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Ventilation is required to provide to remove or dilute pollutants and incidentally meets metabolic oxygen requirements for occupants. In addition ventilation may also be required to provide oxygen for combustion devices and as a means of summer cooling.
It is estimated that, within the OECD countries, around 28EJ of energy is consumed in residential dwellings, of which around 12EJ is associated with ventilation. Calculations suggest that it may be possible to reduce this energy consumption associated with ventilation to less than 1EJ. It is therefore important to ensure that the need for ventilation within dwellings is met with the minimum of energy consumption.
A wide range of systems are used to provide ventilation in dwellings. Each system has advantages and disadvantages and therefore the applicability of any one system will depend on a number of local factors such as climate or standards.
Work undertaken as part of Annex 27 has found that natural ventilation remains the most common ventilation method in OECD countries. Countries with cold climates have a more rigorous approach to building air tightness and ventilation systems that offer good control such as balanced mechanical systems with heat recovery. Milder and moderate climates favour ventilation systems with less control, usually natural. However, there is now a move towards reducing energy consumption by the use of more controlled ventilation methods.
Ventilation and thermal standards will have a significant influence on the energy consumption of ventilation systems. Ventilation standards usually aim to provide the minimum ventilation for metabolic needs and the removal of major indoor pollutants such as moisture. Thermal standards can cover, fabric conduction losses, heating and cooling plant performance and infiltration losses.
Infiltration can have a detrimental effect on both energy consumption and ventilation effectiveness, hence indoor air quality and comfort. Each method of ventilation operates most effectively if the building envelope is constructed to the appropriate air tightness standard for the chosen ventilation method.
Indoor air quality must not be sacrificed in pursuit of reductions in energy consumption. There are a wide range of pollutants, which are derived from an equally extensive number of sources. Source control is the most effect way to avoid problems and regulations aim to achieve this for may major external pollution sources and some internal sources. Other sources can be avoided by correct specification and design. For those sources that cannot be completely avoided, such as moisture production, dilution by ventilation is the only alternative.
Occupant behaviour has been shown to have a significant impact on energy consumption. Annex 8 investigations indicated that occupants used windows to influence indoor air quality and thermal comfort, but with little conscious attempt to minimise energy consumption. Other studies have indicated that there is a correlation between health problems and dissatisfaction with the ventilation system. Calculations have suggested that occupant window opening may increase average ventilation rates by 0.32 ach for natural systems and 0.34 ach for mechanical systems, while studies in Japan suggest that as much as 87% of the total air change rate may be due to occupant behaviour. A set of occupant guidance to provide good indoor air quality and thermal comfort without excessive energy consumption has been provided in AIVC Technical Note 53.
Other design issue that need to be considered when designing ventilation systems include safety, avoidance of external pollution and re-entrainment of extract air, noise, visual appearance, build ability, reliability and cost.
Commissioning for residential ventilation systems is not currently common, but could have a significant impact on system performance. The Swedish Boverket procedure is the only practical performance-orientated approach for system checking currently in use. Work is however, being carried out in Europe as part of the European Commission's Joule programme (TIPVENT) and in the USA by The Energy Performance of Buildings Group at Berkeley Laboratories.