Civil Engineering Reference
In-Depth Information
the trade-off. The choice of a conversion framework, e.g. energy, primary energy
(IEA
2008a
,
b
), carbon dioxide emission (IEA
2010
; Soimakallio and Saikku
2012
) or exergy, has a significant effect on the performance of the fan-supported
systems (Laverge and Janssens
2012
). The implementation of filter technology is
virtually exclusively reserved for fan-supported systems, but again requires
additional fan energy (Montgomery et al.
2012
; Stephens et al.
2010
). Fan-sup-
ported systems also require adequate commissioning, cleaning and maintenance,
as well as a minimum of occupant education to function properly. A large number
of installed systems fail in one of these aspects (Balvers et al.
2012
; Dorer and
Breer
1998
).
In this chapter, the potential of air movement to create thermal comfort con-
ditions is not discussed. The supply air is assumed to be at the minimal temper-
ature required to eliminate the heating demand. During the heating season, when
the outdoor air temperature is below this threshold, the supply air has to be heated
to achieve this. Mutatis mutandis, the same can be said for the cooling season.
Modifying factors determining the amount of energy required to do so obviously
include climate conditions and the thermal performance of the building (Laverge
and Janssens
2012
) as well as the extent to which the energy contained in the
exhaust air can be reused to heat the supply air. Most heat recovery systems
require additional energy input to function. Their performance is discussed in the
following section dealing with specific types of ventilation.
4 Ventilation: Strategies and Technology
Ventilation, as a means of risk management, can be achieved by simple low-tech
solutions relying on leakage and window opening by occupants, or by fully
mechanical ventilation systems that use fans to move the air where it is needed, or
by any conceivable compromise between these extremes. In this section, the merits
of a few of these options are discussed.
4.1 Leakage
Traditionally, occupants have relied on infiltration of outdoor air through the
building envelope to maintain acceptable contaminant concentrations indoor
(Younes et al.
2012
). Assuming a required air change rate of 0.5 ACH and an
average available driving force due to wind and buoyancy of 1.5 Pa, a leakage rate
of 10 ACH during a pressurization test at 50 Pa (CEN
2001
) is required to
accommodate this. In the USA, estimates show that about 50 % of the dwelling
achieve a median air change rate of 0.5 ACH due to infiltration (Persily et al.),
although mean values in traditional construction in Europe are smaller, at about
0.1-0.2 ACH (Pietrzyk and Hagentoft
2008
; Jokisalo et al.
2009
; Kalamees
2007
).
