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Low-energy house: Use solar energy efficiently
Low-energy house: Use solar energy efficiently

Video: Low-energy house: Use solar energy efficiently

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Video: Sunnyvale Passive House - Life With No Power Bills 2023, February

A low-energy house saves a lot of heating costs. Here you can find out what you should pay attention to when planning the building and what options there are for using solar energy efficiently.

A low-energy house is mainly characterized by optimal thermal insulation of the roof and the outer walls. Insulated windows and the exterior doors of the house also ensure that the heating can only leave the house very slowly.

Nowadays, a new building is almost always built using the low-energy method, so that the low-energy house has already been declared a standard in accordance with the requirements of the Energy Saving Ordinance (EnEV). However, older buildings can also become more energy-efficient through suitable conversion measures.

Sonnenstand während eines Jahres
Sonnenstand während eines Jahres

As the position of the sun changes over the course of the year, it is important to align the house to the south. Because with a large window front, solar energy can also be optimally used in winter.

Ideal floor plan: plan with the sun

In order to be able to optimally implement the principle of passive solar energy use, the orientation of the house should be such that it uses its building material for gentle solar energy production in winter and in the transitional periods without using additional energy.

When planning the building, it should be considered that living rooms are best oriented towards the south, and thus towards the sun, while adjoining rooms, entrances and stairs should occupy the north side of the house. To be able to use the sun as a free energy source, plan as many windows as possible with a large glass surface on the south side of the house. These serve as "sun traps" and provide free heat. In the adjoining rooms and thus on the north side of the house, small window sizes are preferred in order to keep the energy losses in a low-energy house as small as possible.

Additions in the north, such as a garage or a porch, are ideal as a climate buffer, towed roofs as a wind spoiler. It is best to ask an architect for advice. He often finds creative solutions if the development plan makes optimal implementation of a low-rise house difficult.

Windows as energy collectors

Windows achieve far higher energy gains than the outer walls, so they play a crucial role in passive solar energy use. The sun does not radiate heat, but sends solar energy to the earth in the form of light rays. If these light rays penetrate the window glass, only part of the rays are reflected. Only when the light radiation hits components, furniture or people is it converted into heat radiation. However, since heat has a different wavelength than light radiation, it can no longer pass through the window glass and therefore remains in the room.


Floor-to-ceiling glass - more perspective and light.

The incidence of light is also decisive for the energy gain. Depending on the direction of the compass, the amount of incident sunlight differs. Good to know: Even if a north window is never directly illuminated by the sun during the heating season, but only receives reflected, diffuse sunlight, you can still expect to gain heat. On the south side, however, you can count on the greatest energy gain, because there the sun shines directly into the house.

It is also a good idea to use components around the window to attract more sun rays. So the lintel, i.e. the wall piece above the window, should be kept close and the roller shutter box should be installed in the ceiling. The same applies to the parapet, the wall under the window. Here the window could also go down to the floor. Furthermore, wide window sills hold back the rays. In thick outer walls, it is advisable to bevel the reveals, the vertical part of the opening in the masonry, in such a way that oblique rays can be directed into the room. This is particularly worthwhile for small windows, so that the exposure is also better.


More rays of light flood into the house at sloping soffits. Light color increases reflection.

Glazing: Quality matters

Glazing with good thermal insulation is the be-all and end-all when choosing a window - you can recognize this by the lowest possible "U-value", the so-called heat transfer coefficient. Because the better the glazing, the larger the window area may be. While the simple panes from the past let the energy of 60 liters of heating oil outside per square meter, the insulating glass was able to halve this loss. Today's high-performance windows for extreme low-energy houses generate even more energy than they lose - except on the north side. However, the frames for these windows have to be complex.

Ventilate low-energy houses properly

Everyone knows that ventilation should be done regularly for health reasons. Leaky, older windows renew about six percent of the air in ten minutes. Tilted windows replace around 38 percent at the same time. However, shock ventilation is best: If you open the window completely, you get 100 percent fresh air in ten minutes. When ventilating, the thermostatic valve should be closed because it tries to maintain the set room air temperature. It may only be opened again after ventilation.

Another way to let fresh air into your home is with a ventilation system. This draws the right amount of used air through ducts into the open air, absorbs a large part of the heat and tempers the fresh supply air. The advantage: noise, pollen and dust stay outside. So if you combine ventilation and heating, you combine two systems in one and pay less overall. However, this form of dehumidification or ventilation of a low-energy house is controversial, because ventilation systems are often very costly to buy. They consume additional electrical energy during their operation and can cause high operating costs through maintenance and repair.

Regelmäßiges Lüften ist auch beim Niedrigenergiehaus wichtig
Regelmäßiges Lüften ist auch beim Niedrigenergiehaus wichtig

With short-term ventilation, the energy losses are lower than with tilt ventilation.

Photo: Gpoint Studio

Thermal protection without much effort

If you are not planning a new building and therefore have no influence on the orientation of the building, you can still increase the energy efficiency of your house. And with a temporary winter protection. The aim of this protection is to make the gains in solar energy achieved during the day greater than the losses at night. This means that heat-insulating components that are only used at night can be attached to the inside or outside of the house. It should be noted that internal components do not have to be weatherproof and stormproof, but they do not protect so well from too much sun. External elements, on the other hand, perform three tasks: heat, sun and weather protection. Whether sliding, folding, folding, rolling and pulling structures - there are various ways to avoid heat loss.

But there are also alternatives that both protect against too much sun and keep warmth in the house. A deciduous planting provides sun protection in summer, but lets the rays into the house in winter. A thick, thick curtain over the radiator or between it and the wall keeps the heat in the room better at night. A tip: If the curtain is close to the window sill or to the floor, the circulation of the warm room air between the window and the curtain can be avoided.

Energieverluste am Fenster
Energieverluste am Fenster

Energy losses at the window can be minimized with curtains and shutters. The data are based on a room temperature of 22 degrees Celsius and a window area of ​​35 percent.

As can be seen from the graphic, curtains in front of the heating without a windowsill cause a 40 percent increase in energy loss. With a window sill and short curtain, you save ten percent. A lowered roller shutter without a window sill saves 20 percent and a short curtain with a window sill and roller shutter saves you 30 percent.

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