Comparing TRNSYS and WUFI plus simulation models- illustrated on models validated on measurements at Schack- Gallery Munich

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1 Comparng TRNSYS and WUFI plus smulaton models- llustrated on models valdated on measurements at Schack- Gallery unch Smon Schm 1, anuel Lndauer 1, and chaela Hoppe 1 Proceedngs of the 5th IBPC, Kyoto, Japan, ay 28-31, Technsche Unverstät ünchen, Insttut of Buldng Physcs, unch, Germany Keywords: TRNSYS, Wuf plus, smulaton, mosture, temperatures, valdaton ABSTRACT The paper shows the valdaton of a smulaton model created out of a part of a museal buldng aganst measured data, as a begnnng. Thereafter the dfferent approach n answerng the questons of plannng wthn the process of refurbshment n both systems wll be outlned. Ths s done by showng the dfferences of the computaton and ther effect on the calculatons. For example, n TRNSYS t s possble to use a detaled radaton model, usng 3D modelng nformaton, whereas n WUFI plus only a GEOSURF-Factor can be used for radaton calculatons. Comparng results from both smulatons show dfferences n, for example temperature levels. Besdes these dfferences and ther effects on the smulaton output, the paper fnshes wth the decson wth whch System the evaluaton of further measurements of refurbshment can be performed best n ths partcular proect. 1. Introducton As part of the research consortum Sustanable Refurbshment of useum Buldngs extensve measurements were performed pror to the refurbshment of the Collecton Schack n unch. These measurements were used for creatng and valdatng a buldng model n order to evaluate further measurements of refurbshment. The resultng model was mplemented nto the systems of TRNSYS and WUFI plus n order to support the refurbshment furthermore. The Insttute for Buldng Physcs of the Technsche Unversttät ünchen thereby was commssoned to analyse the most effectve and cost-effcent method of refurbshment through these smulatons. Accordng to (Künzel 2006) one method n achevng ths goal s usng a coupled hygrothermal and energetc buldng smulaton tool such as WUFI plus. The context of ths analyss gave the possblty of a comparson of two dfferent smulaton tools used durng the analysng process wth regards to the queston whether n ths specal case a coupled hygrothermal and energetc buldng smulaton leads to more effectve and cost-effcent refurbshments. 2. The Schack Collecton Erected n 1909, the Schack collecton house (fg. 1) s one of the most mportant collectons of 19th-century German pantng, founded by Adolf Fredrch von Schack ( ). Sufferng mnmal damage durng WW2, the buldng largely remans n ts orgnal state. Yet today, only two of the three exstng floors (ground floor and 1st floor) are used as exhbton space. However, the collectons owner, the Bavaran State Pcture Collectons, wshes to reactvate the vacant 2nd floor attc galleres. Therefore a redesgn of the fre escape routes became necessary, tself resultng n an overall refurbshment of the 2nd floor and roofng areas. Ths enabled the responsble buldng authortes to take n a more holstc approach by partcpatng n a natonal research programme. Fg 1: Pantng of collecton Schack at about odel and Smulaton tools descrpton 3.1 Smulaton model The focus of refurbshment actvtes was located wthn the gallery rooms of the second floor (fg. 2 / 3). Snce all other rooms are stll used as exhbton space and all actvtes of refurbshment are lmted to the gallery rooms, only ths secton of the second floor was modelled. All adacent areas, lke the frst floor, the so called Feuerbachsaal to the north and others, are smulated as adabatc borders. Only the starcase domnatng the roof of the second floor was modelled as a shadowng devce (purple area wthn fg. 4). Fg 2: Floor plan of second floor of collecton Schack wth smulated area marked red and turquose (top sde orentated west) 1143

2 Proceedngs of the 5th IBPC, Kyoto, Japan, ay 28-31, 2012 Fg 4: 3D drawng of the fnal smulaton model wth towerng starcase as shadow devce Fg 3: Longtudnal secton of collecton Schack wth smulated area marked red and yellow The modelled secton wthn the second floor s dvded nto the three gallery rooms, wth attcs (fg. 4). Adonally, there are rooms coverng the whole east and west sdes of the galleres, n whch radators at the exteror walls are nstalled as the only heatng system. The constructon for the exteror and nteror walls, floors and the roof s lsted at table 1, 2, 3 and 4. Table 1 Constructon and resultng U-value of exteror walls Layer ateral Thckness 1 nteror renderng 15 0,70 2 sold brck 450/600/1000 0,81 3 exteror renderng 20 1,00 U exteror wall = 1,3/1,1/0,69 [W/(m²K)] Solar radaton enters the gallery room through the skylghts of the roof sectons and the sem-transparent dust cover. The parameters of the used wndows are those of a sngle pane glazng wth U g = 5,0 W/(m²K) and SHGC of 0,85. Table 2 Constructon and resultng U-value nteror walls Layer ateral Thckness 1 nteror renderng 15 0,70 2a 2b 2c honeycomb brck concrete blocks sold brck /450/900 0,50 2,10 0,81 3 nteror renderng 15 0,70 U nteror wall a = U nteror wall b = U nteror wall c = 1,9 2,7 1,5/1,2/0,71 [W/(m²K)] The used weather data s obtaned from the nearby weather staton at the Deutsches useum approx. 1 km away. The heatng system, n the eastern and western rooms, s controlled by a set pont temperature of 21.5 C for all 4 radators. Adonally to the heatng system a humdfcaton wth a set pont of 40 % rel. humy s nstalled n the adacent eastern and western room also. echancal ventlaton s not nstalled, but from the western room there are ar channels to the gallery rooms and from the eastern room ar channels lead to the attcs, so a knd of natural drven ventlaton through the rooms s possble. These ar changes were smulated n a knd of pre-processng wth natural ventlaton calculated by usng a formula of buoyant force. The results then were mplemented nto the fnal model. Table 3 Constructon and resultng U-value of floor slabs Layer ateral Thckness 1* parquet floorng, structural sold tmber 30 0,13 2 cement screed 50 1,40 3 sold brck 200 0,81 4 nteror renderng 15 0,70 U floor = 1,1 U top floor = 1,4 [W/(m²K)] * not on top floor Table 4 Constructon and resultng U-value of unsolated steep roof Layer ateral Thckness 1 roof tles tmber plankng 30 0,130 3 tmber rafter 8/14, e= U steep roof = 2,5 [W/(m²K)] 3.2 TRNSYS 17 TRNSYS s a modular transent systems smulaton program developed by the Unversty of Wsconsn, adson. It s prmarly used n the felds of renewable energy engneerng and buldng smulaton for passve as well as actve solar desgn (Wkpeda 2011). The correspondng TRNSYS lbrary conssts of components ( types ), whch can be assembled to form a system, for example a buldng exposed to the weather n unch, ncludng the overhead lghts, some ar exchange between rooms, and the heatng system used n ths buldng. Also t s possble to actvate a buffer storage model whch takes nto account the humy storage capactes of the surroundng elements. 3.3 Wuf Plus WUFI plus s a room clmate model whch connects the energetc buldng smulaton and the hygrothermal component calculaton. Wth the buldng smulaton software WUFI plus the hygrc and thermal ratos n a buldng, n ts permeter and ther nteracton can be calculated and quantfed as well as the energy demand and consumpton of system engneerng (Fraunhofer 2010). The program conssts of a graphcal user nterface wthn whch all nputs are made by clckng and typng, wthout fllng n and connectng types. In contrast to TRNSYS the humy model s calculated as a standard model, but can be swtched off. 4. Valdaton of smulaton aganst measured data easurement System For the acquston of the ar-temperature, ace-

3 Proceedngs of the 5th IBPC, Kyoto, Japan, ay 28-31, 2012 Fg. 7: Comparson of relatve humy n room 19 of collecton Schack of measurement and smulaton data Fg. 5: Cross secton of frst and second floor of collecton Schack wth horzontal and vertcal measurement axes temperatures, heat-fluxes and relatve humy of the ar a measurement-system based on Beckhoff-SPS-technology was set up. In the area of nterest on the second floor three measurement axes were nstalled, one n north-south orentaton over all three rooms, another one n east-west orentaton n the mddle of the centre room (fg. 5), and the thrd vertcal axs also n ths room for ar temperature, relatve humy and heat flux through the dust cover and to the floor below (fg. 5). Adonally some data loggers from Onset Computer were used ( Hobos ), whch save the acqured temperature and humy data on a local memory and were read out regularly. The correspondng outsde-conons were, as mentoned before, taken from a nearby weather staton. The measurement accuracy for the Hobos s ±0.35 K for the temperature and typcally ±2.5 % for the relatve humy wth a maxmal uncertanty of ±3.5 % (Hobo 2011). The measurement accuracy for the Rotronc sensors used n the Beckhoff-system s gven by ±0.1 K for temperature and ±0.8 % for relatve humy, wth longtme stablty smaller than 1 % per year, so for the sensors nstalled whch were used for 3 years approxmately ±3.8 % accuracy for relatve humy (Rotronc 2011). 4.2 Valdaton results In a frst step the resultng temperatures of both programs, calculated wth the mosture bufferng method actvated, were compared to the measurement data. The resultng graph s shown n fg. 6. The second step was then to compare the measured relatve humy wth the one calculated (fg. 7). Fg. 6: Comparson of nner ar temperature n room 19 of collecton Schack of measurement and smulaton data The dfferences found between measurement and both smulaton results have ther source manly wthn the dffculty to model the correct ar change between the modelled zones, caused by the ar channels between the rooms. Ths problem was addressed by calculatng the ar change n a pre-processng as shortly descrbed before. The standard devaton and s found between measurement and smulaton wthn the fnal models can be seen n table 5 and 6. It s clear that all values are qute smlar and wthn the range of errors obtaned from the measurement results. The models therefore can be seen as valdated aganst the measured data. Table 5 Standard devaton and of dfferences between measured data and smulaton calculated wth humy model for TRNSYS standard devaton for temperature K K for rel. humy % % Table 6 Standard devaton and of dfferences between measured data and smulaton calculated wth humy model for WUFI plus standard devaton for temperature K K for rel. humy % % 5. Dfferent approaches of both tools 5.1 Ventlaton model Possbltes wthn the TRNSYS ventlaton model In TRNSYS there are several possbltes to calculate ar flows between zones, as there are self-defned formulas usng the equaton type, TRNFlow, couplng ar flows through aces and nterzonal ventlaton. The mplemented ventlaton model n TRNSYS s based on couplng ar flows through aces wth user gven ventlaton rates, whch were approxmated by a preprocessng usng natural ventlaton based on temperature dfferences, the area and the heght dfference of n- and outlets. 1145

4 5.1.2 Ventlaton model wthn WUFI plus The mplemented ventlaton model n WUFI plus s based on user gven ventlaton rates wth the possblty of varaton over tme. Three models are avalable, a model for natural ventlaton, mechancal ventlaton ncludng nfltraton both wth ar from the outsde and an nterzonal ventlaton wth ar from the nsde. All models can be addressed smultaneously. The system also conssts of the possblty to ntegrate a prevous generated fle wth gven ar change rates for all descrbed models. A calculaton of ar flows s not possble. Only a balance over all n- and outflows wthn every room s calculated. Dependent on the prevous settng the tool automatcally aborts calculaton or compensates the error resultng out of a msbalance. 5.2 Radaton model Radaton model n TRNSYS In TRNSYS two radaton models can be used, the frst based on geo-factors whch can be adusted by the user. The second s based on vew factor matrces for every ace, whch are automatcally calculated from the geometry of the underlyng SketchUp-model. The radaton model mplemented n the smulaton s based on geo-factors, whch were set to the same values as n WUFI plus Radaton model n WUFI plus The radaton model n WUFI plus contans only the so called geo- factor method whch dstrbutes the ncomng radaton accordng to factor on every ace. These factor are fxed wthn WUFI plus. 5.3 osture behavour Effectve Capactance Humy odel n TRNSYS In ths model, the buffer effect of adsorptve and desorptve materals are consdered by an effectve mosture capactance whch s defned as the product of the ar mass and a mosture capactance rato: = (1) eff, R ar, where eff, s effectve mosture capactance n the arnode (kg), ar, s the mass of ar n the arnode (kg) and R s a multplcaton factor, generally n the range 1 to 10 (-). A mosture balance for any arnode results n the followng dfferental equaton: eff, dω = nf, nvent k W ω ) g, a k, naces k, ω ) cplg, s ω ) (2) Fg. 8: Buffer storage humy model of TRNSYS where eff, s the effectve mosture capactance n the arnode (kg), ω s the humy rato of the arnode (-), ω a s the ambent humy rato (-), ω k, s the humy rato of the ventlaton ar from ventlaton type k (-), Ẇ g, are the nternal mosture gans (kg/s), ω s the humy rato of an adacent arnode (-), ṁ nf, s the ar mass flow rate from nfltraton (kg/s), ṁ k, s the ar mass flow rate from ventlaton type k (kg/s), ṁ cp,lg,s s the ar mass flow rate of ar enterng arnode I (kg/s). Ths s descrbed n detal n (TRNSYS 2010) Buffer Storage Humy odel n TRNSYS Ths model descrbes a separate humy buffer dvded nto a ace and storage. These are connected to each other as shown n fg. 8, the ace buffer s adonally connected wth the ar node. In ths model the mosture balance results n the followng dfferental equatons: ar, dω = κ Proceedngs of the 5th IBPC, Kyoto, Japan, ay 28-31, 2012 κ nf, nvent k W ω ) g, a k, β dω f ( ϕ, ω) β dω f ϕ, ω) naces k, ω ) = β ω ) cplg, s ω ω ) ) ω (3) ) ( (4) = β ω ) (5) Where ω s the humy rato of the ace storage (-), ω s the humy rato of the storage (-), β s the exchange coeffcent between arnode and ace storage (-), β s the exchange coeffcent between ace storage and storage (-), κ s the gradent of sorptve sothermal lne of ace buffer (kg water /kg materal /rel. humy), κ s the gradent of sorptve sothermal lne of buffer (kg water /kg materal /rel. humy), f(φ,ω) the converson factor from relatve humy to humy rato (-). It s descrbed n detal n (TRNSYS 2010). 1146

5 5.3.3 Comparson of humy models n TRNSYS Proceedngs of the 5th IBPC, Kyoto, Japan, ay 28-31, 2012 Fg. 9: Result of smulaton wth TRNSYS usng and gnorng the humy model In fgure 10 the relatve humy calculated n the two dfferent TRNSYS humy models are compared. As expected, the buffer effect n the buffer storage model leads to some slower change of humy. But both models do not represent exactly the measured humy development. Table 7 : Standard devaton and of dfferences between smulaton wth and wthout humy model for TRNSYS standard devaton for temperature 0 K 0 K for rel. humy % % Humy model n WUFI plus The humy model n WUFI plus s the same as n the related program WUFI pro, whch s a smulaton tool to calculate mosture problems n structures wthout a coupled thermal smulaton. Fg. 11: Flow chart of the calculaton technque of WUFI pro (Künzel 1995) The program WUFI pro smultaneously solves equatons related to heat and mosture transfer n a mult-layer buldng component usng the equatons shown n fg. 10. The flow chart of ths calculaton s shown n fg. 11. As clmatc boundares WUFI pro uses realstc weather data for outsde and generated data for nsde conons. As ace transfer conons average values for the exteror and nteror heat and vapour transfer coeffcents are used. WUFI plus uses, as mentoned before, the same method of calculaton for structures as descrpted for WUFI pro, wth the extenson of calculatng the nner conons, unlke usng pre generated data. The man dfference to TRNSYS s the calculaton of heat and mosture transport through the whole mult-layer buldng component and the couplng of these processes wth the parallel computed thermal conons wthn the room model Comparson of result of calculaton wth an wthout humy model n WUFI plus The comparson shows that the humy model has only lttle but exstng mpact on nner ar temperatures, whereas the mpact on relatve humy s recognsable (table 4). Fg. 10: Equatons of heat and mosture transport mplemented wthn WUFI pro/plus (Künzel 1995) 1147 Due to the fact that mult-layer components are calculated the bufferng and humy transport through the boundary components dmnshes the ampltude of relatve humy. The mean of the results calculated wth the humy les wth % underneath the mean result calculated wthout the humy model. Comparng these results wth the measured data also shows, that the results obtaned wth the humy model are closer to the measured data results. As a matter of fact a lttle nfluence s shown after swtchng from smulaton wth humy model to one wthout accordng to the resultng temperatures. Ths nfluence

6 Fg. 12: Result of smulaton wth WUFI plus usng and gnorng the humy model ndcates not only s the heat and mosture transport calculated through the mult-layer buldng component, but also over the boundary layer between the components ace and the ar node wthn the room. Therefore the sensble and latent heat s balanced. Table 8 : Standard devaton and of dfferences between smulaton wth and wthout humy model for WUFI plus standard devaton for temperature K K for rel. humy % % 6. Concluson The comparson led to the concluson that regardng the achevable results both tools are lkely to be used n ths specfc case. Also there are dfferences wthn the resultng values these dstnctons are qute small. The range of the standard devaton for temperature s between approx. 1.4 K and 1.2 K. The range of the standard devaton accordng relatve humy s between approx. 4.2 % and 3.1 %. Although there are dfferences wthn the calculaton wth and wthout humy models, an nfluence on relatve humy of approx. 1% or more s seen only wthn the smulaton of TRNSYS. After actvaton of the buffer storage model the standard devaton for relatve humy decreases. A sgnfcant nfluence on temperature behavour of results of both tools calculated wth the dfferences n modellng descrbed cannot be obtaned. In ths specfc case the leadng nfluence on both temperature and relatve humy s the ar change rate, so the nfluence of modellng wth or wthout humy models s dmnshed. Takng nto account that the calculaton tme ncreases by usng the humy model, for example a factor of approx. 2 s obtaned wthn WUFI plus, these models should only be used to calculate problems wth low ar changng rates. References Antretter F, tterer C, Jung S-, Holm A H Use of mosture bufferng tles for ndoor clmate stablty under dfferent clmatc requrements. Paper presented at IAQVEC Antretter F, Sauer F, Schöpfer T, Holm A H Valdaton of a hygrothermal whole buldng smulaton software, n Proceedngs of Buldng Smulaton 2011, Sydney, November 14 16, 2011, pp Proceedngs of the 5th IBPC, Kyoto, Japan, ay 28-31, 2012 Frank T EN-ISO Normen zur Valderung von Gebäudesmulatonsprogrammen, n Proceedngs BauSI 2006, ünchen, October 9-11, 2006, pp. 36. Fraunhofer IBP Holzkrchen 2010, Overvew of WUFI. URL Hobo 2011, Product Specfcaton HOBO U12-011, URL Holm A H ANNEX 41 Whole Buldng Heat, Ar and osture Response (OIST-EN). Holm A H, Künzel H The Impact of the Indoor Clmate on the Hygrothermal Behavour of External Components Standard Boundary Conons vs. Hygrothermal Indoor Clmate Smulaton,, n Proceedngs Buldng Physcs Symposum, Leuven, October 29 31, 2008, pp Künzel H Smultaneous Heat and osture Transport n Buldng Components, Fraunhofer IRB Verlag Stuttgart, Germany. Künzel H Verfahren zur en- und zwedmensonalen Berechnung des gekoppelten Wärme- und Feuchtetransports n Bautelen mt enfachen Kennwerten. Unversty Stuttgart. Künzel H, Sedlbauer K, Holm A H, Krus Entwcklung der hygrothermschen Smulaton m Bauwesen am Bespel der Softwarefamle WUFI. WKSB Band 55, 2006, pp Lengsfeld K, Holm A H Entwcklung und Valderung ener hygrothermschen Raumklma-Smulatonssoftware WUFI -Plus. Bauphysk 29 (3). ahdav A, Lambeva L Calbratng buldng smulaton models based on ndoor and outdoor envronmental montorng, n Proceedngs BauSI 2006, ünchen, October 9-11, 2006, pp Rode C, Woloszyn Whole buldng hygrothermal modelng n IEA Annex 41. Thermal Performance of Exteror Envelopes of Whole Buldngs X, Clearwater, USA Rotronc 2011, Product Specfcaton Hygroclp HC2-S, URL Sauer F Valderung der hygrothermschen Gebäudesmulaton WUFI plus mt ASHRAE Hochschule ünchen. Steeman, Janssens A, De Paepe odellng combned heat and mosture transport n porous materals:couplng wth a multzone model n TRNSYS, n Proceedngs Buldng Physcs Symposum, Leuven, October 29 31, 2008, pp TRNSYS 2010, TRNSYS 17 Documentaton, Solar Energy Laboratory, UW-adson Wkpeda 2011, TRNSYS, URL en.wkpeda.org, Zach R, ahdav A ontorng for smulaton valdaton, n Proceedngs BauSI 2010, Wen, September 22-24,