r-value method?

Question

I am doing a project, regarding the energy benefit saved by an efficient window thermal blind. I am able to find many variations of improved r-value window blinds, and I can find the current heating system bills which is required for this building, as well as the number of windows which can be improved...but I still need a method to determine this cost/benefited analysis.... please help....

Answer 1

This is a pretty complex thing to model. You first need to know the number of BTUs required to heat the building at a certain outdoor temperature, given a certain r-value. I have no idea how to do this, but i'll bet the EPA or some gas company has tools to calculate this. I would then calculate the average temperature for the period of time you have billing records, excluding those months when heating isn't needed.

Then you need to figure out how much the r-value of the building changes by replacing the windows. Measure the window dimensions, and then visit a building supply store like Home Depot to get estimates for the same style windows with plain glass and various r-factors. Then calculate the surface area of the windows, and the surface area of the outer walls which are not windows. The r-value of the building walls will be proportional to the weighted amounts of ceiling, glass, and non-glass surface areas and their corresponding r-values.

Then plug this back into the heating cost formula from the first step.