Dampness and Mould - WHO guidelines for indoor air quality - PRWeb

48
WHO GUIDELINES FOR INDOOR AIR QUALITY: DAMPNESS AND MOULD
In decentralized systems, more components require maintenance and are more
widely spread out, but ventilation is easier to control by demand.
3.5.3 Hybrid (mixed-mode) ventilation
It is often possible to improve the reliability of natural ventilation or to increase
the range over which low-energy ventilation methods can be applied by introducing
mechanical assistance. Often, hybrid ventilation consists of no more than
an auxiliary low-energy extract fan located in a natural ventilation extract duct.
The fan is operated when driving forces are low or when priming a natural ventilation
stack to prevent reverse flow. At the opposite extreme, a hybrid system
can include a natural ventilation system combined with a fully independent mechanical
system. In this case, natural ventilation is used for as long as climate
and operational conditions permit, after which the mechanical system takes over.
Efficiency can be improved by zoning the building so that some parts operate
under natural conditions while others are mechanically ventilated. Depending
on the approach, hybrid systems extend the applicability of ventilation to a wider
range of buildings, including multi-storey buildings, urban locations and shopping
malls.
Hybrid ventilation approaches may provide advantages in energy and cost
over fully air-conditioned mechanical approaches in a wide variety of climatic
regions and even in very complex buildings (Aggerholm, 2003).
Figure 6. Centralized
mechanical supply
and exhaust system
with heat recovery
in an apartment
building