Charles R. Boardman

Moisture storage and transport properties of preservative treated and untreated southern pine wood

Abstract Moisture storage and transport properties of southern pine (Pinus spp.) wood were measured for implementation into hygrothermal models. Specimens were untreated or pressure-treated with alkaline copper quaternary (ACQ) preservative. Moisture storage was characterized with sorption isotherms in the hygroscopic region (high capillary pressures) and documented with mercury intrusion porosimetry in the overhygroscopic region (low capillary pressures). The data were then combined into a single moisture retention curve as a function of capillary pressure. Moisture transport was evaluated from steady-state water vapor transmission and dynamic capillary water absorption experiments. These data were used to calculate the moisture permeability over the entire range of capillary pressures using the diffusivity approach of Carmeliet et al. Moisture storage and transport properties were similar for the untreated and ACQ-treated southern pine, except for the permeability of the treated wood which was lower in the radial direction. The data presented here can be used to improve the accuracy of hygrothermal and combined hygrothermal–corrosion modeling simulations.

Moisture transfer through the membrane of a cross-flow energy recovery ventilator: Measurement and simple data-driven modeling

The moisture transfer effectiveness (or latent effectiveness) of a cross-flow, membrane-based energy recovery ventilator is measured and modeled. Analysis of in situ measurements for a full year shows that energy recovery ventilator latent effectiveness increases with increasing average relative humidity and surprisingly increases with decreasing average temperature. A simple finite difference heat and moisture transfer model is developed, which can explain these results and predict energy recovery ventilator latent effectiveness based on simplified physics and material properties. The model parameters are discussed and, in the case of the membrane’s moisture sorption curve and moisture permeability, compared to direct laboratory measurements.

Moisture Meter Calibrations for Untreated and ACQ-Treated Southern Yellow Pine Lumber and Plywood

This study investigates the effects of alkaline copper quaternary (ACQ) preservative treatment and of plywood glue lines on resistance-based moisture content (MC) measurements. Moisture meter readings using stainless steel screws as electrodes were acquired over a range of moisture conditions in Southern Yellow Pine (SYP) lumber and plywood. Calibration equations are presented for predicting gravimetric MC from meter readings taken in SYP lumber and SYP plywood with or without ACQ treatment. These corrections assume that the meter has been set for SYP. Correlation equations are also presented for directly relating resistance to gravimetric MC, which may be useful for automated data collection systems employed in monitoring moisture levels in buildings. The conductance of SYP lumber was raised by treatment with ACQ, particularly at higher moisture contents, but was unaffected by vacuum-pressure treatment with water. The conductance of untreated SYP plywood, measured with electrodes penetrating the glue lines, exceeded that of untreated SYP lumber. The conductance of SYP plywood was lowered by treatment with ACQ, by vacuum-pressure soaking with water, and by exposure to rain. We suggest that electrolytes in the plywood glue lines increase the conductance of untreated plywood relative to that of untreated lumber, and that the concentration of these electrolytes is lowered by the (aqueous) preservative treatment process, thereby lowering the conductance of these high-conductance pathways.

Improvements to Water Vapor Transmission and Capillary Absorption Measurements in Porous Materials

The vapor permeability (or equivalently the vapor diffusion resistance factor) and the capillary absorption coefficient are frequently used as inputs in hygrothermal or heat, air, and moisture (HAM) models. However, it has been well documented that the methods used to determine these properties are sensitive to the operator, and wide variations in the properties have been reported in round-robin testing. This paper presented an investigation into how these errors can be minimized for porous materials by different edge sealing techniques and also looked at whether automating these techniques can reduce operator artifacts. To automate the measurements, specimens were attached to a balance or load cell and then required no further interaction, which allows massive amounts of data to be collected. The extra data is advantageous for the beginning of the capillary absorption test where the moisture uptake is rapid. Most of the potential for errors in the vapor diffusion tests resulted from uncertainties in how the sample was sealed between the chambers and determining when the steady state region was reached, neither of which can be improved by automation.