The Air We Breathe - Indoor Air Quality and Natural Ventilation

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The Air We Breathe- Indoor Air Quality and
Natural Ventilation
Sustainability in Built Environment

• Dr Yuguo Li
• Associate Professor
• Department of Mechanical Engineering
• The University of Hong Kong

Sustainable Built Environment
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IAQ Information

• http//www.iaq.gov.hk/
• IAQ Information Centre
• IAQ Management Group
• http//www.epa.gov/iaq/

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What is sustainability?

• Sustainable development is development that
  meets the needs of the present without
  compromising the ability of future generations to
  meet their own needs.
• The United Nations World Commission on
  Environment and Development,
• The Brundtland Report, 1987

Environmental Impact Population ? Affluence
per person ? Technology Proposed by Paul
Ehrlich and John Holden
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Ambient air quality
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Topics

• Indoor air quality is more important than ambient
  air quality
• Natural ventilation can be an effective and
  energy-efficient ventilation and cooling strategy
• Discussion - What can we do?

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Our basic needs

• Healthy and comfortable - Thermal, visual,
  acoustical, tongue, air quality
• We spend more than 90 of our time indoors
• Indoor air quality is defined as the nature of
  indoor air that affects the health and well-being
  of occupants

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Chemical balance of human body

• The energy supply of life provided by chemical
  reaction of carbohydrates, fats and proteins with
  oxygen and produces CO2 and H2O.
• Carbohydrates from food, can be stored in out
  body
• We extract oxygen from breathing air. Oxygen
  cannot be stored in our body.

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Do you know?

• For normal conditions and a sedentary person
• Takes about 15-40 breaths per minute or 22 k to
  57 k breaths per day
• During each air change, about 1 litre of air is
  replaced
• We breathe about 10 to 45 m3 of air per day. How
  big is out bed room? 3 X 5 X 3 45 m3?
• Other way to find out how much oxygen is needed?
  We need 1500 to 4000 kcal per day. As one litre
  of oxygen is needed to produce 4.8 kcal, we need
  300-800 litres of oxygen per day, I.e. 1.5 to 4
  m3 of air.
• Not all the oxygen is extracted from the air
  inhaled with each breath and exhaled air contains
  16 residual oxygen.

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Acceptable IAQ

• Simplistic views Good air quality means freedom
  from unwanted odours, and restriction of air
  contaminant concentrations below the levels at
  which irritation or toxic effects manifest
  themselves.
• Cost of poor indoor air quality costs Australians
  A12 billion per year CSIRO
• There is a need for compromise between good IAQ
  and cost of achieving good IAQ
• ASHRAE 62-1999 Acceptable IAQ means 80 or more
  people do not express dissatisfaction.

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Indoor Air Quality

• Typical indoor spaces
• Homes, offices, public spaces
• Main indoor pollutants
• Indoor generated
• Outdoor sources
• Control

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Two approaches to control IAQ

• Source control
• Use better materials
• Cleaning and filtration
• Ventilation control
• Local ventilation
• General ventilation

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Questions so far -

• Is IAQ different from thermal comfort?
• Is ventilation different from air conditioning?
• Indoor air and outdoor air, which one is better?
• What are the factors affecting indoor air
  quality?

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Why individual control?

1. To handle personal difference and it may be
   difficult to ensure everyone is thermally
   comfortable.
2. Most occupants prefer some degree of individual
   control

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Why provide HVAC?

• For IAQ
• Fresh air delivery
• Removal or dilution of pollutants
• For thermal comfort
• Removal or addition of heat loads
• Comfortable living or working conditions
• Certainty of the thermal environment
• Other issues - productivity, cost, flexibility,
  risk, energy efficiency, environment...

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Whats wrong with the old HVAC and natural
ventilation?

• Old HVAC
• Energy consuming
• Sick building syndrome
• Minimum ventilation rate
• Mostly centralised
• Natural ventilation
• Do not work at extreme conditions
• Difficult to control
• Difficult to predict and design

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Issues

• Air conditioning use 48 of energy in
  commercial buildings and 30 in residential
  buildings
• 30 of offices in HK are sick buildings
• Energy CO2
• Poor indoor air quality poor productivity
• Fangers study showed 6 improvement in
  productivity

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Three Periods in Indoor Environment Design
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Wind Ventilation

• Wind causes a positive pressure on the windward
  and negative on the leeward, thus air flows into
  the windward opening and out of the leeward one.

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Especially effective in summer
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Stack Ventilation

• Difference in air density induced by temperature
  or humidity differences drives vertical air flows

Especially effective in winter
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Combined Ventilation

• Wind assists (??) stack ventilation

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Flow rate (m3/s) qs - flow rate due to stack
alone (m3/s) qw - flow rate due to wind alone
(m3/s)
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Questions so far -

• With ASHRAE 62-1999, we need 10 litre per second
  outdoor air per person, do we need really so high
  natural ventilation flow rate as shown earlier?
• Do you always turn on your air conditioner at
  home?
• Is natural ventilation always good?

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What Natural Ventilation Can Offer Us?

• Fresh air, dilute or remove pollutants
• Remove heat, provide thermally comfortable air
• Connect us to natural environment
• Remove smoke
• ...

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Opportunities

• Energy saving by 10-50
• Better indoor air quality in winter, spring and
  autumn
• Adaptive thermal comfort
• Connect users to environment
• Improved productivity if designed properly

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Top-down ventilation

• Better air quality at roof level in urban areas
• Experimentally proved by Hunt and Holford (1998)

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Wind towers

• Features in Arabic architecture
• Direct winds into building
• Together with evaporative cooling - cool towers
• At night, acts as chimney?

Room
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Questions so far -

• In order to use more natural ventilation, is it
  useful to improve ambient air quality?
• What are the differences between outdoor air and
  fresh air?
• Please list three example natural ventilation
  strategies

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Examples

• Grong School, Norway
• BRE Energy Building, UK
• Manly Lab, Sydney

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Questions so far -

• Is it possible to use natural ventilation in an
  urban environment?
• What are the roles that architects, engineers,
  users, developers and users play in sustainable
  building design?

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Summary

• Indoor air quality can be more significant than
  outdoor air quality
• Indoor air quality is related to our health, our
  productivity and out living
• Ventilation is different from air-conditioning
• Natural ventilation a natural choice, but not
  the only one.
• Air is just one element of the environment.