Since its start in 1978, the Laboratory and Entity of Building Physics has been involved in basic applied research, consultancy and educational activities in the fields of heat, air and mass transfer in porous materials and building elements, durability, energy consumption in buildings, sustainable construction, building acoustics and room acoustics. To manage that broad field of activity, the entity consists of two units: acoustics and heat&mass. In the period 1996- 1998, the acoustics unit, headed by G. Vermeir, intensified its co-operation with the Entity of Acoustics and Thermal Physics of the Department of Physics within the Faculty of Sciences. This allowed a better usage of the extended infrastructure at the Physics Department. With the aid of the university, the industry and the Flemish government, the heat&mass unit, headed by H. Hens, realized a unique new construction for field testing, called the VLIET Test Building. In attendance of a new laboratory building, which should be constructed close to the principal building of the department, all other laboratory facilities are parceled over three locations.
Current research and consultancy activities are concentrated on the performance
based design of highly insulated envelopes, risk analysis, durability and
service life, low energy buildings and sustainable construction. The approach
contains three levels: materials, building components and whole buildings.
At the material level, the measurement and modeling of the thermal, moisture and
airflow properties and the analysis of damage development have the largest share
in the overall activity. At the component level, the research activity focuses
on the combined heat, air, moisture and salt transfer in highly insulated wall,
roof and floor systems and its relation with durability of the outside cladding
and finish. The methodology includes modeling, accelerated laboratory testing,
hot box measurements and field testing. At the building level, energy
consumption and sustainable construction are the main key interests. Here, field
work in buildings plays a vital role.
1.1. Single Mode Nonlinear Resonant Acoustic Spectroscopy (SIMONRAS) for damage
detection in quasi-brittle materials
Due to the complex compliance of micro-inhomogeneities, the elastic behaviour of
brittle materials is manifest by strong nonlinearity, hysteresis in stress-
strain relation, and discrete memory. In order to quantify the presence of
mesoscopic features (micro-cracks, low aspect ratio pores, grain-to-grain
contacts, etc) and damage in quasi-brittle materials, we developed a new tool
for non-destructive testing, which focuses on the acoustic nonlinear (i.e.,
amplitude dependent) response of the material's resonance modes when driven at
relatively small wave amplitudes. Granular and micro-cracked (or damaged)
materials always show softening of the elastic modulus and generation of
harmonics with increasing drive levels in resonance experiments at strains as
low as 10-8. For example, the included figure shows the nonlinear resonance
behaviour (measured acceleration versus frequency) of the first mode in the case
of two slate beams. For an intact sample the resonance frequency is constant
and there's no evidence of harmonics generated by the material. In a damaged
sample the resonance frequency shifts significantly as a function of drive
amplitude and the level of harmonics increases dramatically.
Figure 1.1: Examples of resonance curves and harmonics
The observed nonlinear behaviour is used as a diagnostic method to quantify the
degree of damage in a material. The technique has been applied to various quasi-
brittle (building) materials in order to discern damage due to mechanical,
hygrothermal, chemo-mechanical loading. In all cases, we observed a rapid and
significant increase of the nonlinear parameters early in the loading process
and only a small to modest variation of the linear parameters (wave speed,
attenuation). We are currently investigating the influence of heat-rain and
frost-thaw cycles on the nonlinear behaviour of slate plates.
1.2. Nonlinear wave modulation spectroscopy
It is known that materials containing structural damage have a far greater
nonlinear elastic response than materials with no structural damage. In order
to discern damage in materials of arbitrary geometry, a technique called
Nonlinear Wave Modulation Spectroscopy (NWMS) has been developed. This method
specifically interrogates the nonlinear response of a sample by exciting it with
continuous waves of two separate frequencies simultaneously, and inspecting the
harmonics of the two waves, and their sum and difference frequencies
(sidebands). Undamaged materials are essentially linear in their response to
the two waves, while the same material, when damaged, becomes highly nonlinear,
manifested by harmonics and sideband generation. The approach has proved to be
time efficient and effective in discerning damage to materials in our
experience. The method has been successfully applied to corrosion detection in
reinforced concrete, investigation of delamination in bonded composites, and
single crack detection in plexiglass, sandstone and automobile engine components
(figure).
Figure 2.1: Examples of nonlinear wave modulation spectroscopy.
Nonlinear Wave Modulation Spectroscopy on an intact and damaged engine
component. The two injected frequencies are 6.7 and 127.4 kHz. The intact sample
does not show modulation, whereas the damaged sample has multiple sidebands
(127.4kHz ( n*6.7 kHz).
1.3. Multi-scale network model for simulating moisture transfer properties of
porous media
A multi-scale network model is presented to model unsaturated moisture transfer
in hygroscopic capillary-porous materials showing a broad pore-size
distribution. Both capillary effects and water sorption phenomena, water vapour
and liquid water transfer are considered. The multi-scale approach is based on
the concept of examining the porous space at different levels of magnification.
The conservation of the water vapour permeability of dry material is used as
scaling criterion to link the different pore scales. A macroscopic permeability
is deduced from the permeabilities calculated at the different levels of
magnification. Each level of magnification is modelled using an isotropic non-
planar 2D cross-squared network. The multi-scale network simulates the
enhancement of water vapour permeability due to capillary condensation, the
hysteresis phenomenon between wetting and drying, and the steep increase of
moisture permeability at the critical moisture saturation level. The calculated
network permeabilities are compared with experimental data for calcium silicate
and ceramic brick and a good agreement is observed.
Figure 3.1: Comparison of the liquid water filling distributions for
wetting (a) and drying (b) at a capillary
1.4. Continuum and discrete modelling of isothermal water and air transfer in
porous media
Water imbibition into porous building materials is a two-phase flow process in
which the imbibing water displaces the air that is initially present in the pore
space. Accurate non-destructive measurements of transient moisture content
profiles during imbibition into calcium silicate brick indicate that the air
outflow boundary condition has a predominant influence on the water imbibition
process. Significant differences are observed in the water sorption coefficients
and the inflow surface moisture contents of water imbibition experiments with
free and bounded air outflow boundary conditions.
The time scale differences between the water and the air flow process and the
limited place resolution of the non-destructive moisture content measurement
preclude the simultaneous and accurate measurement of both transfer potentials.
A direct calculation of the water and air transfer coefficients from an
imbibition experiment is thus impossible.
Discrete modelling of the pore space is used as an indirect way to calculate
these coefficients. Six parameters are identified that characterise the
geometrical and topological properties of the pore space. The values of these
parameters for calcium silicate brick are calculated so as to conserve the
crucial water transfer properties of the porous medium: (i) the critical
moisture content, (ii) the capillary moisture content and (iii) the moisture
content dependence of the water diffusivity. Percolation concepts are used to
incorporate these macroscopic water transfer properties into the discrete
network model. In a second step, the one-phase mass transfer coefficients of
water and air are calculated from the discrete network model using a stationary
approach. The residual air saturation for different boundary conditions is
calculated from a dynamic immiscible displacement approach.
Continuum modelling of the imbibition process using a two-phase flow approach
and the calculated mass transfer coefficients confirms the experimental
observations.
1.5. Development of a new methodology to analyse the durability of facade repair
systems
Brite-Euram
The main objective of the project is to establish an overall
system of envelope repair and retro-fitting performances,
associated design criteria, rules, practices and controls. The
deterioration of building envelopes is strongly related to
HAMST-effects (heat, air, moisture and salt transfer). The
scientific objectives of the project are the enhancement of the
basic HAMST-knowledge, the development of an extended database
of material properties and testing procedures relevant for HAMST
and a HAMST-software programme.
Project tasks:
1.6. Damage model for quasi-brittle non-saturated porous media
Porous materials like concrete are strongly hydrophilic. They have pores with a
large specific surface. As a result, such materials exhibit strong fluid-solid
interaction. In cementitious materials, the following microscopic fluid-solid
interactions are documented in literature: capillary pressure, disjoining
pressures due to hindered adsorption in the micropores, and pressures due to the
presence of interlayer hydrate water in the nanopores of the CHS hydrate. The
fluid-solid interaction induces high micro-stresses in the skeleton. The level
depends on the degree of saturation. Therefore, changes in that degree may
significantly affect the macroscopic poro-mechanical behaviour. We distinguish
the following phenomena are: change of static and dynamic mechanical properties
including damage and fracture, volumetric changes, time-dependent behaviour.
Quasi-brittle materials are sensitive to micro-crack initiation, growth and
coalescence of micro-cracks, which finally leads to localisation in the form of
macro-cracks. The growth of micro-cracks not only induces a degradation of
mechanical properties, but it also implies a change in the solid-fluid coupling
coefficients.
Advanced plasticity and damage models have been developed to model strain
softening behaviour of damaged materials. However, moisture dependence is often
included in a simple way by considering the model parameters to be dependent on
moisture content. When dealing with the complex interaction of different
phenomena, such as damage, time-dependence and moisture behaviour, new
constitutive equations, which formulate the coupling in an explicit way are
required. In this study a poro-visco-elastic damage model is proposed. The
constitutive equations introduce coefficients coupling elastic-damageable,
viscous and poro-mechanical behaviour. The coupling coefficients are derived for
the non-saturated case from a micro-mechanical model. The identified coupling
coefficients account for the following phenomena: elastic behaviour of the
undamaged skeleton, elastic opening of the existing micro-cracks, damage growth
due to micro-crack development, permanent strains due to an imperfect closing of
the micro-cracks and viscous behaviour of the undamaged skeleton. An incremental
finite element model is formulated. The model is used to simulate the poro-
mechanical response for standard experiments. In the uniaxial tensile test, the
influence of drained and undrained boundary conditions on the damage behaviour
is analysed. Also the influence of damage and viscous effects on the swelling
behaviour of porous materials is studied.
Non-local and gradient enhanced damage models are able to properly model
localisation phenomena in quasi-brittle materials. By the introduction of an
internal length scale they avoid mesh-size sensitivity in finite element
calculations and are capable of describing size effects. To experimentally
determine the internal length scale and other damage model parameters, indirect
identification methods have to be used. The method presented is based on the
Markov estimation procedure, which also permits to evaluate the accuracy and the
well-posedness of the identification problem, characterised by the uniqueness
and identifiability of the estimated values. This information offers the
possibility to compare and optimise the designs of laboratory tests in order to
minimise the effect of errors on the estimated values. The indirect
determination of the gradient damage parameters based on global response
measurements far from the crack on one-size specimens is sensitive to the
problem of ill-posedness due the high correlation between the gradient damage
parameters, which dominate the localisation process. The size effect method can
be used as an accurate identification method for the gradient damage parameters,
when information on the tensile behaviour is included and a sufficient size
range is considered. Local displacement analysis close to the crack provides
sufficient information with respect to the identification problem independently
of the size of the specimen and gives the most accurate parameter estimations.
1.8. Water and salt transfer in porous building materials
Salt-induced decay processes are one of the major reasons for the decay of stone
buildings and monuments. Salt attack is due to the combined action of hygric,
thermal, physical and chemical factors. Efflorescence only causes aesthetic
damage. Hydration and crystallisation of salts in the pore system however cause
an increase in volume and a pressure build-up, which may lead to damage.
The experimental part of the research concentrates on the changes of the hygric
properties of a material caused by the presence of salts in the pore structure.
These influences are investigated on a classical red clay brick. At relative
humidities, higher then the equilibrium relative humidity at salt saturation the
moisture content increases and the hygroscopic curve is lifted up. This results
in higher moisture content and a more difficult drying-out of the material. The
moisture transport properties of the material change due to salt presence: salt
solutions have a higher viscosity and another contact angle, density and surface
tension than water and the pore structure is changed due to the presence of
salts. The diffusion-dispersion coefficient of salts is calculated from a
break-through column experiment.
The main part of the research focuses on the modelling of these salt phenomena:
the coupled heat- and moisture transfer, diffusion of salt ions due to a
concentration gradient, the transport of soluble salts, crystallisation and
dissolution of salts, hydration of salts. The influence of the salt
concentration on the moisture properties causes a non-linear coupling of both
transfer processes. A finite element code has been developed in order to model
the combined heat- and moisture transfer in porous materials. The salt transfer
equation is a convection-diffusion equation. The accurate modelling of the
interaction between convective and diffusive processes coupled to sharp-front
transport problems necessitates special numerical techniques. A stream-line
upwind Petrov-Galerkin technique is used to tackle the numerical problems. The
combination of element free Galerkin techniques (EFG) with classical numerical
techniques for convection-diffusion problems is investigated. The EFG method
only requires nodes and no element connectivity, so it allows easily a mesh
enrichment at sharp moving fronts.
1.9. Service life prediction of building materials and structures
FWO-project + OT-project
Service life prediction is an important topic within the larger
research area of Life Cycle Assessment of buildings. LCA
intends to develop rationales for an optimisation of building
materials and components with respect to their energetic,
economical and environmental qualities.
The service life of a building material or a structure is the
space of time during which it fulfils all functional and
performance requirements imposed. The scatter in observed
service live is generally high due to the complex deterioration
mechanisms involved and the random nature of environmental
conditions and structural properties. Consequently, there is an
increasing tendency to a probabilistic approach, called
reliability analysis. In this context the service life is
defined as the probability of failure at any stage during life.
The analysis is based on a systematic methodology including the
following steps:
The project is dedicated to the development of the necessary
numerical simulation capabilities and the experimental
equipment and procedures, which should allow an in-depth
investigation of the novel design philosophy. In the project
the service life prediction is applied to quasi-brittle porous
media such as cementitious materials, ceramics and natural
stones, focusing on the combined deterioration processes
related to hygro-thermal load and chemical attack.
This research should result in 2 Ph.D.'s: 1) moisture transfer
at interfaces of combined porous materials, carried out by
W. Depraetere within the framework of the FWO-project 2) a
stochastic approach to heat and moisture transfer in
heterogeneous porous media, carried out by S. Roels within the
framework of the OT-project.
1) Moisture transfer at interfaces of combined porous materials:
2) A stochastic approach to heat and moisture transfer in
heterogeneous porous media:
Measurements of density, porosity, capillary moisture content,
water absorption coefficients and moisture retention curves are
performed on these samples. Differences in material properties
are linked to the micro-structural composition obtained by
scanning electron microscopy (SEM). With all the information a
stochastic random field-model of the material properties is
developed to come to reliable 1D- and 2D-simulations.
1.10. The influence of water repellant agents on moisture transfer properties of
porous media
IWT-project
Nowadays, a water repellent treatment is part of almost every
restoration or renovation project, and even a lot of new
constructions are treated with a hydrophobic protection. The
use of water-repellents can indeed be very beneficial, both to
prevent various types of deterioration and to cure certain
damages. Treatment of masonry with hydrophobic agents makes it
less penetrable for rain water which is often composed of
aggressive constituents. A lowered moisture content in the
facade reduces biological growth, efflorescences and frost
damage.
Water repellent treatments suppress the capillary forces which
suck water into porous media. Rather than blocking the pores,
ideal water repellents only influence the surface tension at
the pore walls. Water repellent agents contain an active
ingredient, dissolved in an organic solvent or emulsified in
water. The active ingredient is in most cases based on silicon:
silicon resins, siloxanes and silanes. In order to avoid
inhomogeneous treatment, often achieved by brush or airless
application, samples are treated in the laboratory by means of
a surface contact with the water repellent mixture at a fixed
contact time. The ideal penetration depth varies between 2 and
10 mm.
The effect of siloxane impregnation on the moisture behaviour
of clay brick and sand-lime brick has been examined in
comparison with untreated substrates. Important hygric
parameters are investigated: the change in water vapour
conductivity due to the surface treatment, the water retention
curve, the resulting liquid diffusivity's for water absorption,
the capillary saturation point and the drying behaviour of the
masonry after an effective impregnation.
The test shows that a siloxane treatment, if properly applied,
repels rain water quite effectively. The question, however,
remains whether the experience gained on rather small test
elements in laboratory conditions can be translated to the
application on a real building.
1.11. The influence of the coupling between heat and moisture transfer on the
heat transfer between buildings and the ground
IWT-project
Forty percent of the total annual energy consumption in Europe
goes to the heating, cooling and use of buildings. In the
efforts to decrease our global energy consumption, buildings
cannot be ignored. The design and application of appropriate
measures however demands a thorough knowledge of the heat
transfer mechanism between a buildings and the environment. The
heat loss from buildings to the ground is one of these
mechanisms.
The largest share of the currently existing research on heat
transfer between buildings and the ground considers the thermal
properties - conductivity and capacity - of soil to be
constant. Furthermore, a simplified heat balance at the
surface generally is applied. In most cases, only convection
is considered, ignoring phenomena as radiation, evaporation and
others. While this approach may have several advantages, it
ignores the important coupling between heat and moisture
transfer in soil, and the possible influence of phenomena other
than convection on the surface temperature. For instance, the
moisture content of the soil is the predominant factor in the
thermal conductivity; ground water flow causes enthalpy
transfer; evaporation may lead to a substantial damping of the
surface temperature.
The aim of this doctoral project is the evaluation of the
influence of the coupling between heat and moisture transfer
and of the complete heat balance at the ground surface, on the
heat loss from buildings to the ground. Therefore, a three-
dimensional finite element model for coupled heat and moisture
transfer in soils is under developement, based on the
description of Milly, whom further elaborated the equations of
Philip and De Vries. Complementarily, the complete heat and
moisture balance at the surface will be implemented.
Comparative calculations with and without coupling between the
temperature and the moisture field and with and without the
complete heat balance at the surface, should allow conclusions
on the importance of the phenomena under consideration. After
that, the thermal performance of some standard insulation
strategies for building parts in contact with the ground will
be reassessed with the coupled model. Perhaps. the effect of
the hygric behaviour could bring new insights.
1.12. The VLIET test building: field evaluation of highly insulated building
components
VLIET-project
This research project dealt with the construction and
management of a test facility for the investigation of highly
insulated building envelope systems exposed to the outside
climate. The facility allows to test twenty wall and twenty
roof components simultaneously. Eight building product
companies, IWT and the university participated in the project.
The companies had their materials and systems tested during the
first measuring campaign (1996-1998).
The main objective of the first campaign was to investigate
whether a better than normal thermal quality is achievable with
current construction practices in Belgium. Therefore the
thermal and moisture performances of following building
components have been monitored in detail: cavity walls, walls
with fibre cement cladding, duo-pitched tiled roofs, low slope
roofs with zinc sheeting and floors on grade, all with design
U-values of 0.2 W/(m2K).
The measuring results revealed physical and technological
difficulties to achieve the designed thermal quality in
reality. The effective performance of the highly insulated
systems was mainly affected by air gaps and thermal bridges
characteristic of existing construction methods. For instance,
the measured thermal permeance of some tiled roofs increased up
to 200% of the predicted value due to wind-driven air
infiltration through vents and joints in the underlay.
Measurements on the cavity walls showed the sensitivity of the
performance of these systems to the workmanship quality of the
insulation: the effective thermal permeance varied from 0.21 to
0.86 W/(m2K)), depending on the size of air gaps around the
insulation boards. The results further indicated that highly
insulated envelope systems need improved and tailored methods
for moisture control to ensure a good durability.
The results of the first measuring campaign generated the
following rules for the design and construction of envelope
systems with high thermal quality and safe moisture performance
in the Belgian climate: (1) continuity of the thermal
insulation layer to prevent air rotation, (2) air barrier at
the inside of the thermal insulation to prevent air
exfiltration, (3) vapour permeable air retarder at the outside
of the thermal insulation to prevent wind-washing and allow
drying and (4) adequately designed structural elements to limit
thermal bridging.
1.13. International Energy Agency, Annex 32: Integral Building Envelope
Performance Assessment
Annex 32's overall objectives are to optimise building envelope
performance and to minimise risk for envelope failure. The
desired level of envelope performance follows from an
integration of the building users requirements with the
societal requirement of lessening the building impact on
overall energy consumption and environmental load. To achieve
both objectives, a methodology has been conceived which
provides the design and construction professionals with the
elements needed to fill in the gaps in present practice. The
methodology includes a framework for identifying in a
systematic and hierarchical way the performances embedded in
the design criteria. She also helps in matching the relation
between the performance requirements specified and the design
solutions. The verification of the performances requirements is
a core process. Annex 32, therefore, provides a package of
design verification tools, design guidelines as well as the
tests needed for verifying the constructed envelope. The Annex
contains two subtasks:
Subtask A: Building Envelope Performance Assessment Methodology
Subtask B: Evaluation of the Assessment Methodology and Design Tools
National teams involved: Belgium (Operating Agent), Canada,
Japan, Greece, Italy, Denmark, Germany, Finland, France, The
Netherlands, UK and USA.
Internet address:
http://www.bwk.kuleuven.ac.be/bwf/projects/annex32/frameanx.htm
1.14. Reliable control of interstitial condensation in lightweight roof systems
The general objective of this Ph.D.-research was to develop
calculation and assessment methods to improve the reliability
of condensation control systems in lightweight roofs,
considering the uncertainty to achieve continuity of
air-tightness in building practice. An assessment method has
been developed based on a stochastic approach to moisture
performance analysis and on concepts of industrial risk
analysis. To predict the thermal and moisture performance of
lightweight systems, a two-dimensional transient model has been
developed for the combined heat, air and water vapour transfer
in building components. The model allows for a two-domain
description in terms of porous media and air channels.
The calculation method has been applied to produce a better
understanding of the effects of air movement and
discontinuities on the performance of lightweight roofs. The
development of the assessment method involved the definition of
design climate values for the evaluation of condensation risk
due to air leakage, the definition of limit state values to
assess the risk and the use of `redundant' protective measures
to reduce the risk. The research has produced tools and
recommendations for the design of lightweight roof systems with
reliable control of interstitial condensation.
Figure 14.1: Predicted velocity and temperature distribution in a 60
degree-sloping roof
with air gaps: global velocity field (left), porous field (middle, scale x15),
condensation profile (right)
1.15. Transparent insulation: an alternative solution for the summer discomfort
VLIET-project
By applying transparent insulation materials (TIM) as an
external insulation, as a glazing system or as a solar
collector, the energy losses in a building are reduced and even
switch to energy gains by passive and/or active use of the
incident solar radiation. Characteristically, because of the
transparency and the structure of the material, solar radiation
is transmitted but convection in and conduction through the
material suppressed, so that the heat losses towards the
surroundings are reduced.
From June 1995 until June 1998 a research project on
transparent insulation went on in co-operation with the Group
for Mathematical Analysis of the University of Gent. In the
project an early developed 1-dimensional model for the
transient heat transfer through TIM was upgraded and extended
to a 2-dimensional model for different applications of TIM in
buildings. The model can be plugged in as an extra component in
the ESP-r simulation program for transient heat transfer in
buildings (from the University of Strathclyde, Glasgow). The
model has been validated through measurements in situ on the
TIM-walls of the VLIET test building. Three different TIM-walls
were designed: a traditional wall with TIM as external
insulation, a TIM-wall with natural convection in the air gap
between the TIM and the massive layer and a third wall, equal
to the second, but with extra mineral wool at the cavity side
of the massive layer. From earlier research we knew that the
traditional TIM-wall without any solar shading gives
substantial energy gains during the heating season, but also an
unacceptable indoor climate during summer. As traditional
outdoor solar shadings are quite expensive, this research was
made to examine alternative and cheaper solutions for the
summer discomfort: natural ventilation of the air gap between
TIM and massive wall and/or extra insulation of the massive
wall with opaque insulation at the cavity side of that wall.
From the analysis of the winter situation the ventilated TIM-
walls seems to be energetically equivalent to the traditional
TIM-wall. The lower conductive gains were compensated by the
heat which the ventilation air could pick up in the cavity. The
summer analysis showed a larger difference between the walls.
Stack induced ventilation of the air cavity in wall 2 lowered
the indoor temperatures during summer quite a lot, but not
enough. Only wall 3, stack induced ventilation in combination
with an extra opaque insulation, achieved an acceptable indoor
climate in summer.
1.16. Performance-based assessment of active envelopes
IWT-project
Today, the development of new technologies to improve building
envelope performances is highly encouraged and provides a clear
challenge for designers and researchers. In this context
several typologies of active envelopes have become very popular
amongst designers and architects. Typically, active envelopes
consist of two panes with in between a cavity, through which
air is drawn by means of forced or natural convection.
This research tries to nuance the common favourable impression
which exists about active envelopes regarding energy
efficiency. Although active envelopes may introduce certain
benefits for certain performances, this cannot be generalised
for all performances. This research compares the energy
efficiency of several active envelope technologies to common
solutions.
Analytical and numerical models will be developed and compared
to experimental data. The models will be used in energy
simulation programs to compare the energy consumption on
building level of active envelopes to common choice solutions.
The performances of the airflow window of the DVV-Headquarters
building in Brussels and a measurement set-up in the Vliet-
test-building, Leuven are the subject of a performance-based
assessment. The DVV case study revealed that especially bad
workmanship and a wrong choice of typology dramatically
decreases the achieved performances.
Only if active envelopes save energy on building level they can
compensate for the increased built-in energy. A life cycle
energy analyses will point out whether the efforts don't lead
to disappointing small results causing the overall energetic,
economic and ecological performance to be very discouraging.
If, finally, active envelopes prove to be a favourable choice
concerning energy efficiency during the whole life span, a set
of rules of thumb will be developed to help designers predict
the performance of their solutions during design and to control
the achieved performances during and after construction.
1.17. CO2-project: Energy use and emissions in the residential sector
Electrabel, SPE
Like all industrialised countries, Belgium accepted to diminish
its greenhouse gas emissions. Electrabel and SPE started an
extended research on that in October 1996, involving
researchers from all universities and scientific institutes.
Aims of the project are (1) to catalogue the energy consumption
and emissions for electricity production in all type of power
stations, (2) to evaluate energy consumption in the residential
and industrial sector and (3) to analyse the impact of energy
efficiency measures on the magnitude of the emissions. The
section Building Physics, together with other labs of KULeuven
and UCL, focuses on the residential sector.
The first part of the research included an analysis of the
annual energy consumption measured in 200 parental houses of
students. Based on the database a model was developed to
predict energy use for household and lighting. An earlier
developed model (VERBRUIK) to calculate energy consumption for
heating in a building was integrated in a bottom-up model
VERBCO2, which predicts the overall energy consumption and
related emissions in the residential sector on the scale of a
city, a district, a whole country. The model uses the
statistical information on the Belgian building stock of NIS
(National Institute for Statistics). After validation we
predicted the impact of different energy conservation measures
for the whole housing stock in Belgium. Three policy scenario's
were considered: (1) restricted retrofit, unlimited expansion,
(2) more retrofit, less expansion, (3) more retrofit, no
expansion beyond 2010. In a second part the database was
extended with information on the annual energy consumption in
1200 social houses and 40 low energy dwellings. The measured
and calculated energy consumption in all 1440 dwellings was
used to further validate the bottom-up model.
The project is still going on, with a focus now on increased
energy efficiency of the heating system and optimal measures
for the building as a whole (including LCA). Conclusions after
the first two year are that although the residential sector may
contribute to the CO2-reduction, major efforts will be needed
to reach the Kyoto-objective. Increased energy efficiency of
new buildings and retrofits is not sufficient. Also the housing
policy should be reviewed, with more emphasis on retrofitting
than is the case today. Even then, reductions in emissions will
proceed slowly, as it takes at least 70 years before most of
the country's housing stock is renewed.
1.18. Optimisation of energy systems in residential buildings, a life-cycle
based analysis
IWT-project, SPE-Electrabel
As the concern about global warming grows, countries around the
world, including Belgium, make efforts to reduce the burden
upon the environment. The Kyoto-agreement aims at a significant
reduction in CO2-emissions. As residential buildings are
responsible for at least 25% of these emissions, it is
important that the residential sector contributes to the
reduction. To minimise the cost of this contribution and to
prevent any deteriorating of comfort levels that might result
from it, it is necessary to look for optimal solution.
A thorough knowledge of the energy consumption in buildings and
its dependency of envelope, habitants, domestic appliances and
heating equipment is a precondition for the study of the energy
related aspects in the life-cycle assessment of residential
buildings. As one of the elements within the strategy to gain a
better understanding of residential energy consumption, fifth
year civil engineering students and fourth year architecture
students, attending the lectures on building services, were
asked as part of the exam to perform an analysis of the energy
and water consumption in their homes. These data were used
later to develop tools for estimating the energy consumption
for heating, warm water supply and domestic appliances.
These estimates form the boundary conditions of the
optimisation problem. The goal function reflects the
optimisation criteria. The criteria can be economic,
environmental or energy related. The ultimate goal is to
construct a flexible tool for architects and designers in order
to be able to make optimal choices in developing a project. The
best solution depends after all heavily upon the boundary
conditions. These tools are not developed yet, but the results
have been used to evaluate governmental policies (insulation
regulation, subsidies,..) and strategies of energy companies.
1.19. EpiGoon
Vliet-bis project
After the energy crises of the seventies, most industrialised
countries adopted mandatory standards for the thermal
insulation of buildings. The first generation of codes focused
on the U-factor of the different envelope parts. For each part,
a maximum value was imposed. A second generation used the
overall U-factor for the envelope as indicator. This factor was
calculated as an area weighted average of the U-factors of all
individual parts. Fixation of a threshold value was based to
principles such as: loss by conduction should be a constant per
cubic meter of heated volume. This ended in reference curves as
given in the figure (Flemish decree, 1993).
Figure 19.1: Overall U-factor as a function of compactness, i.e. the
ratio between
heated volume and encapsulating surface
At the end of the eighties the goal to lower energy consumption
was bypassed by an ever growing environmental concern on global
warming and ozone depletion. This lead to decreasing U-factors.
The U-factor however governs only part of the energy
consumption in buildings, the one due to conduction losses and
gains. Ventilation, hot water production, lighting and
appliances, solar gains, are not covered at all. The lower U,
the lower the conduction losses and the less their share in the
overall energy consumption. With other words, restricting the
regulations to U-factors has a decreasing impact on total
consumption with increasing severity of the value imposed. This
tended the developed world to adopt a new approach: the energy
performance. This number represents the allowable standardised
energy consumption per m2 of heated surface, per m3 of
heated
volume or per m2 of encapsulating surface. The project aims to
develop a energy performance standard for Flanders. Partners
are: WTCB, Physibel, Daidalos, Wenk.
During the period 1996-1998, the laboratory proceeded through
99 smaller and larger industrial projects and demands for
consultancy. These projects and demands concerned (1) extended
measurements of hygro-thermal material properties, (2)
analysing and upgrading the performance of new designs for
roofs, walls and windows, (3) evaluation of industrial
processes (f.e.: accelerated drying of wet formed judo mats),
(4) damages on roofs and walls (among them the Opel industrial
plant in Antwerp, a subtropic swimming pool in Herfort
(Germany), the new metro station near the Erasmus bridge in
Rotterdam, several cases of exterior insulation in the
Netherlands, a huge fitness centre in Limburg, a modernist
school building in Vlaams Brabant, dwellings in Belgium and
abroad (i.e. Berlin), a museum in Gouda, the Netherlands.
Especially metallic roofs entered the damage files. These files
were of great help in feeding the doctoral study of Arnold
Janssens), (5) low energy dwellings and office buildings, (6)
the MIRA environmental reports Flanders, (7) large scale energy
consumption prognosis for the tertiary sector in Flanders, (8)
the competition 'Zonnewoningen' of Electrabel, where the lab.
was involved in a technical evaluation of all participating
projects
Each project ended with an extended report. These reports can
be used for research purposes.
Since its start in 1978, the Laboratory of Building Physics has been involved in
research and
educational activities in the field of acoustics in the Faculty of Applied
Sciences. There are courses on building acoustics, room acoustics and noise
control. The lessons are taught in Dutch and are attended by civil engineering
students of the building construction and architecture departments, and by
postgraduate students in environmental engineering.
The research activity concerns the sound insulation of sandwich panels, the
flanking transmission in building structures, room acoustical prediction and
measurement methods, including applications in the field of indoor noise
control, and the study of the acoustic comfort in buildings.
In the research on sound insulation of sandwich panels, the basic phenomena
related to airborne and structure-borne sound transmission through layered
plates are studied. In the theoretical modelling, panels of infinite and finite
extent are considered. The model of an infinite panel allows the study of the
influence of the different wave types in the layers, of the boundary conditions
between the layers and of the mechanical properties of the layer materials. The
model of a finite panel allows the study of the modal vibrational response and
the sound radiation of the panel. The experimental study relies on a combination
of vibration and sound intensity measurements. These experiments are
complemented by the measurement of the elastic parameters of the materials.
In the research on flanking transmission in buildings structures, the
vibrational sound transmission at junctions between plates is studied. In the
theoretical modelling, plates of infinite and finite extent are considered, and
different joint designs including rigid, pinned and elastic joints are studied.
The experimental study is performed on a scale model of a plate structure, using
vibration and structural intensity measurements.
In the room acoustics research, methods to predict, measure and control the room
acoustical properties in closed spaces are studied. The prediction method is
based on cone/ray tracing, and allows the control of most relevant room
acoustical quantities for the case of single and multiple sound sources. By
comparison with analytical models and experimental results, the validity of the
model is investigated. The model has been applied in the design of lecture and
concert halls, and in the study of the sound propagation and sound reduction in
factory halls. The experimental room acoustics research focuses on the
development and the use of signal analysis methods that allow for an accurate
and repetitive measurement of the room impulse response and related quantities.
In the study of the acoustic comfort, the relation between environmental sound
sources, the sound insulation of building constructions and the (dis)comfort
resulting from the residual sound exposure is investigated. The purpose of the
research is the establishment of guidelines to realise sufficient acoustic
comfort indoors and in the direct surrounding of the building.
Finally, the Laboratory is involved in industrial projects including the
measurement of material and construction properties, room acoustics and noise
control consultancy, and environmental noise studies.
Preparing the future
Since 1996 great effort has been delivered for the preparation of a merging
between the acoustics group of the Laboratory of Building Physics and de
Laboratory of Acoustics and Thermal Physics. This resulted in an agreement by
the Directory Council of the University in 1997. A budget was attributed for
the construction of an extension to the laboratory facilities.
The construction will start in august 1999.
Since 1998 the already long lasting collaboration was intensified, resulting in
several research, development and consultancy projects.
The investigations at the Laboratory of Building Physics were concerned with the
improvement of the accuracy and applicability of Statistical Energy Analysis for
predicting airborne and impact sound insulation in buildings. In view of the
importance of flanking transmission, which is largely determined by vibration
transmission between walls and floors, accurate SEA predictions require accurate
coupling loss factors describing the energy flow between plates. The research at
the Laboratory of Building Physics aimed at enhancing SEA, by extending the
state-of-the-art of calculating coupling loss factors to junctions of
orthotropic and point connected plates. While most of the work was concerned
with calculating coupling loss factors using the wave approach for semi-infinite
plates, much attention has been paid to the evaluation of the restrictive
assumptions inherent to SEA by means of a semi-modal superposition technique for
finite-sized plates.
The scientific results were obtained in the context of a Ph.D. research. The
following paragraphs will summarize the various conclusions while relating the
results to the publications generated during the research project.
Structure-borne sound transmission between orthotropic plates
Structure-borne sound transmission between point connected
plates
Validation of Statistical Energy Analysis using semi-analytical
calculation models
Figure 2.1: SEA experimental verification
2.2. Sound insulation of composite walls
The purpose of this project is to study the sound transmission through double
wall constructions with local coupling elements. The modelling uses the wave
approach and results obtained with a description of the coupling by introducing
local stiffnesses for differential movement of both blades for translation and
rotation (see figure).
A holographic measuring set-up is developed for the measurement of the sound
transmission on scale 1:4. The test-wall is placed between two rectangular
reflecting concrete boxes. The sound field is scanned in a plane close to the
radiating wall (see figure).
2.3. In-situ determination of the elastic properties of building materials
In this research we looked for methods to measure the stiffness properties of
beams and plates. This work resulted in three measuring methods in the range
from 100 to 4000 Hz. The first technique the bending wave velocity for
acoustically thin beams and is based on the finite difference approximation of
the bending wave-number. The other two methods involve the measurement of the
plate response in two points in order to determine the bending wave
velocity for acoustically thin as well as for acoustically thick plated. Both
these methods are convenient to estimate the angle dependent wavespeed of
orthotropic plates. The three measurement methods have been verified by
experiments on beams and plates of various materials and thicknesses.
Figure 2.3: Measurement set-up used in the experiments on the
acoustically thin PVC beam
2.4. Low-frequency airborne-sound transmission through single partitions in
buildings
The low-frequency (20-250 Hz) airborne sound transmission of single partitions
is investigated. Three theoretical models are used for the prediction: an
infinite plate model, a baffled plate model and a room-plate-room
model.(illustration). The calculation models are verified
by detailed comparisons with experimental results obtained in the laboratory. A
parametric study is carried out to examine the influence of the dimensions of
the room and the partition. The results demonstrate the strong modal behaviour
of the low-frequency sound transmission. As a result, the low-frequency sound
insulation depends not only on the properties of the test wall, but also on the
geometry and the dimensions of the room-wall-room system (see illustration for a
measurement and calculation of a test on a window pane). In general, the large
variation of the low-frequency insulation compromises the accuracy of a
prediction of the sound insulation in situ.
Figure 2.4: CSTC/KUL transmission rooms. Measured SRI and transmission
loss (TL).
2.5. Room acoustical simulation: further development and research
The prediction of room acoustical properties and sound propagation in closed
spaces is a fundamental topic in architectural acoustics and indoor noise
control. The problem essentially concerns the calculation of the sound field in
a closed space with sound-absorbing boundaries, possibly fitted with arbitrarily
positioned objects, and excited by a single or multiple sound
sources. An exact solution of this problem without excessive computational
effort is only feasible for idealised room geometry's and boundary conditions,
or for a limited frequency range.
However, it is not strictly necessary to calculate the deterministic room
response in order to evaluate room acoustical quantities related to perception
or acoustic comfort. For the study of the acoustics of general room shapes over
the whole audio frequency range, approximate methods can provide satisfactory
results. In this study, the application of an approximate
model known as the cone/ray tracing method to the solution of the problem is
investigated.
The input data of the model include the definition of the room geometry as an
assembly of plane surfaces; the position, directivity and strength of the sound
sources for different frequency bands; the position of the receivers; the sound
absorption and diffusion coefficients of the room surfaces for different
frequency bands. The geometry of a large lecture room is
shown in figure 1. In the cone tracing method, a number of image sources related
to the actual sound sources are calculated by scanning the interior room volume
by means of a small 'light-beam'. The contributions of the individual image
sources sum up to the global room response at a receiver point. In the ray
tracing method, it is assumed that the wave front emitted by a source can be
digitised as energy particles and that wave propagation can be simulated by
propagating these particles through the room along straight lines or rays. The
sound radiation of each source is modelled by emitting a large number of rays.
In both methods, specular or diffuse reflection and absorption on the room
boundary surfaces is taken into account. The calculations finally result in the
impulse (sound pressure) response or the energy (sound pressure squared)
response for the different frequency bands at each receiver position and for
each sound source. From these detailed calculation results, other room
acoustical quantities are derived: the sound pressure level, the reverberation
time, the speech intelligibility, ... Digital convolution of the broadband
impulse response with anechoically recorded speech or music
allows for an auditory assessment of the room acoustics quality.
The development of the corresponding EPIKUL software was continued. The
evaluation is done in the context of thesisworks and consultancy work. The
program was applied in the consultancy of the project `Grande Aula' of the
UCLouvain (project in collaboration with P. Mees, Daidalos, architect Ph. Samyn,
see 3D view of the simulation model) and for the consultancy concerning the
retrofitting of the famous concert hall Henri Le Boeuf of the Paleis
voor Schone Kunsten / Palais des Beaux Arts (architect Baron Victor Horta, 1929,
architect of the renovation: G. Baines). Auralisation facilities where
developed and applied in order to be able to listen to the predictions.
Figure 2.5: 3D view of the "Grande Aula", UCL, Louvan-la-Neuve.
2.6. Study of the reflection and diffusion of sound using acoustic holography.
Application to room acoustics
This project, started in 1998. It concerns the modelling of porous materials,
the application in the room acoustical modelling and the development of
holographic measuring techniques. The fundamental work focuses on the study of
surface waves which is of particular interest for long range outdoor sound
propagation and for material research.
The experience in this field will be used to improve the quality of the input
data for the acoustical simulation program. This is necessary in relation to
the auralisation of the first reflections and for understanding and
characterising the propagation of the `grazing' sound wave over the seating
area. A laboratory set-up is developed for the application of the
near-field acoustic holography (see illustration). Acoustic holography refers
to the reconstruction of a sound field in three dimensions based on the
recording of the sound field on a two dimensional plane (hologram). It has been
used whenever there is a need to visualise objects that cannot be observed
optically. Although the mathematical principles are identical to optical
holography, there are less technical restrictions to acoustic holography. The
reason for this is that the phase of the (optical) field can only be recorded by
exploiting interference with a reference beam (due to the extremely rapid
oscillations of the optical wave), whereas amplitude and phase of the acoustic
field can be recorded with great precision with microphones (enabling even broad
band recording). Since the data can be digitised, there is no need for a
diffraction pattern like in optical holography to reconstruct the field or
image. Instead, the acoustic field can be reconstructed using numerical
techniques. From the Fourier transform in wave number spectrum the
inhomogeneous plane wave components can be determined and the propagation of
surface waves can be analysed.
2.7. Distributed construction of a virtual science museum with guide,
application to education in acoustics
The aim of this project is to establish a co-operation between acoustical
experts of universities and high schools in order to develop a multimedia
learning environment. This learning environment will be build similar to a
science museum that students can visit alone or together with a guide. The
museum will be virtual and will contain a database of high-quality multimedia
materials about acoustics. The multimedia materials in the museum will be
created by the specialists in the specific fields of acoustics and using
internet tools these materials can be held up to date by those experts. The
guide is the instructor of the students and still has important didactical
tasks, like focussing the students' attention to the most important aspects,
instructing the students how to use the multimedia for effective learning, etc.
To realise this project, we focus on:
Specific goals for the building acoustics research group
For further information, see: http://educinno.rug.ac.be/onder
wijsinnov/
The research group was involved in numerous projects on materials research and
performed a large series of laboratory measurements on building products
concerning airborne sound insulation, sound absorption,.The research in room
acoustics was stimulated by several important study contracts. We mention the
design of the Aula of the UCLouvain, with the architect Ph. Samyn and the study
concerning the retrofitting of the famous concert hall Henri Le Boeuf of the
Paleis voor Schone Kunsten / Palais des Beaux Arts (architect Baron Victor
Horta, 1929, architect of the renovation: G. Baines.
1. Heat & Mass
Research Activities
Koen Van Den Abeele and Jan Carmeliet
Koen Van Den Abeele
J. Carmeliet, F. Descamps, G. Houvenaghel
pressure pc = 4.9 104 Pa. In drying a fingering effect of
the dry pores is observed.
F. Descamps
H. Hens, J.Carmeliet
Proposal No.: BE96-3290 / Contract No.: BRPR CT96 0229
Starting date: 1 December 1996 - Duration: 36 months
Co-ordinators: H.Hens, J.Carmeliet, Katholieke Universiteit Leuven (BE).
Partners: Technische Universität Dresden (D),
Helsinki University of Technology (SF), Eternit N.V. (B), Cape
Building products limited (GB), Ahlborn Messtechnik GmbH (D),
Cottbuser und Roxeler Ingenieurgesellschaft (D), Polar
Construction ldt (GB), Ct Laastit Oy (SF), Rautaruukki (SF)
Tasks (T2-T5) concern the enhancement of HAMST-knowledge,
the development of an extended database of material
properties and testing procedures and the development of
HAMST-software.
Integration task (T7) concerning the formulation of the performance
methodology.
Jan Carmeliet
Geert Houvenaghel, Jan Carmeliet
W. Depraetere (FWO), S. Roels (OT), J. Carmeliet, H. Hens
The moisture behaviour of combined porous materials is highly
determined by the interaction of the moisture characteristics
of both materials and the nature of their hygric contact.
Dependent on the porous structure of the different composing
materials, water transfer may occur from one material to
another material, but not in the opposite direction. Four types
of hygric contact can be distinguished: hygroscopic contact (a
small air layer), natural capillar contact (a small crack),
ideal and real capillar contact. Due to physical and chemical
processes (during curing), one material can influence the
porous structure of the other one at the interface of a real
capillar contact. This often results in a boundary layer at the
interface with a high hygric resistance. Also the presence of
air cavities in the interface zone may disturb the hygric
contact. All these complex phenomena can significantly change
the moisture behaviour of combined porous materials. Research
at the laboratory has been done on combinations of brick and
mortar. A finite element-model is developed to simulate the
isothermal moisture transfer in combined porous materials
including different contact conditions.
A 2D Finite Element Model is developed to simulate the
transient heat and moisture transport in open porous media. The
moisture transfer is characterised by high moisture gradients
at the waterfront during water imbibition or drying. For an
accurate description of the steep gradients very small elements
are needed in a finite element analysis. Due to the moving
water front a fine mesh over the whole domain would be
necessary. To reduce computational costs a mesh adaptive
method is implemented. The method allows to uncouple nodes
from both material particles and spatial points and to
continuously relocate the nodes around the sharp water front.
Hence, the number of elements can significantly decrease.
The influence of material properties heterogeneities on heat
and moisture transfer is investigated on Savonnières, a French,
layered limestone. To study the spatial variability of the
transport properties and the moisture retention curves, a plate
of limestone has been subdivided in small samples.
K. Bertels, C. Van den bossche, J. Carmeliet
H. Janssen, J. Carmeliet, H. Hens
A. Janssens, A. Morel, W. Depraetere, H. Janssen, S. Roels, J. Carmeliet, H.
Hens
H. Hens & F. Ali Mohamed
The objective of this subtask is to develop the Assessment
Methodology. The methodology focus on ways to apply new
concepts and making use of existing (inter-)national
experiences and guidelines. It is of use in the different
stages in the design process, and takes into account the
relation between the envelope, the climate, the building and
all services.
The objectives of this subtask are to evaluate and refine the
Methodology developed; and, to evaluate design tools and
guidelines which contribute to a lower energy consumption and a
high quality thermal and visual indoor comfort. The activities
are divided between three Thematic Groups: (1) Envelop
Laboratory & Modelling Characterisation Group, (2) Advanced
Envelopes Group, (3) Retrofitting and Traditional Envelopes
Group.
A. Janssens, H. Hens
G. Verbeeck, H. Hens
D. Saelens, H. Hens
G. Verbeeck, B. Verdonck, H. Hens
B. Verdonck, H. Hens
H. Hens, G. Verbeeck
Industrial Projects & Consultancy
Building and Room Acoustics
Research Activities
The wave approach for semi-infinite plates and the semi-modal superposition
technique for finite-sized plates were applied to junctions of thin orthotropic
plates. For this purpose, wave propagation in thin orthotropic plates was
investigated by deriving analytical solutions for the equations of motion. The
analysis emphasised on the influence of orthotropic plate characteristics on the
description of bending and in-plane wave response and on the energy flow
associated with plane wave propagation. The calculation model based on the wave
approach was integrated in an SEA calculation scheme by deriving expressions for
the modal density and the coupling loss factor for subsystems associated with
orthotropic plates. The influence of the degree of orthotropy on the structure-
borne sound transmission was studied by a parametric calculation on a range of
corner, tee- and cross-junctions. The calculation models were verified
experimentally on three corner junctions between two grooved plywood plates.
The theory of the wave approach and the semi-modal superposition technique was
extended towards the case of point connected plate junctions. Local rigid
connections were modelled by introducing an elastic interlayer with a space
dependent stiffness. The analysis was concerned with the formulation of the
boundary conditions and the implications of these boundary conditions on the
solutions to the equations of motion. A parametric calculation for a variety of
point connected plate junctions demonstrated the influence of the location, the
dimensions and the elastic properties of the coupling elements on bending and
in-plane wave transmission. The predictive performance of both calculation
models was validated on a set of corner junctions between two PVC plates.
Finally, it was shown that the reliability of SEA can be evaluated by comparing
results of SEA and the semi-modal superposition approach. It was found that SEA
predictions of structure-borne sound transmission between plates with different
properties are unreliable under the condition of low modal overlap. In addition,
the accuracy of SEA increases with increasing modal overlap factor, but a
tendency towards overestimation of transmission remains, even for a modal
overlap factor exceeding unity. The experimental verification (illustration)
demonstrated the ability of the semi-modal superposition approach to determine
whether discrepancies between SEA predictions and measured data are caused by a
violation of the basic SEA assumptions, or by an incorrect model of the
junction.
F. Nuytten( +1997) (IWT), I. Roelens, G. Vermeir (FWO Support)
I. Roelens, F. Nuytten( +1997), I. Bosmans, G. Vermeir
according to the first measurement technique.
A. Ossipov, P. Mees, G. Vermeir
(IWONL, WTCB, CEDIA U.Liège, K.U.Leuven)
L. De Geetere, G. Vermeir, P. Mees
W. Lauriks, G. Vermeir, G. Janssens, L. De Geetere
(project supported by the research council of the K.U.Leuven, 1998).
G. Vermeir, V. Meerbergen, I. Bosmans
(project supported by the Flemish Community in collaboration with 4 partners:
RUGent INTEC, VUB Werktuigkunde en Akoestiek, KULeuven, Laboratorium Bouwfysica
KAHO St.Lieven Gent)
Offering visual and auditory illustrations for use in lectures. Moreover it is
necessary to put the illustrations at the disposal of the students in order that
they are able to look at them and to listen to them at home. These
illustrations contribute to a better understanding of the theoretical
principals, as explained during the lectures.
Consultancy
Last updated by
Erik.Toorman@bwk.kuleuven.ac.be on 24 June 1999