Making the building do the work: natural ventilation design

Article By John Brodie

‘The Fifth Estate’, 8 February 2012 

In the world of climate change and inefficient buildings everyone is clamouring for more efficient air conditioning systems and improved lighting to reduce energy loads and carbon.

Air conditioning uses a large proportion of energy in buildings. The rule of thumb in trying to drop air temperature down from something quite hot – say 38 degrees Celsius external temperature to a default comfort level of around 22 degrees – is that air conditioning uses around 40 per cent of the energy in a building.

If we stand back and take an objective look at building design and what inhabitant thermal comfort is really about we may be able to significantly reduce that air conditioning energy use by adjusting our notions of comfort.

We would need to consider natural ventilation as either the main option for ventilative cooling and providing fresh air or at least have it working in conjunction with air conditioning.

In an air conditioned building with comfort levels controlled through the commonly used temperature set points, there will always be 10-15 per cent of occupants dissatisfied.

The empirical research undertaken worldwide across a range of climates and buildings indicates a naturally ventilated facility will have around the same levels of user dissatisfaction.

We also need to remember that occupant comfort isn’t just based around temperature related conditions it is also based around air quality. Air quality in naturally ventilated buildings is higher than in air conditioned buildings.

If we utilise the hybrid technology of natural ventilation and air conditioning then we can significantly reduce the amount of energy used and carbon created to make a building comfortable.

Combine that initiative with the proven concept of adaptive comfort and how valuable that is in improving user comfort and reducing energy use in naturally ventilated buildings then natural ventilation should be considered as a major option across most of the Australian climate range.

The National Institute of Science and Technology, USA has some preliminary analysis software that indicates that with an adaptive comfort range of 20-27 natural ventilation cooling for around 78 per cent of the year in Sydney.

In Melbourne that figure becomes 93 per cent of the year because of climate conditions which are even more conducive to natural ventilation. This is using an internal heat load of 100 watts a square metre which is very high and would be considered the worst case scenario for internal heat loads in a commercial building. That is a lot of energy saving and reduced carbon. That is not to mention the major improvements in indoor climate that are often credited with increased user satisfaction, higher retail sales, productivity and improved learning outcomes.

Natural or passive ventilation has not been readily embraced in Australia for the past 50 years but in Europe and the hot dry humid climates of the Middle East and Asia it is traditionally very popular.

What these countries have learned is that natural ventilation must have the appropriate control strategies to work effectively in modern building types. Simply opening or closing a window manually has been shown to not be effective.

Users will open or close too early or too late. With a smart control system designed specifically for the nuances and broad range of criteria needed to control natural ventilation that still offer user control and override, natural ventilation will maximise comfort and energy efficiency.

There are many ways to assist the efficacy of natural ventilation through the building based on the use of pressure differences across the façade and inside the building. Click here for more

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