Energy
What is aerothermal energy in a home
Today we explain in detail what a home with aerothermal energy is, how it works, and when it is worth installing this system.
Many clients come to the studio after comparing several construction companies that offer closed-price packages, selling homes in a catalog format. The construction company in question typically defines (without even having seen the land) the insulation system, finishing materials, and even the aerothermal climate control system, which sounds very modern and ecological.
At the firm, we consider this way of working to be an absolute lack of rigor. While it is true that aerothermal energy is an innovative system that works very well and can also be highly ecological or efficient—since it operates on electrical energy, we can connect it to a photovoltaic solar panel.
But is it suitable for all climates? Is it suitable for all budgets? Is it suitable for all lifestyles?
Not at all!
The operation of a passive house is highly complex. It is not simply a matter of adding technological devices to heat or cool it, as each location, climate, terrain, family, and lifestyle has very different requirements.
Building a house in Mallorca is not the same as building one in the Pyrenees. In fact, a passive house, if well designed and maximizing bioclimatic strategies, does not require any heating system.
Thus, in today’s article, we explain in detail what a home with aerothermal energy is, how it works, and when it will be cost-effective and coherent to install aerothermal energy and when it will not.
In fact, at the studio we have more than 30 passive house projects underway or completed, and in many cases, it is the efficiency calculations that lead us to install or not install aerothermal energy. Let us see why.
What is aerothermal energy
First, let us clarify three important concepts to understand how a home with aerothermal energy works.
These are the differences between capture system, energy generation system, and distribution system.
– The capture system consists of the solar panel we wish to install or the electrical energy coming from the grid to which we are connected.
– The energy generation system, connected to the capture system, is the subject of this article: aerothermal energy, which can serve both to generate hot water and hot/cold air. Another energy generation system could be, for example, a gas boiler.
– Finally, the distribution system consists of the devices/elements implemented to heat both the water and the dwelling itself. That is, how do I distribute this hot water that I have heated using aerothermal energy? The mechanisms are varied, ranging from the radiator we all know to radiant floor or wall heating, or even air distribution—mechanisms we will explain later.
Once this is clarified, we can state that aerothermal energy is an energy generation system that works by extracting the energy contained in the air, as its name indicates. It can provide both heating in winter and cooling in summer.
It is true that when we speak of aerothermal energy, the vast majority of manufacturers market it as an ecological system, since it is an electrically operated installation—meaning you can connect it to photovoltaic panels and it works—so we are talking about solar energy, therefore renewable.
However, this does not make it suitable for any dwelling in a generalized manner, nor does it imply that it is cost-effective to install in many cases. Below, we will evaluate the pros and cons of this model.
Elements of an aerothermal installation
The operation of an aerothermal installation consists of a unit located outside the dwelling where we find an essential heat pump and, in some cases, this pump is complemented by an inertia tank.
According to manufacturers, aerothermal energy produces more energy than it consumes, in a percentage that depends on the quality of the equipment and its energy rating, but which can reach up to 70% of energy extracted from the air compared to 30% of electrical input. One advantage of this is that the entire house can operate on electricity, meaning there is no need to contract gas or fuel supplies, as we generate hot water for bathrooms and heating through the electrical supply.
Heat pump
The main element of this installation consists of a heat pump that extracts the energy contained in the air, even at very low outdoor temperatures.
The surrounding air is continuously heated by solar radiation energy, and the pump uses a thermodynamic cycle that employs a refrigerant gas to extract it.
Inertia tank
The inertia tank is an active element that serves to accumulate domestic hot water, storing the energy produced to administer it as efficiently as possible.
As we have already indicated, the inertia tank will not be necessary in all cases; it will depend on the distribution system we use. If we are going to use, for example, a radiant floor heating system, we can save this tank, since the floor itself already functions as such, being a long circuit with a large volume of water.
Distribution systems for a home with aerothermal energy
One of the advantages of aerothermal energy compared to other energy generation systems is that we can connect it to a hot water generation system or to a hot/cold air system.
This means that a single machine generates hot water for bathrooms/kitchens and heating or hot/cold air.
Thus, we can connect it to an air or water heating distribution system. Let us examine the options in detail:
Water heating systems
Radiant floor or radiant wall
Broadly speaking, this is a heating system that uses one of the surfaces of a space as a heat emitter—whether floor, walls, or ceiling, with the floor being the most common. Given the surface area of the emitter, low temperatures are used, so in this respect aerothermal energy can be implemented.
Additionally, this distribution system also allows cooling in summer, bearing in mind that in certain climates it can condense. When it condenses, the device stops, as it has humidity detectors, which is a disadvantage.
It should be noted that in a passive house, we are normally interested in accumulating heat through materials with thermal inertia, which are materials that accumulate heat such as dense floors or walls. In the case of installing radiant floor heating, the floor loses all its density as it is perforated by hundreds of tubes and therefore loses its natural heat accumulation capacity and will depend solely on the supply of hot water.
This is a common question in many projects: sacrificing the natural thermal inertia of the floor, which would allow us to accumulate heat from the sun, to install a radiant floor system that is, after all, an active energy generation system.
This can be resolved by using radiant walls.
Low-emissivity radiators
As we have mentioned, aerothermal energy typically works at low temperatures, around 50°C. It is true that machines are already appearing on the market, from Nordic manufacturers, that raise temperatures to 60°C or 70°C.
Again, it is important to evaluate everything as a whole. How do I know if my house will need water at 50, 60, or 70°C? We do not know the answer; it is impossible to determine the energy demand of a dwelling until it is designed and located in a specific area with a temperature history of at least 10 or 20 years on which to base calculations and size thermal comfort installations, if these are necessary.
In any case, it should be noted that low-emissivity radiators, while much more expensive than conventional ones, are devices that work very efficiently with water at low temperatures, which allows us to use conventional aerothermal machines that heat water to low temperatures around 50°C.
These are small radiators that operate by convection and are forced with a small fan. The result is that they distribute heat in the dwelling much more evenly, eliminating cold zones.
Let us not forget that in terms of healthy indoor environment, convection heating moves air and can therefore raise and displace dust, which is unhealthy for our respiratory system, even if imperceptible.
Air heating/air conditioning systems
Air distribution
This is a heating device that basically consists of an air conditioner with a heat pump, a distribution system that few energy generation systems allow to be installed.
In terms of health, it should be noted that in terms of indoor environment it is not the most advisable, as, in the same way as the air conditioning we know, this type of heating also dries the environment excessively, reducing relative humidity excessively. Below 30%, this is unhealthy for the user, drying out the mucous membranes with the consequent reduction in defenses.
Building a house with aerothermal energy
Having developed this predominantly technical definition, let us focus on the real implications for the user when building their home with aerothermal energy.
In terms of permits, it is true that some municipalities facilitate the installation of aerothermal energy instead of an accumulator tank with a thermodynamic panel, since aerothermal energy is treated as a highly ecological system, a classification that does not always do it justice.
A home with aerothermal energy may be convenient or not depending on the capacity of this system to meet the energy demand of the future home—which we calculate in kW, per hour, per m2, and per year. The per-year factor responds to the fact that in summer cooling has one demand and in winter heating has another. From this figure come all the sizing calculations for radiators, gas/biomass/aerothermal boilers, to determine which is most suitable.
It is also true that a well-oriented and well-insulated house has a much lower energy demand, as good architecture is what provides improvements in energy demand. To give an idea, this demand we are talking about is the document from which the energy certification of our house is subsequently obtained (A, B, C, D…).
A positive characteristic of aerothermal energy is that it is the only element that works well in summer, because it provides cooling. When it is hottest and there is the most sun—remember it can operate with a photovoltaic panel—is when it generates the most cooling. Conversely, in winter, when we have the highest demand, is when it provides the least energy.
Furthermore, winter demand is higher because it is heating demand, considered high demand. Thus, the winter/summer demand graph does not work very well, as there is generally higher demand in winter.
There is the possibility of constructing a building where it is more cost-effective to install aerothermal energy, if we have a constant energy demand throughout the year, but this is not common in our climate.
Another aspect to consider is the existence of alternatives to aerothermal energy that may be more suitable depending on the project characteristics. Geothermal energy, for example, offers more stable performance throughout the year, as it takes advantage of the constant temperature of the subsoil, although its initial installation is more costly. Likewise, biomass systems can be an interesting option in areas with easy access to this resource, providing efficient and sustainable heating. On the other hand, solar thermal or wind energy is a complementary alternative that can reduce the demand for heating and domestic hot water.
How much does a house with aerothermal energy cost
Throughout this article, we have highlighted an important negative aspect in the construction of a house with aerothermal energy: the cost, given that it requires a series of installations that can be quite expensive. A clear example of this is the inertia tanks, which are necessary because aerothermal energy does not provide instantaneous hot water like a gas boiler, resulting in an additional cost compared to other traditional systems.
Furthermore, the heat emitters associated with this energy generation system also have a high price. Both radiant floor heating and low-emissivity radiators are costly components. As previously mentioned, radiant floor heating could allow dispensing with the installation of an accumulator; however, the option of using low-emissivity radiators involves adding these high costs.
The possibility of connecting aerothermal energy solely to an air distribution system is also not a recommended option. Heating spaces by air is one of the least efficient solutions, as air lacks thermal inertia, making it less effective. Additionally, it presents disadvantages in terms of health, due to ambient humidity, and is less comfortable, given that the human body responds better to radiant heat than to convective heat.
Consequently, we can conclude that the installation of aerothermal energy must be justified by high efficiency in energy demand for the increase in budget to be truly cost-effective.
A house must prioritize the natural use of solar heat, accumulating this heat through building elements such as walls or floors with high thermal inertia. Additionally, enclosures must be airtight and well insulated, with double or triple glazing windows, to prevent heat loss.
From here, if the energy demand analysis reveals that the solar heat input is not sufficient, we must evaluate which is the best option to provide heat actively. Is aerothermal energy the most suitable option? If the heat demand is low, perhaps a small electric radiator connected to the grid is sufficient to ensure comfort.
On many occasions, the investment in a passive house with aerothermal energy, together with its heat accumulation and distribution systems, is not recoverable if we compare the energy consumption over the useful life of the dwelling.
Aerothermal energy is an excellent system and can be highly efficient when complemented with a solar energy generation system. However, it is essential to evaluate each case individually, as there is no single solution applicable to all dwellings or all locations.
This is why, when a client arrives with a specification sheet provided by a construction company, indicating the model of aerothermal machine to be installed without considering the specific location of the dwelling, we are concerned about the lack of professionalism in the sector.
In conclusion, the choice of an appropriate climate control system, such as aerothermal energy, will depend on multiple factors, including the specific characteristics of the project, the location of the dwelling, and the specific energy needs. It is essential to conduct a detailed analysis to assess the viability and cost-effectiveness of each option, thus ensuring the best long-term solution, with the objective of minimizing the environmental impact of the dwelling and optimizing its energy efficiency over time.