Hugo Hens

Interlaboratory comparison of hygric properties of porous building materials

The precision of methods used for the determination of hygric properties of porous building materials was investigated. The study was performed in the framework of the EU-initiated HAMSTAD-project. Six laboratories measured the selected hygric properties of three porous building materials. While the most measured properties show acceptable agreement, yet, it was found that some of the existing standards or commonly accepted measurement methods need improvement. Most striking were large variations in the results of the vapour transmission tests performed in accordance to the existing European Standard.

Assessment method of numerical prediction models for combined heat, air and moisture transfer in building components: benchmarks for one-dimensional cases

The standardised Glaser method for calculation, prediction and evaluation of moisture performance is considered as rarely applicable. The present state of knowledge, analytical as well as experimental, concerning heat, air and moisture demands updating of standards. This paper presents five numerical benchmark cases for the quality assessment of simulation models for one-dimensional heat, air and moisture (HAM) transfer. In one case, the analytical solution is known and excellent agreement between several solutions from different universities and institutes is obtained. In the remaining four cases, consensus solutions have been found, with good agreement between different HAM models. The work presented here is an outcome of the EU-initiated project for standardisation of HAM calculation methods (HAMSTAD WP2).

Life Cycle Optimization of Extremely Low Energy Dwellings

A global methodology is developed to optimize concepts for extremely low energy dwellings, taking into account energy use, environmental impact, and financial costs over the life cycle of the buildings. Energy simulations are executed with TRNSYS. The ecological impact is evaluated through a life cycle inventory of the whole building, whereas costs are evaluated through a cost-benefit analysis. The multi-objective optimization problem is tackled by combining genetic algorithms and the Pareto concept. First, the optimization methodology is presented. Subsequently, the validity as well as the strengths and weaknesses of the methodology are discussed. Finally, the main results are presented followed by a discussion of the trade-off curves of primary energy consumption and net present value, an analysis of the embodied energy, and a study of the impact of economic parameters, such as price evolutions above inflation and discount rate.

A Comparison of Different Techniques to Quantify Moisture Content Profiles in Porous Building Materials

Several advanced non-destructive techniques are available to measure the evolution of content profiles with time, allowing the analysis of unsaturated flow and the determination of the moisture diffusivity of porous building materials. The reliability of six different techniques is investigated: the NMR-technique, the MRItechnique, the γ-ray attenuation technique, the capacitance method, the X-ray projection method and the TDR-technique. All of them were applied to measure the moisture content evolution during free uptake experiments on two building materials. Considering the limitations of some of the techniques, a good overall agreement is obtained. The work presented is an outcome of the EU-initiated HAMSTAD-project.

Coupling of dynamic building simulation with stochastic modelling of occupant behaviour in offices – a review-based integrated methodology

A comprehensive modular behavioural model for office buildings and its coupling to building simulation software is introduced, developed to be used in energy uncertainty analysis in a straightforward manner. The model includes the inherent variability in behaviour amongst individuals by defining representative active and passive users. The ratio of the latter serves as an input for the uncertainty analysis. The behavioural model consists of submodels for occupancy, use of shading system, window operation, control of artificial lighting, heat gains by appliances and the control of heating and cooling set points. All these submodels are selected from a literature review. The review revealed a lack of validation and intercomparison of the models as the principal weakness of the research field. The methodology is applied in a Monte Carlo analysis of the uncertainty on the simulated energy demands of an office building at the building level, yielding moderate uncertainties.

Determination of the liquid water diffusivity from transient moisture transfer experiments

The Boltzmann transformation method is used to determine the liquid water diffusivity from moisture content profiles as measured in a capillary water absorption experiment. An inter-laboratory comparison for analyzing the reliability of the determination method showed that the inaccuracy in the liquid water diffusivity is caused by scatter in the transformed data and by uncertainty in the boundary conditions at the intake surface and ahead of the steep moisture front. A methodology is proposed based on (1) the evaluation of the validity of the diffusion approach, (2) a simplified handling of the boundary conditions, (3) smoothing of the scattered data and (4) the evaluation of the quality of the determined liquid water diffusivity. For HAM (Heat-Air-Moisture transport) calculations values of the liquid water diffusivity for moisture contents higher than the capillary moisture content are disregarded. The liquid water diffusivity can be described by an exponential function limited at a lower moisture content bound. To describe the moisture diffusivity including liquid water and water vapour transports, a new parametric description of the moisture diffusivity is presented, which shows sufficient flexibility both in the hygroscopic and overhygroscopic ranges. When permeability is calculated from diffusivity, the permeability should monotonically increase with decreasing capillary pressure. In the hygroscopic region it should coincide with the measured water vapour permeabilities.

IMPACT OF ENERGY EFFICIENCY MEASURES ON THE CO2 EMISSIONS IN THE RESIDENTIAL SECTOR, A LARGE SCALE ANALYSIS

Like all industrialised countries, Belgium accepted to diminish its greenhouse gas emissions in the frame of the Kyoto agreement. On top of the list figures CO2. A major emission source for CO2 is burning fossil fuels. As the residential sector accounts for 28% of the country’s annual energy consumption and as this consumption mainly concerns fossil fuels, it has an equally important share in the CO2 release. Hence, at first sight, the best policy for a decrease is by improving the energy efficiency. The question to be solved, however, is which improvement could generate the reduction needed? This study discusses a methodology and comments simulations that help in answering that question. The results are not as simple as one should like. The housing stock in fact acts as a conservatory system. For the case being, the impact of energy efficient new construction on the CO2 release remains quite marginal if the period considered does not extend beyond a decade. The effect becomes significant only over a longer period, on condition that more stringent energy efficiency measures are combined with a shift from new construction to retrofit and reconstruction. Also a diminishing increase in the number of households may help in reducing energy consumption and CO2 release.

Brick Cavity Walls: A Performance Analysis Based on Measurements and Simulations

After world war two, cavity walls became a widespread external wall type in the cool but humid climate of North Western Europe. Moisture tolerance of the unfilled construction was excellent. Instead, calculation and testing underlined that the unfilled cavity walls of that era performed poorly from a thermal insulation point of view. After the energy crisis of 1973, cavity filling was therefore introduced as the main upgrade. Hence, extensive testing revealed upgrading was less simple than expected. Air in- and exfiltration through the wall, wind washing behind the fill, thermal stack induced air looping around the fill and thermal bridging all cooperated in lowering expected thermal quality of the filled walls. Anyhow, at the same time testing underlined that moisture tolerance remained outstanding in the cool, humid climate of North Western Europe also without cavity ventilation. That resulted in a set of recommendations how to construct high performing filled cavity walls.

Modelling Unsaturated Moisture Transport in Heterogeneous Limestone

In this paper we investigate the influence of microheterogeneity on the phenomenological macroscopic material properties. The material analysed is Savonnières: a French layered oolitic limestone. Due to the complex microstructure of the material the moisture permeability cannot uniquely be determined based on indirect measurement data. To overcome this problem we present an upscaling technique based on the modelling of transport phenomena on the mesoscale. The technique allows to determine an equivalent macroscopic permeability based on the geometric configuration and the permeability of the composing constituents.

Interstitial Condensation Due to Air Leakage: A Sensitivity Analysis

This paper presents an approach to evaluate the sensitivity of a roof design to condensation problems, given the uncertainty to achieve continuity of airtightness in practice. The approach consists of a repeated number of simulations with a 2D heat, air and vapour transfer model to predict the variation in roof moisture performance due to various discontinuities in roof geometry. The set of discontinuities is calibrated by comparing measuring data of roof airtightness to simulation results. On the basis of the methodology, the paper explores the effectiveness of different measures to reduce the sensitivity of cavity insulated roofs to condensation problems. The results show that even when a roof design complies with condensation control standards, a lightweight system remains sensitive to condensation problems as a result of air leakage through the discontinuities, joints and perforations, common to most existing construction methods. The sensitivity of a roof to interstitial condensation due to air leakage essentially depends on the heat and vapour transfer properties and design of the layers outside of the thermal insulation (roofing and underlay)