Summer heat protection for buildings

Buildings protect users from cold, damp and heat. Summer heat protection is an issue that is becoming increasingly important in Germany due to climate change and the resulting longer periods of heat. If summer heat protection is inadequate, unpleasant heat can quickly develop inside the building during the warmer months of the year, which can affect the well-being and health of the occupants and users. Indoor temperatures above 25-27° C must therefore be avoided.

Heat protection measures therefore have a positive influence on the indoor climate. In contrast, buildings with insufficient thermal protection often have a greatly increased energy consumption for cooling. It is therefore important to pay attention to an ideal combination of solar protection, insulation, ventilation and choice of materials when planning a building in order to ensure a pleasant indoor climate and minimise energy consumption.

In this blog you will learn

Causes of overheating due to lack of thermal protection measures,
as well as measures to avoid overheating of buildings.
We list some regulations and standards that regulate summer thermal protection,
give examples of good summer heat protection and
an outlook on future developments including the presentation of some innovations in the field.

Causes of overheating due to lack of thermal protection measures:

Solar radiation onto or into the building, especially with large window areas.
Positioning of windows so that they let too much solar radiation into the building.
Inadequate or incorrect ventilation, so that warm air accumulates in the building and increases the room temperature.
Unfavourable orientation of the building
Insufficient storage capacity of building components
Excessive heat emission from electrical appliances

A combination of these factors can lead to particularly severe overheating. This has negative effects on the building users: in office buildings, the work performance of those present deteriorates; in residential buildings, the quality of life decreases and, due to overheated bedrooms, so do the regeneration phases.
In order to achieve cooling in spite of this, cooling technology must be used in conventional buildings, which leads to high energy costs. In the interest of a better energy balance and CO₂ reduction, natural and passive measures against overheating should therefore be used as much as possible and little system technology should be installed.

Graphic showing the effect of the position of window slats — Light-directing elements guide the incident light specifically into the room and reduce radiation and heat at the same time

Measures to avoid overheating of buildings:

To avoid overheating of buildings in summer, there are various strategies and technologies. Here are some possibilities:

Shading systems: The use of shutters, blinds or solar sails on windows and facades can reduce the amount of sunlight entering the building. This leads to reduced heat absorption through the building skin and helps to keep the inside of the building cooler. External solar shading is preferable here because it blocks the heat before it enters the building. Sun shading with daylight control is ideal: it allows natural light to be retained indoors and at the same time prevents overheating. This is achieved by combining sun shading and light control elements that direct incident light specifically into the room while reducing radiation and heat. This technology can reduce the energy demand for artificial lighting and air conditioning and improve the indoor climate.

Graph of solar input by compass direction, which shows that north-facing windows do receive solar radiation — North-facing windows also receive solar radiation input

Orientation and inclination of window areas: Careful planning of window positions can help to avoid overheating the building in summer. By orienting the windows to the north and by tilting the (roof) window surfaces at an angle that avoids direct solar radiation, the heat impact can be reduced. However, south-facing windows are not generally undesirable, as they are important in terms of energy in winter. This is where the demands of architects and building physicists diverge: while some want the largest possible window areas to illuminate the rooms, engineers would like to keep them as small as possible or place them on the north façade with regard to room overheating. The aim is therefore to achieve an optimised distribution, positioning and size of the windows. It should be noted, however, that north-facing windows also have a solar input, as can be seen in the following diagram:

Table showing the air exchange rate with different window positions - highest with cross-ventilation — Cross-ventilation enables a high air exchange in a relatively short time

Type of glazing (window coatings): Special window coatings can help prevent the building from overheating in summer. These coatings reduce solar radiation and still allow sufficient daylight into the room. The total transmittance, the so-called g-value of a thermal glazing is normally between 0.72 and 0.65. A g-value of 0.65 means that only 65% of the energy (transmission and heat emission) is let through by the glass. With solar control glazing, on the other hand, g-values as low as 0.20 are possible. While older solar control glasses were still brownish, today they are almost neutral in colour. The coating is usually applied by vapour deposition, e.g. with silver or chrome, and is thus wafer-thin.
Window ventilators: Window ventilators enable natural ventilation of the room. The ventilators can be controlled either manually or automatically and provide a continuous supply of fresh air. Night ventilation flaps enable controlled air circulation when the windows are closed. As they are equipped with special security features such as reinforced frames, lockable flaps and lockable handles, they are burglar-proof and can thus provide office buildings in particular with the cool night air.
Different types of room ventilation: Targeted room ventilation can help prevent the building from overheating in summer. For example, windows and doors can be opened on opposite sides of the building to create an increased air exchange through draught (cross-ventilation). It also makes sense to ventilate at night when the outside temperature is lower and to keep the windows closed during the day in summer. A high air exchange (exchange of air in one hour) takes place if the air exchange occurs even over several floors.

Construction method of the building components surrounding the room: Heat transfer can be reduced by appropriate construction of walls, roofs and floors. A solid wall construction, for example, helps the walls store heat or heat up less quickly. In addition, a phase shift takes place, i.e. the delayed transfer of temperature from the outer surface of a building component to its inner surface, which favours the indoor climate, especially in summer: The maximum outside temperatures only reach the inside of the wall with a time delay, i.e. only in the cool night hours and vice versa.
Passive cooling: Passive cooling systems use natural energy sources such as geothermal probes, aquathermy probes or ice storage to keep the building cool in summer. By maintaining a constant temperature of around 10-12° C all year round and reversing the function of the heat pump, these renewable sources can cool a building in summer - without any costs or CO₂ emissions when combined with electricity generation for the heat pump from a solar system. Ice storage tanks can also be used as a source of building cooling, allowing them to thaw and regenerate in summer. This type of cooling is best combined with surface heating or component activation.

Regulations and standards governing summer thermal protection in Germany:

The Building Energy Act (GEG) regulates summer thermal insulation and requires that certain requirements be met for new buildings and renovations.
DIN 4108-2 specifies the minimum requirements for thermal insulation and thus the rules for summer thermal insulation that must be observed in particular when planning and constructing buildings. Among other things, measures such as sun protection and ventilation are taken into account here.
The Federal Promotion for Efficient Buildings (BEG) promotes measures to improve summer thermal insulation.
Other standards and regulations include DIN EN 1737, DIN 5034, the Daylight Ordinance and various state-specific regulations.

Pueblo house made of clay with thick walls — The thick walls of the pueblo architecture ensure a time-delayed release of heat into the interior spaces

Examples from practice with good summer heat protection:

An example of a modern building in Germany with successfully implemented summer heat protection is the Oscar-von-Miller-Forum in Munich. A building-integrated photovoltaic system protects the south-facing, double and rear-ventilated glass façade from excessive heat build-up and prevents overheating in summer, while solar radiation is used for heating in winter. Photovolatic elements on the roof also serve as shading in summer, and the roof is also greened. Air conditioning is provided by concrete core activation and geothermal cooling. (http://thomasherzogarchitekten.de/wp-content/uploads/2017/04/DE-2010-OvMF.jpg).

Other examples include the Cube Berlin, a sustainable office building that has an innovative façade as well as an intelligent ventilation system. The building's green roof also helps to reduce the urban heat island effect (https://3xn.com/project/cube-berlin). The Elbphilharmonie in Hamburg also has an innovative summer heat protection system with its unique glass façade with curved panels that reflect sunlight and reduce solar heat gain. In addition, the ventilation system uses water from the Elbe River to cool the building. (https://transsolar.com/de/projects/concert-hall-elbphilharmonie).

It is also worth taking a look at the past: traditional buildings often provide very good summer heat protection, for example the Pueblo architecture in the southwest of the United States. These buildings are usually made of clay or other natural materials that provide thermal mass, and they have thick walls and small windows to keep the summer heat out. The buildings also often have overhanging flat roofs that provide shade. The typical white buildings in Greece also serve to protect from the sun by reflecting solar steels and thus heating up less.

Outlook and innovations:

The heat protection of buildings will play an increasingly important role in the future due to climate change and rising temperatures. This is because most buildings in Germany are not yet sufficiently prepared for hot summers and may experience major problems in the coming years.
Innovative technologies and materials help to improve heat protection in summer.

One promising development is so-called "smart materials" that can adapt their properties depending on the ambient temperature. These are materials that, due to their chemical or physical properties, change their structure or colour at higher temperatures and can thus reduce the amount of heat entering the building. An example of such a material is "thermochromic coatings", which change their colour at higher temperatures and thus have a higher degree of reflection. As a result, less heat radiation can enter the building and it remains cooler.
Phase-changing materials (PCMs) can also control heat build-up in buildings. These are latent heat storage materials that can store a high proportion of heat and cold energy over a long period of time and release it again without loss. When added to aerated concrete blocks, for example, PCMs can store excess heat energy during the day and release it at night.
A promising technology can also be found in so-called "active façade systems", which combine different methods. They can automatically adapt to the ambient temperature and thus improve summer heat protection. The systems consist of various elements, such as sunshade slats or flaps, which open or close depending on the temperature and thus regulate the heat input into the building.

In addition to these innovative technologies, we also expect an increased use of renewable energies in the area of building cooling. For example, heat pumps or cooling generators will be powered by renewable energies and thus make a sustainable contribution to summer heat protection.
Innovative technologies and materials, renewable energy sources as well as a return to traditional construction methods offer promising possibilities for reducing the heat input into buildings in the future as well as the the CO₂ emissions and thus creating a comfortable indoor climate.

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