Fuel Savings Disclaimer
The following assumptions were made to calculate our average annual fuel savings per home.
The annual energy performance figures were generated with RESFEN provided by Lawrence Berkeley National Laboratory. Results assume a typical house based on the criteria set in the Window Selection Tool. This criteria includes the type of construction, type of house, window area, orientation, shading, and window types. U-factor and SHGC are for the total window including frame.
The annual costs are for space heating and space cooling only and thus will be less than total utility bills. Costs for lights, appliances, hot water, cooking, and other uses are not included in these figures. The mechanical system uses a gas furnace for heating and air conditioning for cooling. Natural gas prices are based on state-specific average natural gas retail price data for the heating seasons (November to March) of 2011-13. Electricity prices are based on average state-specific electricity retail price data for the cooling seasons (May-September) of 2011-2013. All price data is from the Energy Information Administration (EIA)exit disclaimer.
Total annual energy costs for each city is calculated by adding the heating cost ($/therm * heating MBtu * 10) and cooling cost ($/kWh * cooling kWh).
The 20-window default set demonstrates systems currently available in the market. The performance ranges are provided and show that each default window type falls into a range of performance for U-factor, SHGC and visible transmittance. The specific performance attributes are provided and were used in the RESFEN simulations. If you know the specific performance attributes of windows, you may want to download RESFEN and perform simulations specific to your design and climate. See the pages on ENERGY STAR and codes to see the required performance requirements to meet each specific standard. Go to http://www.efficientwindows.org/attributes.php for specific performance information.
Home Size Average
We averaged the difference in savings between 1 story homes (1700 sf) and 2 story homes (2600 sf) to get an even coverage of home sizes. Each home uses a 15% window coverage with typical shading conditions as provided by the RESFEN study.
We took an average savings from clear single glazing vs triple glazing (low-e) and double glazing vs. triple glazing (low-e). This gives us a a good estimate of the savings difference we see from our product over the product we’re replacing.
Conversion to Gallons
To convert to gallons we took the Mbtu (heating) and the kWh (cooling) numbers as projected by the RESFEN study, and converted to gallons using the following multipliers: Mbtu to Gallons (.008 multiplier) and kWh to Gallons (0.024 multiplier). Source: http://www.think-energy.net/energy_units.htm