Meeting 14: Predavanje na temo Toplotna prehodnost (U) s strani prof. Sašo Medved / Lecture about Thermal conductivity by prof. Sašo Medved

Slovenian:

Toplotna prehodnost

Prevajanje toplote je pojav, pri katerem toplota v obliki energije potuje samodejno skozi snov z mest, ki imajo višjo temperaturo, do mest z nižjo temperaturo. Toploto merimo v J (Wh).Toplotni tok prek nekega telesa je odvisen od temperaturne razlike, od oblike in velikosti telesa ter od snovi, iz katere je. Tako se je v gradbeni fiziki uveljavil pojem toplotna prevodnost. Merilo za toplotne izgube skozi element ovoja zgradbe je toplotna prehodnost λ [W/m2K], ki mora biti čim manjša, če želimo dobro toplotno izoliran ovoj stavbe.  Manjša kot je toplotna prevodnost, boljši toploti isolator  je material. Z višanjem delovne temperature toplotna prevodnost materialom raste. Običajne toplotne prevodnosti toplotno izolacijskih materialov se gibljejo od 0,030 do 0,05 W/mK. Snovi z nizko (λ < 0,1 W/mK ) toplotno prevodnostjo so kamena ali steklena volna, ovčja volna, bombaž, les, slama, pluta, itd.

Kot delimo snovi po električnih lastnostih na prevodnike in izolatorje, jih lahko tudi po toplotnih lastnostih delimo na izolatorje in prevodnike. Dobre prevodnike toplote, na primer, potrebujemo pri zračnih hladilnikih, grelnih telesih in povsod tam, kjer želimo toploto s čim manj izgube prenesti s prve na drugo stran snovi (na primer dno posode za kuhanje). S toplotnimi izolatorji pa, nasprotno, želimo čim več toplote zadržati na primarni strani snovi. Medtem ko tehnologija toplotnih prevodnikov ni bistveno napredovala, saj med najboljše uporabne toplotne prevodnike še vedno štejemo baker in aluminij (kot zanimivost  oba sta tudi najboljša v splošnem uporabna električna prevodnika), pa je tehnologija izdelave toplotnih izolacijskih materialov naredila pravi skok.

Ker okna predstavljajo precejšnjo površino na fasadi hiše, je zelo pomembno, da imajo čim manjšo toplotno prehodnost. Na splošno pri oknih ne moremo dosegati tako nizke toplotne prehodnosti kot pri izolirani fasadi.

Razvoj toplotnih izolatorjev je narekovala predvsem gradbena stroka zaradi vedno večjih zahtev po kakovostni toplotni izolaciji, ki omogoča nižje stroške ogrevanja, z manjšo rabo energije manjše onesnaževanje okolja in ugodnejše pogoje za bivanje.

English:

Thermal conductivity

Heat transfer is a phenomenon in which heat energy automatically moves through the material from sites which have a higher temperature to sites with lower temperatures. Heat is measured in J (Wh). Heat  flow through a body depends on the temperature difference, the shape and body size and the material of subject. The criteria for the heat loss through the building envelope element is the thermal conductivity λ [W/m2 K], which must be minimized if we want well-insulated building envelope. The smaller the thermal conductivity, better heat insulation a material is. By increasing the operating temperature thermal conductivity of the material grows.

Typical thermal conductivity of thermal insulation materials ranging from 0.030 to 0.05 W / mK.  Substances with low (λ <0.1 W / mK) thermal conductivity are  rock or glass wool, sheep wool, cotton, wood, straw, cork, etc. As we can divide the substance by electrical properties into conductors and  insulators, also thermal properties can be divided into insulators and conductors. Good conductors of heat, for example,  need for air coolers, heaters, and wherever we want to minimize heat losses. With the thermal insulators  is contrary, we want to retain as much heat on primary materials. While technology  in thermal conductor is substantially progressed, the production technology of thermal insulation materials make a real jump.

Development of thermal insulators is mainly dictated by building profession in ever-increasing demands for quality thermal insulation, which allows lower heating costs, reduced energy use, smaller pollution of the environment and favorable conditions for the living.

Since the windows represent a significant area of ​​the house facade, it is very important to have a minimal
thermal conductivity. In general, the windows can not reach as low as the heat transfer in insulated facade.

Author: Ana Bilobrk

Technology workshop (prof. Sašo Medved, doc. dr. Arkar Ciril)

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About selfsufficientcell

A group of students of the Faculty of Architecture, who will participate in project design and implementation of energy self-sufficient living units. It will be constructed on a test track in Gameljne near Ljubljana.

Posted on May 30, 2011, in 2. Tedenska poročila / Weekly reports. Bookmark the permalink. Comments Off on Meeting 14: Predavanje na temo Toplotna prehodnost (U) s strani prof. Sašo Medved / Lecture about Thermal conductivity by prof. Sašo Medved.

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