Energy
Designing a zero-energy home
One of the questions some clients ask us when they come to seek advice is what designing a zero-energy home involves.
Who wouldn’t want to build a home that uses no energy?
Most people have heard of the concept of designing a zero-energy home, although its features may not be entirely clear, and there are many questions about its cost, regulations, or maintenance.
For this reason, today we have decided to address the topic in depth: to explain that designing a zero-energy home is somewhat more expensive but pays for itself quickly, that it is viable from a regulatory standpoint, and that its maintenance is minimal.
So, what does designing a zero-energy home involve? We will start from two key factors: reducing consumption and using renewable energy.
Reducing energy demand and using renewable energy are the two main strategies in designing a zero-energy home.
What is a zero-energy home and what features does it have?
A zero-energy home is a dwelling that does not depend on external supplies to function properly.
This means it has very low energy consumption, and the little energy it needs is produced within the building itself through renewable energy sources.
This is how we have structured this post: first, explaining how we reduce our home’s energy demand, and second, assessing the different ways of supplying renewable energy by harnessing the site’s natural resources.
In any case, we must bear in mind that all zero-energy home design strategies—such as orientation, natural ventilation, high levels of insulation, or energy generation through the use of solar or photovoltaic panels—will always depend on the project being built and its location, since on each plot it will be more or less cost-effective to apply one strategy or another.
Reducing energy consumption
Reducing a home’s energy consumption is the first step towards achieving a zero-energy home design. To do so, there are a series of architectural features that, when used correctly, can contribute significantly to energy savings.
Solar radiation harvesting
Solar gain is one of the main features of a home—not only a net-zero home, but any type of dwelling you want to build.
The sun is an inexhaustible source of energy within our reach that must be utilized to its full potential.
For this reason, the placement and size of windows are extremely important in designing a zero-energy home.
A south-facing orientation is ideal for harnessing solar radiation, especially in winter. In summer, natural light is also desirable, but filters will be needed to limit heat gain. Porches, pergolas, or simply extending the roof with eaves are a good solution to prevent direct sun exposure.
Thermal Insulation
Once solar radiation reaches the interior of the home, it is essential to prevent heat loss through the façades. Therefore, the thickness of the thermal insulation must be suited to local conditions.
In the Mediterranean climate, between 5 and 10 cm of insulation was traditionally used, but in the design of a zero-consumption house, we will increase the thickness to at least 12 or 15 cm, ideally reaching 20 cm depending on the energy demand of each wall.
It is also important to ensure the insulation is breathable regardless of its thickness, to avoid condensation caused by insufficient moisture permeability from the indoor environment.
On the other hand, a poor choice of windows can undermine all the work done on façade insulation. If we use high insulation but an inadequate window, we will create a temperature difference that will cause condensation at the joints.
When choosing glazing, it is important to assess its U-value—the ability to transfer heat from inside to outside or vice versa—which should be low and aligned with the U-value of the walls.
Finally, we must not forget that solar harvesting must be sufficient; therefore, we must orient the house properly toward the south and place sufficiently large openings.
Thermal Mass
In addition to insulation, the heat we capture can also be retained indoors through thermal mass. Materials such as concrete or stone have a great capacity to store heat, which they release after a few hours.
Therefore, if there are high-thermal-mass materials in areas that receive sun, at night they will release the heat accumulated during the day. In summer, it will be enough to avoid direct radiation so they do not absorb heat, or to ventilate at night to remove the heat they have stored.
Natural Ventilation
In designing a zero-energy home, natural ventilation must also be ensured.
In summer, ventilation through porches, courtyards, and windows will help dissipate the heat that builds up in the house.
In addition, good ventilation throughout the year will ensure air renewal, although this can also be done mechanically, as in the case of Passivhaus homes.
We should place windows on different façades to achieve cross-ventilation. If openings were limited to a single façade, air would not circulate properly and good air renewal would not occur, in addition to not dissipating heat correctly.
Other strategies
Although these are the main strategies for designing a zero-energy home, there are also other factors that can influence consumption.
On sloping plots, the building’s siting within the terrain itself can be of interest. This leaves part of the home semi-buried. It is advisable for this to be on the north façade, as this is where the most heat is lost. The siting would then help insulate the home even further from external conditions, both climatic and acoustic.
If the façade is the point of energy exchange with the outside, the home’s compactness is something to consider. The more compact the building, the less façade area it will have, and therefore the fewer energy losses we will have.
And although they reduce compactness, courtyards are a good solution in the Mediterranean climate. A courtyard lets in light and is protected from prevailing winds, so it offers somewhat more controlled outdoor conditions.
On the other hand, the presence of vegetation can improve the home’s performance. In terms of acoustics and wind protection, it is an improvement because it helps buffer air movement and noise.
In terms of sunlight, trees can be an obstacle that prevents direct solar radiation from reaching the façade and windows. For this reason, it is advisable to use deciduous trees, which will provide shade only in summer, when it is needed.
Finally, internal compartmentalisation can also change how a home is heated and cooled. It takes more energy to heat a large space than a small one. Ceiling height is also important because, depending on it, air convection currents may occur.
Once we have reduced the home’s energy consumption to a minimum, renewable sources will need to be implemented in the project. The best known are probably solar thermal or photovoltaic panels. However, there are also other methods that can be applied in designing a zero-energy home.
Using renewable energy
A renewable energy installation that serves the entire home is a considerable investment that pays for itself in an average of 5 to 10 years. There are installations such as solar thermal panels (for hot water) that pay for themselves in a very short time—around 5 years—while others, such as water collection and filtration, take longer—around 15 years.
Solar panels
Solar panels can be used to generate electricity or to heat water. Today there are three types of panels on the market:
Photovoltaic solar panels: these were the first to be installed and made people think it was possible not to depend on electricity companies. When radiation reaches the panels, electrons gain energy and move, creating an electric current. Although photovoltaics had their boom period, they are now being replaced by other, more efficient types of panels, as these are quite expensive.
Photovoltaic-thermal panels: instead of generating electricity directly, these panels work by heating the tubes they are made of. Inside these elements there is a heat-transfer fluid that is heated and then circulated through the home. These panels require more space, since they transport liquid rather than electricity, and they are used to produce hot water for bathrooms or heating.
Thermodynamic solar panels: these are the panels most commonly used today. Their advantages include higher efficiency and smaller size. While they are somewhat more expensive, they are also more efficient because they do not depend directly on the sun to capture energy. This type of panel is also capable of generating energy on rainy or cloudy days.
Geothermal energy
In short, geothermal energy is energy that comes from the earth. Geothermal systems are based on the fact that underground the temperature is higher, and this is used to heat a fluid or air that is introduced into the home at a stable temperature of around 20 degrees in both winter and summer.
On a private level, installing a pipe that goes down to great depth does not make much sense and takes a long time to pay back the investment. There are more coherent geothermal systems that work at shallow depth over a larger area, but at Slow Studio we usually recommend installing other energy systems that are more efficient and cost-effective.
Canadian well
The Canadian well, although less well known, is a system very similar to geothermal energy, harnessing heat from within the earth, but instead of being installed at depth, it is usually best installed in the semi-buried area of a sloping plot.
Its operation is based on circulating exterior air through the pipe, where the temperature is higher, to introduce it indoors, generally with the aim of renewing interior air at a comfortable ambient temperature.
This is a system we have installed in one of the homes we currently have underway: it is a plot with a house that must adapt to the slope, where a Canadian well pipe is installed between the earth retaining structure and the house below the slope.
It is a very cost-effective and extremely efficient system, as it allows us to renew the home’s indoor air without it cooling down, as happens in most homes when we ventilate directly through windows.
At Slow Studio we work with efficient, environmentally friendly homes. You can consult us with any questions, and we will be happy to assist you with no obligation.