A Lesson on Passive Solar Design. . .

While I have some time (the rain has slowed excavation, and Kenny is building and installing the temporary electric pole), I thought I'd post a little information about Passive Solar design. There are many great resources out there about Passive Solar design. Check online or your local library. One book I found very helpful was Daniel Chiras' "Solar Home" and also, his "New Ecological Home." There are also many websites based in Austrailia that are helpful, but remember to reverse their information because they are in the southern hemisphere - so when they refer to passive solar gain from the north, remember, for us in the northern hemisphere our solar gain is from the south. These guidelines are generally to maximize winter passive solar gain and minimize summer gain. This works for cold or temperate climates. For those in hot climates with no need for winter passive solar gain, an opposite approach may be best. Anyway, here's a quick break down:

Building Proportions and Solar Orientation:
For best results, rectangular buildings yield the best results for passive solar gain and passive cooling You can get the specific proportion recommendations from a number of sources, but generally the building must be longer in the east-west direction than in the north-south direction. A building oriented true south or within 15-degrees of true south will provide the best results. (Keep in mind that true south and magnetic south are different! You'll need to research and find how many degrees away true south is from magnetic south. In my area, true south is about 5 degrees off from magnetic south).

So we've established that a rectangle with the long sides facing true north and south work best. You also need to make sure that you have no solar obstructions such as large trees, other buildings, or obstacles toward the south side. Depending on your location, a few deciduous trees to the south east and south west are ok and assist in summer cooling - this is especially helpful in warmer temperate climates, but for cold northern climates, you want to minimize solar blockage. In all climates trees due east and west are a good idea to help block low angle sun and glare. Coniferours trees to the north create protection from winter winds.

Window Selection and Building Envelope Efficiency:
Your window selection and efficiency of your building envelope are both very important. In passive solar construction, window selection will be based on location. Windows on the north, east, and west sides should be as efficient as possible with a low-e coating to block the sun's rays. We can talk window specifics another time, but for now just know that low-e on three sides is ok. For the south side windows, however, you WANT to let in the heat, so you need windows that permit heat gain, but are still energy efficient and don't let heat out of your home. These are hard to find and can be the priciest part of the design. Your exterior walls also need to be very energy efficient and sealed well to prevent air infiltration and leakage. This is done through sealing, insulation, and building wraps. The more efficient your envelope is, the more effective your passive solar design will be. You will want most of your windows on the south side. Depending on if you are doing a sun-tempered design, a direct gain design, a sun space, or a trombe-wall (see the books I referenced above for more detai on these) - you will determine the amount of windows on each side. Our design is a Direct Gain design, so our total sqare footage of south-facing glazing is equal to about 8-9% of our total conditioned floor sq footage. For the north, east, and west sides, the windows make up about 2% on each side.

Thermal Mass:
Thermal Mass is the means of retaining or storing the sun's heat in your house until it's needed. You see, the sun's rays coming in the window heat not only the air, but also the objects in your house. For example, you want something in your house, that will attract and hold the heat for long periods of time, so that when the sun goes down, that object stays warm and releases its heat back out into the room. Metal for example is a poor choice because it heats up and cools down very quickly. The thermal mass in our home will be provided by our suspended concrete floor. (More specifics on that later, but here's why we need it). Our main level floors will be 3"thick reinforced concrete floors (with some "beam" areas as thick as 11"). The sun will shine through the windows and be absorbed by our concrete floors. The air will be heated slightly, but the excess heat will be absorbed into the conctete slab. Then after the sun goes down and the air in the room begins to cool, the concrete will then begin releasing heat into the air in an attempt to gain an equallibrium in temperature between the concrete surface and air. The amount of thermal mass in a passive solar home is important - otherwise the heating will not be effective, and there is a huge risk of summer overheating. There are mathematical calculations and formulas to determine the glass to mass ratio that will be most effective. So as you can see, thermal mass is very important not only to passive solar heating, but also to passive cooling in summer.

Passive Cooling:
In summer, the thermal mass absorbs excess heat from the air during the day, and then is purged from the space at night by opening windows and flushing out the heat with fans or simply the "chimney effect". Additionally, passive cooling uses landscaping to shade and cool the exterior of the home. Our home also incorporates exterior sunshades to block the sun's high angle rays in summer, while still allowing the sun's low-angle rays to enter the windows in winter.

Goals:
So based on all of the principles above, our goal is provide at least 60% of our total heating requirement from the sun - thus reducing our fossil-fuel heating consumption (and heating bill) by the same 60% (based on the usage by a similarly sized, traditionally built - non-passive solar - house in our area).

While passive solar design is not as complicated as some may think, there are still some specific requirements that are important to keep in mind. I'm sure there is more that I could go into, but I just wanted to give a brief overview. For those who are interested in more of the intricacies of passive solar design, I urge you to go online or consult the books I mentioned above to study this ancient practice in more detail.

Remember, only since the dawning of the Industrial Revolution in the late 1800s and early 1900s, did humans begin to approach the world with an attitude of "conquer with force." As William McDonough says, the human race's motto appears to be "If brute force doesn't work, you're not using enough of it." In a sense, we began to think that if it's too hot, just turn up the AC - don't worry about anything else. And for those of us who don't realize that we are ALL burning fossil fuels for our heating systems - it's time for a wake-up call. I actually had a student who told me that her heating system was very environmentatl - her home had electric baseboard heaters and there was absolutely no pollution emitted from her baseboards. (I guess she's never been to her local coal-burning power plant that provides her electricity).

For centuries prior to the Industrial Revolution, humans worked WITH the environment to provide for comfort, heat, cooling, etc. It can be done - quite easily actually - and the goal of our house is to show you how. Thanks for reading!