High quality living powered by photovoltaics
The idea
It is usually once in a lifetime opportunity to build your own house. Therefore, one must carefully plan it. For me, the idea of sustainability was there already when I was a child in the form of a small wooden cottage somewhere in the woods. That was way before I was aware of climate change. Later, other aspects also become important, such as economics, quality of living and individual spatial needs and wishes. It is very difficult if not impossible for an average individual to combine all these aspects and lead all the legal procedures, therefore we hired an excellent architect who found the optimal solution for us.
The project
Despite the architect, the final decisions are the ones of the investor. The first decision is the location of the house. While living in urban areas has some obvious benefits, rural areas, especially the ones close to forests, provide some natural cooling during the summer and cleaner air. The second choice is the one of building materials. While foundations are almost mandatorily made of concrete, the house itself can be made of wood, an abundant sustainable material. In addition to wood being the material for the structural frame of the house, it can also be used as an insulation material in the form of different densities of wood wool. Thus, the building itself becomes a long-term carbon storage.
Energy management
The house should provide stable and comfortable living conditions, notably temperature and humidity, throughout the year. Several factors allow us to achieve this stability using the least amount of additional energy. The house itself passively provides thermal capacity protected from the outside conditions by air-tight insulating layers. Large windows on the south walls provide additional passive heating by the sun, while shades are used in the summer to passively keep the house cool. During the winter months, the house must still be actively heated, which is efficiently done by a heat pump and floor heating. We also use a fireplace for occasional additional heating during the transition period and to create a good atmosphere in the winter period. To provide fresh air, central ventilation system is used with heat and moisture recovery. The energy that is used in the house is provided by a 7 kW photovoltaic power plant installed on the roof.
Energy balance
Careful planning of the house as a whole system results in significantly reduced energy demand. Additional heating of the house is only required for four winter months and amounts to 1.1 MWh of electricity. That is the same amount as energy consumed for water heating. The consumption of the ventilation system amounts to 0.3 MWh and is negligible compared to the 7 MWh of energy saved by not ventilating the house by opening the windows. General electricity consumption of 3.3 MWh is in the range of average Slovenian household consumption. This gives a total sum of electricity consumption of 5.7 MW. In the same year, the 7 kW power plant on the roof of the house produced 8.5 MWh of electricity, thus making our house a net positive house with a surplus electricity of 2.8 MWh.
It must be noted, that this is a yearly net outcome and that the house still needs the electrical grid. However, looking at the net monthly balance, we can see that the house is net negative for four winter months only and that during the other eight months, which are net positive, the house could be off-grid by using a battery with a capacity of a few tens of kilowatt-hours.
Comfort of living
While a sustainable house minimizes its impact on the environment, it, by the nature of its design, also maximizes the comfort inside the house. Relatively high heat capacitance with respect to the insulation thickness by itself results in thermal stability. Wooden insulation also acts as a moisture reservoir and provides stable air humidity. Both the temperature and the humidity are further stabilized by ventilation with heat and humidity recovery.
This results in excellent living comfort at temperatures between 21 and 23°C in the winter and between 23 and 25°C in the summer, with constant air humidity between 50 and 60%. Simultaneously all the air in the house is exchanged in 4 to 6 hours, keeping it fresh throughout the day.
Conclusion
After living in the house for several years, we can only recommend a sustainable approach to housing. Not only is the quality of living on a very high level with low environmental impact but the cost of living is reduced to almost zero. Of course, the investment is slightly higher, but most, if not all of it, can be recovered by government subsidies that promote green transition.
Finally, we would choose the sustainable house again for all the benefits that it brings.
dr. Matevž Bokalič, the AURORA Ambassador
