The Art of Natural Ventilation Balancing Heat and Air Flows?

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1 The Art of Natural Ventilation Balancing Heat and Air Flows? Rowan Williams Davis & Irwin (RWDI) Inc. Consulting in the Science of Buildings, Structures and Environment

2 Acknowledgements This presentation is possible because of the efforts of the many bright and committed colleagues I have the pleasure of working with at RWDI. I d also like to acknowledge my appreciation for the opportunity to work on great projects, with cool teams for inspired clients. 2

3 Outline What is natural ventilation Human requirements Driving forces Design process Examples Is it working? 2012/01/18 WES Seminar Is Natural Ventilation Working as Advertised? 3

4 Outline What is natural ventilation Human requirements Driving forces Design process Examples Is it working? Does wind help or hurt? 4

5 What do we naturally ventilate? We naturally ventilate many spaces Hospital patient rooms - parking garages Offices - arenas / stadia Schools Homes Sometimes the spaces are about processes and not humans Transformer vaults Industrial processes Antenna arrays Road and rail tunnels Emergency (smoke) ventilation 5

6 Princess Noura University, Riyadh Saudi Arabia Natural Ventilation of Courtyards With Wind Towers 60% Spring % 40% 30% 20% 10% 0% Morning Midday Afternoon Evening Night Open no tower single direction bi-directional bi-directional with fan

7 Why do we naturally ventilate? Save cooling and fan energy Only 50% of the net zero capable buildings use natural ventilation Provide acceptable indoor air quality through fresh air ** Enhance productivity Connect people to outdoors 7

8 Most people think of this. 8

9 For many the reality is different Hong Kong Cairo Photo Courtesy Hanqing Wu, RWDI Photo Courtesy Hanqing Wu, RWDI 9

feel it working Large consequences can come from (small) annoyances making a

10 Issues to Remember Natural ventilation must meet people s needs Temperatures & RH Biological airflow requirements Contaminants AQ Ideally people should be able to feel it working Large consequences can come from (small) annoyances making a building undesirable: Noise Odour Excessive temperatures Dust Insects, and Allergens 10

11 11

SPMV* How People Perceive Comfort Comfort is a complex phenomena It varies from person to person A combination of four environment variables Wind speed Temperature RH Radiant temperatures (solar

12 SPMV* How People Perceive Comfort 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) Hot Warm Slightly Warm Neutral Slightly Cool Cool Cold Plus three personal factors Clothing levels Activity Other parameters like gender, height have a lesser role.

13 Thermal Comfort Indices There are lots of different indices promoted to describe thermal comfort Index Parameters Observations PMV Wind, sun, temperature, RH, activity, clothing Wide acceptance Only good for indoors Operative Temp Air temperature, radiation Does not include the impact of RH or activity. WBGT PET Humidex / Heat Index RH, air temperature, radiation, (wind speed) RH, air temperature, radiation, wind speed Air temperature and relative humidity Used to define heat stress on a body Defines conditions to an equivalent indoor T. Described as a perceived temperature. 13

14 ARRANGEMENTS 14

15 Two Airflow Issues Get the air in Related to the flow through the perimeter Circulated it well Dictates how efficiently we use the air that is available Internal quantities (AQ, temperature) scale with air flow rate makes envelope flows very important 15

16 Natural ventilation is designed leakage Wind Driven Cross Ventilation Single Sided Ventilation Buoyancy Driven Stack Ventilation 16

17 Scale of Natural Ventilation System is Important Single Room Full building Etheridge, Natural Ventilation of Buildings Theory, Measurement and Design, John Wiley & Sons,

18 Some Physics STACK EFFECT 18

19 Stack Effect Building Top Height Height Summer Winter Open skylight Pressure Pressure

20 Stack Effect Building Top Height Height Summer Winter Open skylight ΔP = P inside P outside Pressure Pressure

21 Stack Effect Building Height Height Summer Winter Open door Pressure Pressure

22 Stack Effect Building Height Height Summer Winter Open door ΔP = P inside P outside Pressure Pressure

23 Stack Effect Distributed Openings Height Height Summer Winter Distributed Pressure Pressure

24 Stack Effect Distributed Openings Height Height Summer Winter Distributed ΔP = P inside P outside Neutral Plane Pressure Pressure

25 Stack Effect Pressurisation Height Height Summer Winter Distributed Pressure Pressure

26 Stack Effect Pressurisation Height Height Summer Winter Distributed ΔP = P inside P outside Pressure Pressure

27 Stack Effect Distributed Openings Wind Impact Windward Side Height Summer Winter Distributed ΔP = P inside P outside Neutral Plane Pressure Pressure

28 Stack Effect Distributed Openings Wind Impact Leeward Side Height Summer Winter Distributed ΔP = P inside P outside Neutral Plane Pressure Pressure

29 Pressure Difference Across Façade With Wind, Summer Conditions Downwind Upwind

30 Picking the Neutral Plane is Important Needs to be above inlet of highest room to be ventilated by stack effect Etheridge, Natural Ventilation of Buildings Theory, Measurement and Design, John Wiley & Sons,

31 CIBSE, AM10 Natural Ventilation of non-domestic buildings,

32 CIBSE, AM10 Natural Ventilation of non-domestic buildings,

33 THE DESIGN PROCESS 33

34 There are two approaches to natural ventilation design Process 1: Draw building Draw arrows going in and out of building Sometimes colour arrows blue in and red out (always sure to help) Install windows Process 2: 1. Understand site & climate 2. Understand needs of building, occupants and/or process 3. Evaluate means to minimise pollutants / heat loads 4. Evaluate mechanisms to achieve sufficient flow 5. Assess success in achieving objective: iterate 34

35 Very Very Well Behaved Arrows (WBAs) 35

36 Very Very Well Behaved Arrows (VWBAs) Sustainability features built into roof element (cooling fins, PV, wind turbines, etc.) CIBSE AM10 36

37 Very Very Well Behaved Arrows (!) 37

38 Natural Ventilation Driving Forces The Art of balancing driving pressure differences and restricting pressure losses Two driving forces for naturally ventilated environments Buoyancy due to heat gain/load: Pa Wind driven pressures: 1 35 Pa One typically draws air from bottom to top Natural ventilation tends to be transient 38

39 The best naturally ventilated buildings are located in sites that are planned for natural ventilation The masterplan can contribute to the success of natural ventilation and prevent it from being possible. 39

40 Success Starts at the Masterplan 40

41 Deep and Complex Urban Cores Lead to Complex Wind Regimes Masterplan site to permit natural ventilation Some urban environments are very challenging 41

42 Even within a Complex Urban Fabric we can Give Buildings Wind Access 42

Masterplan for Natural Ventilation in Dense Urban Fabric Results of

positive for the west winds due to building alignment with the winds.

43 Masterplan for Natural Ventilation in Dense Urban Fabric Results of Assessment - Winds at Lower Roof Level Ventilation at this level is positive for the west winds due to building alignment with the winds. In courtyard areas between the towers, winds were very stagnant, even at this level. Northwest Winds Increased spacing of the towers would allow for better ventilation of areas between the buildings. Southwest Winds West Winds Page 43

44 Guess at wind Cp values EXAMPLE: LAB BUILDING UNIVERSITY NEAR TORONTO 44

45 Problem Statement Energy and network flow modelling tools have built in wind values Varying levels of complexity Not always appropriate The issue is sometimes how wrong are they? Summary of information from Sim Build Paper The Role of Wind in Natural Ventilation Simulations Using Airflow Network Models J Good, A Frisque, D Phillips 45

46 46

47 Comparison of Cp values for different wind directions Wind Pressure Coefficient (Cp) Comparison of Predictions at 90º angle of attack Avg diff = 28% Winds from East Wind tunnel Wind Tunnel IES VE Model Commercial Code Estimate 0.80 Zone1 Zone2 Zone3 Zone4 Zone5 Zone6 Zone7 Zone8 Zone9 Zone10 Zone11 Zone12 Zone13 Zone14 Zone15 Zone16 Zone17 Zone18 Zone19 Zone20 Zone21 Zone22 Zone23 Zone Winds from South Wind Pressure Coefficient (Cp) Comparison of Predictions at 180º angle of attack Avg diff = 29% Wind tunnel Wind Tunnel IES VE Model Commercial Code Estimate Zone1 Zone2 Zone3 Zone4 Zone5 Zone6 Zone7 Zone8 Zone9 Zone10 Zone11 Zone12 Zone13 Zone14 Zone15 Zone16 Zone17 Zone18 Zone19 Zone20 Zone21 Zone22 Zone23 Zone24 47

48 Comparison of Cp values for different wind directions Avg diff = 46% Pressure Coefficient (Cp) Winds Comparison of Predictions from at 0º North angle of attack Wind Tunnel Wind tunnel IES VE Model Commercial Code Estimate Zone1 Zone2 Zone3 Zone4 Zone5 Zone6 Zone7 Zone8 Zone9 Zone10 Zone11 Zone12 Zone13 Zone14 Zone15 Zone16 Zone17 Zone18 Zone19 Zone20 Zone21 Zone22 Zone23 Zone Winds from West Wind Pressure Coefficient (Cp) Comparison of Predictions at 270º angle of attack Avg diff = 38% Wind tunnel Wind Tunnel IES VE Model Commercial Code Estimate Zone1 Zone2 Zone3 Zone4 Zone5 Zone6 Zone7 Zone8 Zone9 Zone10 Zone11 Zone12 Zone13 Zone14 Zone15 Zone16 Zone17 Zone18 Zone19 Zone20 Zone21 Zone22 Zone23 Zone24 48

49 EXAMPLE: HIGH SCHOOL NEAR SEATTLE, WA 49

50 Courtesy of Bassetti Architects Courtesy Basseti Archicats 50

51 Site Plan & Orientation with Winds Classroom wings All Seasons (SEATAC) classrooms 51

52 Targets: 500 cfm = 850 m 3 /hr Temperature at or below ASHRAE Adaptive Target ASHRAE , Figure

53 Courtesy Basseti Archicats 54

54 Building Configuration North 55

55 56

56 57

57 Stacked Arrangement of Rooms Anticipated using one side of chimney as outlet Inlets need to heat air in Winter mode 59

58 4 to 6 8 to to to to to to to to to to to to to to 62 Median T=12ºC 1.60% 1.40% 1.20% 1.00% 0.80% -9 to -8-5 to -4-1 to 0 3 to 4 7 to 8 11 to to to 20 Temperature [ºC] 23 to to to % 0.40% 0.20% 0.00% Wind Direction 1.8% 1.6% 1.4% 1.2% 1.0% 0.8% 0.6% 0.4% 0.2% 0.0% Wind Speed Wind Direction 60

59 Heat Loads Must be Distributed Occupants W Laptops W LCD Projector 150 W Printer 100 W Lighting 1080 Solar depends on month & time of day W <- ironically both in December 61

60 Modelling Results January Volume flow (cfm) Lower class airflow Upper and Lower Temperature Temperature ( F) Upper class airflow Outdoor Temperature Tue Wed Thu Fri Sat Sun Mon Tue Date: Tue 01/Jan to Mon 07/Jan MacroFlo external vent: Lower class (1zone 2004 nowind louversonly.aps) MacroFlo external vent: Upper class (1zone 2004 nowind louversonly.aps) Dry-bulb temperature: (1zone 2004 nowind louversonly.aps) Air temperature: Lower class (1zone 2004 nowind louversonly.aps) Air temperature: Upper class (1zone 2004 nowind louversonly.aps) 62

61 Modelling Results March Volume flow (cfm) Temperature exceedance Lower class airflow Upper and Lower Temperature Temperature ( F) Upper class airflow Outdoor Temperature Tue Wed Thu Fri Sat Sun Mon Tue Date: Tue 26/Mar to Mon 01/Apr MacroFlo external vent: Lower class (1zone 2004 nowind louversonly.aps) MacroFlo external vent: Upper class (1zone 2004 nowind louversonly.aps) Dry-bulb temperature: (1zone 2004 nowind louversonly.aps) Air temperature: Lower class (1zone 2004 nowind louversonly.aps) Air temperature: Upper class (1zone 2004 nowind louversonly.aps) 63

62 Modelling Results Annual Daytime Hours 64

63 Pressure Losses & CFD Modeling of Inlet Box Inlet (K=2.5): Louver Damper Grille Outlet (K=1.5) Flow turn x 2 Louver Driving pressure = in H2O ( Pa) 65

64 Motivation for Wind Tunnel Measurements Some chimneys in recirculation zone Some locations of classroom intakes in recirculation zone 66

65 67

66 Windtunnel Measurements Chimneys 68

67 Conclusions from Wind Tunnel Testing Took measurements on three surfaces of chimney Adverse pressure differences could lead to flow reversal Frequency of low flow rates at acceptable levels All calculations done assuming window closed. depends on orientation of classroom 2012/01/18 WES Seminar Is Natural Ventilation Working as Advertised? 69

68 Hypothetical NATURAL VENTILATION OF TALL TOWERS 2012/01/18 WES Seminar Is Natural Ventilation Working as Advertised? 70

69 Natural ventilation in tall towers Is difficult Wind impacts Stack effect The benefit is not always apparent 2012/01/18 WES Seminar Is Natural Ventilation Working as Advertised? 71

70 Internal Flows Level 31 North Wind Δt = 0

71 Internal Flows Level 31 North Wind Δt = 30

72 Internal Flows Level 31 North Wind Δt = 60

73 Internal Flows Level 31 North Wind Δt = 90

74 Internal Flows Level 31 North Wind Δt = 120

75 Internal Flows Level 31 North Wind Δt = 150

76 Internal Flows Level 31 North Wind Δt = 180

Energy Model Using Meteorological Modelling for Upper Elevations Interested in seeing impact Built a small model and ran it at two elevations Office

77 Energy Model Using Meteorological Modelling for Upper Elevations Interested in seeing impact Built a small model and ran it at two elevations Office typology Occupancy of 0.04 p/m2, plug loads of 8 W/m2, lighting of 11 W/m2, fresh air of 2.5 L/s-person and 0.3 L/s-m2 Energy Model at Grade Energy Model at 600 m 79

78 Comparison of Data Lighting Occupants Plug Loads Cooling Heating DHW Fans + Pumps Total (kwh) (kwh) (kwh) (kwh) (kwh) (kwh) (kwh) (kwh) Ground - orig EPW Ground - WRF EPW Ground - WRF EPW no INF or NV m - WRF EPW m - WRF EPW no INF or NV Comparing Line 1 with Line 2 shows the WRF data is close Comparing Line 2 with Line 4 shows there is little difference between h=0 and h=600 Comparing Line 2 with 3 and 4 with 5 shows that the consequence of natural ventilation is an increase in energy demand Further analysis shows that the increase in infiltration offsets the benefit of natural ventilation. 80

79 Natural Ventilation Is Helpful Natural Ventilation 82

80 Seasonal Airflow & Cooling February Infiltration Rates In Winter and shoulder seasons, when outdoor temperatures are cooler, natural ventilation is beneficial During these cooler months, infiltration rates are typically greater at lower levels 83

81 Seasonal Airflow & Cooling February Cooling Load w/ & w/o Nat Vent Ground 600 m Without natural ventilation (LEFT), cooling loads are very similar at low and high elevations With natural ventilation (RIGHT), significant reductions in cooling loads are realized during Winter and shoulder seasons 84

Seasonal Airflow & Cooling February Cooling Load w/ & w/o Nat Vent Without Natural Ventilation With Natural Ventilation Only modest reductions in cooling load are seen at ground

82 Seasonal Airflow & Cooling February Cooling Load w/ & w/o Nat Vent Without Natural Ventilation With Natural Ventilation Only modest reductions in cooling load are seen at ground level, even though infiltration rates are higher Significant cooling load savings are seen at higher elevations Likely attributed to lower air temperatures at higher elevations 85

83 Closing Thoughts Lots of opportunity for natural ventilation design in buildings Stack effect control We haven t discussed thermal mass, turbulence benefits, designing openings, etc. This requires close coordination at beginning of project between architect, MEP, SE, climate consultant, QS, Construction, FM 89

PLEA th Conference, Opportunities, Limits & Needs Towards an environmentally responsible architecture Lima, Perú 7-9 November 2012

PLEA th Conference, Opportunities, Limits & Needs Towards an environmentally responsible architecture Lima, Perú 7-9 November 2012 Natural Ventilation using Ventilation shafts Multiple Interconnected Openings in a Ventilation Shaft Reduce the Overall Height of the Shaft While Maintaining the Effectiveness of Natural Ventilation ABHAY