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Ventilation research on Australian residential construction.

Article Excerpt
A Background to Ventilation and Air Leakage Research in Buildings

The International Energy Agency (IEA, 1996) Annex 26, Energy Efficient Ventilation of Large Enclosure, declared building ventilation as the single most influencing component in the future of building energy consumption. This statement was made on the basis that buildings in the future would undoubtedly have solved the problems of thermal insulation, effective construction and optimised building control services. Australian building codes have acknowledged the value of thermal insulation in the building envelope improving energy consumption. In recent years, overseas standards and research recognise that the sealing of air leaks in houses (tightening) is the most cost effective method of achieving direct energy savings. These practices and testing methods have yet to be taken into account within Australian building codes.

Several reasons for researching the 'air-tightness' in buildings include:

* Reducing energy costs through the reduction of unpredicted infiltrated and exfiltrated air leakages.

* Reducing energy demand for heating and cooling unconditioned air entry and replaced leaked air.

* Establishing better predictability for unknown air leakage quantities in energy load calculations.

* Reduced size of mechanical equipment.

* Eliminating interference with the mechanical (HVAC) system control.

* Reducing moisture deposition within the building envelope.

* Better health performance through limiting external pollutants.

* IAQ (Indoor Air Quality) control through reducing the permeability ([m.sup.3]/hr/[m.sup.2]) of a particular building envelope system.

* Reducing external noise nuisance.

* Improved thermal comfort through fewer (cold) draughts.

* Better construction details through location and quantification of air leakage.

* Better control of the actual pressurisation differentials between building interior and exterior spaces.

Overseas legislation recognises building envelope performance as one of the most cost effective methods in reducing energy consumption. While the energy savings of sealed buildings can be quickly translated into C[O.sub.2] and other Greenhouse Gas reductions, Australia might acknowledge other environmental benefits of air-tight houses such as 'shelter-in-place' bushfire relief or 'a place of refuge' for asthma attacks, provided by weatherisation. The health aspects of a controlled clean and sealed environment have been shown to be of benefit in achieving reductions in asthmatic attacks and allergenic reactions in children (Committee on Environmental Health, 2004). This is thought to be due in part to their ability to seek refuge in a controlled (appropriately filtered) environment.

[FIGURE 1 OMITTED]

The study of airflow within buildings pertains to developing an understanding of the mechanics of ventilation (Liddament, 1996). Ideally, the information required for such would be the:

* External air flow rate ([m.sup.3]/s) into a building (ventilation and infiltration).

* Air change rate effectiveness within a particular space (room) of a building.

* Maximum and minimum infiltration rates ([m.sup.3]/s) into a building.

* Qualitative air movement (flow visualization pattern) for a space.

* Quantitative air movement in a space (flow velocity, direction, turbulence, etc.).

* Non-mechanically assisted air change rate--infiltration--ACH.

* Mechanically assisted air change rate--ventilation--ACH.

* Location and quantification of air leakages.

* The average pressurisation of the building (positive or negative).

[FIGURE 2 OMITTED]

Ventilation is defined as the 'wanted and known' quantity of air coming into a building and generally applies to the quantity supplied by mechanical ventilation. However, ventilation air quantities under natural conditions, such as entering through windows, are quite complex to measure. Air leakage, on the other hand, is defined as infiltration or the unknown and unwanted quantity of air entering the building (ASHRAE). Designers should not necessarily fixate on making buildings 'air-tight', because even if gaps were completely sealed, buildings have doors and openings, which allow large volumes of air changes at the occupants' discretion. The idea instead is to quantify leakage, reduce excessive leakage and control leakage by managing air pressure with the HVAC system (Ask, 2003).

There are two different but internationally accepted testing methods for determining air leakage (infiltration) rates in buildings: the fan pressurisation...

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