Guidelines for Heat and Moisture Modelling in Constructions Using Mutliphysics FEM Software van Schijndel, A.W.M.

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1 Gudelnes for Heat and Mosture Modellng n onstructons Usng Mutlhyscs FEM Software van Schjndel, A.W.M. Publshed n: Buldng Physcs Symosum, Leuven, October 2008 Publshed: 01/01/2008 Document Verson Publsher s PDF, also known as Verson of Record (ncludes fnal age, ssue and volume numbers) Please check the document verson of ths ublcaton: A submtted manuscrt s the author's verson of the artcle uon submsson and before eer-revew. There can be mortant dfferences between the submtted verson and the offcal ublshed verson of record. Peole nterested n the research are advsed to contact the author for the fnal verson of the ublcaton, or vst the DOI to the ublsher's webste. The fnal author verson and the galley roof are versons of the ublcaton after eer revew. The fnal ublshed verson features the fnal layout of the aer ncludng the volume, ssue and age numbers. Lnk to ublcaton taton for ublshed verson (APA): Schjndel, van, A. W. M. (2008). Gudelnes for Heat and Mosture Modellng n onstructons Usng Mutlhyscs FEM Software. In Buldng Physcs Symosum, Leuven, October 2008 ( ) General rghts oyrght and moral rghts for the ublcatons made accessble n the ublc ortal are retaned by the authors and/or other coyrght owners and t s a condton of accessng ublcatons that users recognse and abde by the legal requrements assocated wth these rghts. Users may download and rnt one coy of any ublcaton from the ublc ortal for the urose of rvate study or research. You may not further dstrbute the materal or use t for any roft-makng actvty or commercal gan You may freely dstrbute the URL dentfyng the ublcaton n the ublc ortal? Take down olcy If you beleve that ths document breaches coyrght lease contact us rovdng detals, and we wll remove access to the work mmedately and nvestgate your clam. Download date: 24. Nov. 2018

2 Sesson 2.2 Buldng enveloes: modellng gudelnes and test set-us Buldng Physcs Symosum Sesson 2.2 Buldng enveloes: modellng gudelnes and test set-us Gudelnes for Heat and Mosture Modellng n onstructons Usng Multhyscs FEM software J. van Schjndel Endhoven Unversty of Technology, Deartment of Archtecture, Buldng and Plannng, Endhoven, Netherlands Tel : ; Emal: A.W.M.v.Schjndel@bwk.tue.nl eywords: Heat, Mosture, Modelng, Multhyscs, FEM 1. Introducton Multhyscs treats smulatons that nvolve multle hyscal models or multle smultaneous hyscal henomena mostly usng the Fnte Element Method (FEM). The commercally avalable software ackages lke ANSYS Multhyscs, LS-DYNA, OMSOL Multhyscs, and FlexPDE are very romsng for alcaton n the area of buldng hyscs. However, usng these Multhyscs tools for modelng heat and mosture transort n constructons, one mght encounter numercal roblems. Esecally the mult-layered mxed mosture transort (.e. vaour and water) art can be trcky to solve. Amongst other ossbltes, the multhyscs modelng aroach of van Schjndel (2007) s selected. A gudelne on how to mlement u to 3D heat ar and mosture (HAM) transort models usng OMSOL (2008) s already rovded (van Schjndel 2006). Another recent develoment concernng OMSOL s resented n Tarku et al. (2008). Ths work shows a successful mlementaton of 1D HAM transort usng relatve humdty as mosture otental. Ths aer resents two major extensons to work of van Schjndel (2006) and Tarku et al. (2008), descrbed n the followng sectons: Frst, the mlementaton of LPc as mosture otental for ncludng both vaour and lqud transort and second, the mlementaton of materal and boundary functons for calculatng the PDE coeffcents from the materal roertes. The mlementaton of the two new extensons s verfed usng the HAMStad benchmark 1 (Hagentoft et al 2002). 2. Extenson 1: Imlementaton of LPc otental The heat and mosture transort can be descrbed by the followng PDEs usng LPc as otental for T T 11 T 12) mosture transfer. t (1) LPc 21 T 22) t Wth: 10 LPc log( Pc) T LPc c l lv M w Psat, RT w M w Psat, RT Psat, T a a (2) 59

3 Sesson 2.2 Buldng enveloes: modellng gudelnes and test set-us Buldng Physcs Symosum Where t s tme [s]; T s temerature [ o ]; P c s callary ressure [Pa]; s materal densty [kg/m 3 ]; c s secfc heat caacty [J/kg]; s thermal conductvty [W/m]; l lv s secfc latent heat of evaoraton [J/kg]; vaour ermeablty [s]; s relatve humdty [-]; Psat s saturaton ressure [Pa]; M w = [kg/mol]; R = [J/mol]; a s ar densty [kg/m 3 ]; w s mosture content [kg/m 3 ]; s lqud water ermeablty [s]. 3. Extenson 2: Imlementaton of advanced materal and boundary functons The second extenson s the mlementaton of advanced materal and boundary functons usng MatLab. These functons are used to convert measurable materal roertes such as,, and whch are deendent on the mosture content nto PDE coeffcents whch are deendent on the LPc and T. Ths s schematcally shown n fgure 1. Fg 1. The converson from measurable materal roertes nto PDE coeffcents The results for materal B (based on HAMstad benchmark 1) s resented n fgure 2. Fg. 2. PDE coeffcents T, LPc, j as functons of LPc and T calculated from the rovded HAMSTAD benchmark no.1 materal roertes for the nsulaton b materal (lease note that ths fgure reles on colour, see dgtal verson) 60

4 Sesson 2.2 Buldng enveloes: modellng gudelnes and test set-us Buldng Physcs Symosum For each materal and at each ont the vaour ressure can be calculated usng smlar corresondng functons. 4. Verfcaton usng HAMSTad benchmark 1 Benchmarks are mortant tools to verfy comutatonal models. In the research area of buldng hyscs, the so-called HAMSTAD (Heat, Ar and Mosture STAnDardzaton) roject s a very well known reference for the testng of smulaton tools. Ths Secton summarzes the results for the HAMSTAD benchmark no.1: Insulated roof. The roof structure s analyzed n 1D regardng dynamc heat and mosture transort. The thermal nsulaton s facng the nteror and a there s mosture barrer facng the exteror. The structure s erfectly artght. Fgure 3 shows the structure: Fg. 3. A schematc of the structure of the benchmark The governng PDE equatons are gven by (1). Fgure 2 rovdes the PDE coeffcents for the nsulaton materal b (the load bearng materal s smlar). The boundary condtons are at the: ()nternal (connected wth materal a) (e)xternal (connected wth materal b) q h ( T T) l g ) lv ) q he ( Te T) (3) g 0 Where q s heat flux [W/m 2 ]; h s convectve heat transfer coeffcent [W/m 2 ]; s vaour transfer coeffcent [kg/pam 2 s]; s vaour ressure [Pa]; g s mosture flux [kg/m 2 s]; The boundary condtons are hourly based values rovded by benchmark. The results are shown n fgure 4. Fg.4. Left. The smulated total mass n the load bearng materal (to) and nsulaton materal (bottom) durng the frst year. Rght. The smulated heat flows nteror (bottom) and exteror (to) to the wall durng the frst year 61

5 Sesson 2.2 Buldng enveloes: modellng gudelnes and test set-us Buldng Physcs Symosum onfrontng these results wth the benchmark, t s concluded that the results are wthn the rovded bandwdths. Other benchmarks wll be evaluated n near future. Moreover, the benchmark 1 model usng OMSOL (2008) and comanyng reort are ublshed at the HAMLab (2008) research and educaton webste. 5. onclusons It s concluded that the followng two man gudelnes rovde a stable numercal solutons for several benchmarks on heat and mosture transfer and for Multhyscs FEM ackages OMSOL: (1) Use the LPc (the natural logarthmc of the sucton ressure Pc) as mosture otental and (2) Use 2-D nterolaton (table looku) based on LPc and temerature for all PDE coeffcents. The OMSOL model resented n ths aer s ublc doman and s downloadable from the HAMLab (2008) webste. 6. Ongong research Alcaton of system dentfcaton. Ths technque seems romsng n reducng the large smulaton tmes of (lnear aroxmated) models wth large degrees of freedom (DOF) such as 3D HAM models of constructons. Evaluaton of full 3D ndoor clmate and constructons HAM models. Prelmnary results show that t s ossble and relatvely easy to model the nteracton between constructons and ar n omsol. Furthermore, t seems ossble to get relable smulaton results n cases for convectve arflow and forced arflow. However, due to the lmted comuter resources used n ths research, the smulated volumes were small: less than 0.1 m3 and 2 m3 for resectvely the convectve and forced arflow case. Inverse modelng. An nverse roblem s the task that often occurs n many branches of scence and mathematcs where the values of some model arameter(s) must be obtaned from the observed data (Wkeda 2008). The man goal of ths work s to nvestgate whether materal roertes can be obtaned usng an nverse roblem technque. A second goal s to evaluate ths technque for heat and mosture engneerng. Alcaton scale of DNS technques. For full sze buldngs, turbulence models are necessary to solve FD equatons. One of the roblems s that there are a lot of dfferent turbulence models and they all gve more or less dfferent results. Wthout turbulence modelng (.e. Drect Numercal Solvng (DNS) technques), accurate results on turbulent flow can only be obtaned usng very small domans comared to buldngs. For DNS the followng statement seems to be vald: The smaller the turbulence the bgger the doman that can be handled. Another roblem s the grd deendency of the soluton. Ths gves rse to the followng man research queston: At what scale s the DNS technque stll usable n relaton wth ndoor arflow and HAM onstructons? REFERENES [1] OMSOL (2008), htt://en.wkeda.org/wk/omsol [2] Hagentoft, -E. (2002). HAMSTAD Fnal reort: Methodology of HAM-modelng, Reort R-02:8. [3] Gothenburg, Deartment of Buldng Physcs, halmers Unversty of Technology. [4] Hagentoft, -E.; alagasds, A.; Adl-Zarrab, B.; Roels, S.; armelet, J.; Hens, H; Grunewald, J.; Funk, [5] M.; Becker, R.; Shamr, D.; Adan, O.; Brocken, H.; umaran,.; Djebbar, R. (2004). Assessment Method of Numercal Predcton Models for ombned Heat, Ar and Mosture Transfer n Buldng omonents: Benchmarks for One-dmensonal ases. Journal of Thermal Enveloe and Buldng Scence. Vol. 27 (4), [6] HAMLab (2008), htt://sts.bwk.tue.nl/hamlab/ [7] Schjndel A.W.M. van (2006), Heat, Ar and Mosture onstructon modelng usng OMSOL wth MatLab, Modelng gude verson 1.0, Proceedngs of the OMSOL Users onference 2006 Endhoven [8] Schjndel A.W.M. van (2007), Integrated Heat Ar and Mosture Modelng and Smulaton, Bouwstenen 116, ISBN: , Endhoven Unversty of Technology [9] Tarku, F., umaran,.,fazo,p. (2008) Develoment and benchmarkng of a new hygrothermal model, NR-NR Reort NR