Eksperimentalne meritve toplotnega toka in določevanje toplotne prehodnosti toplotnega ovoja stavbe

[diplomska naloga]

Jan Kalar (Author), Roman Kunič (Mentor), Mateja Dovjak (Co-mentor), David Božiček (Co-mentor)

Abstract

Ustrezno bioklimatsko načrtovanje, tako novih stavb kot tudi rekonstrukcij in sanacij obstoječih objektov, zagotavlja kakovostno notranje okolje, smotrno rabo energije in s tem energetsko učinkovitost ter varovanje okolja. Poglavitni dejavnik, ki vpliva na energetsko bilanco celotnega objekta, je pogosto ravno toplotna prehodnost stavbnega ovoja. Netransparentni del ovoja stavbe predstavljajo konstrukcijski sklopi, ki jih sestavljajo različni sloji materialov, pogosto tudi v kombinaciji z zračnimi plastmi. S svojimi materialnimi in termodinamičnimi lastnostmi določajo toplotni odziv konstrukcijskega sklopa glede na spreminjajoče robne pogoje (temperatura, vlažnost ipd.). Toplotno prehodnost konstrukcijskih sklopov z znano sestavo ter materialnimi in fizikalnimi lastnostmi uporabljenih materialov navadno določamo z uporabo računske metode. V tem primeru vpeljemo ustrezne poenostavitve in dejansko stanje zaradi uporabe računskega modela nekoliko prilagodimo. Pogosto se izkaže, da je zaradi nepoznavanja sestave in uporabljenih materialov tako določevanje netočno in privede do odstopanj od dejanskih vrednosti. V teh primerih so primernejše in-situ meritve (npr. merjenje gostote pretečenega toplotnega toka in temperature) na podlagi katerih ocenimo vrednosti toplotne prehodnosti. Z namenom ugotavljanja odstopanj med merjenimi in računsko določenimi vrednostmi toplotne prehodnosti smo v diplomskem delu za določevanje uporabili obe metodi. Računsko vrednost toplotne prehodnosti smo določali skladno s standardom ISO 6946:2017, vrednosti toplotne prehodnosti na podlagi in-situ meritev pa smo ocenili s povprečno metodo, ki je določena s standardom ISO 9869-1:2014. Z nadaljnjo analizo rezultatov smo želeli poiskati vzroke, ki privedejo do razlik med vrednostmi toplotne prehodnosti. Ugotovili smo, da so razlike med vrednostmi očitne. Do večjih odstopanj je prihajalo v konstrukcijskih sklopih, ki so vsebovali tako prezračevane kot neprezračevane sloje. V našem primeru so bili to sklopi analiziranih streh v naklonu, kjer so se vrednosti med izračunano in ocenjeno toplotno prehodnostjo na podlagi izvedenih meritev razlikovale tudi do 41,1 %. Manjša odstopanja so bila tudi pri konstrukcijskih sklopih zunanjih sten, kjer je bila razlika med vrednostmi do 12,5 %. Ugotovili smo, da so bile merjene vrednosti toplotne prehodnosti v štirih primerih višje, v dveh primerih pa je bila višja izračunana vrednost. Na podlagi rezultatov lahko sklepamo, da z računskim določanjem vrednosti toplotne prehodnosti idealiziramo dejansko stanje in s takim matematičnim modelom zanemarimo dejanske dinamične vplive ter morebitne nepravilnosti v konstrukcijskih sklopih, izračunane vrednosti pa so tako podcenjene in ne odražajo dejanskega stanja na objektu. Ker je toplotna prehodnost pomemben faktor tudi pri izračunu energijske bilance stavbe, se je potrebno zavedati, da odstopanje od dejanskih vrednosti toplotne prehodnosti privede do zavajajočih in netočnih izkazov dejanske rabe energije v stavbah.

Keywords

gradbeništvo;diplomska naloga;UNI;GR;B-GR;toplotna prehodnost;toplotna upornost;konstrukcijski sklop;toplotni tok;in-situ meritev;

Data

Language:	Slovenian
Year of publishing:	2020
Typology:	2.11 - Undergraduate Thesis
Organization:	UL FGG - Faculty of Civil and Geodetic Engineering
Publisher:	[J. Kalar]
UDC:	691:699.8(497.4)(043.2)
COBISS:	186023939
Views:	81
Downloads:	9
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	English
Secondary title:	Experimental measurments of heat flux and determination of thermal transmittance of building envelope
Secondary abstract:	Proper bioclimatic design of both new buildings as well as the reconstructed and rehabilitated ones provides rational energy use and energy efficiency. Envelope thermal transmittance is a key factor affecting energy balance of buildings. A non – transparent part of building envelope are constructional complexes with different material layers, often combined with air layers. Their material and thermodynamic properties define thermal response of a certain constructional element according to weather conditions such as temperature, humidity and others. Thermal transmittance of a constructional element is usually set by using a calculation method, provided that both structure as well as material and physical properties of used materials are known. If so, proper simplification is used and due to a certain calculation model of steady state conduction of the heat flow can be defined. Yet not knowing the structure and the materials used can often lead to inaccurate calculations and greater deviations from true value. In such cases insitu measurements are more suitable - e.g. density of heat flow rate and temperature measurement. They make it possible to evaluate the transmittance value, which presents the constructional element condition factually. In order to establish deviations between the measured and calculated values of thermal transmittance and their possible causes I decided for both methods in my thesis; I used calculation methods based on standard ISO 6946:2017, and decided to evaluate in-situ measurements with an average method as defined by ISO 9869-1:2014. Results have given obvious differences. Notable deviations can be seen in constructional complexes with ventilated or unventilated air layers. The analysis of pitched roof systems proved up to 41,1 % difference between the calculated and assessed values on the basis of measurements. There were some minor deviations in exterior walls as well but not more than up to 12,5 %. I established that in general assessed thermal transmittance values tended to be higher than the ones given by calculation method. The results have shown an idealized or incorrect thermal transmittance situation based only on calculation method rather than taking into consideration the real dynamic effects, as well as possible construction complexes flaws, where the calculated values remain underestimated and do not reflect the real condition of the building itself. Thermal transmittance influences the energy performance calculations to a large extent. Thus we have to take into consideration the fact that possible real value deviations influence energy efficiency demonstration. Results could show misleading or incorrect calculations of real energy use in buildings.
Secondary keywords:	construction;graduation thesis;civil engineering;thermal transmittance;thermal resistance;constructional complex;heat flux;in-situ measurments;
Type (COBISS):	Bachelor thesis/paper
Thesis comment:	Univ. v Ljubljani, Fak. za gradbeništvo in geodezijo
Pages:	XVI, 48 str.
ID:	22947211