RESFEN 3.1

SYSTEM REQUIREMENTS
GET A COPY
DOCUMENTATION
KNOWLEDGE BASE
 

Overview

Today's energy-efficient windows can dramatically lower the heating and cooling costs associated with windows while increasing occupant comfort and minimizing window surface condensation problems. However, consumers are often confused about how to pick the most efficient window for a residence. Product information typically offers window properties: U-factors or R-values, Solar Heat Gain Coefficients or Shading Coefficients, and air leakage rates. However, the relative importance of these properties depends on site- and building-specific conditions. Furthermore, these properties are based on static evaluation conditions that are very different from the real situation a window will be used in.

A computer tool such as RESFEN can help consumers and builders pick the most energy-efficient and cost-effective window for a given application, whether it is a new home, an addition, or a window replacement. It calculates heating and cooling energy use and associated costs as well as peak heating and cooling demand for specific window products. Users define a specific "scenario" by specifying house type (single-story or two-story), geographic location, orientation, electricity and gas cost, and building configuration details (such as wall, floor, and HVAC system type). Users also specify size, shading, and thermal properties of the window they wish to investigate. The thermal properties that RESFEN requires are: U-factor, Solar Heat Gain Coefficient, and air leakage rate. RESFEN calculates the energy and cost implications of the window compared to an insulated wall. The relative energy and cost impacts of two different windows can be compared.

RESFEN 3.0 was a major improvement over previous versions because it performs hourly calculations using a version of the DOE 2.1E (LBL 1980, Winkelmann et al. 1993) energy analysis simulation program. RESFEN 3.1 incorporates additional improvements including input assumptions for the base case buildings taken from the National Fenestration Rating Council (NFRC) Annual Energy Subcommittee's efforts.

Changes from RESFEN 3.0

The significant changes that differentiate RESFEN 3.1 from RESFEN 3.0 are listed below. Some of these changes affect program results. Engineering judgement suggests that the results obtained from RESFEN 3.1 are more accurate than the results from version 3.0. As a result, it is strongly recommended that all users switch to version 3.1.

Whole House Results: RESFEN 3.0 evaluated the energy impact of windows compared to a windowless insulated wall. In RESFEN 3.1, analysis results for the whole house (energy consumption from all the envelope components of the building, including windows on all orientations, walls, roofs, and foundations) are also presented. Whole house results are calculated during a DOE2 simulation that is automatically generated by RESFEN when you press either of the calculation buttons. Results for only windows, by orientation, are still included and are useful for looking at specific cases where different windows may perform more efficiently depending on the direction they are facing. See Section 4.7, "Results" for more information on this feature.
NFRC Input Assumptions: For each set of RESFEN 3.1 results, many input assumptions are made including insulation levels in the building envelope and HVAC equipment efficiencies. The assumptions in RESFEN 3.1 are the same as those used in the National Fenestration Rating Council (NFRC) Annual Energy Rating Subcommittee efforts. These assumptions are documented in Table 6.2.
Building Floor Area: It is now possible to input the floor area of the building being modeled, up to 4,000 square feet. Many assumptions, such as wall area, internal gain, infiltration rates, and internal mass, depend on the floor area, and the program automatically changes these values when the floor area changes.
Location-based Defaults: The following values are defaulted based on location: foundation type, electricity cost, and gas cost. The foundation types that appear in the Foundation List depend on location, reflecting that common building practice is different based on geographical areas.
Skylights: A column has been added in the Window Data section for skylights. These are modeled as vertical glazing in the roof of the building, with solar heat gain reduced by 50% to account for skylight-well effects. This correction factor is a placeholder; research is ongoing to improve the skylight well solar gain correction.
Toolbar: A toolbar has been added below the menu for the most commonly used functions, including Print and Calc. See Section 4 for a more complete description.
File Format: The format and name of the RESFEN input files has changed from RESFEN 3.0. The extension for RESFEN 3.1 is "RSF" rather than "BSE". RESFEN 3.1 can read BSE files but RESFEN 3.0 cannot read the RESFEN 3.1 RSF files. If you open a RESFEN 3.0 BSE file check the input values very carefully because some of the information may not translate correctly, in particular the Solar Gain Reduction choices, the electricity and gas costs, the house type, and foundation type.

Screen Shots

Click on image to view the screen shot.

If you have questions or need program support, please DO NOT telephone Santosh Philip at Gabel Associates (as shown in the RESFEN Help/About screen). Instead send email to RESFENHelp@lbl.gov