Wind Analogue or Digital?

Transcription

1 CONSULTING ENGINEERS & SCIENTISTS Wind Analogue or Digital? CIBSE Building Simulation Group and Natural Ventilation Group 30 th April 2014 Wayne Pearce Principal, Regional Manager (UK) David Hamlyn Senior Engineer Canada China Hong Kong India Singapore UK USA CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT rwdi.com

2 Contents About RWDI Wind Engineering Comparison of CFD and Experimental Methods Modelling Challenges Accuracy Purpose of Analysis Costs and Time Regulation Other Approaches Case Study Examples Masterplanning Exhaust Re-Entrainment Conclusions

3 About RWDI

4 About RWDI Headquarters in Guelph, Ontario Established in employees Office Locations Project Experience

5 About RWDI Our Activities Structure Masterplanning Facades External Spaces Energy Consumption Comfort Internal Spaces Concept Design Detailed Design Cladding Wind Loads Pedestrian Comfort Structural Wind Loads Exhaust Reentrainment Daylighting Wind Pressure Ventilation Sand and Dust Issues Aeroacoustics Snow and Ice Studies Glare Stack Effect Rain Ingress Studies

6 About RWDI a selection of what we do Design Advice / Consultation Physical Scale Modeling (Wind Tunnel / Water Flume) Computer Modelling On-site Monitoring & Measurement

7 About RWDI Don t think of the wind as something that creates problems that need to be solved consider all the issues at a concept stage and design to take advantage of the wind

8 Selected Projects

9 Wind Engineering Comparison of CFD and Experimental Methods

10 CFD or Experiment in Wind Engineering?.OR BOTH? CFD or experiment?.or SOMETHING ELSE? Consider APPROPRIATENESS in terms of: Technical suitability Purpose of analysis, now and future? Costs and speed Regulation and best practice We use both approaches, but not for the same things!

11 Modelling Challenges : Scale weather CFD Global ~ 10,000 km Synoptic ~ 1,000 km Meso ~ 100 km City ~ 10 km wind tunnel Neighbourhood~ 1 km Building ~ 0.1 km Occupant ~ 0.01 km 11

12 Modelling CHARACTERISTICS Challenges OF Variability THE WIND of Wind Wind Roses Regional Variation Calm Light air Light breeze Gentle breeze Moderate breeze Fresh breeze Strong breeze Squires Gate London Annual variability requires modelling full 360 wind environment Substantial overhead in CFD

13 Modelling Challenges Depiction of Wind Synoptic winds height profiles 300 Effective height (m) Mean Speed Town Country Sea 300 Shear Turbulence Terrain Roughness Gust Speed Mean wind speed factor 300 Effective height (m) Town Country Sea 250 Town 50 Effective height (m) Sea Country s gust wind speed factor 50 Turbulence Turbulence intensity factor

14 Gustiness Modelling Challenges Depiction of Wind Gustiness 15 ORIGINAL ACTUAL 10 5 WINDSPEED TIME Variability better represented in wind tunnel Critical example: Helipad studies

15 Accuracy Wind Tunnel An analogue computer Unlimited resolution mesh is automatically generated Full turbulence modelling Short run times to converge CFD On a digital computer Mesh resolution limited and requires generation process Simplified turbulence modelling Convergence times can be long Required accuracy will depend on purpose of analysis. Spurious statistics: Config x θ x locations x Sample = ca. 450,000,000 data points / study

16 Purpose of Analysis Scoping Analysis / Parametric Studies CFD easily altered, can be run quickly to evaluate directions of concern

17 Purpose of Analysis CFD convenient for combining wind and other climate modelling Provides excellent visualisation for early stage parametric analysis Example: Masterplanning

18 Purpose of Analysis Detailed assessment for planning best practice accuracy needed Capturing and adjusting fine detail challenging in CFD Examining statistical wind environment expensive in CFD Balconies and Landscaping Fine Detail Wind Mitigation Measures

19 Costs and Time Wind Tunnel Model more costly Short and low-cost running times CFD Lower cost for model Longer, more costly running times Phasing or Fine tuning model adaptations quick to run Adaptations slow - require remeshing/running Full 360 wind environment at 10 resolution quickly Multiple directions increase cost very substantially Wind tunnel experiments often thought of as costly but Costs reduced via modern data capture and processing techniques Cost often less than equivalent CFD for all but simple scoping runs

20 Regulation Generally, regulation not prescriptive in terms of methodology Advantages Promotes development of new techniques Disadvantages Technologies may be misused Detailed wind engineering regulatory requirements more easily proved by experiment than CFD (e.g. Lawson comfort criteria for pedestrian wind studies)

21 Other Approaches - Example

22 Other Approaches - Example Desk Study Pedestrian Comfort T T93 T95 T T94 T T T Sitting Standing/En Leisure walk Business wa Car park/roa N 88 LAWSON COMFORT CRITERIA (Worst case season): Proposed Development Notes: Locations T93 -T97, T99- T101 are on Terraces (marked with red circle) Locations 2-92 are on Ground level

23 Other Approaches - Example Desk Study Pedestrian Comfort Sitting Standing/En Leisure walk Business wa Car park/roa N Courtyards suitable for sitting in BOTH studies LAWSON COMFORT CRITERIA (Worst case season): Proposed Development Notes: Locations T93 -T97, T99- T101 are on Terraces (marked with red circle) Locations 2-92 are on Ground level T T93 T95 T T94 86 T T T

24 Other Approaches - Example Desk Study Pedestrian Comfort Sitting Standing/En Leisure walk Business wa Car park/roa N Corners suitable for strolling in BOTH studies LAWSON COMFORT CRITERIA (Worst case season): Proposed Development Notes: Locations T93 -T97, T99- T101 are on Terraces (marked with red circle) Locations 2-92 are on Ground level T T93 T95 T T94 86 T T T

25 Other Approaches - Example Desk Study Pedestrian Comfort Sitting Standing/En Leisure walk Business wa Car park/roa N Corners suitable for mix of business walking, strolling LAWSON COMFORT CRITERIA (Worst case season): Proposed Development Notes: Locations T93 -T97, T99- T101 are on Terraces (marked with red circle) Locations 2-92 are on Ground level T T93 T95 T T94 86 T T T

26 Other Approaches - Example Desk Study Pedestrian Comfort Sitting Standing/En Leisure walk Business wa Car park/roa N Predicted strolling calmer in reality LAWSON COMFORT CRITERIA (Worst case season): Proposed Development Notes: Locations T93 -T97, T99- T101 are on Terraces (marked with red circle) Locations 2-92 are on Ground level T T93 T95 T T94 86 T T T

27 Case Study Example Case Study: Using CFD to Examine Masterplan Microclimate

28 Masterplanning - Why Examine Urban Microclimate? How People Perceive Climate 4 Comfort is a complex phenomena It varies from person to person A combination of four environment variables Wind speed Temperature RH Radiant temperatures (solar impact, hot surfaces) SPMV* Hot Warm Slightly Warm Neutral Slightly Cool Cool Cold Plus personal factors Clothing levels Activity Other parameters like gender, height have a lesser role.

29 Masterplanning How to Improve Comfort Layout & Orientation Limited cross flow Broken lines encourage wind flow into side streets East-West main streets are in direct sun all day during the summer months This orientation allows maximum self-shading. Main streets encourage penetration of prevailing winds

30 Typical Study Requirements - Masterplanning Scoping level Identify main factors, make improvements Ease of visualisation important for client High-level decisions Not for regulatory purposes Desk-based assessment or CFD appropriate

31 Berlin Aerial Image of Site CONSULTING ENGINEERS & SCIENTISTS Canada China Hong Kong India Singapore UK USA CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT rwdi.com

32 Berlin Development CONSULTING ENGINEERS & SCIENTISTS Canada China Hong Kong India Singapore UK USA Modelling carried out combining CFD, solar modelling and statistical meteorological records CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT rwdi.com

33 Berlin Wind Speed CONSULTING ENGINEERS & SCIENTISTS Canada China Hong Kong India Singapore UK USA Annual mean wind speed (all directions) low high CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT rwdi.com

34 Berlin Solar Exposure CONSULTING ENGINEERS & SCIENTISTS Canada China Hong Kong India Singapore UK USA Sky view factors annual average low high CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT rwdi.com

35 Berlin Thermal Comfort CONSULTING ENGINEERS & SCIENTISTS SPMV* Canada China Hong Kong India Singapore UK USA worse comfort CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT better rwdi.com

36 Berlin Wind Chill CONSULTING ENGINEERS & SCIENTISTS Canada China Hong Kong India Singapore UK USA Wind chill low high CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT rwdi.com

37 Berlin Wind Energy Potential CONSULTING ENGINEERS & SCIENTISTS Canada China Hong Kong India Singapore UK USA Wind energy potential low high CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT rwdi.com

38 Berlin Annual Solar CONSULTING ENGINEERS & SCIENTISTS Canada China Hong Kong India Singapore UK USA Solar radiation to surfaces (e.g. MWh/m 2 /yr) low high CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT rwdi.com

39 Berlin Façade Illuminance CONSULTING ENGINEERS & SCIENTISTS Canada China Hong Kong India Singapore UK USA Annual availability of daylight on facades low high CONSULTING IN THE SCIENCE OF BUILDINGS, STRUCTURES & ENVIRONMENT rwdi.com

40 Case Study Example Case Study: Exhaust Re-Entrainment

41 Exhaust Re-Entrainment What is Exhaust Re-entrainment? Entry or re-entry of exhaust gases into a building that can lead to indoor air quality problems Building exhausts into own air intakes Building exhausts into neighbouring air intakes Neighbour s exhausts into our building air intakes 41

42 Exhaust Re-Entrainment before raising stack height after raising stack height

43 CFD Modelling: Exhaust Re-Entrainment Computational Fluid Dynamics (CFD) Quickly highlights potential issues

44 Example Results : Exhaust Re-Entrainment

45 Wind Tunnel Modeling : Exhaust Re-Entrainment Most accurate and reliable Accuracy important when dealing with gases with health impacts Fine-tuning designs Includes complex geometry Wind Direction Exhaust Stack Air Intake Gas Analyzer Pump Modeled Air Flow Tracer Gas PC Results 45

46 Typical Study Requirements Exhaust Re-Entrainment Scoping level Identify if a problem is likely Few wind directions of concern Lower-impact problem Not for regulatory purposes Detailed design Need to examine full wind environment Higher-impact problem Study to demonstrate regulatory compliance Desk study or CFD appropriate Wind tunnel study appropriate

47 Conclusions

48 Conclusions Choice of approach dependent on the purpose of the analysis q CFD useful for scoping problems; less appropriate for final approval and fine detailing. q Experimental methods fast to run once model is built; both mean and gust conditions are simulated; requires expert teams q Pedestrian comfort and structural regulations generally don t favour specific methods but standards more easily met by wind tunnel experiments. User should define purpose of the study, configurations to be assessed and required future flexibility before deciding on approach. q Wind tunnel experiment costs biased towards creation of model, CFD spread between model creation and run time. q Costs of experiments can be competitive with CFD (particularly when the unexpected happens!).

49 Thank you for your time and attention Are there any questions?