Methodology for the Evaluation of Natural Ventilation in ... - Cham

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It is more common to compare similar reduced-scale models with full-scale prototypes, asChandra et al. (1983) did in investigating the natural wind on a 1/25 th scale clear plastic modelwith the full-scale prototype building next to it. Also common are wind tunnel investigations ofairflow due to wind-driven ventilation.Wind tunnel experiments examine the pressure fields on the façades and the internal flows.Ernest et al (1991) compared both internal and external measurements of a reduced-scale modelin a wind tunnel to determine indoor air motion as a function of wind direction. Depending onthe scale and the model construction materials, the determination of flow patterns can be donethrough flow visualization or measurements. When comparing the scaled wind models to theprototype, one common issue is the variation of the wind speed and direction that is experiencedby the prototype building versus the normally constant wind speed controlled in the test chamberor wind tunnel. Depending on the frequency of the data measurements, some wind tunnels areoutfitted with a turntable, so that the direction of approach of the wind speed can be varied, asdone by Dutt et al (1992).4.1.6 Combined Buoyancy-Wind ModelingCloser to the actual building case, is the more complex combined wind and buoyancy drivenflow. The wind direction in this case has a significant impact on the flow direction through theopenings. The wind force can either work with or against the buoyancy force. Li and Delsante(2001) presented the analytical solutions to this complex natural ventilation case, and determinedthe stable solutions based on the strength of the heat source and wind. Salt-water models (Huntand Linden 1996, 1997, 2001) have been used extensively to evaluate combined ventilation toprovide quantitative results, including flow velocities and densities. Their model is for a simplesingle space configuration with multiple upper and lower openings. Additionally, some workhas been completed using CFD simulations to evaluate the combined buoyancy and wind forcesin a naturally ventilated building as a method for validating heated water models (Heiselberg etal. 2004). They furthered the analysis by investigating the effect of wind direction in enhancingor hampering the effectiveness of the flow through a simple space.Combined buoyancy-wind driven natural ventilation is complex, with some concern over howbest to model and analyze this complex case. As described in Chapter 2, it is often not as simpleas adding the equations of each type of ventilation. Nevertheless, combined buoyancy-windventilation occurs most often in real world applications, and therefore is an important scenario tocarefully model and understand for application to full-scale buildings.4.2 Flow VisualizationMeasuring airflow at inlet and outlet openings and temperature distribution is not enough tocomprehend fully the airflow patterns within the space or interactions between spaces within abuilding. Flow visualization has historically been used to understand complex fluid flowpatterns. In buildings, it plays an important role. In naturally ventilated buildings, this isparticularly true in understanding how air will enter, flow through, and exit a space, floor, andbuilding. These different scales of airflow require different characteristics in the media used tovisualize the flow patterns. The application and scale of the space being evaluated and fluid usedin scale modeling have a significant impact on the visualization technique used. Issues such as76
the acceptable diffusion rate, or ‗hang-time‘, are of importance and are influenced by both theamount of air movement in the space and the volume of the space. The fluid of the space beinganalyzed also will affect the selection of media used for flow visualization. This chapter willdiscuss current practices for applications used in analyzing buildings, and then describe theselection of media used in both the prototype building analysis and the reduced-scale air model.4.2.1 Principles of Flow VisualizationThere are three main aspects of flow visualization, application and scale, media selection andparticle seeding, and visualization and imaging. Qualitative flow visualization experimentscombined with quantitative measurements provide a more comprehensive analysis into the flowphenomena being investigated. The principles in selecting an appropriate flow visualizationtechnique will be discussed, with an overview of the issues that can arise with using thesemethods, each of which was evaluated when the final flow visualization method was selected forapplication in the building and reduced-scale model.Flow visualization is comprised of several important components necessary to not only visualizethe flow, but also capture it for further analysis. This includes marking the fluid flow,illuminating the flow field, and imaging of the flow pattern. Marking the fluid occurs in a varietyof ways, most commonly through the use of dyes in water models and smoke with air models.Important aspects arise when applying these techniques to either water or air models, such asdiffusion of the marking material and neutral buoyancy. If either of these issues is not addressed,the results of the flow visualization can be inconclusive.When a foreign substance is used, visualizing the movement of the substance rather than thefluid itself, it is considered an indirect method of flow visualization. It is assumed that if thetracer material is neutrally buoyant and its particle size small enough then it is accuratelyrepresenting the fluid flow being studied. This method is applicable to the building fluid flowapplication under investigation, both at various scales and using different fluids. However, thismethod is only applicable to steady flows, because with unsteady flows the size of the particlesbecomes more of an influencing factor (Merzkirch 1987). Under steady flows, the particles areselected for visibility and weight neutrality for a particular condition; however with unsteadyflows, the particles must be sized for the slowest velocities, while taking into account rate ofdiffusion to ensure visibility. The tracer material used will also vary depending on the fluid usedin the modeling. In water, dyes are often used, providing high impact visualization of fluid flowpatterns, while keeping the tracer material neutrally buoyant. This is assisted by the constructionof the reduced-scale water models with Plexiglas.The size of the individual particles in the media selected for use in airflow visualization is criticalto its effectiveness in accurately portraying the flow under analysis. The media introduced isused to analyze the flow velocity based on the movement of the foreign particles in the flowmedia. In order to track the flow under investigation accurately, the particles must besufficiently small so that the flow is not disrupted and the movement of the particles imitates themotion of the flow. The media can be introduced either at a single point or at multiple pointssimultaneously.77
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Thesis Committee:Leon R. Glicksman,
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Table of ContentsTable of Contents
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7.1.3 Full Model Case .............
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Figure 41. Wind Direction Data for
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List of TablesTable 1. Energy End U
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Table 64. Comparison of Dimensionle
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Chapter 1.0IntroductionEnergy consu
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insulated building envelopes with t
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energy usage and efficient design.
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Figure 3. European Patent Office Bu
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selecting boundary conditions) to e
Page 26 and 27: 2.2.1 Buoyancy-Driven VentilationVe
Page 28 and 29: Figure 7. Neutral Pressure Level fo
Page 30 and 31: Combined wind-buoyancy flow is more
Page 32 and 33: design. The depth of natural ventil
Page 34 and 35: of cooling required by 30 percent o
Page 36 and 37: considered when determining how the
Page 38 and 39: environmental conditions are examin
Page 40 and 41: As natural ventilation is prevalent
Page 43 and 44: Chapter 3.0Evaluation of Prototype
Page 45 and 46: Figure 12. Interior Atrium ViewFigu
Page 47 and 48: Table 8. Prototype Building Window
Page 49 and 50: Figure 15. HOBO® H8 Series Tempera
Page 51 and 52: Finally, airflow visualization was
Page 53 and 54: only is the airflow almost never at
Page 55 and 56: Table 10. Window Bag Device Measure
Page 57 and 58: Mon 7-21Tue 7-22Wed 7-23Thu 7-24Fri
Page 59 and 60: 12:00 AM1:00 AM2:00 AM3:00 AM4:00 A
Page 61 and 62: 27-Jul27-Jul28-Jul28-Jul29-Jul30-Ju
Page 63 and 64: A range of air exchange rates was f
Page 65 and 66: the windows on the second floor, or
Page 67 and 68: Total Electric (kWh/m2)Total Gas (k
Page 69 and 70: movement, Houghton Hall has much le
Page 71 and 72: Chapter 4.0Modeling and Visualizati
Page 73 and 74: for future design of similar type b
Page 75: lower and upper openings and natura
Page 79 and 80: applications involving full-scale b
Page 81 and 82: digital camera with both manually o
Page 83 and 84: Chapter 5.0Dimensional Analysis and
Page 85 and 86: u oHgHT2uocu Hpo1Re Ar1Re Pr(5.7)(5
Page 87 and 88: X HM X HP(5.16)5.3.2 Kinematic Sim
Page 89 and 90: Radiation was found to have an impa
Page 91: height is used for the full-scale b
Page 94 and 95: 6.3 Model Descriptions6.3.1 Physica
Page 96 and 97: Figure 30. Floor Plan of the Protot
Page 98 and 99: Figure 31. North Facade of Model wi
Page 100 and 101: Monitoring data collected from the
Page 102 and 103: By default, there was no accounting
Page 104 and 105: 40-location card inserted into the
Page 106 and 107: 6.5 ExperimentsTo evaluate the mode
Page 108 and 109: modified to determine the impact of
Page 110 and 111: Figure 39. Two Heated Zone ModelWit
Page 112 and 113: minute interval, the model was assu
Page 114 and 115: Figure 42. Cross-Section of Wind-Ge
Page 116 and 117: Table 25. Wind-Assisted Ventilation
Page 118 and 119: Figure 44. Heaters and Zones for a)
Page 120 and 121: Height from Floor (m)Height from Fl
Page 122 and 123: Where V is the outlet velocity, A o
Page 124 and 125: Table 32. Conduction Heat Loss for
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a) Air Modelb) Water ModelFigure 50
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Height from Floor (m)The temperatur
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Height from Floor (m)In the atrium
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First NorthUpper Window 0.17 m/s -0
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Height from Floor (m)the column at
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Height from Floor (m)Height from Fl
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Height from Floor (m)3.53.02.52.01.
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was less than 12 percent. These val
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Table 39. Variation of Outlet Wind
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temperature of the air was the same
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3.532.521.55m/s4m/s3m/s2m/s1m/s1.5m
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3.532.521.55m/s4m/s3m/s2m/s1m/s1.5m
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The average and exhaust internal bu
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Table 43. Calculated Wind and Buoya
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In the last two lines, for both the
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Figure 80. CFD Simulation of the Te
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uoyancy case the air from the groun
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160
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windows of naturally ventilated bui
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difficult to select the boundary co
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simulations are able to do would al
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Bordass, W.T., A.K.R. Bromley and A
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Linddament, M. 1996. Why CO2? Air I
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172
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MODEL: K20-8SERIAL: 10047RECORDER_I
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2 Boiler-3 50.00 C1 N1 1.0 ON ON OF
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|PW|DESCRIP |KW |KWH|KVA|KVH|------
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2:5 ;day_ofYr17:P30 ;EOT = 0.000075
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2:3136:P30 ;DUM2 = -0.040891:-4.089
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;7:21 ;input location;8:0 ;mulptipl
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;79:P22 ;EXC w/DELAY (only for dela
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1:45 ;port5 (homeSense)2:31 ;exit l
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13:P95 ;ENDIF14:P95 ;ENDIF15:P3 ;pu
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2:20 ;RH30:P70 ;sample1:12:20 ;RH31
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194
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Five Windows Open: Upper versus Low
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One Window Open: Upper versus Lower
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25 cm / 3 m 24.33 26.62 22.68 22.93
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25 cm / 3 m 24.07 25.26 22.65 22.78
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Two Stacks Open Temperature Stratif
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Stacks Closed Temperature Stratific
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2.3 24.31 24.65 24.781.4 23.35 23.6
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0.6 20.56 20.67 20.94 21.22 21.41 2
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