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In general, it is possible to distinguish different energy performance classes of buildings, the indicators of which are given by the energy performance certificate  certification  energy, a document that certifies the energy consumption of a building, reporting the amount of energy, as well as detailed information on the building envelope and  installed systems. Introduced with the 2007 budget, the energy certification is drawn up by specialized technicians thanks to which it is possible to classify buildings, a bit like it is done with the energy labeling of  domestic appliances. This certificate affects the value of the property which, in fact, specifies the consumption referring to the heated living area. But beyond mere numerical values it is also possible to make one  qualitative classification of buildings according to the scheme  following:


- Conventional buildings that do not comply with energy saving regulations  energy saving.  This term refers to all the initiatives undertaken to reduce energy consumption, both in terms of primary energy and in terms of electricity, by adopting lifestyles and consumption models based on a more responsible use of resources.
  - Conventional buildings that fall within the standard values.
  - Energy-efficient buildings.
  - Passive buildings.
  - Zero consumption buildings.

From this classification it is evident that the energy performances are all the more efficient the closer we get to the last item on the list.
  It is therefore interesting to analyze what the discriminating factors between these categories may be.  Certainly, as already specified, one of the main objectives is to reduce the transmittance which therefore means increasing the quality of the insulation, also called insulation, of the envelope. This is the most important parameter, but not the only one.

Along with insulation, another parameter that holds the greatest importance is ventilation, which therefore affects the movement of air inside the building. Typically buildings with poor energy performance do not
  they have a forced ventilation system, but the air exchange takes place  only through the openings of the casing or the opening of windows and doors. For a long time the value of this air exchange was estimated at 0.5  volumes / hour which means that every two hours the entire air is present in the environment  is changed. In reality this value was reliable until a few years ago,  when there were no stringent regulations on energy saving. To date, with the improvement of the insulation, this value is a bit high  a point that many designers use as a reference value 0.3 volumes / hour which means that the environment requires three hours to have an air change  full. 
This improvement in the energy performance of the envelope has therefore caused a worsening of the air quality in the environment, remaining the latter for a longer time inside the environment itself. And so the so-called forced ventilation was born. The term forced, as opposed to the natural term that is used for traditional ventilation, indicates
  that there is a special system that "forces" the air to enter and exit the environment according to specific project canons. Such plant raises  enormously the energy quality of the building as it is possible to recover the heat of the hot but exhausted air present in the environment, pre-heating the renewal air by means of special exchangers.

  two very interesting parameters that influence the performance of the building for 15% are the window components and the bridges  thermal.
First of all, confirming what has already been said above, as far as the transmittance of the
  windows is much higher than that of opaque components, the overall influence of the insulation of opaque structures is however  greater than that of transparent structures due to the clear difference in surface between the two. However, reducing the transmittance of the windowed components remains very important and this reduction can be achieved through the use of energy-efficient glass.  energy efficiency.
These terms mean the improvements that can be made to the technology to produce the same goods and services using less energy, with a consequent reduction in environmental impact and associated costs., Typically
  double or triple selective glazing with low remissivity.
Thermal bridges, on the other hand, are interruptions in the insulation, for example in
  correspondence of edges, corners, balconies, beams etc. The interruption of the insulation is detrimental to the energy efficiency of the building as it partially nullifies the work carried out by the insulation itself, allowing heat to pass to the outside. And the importance of this parameter is of great importance  attention to insulation designers who are looking for more and more  reduce thermal bridges through more refined insulation installations and possibly reducing the number of points of  break.

Another, albeit less important, parameter is the orientation of the buildings, while the discussion on electrical appliances already discussed in another section will be omitted. The orientation of the building clearly concerns only the
  glazed windows, or the only ones able to let the radiation pass  solar and therefore those that are defined free contributions to the building. The  in fact, the sun with its irradiation  irradiation  Heat transmission mechanism  by means of electromagnetic waves. Unlike conduction and convection, radiation can also take place in a vacuum (it is something that propagates heat from the sun to the earth). All bodies emit radiation because  all bodies have a certain temperature; however the extent of the heat exchange depends on the nature of the bodies, on their reciprocal position,  the possible absorption of the interposed medium and the temperature of their surfaces. The amount of heat emitted by a body by radiation, in fact, is proportional to the fourth power of the temperature. This means that as the temperature rises, radiation becomes the conduction mechanism  of the preponderant heat, with respect to conduction and convection. is  able to partially heat the environment completely free of charge. Turns out  therefore recommended, in our country which is located in the northern hemisphere, to expose the  windows facing south as far as possible. In reality then this becomes a  opposite problem in the summer, when the free contributions of the sun are not  and it is for this reason, also given the scarce influence of this parameter,  that there is an optimum point which roughly estimates the optimum surface  of the glazed walls on the south side in about 40% of the 



There  compactness  of a building is a parameter that affects its  energy performance. The smaller it is,  at the same volume, his  surface exposed to the outside, the more compact a building is. So the more compact a building is  improve  we can consider it from an energetic point of view. But let's try to understand this concept better.  Let's consider  two buildings of equal volume. One of shape A (in figure) and another of cubic (figure B). It is easy to understand how in the first case, the internal heat finds many more surfaces  dispersants from which to exit with respect to the second which, being more compact, has a smaller dispersant surface for the same  volume.

The solid figure for which the compactness parameter is the maximum possible, is  the sphere, but it is evident that such a figure is not usable in construction. We then opt for the  cube: the geometric shape that comes closest to the sphere in terms of compactness. However, sides of the cube 12-13 meters long can cause  lighting and ventilation problems. Furthermore, the cubic shape is the ideal one in the case of walls with the same  transmittance  thermal. Conversely, in reality, the roof for example, is characterized by a different transmittance from that of the other walls, therefore, in order to obtain a  overall thermal equilibrium, we opt for a shape  parallelepiped  with  walls  differently characterized according to the exposures.

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