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

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Where V is the outlet velocity, A o is the area of the outlet, A S is the total surface area of themodel, U is the weighted average overall heat transfer coefficient of the model materials, and ΔTis the temperature difference between the outlet or exhaust temperature and the inlet temperature.The heat input, Q input , equals the heat loss due to advection (ρVA o ΔT) plus the heat loss due toconduction through the envelope (UA S ΔT). The heat loss due to advection uses the velocity andproperties of air at either the inlet or the outlet measurement locations, and the temperaturedifference in both parts of the equation is the inlet minus the ambient temperature. For the sevenwindows, three-stack case, the values needed for the calculation are provided in Table 28.Table 28. Data from the 7 Window, 3 Stack Single Heated Zone Model7 Windows, 3 StacksLower Windows Upper WindowsV inlet 0.6 m/s 0.75 m/sV outlet 0.7 m/s 0.8 m/sA inlet 0.0168 m 2 0.0168 m 2A outlet 0.016875 m 2 0.016875 m 2T inlet 13°C 13°CT outlet 36.3°C 36.9°CThe theoretical flow rate, Q, was calculated and compared to the measured velocities and airflowrates for the single heated zone experiment. The theoretical flow rate was calculated using anequation for two resistances in series for a simple model: TgH 1 o TiQ cd A1(7.5)2 A1 1 A2where A 1 is the inlet area, A 2 is the outlet area, and c d is the discharge coefficient, 0.6 for sharpedged orifices. The comparison of measured flow rates, Q, and theoretical flow rates, Theory Q,that do not account for the heat loss through the envelope, are presented in Table 29.Table 29. Air Velocities and Flow rates for Several Cases7 Windows 5 Windows 2 Windows# of Stacks 3 2 1 3 2 1 3 2 1V inlet (m/s) 0.6 0.7 0.9 0.4 0.5 0.8 0.4 0.5 0.6V outlet (m/s) 0.7 0.8 1 0.4 0.6 0.7 0.3 0.4 0.5Measured Q (m 3 /s) 0.0101 0.0118 0.0151 0.0068 0.0068 0.0039 0.0051 0.0045 0.0028Theory Q (m 3 /s) 0.0096 0.0079 0.0042 0.0066 0.0057 0.0037 0.0033 0.0030 0.0026For the 7 window, 3 stack case, two-thirds of the heat loss was due to advection, while theremaining one-third was due to heat conduction through the envelope of the model. As thenumber of openings decreased, the interior temperature in the model increased, and thepercentage of heat loss through the envelope increased.122
Table 30. Percentage of Heat Loss through Advection for Various Window and StackConfigurations for Single Zone Model7 windows(0.0168 m 2 )5 windows(0.012 m 2 )2 windows(0.0048 m 2 )3 stacks (0.016875 m 2 ) 74.57% 73.45% 71.98%2 stacks (0.01125 m 2 ) 59.84% 67.05% 63.08%1 stack (0.005625 m 2 ) 39.02% 44.04% 41.71%In the three stacks case, the outlet area was always greater than the inlet area, causing the inletarea to restrict the airflow. In the single stack case, it was the outlet area that restricted the flowfor the 3 window through 7 window cases. Only when one opening area was significantlysmaller than the other was a reduction in airflow apparent, as in the 7 windows, 1 stack case.The numerical models created to simulate the experimental case for the single heated zone modelprovided information on some of the limitations with the PHOENICS software package. Initialruns of the simulation modeled the reduced-scale air model, using the exact dimensions andinterior heat loads (heaters) as the physical model. However, as discussed in Chapter 4, there isno conduction through the envelope of the model in PHOENICS. This was apparent in the initialrun when the resulting numerical model had much higher internal temperatures than observed inthe experimental model. Surface temperature measurements were recorded for the single zonemodel, and the resulting heat loss through the main surfaces of the model determined. It wasfound that the main heat loss was through the atrium walls, as much as 69 percent of the totalheat loss in some cases. The heat losses due to conduction through the model envelope for thephysical model are presented in Table 32.The heat losses were calculated using the surface temperatures measured on the exterior of themodel, the floor and ceiling temperatures on the interior of the model, and air temperatures ineach interior zone and the air surrounding the model (the ambient air). The material propertiesobtained from ASHRAE 2001 Fundamentals were used to calculate an overall heat transfercoefficient for each separate wall construction. Two wall constructions were identified and theheat transfer coefficient and surface area determined (Table 31). From the heat transfercoefficient, surface area and temperature measurements, the relative heat loss for each surfacewas calculated.Table 31. Material Properties and Surface Areas for Heat Loss CalculationMaterialsU-Value Total Surface Location(W/m 2 K) Area (m 2 )1-layer Insulation board, MDF 0.38 7.2 All Walls, and Atrium1-layer Insulation board, MDF, batt-insulation 0.37 5.2 Ceiling and FloorThe atrium had the most surface area, primarily due to the north wall, and accounted for 34percent of the total surface area. However, the floors and ceilings of the heated zone were betterinsulated, and so contributed less to the overall heat loss for the model.123
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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
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2.2.1 Buoyancy-Driven VentilationVe
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Figure 7. Neutral Pressure Level fo
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Combined wind-buoyancy flow is more
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design. The depth of natural ventil
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of cooling required by 30 percent o
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considered when determining how the
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environmental conditions are examin
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As natural ventilation is prevalent
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Chapter 3.0Evaluation of Prototype
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Figure 12. Interior Atrium ViewFigu
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Table 8. Prototype Building Window
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Figure 15. HOBO® H8 Series Tempera
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Finally, airflow visualization was
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only is the airflow almost never at
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Table 10. Window Bag Device Measure
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Mon 7-21Tue 7-22Wed 7-23Thu 7-24Fri
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12:00 AM1:00 AM2:00 AM3:00 AM4:00 A
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27-Jul27-Jul28-Jul28-Jul29-Jul30-Ju
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A range of air exchange rates was f
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the windows on the second floor, or
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Total Electric (kWh/m2)Total Gas (k
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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 and 76: lower and upper openings and natura
Page 77 and 78: the acceptable diffusion rate, or
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 124 and 125: Table 32. Conduction Heat Loss for
Page 126 and 127: a) Air Modelb) Water ModelFigure 50
Page 128 and 129: Height from Floor (m)The temperatur
Page 130 and 131: Height from Floor (m)In the atrium
Page 132 and 133: First NorthUpper Window 0.17 m/s -0
Page 134 and 135: Height from Floor (m)the column at
Page 136 and 137: Height from Floor (m)Height from Fl
Page 138 and 139: Height from Floor (m)3.53.02.52.01.
Page 140 and 141: was less than 12 percent. These val
Page 142 and 143: Table 39. Variation of Outlet Wind
Page 144 and 145: temperature of the air was the same
Page 146 and 147: 3.532.521.55m/s4m/s3m/s2m/s1m/s1.5m
Page 148 and 149: 3.532.521.55m/s4m/s3m/s2m/s1m/s1.5m
Page 150 and 151: The average and exhaust internal bu
Page 152 and 153: Table 43. Calculated Wind and Buoya
Page 154 and 155: In the last two lines, for both the
Page 156 and 157: Figure 80. CFD Simulation of the Te
Page 158 and 159: uoyancy case the air from the groun
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Page 162 and 163: windows of naturally ventilated bui
Page 164 and 165: difficult to select the boundary co
Page 166 and 167: simulations are able to do would al
Page 168 and 169: Bordass, W.T., A.K.R. Bromley and A
Page 170 and 171: 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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