OVERVIEW TERMS & CONCEPTS PRINCIPLES OF VENTILATION FILTRATION THERMAL COMFORT CONTAMINATION CONTROL CONCEPTS DESIGN TRENDS 02/05/2013

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1 5 Th International TB/HIV Course for Clinicians in South Africa Tobias van Reenen CSIR 1 OVERVIEW OVERVIEW PRINCIPLES OF VENTILATION CONTAMINATION CONTROL CONCEPTS DESIGN TRENDS 2 1

2 HVAC:- Heating Ventilation and Air Conditioning ICAN: 2012 Ventilation:- The process of supplying air toor removing air from a space for the purpose of selectively controlling: -air contaminant levels, -humidity -or temperature within the space Ventilation rate:- Air changes per hour (AC/h) (Air Change Rate) 3 Air-Conditioning:- In/Exfiltration:- Supply Air:- A process for controlling the: -Temperature, -Humidity and -Sometimes the Purity of the air. Air leaking into or out of a space (m³/s) Air forced into the space (m³/s) 4 2

3 AIRBORNE CONTAMINATION CONTROL CONCEPTS Physical Segregation:- Isolation & Containment Aerodynamic Effects:- Where: N t /N o =e - kt N = initial concentration N t = concentration at time t k = rate of removal in ACH Displacement-Laminar Flow (operating theatres etc.) Dilution- Contaminants generated in the space are continuously diluted by the portion of fresh/treated air supplied into the space. 5 VENTILATION RATES How to calculate Air Changes per Hour : Room Volume:- Air Change Rate:- V room = L x B x H (mean) AC/h = (Q/V) Where: Q = volumetric flow rate (m³/h) V = room volume (m³) 6 3

4 VENTILATION RATES WHO recommendations: Target = 12 ACH or 60 litres per second per patient in medium risk settings (congregate areas) or litres per second per patient for high risk areas Source: WHO policy on TB Infection Control; Reducing transmission of TB in health-care facilities (WHO) 7 1. Central ducted systems 2. Split Units: 1. Ducted Hide-Away 2. Ceiling or Cassette 3. High Wall Split 4. Consoles 5. WINDOW UNITS Normally offer no Fresh air / Outside air Window units obstruct perfectly good openable windows. Rather Install as through-wall unit & keep window open 8 4

5 Air Conditioning (Both) Ventilation Neither> 9 Infection control: Poor Good 10 5

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8 15 PRINCIPLES OF VENTILATION Room Air Distribution Modes:- Displacement: (Stratified Distribution) Dilution: (Mixed Air Distribution) PRINCIPLES OF VENTILATION 16 8

9 PRINCIPLES OF VENTILATION Displacement: (Stratified Distribution) PRINCIPLES OF VENTILATION 17 PRINCIPLES OF VENTILATION Dilution: (Mixed Air Distribution) PRINCIPLES OF VENTILATION 18 9

10 PRINCIPLES OF VENTILATION Contamination Removal Effectiveness:- Contaminants Close to Exhaust PRINCIPLES OF VENTILATION Contaminants in Stagnant Zone (Short Circuit Flow) 19 Ventilation Effectiveness:- Piston Flow PRINCIPLES OF VENTILATION PRINCIPLES OF VENTILATION Fully Mixed flow 20 10

11 PRINCIPLES OF VENTILATION Ventilation Performance Indices The ability of a system to exchange air in the room: Air Change Efficiency, e a PRINCIPLES OF VENTILATION LocalAir Change Efficiency, e a p The ability of a system to remove contaminants: Contaminant Removal Effectiveness (CRE), e c LocalAir Quality Index, e c p 21 Filtration Efficiency A filter with an overall filter efficiencyof 99,95 % according to EN The filter penetrationshould not exceed 0,05% 99,95%+ 0,05%= 100% HFP : July

12 Types of Filters (Dust) 23 Course Filters Medium Filters Fine Filters Aerosol Filters Used to protect building services from Atmospheric dust Used to keep interior spaces visibly clean Used to keep interior spaces free of bioaerosols and microscopic dust 23 Aerosol Filtration Standards 24 12

13 Dust Filtration Standards EN 779:2012 EN 1822: Course Filters G1-G4 Average arrestance (Am) of synthetic dust % Medium Filters M5-M6 Average efficiency (Em) for 0.4 μm particles % Fine Filters F7-F9 Minimum efficiency (ME) for 0.4 μm particles % E10- E12 Integral efficiency MPPS Aerosol Filters H13- E14 HFP : July 2012 U15- U17 Integral and Local efficiency MPPS 25 Dust Filtration Standards -SA SANS 1424: Filters for use in air-conditioning and general ventilation (EN 779:2012) Course Filters Medium Filters Fine Filters EN 1822:2009 Aerosol Filters 26 13

14 Filter Testing and Maintenance Installed filter leak test (HEPA Filters): The installed filter challenge tests (ISO :B6) should not be confused with the manufacturer s efficiency classification tests (EN1822-4) EN 1822:2009 ISO Filter manufacturer s QC test Installed filter in-situ testing, proving absence of leaks 27 Thermal Comfort concerns how people respond to: Heat Transfer from their bodies and Air Quality Body's Thermal Loss: Moderate Conditions 30% 45% 25% Evaporation Radiation Convection CIBSE KS

15 CIBSE KS06 29 Factors that influence how we perceive thermal comfort: Activity Level Clothing Level Social & Psychological Factors Air movement (Velocity) Air Temperature Relative Humidity Mean Radiant Temperature 30 15

16 Lab Studies:- During WW2, submarine crews proved useful as guinea pigs for early studies on thermal comfort Lab studies related Space Conditions, Clothing Levels and Activity Levels to likely levels of Occupant Comfort 100% Satisfaction is impossible Predicted Mean Vote (PMV) Predicted Percentage Satisfied (PPS) 31 Adaptive Approach Field study results don't agree with lab studies! B.WOlesen, Thermal comfort, Developed from field studies of people in daily life. Given the timeand opportunity people adapt to their environment to achieve comfort. People adapt through voluntary and involuntary mechanisms 32 16

17 Adaptive Approach People Adapt by: Changing activity levels Taking warm or cool drinks Adding or removing clothing or blankets Modifying local environment Windows Blinds Heating Changing their environment: Moving into or out of shade Moving to a different part of a building 33 Adaptive Approach Discomfort occurs when temperatures: Change more quickly than adaption rates Are unexpected(seasonally) Are outside individual control Are outside accepted limits 34 17

18 Adaptive Approach Ways to reduce discomfort at temperatures above 25 C Relaxation of formal office dress Individual control opening windows the use of blinds or moving out of sunny areas Flexible working times more comfortable occupancy hours 35 Adaptive Approach Ways to reduce discomfort at temperatures above 25 C: Provide cool drinks Increased air movement (-2 C) Temperatures above 30 C will seldom be acceptable Acceptable comfort temperatures will differ between: Winter and Summer Naturally ventilated and air-conditioned spaces 36 18

19 Adaptive Approach Acceptable Conditions: Humidity of 40-70% RH Air velocities of m/s Conditions can vary within a single space. 37 AIRBORNE CONTAMINATION CONTROL Barrier Concept: AIRBORNE CONTAMINATION CONTROL SANS

20 AIRBORNE CONTAMINATION CONTROL Aerodynamic Concept (SANS ): Displacement Pressure Differential Dilution Not described in SANS AIRBORNE CONTAMINATION CONTROL 39 AIRBORNE CONTAMINATION CONTROL Barrier Concept: AIRBORNE CONTAMINATION CONTROL 40 20

21 DESIGN TRENDS Optimised Buildings Demand Ingenious Design The adoption of better design tools will yield: Reduced safety margins in design solutions Improved Building Performance Accurate Lifecycle Cost Predictions Optimised (reduced) Lifecycle Costs DESIGN 41 DESIGN TRENDS SOFTWARE TOOLS: Computational Fluid Dynamics (CFD) Solves partial differential equations to describe physical behaviour of complex flow and thermal systems Optimise locations of air inlets/outlets Predict Velocity and Flow fields Predict Temperature distributions Predict Contaminant Transport Dynamics DESIGN 42 21

22 DESIGN TRENDS SOFTWARE TOOLS: Building Simulation Software Delivers a bigger picture of long term building performance and energy usage Static systems with normalised results Certain software can develop a detailed life cycle cost analysis DESIGN 43 DESIGN TRENDS Adoption of Building Modelling Tools Requires: Good source data (GIGO applies) Significant capital investment by designer Specialist technical knowledge A tool is not a solution Time and money DESIGN 44 22

23 DESIGN TRENDS Adoption of Building Performance Modelling: Benefits easily outweigh investment for high value & complex buildings. Design effort should be proportionate to the potential for life cycle cost savings DESIGN 45 QUESTIONS? 46 23