“Passive solar always works; it either works well or it works badly.” – Texas builder Jim Sargent
Whether in the heat of summer or winter freeze, the wisdom of Jim’s words rings true. At this particular time, late November in Denver, the sun shines deeper into the dining room through miraculously well-placed windows that benefit from nuclear fusion a mere ninety-three million miles away. Those who, either deliberately or by dumb luck, designed their home to both pick up the warmth of the sun during the winter months and reject the afternoon heat in the summer are enjoying the simple pleasures of Nature’s gifts and “good” passive solar design. Those “gifts” are still in force, regardless of our level of exploitation of them. I guess it depends on priorities. For example, views in this country seem to be primarily east or west – for views of mountain peaks or ocean panoramas or desert sunsets – so of course that’s where we want the windows. Bad idea, generally. In the excitement over having breakfast or an afternoon cocktail with that glorious visual smorgasbord, the possibility of living in a solar oven escaped some. A figurative solar oven, but the concept is the same; put glass on a box and aim it towards the sun, and bake your favorite cookies. Makes a great Saturday project for the kids, but a poor design strategy. But back to the point. If you absolutely have to have that wall of windows facing west, there are partial, if not economical, solutions. Just turn down the air conditioner, install reflective blinds or curtains and…wait, what happened to the view?
Passive solar design fundamentally looks at the local environmental characteristics like sun location, wind patterns, topography and the like, and then fashions the building to take advantage of the virtually free energy to keep the building comfortable. Good intentions for passive solar design in the north have occasionally gone south, so to speak. Walls of southern-facing windows in places like Minnesota or the mountains of Colorado will most certainly capture the heat of the sun, but there are a couple of significant problems with that: (1) too much of a good thing can go bad, and the aforementioned solar oven ensues, and (2) the same glass that welcomes the sun in the daylight hours allows the collected heat to escape at night because the insulating value of that glass is minimal compared to the insulation of the wall. It was expected that homeowners would pull drapes or insulating blinds at night to fully exploit the wonders of solar rays and the collected heat thereof, but they didn’t for the most part, and anyone who bought the home later was unlikely to as well. So, good intentions went awry, and some of these “energy efficient” homes ended up using more energy than the folks in the conventional ranch home down the street. The point – there should always be a point – is that effective design needs to be intelligent design (no, not that I.D.). Also, as an aside, more is not necessarily better.
Passive solar done right collects free energy, but it also keeps that energy in the building longer, smoothing out the swings in temperature, a graph of which more resembles the gentle rolling hills of Iowa than the Canadian Rockies. Hence, the “inherently comfortable” part. Well-insulated, a passive solar home should sustain reasonable comfort for a long time without electricity of gas, which comes in handy when power lines are taken out by a massive snowstorm or the climate disaster du jour.
Thus far in this post, the emphasis has been on staying warm, but there are increasingly more locations where staying cool is the primary objective because of, you know, that “Chinese hoax.” It seems this gets a little trickier; getting warmer generally means putting more insulation around the body until one reaches the desired comfort level, but we can only shed so much before we’re down to birthday suits, which does limit our ability to venture far from home. Homes in tropical climates are open and airy, generally light in color, with high ceilings and ample ventilation options. People in many of these areas dress for the climate and, to be sure, have a much greater range of temperature tolerance. “But wait!” you say. “How does this work in Houston?” Good point. The ideals of building for the local hot/humid climate pretty much fall apart in typical urban and suburban locations, partly because we’ve gone way too far down the path of “conventional” design, but also for reasons of land use efficiency, economy of scale, topography and a litany of other factors. That brings us to Plan B, isolating the indoor environment to maintain comfort with minimum expense and carbon footprint. Like it is for heating, knowing where the sun is at any given point during the day is pretty important. OK, very important. The depth of the eaves matters, shading the walls and windows of the house except when you want the sun shining through the [south] windows. In Houston, I’m assuming that would be seldom. The characteristics of indigenous tropical island structures – reflective roofs and walls, high ceilings and flow-through ventilation – still apply, where practical.
Heavy building materials (“high mass,” in energy geek vernacular) work for either warm or cold climates, but the location is important. The Pueblos had this down around a thousand years ago, but they also lived in a dry climate, which matters. Thick walls warmed during the day from the sun’s lower position in the sky, and kept the living space comfortable at night. In the summer, the sun’s higher position and cool nights combined to keep the interiors cooler than the intense outside heat. High mass material works in hot/humid climates, but mostly if it’s in the interior, stabilizing the inside temperatures. Uncarpeted concrete and tile floors are a good way to make use of “thermal mass.”
The Cliff Dwellers weren’t the only – or first – predecessors to practical use of Nature’s heating and cooling systems. You may have heard of the termite mounds in Africa, architectural feats of wonder from very industrious insects, that inspired the design of the Eastgate Centre in Harare, Zimbabwe. The Greeks and Chinese, among other cultures, designed cities around natural conditions and solar patterns. Ken Butti and John Perlin, in their classic book on solar energy history, A Golden Thread: 2500 Years of Solar Architecture, noted that the Greek philosopher Aeschylus wrote, “Only primitives & barbarians lack knowledge of houses turned to face the winter sun.” Ouch.
This post isn’t meant to be a design tool of course, but only meant to point out that buildings can be designed with some attention to the climate within which they sit and, more topical, to withstand the potential punishments of an annoyed Mother Nature. The result will be a building or home that can serve its occupants with extended comfort and reduced energy bills. With some further modification, it may also be more resilient to the more dire consequences of climate change. More on that later.