Samuel V. Glass

Water Vapor Sorption Isotherms for Southern Pine Treated with Several Waterborne Preservatives

Equilibrium moisture content (EMC) was measured over a range of relative humidities at 22.5°C to determine whether certain wood preservatives increase the hygroscopicity of southern pine (Pinus sp.) The treatments studied were alkaline copper quaternary (ACQ) at a retention of 6.6 kg⋅m−3, chromated copper arsenate (CCA) at 6.9 kg⋅m−3, and disodium octaborate tetrahydrate (DOT) at 3.8 kg⋅m−3 (equivalent to 2.6 kg⋅m−3 as B2O3). All treatments examined increased the EMC at relative humidities above 60 %. Wood treated with DOT was the most hygroscopic. At high relative humidities, the ratio of the EMC of ACQ-treated wood to CCA-treated wood was 1.08. It is unlikely that the higher corrosiveness of ACQ compared with CCA is due to this slight increase in hygroscopicity.

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.

Anatomically informed mesoscale electrical impedance spectroscopy in southern pine and the electric field distribution for pin-type electric moisture metres

Abstract Electrical impedance spectra of wood taken at macroscopic scales below the fibre saturation point have led to inferences that the mechanism of charge conduction involves a percolation phenomenon. The pathways responsible for charge conduction would necessarily be influenced by wood structure at a variety of sub-macroscopic scales – at a mesoscale – but these questions have not yet been addressed. The goal of this work is to explore if mesoscale anatomical features in wood affect impedance spectra. Small (0.5 mm diameter) needles were used as electrodes and were configured such that the line segment between the electrodes could be oriented radially, tangentially, longitudinally and in combinations of those directions in both earlywood and latewood, including comparisons of earlywood–latewood transitions. The spectra were fit to an equivalent circuit model with a constant phase element in parallel with a resistor and Warburg element that describes ionic conduction. Finite element simulations were run to examine the effect of the fringing electric field near the electrodes. The simulations revealed that the current density was concentrated at the electrodes, resulting in a lack of dependence on electrode spacing thus explaining why measurements taken with pin-type electric moisture metres are nearly independent of electrode geometry.

Force–displacement measurements of earlywood bordered pits using a mesomechanical tester

The elastic properties of pit membranes are reported to have important implications in understanding air-seeding phenomena in gymnosperms, and pit aspiration plays a large role in wood technological applications such as wood drying and preservative treatment. Here we present force-displacement measurements for pit membranes of circular bordered pits, collected on a mesomechanical testing system. The system consists of a quartz microprobe attached to a microforce sensor that is positioned and advanced with a micromanipulator mounted on an inverted microscope. Membrane displacement is measured from digital image analysis. Unaspirated pits from earlywood of never-dried wood of Larix and Pinus and aspirated pits from earlywood of dried wood of Larix were tested to generate force-displacement curves up to the point of membrane failure. Two failure modes were observed: rupture or tearing of the pit membrane by the microprobe tip, and the stretching of the pit membrane until the torus was forced out of the pit chamber through the pit aperture without rupture, a condition we refer to as torus prolapse.

Effect of weight percent gain and experimental method on fiber saturation point of acetylated wood determined by differential scanning calorimetry

This paper evaluates the effects of acetylation level and experimental method on the observed fiber saturation point (FSP) of loblolly pine (Pinus taeda) wood measured using differential scanning calorimetry. To achieve this goal, 1-mm-thick latewood samples were tested over a wide range of equilibrium moisture content (EMC). In this work, the FSP was defined as the non-freezable portion of water of the samples. Two experimental methods were used: the extrapolation of the melting enthalpy to zero and the direct calculation of the non-freezable water amount. For both methods, the FSP decreased with increasing acetylation, varying from about 27% reduced EMC (EMCR) for control to about 9% EMCR for the highest level of acetylation. For unmodified samples, the measured FSP was higher with faster scan rates. Moreover, under a specific range of EMCR, freezing curves revealed the occurrence of two water phase transitions for samples at the highest level of acetylation. Based on previous studies and in present findings, there is strong evidence that the lower temperature freezing peak may result from the homogenous nucleation of water, which is physically separated from water that freezes heterogeneously.

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.

[Technical Note] Thermal Insulation System Made of Wood and Paper for Use in Residential Construction

Abstract This article introduces an insulation system that takes advantage of the low thermal conductivity of still air and is made of wood and paper. The insulation, called the Mirrorpanel, is constructed as a panel of closely spaced layers of coated paper and held together in a frame of wood or fiberboard. Panels have been fabricated and tested at the laboratory scale, whole wall scale, and the building scale. A 1.2-m by 2-m by 0.185-m-thick wall section had an apparent thermal conductance of only 0.204 W m−2 K−1 including the structural wood frame, which is equivalent to a US R-value of 27.9 h ft2 °F Btu−1 (3.8 h ft2 °F Btu−1 in.−1 for the 7.3-in.-thick wall section). The Mirrorpanel could be used as an environmentally friendly alternative to foam insulation in high-performance residential buildings and would fulfill the continuous insulation requirements in the 2012 version of the International Energy Conservation Code.

Analysis of Improved Criteria for Mold Growth in ASHRAE Standard 160 by Comparison with Field Observations

ASHRAE Standard 160, Criteria for Moisture-Control Design Analysis in Buildings, was published in 2009. The standard sets criteria for moisture design loads, hygrothermal analysis methods, and satisfactory moisture performance of the building envelope. One of the evaluation criteria specifies conditions necessary to avoid mold growth. The current standard requires that the 30-day running average relative humidity at the material surface be less than 80 % when the 30-day running average surface temperature is between 5 C (41 F) and 40 C (104 F). This criterion was intended to strike a balance between the need for simplicity to make the standard useful and the complex reality of mold growth, which varies with mold species and depends on the type of material, water activity, temperature, and other factors. Since the standard was Manuscript received July 15, 2016; accepted for publication November 1, 2016. USDA Forest Service Forest Products Laboratory, Building and Fire Sciences, 1 Gifford Pinchot Dr., Madison, WI 53726 CertainTeed Corp., Malvern Innovation Center, 18 Moores Rd., Malvern, PA 19355 Building Science Corp., 70 Main St., Westford, MA 01886 RDH Building Science Laboratories, 167 Lexington Ct., Unit 6, Waterloo, ON, N2J 4R9, Canada ASTM Symposium on Advances in Hygrothermal Performance of Building Envelopes: Materials, Systems and Simulations on October 26–27, 2016 in Orlando, FL. This work is not subject to copyright law. ADVANCES IN HYGROTHERMAL PERFORMANCE OF BUILDING ENVELOPES 1 STP 1599, 2017 / available online at www.astm.org / doi: 10.1520/STP159920160106 published, many practitioners have maintained that the mold criterion is too stringent. Assemblies known to have satisfactory performance in the field do not meet the criterion under hygrothermal simulation. A recent addendum to ASHRAE Standard 160 replaced the simplified mold criterion with a state-ofthe-art empirical model that describes mold growth and decline over time using a mold index. This model takes into account the sensitivity of the material, the surface temperature, and the surface relative humidity. This paper provides an overview of the mold index model and a series of comparisons between field observations of visible mold growth or lack thereof on woodbased sheathing and model predictions that use measured surface temperature and relative humidity values as inputs. The field data are from published studies on above-grade wood-frame wall assemblies and roof assemblies covering a range of climate zones. Our analysis indicates that the current 30-day criterion in ASHRAE Standard 160 fails many assemblies in which visible mold growth did not occur. In contrast, the mold index model predictions give better agreement with observations.