Taking advantage of passive solar energy is simple! In our wonderful world, light passing through glass turns to heat. So placing double-pane clear glass (which has the best solar transmission of all readily available inexpensive glass) where the winter sun shines will add heat to your building.
FIRST ORIENTATION: Because the sun is exclusively in the south in the winter, any orientation in a southern direction will be effective. Not everyone agrees on the most effective direction. Where we live, we think it best to orient the sunroom a few degrees west of south, the argument being we have more cloudy mornings with clear afternoons than the other way around. If you can end up with the glass wall of the sunroom pointing anywhere from 20 degrees east of due south to 20 degrees west of due south, you will still come out ahead.
NOW THE SIZE: One way to control the cost of the passive solar installation is by controlling the size. My house is 52′ x 26′ and has a sunroom 38′ x 18′, This is large, but the existing porch I covered up was 32′ x 14′, It didn’t cost a lot for the extra few feet. A good rule of thumb is to have 25% of the house’s square footage in south facing glass. If you can’t afford a sunroom of that magnitude, remember: any sunroom is better than no sunroom. Also, the deeper the sunroom, the more heat it will use to heat itself, and the less you will have available to heat your existing house.
THE ROOF: Once you have a size in mind, remember that what you are building is a well-insulated room with a glass wall facing south. Many first-time sunroom builders want a glass roof on their new sunroom. Don’t do this! If you do, you will have a room that will bake all day when the sun is out, and will freeze all night when the sun sets. In the summer, when the sun is high, it will be an oven. If you want a skylight or two for a dramatic affect, go ahead. But remember that a roof can be R=50 , while the warmest skylight will be one tenth of that.
OVERHANG: Another important design element is overhang. To keep the summer sun out, you will need an overhang that equals about 25% of the height of your south facing glass. So, an eight-foot south wall gets two feet of overhang. This is very important. And keep in mind that too much overhang is better than too little.
SLOPE: A question I get asked frequently is, “Should I slope the south facing wall, or leave it vertical?” I recommend that you leave it vertical. If you slope the wall it becomes “roof” and must be able to shed water. This makes the construction difficult. It is much harder to insulate a sloped wall at night. A vertical wall is easy to insulate with a curtain or shutter system. Also, as you slope the wall away from a vertical position, you lose the reflected light bouncing off the snow on the ground. So keep it simple, keep it vertical.
HEAT STORAGE: Sun rooms become much more efficient if you include some type of thermal storage. This will keep your sunroom warm in the event of several consecutive days of cloudy weather, by storing the suns heat in whatever type of storage media you decide to use. ss Cement, rocks, quarry tile, or plain old H20, any masonry that is exposed to sunlight will absorb heat, especially if the cement, tile, etc. is a dark color and not shiny or glossy. However, good old H20 is free, and the water can be stored in drums, tanks, or even 1-gallon plastic jugs. Water is great for heat storage because you can easily adjust the total amount. This is much more difficult with masonry. All water should be in sealed containers so it will not evaporate and cause condensation problems. Another advantage to water is that if stored in clean containers, it can serve as an emergency water supply if your domestic water supply is interrupted. In my own sunroom I have black cement floors, dark brick on the walls, and 400 gallons of water in 1-gallon jugs. The masonry cost over $5000 and the water was free. The milk jugs cost $200 in deposits but I can get that back if I return the jugs to the Super Valu. I drink a lot of milk!
I could write volumes on the subject of heat storage! If you have specific questions, call me.
NIGHT INSULATION: This is important. It can be as simple as foam panels placed against the glass at night, or as elaborate as the motorized Window Quilt system I have in my sunroom. It could be a solar pool cover that unrolls off a reel attached to the ceiling or a simple insulated curtain. Any night insulation helps increase efficiency. As long as you plan room for the insulation to slide or store during the daytime, you can add it or upgrade it at a later date.
NOW PICTURE THIS: It’s late February at your house. You are sitting in your new sunroom, which is eighty degrees, and the sun is pouring in all day. You are sipping a cold glass of lemonade and remembering how much you used to hate winter. Isn’t life grand?