Evaluation of a four-zone indoor exposure model for predicting TCPP concentrations in a low-energy test house

Abstract

The Indoor Environmental Concentrations in Buildings with Conditioned and Unconditioned Zones (IECCU) model was developed by the United States Environmental Protection Agency to predict indoor exposures. This study evaluated IECCU by comparing airborne tris(1-chloro-2-propyl) phosphate (TCPP) concentrations measured over five years in a test house to IECCU predictions. IECCU inputs included building environment (air zone configuration, airflow rates and temperature), source (spray polyurethane foam (SPF)) and sink (gypsum and wallboard) parameters, and simulation conditions. Simulations were conducted using three sets of inputs. Simulation 1 and 2 differed in using quantified versus design inputs for temperatures and airflows. Simulation 1 and 3 differed in air zone configuration. Given the best available inputs (Simulation 1), IECCU predicted basement concentrations were generally higher but within three times of the measured values. The basement prediction/measurement ratios for all three simulations ranged from 0.5 to 8.3 (average: 2.9), while the predicted living zone concentrations were generally lower but within ten times of the measurements. The design inputs of Simulation 2 resulted in greater discrepancy between and predictions and measurements than the quantified inputs of Simulation 1. Simulation 2 also did not capture diurnal variation as well as Simulation 1. Comparisons of Simulation 1 and 2 demonstrate the importance of modeling with accurate temperatures and airflows. Furthermore, a sensitivity analysis indicates that to improve IECCU prediction for TCPP emission from SPF, efforts are needed to accurately measure SPF mass transfer parameters, especially the SPF/air partition coefficient and the initial TCPP concentration in SPF.