Making the most of passive energy efficiency

Big old windows. The downside is their large area of draftiness. The upside -- for our windows, anyway -- is they are south-facing. In the northern hemisphere, that means sunlight! Over the winter, I began making notes about the excellence of passive solar energy. As the temperatures fall, so too does the angle of the sun, until it dips below the overhang of our house's roof, which shades these windows in the summer but in winter is like a hat tipping hello and letting the sun beam into the dining room, the most popular room in the house during cold months, according to the cat and me. 

The thermostat is in the dining room, too. I noticed on a sunny autumn day, the temperature in here held at 72 for a good six hours, even though it was chilly outside. Our heat is set to 68. That means the furnace didn't kick on for all that time. Passive solar energy, baby!

So, in the winter, it's a little cool upstairs. There are windows up there, but they don't offer the same greenhouse effect as the big bay window in the dining room. That's OK. It's not literally freezing on the second floor. The pipes aren't going to burst (she said, fingers crossed and throwing salt over her left shoulder so as not to jinx anything, and then wondering how long you have to wait before you can let the dog lick up the salt). 

The point is, finding the warmest spot in the house and parking it there all day is just what you do in the winter instead of choosing to reside in the coldest room of the house and trying to heat it to optimal comfort. You don't force the universe to bend to your will, you make do with what the universe has given you. ...Don't you?

Now that we're leaning back into warmer months, the sun is higher in the sky, and its rays don't stretch across the dining room floor as they did in winter. I've moved the cat bed onto the ledge right up against the windows, so she still gets some direct sunlight for napping. Now also, the leaves are filling out on the trees that surround us, further shading the house.

Last week, I saw a Popular Science article about cooling your house without air conditioning. It offered the flip side of my passive solar energy ponderings, quoting architect David Wright on passive solar design: “all the things that you can do when you’re designing a building to basically naturally condition it and make it a better place to live.” I.e., working with the universe to keep yourself comfortable instead of cranking up all the utilities in a battle against the weather. 

Our roof has that nice overhang, wide enough to shade the house in the summer, but not sticking out so far that it would also block the winter sun. It works well for both seasons. I mentioned the trees. In the winter, their leaves are gone, allowing sunlight to hit the house and heat it up. In the summer, the foliage blocks the sun somewhat, helping to keep the house cool.

One of the things I disliked about our previous home was the lack of windows, or maybe more specifically, the positions of the windows in relation to each other. It was near impossible to get a cross-breeze going to cool that house on a warm day. In our new old house, however, we have windows on all four sides, plus a nice open floor plan, plus a whole-house fan that can draw air up and out through the attic. Yes, the fan uses electricity but far less than the air conditioner. (And, once we've fully restored the windows to good-as-new functionality, it will be even easier to open them up strategically to take advantage of wind direction and get optimal airflow through the rooms.)

Our house's age gets credit for these energy-friendly design elements, and around the world you'll find other examples of ancient buildings designed perfectly for their climates, because they were built before electricity was a given, before you could simply install central AC and forced-air heat. Modern materials and technology can help us take these climate-intuitive designs to the next level. 

As weather extremes become more common, and our energy needs push our power grids to the max, structural designs that are resilient within the climate are a necessity. Passive solar design helps us use less energy and saves us money on ordinary days, but it will also literally save us in the future when we'll need to survive sweltering temperatures during an extended power outage, an increasing likelihood as more frequent storms, fires, and other extreme weather events threaten the reliability of our already strained utility systems.

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