ASHRAE - American Society of Heating@ Refrigerating and Air-Conditioning Engineers@ Inc.
Scope
"INTRODUCTION The work presented here was performed in the framework of ASHRAE project 1235 entitled ""The nature@ significance and control of solar-driven diffusion in wall systems""@ initiated by ASHRAE Technical Committee 4.4. The verification of modeling capacities was part of the project. Modeling is used to predict the hygrothermal transport during solar-driven moisture transport. This paper presents work done to test and demonstrate the ability of the Oak Ridge National Laboratory (ORNL) advanced hygrothermal model (MOISTUREEXPERT)@ developed by Karagiozis (2001@ 2004)@ to predict complex hygrothermal processes that are involved in the moisture redistribution processes when wetting (water saturation)@ and drying with and without the presence of solar radiation@ takes place in walls. Researched performed by Derome (2009) and Carmeliet (2009) at both the small scale and intermediate scale level further contributed to the knowledge base. The physical processes present are: water storage@ liquid transport@ vapor transport@ evaporation@ and condensation. A field study Karagiozis (2009a) provided data that were compared against model MOISTURE-EXPERT predictions. The purposes of this activity of the ASHRAE TRP-1235 research project were: ? To use advanced hygrothermal modeling and compare with experimental data developed from the ASHRAE project. This benchmark activity is an important one as the intent for this ASHRAE project was to use modeling for the development of climate specific recommendations for the impact of solar driven moisture. The intent was to enhance confidence towards the implementation of the model to undertake broader parametric studies for the ASHRAE 1235 project. ? To evaluate further and identify performance characteristics that are specifically present in solar driven moisture transport mechanisms. Specifically to address the question of whether there are some mechanisms present that need to be accounted for. The aim of any numerical modeling is obviously to represent reality@ but this is challenging as one cannot easily model the physical enclosure exactly (each crack@ twist@ and imperfection). Our knowledge of needed material properties is always incomplete and the properties are variable@ and our ability to model every hygrothermal mechanisms is somewhat limited. Constraints of time and resources oblige us to do the following: ? be as complex and comprehensive as possible when accuracy is required@ and ? be as complex and comprehensive as needed when relative accuracy is sufficient. We believe that the benchmark results presented in this paper show that the verification objectives were met."