Up to now, energy-conscious building has focused on reducing energy consumption in winter. Thanks to sufficiently thick insulation layers for thermal insulation, builders and experts now have this aspect well under control. Now it is time to go one step further and consider protection against heat as an important aspect of energy consumption.
People's expectations of comfort are rising. Living comfort means not only warm temperatures in winter but also pleasantly cool ones in summer. Currently, we save heating energy in the winter, but energy consumption has increased significantly in the summer due to more air conditioning.
In fact, Italy already uses more energy in the summer than in the winter. The power supply failures of recent years have highlighted the peak of the problem and brought the issue of summer overheating into focus. Here, a professional discussion on the topic is indispensable. Experts, planners, builders and construction companies are called upon to pay more attention to heat protection in order to achieve energy savings in the summer as well.
Need for education and information!
First and foremost, there is a need for education, because many people believe that good thermal insulation automatically results in stuffy air in the summer and overheating of the living environment. Studies prove the opposite.
In addition, on the subject of insulation, we think first and foremost about the winter. However, good thermal insulation alone does not automatically provide protection against summer heat!
It is essential that appropriate measures are provided for during the design and construction phase.
Climate change and energy consumption
The guidelines for climate houses so far only take into account the energy consumption for heating, but not for cooling, for the calculations. However, practice shows that we have more and more demand for energy in the summer, because
- Expectations for air-conditioned spaces are rising
- the climate will change dramatically and summers will become warmer and warmer.
Already in 2001, out of 100 families in Italy, 11 owned an air conditioner, which is an average of 11% (ISTAT)
The diagram points out two aspects in particular:
- a general increase in energy consumption
- an increase in energy consumption in the summer compared to the winter months.
Peak values arouse the need for action
Already in 2003, consumption peaks were higher in summer than in winter. We remember the blackout of electricity in the whole territory of the country. The reason for this consumption record is the increased installation of air conditioning systems.
The hottest month for 100 years in Bolzano was June 2003 (Hydrographic Office).
The maximum daytime temperature in Bolzano in June 2003 was always above 30°C, d.h. Between 30-40°C. These temperatures are far outside the range that is comfortable for humans, which is a maximum of 27°C.
Interestingly, the minimum temperatures were always between 17-21°C. D.h. at night, despite the daytime peaks, it was cool and temperatures were outside the range that the human organism finds comfortable.
The goal is therefore to find construction methods or measures that protect a house from elevated daytime temperatures and cool it with the help of the night temperature.
The construction history proves different examples z.B.:
- the Trulli in Apulia
- Church buildings
- Ancient stone-walled buildings
As a negative example, however, the booming glass construction method should be mentioned, as it u.a. can be seen in larger office buildings. Here summer overheating can be a serious problem.
Important measures for a cool living climate
What measures are important in construction to achieve a house with balanced indoor temperatures?? In essence, there are four points:
- Shading and shielding of solar radiation: Sun protection must be planned for all glazed surfaces.
- Thermal inertia: The remaining surfaces of the building envelope, which are not glazed, must have a certain inertia for thermal transmittance (phase shift).
- Night cooling: it must be possible to cool the building during the night with cool outside air.
- Cold retaining surfaces: Inside the house, many cold (or. technically correct: heat) storing surfaces must be available. They slow down temperature fluctuations and slow down rapid warming. The effect works according to the same principle as ice bags in the cool box, for example.
To point 1: Shading
In summer the sun has an intensity of approx. 1000 Watt/m². With standard thermal insulation glazing, this high heat output can enter the interior of the house almost unhindered through window surfaces, thus overheating is unavoidable. There are special glasses, which soften the solar radiation, but through these glasses the useful heat input is lost in winter.
The best way is therefore the shading of the glass surfaces. Shading elements should be placed on the outside if possible, because placed on the inside they lose their effect. (z.B. Roller blinds, awnings, Venetian blinds or projections such as balconies, etc.)
The shielding of solar radiation is particularly important in the roof area, where the sun hits the glass surface perpendicularly and can thus reach the interior almost unhindered to its full extent.
To point 2: Thermal inertia
Walls and roof surfaces which are not made of glass do not need to be shaded. However, these surfaces must be designed in such a way that they can absorb solar radiation for at least one day. This property is called thermal inertia.
Examples: To illustrate the effect of more or less inert materials, imagine the sun shining on a thin metal sheet. Within only a few seconds there will be a rise in temperature on the back of the panel. On the other hand, for a gypsum board of 1 cm thickness, it takes 10 minutes for heat to pass through. For a 40 cm thick wall made of perforated bricks it takes 15 hours. A masonry of stone with 60 cm thickness comes to 36 hours of heat inertia.
D.h. a common masonry has enough thermal inertia to last a sunny day. It is assumed that the sun does not shine on the same surface for more than 10 hours during the day.
As soon as the inert material gives off heat after 10-15 hours, the outside temperature has already dropped and the heat input is compensated for by the coolness at night.
Thermal inertia in lightweight construction: Lightweight construction refers to building methods made of wood, plaster, and other non-solid building structures. In this case, there is naturally a lower thermal inertia, which must be compensated for by the use of appropriate insulating materials in order to ensure at least 10 hours of phase shift at the end despite the low weight.
Particularly suitable are insulating materials with a high density, such as e.B. Wood fiber insulation boards. They have a bulk density of about 150 kg/m³ compared to light insulation materials such as z.B. glass wool or plastics with ca. 20 kg/m³. D.h. on the roof can z.B. already with 14 cm thick wood fiber boards a thermal inertia of 10 hours can be achieved. Whereas with light insulating materials 30 cm would be necessary for this purpose.
Lightweight insulation materials and low thermal inertia lead to sog. barrack climate: when the sun is shining, the building overheats quickly; as soon as the sun is gone, the building cools down immediately. Travelers know this phenomenon z.B. from the camper or caravan.
Heavy insulating materials with a high density increase thermal inertia.
Lightweight insulation materials lead to the so-called. barrack climate.
To point 3: Night cooling
Even if we can prevent the sun from getting inside by shading, heating can still occur in the house. The reason for this are the so called. internal heat sources, z.B.:
- the refrigerator, which gives off heat day and night
- Stove, oven, household appliances, computers and other electrical appliances, etc.
- Lighting
Heat accumulated during the day from internal heat sources must be cooled by nighttime ventilation. This can be done manually by opening the windows at night, or automatically by means of fans of a ventilation system. In principle, ventilation should only be used when it is cooler outside than inside. The best time to ventilate is between midnight and 6 a.m.
To point 4: Cold storing surfaces
An illustrative example of a surface that stores cold is the cotto floor. It gives the feeling of coolness in summer. Heavy materials can store more cold than light building materials, such as z.B. a carpet. In traditionally built houses of masonry and plaster, this circumstance is already given by the heavy material choice of the construction. In lightweight construction, on the other hand, the design of the internal surfaces plays an important role in cooling the house. Here, for covering the ceilings and walls, the heaviest possible building materials should be used, such as plaster, plasterboard, tiles, clay panels, etc. be used. The more it is possible to realize such surfaces of heavy building materials, the longer into the day the coolness stored at night will last.
It is especially important to install heavy interior surfaces in rooms that are most exposed to the sun. In general, the rooms located in the west are particularly affected by this, because there the evening sun can shine particularly deep into the interior.
Views and alternatives
Geothermal energy – at the bottom of reality
An interesting method of energy saving, which works all year round, is based on geothermal energy. It makes use of the temperature of the earth. In contrast to the sun, which is most available when we need it least for heating (summer), geothermal energy is available to us in sufficient quantities all year round. Therefore, geothermal energy z.B. very good for cooling our houses in summer.
Even with a ventilation system that draws in air through a pipe installed underground, these factors can be targeted. It preheats the air in winter and cools it in summer before it enters the house.
The tip
The use of geothermal energy makes it possible to reduce the amount of energy required for both heating and cooling.
Future dreams: solar technology for cooling
If you look at the curve of solar intensity over the course of a year, it's easy to see that the sun gives off the least amount of heat when it's needed the most – in the winter, that is – and is most abundant when we can use it the least for heating – in the summer.
Ideal would be a technology that allows to use the solar energy for cooling… Do not laugh, this system has already been invented and is the subject of various studies, but not yet sufficiently tested in practice.