Development of a response factor approach for modeling the energy effects of combined heat and mass transfer with vapor adsorption in building elements
Liesen, Richard John
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Permalink
https://hdl.handle.net/2142/22558
Description
Title
Development of a response factor approach for modeling the energy effects of combined heat and mass transfer with vapor adsorption in building elements
Author(s)
Liesen, Richard John
Issue Date
1994
Doctoral Committee Chair(s)
Pedersen, Curtis O.
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Engineering, Mechanical
Language
eng
Abstract
High humidity levels in a building adversely affect occupant comfort, and air conditioning equipment performance. In many situations condensation can lead to damage of materials in storage through corrosion, deterioration, and other destructive processes. Other detrimental effects from high indoor moisture levels are growth of mold, mildew, and deterioration of building materials. Most building materials like concrete, wood, wall finishes, etc., are porous materials. In porous materials, moisture tends to migrate to the cooler material side under the influence of a temperature gradient. This can occur through a process of evaporation, vapor flow, liquid flow, and condensation in the material. The heat transmission process through moist materials is very complex whenever there is appreciable moisture migration. Under these conditions, calculation of heat transfer with heat conduction theory alone is just an approximation.
Air conditioning systems can rapidly remove stored moisture in the zone air, but removing the adsorbed moisture in the building elements, furniture, window treatments, etc., often accounts for a significant fraction of the overall cooling load, especially upon starting the system after a shut-down period. To determine the contribution of the moisture capacitance in the building, an analysis that takes into account simultaneous diffusion of heat and mass in the building elements is required.
The thesis used the Evaporation-Condensation theory to develop and implement combined heat and mass transfer models with vapor adsorption using moisture transfer functions (MTF's) in an existing hourly energy analysis building simulation program, Integrated Building Load Analysis & System Thermodynamic (IBLAST). The analysis takes into account the vapor adsorption/desorption, and diffusion in composite building elements. Vapor adsorption is one of the primary parameters that couples the mass and energy equations and is crucial for interactions between the mass and heat equations. The model is capable of analyzing the entire building (not just one building element) with moisture effects for a Design Day or an entire year, with an hourly simulation. The development and implementation of these algorithms in the IBLAST program will advance the energy analysis technology to the next level, but still maintain a simulation with a reasonable execution time.
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