Intelligent Building Enclosure
as Energy and Information Mediator
Ardeshir Mahdavi and Khee Poh Lam
One essential aspect of building activity may be interpreted as defining
boundaries between 'inside' and 'outside'. The notion of the building as
a protective shell or a climate modifier emphasizes this utilitarian view. 1
In fact, building enclosures define physically the interface between the
(principally) non-controllable outdoor space and the (commonly) controlled
indoor space. This control aspect implies that the building enclosure handles
environmental factors as a selective and flexible 'filter'.
Traditionally, this filtering function has often been seen to be limited to
the domain of matter/energy flows. Solar radiation and mechanical waves
(sound, vibration) are typical examples of energetic impact, whereas air and
water impact involve mass transfer. The informatory aspect of the underlying
environmental relationships has often been either neglected or insufficiently
addressed. However, the informatory aspect of the building enclosure is by
no means limited to the variations of information flux as a result of the
material-energetic filtering effect. Building enclosures also mark the extension
of architectural artifacts (elements of the built environment) both in the
spatial and 'programmatic' sense. They thus define structures that can be
recognized, attributed, referenced and viewed in relation to other components
of the environment. Enclosures not only modify the informatory flux relevant
to building occupants but act simultaneously as sources of information for
observers and/or visitors.
This multi-fold functionality and the related, complex pattern of
concurrent formal and functional requirements explain why the realization of
high-quality enclosure systems has always been regarded as a critical and
demanding challenge for building designers. At the same time, it implies
the necessity of a conceptual framework for an integrative approach to the
design and evaluation of building enclosure systems. 2 Based on human
ecological terminology and studies in building physics, this contribution
deals particularly with the informatory aspect of building enclosures as a
'mediator' between building inhabitants and environmental factors. To
demonstrate the wide pertinence of this concept, different strategic levels
of information processing have been considered. The topics discussed here
include (in increasing order of the dominance of the informatory aspect) the
importance of energy distribution patterns for the hygro-thermal evaluation
of building components, the role of information processing considerations in
the definition of acoustic performance requirements of building envelopes,
the importance of flexible control strategies to assure adequate degrees of
freedom in the determination of indoor climate, and the significance of the
communicative function of building enclosures.
Hygro-Thermal Evaluation of Building Components
Architectural heat transfer computation has relied traditionally on the
concept of U-value, which may be regarded as a single energetic specifier in
terms of its dimensional reference (conductive thermal energy flux) and the
related quantitative/scalar nature. The concept of U-value is based on the
notion of 'uniform' one-dimensional heat transfer across the boundaries of
planar building components. This concept cannot be applied to describe
the thermal behavior of building components which involve more complex
distribution patterns of thermal energy (higher 'structural complexity')
and thus require a higher level of information processing in terms of the
description of the phenomena involved. 3 Numerous studies have shown that
the assessment of this higher degree of complexity is necessary if significant
indicators of the hygro-thermal behavior of building components, such as
the minimum indoor surface temperature (important for the evaluation
of surface condensation risk) need to be accurately predicted (Heindl et al.,
1987; Mahdavi 1993a; Mahdavi and Mathew, 1992; Panzhauser et al., 1990;
Panzhauser and Mahdavi, 1989).
Illustrating this point are the results of a study of a significant number
of constructions that are typical in residential and light commercial buildings
in North America (Mahdavi and Mathew, 1992; Mahdavi et al., 1992).

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