A Comparison of Empirical Indoor Relative Humidity Models with Measured Data

Abstract

The focus of this study is to examine the reliability of models that are available in the open literature for simulating the interior moisture conditions, comparing the predicted interior relative humidity (RH) to measured data. Four models, for predicting the indoor RH in houses are tested against measured RH data for 25 houses. The models considered are primarily developed as design tools. The models tested are the European Indoor Class Model, the BRE model, and the ASHRAE 160P simple and intermediate models. The RH in each house is measured in two different locations producing 50 data sets. The ASHRAE intermediate model seemed to be the most robust exhibiting lower errors when compared to measured data. The European Indoor Class also performed well and can be used when data regarding moisture generation and/or air change rates is not available. As a design tool, however, it is not universally conservative in estimating the indoor RH. The BRE is problematic and generally exhibits large positive errors for most of the houses surveyed. It is found to be not reliable for the North American houses investigated in the comparisons. The ASHRAE simple model also exhibited large positive errors and does not trend well with the measured conditions. Models that greatly overestimate the design loads should be used with caution as they may lead to complicated inefficient designs.