Teaching Students about Two-Dimensional Heat Transfer Effects in Buildings, Building Components, Equipment and Appliances using THERM 2.0,

Abstract THERM 2.0 is a state-of-the-art software program, available for free, that uses the finite-element method to model steady-state, two-dimensional heat-transfer effects. It is being used internationally in graduate and undergraduate laboratories and classes as an interactive educational tool to help students gain a better understanding of heat transfer. THERM offers students a powerful simulation engine combined with a simple, interactive interface and graphic results. Although it was developed to model thermal properties of building components such as windows, walls, doors, roofs, and foundations, it is useful for modeling thermal bridges in many other contexts, such as the design of equipment. These capabilities make THERM a useful teaching tool in classes on: heating, ventilation, and air-conditioning (HVAC); energy conservation; building design; and other subjects where heat-transfer theory and applications are important. THERM's state-of-the-art interface and graphic presentation allow students to see heattransfer paths and to learn how changes in materials affect heat transfer. THERM is an excellent tool for helping students understand the practical application of heat-transfer theory

High-Performance Integrated Window and Façade Solutions for California

The researchers developed a new generation of high-performance façade systems and supporting design and management tools to support industry in meeting California’s greenhouse gas reduction targets, reduce energy consumption, and enable an adaptable response to minimize real-time demands on the electricity grid. The project resulted in five outcomes: (1) The research team developed an R-5, 1-inch thick, triplepane, insulating glass unit with a novel low-conductance aluminum frame. This technology can help significantly reduce residential cooling and heating loads, particularly during the evening. (2) The team developed a prototype of a windowintegrated local ventilation and energy recovery device that provides clean, dry fresh air through the façade with minimal energy requirements. (3) A daylight-redirecting louver system was prototyped to redirect sunlight 15–40 feet from the window. Simulations estimated that lighting energy use could be reduced by 35–54 percent without glare. (4) A control system incorporating physics-based equations and a mathematical solver was prototyped and field tested to demonstrate feasibility. Simulations estimated that total electricity costs could be reduced by 9-28 percent on sunny summer days through adaptive control of operable shading and daylighting components and the thermostat compared to state-of-the-art automatic façade controls in commercial building perimeter zones. (5) Supporting models and tools needed by industry for technology R&D and market transformation activities were validated. Attaining California’s clean energy goals require making a fundamental shift from today’s ad-hoc assemblages of static components to turnkey, intelligent, responsive, integrated building façade systems. These systems offered significant reductions in energy use, peak demand, and operating cost in California

Developing Low-Conductance Window Frames: Capabilities and Limitations of Current Window Heat Transfer Design Tools

While window frames typically represent 20-30% of the overall window area, their impact on the total window heat transfer rates may be much larger. This effect is even greater in low-conductance (highly insulating) windows that incorporate very low-conductance glazing. Developing low-conductance window frames requires accurate simulation tools for product research and development. Based on a literature review and an evaluation of current methods of modeling heat transfer through window frames, we conclude that current procedures specified in ISO standards are not sufficiently adequate for accurately evaluating heat transfer through the low-conductance frames. We conclude that the near-term priorities for improving the modeling of heat transfer through low-conductance frames are: (1) Add 2D view-factor radiation to standard modeling and examine the current practice of averaging surface emissivity based on area weighting and the process of making an equivalent rectangular frame cavity. (2) Asses 3D radiation effects in frame cavities and develop recommendation for inclusion into the design fenestration tools. (3) Assess existing correlations for convection in vertical cavities using CFD. (4) Study 2D and 3D natural convection heat transfer in frame cavities for cavities that are proven to be deficient from item 3 above. Recommend improved correlations or full CFD modeling into ISO standards and design fenestration tools, if appropriate. (5) Study 3D hardware short-circuits and propose methods to ensure that these effects are incorporated into ratings. (6) Study the heat transfer effects of ventilated frame cavities and propose updated correlations

Breaking the 20 Year Logjam to Better Insulating Windows

Windows account for about 4 Quads of US energy consumption or 12% of building energy use. After 20 years of public/private investment (from 1980 to 2000) in technology R&D, coupled with new rating and labeling organizations (NFRC) and with subsequent voluntary ENERGY STAR programs and tighter codes and standards, windows using low-E/argon gas fill (~R3) gained a dominant market share and now account for >86% of all annual sales. However, this remarkable transformation of prior markets has stagnated, with triple glazing (~R5-R7) comprising less than 2% of all window sales in 2016. U.S. Department of Energy (DOE) estimates the national technical potential savings using R5-R7 windows at ~ 2Q annually, but manufacturers claim they would have to redesign their entire sash/frame inventory to accommodate the thicker and heavier insulating glass units (IGUs) in conventional triple glazed window designs. This paper outlines the initial findings from the first phase of a new collaborative effort, now underway with industry partners, to transform window markets to the R5-R7 insulating levels by introducing a novel packaging of existing technology elements, implemented as a “drop-in replacement” for current IGUs. The program involves working with supply chain partners to ensure component availability, with leading window manufacturers to integrate the key technology elements and initially deploy the new designs, and with market pull partners to speed adoptions rates. Market pull partners include building code officials, utility rebate/incentive programs and ENERGY STAR, along with early adopters such as builders targeting net zero and passive house designers

Evaluating Fenestration Products for Zero-Energy Buildings: Issues for Discussion

Computer modeling to determine fenestration product energy properties (U-factor, SHGC, VT) has emerged as the most cost-effective and accurate means to quantify them. Fenestration product simulation tools have been effective in increasing the use of low-e coatings and gas fills in insulating glass and in the widespread use of insulating frame designs and materials. However, for more efficient fenestration products (low heat loss products, dynamic products, products with non-specular optical characteristics, light re-directing products) to achieve widespread use, fenestration modeling software needs to be improved. This paper addresses the following questions: (1) Are the current properties (U, SHGC, VT) calculated sufficient to compare and distinguish between windows suitable for Zero Energy Buildings and conventional window products? If not, what data on the thermal and optical performance, on comfort, and on peak demand of windows is needed. (2) Are the algorithms in the tools sufficient to model the thermal and optical processes? Are specific heat transfer and optical effects not accounted for? Is the existing level of accuracy enough to distinguish between products designed for Zero Energy Buildings? Is the current input data adequate

Experimental validation and model development for thermal transmittances of porous window screens and horizontal louvred blind systems

Virtually every home in the US has some form of shades, blinds, drapes, or other window attachment, but few have been designed for energy savings. In order to provide a common basis of comparison for thermal performance it is important to have validated simulation tools. This paper outlines a review and validation of the ISO 15099 centre-of-glass thermal transmittance correlations for naturally ventilated cavities through measurement and detailed simulations. The focus is on the impacts of room-side ventilated cavities, such as those found with solar screens and horizontal louvred blinds. The thermal transmittance of these systems is measured experimentally, simulated using computational fluid dynamics analysis, and simulated utilizing simplified correlations from ISO 15099. Correlation coefficients are proposed for the ISO 15099 algorithm that reduces the mean error between measured and simulated heat flux for typical solar screens from 16% to 3.5% and from 13% to 1% for horizontal blinds

Experimental validation for thermal transmittances of window shading systems with perimeter gaps

Virtually all residential and commercial windows in the U.S. have some form of window attachment, but few have been designed for energy savings. ISO 15099 presents a simulation framework to determine thermal performance of window attachments, but the model has not been validated for these products. This paper outlines a review and validation of the ISO 15099 centre-of-glass heat transfer correlations for perimeter gaps (top, bottom, and side) in naturally ventilated cavities through measurement and simulation. The thermal transmittance impact due to dimensional variations of these gaps is measured experimentally, simulated using computational fluid dynamics, and simulated utilizing simplified correlations from ISO 15099. Results show that the ISO 15099 correlations produce a mean error between measured and simulated heat flux of 2.5 ± 7%. These tolerances are similar to those obtained from sealed cavity comparisons and are deemed acceptable within the ISO 15099 framework

Improving information technology to maximize fenestration energy efficiency

Improving software for the analysis of fenestration product energy efficiency and developing related information technology products that aid in optimizing the use of fenestration products for energy efficiency are essential steps toward ensuring that more efficient products are developed and that existing and emerging products are utilized in the applications where they will produce the greatest energy savings. Given the diversity of building types and designs and the climates in the U.S., no one fenestration product or set of properties is optimal for all applications. Future tools and procedures to analyze fenestration product energy efficiency will need to both accurately analyze fenestration product performance under a specific set of conditions and to look at whole fenestration product energy performance over the course of a yearly cycle and in the context of whole buildings. Several steps have already been taken toward creating fenestration product software that will provide the information necessary to determine which details of a fenestration product's design can be improved to have the greatest impact on energy efficiency, what effects changes in fenestration product design will have on the comfort parameters that are important to consumers, and how specific fenestration product designs will perform in specific applications. Much work remains to be done, but the energy savings potential justifies the effort. Information is relatively cheap compared to manufacturing. Information technology has already been responsible for many improvements in the global economy--it can similarly facilitate many improvements in fenestration product energy efficiency

Improving Information Technology to Maximize Fenestration Energy Efficiency

Improving software for the analysis of fenestration product energy efficiency and developing related information technology products that aid in optimizing the use of fenestration products for energy efficiency are essential steps toward ensuring that more efficient products are developed and that existing and emerging products are utilized in the applications where they will produce the greatest energy savings. Given the diversity of building types and designs and the climates in the U.S., no one fenestration product or set of properties is optimal for all applications. Future tools and procedures to analyze fenestration product energy efficiency will need to both accurately analyze fenestration product performance under a specific set of conditions and to look at whole fenestration product energy performance over the course of a yearly cycle and in the context of whole buildings. Several steps have already been taken toward creating fenestration product software that will provide the information necessary to determine which details of a fenestration product's design can be improved to have the greatest impact on energy efficiency, what effects changes in fenestration product design will have on the comfort parameters that are important to consumers, and how specific fenestration product designs will perform in specific applications. Much work remains to be done, but the energy savings potential justifies the effort. Information is relatively cheap compared to manufacturing. Information technology has already been responsible for many improvements in the global economy--it can similarly facilitate many improvements in fenestration product energy efficiency

New Rating Opening Windows to a World of Comfort, Opportunity, and Cost-Effective Savings

Window attachments offer a huge, cost-effective energy-saving opportunity that remains largely untapped. The newly launched window attachment energy rating and certification program, through the Attachments Energy Rating Council (AERC), is altering the way people think about residential and commercial window attachments by providing reliable, easy-to-understand energy performance information to consumers. Window attachments, such as blinds, shades, shutters, awnings, and low-emissivity (low-e) storm windows, represent an enormous existing market. With 64% of U.S. homes having single- or double-pane clear (non-low-e) less-efficient windows, the savings opportunity is significant. Studies of model homes show energy savings of 10% or more after installing more efficient storm window and cellular shades technologies (AERC 2016).In a study conducted by Efficiency Vermont, 68% of respondents had concerns with their existing windows and could benefit from an upgrade (Efficiency Vermont 2016).Through AERC, window attachment products are rated based on their Energy Performance (EP). The EP metric is an easy-to-understand comparative metric created for consumers. This rating not only allows consumers to make more informed decisions when buying attachments products, but also creates a new energy savings measure for utilities and efficiency programs to incentivize energy efficient window attachment products. This paper will outline the savings potential of window attachments, introduce the AERC rating program, detail the methodology behind the Energy Performance ratings, and explain the AERCalc tool that generates the ratings