buildings by 20 percent, we could save approximately $80 billion annually on energy bills, reduce greenhouse gas emissions, and create jobs.” ( )Īdditionally, reduction of energy use by upgrading insulation amounts in our commercial and residential buildings also has significant co-benefits. And much of this energy and money is wasted - 20 percent or more on average. Energy efficiency and the subsequent reduction of energy use is paramount in the building industry.Īccording to the US Department of Energy’s Energy Efficiency and Renewable Energy website, “We spend more than $400 billion each year to power our homes and commercial buildings, consuming more than 70 percent of all electricity used in the United States, about 40 percent of our nation's total energy bill, and contributing to almost 40 percent of the nation's carbon dioxide emissions. The advancement of the levels of insulation matches the awareness and activities taking place, not just in the US, but across North America and the world. (For an overview of the I-Codes, see “Model Codes 101”.)
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#Ashrae 90.1 u values code
Not only does the 2012 International Energy Conservation Code (IECC) include new and higher thermal standards for almost every roof and wall assembly, but these standards are further increased in the new International Green Construction Code (IgCC), which is intended to serve as an overlay code, or “above the code” standard for sustainable buildings. The 2012 edition of the I-Codes includes several landmark advances in building energy efficiency and sustainability. Since 2000, the I-Codes have served as models for almost all state and local building codes in the United States. The basis for R-values (Air Film Resistances used to calculate U-Factor with Film) is ASHRAE Standard 90.1 (I-P Edition) Section A9.4.1. After changing Outside Boundary Condition of the roof from Surface to Outdoor, 0.0299387 was used for Exterior Air Film Resistance, and ( Interior Air Film Resistance) + ( Exterior Air Film Resistance) = 0.1074271+0.0299387 ≈ 0.1373.įor the best answer, please refer to the link that attached in his comment. Therefore, the roof was recognised as "semi-exterior" surface and 0.0810106 was used, which resulted in 0.1074271+0.0810106≈0.189. In my case study, I mistakenly selected Surface as Outside Boundary Condition of the roof in BuildingSurface:Detailed. Interior Air Film Resistance for roof is 0.1074271, and Exterior Air Film Resistance for roof is 0.0299387. ( Interior Air Film Resistance) + ( Exterior Air Film Resistance) for roof is not about 0.189 but about 0.1373. I noticed my mistake, so please let me correct it. If possible, I want to know each value of Air Film Resistance: Interior Air Film Resistance and Exterior Air Film Resistance. I may have overlooked it, but I couldn't find the basis in EngineeringReference and I/O Reference.
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But I don't know what is the basis for these Air Film Resistances? Does anyone know how they are calculated? They had nothing to do with weather data. But for this U-Factor with Film, I did some case studies with different Thermal Resistance and different weather data, calculated ( Interior Air Film Resistance) + ( Exterior Air Film Resistance) from the above equation, and found that ( Interior Air Film Resistance) + ( Exterior Air Film Resistance) was always about 0.150 for external wall and about 0.189 for roof. I know that air film resistance is calculated for each time step based on weather data during energy simulation. Therefore, in order to match U-Factor with Film with the assembly maximum U-factor prescribed in ASHRAE 90.1, we need to know the Interior Air Film Resistance and Exterior Air Film Resistance that are used to calculate U-Factor with Film. The input Thermal Resistance is equal to the reciprocal of U-Factor no Film. However, Thermal Resistance in Material:NoMass does Not include Interior/Exterior Air Film Resistances. I think we must match U-Factor with Film with the assembly maximum U-factor prescribed in ASHRAE 90.1 for baseline case. U-Factor with Film can be found in Report: Envelope Summary. ASHRAE 90.1 prescribes assembly maximum U-factors for walls and roofs, and the U-factors need to be used for baseline case.įrom the definition of U-factor in ASHRAE 90.1, it includes resistances of interior air film and exterior air film.