Heat, air and moisture (HAM) transfer in buildings

Background

Humidity of indoor air is an important factor influencing the indoor air quality, energy consumption of buildings, conservation of valuable objects and durability of building components. The relative humidity in buildings depends on several factors such as moisture sources, air change, possible condensation and absorption and release of vapor by porous materials. Porous materials are characterized by their possibility to store moisture in a liquid phase even at a relative humidity below 100% and can be found in most buildings (e.g. in the building envelope, furnishings, books, wooden objects, textiles, ...). In order to predict the relative humidity in a detailed way, the effect of moisture buffering needs to be integrated into heat and airflow simulation tools. Heat Air and Moisture (HAM) models allow describing coupled heat and mass transfer in porous materials. The research conducted in this field mainly focuses on coupling HAM models with CFD-tools (Computational Fluid Dynamics) or BES-tools (Building Energy Simulation) to predict either the local indoor humidity around objects or the indoor humidity in multizone buildings.

Scope of research

The 3D CFD-HAM model, which was previously developed, is limited to vapor diffusion in porous materials. To be able to account for condensation in building materials, this model needs to be expanded. This research project forms a continuation of the previous work and focuses both on numerical modeling and experimental validation.

A model for film condensation will be developed. Film condensation is a phenomenon in which a liquid film is formed at the surface of non-hygroscopic materials such as tiles. In a next phase this model will be extended to describe droplet condensation. Run-off of droplets will be taken into account. Both newly developed models will be implemented in the currently existing CFD-HAM model. Thirdly the CFD-HAM model will be extended to liquid moisture flow. In this way a complete coupled model is established which allows to combine liquid moisture transport, air transport and interstitial condensation. This model will be used to compare numerical modeling results with in-situ measurements.

Each of the different modeling steps will be extensively validated by means of laboratory experiments. An experimental setup is built which can be used to validate the newly developed coupled model. To validate the original CFD-HAM model, laboratory tests in a climatic chamber where a conditioned air jet enters at the opposite side of a test sample are performed. The newly developed models describing film condensation and droplet condensation in CFD, will be validated by using free water surface experiments and experiments on a cold impermeable surface respectively.

This research is performed in cooperation with the Building Physics Research Group of the Department of Architecture and Urban Planning at the Ghent University.

Schematic representation of the climatic chamber.