the air we breathe - indoor air quality and natural ventilation dr yuguo li associate professor...

The Air We Breathe- Indoor Air Quality and Natural Ventilation

Dr Yuguo Li

Associate Professor

Department of Mechanical Engineering

The University of Hong Kong

Sustainable Built Environment

Sustainability in Built Environment


IAQ Information

http://www.iaq.gov.hk/IAQ Information Centre; IAQ Management Group

http://www.epa.gov/iaq/


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


Ambient air quality

City Population (Million) TSP (mg/m3)

Dalian 3 185Shanghai 13 246

Beijing 11 377Stockholm 1.5 9Melbourne 3 35Hong Kong 6 95

Note: Data from Air Quality in Hong Kong, 1999, EPD, HK and 2000 World Development Indicators, World Bank


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?


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


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.


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.


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 A$12 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.


Indoor Air Quality

Typical indoor spacesHomes, offices, public spaces

Main indoor pollutantsIndoor generatedOutdoor sources

Control


Two approaches to control IAQ

Source controlUse better materialsCleaning and filtration

Ventilation controlLocal ventilationGeneral ventilation


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?


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

Desired Control Over Office Environment

6%

23%

67%

4%

No Control

Little Control

Some Control

Complete Control


Why provide HVAC?

For IAQFresh air deliveryRemoval or dilution of pollutants

For thermal comfortRemoval or addition of heat loadsComfortable living or working conditionsCertainty of the thermal environment

Other issues - productivity, cost, flexibility, risk, energy efficiency, environment...


What’s 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


Issues

Air conditioning – use 48% of energy in

commercial buildings and 30% in residential buildings

30% of offices in HK are sick buildingsEnergy = CO2 + $Poor indoor air quality = poor productivityFanger’s study showed 6% improvement in

productivity


Three Periods in Indoor Environment Design

1900 1973

Natural Design Mech Design Hybrid/IntegratedDesign

199?


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.

+ -

Especially effective in summer


Stack Ventilation Difference in air density induced by

temperature or humidity differences drives vertical air flows

Especially effective in winter


Combined Ventilation

Wind assists (??) stack ventilation

22ws qqq

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

+ -


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?


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 …...

Ventilation for IAQ

Ventilation for Cooling


Opportunities

Energy saving by 10-50%Better indoor air quality in winter, spring

and autumnAdaptive thermal comfort Connect users to environmentImproved productivity if designed properly


Top-down ventilation

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

Room


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

Room


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


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

Examples


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?


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.

the air we breathe - indoor air quality and natural ventilation dr yuguo li associate professor...

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