Studio Apxe house generates more energy than it consumes


January 30, 2014

Studio Apxe has completed a new house that generates more energy than it uses (Photo: Missirkov / Bogdanov)

Studio Apxe has completed a new house that generates more energy than it uses (Photo: Missirkov / Bogdanov)

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Architecture firm Studio Apxe has completed a new house that will generate more energy than it uses. As well as high efficiency, the house, in Kladnica, Bulgaria, features biomass heating and solar panels on its roof to generate electricity.

Studio Apxe cites sustainable development and energy efficiency as its main design focuses. Coupled with these, the aim of this project was to build a large, one-story house in a green landscape without it appearing too conspicuous.

The 970 sq m (10,441 sq ft) building is comprised of lightweight steel and timber structures, with concrete used sparingly. The construction used local materials where possible, such as stone and timber. The main living areas sit above the garage, which is dug into the rock at street level. Colder service spaces, such as the garage, are kept separate from the living spaces so as to minimize heat loss.

A variety of architectural measures were taken to ensure the house was kept as efficient as possible. Keeping glazed areas out of the shade, triple glazed windows and super-insulation of the building are all contributory factors. Indoor air quality is managed by a mechanical ventilation system with heat recovery.

The efficiency of the house is also contributed to by excellent levels of air tightness. According to Studio Apxe, hundreds of details in the house were designed with air tightness in mind. The target was to reach a level of 0.6 air changes per hour at 50 pascals pressure, the level required for Passive House accreditation. The Kladnica house reached levels of 0.13 and 0.19 air changes per hour across two tests.

The house's biomass heating helps to keep energy requirements down to 38 kWh per square meter annually, well below the 120 kWh per square meter figure needed to be counted as a "passive house," the international standard for high energy efficiency that was developed in Germany during the 1990s.

The costs expended on achieving the passive house standard came to 5.93 percent of the overall construction costs. The further investment to reach "energy plus" levels were a further 9.24 percent of the overall costs.

Energy needs, such as for lighting and household appliances, are met by an array of 50 12.25 kWp photovoltaic panels installed on the roof with an annual yield of 10,750 kWh. This represents 52 kWh per square meter of energy generated on an annual basis, putting the house 14 kWh per square meter in the black each year. Meanwhile, 12 solar collection units heat the swimming pool in summer and feed into the heating system during the winter. The electricity generated is stored in batteries with any surplus transferred to grid.

The house took just under a year and a half to complete with an estimated final production cost of €953 (US$1,301) per square meter, something that Apxe views as an achievement to be proud of, given the materials and systems used.

Silvia Draganova, one of the project architects, told Gizmag, "We believe that buildings in the future should be more comfortable, providing joy and healthy indoor environment to the residents. This can be achieved only through the most advanced international environmental standards."

Source: Studio Apxe

About the Author
Stu Robarts Stu is a tech writer based in Liverpool, UK. He has previously worked on global digital estate management at Amaze and headed up digital strategy for FACT (Foundation for Art and Creative Technology). He likes cups of tea, bacon sandwiches and RSS feeds. All articles by Stu Robarts

Pretty pictures but as an engineer that is all I see.

Yes, they give figures for expected output from the solar panels and heat output from the wood burning stove but until they have gathered at least a years worth of actual figures they are nothing more than wishful thinking.

Another piece of information that is conspicuous by its absence is the size of the battery bank and the inverters that are necessary to store the energy from the panels and supply power at night when it is needed. .


Further to ivan4's comment, what is the embodied energy/CO2 of all the materials and systems in this house? It would be helpful to be able to compare it with, for example, the Hobbit house, to understand the relative impact of building with all the latest tech versus a back-to-basics approach.


limited air-exchange, this is going to be a problem, once a bug gets in you will have to live with it, fresh air is a requirement for good living, and no amount of technology can deal with the problem. This is proved in Hospitals. Other that that I liked the house but could never afford to think if having one.


Never have I read such an uninformative article... It recites statistics obviously provided by the designers ,but offers no explanations... the "how" .... Is the "biomass heating" really only a wood stove? What have solar thermal collectors to heat the pool got to do with storing electricity. It is time that projects like this, and all alleged net zero energy projects, are exposed for what they really best marginal improvements in the amount of energy being consumed and a fraud when it comes to actually offsetting this with energy produced.....

Ned Baldwin

An excellent demonstration of current architectural engineering! Depending upon the materials used, the limited air-exchange number might require lower energy levels, but also could trap CO and poisonous out-gassing of materials initially, as well as the results of occupant activities, (bathroom smells, cleaning chemicals, dust, allergens, etc). The US minimum standard is now 0.35 ACH, (ASHRAE Standard 62.2- 2004) with anything less requiring forced ventilation. This is a highly controversial issue though, with some respected HVAC engineers stating the rules are based on flawed or ambiguous math. The higher European standard reflects this concern, while trying to address energy needs. Ultimately, traditional construction methods will always result in a "leaky shell", even with high-tech sealants. But as tech progresses, like the potential to 3D-print entire wall sections, assembly gaps could be reduced to thousandths-of-an-inch. This will require new standards for infiltration and ventilation to balance energy and comfort.

Brian Sharpe

The other comments are all valid but this house still stands as an example to evaluate further. Hopefully, the building industry will succeed at finding ways to get the cost-per-square-foot (or Metre), down to a more tolerable level. Achieving these results in a few demonstration houses does not pay off until all builders can get there at a price society can live with. Regarding indoor air quality the best & most relevant work was done at NASA forty years ago. The short answer is that about a dozen moderately sized house plants can clean indoor air to clean outdoor quality for a family of four in a typically sized home. The previous sentence has lots of moveable, imprecise variables so do'nt get cranky about the details. Also, the best house plant for this is the spider plant, cheap, incredibly durable (Except to my cats), and easy to propagate. and good at cleaning air.

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