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

Sustainable Built Environment IAQ Information IAQ Information Centre; IAQ Management Group

Sustainable Built Environment 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

Sustainable Built Environment Ambient air quality

Sustainable Built Environment 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?

Sustainable Built Environment 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

Sustainable Built Environment Chemical balance of human body The energy supply of life provided by chemical reaction of carbohydrates, fats and proteins with oxygen and produces CO 2 and H 2 O. Carbohydrates from food, can be stored in out body We extract oxygen from breathing air. Oxygen cannot be stored in our body.

Sustainable Built Environment Do you know? For normal conditions and a sedentary person: Takes about 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 m 3 of air per day. How big is out bed room? 3 X 5 X 3 = 45 m 3 ? 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 litres of oxygen per day, I.e. 1.5 to 4 m 3 of air. Not all the oxygen is extracted from the air inhaled with each breath and exhaled air contains 16% residual oxygen.

Sustainable Built Environment 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 : Acceptable IAQ means 80% or more people do not express dissatisfaction.

Sustainable Built Environment Indoor Air Quality Typical indoor spaces Homes, offices, public spaces Main indoor pollutants Indoor generated Outdoor sources Control

Sustainable Built Environment Two approaches to control IAQ Source control Use better materials Cleaning and filtration Ventilation control Local ventilation General ventilation

Sustainable Built Environment 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?

Sustainable Built Environment 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

Sustainable Built Environment 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...

Sustainable Built 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

Sustainable Built Environment 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 Fanger’s study showed 6% improvement in productivity

Sustainable Built Environment Three Periods in Indoor Environment Design Natural DesignMech Design Hybrid/Integrated Design 199?

Sustainable Built Environment 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

Sustainable Built Environment Stack Ventilation 4 Difference in air density induced by temperature or humidity differences drives vertical air flows Especially effective in winter

Sustainable Built Environment Combined Ventilation Wind assists (??) stack ventilation Flow rate (m 3 /s) q s - flow rate due to stack alone (m 3 /s) q w - flow rate due to wind alone (m 3 /s) + -

Sustainable Built Environment Questions so far - With ASHRAE , 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?

Sustainable Built Environment 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

Sustainable Built Environment 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

Sustainable Built Environment Top-down ventilation Better air quality at roof level in urban areas Experimentally proved by Hunt and Holford (1998) Room

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

Sustainable Built Environment 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

Sustainable Built Environment 4 Grong School, Norway 4 BRE Energy Building, UK 4 Manly Lab, Sydney Examples

Sustainable Built Environment 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?

Sustainable Built Environment 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.