Passive Solar Window Package – A Case Study

Recently, one of our single family home clients asked me to review two window quotes they received, one from Windsor and the other from a Pella supplier. The scope of my review included a general cursory review for quantity and size verification and also to verify that our design intent was being followed with respect to a passive solar window design. The following is my evaluation sent to the client and builder.

“I have reviewed the window bids you had sent and here are my findings…

For Pella Proline: In general they did follow our guidance for a passive solar design. The ‘Advanced’ product is what we would intend on going on the north, east and west facing windows, where the NaturalSun product is what we intend for the south facing glass. There are just a couple observations and questions I have for the window representative.

  • With either spec they offer the same u-value which is great, the same transmittance across the whole home.
  • All of the south facing lower level glass is Advanced, which due to the deck covering almost the whole lower level makes sense. We don’t need the extra solar gain cause the sun won’t reach these areas directly, or for any quantifiable period of time anyway.
  • But, I would suggest that we make the double unit in bedroom 2 (but is a triple unit in their bid before we made the change to double) to be the NaturalSun product, as we will have direct south sun here.
  • Now, in looking at other areas of the home, the package features windows of the same spec for the whole room, not with respect to orientation necessarily. In other words, in the sitting nook for example, the rep. has designated all of these windows to be the NaturalSun, which is not really necessary for the east and west facing glass. So my question would be, is there a reason that they should be the same, some sort of difference in the quality of viewing out one as opposed to the other maybe? The same example is found for the study and would be for bedroom 2 as well.

For Windsor: This bid does not include passive solar. Although the specs vary slightly, it appears that is just due to whether they are fixed or operable. Every window is the low-e 366, or to my understanding, a triple low-e window. On a previous project, although not Windsor, the windows featured the same 366 designation and in working with the rep. and owner, we decided to go with low-e 366 for all north, east and west facing and a designation of low-e 179 for all south facing glass, a single low-e window that gave us the additional SHGC (solar gain) that we were looking for. So in following with the same areas that make sense for passive solar, as stated above for Pella, I would ask Windsor to rebid the package with this guidance and see what they can do.


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