Thermal And Energy Performance Of Double Skin Facades In Different .

2.2 COMPUTATIONAL FLUID DYNAMICS (CFD) ANALYSISComputational Fluid Dynamics (CFD) analysis implements numerical simulation methods to seeksolutions to fluid flow problems. For this study, Ansys Fluent 17.1 CFD simulation program wasused, where models for the investigated DSF types were developed using the same dimensions,components and materials properties as THERM heat transfer analysis. Different scenarios weredeveloped to simulate how box window, corridor type and multistory DSFs perform under variousenvironmental conditions. For each facade type, different models were developed to representexterior temperatures of 32 C, 16 C, -1 C and -18 C, while the interior temperature was constantat 20 C. The geometries were built as 3D models in Rhino modeling software, and imported toFluent. Boundary conditions for each identified facade component were set according to differenttemperature scenarios. DSFs’ vertical sides were identified as adiabatic and the velocity input forair inlet depended on wind speed in different seasons. Sixteen different models were developed,representing four facade types and four exterior environmental conditions.2.3 ENERGY MODELINGEnergy modeling was performed by EnergyPlus 8.4.0, where the models were created in SketchUp2016 and OpenStudio 1.10.0. This method utilized OpenStudio as the model builder, and EnergyPlusas the energy analysis engine. The methodology for energy modeling consisted of building individualmodels for each type of investigated facade, which would enclose a commercial office space.The models did not represent whole building, but rather a single south-facing zone. The modelswere created for fifteen different climate types, representing all climate zones in the U.S., whereTMY3 weather data files were used for the simulations. Table 1 shows representative cities that werechosen for energy modeling. The dimensions and material properties of the facades were identicalto previously discussed characteristics. The baseline model was a standard curtain wall, and allother models were enclosed by the different types of DSF. The energy models represented a singlezone per floor, totaling 12 m2 per floor (3 m wide and 4 m deep office space). Also, models weredeveloped for a two-story and four-story application in order to investigate the effects of height onthe performance of multistory DSF. All investigated DSFs considered only natural ventilation withinthe air cavity. Therefore, 120 different energy models were developed and simulated.The inputs for occupancy loads, system loads, equipment loads, lighting and ventilation werebased on ASHRAE 90.1 energy code and recommendations prescribed by the ASHRAE 189standard (ASHRAE, 2014; ASHRAE 2013). The material properties and optical properties of glazingwere identical to heat transfer analysis. Operating schedule was based on a typical office spaceoperation (weekday schedule from 8 AM to 6 PM). The HVAC system consisted of a packagedheating/cooling pump with DX coils, and natural gas used for heating. The results were calculatedfor all models, where total annual energy consumption was determined for each individualscenario, as well as the heating, cooling and lighting loads. Also, Energy Usage Intensity (EUI) wascalculated for all scenarios.074JANUARY 19TH 2017 – MUNICH POWERSKIN CONFERENCE PROCEEDINGSThermal and Energy Performance of Double Skin Facades in Different Climate TypesTOC

CLIMATE ZONECITYSTATEZONEREGION1AMiamiFloridaVery ry3AMemphisTennesseeWarmMoist3BEl PasoTexasWarmDry3CSan xedMoist4BAlbuquerqueNew ery cold-8FairbanksAlaskaSubarctic-Table 1 Climate zones and representative cities that were incorporated into energy modeling3RESULTS3.1 HEAT TRANSFER ANALYSISThe results of the 2D heat transfer analysis consisted of two sets of data—the first set of data indicatedthermal gradients through investigated facade systems for four exterior environmental conditions, asseen in Fig. 1 for exterior temperature of -18 C, and the second set of data demonstrated U-values.Fig. 1 Results of heat transfer analysis, showing thermal gradients in DSFs (exterior temperature of -18 C)075JANUARY 19TH 2017 – MUNICH POWERSKIN CONFERENCE PROCEEDINGSThermal and Energy Performance of Double Skin Facades in Different Climate TypesTOC

Fig. 2 Results of heat transfer analysis, showing temperatures in air cavity for investigated DSFsFig. 2 indicates temperatures within upper and lower parts of cavities for all three DSF types (and forall four exterior environmental conditions), as well as the inner and central parts. Results indicatethat for exterior temperatures of -1 C and -18 C, there is a larger difference in temperature withinlower and upper parts of the air cavity. As the exterior temperature increases (such as 16 C and32 C), there is less differentiation between the lower and upper parts of the air cavity. Anotherobservation is that there is slight variation in results based on the DSF typology. For example,multistory DSF shows smaller discrepancies than corridor type or box window DSF.076JANUARY 19TH 2017 – MUNICH POWERSKIN CONFERENCE PROCEEDINGSThermal and Energy Performance of Double Skin Facades in Different Climate TypesTOC

U-value (W/m2-K)SINGLE SKIN(CURTAIN WALL)BOX WINDOW DSFCORRIDOR TYPE DSFMULTISTORY DSF1.0220.1820.2040.176Table 2 Calculated U-values for the investigated facade typesHeat transfer coefficients (U-values) were calculated for conventional curtain wall, as well as threeinvestigated DSF types. Table 2 shows the results, indicating the relative thermal performance ofeach investigated facade type. All DSF types have much lower U-value than a standard curtain wall,indicating that these facade types would have improved thermal performance. The differencesbetween different DSF typologies are relatively small; however, multistory DSF would have thesmallest U-value, followed by box window and corridor type DSF. Nevertheless, the significantdifference between U-values of DSF types and conventional curtain wall suggests that all types ofDSFs would provide savings in heating and cooling loads due to improved thermal performance.3.2 CFD ANALYSIS RESULTSThe results of CFD analysis indicated temperature gradients within air cavity of the investigatedDSF types in 3D form, as well as air velocity and airflow patterns, as seen in Fig. 3. CFD analysisresults for multistory DSF show that when exterior temperature is -18 C, the temperature in the aircavity fluctuates between -17.7 C to -15.3 F, and the upper part of the cavity demonstrated highertemperature. The velocity was relatively stable within the air cavity. Inlet velocity was 4.9 m/s andoutlet velocity was 5.9 m/s, and the increased velocity can be caused by the stack effect. Whenexterior temperature was increased to -1 C, air temperature inside the cavity was -1.0 C to 2.9 C.If the exterior temperature was increased to 16 C or 32 C, temperatures within the cavity fall withinthe range between 15.7 C and 19.7 C, and 32.3 C and 36.2 C. The simulation results demonstrate aconsistent temperature change pattern. Within the cavity of multistory DSF, there is a temperaturefluctuation caused by solar radiation, exterior and interior temperature, as well as the ventilationeffects. However, the temperature change is not significant mainly because of the configurationcharacteristics of multistory DSF.077JANUARY 19TH 2017 – MUNICH POWERSKIN CONFERENCE PROCEEDINGSThermal and Energy Performance of Double Skin Facades in Different Climate TypesTOC

Fig. 3 CFD analysis results for investigated DSFsCompared to multistory, corridor type DSF showed similar rising trend in cavity temperature. Withexterior temperature of -18 C, the cavity temperature fluctuated between -17.7 C and -17.3 F. Withexterior temperature of -1 C, the temperature inside the cavity was between -7.3 C and 1.8 C, whichis lower than the temperature gradient for multistory DSF. In addition, with exterior temperaturesof 16 C and 32 C, the temperatures within the cavity area fluctuated between 15.6 C and 16.3 C,and 31.7 C and 33.8 C, respectively. The cavity temperature also showed discrepancies in the lowerand upper parts. The higher temperature in the upper part of DSF cavity indicates that the heatrises. Moreover, airflow patterns were different from multistory DSF due to the addition of horizontalpartitions between floors. This caused more turbulence within the air cavity.The results for the box DSF indicate that the cavity temperatures are relatively constant. With exteriortemperature of -18 C, the temperature within the cavity fluctuates between -17.7 C and -17.0 C.When exterior temperature increased to 16 C, cavity temperature showed a range between 15.5 Cand 16.2 C. Also, for the exterior temperature of 32 C, the cavity temperature was between 32.0 Cand 32.2 C. The smaller ranges in temperatures could be due to the geometry and components of thebox window DSF, since this typology has horizontal and vertical divisions that limit the movementof air within the cavity. However, these components influence airflow patterns and create moreturbulence than other types of DSFs.078JANUARY 19TH 2017 – MUNICH POWERSKIN CONFERENCE PROCEEDINGSThermal and Energy Performance of Double Skin Facades in Different Climate TypesTOC

3.3 ENERGY MODELING RESULTSAlthough benefits of DSFs in temperate and heating dominated climates have been reported innumerous earlier studies, this study investigated the effects of DSFs on energy consumption in allclimate types. As stated earlier, the methodology consisted of modeling annual energy consumptionof a south-oriented office space, which would be enclosed by the investigated facade types. Two setsof models were developed—representing two levels and four levels. This was necessary to accuratelydepict the application of the multistory facade. Results for heating, cooling, interior lighting, interiorequipment and fans were calculated, as well as total energy consumption.Fig. 4 shows results for all climates and analyzed facade types (four level models), where EUI isdepicted. All types of DSF performed better than the base case, single skin conventional curtain wall.Both the two level and four level DSFs demonstrate considerable energy savings when compared tothe base case models. However, there are slight variations between different types of DSF. But, thereare variations in performance based on climate subzone.Fig. 5 shows annual energy consumption for all climate types and facades, where heating, cooling,lighting, equipment and fan loads are presented. It should be noted that the lighting loads areidentical in all cases since the investigated models represented an office space that would be4 m deep. In all of these scenarios, sufficient amount of daylight would be available for the interiorspace. However, DSFs generally perform worse than single skin facades in providing daylight, sincethe two glazed skins reduce the amount of visible light that can be transmitted to the interior space.The author is currently investigating energy performance for a deeper office space to determine theeffects on lighting. The author is also investigating the effects of DSF typologies, orientations andair cavity depth on available daylight in different climate types, where daylight simulations are usedto compare performance of a conventional curtain wall and different DSF types. The results of thatresearch will be reported at a later time. However, there are significant variations in heating andcooling loads, depending on the climate and investigated facade types. There are slight variations inequipment and fan loads.These results indicate that all DSF types would improve energy performance compared to the basecase scenario (standard curtain wall). The energy savings vary depending on the climate type, aswell as the effects on heating and cooling loads. However, general trend that can be observed is thatin heating-dominated climates, heating loads are significantly reduced, as well as cooling loadssince DSFs have improved thermal performance. In cooling-dominated climates, cooling loads forthe interior space are also lower for scenarios with DSFs. This also relates to improved thermalperformance and lower heat transfer coefficients of DSFs compared to single skin. However, thestudy only considered natural ventilation for the air cavity and did not take into account mechanicalventilation of the air cavity when it may become overheated. If mechanical fans are used to exhaustair from the air cavity and assist natural stack effect in extremely hot weather, this would impact theoverall cooling loads.Results also show that there is very little variation in energy consumption between different typesof DSFs (box window, corridor type and multistory) for the analyzed south-oriented office space.Variations might be more prominent for a scenario that considers deeper space, since the effects ondaylight would be different due to different components and variations between these types of DSFs.The author is currently conducting a study to investigate energy consumption of these different typesof DSFs in larger office space, as well as the effects of different orientations (north, east, west andsouth), air cavity depth and sky conditions (sunny sky, intermediate and cloudy) on available daylight.Results will be reported in a future study.079JANUARY 19TH 2017 – MUNICH POWERSKIN CONFERENCE PROCEEDINGSThermal and Energy Performance of Double Skin Facades in Different Climate TypesTOC

Fig. 4 Energy modeling results, showing EUI for investigated DSFs and different climate types4CONCLUSIONSThe purpose of this research was to investigate thermal performance of different types of DSFs,and to investigate their effects on energy performance in all climate types. The research addressedseveral aspects: 1) thermal performance of different types of DSFs (box window, corridor type andmultistory); 2) the effects of outside temperature and solar radiation on air cavity temperature andairflow patterns within the air cavity of different types of DSFs; 3) energy performance of DSFs indifferent climate types; and 4) the effects of DSFs on heating and cooling loads.080JANUARY 19TH 2017 – MUNICH POWERSKIN CONFERENCE PROCEEDINGSThermal and Energy Performance of Double Skin Facades in Different Climate TypesTOC

Fig. 5 Energy modeling results, showing annual energy consumption for investigated DSFs and different climate typesResearch methods consisted of simulations and modeling, where different modeling techniqueswere used for specific parts of the study. Specifically, 2D heat transfer analysis was used toinvestigate thermal behavior of analyzed facade types under varying exterior temperatures, and tocalculate heat transfer coefficients. CFD analysis was used to determine 3D heat flow within the aircavity of investigated DSFs, as well as airflow patterns and air velocity. Energy modeling was usedto investigate energy performance, where south-oriented office space was modeled for all differentclimate types, which would be enclosed by the investigated facades. The base case considered singleskin facade, consisting of a standard curtain wall.081JANUARY 19TH 2017 – MUNICH POWERSKIN CONFERENCE PROCEEDINGSThermal and Energy Performance of Double Skin Facades in Different Climate TypesTOC

Results indicate that the components and the assembly of DSFs would affect their thermalperformance; however, lower U-values would be achieved compared to a standard curtain wall.Also, heat transfer analysis and CFD analysis results show temperature within the air cavity undervarious exterior temperature conditions. Comparison of 2D heat transfer and CFD analysis resultsindicated variations in results, which can be accounted to different calculation methods. Heattransfer analysis considers 2D convective heat transfer, while CFD analysis considers 3D heattransfer and takes into account radiation, convection and the effects of wind on naturally ventilatedsystem. CFD analysis results also show air flow patterns for investigated DSF types and undervarious exterior temperature conditions. CFD results demonstrated a consistent temperature changepattern for the analyzed DSFs, where higher temperatures would be present in the upper parts of theair cavity. However, airflow patterns would be different for investigated DSF types. Box window andcorridor DSFs exhibited higher turbulance within the air cavity, which would be caused by geometryand components, specifically horizontal divisions between floors (and vertical partitions in the caseof box window DSF). Moreover, different facade orientations would have different solar exposures,which should be taken into account during design process. This study considered south-orientedfacades, but impacts on the north, east and west orientations would be different. North orientationswould have lower solar exposure (in northern hempishere), while east orientation would have highersolar exposures in the morning, and west would have higher exposures in the afternoon. Shadingdevices can be incorporated within the air cavity to control solar heat gain, but they would impacttemperature and air flow patterns.Results of energy modeling showed that all DSF types would improve energy performance comparedto the base case scenario (standard curtain wall). However, the energy savings vary dependingon the climate type. In heating-dominated climates, heating loads are significantly reduced, aswell as cooling loads due to lower U-values of investigated DSFs. In cooling-dominated climates,cooling loads are also lower for DSFs. Results also indicate that there is very little variation inenergy consumption between different types of DSFs (box window, corridor type and multistory DSF)for the analyzed south-oriented office space. Variations might be more prominent for a scenariothat considers deeper office space, since the effects on daylight would be different due to differentcomponents and variations between various types of DSFs. The author is currently conducting astudy that considers these aspects, and the results will be reported at a later time.ReferencesAksamija, A. (2013). Sustainable facades: design methods for high-performance building envelopes. Hoboken: John Wiley & Sons.Pomponi, F., Piroozfar, P., Southall, R., Ashton, P., & Farr, E. (2016). Energy performance of double-skin façades in temperateclimates: a systematic review and meta-analysis. Renewable and Sustainable Energy Reviews, Vol. 54, pp. 1525-1536.Gratia, E., & De Herde, A., (2007). Are energy consumptions decreased with the addition of a double-skin?, Energy and Buildings,Vol. 39, pp. 605-619.Gelesz, A., & Reith, A., (2015). Climate-based performance evaluation of double skin facades by building energy modelling inCentral Europe, Energy Procedia, Vol. 78, pp. 555 – 560.Eicker, U., Fux, V., Bauer, U., Mei, L. & Infield, D., (2008). Facades and summer performance of buildings, Energy and Buildings, Vol.40, pp. 600–611.Guardo, A, Coussirat, M., Valero, C., & Egusquiza, E., (2011). Assessment of the performance of lateral ventilation in double-glazedfacades in Mediterranean climates, Energy and Buildings, Vol. 43 (2011): 2539–2547.Brandl, D., Mach, T., Grobbauer, M., & Hochenauer, C., (2014). Analysis of ventilation effects and the thermal behavior ofmultifunctional facade elements with 3d cfd models, Energy and Buildings, Vol. 85, pp. 305–320.NFRC (2004)

Thermal and Energy Performance of Double Skin Facades in Different Climate Types 2.2 COMPUTATIONAL FLUID DYNAMICS (CFD) ANALYSIS Computational Fluid Dynamics (CFD) analysis implements numerical simulation methods to seek solutions to fluid flow problems. For this study, Ansys Fluent 17.1 CFD simulation program was