Effective U-values and Shading Coefficients of Preheat/Supply Air Glazing Systems

Research is documented which makes use of a computer program called VISION, This computer program was developed specifically to provide a detailed analysis of heat transfer occurring in glazing systems. VISION was modified to perform an analysis of the energy flows in supply air windows. A model used to quantify heat transfer in the supply air flow is described. Ventilation air is brought in through supply air windows and the energy recovered by the preheat of the air flow is credited to the thermal performance of the window itself, Thus, the net energy flow between the conditioned space and the window was used to calculate an effective U-value and shading coefficient, The use of these "effective" window performance parameters permits the subsequent quantification of energy flows to or from the supply air glazing system without the necessity of modelling the detailed mechanisms of energy transport within the glazing system itself. A variety of glazing system designs are simulated. Indoor glazing temperature is reported for each system. In all cases the presence of preheat ventilation improved the effective shading coefficient moderately and increased the effective thermal resistance appreciably.Renewable Energy Branch of the Department of Energy, Mines and Resource

A Simplified Analysis of Radiant Heat Loss Through Projecting Fenestration Products

© 2001 ASHRAE (www.ashrae.org). Published in ASHRAE Transactions, Volume 107, 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 permissioCurrent window analysis algorithms can deal with many features, including low-e coatings and substitute fill gases. These methods were developed for products with planar glazings. Results can be generated for projecting products such as greenhouse windows, but the indoor-side heat transfer coefficient must be reduced to reflect differences in convection and radiant exchange for this geometry. Two simplified models are developed for radiant heat loss to projecting windows and are shown to agree well with a pseudo three-dimensional multi-element computer-based calculation. It is confirmed that the indoor-side heat transfer coefficient does not need to be accurately known to characterize a well-insulated window. More research is needed to quantify indoor-side convective heat loss before radiant exchange models can be verified and projecting products can be well characterized in general.Natural Sciences and Engineering Research Council of Canada || Natural Resources Canad

Thermal Resistance Measurement Of Glazing System Edge-seals

The existing design of glazing system edge-seals creates increased edge-glass heat transfer at the perimeter of sealed glazing units. This thermal short-circuit caused by edge-seal conduction results in added mechanical stress. condensation problems in cold climates and augments the building energy load. New edge-seal designs are being marketed but very few data are available regarding the thermal resistance of any of the various edge-seal configurations that are available. An experimental procedure hos been devised whereby the thermal resistance of an edge-seal can be directly measured using a guarded heater plate apparatus. Results for nine edge-seal test samples are reported and discussed. A variety of conclusions and design guidelines are presented.Energy Efficiency Technology Division || Department of Energy, Mines and Resources Canada

Calculating Window Solar Heat Gain

© American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in Ashrae Journal, July 1995. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission.Window design has been revolutionized-largely by the introduction of low emissivity (low-e) coatings and substitute fill gases. The large number of design options necessitates the use of computer simulation for development and rating. Two window analysis programs, VISION1 and WINDOW,2 are widely used in North America. Both have been released in several versions-the most recent being WINDOW 4.1 and VISION3. They differ in appearance because WINDOW is text based and VISION3 incorporates a graphical user interface (GUI) but they perform similar solar optical and heat transfer calculations to arrive at center-glass U-factors and solar heat gain values. More detail can be found in Wright's "Summary and comparison of methods to calculate Solar heat gain". This article examines window solar heat gain-how it is calculated and what affects it. Solar heat gain is quantified by the Solar Heat Gain Coefficient (SHGC). SHGC is the fraction of inci­dent solar radiation that reaches the conditioned space. It is customary to consider each of three areas: (1) the center-glass area, A, (i.e., the glazed area more than 2.5 inches (63.5 mm) from any sight line, (2) the edge-glass area, and (3) the frame area, Component SHGC values are area-weighted to give a total window SHGC.Supported by ASHRAE technical committee TC-4.5 (Fenestration) under technical research project 713-TRP

Calculating Center-Glass Performance Indices of Glazing Systems with Shading Devices

© 2008, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions Vol. 114, 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.Building energy consumption and loads are strongly influ-enced by solar gain and heat transfer through the centre-glass area of windows. Methods have been devised to calculate the corresponding energy performance indices (e.g., SHGC and U-factor). Simulation offers the opportunity to examine design options such as low-emissivity or solar-control coatings, glass tints, substitute fill gases and diathermanous glazing layers. Current models use a radiosity-based approach to quantify longwave radiant exchange. A new method is presented for the thermal analysis of multilayer systems. This method, by using a resistor network to quantify both convective and radiant exchange, offers exceptional generality. “Jump” resistors allow for airflow between layers, or diathermanous layers, or any combination of the two. The air and mean radiant temper-atures can differ on both the indoor and outdoor sides. In addi-tion a more general method has been devised for calculating indices of merit without restricting the generality of the simu-lation model – for any set of environmental temperature and insolation conditions. These methods are especially useful for the analysis of glazing systems used in combination with shad-ing layers such as venetian blinds, curtains, roller blinds and insect screens. These methods also offer new possibilities, speed and convenience when used in conjunction with whole building performance simulations.Natural Sciences and Engineering Research Council (NSERC) of Canad

Summary and comparison of methods to calculate solar heat gain

© 1995. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Vol. 101, Part 1. For personal use only. Additional reproduction, distribution, ortransmission in either print or digital form is not permitted without ASHRAE’s prior written permission.Methods used to calculate the solar gain of windows (including center-glass, edge-glass, and frame) are examined and compared Particular attention is devoted to the public-domain computer programs VISION3 and WINDOW 4.1. Calculated results are presented to quantify the sensitivity of solar heat gain with respect to a wide range of glazing system design parameters and operating conditions. Details concerning solar optical properties and heat transfer mechanisms are examined and discussed When possible, comments are made concerning the development of solar gain measurement procedures. Solar gain is most sensitive to the solar optical properties of the glazings--the most important property being the transmittance of the outdoor glazing. Variables that directly affect heat transfer rates (e.g., fill gas type, convective heat transfer coefficients) have a significantly smaller effect.ASHRAE technical committee TC-4.5 (Fenestration) under technical research project 713-TR

OEXP Analysis Tools Workshop

This publication summarizes the software needs and available analysis tools presented at the OEXP Analysis Tools Workshop held at the NASA Langley Research Center, Hampton, Virginia on June 21 to 22, 1988. The objective of the workshop was to identify available spacecraft system (and subsystem) analysis and engineering design tools, and mission planning and analysis software that could be used for various NASA Office of Exploration (code Z) studies, specifically lunar and Mars missions

Mitigation of Peak Cooling Demand through the Combination of Residential Zoned Cooling and Window Shading: A Building Simulation Case Study

The present study expands on previous building simulation work con-cerning the potential benefits of residential zoned cooling systems during peak summer days. Such zoned systems provide an opportunity for peak reduction on hot and humid days when the electricity peak is largely caused by increased space cooling demand. In the previous study, control strategies for different occupancy profiles were consid-ered and their impact on peak and cooling energy reduction were compared. The present study builds on these results by considering the benefits of shading as a passive means of reducing the peak cooling load. The analysis is based on integrated building energy simulations of a newer-vintage house using the zoned cooling system model in con-junction with the expanded set of shading models. Total cooling ener-gy demand, peak cooling power reductions and their impact on even-ing recovery times are examined. It was found that zoned control strategies alone can yield signifi-cant peak power reductions, but the long recovery periods limit their practical application. Only with between-pane or outdoor shade con-figurations can very large reductions can be realized without compro-mising occupant comfort during the evening recovery period

Heat Transfer Analysis Of Windows With Venetian Blinds: A Comparative Study

The potential to reduce building load and annual energy consumption is widely recognized in the use of shading devices to control solar gain. Consequently, the ability to include and model shading layers in complex glazing systems is needed in evaluating the energy performance of a building envelope. In a previous study, solar-optical calculations were presented for a window with a light and dark coloured venetian blind using simplified models for three different glazing/shading configurations. Results were presented for the hourly transmitted, reflected and absorbed quantities of solar radiation for summer and winter conditions. In this study, a heat transfer analysis is presented to complement the previous study and provide all the relevant information required for building energy analysis. The individual contributions to the net heat gain consisting of total solar transmission, longwave radiant gain and convective gain are presented. The ability to quantify the relative importance of each heat gain component offers significant insight into the thermal characteristics of complex glazing/shading systems.Natural Sciences and Engineering Research Council of Canad