Calculating Center-Glass Performance Indices of Windows with a Diathermanous Layer

©2006, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 112, Part 2. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE’s prior written permission.The fenestration chapter of the 2005 ASHRAE Hand-book—Fundamentals (ASHRAE 2005) has long included methods for determining the U-factor and solar heat gain coef-ficient (SHGC), or window performance indices, using the radiative and convective heat transfer coefficients around a glazing layer. The present work examines the errors inherent in applying these standard calculation methods to window systems that include a single diathermanous layer (such as a shading layer), and new equations for calculating the perfor-mance indices are derived. Furthermore, the radiative heat transfer coefficients used in these calculations can be difficult to determine in the presence of a diathermanous layer. There-fore, a new and stable method of calculating radiative heat transfer coefficients is also presented. The effects of using the existing procedures are demonstrated using industry-standard software.ASHRAE is acknowledged for their support of this work through RP-1311

Laser Scanner Technology

This paper addresses the basic principles, performance measures and applications associated with laser scanner technologies. The objective of this report is to communicate and disseminate pertinent information related to state-of-the-art laser measurement systems that are currently available through commercial and research means. This paper should serve two-fold: (1) as a basic tutorial to laser scanning technology and (2) as a guide to current manufacturers and researchers of this technology

The TRENDS High-Contrast Imaging Survey. V. Discovery of an Old and Cold Benchmark T-dwarf Orbiting the Nearby G-star HD 19467

The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV) acceleration of -1.37+/-0.09 m/s/yr over an 16.9 year time baseline (an RV trend), hinting at the existence of a distant orbiting companion. We have obtained high-contrast adaptive optics images of the star using NIRC2 at Keck Observatory and report the direct detection of the body that causes the acceleration. The companion, HD 19467 B, is dK=12.57+/-0.09 mag fainter than its parent star (contrast ratio of 9.4e-6), has blue colors J-K_s=-0.36+/-0.14 (J-H=-0.29+/-0.15), and is separated by 1.653+/-0.004" (51.1+/-1.0 AU). Follow-up astrometric measurements obtained over an 1.1 year time baseline demonstrate physical association through common parallactic and proper motion. We calculate a firm lower-limit of m>51.9^{+3.6}_{-4.3}Mjup for the companion mass from orbital dynamics using a combination of Doppler observations and imaging. We estimate a model-dependent mass of m=56.7^{+4.6}_{-7.2}Mjup from a gyrochronological age of 4.3^{+1.0}_{-1.2} Gyr. Isochronal analysis suggests a much older age of $9\pm1$ Gyr, which corresponds to a mass of m=67.4^{+0.9}_{-1.5}Mjup. HD 19467 B's measured colors and absolute magnitude are consistent with a late T-dwarf [~T5-T7]. We may infer a low metallicity of [Fe/H]=-0.15+/-0.04 for the companion from its G3V parent star. HD 19467 B is the first directly imaged benchmark T-dwarf found orbiting a Sun-like star with a measured RV acceleration.Comment: Updated to reflect ApJ versio

The Formation and Runoff of Condensate on a Vertical Glass Surface

© 2014 ASHRAE (www.ashrae.org). Published in ASHRAE Transactions, Volume 120, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission.An experimental study of condensate formation and runoff was performed by exposing a sheet of glass, cooled at its bottom edge, to an enclosure with a controlled environment. This arrangement mimics the indoor glass surface at the bottom edge of a window when the window is exposed to a cold, outdoor environment. The air in the enclosure was maintained at a constant dry-bulb temperature (Tdb = 22.1°C [Tdb = 71.8°F]) and constant relative humidity (RH = 30%, 35%, 40%, 45%, or 50%) during individual experiments. It was found that the time until initial runoff, tir, decreased with increasing RH, and tir was sensitive to RH at low RH, but insen-sitive to RH at high RH. At first, condensate runoff occurred near the bottom of the glass and left one to believe that the remaining condensate was at steady state. But over a 16-hour period, it was found that the condensate runoff front, in every case, progressed upward to include the entire condensate area. The speed of the condensate runoff front increased with RH, and was less sensitive to RH at low RH. Measurement results were used to produce a summary plot showing runoff front position as a function of glass surface temperature and RH. This chart can be used to predict tir and runoff front progression at the bottom edge of any window if the surface temperature profile is known.Canadian Window & Door Manufacturers Associatio

Determining Off-Normal Solar Optical Properties of Drapery Fabrics

© 2009, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2009, vol. 115, part 2. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE’s prior written permission.The determination of off-normal solar optical properties of drapery fabrics is particularly useful in modelling the effective solar optical properties of pleated drapery. Special sample holders were designed and fabricated to facilitate measurements using an integrating sphere installed in a commercially available spectrophotometer. Measurements were taken for eight of the nine fabric designations documented in the ASHRAE Handbook – Fundamentals. Measurements were also obtained for a sheer fabric which does not fall into any of the customary fabric designations. Semi-empirical models were developed to quantify the variation of solar optical properties with respect to incidence angle. Given solar optical properties obtained at normal incidence, these models can be used to characterize the off-normal beam-beam and beam-diffuse properties of a drapery fabric. The fabric models comprise a useful component of pleated drapery models and, in turn, a valuable tool for building energy simulation. The measurement technique described in this study can be used to obtain the off-normal solar optical properties of additional flat shading devices such as roller blinds and insect screens.Natural Sciences and Engineering Research Council (NSERC) || ASHRA

Determining Longwave Radiative Properties Of Flat Shading Materials

Solar gain through fenestration has a significant impact on building peak load and annual energy consumption. Shading devices, attached to fenestration, offer a cost effective strategy in controlling solar gain. The performance of a particular shading device is dependent on solar optical and longwave radiative properties of the device. The current study considers longwave properties of three flat shading materials; drapery fabrics, insect screens and roller blinds. Each of these materials consists of a structure (i.e., yarn, wire, sheet) that is opaque with respect to longwave (infrared) radiation and each material is likely to have some openness. Material emittance and longwave transmittance measurements were taken with an infrared reflectometer using two backing surfaces. The results show emittance and longwave transmittance to be simple functions of openness, emittance and longwave transmittance of the structure. This is especially useful because openness can be determined from solar transmittance measurements while emittance and longwave transmittance of the structure was found to be constant for each category of shading material.NSERC || ASHRA

A Simplified Method For Calculating The Effective Solar Optical Properties Of a Drapery

The use of draperies to control solar gain through windows is common in residential and commercial buildings and their potential for reduction of building peak load and annual energy consumption is recognized to be large. Thus, there is a strong need for models that allow a drapery to be included in glazing system analysis. As an approximation, the drapery is modelled as a series of uniformly arranged rectangular pleats with fabric transmitting and reflecting diffusely any incident radiation. The “effective” solar optical properties of the drapery are then determined by considering an enclosure which is representative of the entire series of pleats. The optical properties of the drapery are functions of the pleat geometry and the optical properties of the fabric. Optical properties are also influenced by the directional nature of the incident radiation. In the case of incident beam radiation, the results are presented as a function of the solar profile angle for a folding ratio corresponding to 100% fullness. The results for incident diffuse radiation on the other hand are presented in terms of fabric properties and the folding ratio of the drapery.Natural Sciences and Engineering Research Council of Canada (NSERC) Graduate Scholarship to N.A. Kotey || ASHRAE 1311-TR

A method for determining the effective longwave radiative properties of pleated draperies

This is an Accepted Manuscript of an article published by Taylor & Francis in HVAC&R Research on October 1, 2011, available online: http://www.tandfonline.com/doi/abs/10.1080/10789669.2011.591257Draperies, attached to fenestration, offer a cost-effective strategy in controlling solar gain since draperies have the potential to reduce building peak load and annual energy consumption. The performance of a drapery is dependent on its solar optical and longwave radiative properties. The current study considers the determination of spatially averaged (effective) longwave radiative properties of draperies. As a first step, the longwave properties of fabrics were obtained by taking measurements with an infrared reflectometer using two backing surfaces. The measurement results enabled simple equations to be developed relating emittance and longwave transmittance to openness, emittance, and longwave transmittance of the fabric structure. In turn, the effective longwave properties of a pleated drapery are modeled using a net radiation scheme with fabric longwave properties as input. The model approximates a drapery as a series of uniformly arranged rectangular pleats. The effective longwave properties of the pleated drapery are calculated by considering an enclosure that is representative of the entire series of pleats. The longwave properties of the drapery are functions of only pleat geometry and openness of the fabric. The model compares favorably with expected trends and limits. The effect of pleating (folding ratio) is also examined.Natural Sciences and Engineering Research Council (NSERC) Postdoctoral Fellowship to N.A. Kote

Determination of convective heat transfer for fenestration with between-the-glass louvered shades

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.ijheatmasstransfer.2007.09.034 © 2008. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/In previous work, a two-dimensional steady laminar natural convection model of a window cavity with between-panes louvers (i.e., slats) was developed by approximating the system as a vertical cavity with isothermal walls at different temperatures, and with rotatable baffles located midway between the walls. The baffles were set to a third temperature so that night-time and day-time conditions, and the effects of low emissivity coatings (low-e), could be considered. It was found that the system is suited to a traditional one-dimensional analysis. A novel approach that allows the use of standard vertical cavity convection correlations and a modified cavity half-width is described, and a cavity modification factor, n∗, is presented. Finally, the n∗ factor and vertical cavity convection correlation are joined with a longwave radiant model, and the results are compared to experimental results. The models show good agreement with experiments.Natural Sciences and Engineering Research Council of Canada || CANMET Energy Technology Centr