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The Green Urban Gingerbread House: Part 2 – The Search for Solar Collectors (a.k.a. Windows)

December 29, 2010

As I began planning for the construction of the Green Urban Gingerbread House, I wanted to find a way to make clear windows that could be baked into the gingerbread. (Good windows are crucial to any passive solar design.) I have used Jolly Ranchers in the past, but couldn’t find any clear ones of those. First try was just baking sugar into the window opening, but that was a failure. As you can see, the red Jolly Rogers work quite well.

Next try was using a clear mint candy from Italy. In the oven, that bubbled up, browned, and ended up looking like something the dog might leave in the yard. Ew.

Next I decided to try making a clear hard candy myself, using just sugar, water, and honey in a pan on the stove. That was a little tricky without any candy-making experience or a candy thermometer, but it seemed to work. The honey made it a little amber in color, but definitely closer to clear.

The next step was to break up the clear/amber candy that I had made and remelt it into the window openings. This is where the effort went horribly wrong and the windows ended up looking globby and opaque. Definitely not the sleek clean modern look I was hoping for.

In the end, I decided to use butterscotch candy. It makes the windows an inviting butterscotch color, which looks really cozy when lit from inside.

Oddly enough, the difficulty in finding good gingerbread windows is somewhat similar to the difficulty of selecting appropriate windows for passive solar homes. There is a whole alphabet soup of ratings that windows go through for the National Fenestration Rating Council (NFRC), which is a great way to compare their performance. The most commonly used is the U-value, which measures the thermal resistance of the window (i.e. how well it keeps heat out or in). Lower is better for U-values and energy efficient windows are key for any green building.

However, there is another rating, called the Solar Heat Gain Coefficient (SHGC), which measures how much solar heat gets through a window. High-tech “low-e” window coatings are able to filter out quite a bit of the solar heat, which can be desirable in many situations. However, the goal with passive solar design is to capture the warmth from the sun during the winter (and use overhangs to shade out the sun in the summer). For this to be most effective, you want to have windows with a high SHGC on the south side of your building. However, this is where it gets tricky. Almost all major American window manufacturers do not offer windows with a high SHGC, particularly in the Pacific Northwest. Some Canadian companies offer it, but then the longer timeframe of ordering internationally gets to be a hassle to get the windows to your construction site when you need them (and it’s not inexpensive).

How to solve this if you don’t have a rich and famous lifestyle? For our recent passive solar addition, we used a triple-pane clear glass window from Andersen Windows, just for the primary solar collection windows. They have three panes of glass, which gives them a low U-value (efficient!) and no low-e coating to filter out the solar heat gain (high SHGC!). Those four windows cost as much as all the other windows in the addition, but still were able to fit in our tight budget – and the windows all look similar since one manufacturer made them.

Back to the butterscotch window – I’m pleased with how it turned out, but I would prefer a higher VT (another NFRC rating for “visible transmittance”, or how well visible light goes through the window). I did get a recommendation for Halls Mentholyptus Cough Drops – maybe next year I’ll try that, but I’m a little leery of how it would affect the delightful gingerbread-baking aroma.

3 Comments leave one →
  1. Joy Pope permalink
    December 29, 2010 7:06 pm

    Looks like it’s really coming along. Can’t wait to see the final pictures!
    And loved the advice on “green” windows.


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