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

More documents

Recommendations

Info

design. The depth of natural ventilation effectiveness in the single sided case is usually said to belimited to approximately 2.5 times the height of the space (Awbi 2003).In open floor plans, cross-ventilation can be considered when there are openings on two sides ofa space or building. In wind and combined wind-buoyancy driven cross ventilation flow, airenters through openings on one side of the building or space, traverses the space, and exitsthrough openings on another side of the building or space, or through the atrium or upper floors.In cross ventilation, the airflow will be driven by wind if there is no significant heightdifferential between inlet and outlet window openings and no vertical connection between floors.The airflow penetrates more deeply into the space than for single-sided ventilation, so the floorplans can be deeper. For cross-ventilation to work effectively, an open floor plan with fewinternal partitions is desired. The maximum depth of the space for effective ventilation by thismethod is said to be approximately five times the height of the space (Awbi 2003).Often atria are included in the design of naturally ventilated office buildings because they notonly increase the amount of natural daylight within the space, but also offer the potential tocontrol and passively enhance buoyancy-driven ventilation. An increase in atrium height canenhance the buoyancy-based ventilation. This enhancement can be obtained by providing anincreased height differential, and can be magnified by the use of glazing at the top of the atriumto increase the temperature of the air near the exhaust opening through solar gain. The use ofglazing makes the stack flow more effective due to the increase in buoyancy-driven flow.Additionally, in the winter the atrium can act as a buffer to the external environment. However,care must be taken when designing stack vents and atria, since the position of the opening canreduce or even reverse the impact of the stack flow.2.3.2 Window CharacteristicsIn naturally ventilated buildings purpose-provided openings allow fresh outside air to enter andexhaust air to exit a building in prescribed locations. Not only how the air enters and exits thebuilding, but also how much air enters, is impacted by the window type, its location, and itsorientation with respect to the dominant wind direction. Summer, spring and fall windconditions are usually of most concern to designers using natural ventilation techniques, asoccupant comfort is more dependent on passive ventilation to cool the building during monthswhen cooling is required.Each window type has its own effective opening area, or the percentage of the overall windowarea through which air can flow, and amount of leakage. Both of these factors can impact theselection of a window for a given climate and application. The three main types of windows aresliding, hinged, and rotating. These classifications also relate to the type of opening; simpleopening, vertical-vane opening, and horizontal-vane opening (Allard 2002). Windows that use atrack are either on a horizontal track, such as sliding windows, or a vertical track, as is the casewith hung windows. Track mounted windows are often referred to as simple openings. Sidehingedcasement windows or vertical-pivot windows pivot or hinge on the vertical axis.Horizontal-vane openings are similar to their vertical counterparts, except that the pivot or hingeis on the horizontal axis. Rotating windows can have either vertical or horizontal pivots, but thepivot is located at the center of the window, so that the window rotates about a central axis. Asummary of the window types and their characteristics is presented in Table 2 and Table 3.32
Table 2. Window Types by Opening TypeSliding Hinged (at edge) Rotating (center pivot)Simple openingXVertical vane X XHorizontal vane X XSimple opening windows do not tend to affect the airflow patterns of the entering air much,except near the window edges as the air is forced through the opening. However, withhorizontal-vane openings in particular, the airflow can be directed either upwards or downwards,depending on the location of the pivot or hinge. Horizontal-pivoted windows, with the pivotlocated in the center of the window offer a larger flow are than the other hinged or pivotedwindows, as air is able to enter the lower half, and exit at the upper half. For vertical-vaneopenings airflow pattern and velocity is mostly impacted in the horizontal direction, due to thelocation of the pivot or hinge.Table 3. Window Geometry and CharacteristicsWindow Geometry Relative Flow Area Ventilation EffectivenessHorizontal Pivot Larger flow area Very effective for single-sidedSide-Hung Smaller effective area Lower airflowVertical Pivot Smaller effective area Effective for directing windTop/Bottom Hung Smallest effective area Effective for single-sidedHorizontal/Vertical Sliding Larger flow area Effective for both types of ventilationAs discussed previously, the window or opening location can impact the type and effectivenessof the airflow rate. Windows that are at a single height are not as efficient for buoyancy drivenflow, as they have decreased height differential, unless very tall windows are used. Windows attwo heights, a lower and upper opening, have a larger potential for flow through a space. Stackopenings have the potential to enhance buoyancy-driven ventilation when designed correctly, i.e.taking into account the dominant wind direction, slope of the roof, and location of the opening onthe roof.The discharge coefficient, which takes into account the effect of contraction at a windowopening, affects the amount of uncertainty within modeling naturally ventilated windows. Thehydraulic resistance across an opening influences the airflow through that opening and dependson the geometry of the window and the Reynolds number. Normally, a discharge coefficient of0.6 is used, approximating the window as a sharp edged orifice (ASHRAE 2001). The majorityof research has been on a rectangular opening, and not other geometries, such as the awning typewindow (Karava 2004). The consensus for use with calculating flow rates through windows fornatural ventilation is 0.6±0.1, based on: full-scale experiments (Flourentzou 1998), analyticalcalculations (Andersen 2002), and experimental compared with numerical simulations(Fracastoro 2002). If the flow rate, pressure difference, and area are known, equations 2.11 and2.13 can be rearranged to calculate the discharge coefficient for a particular window geometry.2.3.3 Thermal MassThermal mass can be used for its capacity to store heating or cooling energy, depending on theseason. The use of heavy mass materials strategically placed in a building can reduce the amount33
Page 2 and 3: Thesis Committee:Leon R. Glicksman,
Page 4 and 5: Table of ContentsTable of Contents
Page 6 and 7: 7.1.3 Full Model Case .............
Page 8 and 9: Figure 41. Wind Direction Data for
Page 10 and 11: List of TablesTable 1. Energy End U
Page 12 and 13: Table 64. Comparison of Dimensionle
Page 15 and 16: Chapter 1.0IntroductionEnergy consu
Page 17 and 18: insulated building envelopes with t
Page 19 and 20: energy usage and efficient design.
Page 21 and 22: Figure 3. European Patent Office Bu
Page 23: 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 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 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 122 and 123:
Where V is the outlet velocity, A o
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
Page 160 and 161:
160
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
Page 172 and 173:
172
Page 174 and 175:
MODEL: K20-8SERIAL: 10047RECORDER_I
Page 176 and 177:
2 Boiler-3 50.00 C1 N1 1.0 ON ON OF
Page 178 and 179:
|PW|DESCRIP |KW |KWH|KVA|KVH|------
Page 180 and 181:
2:5 ;day_ofYr17:P30 ;EOT = 0.000075
Page 182 and 183:
2:3136:P30 ;DUM2 = -0.040891:-4.089
Page 184 and 185:
;7:21 ;input location;8:0 ;mulptipl
Page 186 and 187:
;79:P22 ;EXC w/DELAY (only for dela
Page 188 and 189:
1:45 ;port5 (homeSense)2:31 ;exit l
Page 190 and 191:
13:P95 ;ENDIF14:P95 ;ENDIF15:P3 ;pu
Page 192 and 193:
2:20 ;RH30:P70 ;sample1:12:20 ;RH31
Page 194 and 195:
194
Page 196 and 197:
Five Windows Open: Upper versus Low
Page 198 and 199:
One Window Open: Upper versus Lower
Page 200 and 201:
25 cm / 3 m 24.33 26.62 22.68 22.93
Page 202 and 203:
25 cm / 3 m 24.07 25.26 22.65 22.78
Page 204 and 205:
Two Stacks Open Temperature Stratif
Page 206 and 207:
Stacks Closed Temperature Stratific
Page 208 and 209:
2.3 24.31 24.65 24.781.4 23.35 23.6
Page 210 and 211:
0.6 20.56 20.67 20.94 21.22 21.41 2
show all

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

Create successful ePaper yourself

Delete template?

Save as template?