Window U-Factor and SHGC are estimates based on center of glass properties and a typical operable size frame area with user selection of frame thermal performance level. These estimates should be used for comparative purposes only within the Cardinal website and analysis tools. Building energy codes require window manufacturer’s to rate U and SHGC per NFRC procedures (www.nfrc.org).
Heating and cooling energy costs are estimated from regression analysis of building simulations using the REM/Design program (www.archenergy.com) and residential building insulation levels described in the Resfen User Guide.
Total window area is set at 18% of floor area for new construction, and 15% for existing houses. Window area distribution is assumed at 50% to the back, 10% on either end, and 30% to the front.
House size, vintage, orientation, shade conditions, and energy costs are user inputs.
Window comfort analysis is derived using ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy protocols (www.ashrae.org) and NFRC sponsored research “Window Performance for Human Thermal Comfort, February 2006”.
ENERGY STAR compliance estimates are for windows only. Northern criteria will be effective in January of 2016, all other zones go into effect January 2015. Go to https://www.energystar.gov/sites/default/files/ES_Final_V6_Residential_WDS_Spec.pdf to see the full set of requirements for windows, doors, and skylights.