Evaluation of the Effective Moisture Penetration Depth Model for Estimating Moisture Buffering in Buildings.

摘要

Building materials and furnishings play an important role in moderating relative humidity fluctuations. Accurately accounting for moisture buffering in building simulations is central in determining the need for, and the energy use from, controlling humidity. In building modeling, moisture buffering has typically either been ignored or has been lumped with the zone air using an effective moisture capacitance multiplier. Researchers have also used finite-difference models to simulate moisture transfer within materials, which are more physically realistic than the effective capacitance model, but require orders of magnitude more computation time. This study examines the effective moisture penetration depth (EMPD) model and its suitability for building simulations. The EMPD model is a compromise between the simple, inaccurate, effective capacitance approach and the complex, yet accurate, finite-difference approach. Two formulations of the EMPD model were examined, including the model used in the EnergyPlus building simulation software. We uncovered an error in the EMPD model in EnergyPlus, which was fixed with the release of EnergyPlus version 7.2. The EMPD model in earlier versions of EnergyPlus should not be used. Three simple building simulation cases were used to compare the two EMPD formulations, the effective capacitance model, and the finite-difference model. An analytical solution for the first case showed that the two EMPD formulations were not equal, but that both were improvements over the effective capacitance model. For the cases that more closely resemble real building loads, the improvement of the EMPD model over the effective capacitance model was small unless the EMPD model included two penetration depths: a surface layer for short-term humidity fluctuations, and a deep layer for longer term fluctuations. We are presently working to implement the dual-depth EMPD model in a future EnergyPlus version.