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Curious layman asks ... … ''What is an energy efficient house?''

15. 10. 2012 RD magazín

Low-energy houses, passive houses, energy efficient buildings, energy efficient housing, energy labels, heat loss... In connection with housing, energy has become a very important issue, but an ordinary mortal would need a dictionary from time to time when they want to read a serious article on this topic. There is a lot of new "energy-related" terminology, it can be confusing and what is more, it can mean different things to different people. How to find one's way in this terminological jungle?

In our series called "Curious layman asks" we would like to introduce the questions of energy efficiency so that everyone understands. A complete layman will ask specialists from the company RD Rýmařov, who know really a lot about energy efficiency. And he will keep asking, until he finally understands!

AN INTERVIEW WITH JIŘÍ POHLOUDEK, COMMERCIAL DIRECTOR OF RD RÝMAŘOV

Curious layman: I came across the term "energy efficient house" when browsing on the Internet. I noticed that this term appears also in some of the houses in the offer of RD Rýmařov. Could you explain to me - as to a layman - what to imagine under this term?

Jiří Pohloudek: Today, a potential builder meets a whole number of terms that indicate different degrees of energy saving houses, from energy saving, over low-energy, to passive, zero-energy or even energy-plus. Practically, it is the extent to which the houses are insulated, airtight, equipped with alternative heating technology independent of traditional sources, with perfect, controlled ventilation with heat recovery or technology that can transmit or accumulate excess energy arising from the operation of the house. From the abovementioned it is clear that the achieved degree of energy efficiency is closely related to the financial possibilities of the builder. And the term "energy efficient house" stands as an equation of the invested resources and the energy savings provided by the technical solutions of the building.

Curious layman: Then, you can often hear the term "energy saving house". It seems to me that "energy efficient" and "energy saving" is practically the same. Am I right?

Jiří Pohloudek: Basically, you are, but an energy efficient house can be efficient "at all costs".

Curious layman: A term that is used perhaps most frequently in the context of energy saving buildings is "low-energy house" or "low-energy building" or sometimes "low-energy housing". I think that is a precise term defined by the law. Is it so? And how is a "low-energy house" different from other houses?

Jiří Pohloudek: A passive house is currently defined by a norm, which sets out that it must, for example, achieve the total energy consumption of 15 kW/m2/yr and it must achieve prescribed values of airtightness in two stages of construction n50 ≤ 0.6 h-1. A low-energy house is an intermediate step to a passive house and is in the optimum value of 25 kW/m2/yr.

Curious layman: Is energy consumption the same as "specific heating requirement"? This term is also very frequent when talking about low-energy technologies.

Jiří Pohloudek: Yes, it is more or less the same. Specific heating requirement is the amount of energy required for heating of the house and heating of water related to an area in a defined period of time.

Curious layman: One must obviously come to a conclusion that one of the disadvantages of low-energy buildings are their higher initial costs. You must invest into insulation, technologies... Can a turnkey low-energy house bring a Czech family such savings in heating costs that the investment into low-energy technologies returns in a reasonable time?

Jiří Pohloudek: With the current prices of energies compared to the invested resources, the payback period is substantially longer. Various payback periods are given. I do not want to be optimistic nor pessimistic in this case, I'd rather be realistic. A regular customer financing their house through mortgage is not able to reach the resources that would enable them to build a house in the above terms.

Curious layman: The company RD Rýmařov guarantees to all of their buildings specific heating requirement of 60 kWh/m2 per year. How have you come to this figure? Have you found out that with this figure you can achieve a perfect compromise between initial costs and future savings for heating?

Jiří Pohloudek: This figure is a binding value for new buildings in the neighbouring countries, e.g. in Germany and Austria. It is optimal in terms of invested resources and consumed operation costs. It is also in compliance with current energy strategies of these countries. We can say that in the Czech Republic this compliance can be achieved through current affordable building technologies.

Curious layman: Your company specializes in wooden houses. Do energy saving houses made of wood have any characteristic features when compared to buildings of other materials.

Jiří Pohloudek: The company does not specialize in wooden houses but in dry building technology using lightweight prefabricated wood. It means that the basic structural system is created by a frame made of massive wooden beams. This way we can create an ecological building with a lightweight structure, using mainly sandwich system insulation. With smaller unit volumes we can achieve smaller heat transfer coefficient than with other building technologies. This effect is then amplified with a larger effective area of the enclosed volume. Simply speaking, the thickness of external walls is smaller and the interior area larger.

Curious layman: The last question for today may be a bit provocative and surely will not be easy to answer. Yet: Are you able to tell, which of your houses has saved its owner the most money? That is, in which of your contracts have you achieved with the lowest investments the highest energy savings compared to average?

Jiří Pohloudek: If I am to judge from the viewpoint of energy efficient houses, the most efficient houses, as far as I can tell, are the NOVA 101, DRAGON 671 and LARGO 98. Our target group, however, comprises also people who are looking for larger and more "luxurious" houses as the KUBIS 88, DRAGON 811, DIMENZE 96, etc. These houses are more expensive than the NOVA 101, but are more affordable than "passive houses" equipped with costly technologies just to fit below an imaginary number in a standard.

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