Aprilie 30, 2009 Lasă un comentariu
As we all know new and existing buildings have to have energetic certificate. But looking on the buildings You can be sure that most of them will have very high level of energy consumption. Correct calculated thermal resistance of construction elements, it’s in fact half of the success to achieve a good, healthy and ecological house. By a good thermal design we can reduce total cost of maintaining house. Money that normally we would have to spend for heating up and cooling down house can be spend on the other things. What is then the reason of such a high energy consumption? Well the answer is not so simple. Probably most of projects are made without any calculation of thermal isolation. Romanian norm C107/2-05 is giving us a minimal requirements for a thermal resistance „R’min .” of building elements. According to C107/2-05 for exterior walls R’min=1,40 m^2K/W, that is giving coefficient of heat transmission U=1/R=0,71 W/(m^2*K). Interesting it’s what differences we have in typical coefficient of heat transmission for a wall build form concrete or B.C.A. The most popular construction materials.
- Concrete d=20 cm – R= 0,12 m^2K/W; U=8,33W/(m^2*K)
- B.C.A. d=24cm – R=1,5 m^2K/W; U=0,66W/(m^2*K)
That simple example is presenting significant difference in heat transmission between those two materials. But, if B.C.A can be use without any additional thermal protection, the concrete have to be always in addition, isolated to respect norm.
Nevertheless, in my personal opinion, require thermal resistance R’min given by C107/2-05 norm is to low, putting buildings in Romania in worse position to compare with other buildings in Central Europe, as less energy efficient. In my expiriance with polish thermal insulation standarts, in which, this same coefficient for a buildings exterior walls, with inside temperature Ti>16 C, is equal Rmin=3,33 m^2K/W and U=0,3 W/(m^2*K). Such a difference is giving significant advantage in a fight for a future costumer.
As an attraction, to compare how different materials can have influence on thermal isolation and energy saves please look on the picture below:
1-polyester 2-wood 3-brick 4-concrete 5-stone
All those walls have the same thermal resistance R=0,25 m^2K/W.
As we see size doesn’t matter. 🙂
(ing. Damian Fordonski)