Design Process
Is it possible to construct zero-energy residential buildings?
Zero-energy residential buildings: What are they?
Starting from the premise that a zero-consumption house is a home that does not depend on external supplies for its proper functioning, we could consider that zero-energy residential buildings are those that meet this same characteristic both at the individual unit level and in a global calculation.
This implies that the building must have very low energy consumption and that the little energy it requires, both in the construction process and in its regular operation, must come from renewable energy sources.
To meet the energy demand of all users in zero-energy residential buildings, strategies for energy utilization and storage must be proposed, knowing how to make the most of the local resources and natural sources while promoting a lifestyle with minimal energy demand.
We must take into account that any design strategy for zero-energy residential buildings, such as orientation, natural ventilation, high insulation, or energy generation through the use of solar or photovoltaic panels, will always depend on the specific project and its location, as each site has unique characteristics that make one strategy or another more or less cost-effective.
Passive strategies for zero-energy residential buildings
Let us begin by discussing the passive strategies that can be applied, if the terrain permits, to any zero-energy residential building project we may consider undertaking.
By following these recommendations, we will certainly ensure the viability and future of zero-energy residential buildings, making them a standard practice that promotes sustainable and environmentally friendly architecture.
Reducing energy consumption
Firstly, it is essential to realize that the first step toward achieving the proper functioning of zero-energy residential buildings starts with the reduction of energy consumption by both the users and the building itself.
We must make the inhabitants of these properties aware that a lifestyle based on maximizing natural resources and reducing energy demand will be favorable not only for their finances but also for the sustainability and future of the planet.
Reducing a home’s energy consumption is the first step toward achieving a zero-consumption house design. To this end, there is a whole series of architectural characteristics and strategies that, when used correctly, can contribute significantly to energy savings.
Solar radiation harvesting
Solar radiation is one of the greatest renewable energy sources currently available and one of the most profitable in architecture, as at least one of the facades will always receive solar irradiation that can be favorably utilized to generate energy inside the building.
The sun is an inexhaustible source of energy within our reach that must be utilized to its full potential.
For zero-energy residential buildings to make the most of solar radiation, we must first work on the control and dimensions of the facade openings.
The size of the windows is extremely important for the design of zero-energy residential buildings.
Generally, a southern orientation is best for taking advantage of solar radiation, especially in winter, although if we work well on the facade and the building’s compactness, we can capture and store energy in any situation.
In summer, natural light is also desirable, but filters must be used to limit heat gain.
Porches, pergolas, or simply extending the roof with eaves are good solutions to avoid direct sun exposure.
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 Insulation
Although it may seem obvious, for any zero-energy residential building project, we must ensure good insulation to avoid losing all the energy captured from solar radiation through the facades.
Just as they capture heat, facades can lose it if they are not properly treated and have points without insulation.
However, one must be strict regarding its thickness, as the appropriate thickness will vary according to the local climatic 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.
Another aspect to consider is that the insulation we install should be breathable, regardless of its thickness. By choosing breathable insulation—and preferably of natural origin—we avoid condensation caused by a lack of moisture transpiration in the interior environment.
On the other hand, we cannot forget a crucial aspect. Windows are the elements that ensure the closure and airtightness of the facade at its points of opening to the exterior.
Therefore, it is vital to choose high-quality windows. A poor choice of windows can undermine all the work done on the facade insulation.
If we use high insulation but an insufficient window, we will create a temperature difference that will cause condensation at the joints.
When choosing glass, it is important to evaluate its transmittance—the ability to transfer heat from the inside to the outside or vice versa—which must be low and in correlation with the transmittance of the walls.
Thermal Mass
The aspect of thermal inertia relates to a building’s ability to retain the heat captured in its interior.
Materials such as concrete or stone have a high capacity to store heat, which they release progressively after a few hours.
For this reason, it is advisable to place these materials in locations that receive direct solar radiation. Thus, during the day (hours of irradiation), the heat penetrates the mass of the material and is released into the interior during the night, when the exterior environment is cooler.
In summer, it will be sufficient to avoid direct radiation through solar filters or vegetation so that the surface in question does not receive radiation, in addition to ensuring good ventilation.
Natural Ventilation
As introduced in the previous section, guaranteeing ventilation in zero-energy residential buildings is vital for their proper functioning and, most importantly, for ensuring the health of their inhabitants by renewing interior oxygen.
But how can this be made compatible with airtightness and insulation?
In summer, it is easier. We can generate ventilation through porches, courtyards, and windows that ensure air renewal while also serving to dissipate the heat that accumulates in each home.
In winter, the issue becomes more complex because the exterior environment can be very cold, and as soon as we open windows or any opening in the wall, we lose the heat accumulated inside.
For this, there are systems that guarantee mechanical air renewal, helping us comply with the air changes required by regulations and taking air from the outside that is pre-heated before being introduced indoors.
A basic strategy for generating air currents is to place windows on opposite facades to achieve cross-ventilation. If openings were limited to a single facade, the air would not circulate as it should and proper air renewal would not occur, nor would heat be dissipated correctly.
Other strategies
Finally, there are other strategies for the design of zero-energy residential buildings that can help achieve their functionality and viability.
1. Building placement:
This involves taking advantage of the morphology of the land or site where the project will be located to semi-bury part of the built volume, achieving natural insulation—the subsoil remains at a constant temperature year-round—as well as isolating it from unfavorable exterior climatic and acoustic conditions.
As a brief side note, it is recommended that the buried or semi-buried facade be the north-facing one, as this is where the most heat is typically lost.
2. Compactness:
The compactness of zero-energy residential buildings is a determining factor, especially if the facade is the main point of energy exchange with the exterior.
The more compact the construction, the less facade area it will have, and therefore, the fewer energy losses we will experience.
And although they reduce compactness, the presence of courtyards is a good solution in the Mediterranean climate. Interior courtyards allow light and ventilation into the homes while remaining protected from the area’s prevailing winds, thus generating climatic conditions similar to the outdoors but more controlled.
3. Vegetation:
When discussing zero-energy residential buildings, this point may be more difficult to control as we quickly increase in height, making the placement of vegetation on upper floors more complex—though not impossible.
The presence of vegetation can improve the home’s performance. At an acoustic and wind protection level, it represents an improvement because it helps isolate against air and noise.
Regarding sunlight, trees can act as an obstacle or filter for direct solar radiation on the facade and windows.
For this reason, it is convenient to use deciduous trees that will provide shade only in summer when it is necessary.
Today, there are systems for creating green roofs and slabs that can bring vegetation to the upper floors of zero-energy residential buildings.
Additionally, there are also means to hang vegetation or create green filters in front of the facade or windows.
4. Interior partitioning:
To conclude this section, interior partitioning can also modify the way a home is climate-controlled.
A greater energy effort is required to heat a large space compared to a small one.
The height of the rooms is also important because, depending on it, air convection currents could appear.
Renewable energies in zero-energy residential buildings
The use and installation of renewable energies in zero-energy residential buildings represents a significant upfront investment, but it will certainly pay for itself in an average of 5–10 years, depending on the installation.
In fact, installations such as solar panels (for hot water) pay for themselves in a very short time—about 5 years—while others, such as water collection and filtration, take longer—about 15 years.
Solar panels
Solar panels serve both to generate electricity and to heat water, depending on the type of panels we install in zero-energy residential buildings.
Currently, there are three types of panels on the market, although for multi-family housing, two are the most useful: thermal photovoltaic solar panels and thermodynamic panels.
– Photovoltaic solar panels:
These were the first to enter the market, and thanks to them, we began to consider the viability of constructing zero-energy residential buildings by not depending on electric utility companies.
Their operation is based on capturing solar radiation across the entire surface of the panel. These are charged with electrons that move upon receiving energy from the radiation, thus producing an electric current.
Although photovoltaics had their peak, they are now being replaced by other more efficient types of panels, as these are quite expensive.
– Thermal photovoltaic panels:
Instead of generating electricity directly, these panels work by heating the tubes that compose them.
Inside these elements is a heat-carrying liquid that is heated to subsequently circulate through the home.
To obtain good performance, these panels require a larger surface area and therefore occupy more space.
They are primarily intended for the production of hot water for bathrooms or heating.
– Thermodynamic solar panels:
Finally, thermodynamic solar panels are the ones most currently in use.
They stand out for offering greater efficiency and a smaller footprint.
Regarding the initial investment, it is true they are somewhat more expensive, but this is offset by their higher efficiency, as they do not depend directly on the sun to capture energy. In fact, these panels are capable of generating energy on rainy or cloudy days.
Geothermal energy
Geothermal energy is that which comes from the earth.
These systems take advantage of the constant temperature of the subsoil 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.
It is a strategy that takes some time to pay for itself, and at Slow Studio, we would not highly recommend it for zero-energy residential buildings, as its installation requires a pipe that goes to a great depth, necessitating a significant investment in construction and technical materials.
Canadian well
In contrast, the Canadian well is a quite affordable and functional option for zero-energy residential buildings.
It is a system very similar to geothermal energy as it also utilizes the constant heat and temperature of the subsoil, but in this case, its installation is usually optimal at a shallower depth.
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.
It is a very economical and efficient system as it allows us to renew the interior air of a home or building without it losing heat.
Viability of zero-energy residential buildings
In conclusion, at Slow Studio, we strongly believe in the viability and future of zero-energy residential buildings.
Achieving the comfort of all users in a zero-energy residential building is feasible if we design a building whose passive strategies for energy harvesting and storage are appropriate and which uses renewable systems and sources as an extra energy source.
The Passivhaus platform provides examples that can be easily consulted of real cases of zero-energy residential buildings worldwide.
For example, in Carquefou, France, there is a zero-energy residential building complex whose capacity of 45 homes and an annual expenditure of less than 15 kWh/m2 is surprising and can serve as a reference for designing zero-energy residential buildings without any fear.
By searching the Passivhaus platform, you can find more examples to consider.
For our part, as always, we remind you that you can contact us without any obligation to evaluate our zero-consumption construction, an area in which we are specialists.