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Lecture Objectives

Lecture Objectives. Ventilation Effectiveness Thermal Comfort Meshing . IAQ parameters. Age-of-air air-change effectiveness (E V ) Specific Contaminant Concentration contaminant removal effectiveness e. Single value IAQ indicators E v and ε. Contaminant removal effectiveness ( e )

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Lecture Objectives

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  1. Lecture Objectives • Ventilation Effectiveness • Thermal Comfort • Meshing

  2. IAQ parameters • Age-of-air air-change effectiveness (EV) • Specific Contaminant Concentration contaminant removal effectiveness e

  3. Single valueIAQ indicatorsEv and ε • Contaminant removal effectiveness (e) • concentration at exhaust • average contaminant concentration Contamination level • 2. Air-change efficiency (Ev) • shortest time for replacing the air • average of local values of age of air Air freshness

  4. Depends only on airflow pattern in a room We need to calculate age of air (t) Average time of exchange What is the age of air at the exhaust? Type of flow Perfect mixing Piston (unidirectional) flow Flow with stagnation and short-circuiting flow Air-change efficiency (Ev)

  5. Air exchange efficiency for characteristic room ventilation flow types

  6. Contaminant removal effectiveness (e) • Depends on: • position of a contaminant source • Airflow in the room • Questions 1) Is the concentration of pollutant in the room with stratified flow larger or smaller that the concentration with perfect mixing? 2) How to find the concentration at exhaust of the room?

  7. Ev= 0.41 e= 0.19 e= 2.20 Differences and similarities of Evande Depending on the source position: - similar or - completely different air quality

  8. Thermal comfort Temperature and relative humidity

  9. Thermal comfort Velocity Can create draft Draft is related to air temperature, air velocity, and turbulence intensity.

  10. Thermal comfort Mean radiant temperature potential problems Asymmetry Warm ceiling (----) Cool wall (---) Cool ceiling (--) Warm wall (-)

  11. Prediction of thermal comfort • Predicted Mean Vote (PMV) • + 3 hot • + 2 warm • + 1 slightly warm • PMV = 0 neutral • -1 slightly cool • -2 cool • -3 cold • PMV = [0.303 exp ( -0.036 M ) + 0.028 ] L • L - Thermal load on the body • L = Internal heat production – heat loss to the actual environment • L = M - W - [( Csk + Rsk + Esk ) + ( Cres + Eres )] • Predicted Percentage Dissatisfied (PPD) • PPD = 100 - 95 exp [ - (0.03353 PMV4 + 0.2179 PMV2)] Empirical correlations Ole Fanger Further Details: ANSI/ASHRAE standard 55, ISO standard 7730

  12. outlet inlet outlet T1=30C T1 inlet outlet inlet T2 T2=20C Meshing (Project 1) Pat a) Numerical diffusion The purpose of this project part is to analyze how mesh size and orientation affects the accuracy of result.

  13. Grid type and resolution Hexa • Uniform hexa • Nonuniform hexa • Unstructured hexa Body-fitted coordinate hexa - Structured • Unstructured Tetra mesh • Structured • Unstructured Polyhedral mesh

  14. Grid type and resolutionhexa Unstructured hexa (2-D) Uniform boundary-fitted, structured grid Nonuniform (2-D)

  15. Grid type and resolutionTetra Structured Unstructured

  16. Grid type and resolutionPolyhedral mesh

  17. Computational resource saving by mesh type

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