The passive house: towards a more sustainable future
From the German term "passive house", the passive house constitutes the current most sustainable housing model in the design scenario. Its origins date back to the 1980s - 1990s, when two North European scholars and physicists started some studies with the aim of identifying construction standards aimed at creating buildings with low environmental impact. The result made it possible to achieve excellent performance for energy saving but rather high manufacturing costs which did not make the proposal applicable by a large user base. However, since it was a type that guaranteed many advantages in terms of energy and comfort, studies were continued and the model developed to the present day as an excellent example of sustainable construction. Although it constitutes an innovative proposal in the construction field, the passive house uses already known technologies and its real novelty consists in the particular combination of these solutions. In fact, ecological construction materials are used, orientation and sun exposure are exploited and compact physical conformation and very large openings are preferred. In fact, thanks to the correct thermal insulation, the containment of energy consumption and the exploitation of passive devices, this type of building requires little auxiliary energy for its heating. It follows that traditional systems used in homes such as boilers and boilers that require the use of a lot of energy are not necessary.
Built with a wide range of materials (wood, concrete, brick), passive houses can be considered almost self-sufficient and guaranteeing high quality standards. Their diffusion initially concerned the territories of Northern Europe (Germany, Sweden, Switzerland, France) and only later did it also spark the interest of the designers of the countries of the Mediterranean area. However, it is important to specify how it is not possible to apply the model without distinction in geographical areas with different climatic characteristics, but it is necessary to shape the design choices on the specificities of the place. For this reason, interest in this type of construction is growing in Italy but the studies necessary for the application of the model in temperate climates are underway. Over time, these building schemes will prove indispensable for the protection of the environment and future generations. To understand the importance of sustainability applied in construction, one must be aware of how destructive the use of non-renewable energy sources in the long term is. Furthermore, as regards the Italian scenario, the economic boom of the 50s and 60s of the twentieth century caused an uncontrolled construction based on the high gain at the expense of quality in terms of energy and comfort. For this reason, today it is good to remedy this situation and to adopt, at the planning stage, some measures considered indispensable: the optimization of resources, the exploitation of renewable sources, the containment of energy consumption and the adoption of passive systems as the only one heating solution. These choices are used in the passive house which, in addition to having a minimal ecological impact on the ecosystem, ensures high living comfort at reduced management costs.
Once the concept of passive house has been clarified, it is necessary to illustrate the technological choices that distinguish it and make it the optimal model for sustainable architecture. As anticipated, the typological scheme combines reasoned design solutions together, paying particular attention to respect for the environment and its protection.
PHYSICAL CONFORMATION AND ORIENTATION
The first aspect to consider concerns the shape of the building: a compact volume with discontinuous and irregular elements is preferable. In fact, the presence of overhanging and overlapping bodies causes the formation of harmful thermal bridges, the origin of huge thermal dispersions. On the other hand, it has been shown that structures with regular and linear lines are able to optimize the energy needs of the entire system, retaining the incident heat on the facade better and longer. The location of the building is also very important if you consider the peculiarities of the place where it will be inserted. In fact, it is necessary to consider some climatic and local phenomena that will necessarily condition the success of the project. In order to choose the optimal orientation for a building, it is necessary to calculate its position in relation to the cardinal axes, the shading deriving from pre-existing buildings, the presence of wind currents and sources of noise.
As for the first aspect, today the east-west axis is preferred with the aim of making the most of the hours of sunshine on the south front during the winter. In fact, as is well known, solar radiation varies according to the season of the year and for this reason it is good to opt for improved solutions compared to the less favorable period. In addition, the sunshine conditions vary greatly depending on where you are located: in colder countries it is preferable to make the most of the solar radiation, while in dry and arid places it is necessary to maximize the fresh air currents. These measures are used in order to improve the thermal comfort of the internal environments by exploiting the local climatic characteristics. Shading also represents an element to be taken into consideration since it is good to consider how the quantity and quality of the sun's rays that hit the facade vary in relation to the presence of buildings or shielding elements, in the immediate vicinity of the building in question. Otherwise, this phenomenon may prove indispensable in particularly arid and sultry territories. In order to mitigate the too hot climate, ventilation currents also come in, very useful for buildings with east-west orientation. In this case, the warm winds from the south will balance the cold ones on the north front. INTERNAL FUNCTIONALIZATION
With the aim of maximizing solar orientation, the choice of the intended use of each individual indoor environment must be undertaken taking into account the solar trend. Given that in the case of residential buildings, the east-west orientation is preferable, it is good to allocate the rooms facing south to the living area (living room / kitchen / study) and to place the sleeping area and the accessory environments (bathrooms / closets) on the north front. In fact, the south side is considered optimal because during the cold seasons there is a greater amount of sun rays, thus enjoying more heat, while in summer the higher sun hits the rooms more indirectly without overheating them. If the apartment has a view to the east, it will be advisable to place the bedrooms which will thus enjoy the first heat of the morning and will not become excessively hot in the summer as it is in the shade of the afternoon. The rooms on the west side, on the other hand, receiving sunrays throughout the afternoon, in the summer require shielding elements to relieve excessive heating.THERMAL INSULATION
In new generation buildings, designed according to passive house standards, the perimeter walls and floors are equipped with a layer of very thick insulation material (30 cm), usually positioned inside the outermost section of the wall. This particular insulation also concerns the roofing of the house, since it forms an integral part of the building in direct contact with external atmospheric agents. If you want to improve the performance of the envelope of a pre-existing building, it will be necessary to intervene with the insertion of a coat that can be external or internal. The first type is usually used in independent houses, while the second is chosen, in case of intervention on the individual units belonging to larger buildings (urban condominiums). In this way, the perimeter walls ensure low transmittance and high thermal insulation, so that in winter the heat necessary to heat the room is retained and in summer it is blocked outside. Thanks to this arrangement, it is possible to enjoy optimal living comfort during all seasons of the year.
PASSIVE HEATING SYSTEM
The adequate thermal insulation that characterizes the passive house allows it not to require traditional heating systems. To guarantee balanced temperatures, heat sources too often underestimated contribute in part: household appliances, luminaires, stoves in the kitchen, occupants of the home. In addition, sustainable solutions are exploited such as solar panels and heat pump; the former produce thermal energy using the incident sun rays, the latter instead, contributes to the same function by using resources such as air, water or the soil. These are alternative methods to the systems used in the past which involved a large expenditure of non-renewable sources and a substantial production of pollution harmful to the fate of the planet.
They have always been the connecting element between the interior and exterior of the building and for this reason, often in traditional homes they can represent a danger for drafts and heat loss. In order to avoid this type of inconvenience, the passive house uses only triple glazing, which, since they are extremely insulating, guarantee air, water and cold tightness. In addition, a few large openings are preferable which allow more sunlight to filter into the indoor environments, thus providing them with a greater amount of heat and lighting. This benefit is maintained inside the building, thanks to the high capacity of the triple glazing to insulate thermally. It is therefore preferable to choose frames with average performing frames but fully insulated, up to the edge of the glass, so as to obtain high performance guaranteed through a preventive calculation.
In order to ensure appropriate hygienic and sanitary conditions within the living spaces, it is known that an adequate exchange of indoor air is necessary. However, especially during the winter season, opening the windows can cause excessive heat loss. To deal with this problem, the passive house model proposes the inclusion of a ventilation control system. This system consists of an equipment designed to monitor heat exchange and can work both for cooling and for heating. In fact, this system allows the incoming cold air to retain the heat of the outlet flow coming from the service areas (bathrooms and kitchen). This triggers an air exchange mechanism between excessively heated rooms and colder rooms (perhaps positioned on the north front of the building), so as to ensure optimal and more balanced comfort between the various rooms.
It is therefore possible to notice how all the phenomena analyzed contribute to making a passive house more or less performing: the thermal insulation of the perimeter walls and the controlled ventilation each have a 30% impact, the type of window and the presence or absence of thermal bridges they contribute 15% of the total and finally the orientation and presence of electrical appliances with 15% each. These standards belong to the passive house model which was introduced and tested in territories belonging to northern Europe, characterized by harsh climates and low temperatures. In order to be able to apply the same scheme in the Mediterranean area, which is distinguished by its mild climate in winter and warm in summer, it is necessary to be aware that standards must be shaped by the particularities of the place. If in the first case the primary need is to heat the interiors of the buildings, in southern Europe the need is the opposite, since there is a greater need to cool the spaces during the summer season.
To remedy this situation, a study was conducted on the territorial specificities that allows the model to be applied by paying attention to the aspect of cooling. In fact, if the dictates of the passive house model, designed for the harshest climates can also be applied in more temperate areas, it is also true that in these territories it is also necessary to provide adequate darkening systems from sunlight (indispensable during the day) and low consumption cooling. These are extremely important measures, especially if applied in highly urbanized contexts, where heat islands and cementing contribute significantly to environmental overheating.