Energy
What is the consumption of a passive house?
Who wouldn’t want a home where you don’t pay heating, water, or electricity bills?
Whether due to ecological conscience or the simple fact of saving money, the truth is that the price of energy and water supplies in Spain has not stopped rising in recent years. In fact, at certain times the increase has been so sharp that the Government has had to approve direct aid to provide relief for families. This reality forces us to reflect on what we consume, how much we consume, and what implications this has for both our economy and the planet.
In this context, energy autonomy becomes a resilience strategy. Today, we have the knowledge and technology necessary to build efficient, nearly zero-energy homes, and the myth that a passive house is more expensive than a conventional one is increasingly being debunked. In our studio, we have managed to design and build passive houses that cost the same as a traditional home, but generate their own energy and drastically reduce dependence on utility companies.
So, how much does a passive house consume? In general, we are talking about annual consumption reductions of around 90% compared to a conventional home, and we expect that in a few years, thanks to the development of battery storage systems, we will be able to achieve 100% savings on energy consumed.
What is a passive house
Before analyzing how much a passive house consumes, it is worth remembering what this type of housing actually consists of. In general, a passive house is one that manages to reduce energy consumption by at least 80% to 90% compared to a conventional construction, thanks to bioclimatic design and passive strategies.
These homes make the most of natural resources. In winter, the sun heats the interior spaces through south-facing windows; this heat is stored in the construction materials and retained by insulation that is superior to the standard, without discontinuities. During the summer, the sun is blocked with porches, pergolas, or solar filters, and cross-ventilation is facilitated through courtyards and strategic openings.
Furthermore, if this architecture is combined with a small energy contribution—preferably renewable—a nearly zero-consumption passive house is achieved, with thermal comfort in any season of the year. Likewise, these homes can include rainwater harvesting and greywater reuse systems.
Regarding certification, the Passivhaus seal establishes specific criteria to guarantee such energy performance: the heating and cooling demand must not exceed 15 kWh/m² per year, or alternatively, the maximum thermal load must not exceed 10 W/m². Additionally, the total primary energy demand (including heating, hot water, and lighting) must not exceed 60 kWh/m² per year.
What is the consumption of a passive house
Before going into figures, it is useful to differentiate between two key concepts:
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Operational consumption: this is the energy and resources that a building uses during its useful life, such as electricity for lighting, climate control, hot water, or appliances. In a passive house, this consumption can be reduced by up to 90% compared to a conventional home. These are known as NZEB (Nearly Zero Energy Buildings).
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Embedded consumption: this is the energy that has been needed to manufacture, transport, and assemble all the building materials. Although it is not always taken into account, it is key to long-term sustainability, as a very efficient house in use can still have a high impact if its construction required a lot of energy and non-renewable materials. These are known as NZIB (Nearly Zero Impact Buildings).
In this article, we are going to focus mainly on operational consumption, as it is the one that has the greatest impact on bills and the energy autonomy of a home.
In Spain, a single-family home consumes an average of 15,500 kWh per year, of which approximately 65% is used for climate control (heating and cooling). The other 35% corresponds to the use of appliances, water heating, cooking, and lighting. This means that climate control is, by far, the largest energy expense of a home, and it is precisely what a passive house can drastically reduce thanks to bioclimatic design.
Regarding water consumption, it is estimated that one person uses 171 liters per day. If we multiply this by 365 days and by a household of 4 people, we obtain a total of 249,660 liters per year. This is another aspect that can also be optimized with passive strategies and reuse systems.
The goal of a passive home is to minimize this operational consumption as much as possible so that it can be covered almost entirely by renewable sources such as solar or wind energy, combined with an efficient use of water and resources.
Climate control consumption
Climate control consumption is, without a doubt, the item that is reduced the most when we talk about a passive house. The main objective of this type of housing is to minimize the need to use active heating and cooling systems as much as possible, opting for a passive architectural design that makes the most of available natural resources to maintain a comfortable interior temperature throughout the year.
Passive architectural design
- Greater thermal insulation: In passive houses, thermal insulation is considerably thicker and more continuous than in a conventional home. This means that the walls, ceilings, and floors are designed to prevent any unwanted thermal loss or gain. Thus, in winter, the heat generated inside the home is retained, and in summer, external heat is prevented from penetrating the interior spaces, keeping the temperature stable without the need for mechanical systems. This insulation is the first barrier against excessive energy consumption for climate control.
- Strategic solar orientation: The correct orientation of the home is fundamental. The house is oriented mostly towards the south (in the northern hemisphere) to capture maximum solar radiation during the cold months, which is stored by the thermal materials of the construction. In summer, elements such as porches, pergolas, or solar filters are used to block direct radiation and avoid overheating. In this way, the home takes advantage of the sun’s natural energy to heat itself and protects itself from heat when necessary.
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Natural cross-ventilation: To maintain a pleasant temperature during the warm months, the passive house is designed with strategically placed openings that allow for cross-ventilation. These natural air currents cool the interior spaces and eliminate accumulated heat without requiring mechanical systems. Additionally, controlled ventilation, with heat recovery systems, ensures that the air entering is clean and at a controlled temperature, without significant energy losses.
Thanks to these passive architecture strategies, energy consumption for climate control can be reduced by between 65% and 90% compared to a conventional home, reaching zero in many cases for a good part of the year, requiring only a specific contribution of heat during the coldest week of winter.
Active climate control systems
Although a passive house is designed to function mostly without active systems, at specific times of the year—such as the coldest days in winter or the warmest in summer—it may be necessary to have a support system to ensure the thermal comfort of its inhabitants.
However, these active systems are avoided or minimized as much as possible, as they contradict the philosophy of the passive house. When they are essential, they must meet very strict efficiency criteria and preferably be powered by renewable energies to maintain the sustainability of the home.
The most common options for these active climate control systems in a passive house are:
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Low-emissivity radiators: These radiators work with water at much lower temperatures than conventional ones (around 35°C instead of 60°C), which implies much lower energy consumption. They are ideal for complementing passive climate control, providing heat when necessary without large consumption peaks.
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Biomass heating: Although biomass involves a combustion process, it is considered a carbon-neutral energy source, as the CO₂ emitted during its use is approximately equal to what the wood absorbed during its growth. Biomass heating can be a sustainable option to cover specific heating needs, especially if residual wood from responsible forest management is used.
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Ceiling fans: Although fans are active systems, their energy consumption is very low compared to other climate control equipment. Used together with cross-ventilation, ceiling fans improve air circulation and help dissipate accumulated heat, increasing the thermal sensation of freshness in summer without the need to resort to air conditioning.
Electricity consumption
We start from the basis that a home, excluding climate control consumption, needs around 5,000 kWh per year. Although it is possible to reduce this figure through the use of efficient appliances, correctly turning off electronic devices, and making the most of natural light, we will always need a minimum of energy for daily activities.
To approach the question of how much a passive house consumes, it is important to consider not only the reduction in consumption but also the options for generating that energy sustainably. At Slow Studio, we propose two widespread systems for producing energy in a renewable way: wind and solar energy.
Wind turbines
Wind turbines work similarly to large wind mills, but on a domestic scale. They take advantage of kinetic energy—the energy of movement—to generate electricity through the rotation of a turbine.
Although it is not usually the first choice for generating electricity in a passive house, a single turbine, depending on the model, can power a medium-sized home. The profitability of this installation depends largely on the wind in the area, and the return on investment can take between 8 and 10 years.
Photovoltaic panels
Photovoltaic panels are, on the other hand, the most widespread option at the domestic level for generating electricity. The solar radiation that hits these panels causes the movement of electrons inside them, thus generating electricity.
It is important not to confuse them with solar thermal panels, which are used solely for heating water without producing electricity. The latter can be complementary, as they allow for increasing the water temperature for domestic use without the need for electricity, which represents additional energy savings.
Photovoltaic panels are generally more profitable than wind turbines, and can be amortized in approximately 5 years, with a useful life that usually exceeds 25 years.
Sun tax
In 2015, the Spanish government approved a regulation that forced homes with photovoltaic panel installations that fed energy into the electrical grid to pay several additional taxes, a levy popularly known as the “Sun Tax.” This measure made domestic electricity production less profitable and hindered the promotion of energy self-consumption.
The law, defended as a “solidarity toll,” forced those who had solar panels connected to the grid to pay not only for the energy they consumed from the electricity company but also an additional tax for the energy they gave for free to the grid. This generated a contradictory situation in which, despite producing clean electricity, the user had to pay extra costs, slowing down the expansion of renewable energies at the domestic level.
However, this tax only affected installations that fed energy into the general grid. Homes with battery storage systems, which allowed for storing the energy generated for later use without feeding it into the grid, were exempt from this levy.
Over time, social pressure, European Union objectives, and the need to promote renewable energies led to this law finally being repealed in 2020. Currently, Spain has a much more favorable regulatory framework for self-consumption, in line with European directives.
Furthermore, thanks to recovery funds and aid from the European Next Generation EU program, there are incentives to install renewable energy systems, especially photovoltaic panels, and domestic batteries for storage. This makes it easier for more and more homes to generate and consume their own renewable electricity, improving energy autonomy and reducing costs.
Therefore, today, the path towards a passive house with practically zero electricity consumption is more accessible and viable than ever, in a context that favors sustainability and efficiency.
Energy consumption for water heating (DHW) is a fundamental part to consider when we evaluate how much a passive house consumes. Although these homes stand out for their efficiency in climate control and electricity, hot water remains an essential resource in daily life.
In a conventional home, DHW can represent approximately between 15% and 20% of the total energy consumption of the household. Therefore, in a passive house, it is crucial to optimize this section to keep energy consumption as low as possible and make the most of renewable sources.
To minimize the energy impact of DHW, it is most recommended to use solar thermal heaters or biomass boilers, systems that take advantage of natural resources to generate hot water efficiently and sustainably. Solar thermal heaters capture energy from the sun to heat water directly, significantly reducing dependence on electrical sources or fossil fuels. For their part, biomass boilers use renewable organic materials, such as wood pellets, which release heat when burned with a very low net balance of CO₂ emissions, making them an environmentally friendly option suitable for passive homes seeking to minimize their energy footprint.
In addition, these DHW production systems are usually integrated with active climate control systems, which often use hot water for heating or cold water for cooling, thus achieving a joint use of resources and greater energy efficiency. Other technological options such as aerothermal and geothermal energy should also be noted, which take advantage of energy from the air or the subsoil, respectively, to generate domestic hot water with very low energy consumption and great reliability throughout the year.
Water consumption
When we analyze the consumption of a passive house, water is a key aspect to consider. Achieving practically zero consumption is more complex than with other resources, although it is not impossible. In advanced passive homes, supply can be achieved exclusively from rainwater harvesting and reuse, provided that consumption is significantly reduced and efficient collection and storage systems are in place.
Reduction of water consumption
In a household of 4 people, the average water consumption is almost 250,000 liters per year, which makes it unfeasible to depend solely on rainwater without reducing consumption.
Therefore, it is essential to apply classic saving measures, such as using efficient dishwashers and washing machines that consume little water and preferring short showers instead of baths.
Another notable measure is the installation of a dry toilet, which does not use water to evacuate waste. Its operation is based on gravity and a composting tank, which can save dozens of liters of water per day. The design and use are very similar to a conventional toilet, but without water consumption.
Finally, we must mention the reuse of greywater, that is, water used in sinks, showers, or washing machines that contains soap and detergents. Although it is not suitable for direct consumption, this water can be treated and used to irrigate gardens or orchards. Its filtering can be done naturally through phytodepuration systems, where plants such as reeds absorb contaminating chemical substances. Thus, we reduce the use of potable water for exterior maintenance.
Rainwater harvesting
The first step to take advantage of rainwater will be to have enough roof surface to collect and store all the water that falls on it. This has no more secret than ensuring that the water will end up in the gutters that we will place around the roof.
The second thing we must take into account is that we will need to have tanks capable of storing the water we collect. They are usually located in the garden and are hermetically sealed to prevent unwanted organisms from entering.
Before use, rainwater must be properly treated to guarantee its potability and safety. There are different methods for this, from ultraviolet filters that eliminate bacteria and toxic particles, to filtration and purification systems that ensure the water is suitable for consumption, even of better quality than that of the conventional supply.
The consumption of a passive house is the result of a careful combination of design, technology, and respect for the environment. It is not just about reducing the energy bill, but about rethinking the way we inhabit and manage resources in our home. By opting for superior thermal insulation, proper solar orientation, and natural ventilation, the need for active climate control is almost completely minimized. This represents a profound transformation in the way we understand housing, where comfort is achieved with less energy expenditure and less environmental impact.
The integration of renewable energy generation systems, such as photovoltaic panels or domestic wind turbines, and the implementation of solutions for rainwater harvesting and greywater reuse, complete a sustainable and efficient home model. Although achieving zero consumption is a challenge that requires investment and favorable conditions, the trend is clear: passive housing is no longer an inaccessible or exclusive concept, but an increasingly close and necessary reality.
This approach not only helps to reduce dependence on traditional grids and increasing energy and water prices, but also contributes to resilience in the face of the climatic and economic changes we face. Therefore, understanding and valuing the consumption of a passive house is taking a step towards a more responsible, conscious way of life aligned with the principles of sustainability and long-term well-being.