Ventilation: Thermal Efficiency and Health Aspects - Nearly Zero Energy Building Refurbishment - page 386

Draft problems, common in leaky construction, are an additional driver for
more airtight construction (Bjarløv and Vladykova 2011 ). Therefore, leakage rates
are often reduced considerably in refurbishments of older buildings, along with the
installation of more efficient ventilation systems (Nabinger and Persily 2011 ; van
der Wal et al. 1991 ).
4.2 Airing
Another traditional ventilation strategy is the opening of windows. Although this
usually generates large flow rates of 4-20 ACH (Caciolo et al. 2012 ; Cheung and
Liu ( 2011 )), especially if cross-ventilation is possible (Bu and Kato, Bangalee
et al. 2012 ) and is, therefore, very effective to evacuate acute high pollution loads,
people tend to close the windows when they are present due to draft, especially
when the outdoor temperature is low.
In a sense, windows are opened to prevent overheating rather than to reduce
indoor air pollution (Dubrul 1988 ; Andersen et al. 2011 ; Fabi et al. 2012 ). Win-
dows are also frequently closed, despite high indoor pollutant concentrations,
because of acoustical discomfort (Barclay et al. 2012 ). The combination of these
factors leads to the conclusion that the possibility of airing by opening windows is
a necessary feature to restore the indoor air quality to acceptable levels within a
short time span in case of acute high pollution loads, but is less appropriate as a
ventilation strategy during occupancy.
4.3 System Sizing
From the discussion of leakage and airing as ventilation strategies, it is clear that
both of these strategies fail to achieve good ventilation efficiency. In both cases,
there is a mismatch between air supply and source strength or occupancy. These
drawbacks are mitigated by the conception of dedicated continuous flow ventila-
tion systems. As shown in Fig. 3 , in optimal conditions, they achieve much better
indoor air quality for a given ventilation heat loss than ventilation through leakage.
There is, however, no consensus about the design and sizing of such systems. This
is reflected in the large differences found in the requirements put forward in
ventilation standards (Brelih and Seppänen 2011 ; Yoshino et al. 2004 ; Dimi-
troulopoulou 2012 ), resulting in a large spread in performance (Koffi 2009 ; La-
verge et al. 2013b ). Suboptimal sizing self-evidently reduces system performance
(Djunaedy et al. ( 2011 ).
Roughly, balanced mechanical ventilation dominates the market in cold cli-
mates (Kurnitski and Seppanen 2008 ), simple exhaust is most prevalent in mod-
erate climate regions (Durier 2008 ), and natural ventilation is the dominant
strategy in mild climates.