CFD in Ventilation, case studies from REHVA CFD guidebook

Transcription

1 CFD in Ventilation, case studies from REHVA CFD guidebook by Peter V. Nielsen Aalborg University Peter V. Nielsen, Aalborg University 1

2 Outline of Lecture Study of ideas behind the air distribution in the Danish Pavilion in Seville Design of the air distribution in an office based on mixing ventilation, vertical ventilation, displacement ventilation or a ceiling-mounted radial diffuser Direct simulation of an air inlet diffuser and room air distribution Evaluation of the air distribution system in a library hall Benchmarks Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 2

3 The Danish Pavilion at the World Exposition EXPO 92 The idea behind the ventilation system is to use an extract fan in the north top of the exhibition hall (smoke ventilation) and flow through cooling elements in the south gable. CFD makes it possible to give an estimate of the downdraught from the 12 m high diffuser in the gable. Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 3

4 The Danish Pavilion at the World Exposition EXPO 92 Be careful if you use a 2D prediction for a 3D problem. Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 4

5 Outline of Lecture Study of ideas behind the air distribution in the Danish Pavilion in Seville Design of the air distribution in an office based on mixing ventilation, vertical ventilation, displacement ventilation or a ceiling-mounted radial diffuser Direct simulation of an air inlet diffuser and room air distribution Evaluation of the air distribution system in a library hall Benchmarks Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 5

6 Case Studies of Different Air Distribution Systems Five air distribution systems are compared with each other. They are all installed in the same room, and they all handle the same situation and the same load. Peter V. Nielsen, Aalborg University 6

7 The Test Room The test room is the IEA Annex 20 room with length, width and height equal to 4.2 m, 3.6 m and 2.5 m. The heat load consists of two PCs, two desk lamps and two manikins producing a total heat load of 480 W. One work place is used in some of the experiments (240 W). Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 7

8 CFD Model Radiation is ignored Convection is estimated to be 50% of total heat flux Wall, ceiling and floor Surface temperature Manikins, PCs and lamps Fixed heat flux Peter V. Nielsen, Aalborg University 8

9 Simulation of Air Terminal Units Inlet opening and an Air Terminal Unit The flow from a diffuser depends on small details. The numerical prediction method should be able to handle small details in dimensions of one tenth of a millimeter as well as dimensions of several meters. Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 9

10 Case Study, Mixing Ventilation with Wall-Mounted ATD Peter V. Nielsen, Aalborg University 10

11 Simulation of the Diffuser Diffuser A 0.68 m m Diffuser B m 0.68 m m Diffuser C m Diffuser A x=3.0 m Diffuser B x=3.0 m Diffuser C x=3.0 m z (m) z (m) z (m) u (m/s) u (m/s) u (m/s) Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 11

12 Mixing Ventilation with End Wall Mounted Diffuser 1 st order steady state equations, k-ε turbulence model, 10 6 cells, Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 12

13 Case Study, Displacement Ventilation Peter V. Nielsen, Aalborg University 13

14 Diffuser for Displacement Ventilation a z x d 2 z x 1 b 2 45 z 1 x e 3 2 z x c z x Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 14

15 Displacement Ventilation Case: c Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 15

16 Displacement Ventilation Case: d Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 16

17 Case Study, Vertical Ventilation Peter V. Nielsen, Aalborg University 17

18 Vertical Ventilation, Diffuser A D B E C F Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 18

19 Vertical Ventilation, Diffuser 1st order steady state equations, k-ε turbulence model, 300,000 cells. Predictions in half of the room Peter V. Nielsen, Aalborg University 19

20 Vertical Ventilation BC: Diffuser F Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 20

21 Vertical Ventilation, Quality Control Monitoring points Velocity in y-direction Peter V. Nielsen, Aalborg University 21

22 Vertical Ventilation Predictions of the whole room n = 5 h grid points Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 22

23 Case Study, Mixing Ventilation with Ceiling-Mounted ATD Peter V. Nielsen, Aalborg University 23

24 Mixing Ventilation with Ceiling Diffuser, Diffuser Models Four-way diffuser Fixed flow diffuser Diffuser with horizontal surface Peter V. Nielsen, Aalborg University 24

25 Diffuser Models Measurements Four-way diffuser Peter V. Nielsen, Aalborg University 25

26 Diffuser Models Fixed flow diffuser Diffuser with horizontal surface Peter V. Nielsen, Aalborg University 26

27 CFD Simulations Temperatures Peter V. Nielsen, Aalborg University 27

28 CFD Simulations Maximum velocity at 1.80 m (top boundary of the occupied zone) Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 28

29 Steady and/or Unsteady Flow Measurements in ceiling region n = 6.02 h -1 n = 3.25 h -1 Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 29

30 Simulation of Unsteady Flow (Time Dependent Equations) y-velocity at 1.80 m y-velocity at different positions n = 3.25 h -1 Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 30

31 Outline of Lecture Study of ideas behind the air distribution in the Danish Pavilion in Seville Design of the air distribution in an office based on mixing ventilation, vertical ventilation, displacement ventilation or a ceiling-mounted radial diffuser Direct simulation of an air inlet diffuser and room air distribution Evaluation of the air distribution system in a library hall Benchmarks Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 31

32 Direct Description of a Diffuser, 1 Diffuser Rectangular cells and multigrid structure, case 1 Unstructured grid, case 2 Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 32

33 Direct Description of a Diffuser, 2 Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 33

34 Direct Description of a Diffuser, 3 CFD simulation of the diffuser based on fine unstructured grid. Prediction based on the PV method. Velocity values are given from the diffuser simulation. Kondo et al Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 34

35 Outline of Lecture Study of ideas behind the air distribution in the Danish Pavilion in Seville Design of the air distribution in an office based on mixing ventilation, vertical ventilation, displacement ventilation or a ceiling-mounted radial diffuser Direct simulation of an air inlet diffuser and room air distribution Evaluation of the air distribution system in a library hall Benchmarks Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 35

36 The Regional Library of Northern Jutland The Regional Library of Northern Jutland is used as a test building where a combination of BEPS and CFD is used for prediction of energy consumption and indoor climate. = Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 36

37 Contaminant Distribution Peter V. Nielsen, Aalborg University 37

38 Outline of Lecture Study of ideas behind the air distribution in the Danish Pavilion in Seville Design of the air distribution in an office based on mixing ventilation, vertical ventilation, displacement ventilation or a ceiling-mounted radial diffuser Direct simulation of an air inlet diffuser and room air distribution Evaluation of the air distribution system in a library hall Benchmarks Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 38

39 Peter V. Nielsen, Aalborg University 39

40 The Background for the 2D Case Urbach (1971) Ego (1970) Scwenke (1975) Restivo (1979) Peter V. Nielsen, Aalborg University 40

41 Exampleof the Useof the Benchmark Streamlines: k-ε, k-ω, k-ω BSL, k-ω SST models k-ε model k-ω model k-ω BSL model k-ω SST model Peter V. Nielsen, Aalborg University 41 Rong and Nielsen

42 Peter V. Nielsen, Aalborg University 42

43 The Idea behind a Benchmark for a Virtual CFD Person Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 43

44 Simulation of a Person How detailed should we make the geometry? Manikin made by 10,000 grid points. Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 44

45 Peter V. Nielsen, Aalborg University 45

46 Computer Simulated Person, Thermal Comfort Nilsson et al. (2007) Peter V. Nielsen, Aalborg University 46

47 CFD in Ventilation Design Computational fluid dynamics in a nutshell Symbols and glossary Mathematical background Turbulence models Numerical methods Boundary conditions Quality control CFD combined with other prediction models Application of CFD codes in building design Case studies Benchmark tests Thank you! Peter V. Nielsen, Aalborg University pvn@civil.auc.dk 47