Because of several motivators, such as the mitigation of global warming, the reaching of peak oil and health concerns related to fossil fuel burning, contemporary building practise is searching for advanced concepts and technological innovations that will allow to maintain or improve the comfort level that is currently reached while reducing the energy consumption that is related to it. Ventilation is ambiguously related with this energy saving rationale. Since it makes up for about half of the energy consumption in well insulated building, it is an attractive target for energy saving measures. However, simply reducing ventilation rates has unwanted repercussions on the indoor air quality. Two main strategies have been developed to reconcile these seemingly opposing interests, namely heat recovery and demand control ventilation. This paper focuses on the energy saving potential of demand controlled mechanical exhaust ventilation in residences and on the influence such systems may have on the indoor air quality to which the occupants of the dwellings are exposed. The conclusions are based on simulations done with a multi-zone airflow model of a detached house that is statistically representative for the average Belgian dwelling. Several approaches to demand based control are tested and reported. Both energy demand and exposures are reported in comparison with a classic system, operating with continuous flowrates, that is building code compliant. This is necessary to assure that the reported energy saving potential does not derogate the indoor air quality. Within the paper exposure to carbon dioxide and to an odour tracer gas are used as indoor air quality indicators. Monte-Carlo techniques are used to ensure that the reported results are representative for the diverse boundary conditions and parameters that may occur with real life implementation of such a system. Under the conditions that were applied, reductions on the energy demand for ventilation -with the exclusion of adventitious ventilation and infiltration -of 5 to 60% can be reported, depending on the control strategy that is implemented.

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Moisture-related damage is an important issue when looking at the performance of building envelopes. In order to accurately predict the moisture behaviour of building components, building designers can resort to Heat, Air and Moisture (HAM) models. In this paper a newly developed heat and mass transfer model that is implemented in a 3D finite volume solver, Fluent®, is presented. This allows a simultaneous modelling approach of both the convective conditions surrounding a porous material and the heat and moisture transport in the porous material governed by diffusion. Unlike most HAM models that often confine to constant convective transport coefficients it is now possible to better predict these convective boundary conditions. An important application of the model is the convective drying of porous building materials. Especially during the first drying stage, the drying rate is determined by the convective boundary conditions. The model was validated against a convective drying experiment from literature, in which a saturated ceramic brick sample is dried by flowing dry air over one side of the sample surface. Temperature and relative humidity measurements at different depths in the sample, moisture distribution profiles and mass loss measurements were compared with simulation results. An overall good agreement between the coupled model and the experiments was found, however, the model predicted the constant drying rate period better than the falling rate period. This was improved by adjusting the material properties. The adjustment of the material properties was supported by neutron radiography measurements.