation in summer through color. The higher the degree of reflectivity, the lower the absorption of radiation by the materials will be, and therefore the demand for cooling will decrease. Light colors will cause heat to be reflected and not overheat the building envelope.
The constructive design of the roofs will be key. Roofs receive the highest radiation loads in summer, and lose a great deal of heat in winter. Thermal insulation and the use of vegetable roofs will be important both in winter to avoid energy losses and in summer to avoid overheating.
So we can conclude the importance of local climate in establishing constructive strategies for passive architecture. The fact that the standard does not define certain building solutions, but rather energy demands for heating and cooling, favours adaptation to each climate by designing local alternatives. Thus, different strategies will be applied in the Mediterranean climate as compared to the continental climate, obtaining the same results in terms of energy savings and gaining comfort inside buildings.
Energiehaus, Definición y funcionamiento de una Passivhaus (http://www.energiehaus.es/passivhaus/)
Plataforma de Edificación Passivhaus (PEP), Los edificios pasivos: edificios de consumo casi nulo (http://www.plataforma-pep.org)
Passivhaus Institut Darmstadt, Passive houses for different climate zones, Darmstadt ,2006
Passive-On Project, El estándar Passivhaus en climas europeos templados, “Una revisión de viviendas confortables de baja energía”, Italy, France, Germany, Portugal, Spain (AICIA), United Kingdom, July 2007
Wassouf, Micheel, Passivhaus: de la casa pasiva al estándar, la arquitectura pasiva en climas cálidos, Gustavo Gili, Barcelona, 2014
Lozano Reina, Marta, Passivhaus: adaptación al clima mediterráneo. Graduate work, ETSAM, Madrid, 2015 (https://issuu.com/marta.lozano.reina/docs/lozano_reina_marta__tfg/)