TO-22-C002 - EMPD OpenStudio Measure for Mass Timber Buildings

Most building energy modeling (BEM) software tend to neglect moisture transfer in the envelope and assume constant material properties. As mass timber construction expands in North America, it is important to have BEM tools that at least partially account for moisture transfer with the envelope. EnergyPlus has four heat transfer algorithms with two capable of doing heat and moisture transfer. However, OpenStudio only uses the default heat balance algorithm: conduction transfer functions. This study presents a new OpenStudio measure that enables the use of the Effective Moisture Penetration Depth (EMPD) model. This algorithm improves the relative humidity predicted by BEM without adding a significant increase in computation time. Making this algorithm available inside OpenStudio allows for more accurate simulation and analysis of buildings with unique hygrothermal characteristics such as those made with mass timber that need to consider air to envelope moisture interaction. This study describes the measure as well as performs a case study highlighting the effect of considering moisture transfer with the envelope in mass timber building models.