Software calculates energy savings for window replacement

Editor's note: The Energy Services Bulletin features real answers to real questions posed to our staff at the Energy Services Power Line. We hope you find it useful.

Question:
We are looking for a simple program to determine the energy savings potential of window replacements for a South Dakota customer. We are hoping to find a program that also determines simple payback in years when some values are plugged in. Can you help us find such a program?

Answer:
Power Line researchers looked into your request and were unable to locate simple software for comparing window retrofits for energy conservation. We found some programs that require a little reading and learning, but appear to be relatively straightforward. They did not appear to determine simple payback, but that function may be buried deeper in the programs.

The first program is called RESFEN, for residential fenestration. This residential window program calculates the energy and cost impacts between two different windows and also compares it to an insulated wall.

THERM is a more robust program that determines two-dimensional heat transfer through wall components. These can be different types of walls or windows. This program may require a bit more work.

WINDOW is an advanced modeling package that can provide the heat transfer through windows. Its purpose is more for education and for design and development of new window products. It uses some downloadable databases to determine U-values, solar heat gain, shading and glass transmittance values.

All three programs are available from the Lawrence Berkeley National Laboratory Web site.

FRAMEplus, a sophisticated program from Enermodal Engineering, uses advanced heat transfer equations for determining the properties of building products. It will analyze the window as a whole: glass, frame, and casing. It will be able to determine the energy loss, but has many other functions you may not need.

The last program, PARASOL is available from Lund University in Sweden. It is a simple program used to determine the effect of different shading scenarios for windows. However, it does determine the heating load for the window as well. So with some creativity, you may be able to adapt it for your use.

The Efficient Windows Collaborative is a great resource to help determine which type of window to select based on a specific region. You can do the comparison of different windows listed there and formulate some estimates on payback with the data.