Numerical Modeling of Indoor Microenvironments with Experimental Validation

Carolyn Roos

ABSTRACT
Indoor biocontaminants, such as dust mites, molds and mildews, have been shown to cause or exacerbate asthma and other diseases, leading to considerable costs managing symptoms. Many biocontaminants require moderate to high relative humidity for survival and so may be controlled psychrometrically. Controlling ambient relative humidity may not be an effective strategy, however, if microenvironmental conditions in carpets, furniture or mattresses differ substantially from ambient conditions. Here the viability of biocontaminants may be favored, despite less favorable ambient conditions. To better understand and control these biocontaminants, a new model of heat and moisture transfer in indoor microenvironments has been developed, relating microenvironmental psychrometric conditions to the room and outdoor climate.

INDOOR, the finite-difference computer model developed in this research, is tailored to investigate psychrometric conditions and moisture control strategies for indoor materials. Other models of coupled heat and moisture transfer in buildings have focused on exterior elements, such as walls and roofs, and their capabilities are generally restricted to those applications.

By including a moisture diffusion term commonly neglected in other models, INDOOR improves the accuracy of results for the highly permeable, insulating materials commonly found in indoor microenvironments, such as textiles, flexible open cell foams, and carpet. Governing equations also include volumetric heat and moisture generation terms important in modeling scenarios including electric blankets, subfloor heating and human contact. Zone balances include source terms which enable simulation of moisture producing events such as showering. Moreover, boundary condition specification is flexible enough to represent both the variety of conditions found in indoor microenvironments and in exterior building elements.

Experimental validation of the governing equations was accomplished by measuring temperature and humidity within flexible open cell polyester foam under controlled transient conditions and comparing that data with model predictions. Model results for polyester foam and plywood were also compared to predictions of MOIST 3.0, a widely used commercial model. Results suggest that INDOOR more accurately predicts moisture transfer in materials that are highly permeable and insulating, while temperature conditions are predicted similarly.

Wednesday, July 10, 2002
DISSERTATION COMMITTEE
Graig Spolek, Chairman
Lemmy L. Meekisho
Gerald Recktenwald
Wayne W. Wakeland
Randy D. Zelick, Graduate Studies Rep.