Passive Solar Homes North Shore of Lake Chapala Part 1

October 29, 2011

We are fortunate to live in a climate that allows us the greatest freedom in home design. We can be very creative and still be within the perimeters of passive solar heating. Here homes in newer gated communities are built of masonry which is good for moderating temperatures (smoothing out, balancing the temperature). Floor tile is used in nearly all our homes, allowing for direct heat gain during the cooler months. On the north shore of Lake Chapala, much of the land slopes downward toward the south to the lake. This provides good southern exposure and a view of the lake. Many of the homes are longer along the east to west axis providing sun exposure to the south. This makes it easy to have solar gain and solar control. We know by studying the weather that heating is only needed for November, December, and January.

Passive Solar Heating
We would think with the above characteristics that passive solar heating would be the norm. Yet we have wood fires or roll around propane gas heaters in winter. We are cold. Luckily, we can convert most existing homes or build new homes so that they are heated by the sun. Direct gain is the easiest, least expensive way to do this.

However, once we let in direct sunlight and it strikes a masonry surface, the masonry is not capable of absorbing all the heat. The surface of the masonry becomes hot, some of the heat is absorbed, and much of the heat is cast off to be absorbed by the air. The air will quickly rise in temperature and the interior will become uncomfortable.

There is a solution. If we use diffuse glazing, the light and heat will be spread around over a much larger area. This will greatly increase the amount of heat absorbed and reduces the temperature increase. Another way is to have the sunlight strike a white wall surface which then diffuses the sunlight.

Sizing of Glazing

We want to know how much glazing we need, and where to place the glazing. We have already distributed the thermal mass storage (the masonry) in the ceilings, walls and floors by accident.  From studies we know in a heavy masonry structure we can bring in more sunlight than in a light structure.  We can use a rule of thumb of 15 to 20 percent of the floor area in glass. We want to place the glass evenly throughout the house. We can actually calculate the amount of glass by the floor area of each room.

We want to see though the glass which is at eye level so we can see our gardens and the lake. The diffuse glazing needs to be placed above eye level in high walls or in the roof. For new homes we can use both south vertical glazing and skylights. Vertical glass in walls has the advantage of using roof overhangs to prevent direct heat gain in the summer. Skylights in the south roof with the glazing set at 20 degrees south from horizontal will place the glazing at 90 degrees to the sun in January. We now have the light spread out in the home, making the home bright and cheery, and making it easier for us to see. This helps balancing the light from other areas of vertical glazing. Perfect!


Now if we drop in skylights into the roof of the outdoor sitting/dining area as seen in photo 1, we bring light to a troublesome area of most of the existing homes, the back area of the outside porch. Using defused glazing spreads out the light and brings light into the interior of the home through the glazing between inside and outside. The vertical glazing below the skylight may be clear, since the skylight has already diffused the light. This [provides daylighting to the interior, to the porch and to the room at the end of the porch.

Ops! We forgot something. We need the heat December, January and February. We do not need any heat from March to November. We want to put the roof glazing in shade during 9 months of the year. We do not want to eliminate the indirect light we get if the skylights are in shade.  Now we have to be creative.  What ways can we think of to shade the skylights totally but not block the indirect light? Let’s make even harder. We want the shading device on the outside above the skylight. If we let the heat inside the home before we block it, then we will have difficult time getting rid of the heat. Finally, we want the device to be automatic, so we don’t have to get up on the roof to put it into place or to adjust it. See next month’s column for a possible solution!

The Lake Chapala Green Group meets the first Tuesday of each month, 3:00, at the Lake Chapala Society, Neill James Patio. The general meeting is suspended for the months of June, July and August. For information on all things green at Lakeside…