1 Effects of Environmental Conditions on the Sorption of VOCs on Building Materials-Part II: Model Evaluation (RP-1097) Jinsong Zhang Student Member ASHRAE Jianshun S. Zhang, Ph.D. Member ASHRAE Qingyan Chen, Ph.D. Member ASHRAE 1 ABSTRACT: Sorption data obtained by using small environmental chambers under different environmental conditions (air temperature, relative humidity, and air velocity) have been used to evaluate the linear Langmuir model and the diffusion model for VOC sorption by different building materials. The two models were evaluated (1) by the goodness of model curve-fitting to the experimental data according to the ASTM recommended statistical indices; and (2) by the ability in predicting the desorption period based on the data from the adsorption period. The linear Langmuir model appeared to be suitable for the painted drywall and ceiling tile while the diffusion model seems more suitable for carpet. The variations of the sorption model parameters are not always in consistence with the changes of the environmental conditions. KEYWORDS: Sorption, adsorption, chamber, indoor air quality, modeling INTRODUCTION Most numerical and empirical models are the simplifications of the reality, and should be evaluated for their applicability, accuracy, and limitations. Sorption models are no exceptions to this rule. For model users, model evaluation will provide them with a clear view of the conditions under which the model can be applied and the associated prediction uncertainties. Such information may prevent the user from misusing the models. For model developers, proper evaluation will identify areas for model improvement and for developing more advanced models. Two typical sorption models: the linear Langmuir model and the diffusion model, have been widely used by researchers in this area as reviewed by Zhang et al. (2002a). Tichenor et al. (1991) evaluated the linear Langmuir model by the goodness of fitting the model to the sorption of ethylbenzene and perchloroethylene on a wallboard, ceiling tile and window glass. According to the standard deviation of the model parameters and correlation coefficient from curve-fitting, An et al. (1999) found that the linear Langmuir model was acceptable in fitting the experimental data for the equilibrium constant (k e ) from 0.004 to 22.2 m. For the diffusion model, Little et al. (1996) found that it can fit the experimental data reasonably well. They also proposed some independent methods to measure the partition coefficient and the diffusion coefficient. However, there seemed to be no direct comparison between the prediction using the measured partition and diffusion coefficients and the chamber test data. Due to the lack Jinsong Zhang is a graduate Research Assistant, and Qingyan (Yan) Chen is a Professor at School of Mechanical Engineering, Purdue University, West Lafayette, IN. Jianshun Zhang is an Associate Professor in the Department of Mechanical, Aerospace, and Manufacturing Engineering, Syracuse University, Syracuse, NY. Zhang, J., Zhang, J.S., and Chen, Q. 2003. “Effects of environmental conditions on the VOC sorption by building materials – part II: model evaluations (RP-1097),” ASHRAE Transactions, 109(1), 167-178.