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1 Application of for Predicting Indoor Airflow and Thermal Comfort
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2 Preview Introduction CFD Theory Thermal Comfort Airpak Case Study Future Works
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3 Introduction Indoor environment design and assessment Airflow pattern, velocity, temperature, and contaminant concentration Indoor energy analysis Energy programs: uniform distribution of air temperature Complication: forced ventilation and natural ventilation
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4 Introduction Experimental measurements and computational simulations Advantages: Low cost, high speed, complete information, ability to simulate realistic conditions and ideal conditions. Disadvantages: fast computer with a large memory Computational Fluid Dynamics (CFD)
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5 Ventilation CFD Model Mass continuity Momentum (u, v, w) Temperature Species The Navier-Stokes equations
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6 Viscosity Models Laminar flow ( Re < 2500 ) Turbulent flow ( Re>= 2500 ) Model Standard ModelRNG Mixing-length model Indoor zero-equation model Computing time Low High Accuracy Low High
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7 CFD Elements Mathematical Description of the Problem of Interest Flux LawsConservation PrinciplesMathematical Models Numerical Method Computer Programs Numerical Predictions Post Processing Tools Interpretation Grid or Mesh Generation Methods Problem Parameters Finite Volume Formulations Finite Element Formulations
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8 Thermal Comfort ASHRAE thermal sensation scale: + 3 Hot + 2 Warm + 1 Slightly Warm 0 Neutral - 1 Slightly Cold - 2 Cool - 3 Cold ASHRAE Summer and Winter Comfort Zone: wintersummer Humidity ratio, g/kg Dew point temperature 0 C Operative temperature (ASHRAE standard 55)
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9 PMV (Predicted Mean Vote) PPD (Predicted Percentage of Dissatisfied) PMV -0.50.5 10 20 PPD % -0.8 0 0.8 5 -1.5 -2.01.52.0 30 50 80 ( ASHRAE Fundamental, 2001)
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10 1.Airflow patterns 2.Air turbulence 3.Contaminant transport 4.Temperature and humidity distribution 5.Thermal comfort 6.Room pressurization 7.Equipment effects 8.Process exhaust Is a virtual prototyping CFD software that lets you evaluate and understand your ventilation system performance. FLUENT
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11 1. Building Objects
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12 2.Physical Modeling and Boundary Conditions Steady or Transient ? Laminar or Turbulent ? Solving variables? Physical models? Initial conditions? Boundary Conditions?
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13 3. Meshing Mesh quality is important!!! Generate first mesh Examine the mesh Re-examine the mesh 1.Flow objects 2.Local mesh control 3.Object-specific meshing control Refine the mesh Generate new mesh Solve OK No 1.Aspect ratio 2.Face alignment 3.Volume
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14 4. Solving the Problem 1.Maximum number of iterations 2.Convergence criteria 3.Discretization scheme 4.Under-relaxation factors Setup: 1.Accuracy of physical models 2.Accuracy of boundary conditions 3.Accuracy of the modeling assumptions 4.Numerical scheme 5.Resolution of mesh Accuracy depends on:
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15 Case study Ben Edward
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16 Case study (a) Computer 108 w People 73 w Induction Unit 40 L/s, 21 0 C Light 120 w 53 L/s, 15.8 0 C 12 L/s 23 L/s 28 L/s Outlet vent Ben 04/06/2003
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17 Temperature 04/06/2003,Cooling
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18 Sensor 3 Sensor 4 Sensor 1 Sensor 2 x z Temperature Validation Ben 5% 2%4% 6% Sensor 04/06/2003
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19 PMV Y = 1.1 m x z Ben 04/06/2003
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20 Airflow Ben 04/06/2003
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21 z y Airflow BenEd
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22 x y Airflow Ed
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23 Case study (b)
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24 Slot diffuser Nozzle diffuser Temperature Comparison
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25 Slot diffuser Nozzle diffuser Airflow Comparison
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26 PMV Comparison Slot diffuser Y = 1.1 m x z Nozzle diffuser Ben
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27 Next! Displacement ventilation www.rehva.com Mixing ventilation www.haltoncompany.com Underfloor ventilation www.york.com Occupied Zone
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28 Recommendations for future works Energy Simulation Program $$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$ + $ $$$$$ $$ $$$$$$$$$$$$$$$$ $$$$$$ $$$$$$$$$$$$$$$$ $$$ $$$$$ = 1. Cost Analysis
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29 Recommendations for future works 2. Office Space Template
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30 Personal Inlet Diffuser Outlet
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31 Airflow Temperature Relative Humidity Indoor Air Quality Thermal Comfort Energy Simulation Program $$$ Cost Analysis A tool to assist Real Property Operations in improving the quality of indoor office environments and reducing energy waste.
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32 Thanks!
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