PASSIVE SOLAR ROOM
My home in Phoenix, Arizona wraps around a south facing patio. (See diagram) It offered a great opportunity to capture winter solar heat for interior use. Although quite a bit has been written about solar greenhouse additions I found little about converting patios, which are enclosed on three sides, into passive solar heat generating spaces. However, the principals are the same so I plunged ahead. Armed by my extensive reading on greenhouses and passive solar space heating and some construction experience, I commenced building what I call a passive solar room. If your home has a south facing patio you too, can build a solar room that will give you years of enjoyment along with energy and cost savings.
Here are some preliminary pointers for this type of solar room:
1. A south facing patio or open unshaded area is the start for a solar room for any house. The longer the room, the more solar gain in the winter months and the more tolerant it can be of fluctuations in the weather.
2. The more rooms of the house that open into the solar room the more heat can be used in the house without fans or blowers. This may require cutting a door or two into a place where a window was previously.
3. Flooring should be reasonably dark to absorb most of the sun's heat. In northern climates the floor slab should be insulated. However in my region the solar heating of the floor will actually eventually turn the ground beneath it into a heat sink.
4. The more insulated the room is, the longer the heat will stay inside.
5. The use of double glazed windows is also important to retain heat.
6. Thermal storage in the room extends the period of time the room will continue to add heat to the rest of the house during the night or overcast days.
Length of the room - this house already had a 36 foot long south facing patio with 3 foot railings all around. The first thing I did was remove the railings and extend the patio another 14 feet in length to connect to the bedroom on the east end of the house. This also made for easy access to two bedrooms and the living room and, after adding a door, access to the family room.
Roof line - Having the roof of the new room match the existing roof was important so we hired the same company which had replaced our roof the year before to add the new section. It's a flat roof covered with 2 lb. density foam primed and coated with a white coating to reflect heat.
Eaves - The existing eaves on the house were 1 foot wide which was perfect for the 10 foot width of the planned solar room. In the heart of winter the sun shines on all of the tile floor as well as my thermal storage, built in adobe seating (bancos). It's enjoyable to walk on the warm floor in the evening when it is cold outside. In the summer the sun does not shine on the floor at all and the floor pleasantly cool.
Sliding Doors - The double pane sliding glass doors, all 8 of them, were purchased for this room were pre-used. We were glad we were able to find matching sets for aesthetic reasons. Since the posts for the original patio were not placed for even spacing, the patio was jacked up an inch or so and the post moved by a few inches to accommodate the doors. Each door is a standard 6 foot door, having 2 doors between each post.
Insulation - The ceiling and end walls insulation was next. Before adding insulation, aluminum foil was pressed, shiny side toward the roof, up against the ceiling to add a radiant heat barrier. The insulation was Celotex "Blackore", a rigid foam board 1 inch think with foil on both sides. These were cut to the width between the 2x6's and force fitted. 3 layers were installed making sure that there was an air gap between each sheet to aid in the effectiveness of the thermal reflectivity of the foil. Each sheet of the foam has a 7.2 "R" value, making the 5,5" (a 2x6 is really only 5.5") space a respectable R-21.6. This would not be possible with standard fiberglass insulation. Although the fiberglass is cheaper, R-14 would be the limit.
End Windows - One window was added in each end, again, double pane sliders where used.
Flooring - Saultio tile was used because it ideally fit the style of the house and was a less expensive option than any other type of flooring. Patterns were made in the flooring to add some "homey" atmosphere and get away from the hall appearance of the long room. A tile saw was necessary for all the cuts to make the patterns. After laying all of the whole tile, the tile saw cut all of the other tiles in one day.
Banco - The seats for most of the 50 foot long room are made of adobe brick. The bricks were made from the dirt in the back yard. Although making the brick is a long process, it is an excellent thermal storage medium, provides nice seating for the room and fits the decor of the home. The adobe bancos were covered with expanded metal prior to application of the finishing coat of stucco for improved adhesion. Recently I have found and used Q-Bond and fiberglass reinforced stucco for this purpose which I like better than regular stucco.
Ceiling fans - 3 ceiling fans were added when the room was completed to add lighting and some air circulation. By setting the middle fan to turn in the opposite direction from the two end fans, it is possible to get a circular air flow in the room.
Paint - Aztec #300, an insulating paint from Insulating Coating Corp., was used for the interior of the room. This paint, which is a radiant barrier and also acts as a sound deadener, provides an R-20 insulation rating during a sunny summer day by acting as an isolating layer blocking out the sun's radiant heat, whereas at night, or during overcast days, it prevents interior heat from escaping by reflecting it back into the interior. Although expensive per gallon, the paint lasts 10 years and is available in any color.
Summer - Summer months are not as hot as would be expected. A high efficiency evaporative cooler is in one end of the solar room. Using a thermostat, the cooler not only keeps the solar room cool but the rest of the house as well. (See diagram)
Transition months - In the transition months, (Sept./Oct. & April/May) the sliding doors are open to either let the heat out or capture cool evening air. By opening the house doors we can maintain comfortable temperatures without heating or cooling. Occasionally the blower in the cooler is used to blow out the warm air in the house for a few minutes during these months.
Savings -The cost savings to heat the house in the winter is dramatic. When Phoenix had 20 degree F temperatures during January mornings and 50-55 highs during the day, our total heating bill was only $14 over the normal gas hot water and dryer costs. The typical temperature of the room in the winter is 80 degrees F in the daytime and 68-70 degrees in the morning.
There are a few other basic assumptions about savings that must be factored in when figuring how much savings there is with the room:
1. How much the doors are left open or continuously opened and closed. This is a big factor in the winter if traffic is heavy. We do not leave the doors open in winter except to pass through.
2. Your comfort zone. If you are cold or hot with only a couple of degrees fluctuation in temperature, the savings will be minimal. We find we are comfortable with an interior temperature of 80 degrees in the summer, if the humidity is low, and 65 degrees in the winter with sweaters and other warm clothing. To maintain our comfort zone we run the A/C approximately 2 hours a day for 30 to 60 days during the humid part of the summer. In Phoenix it can reach 100 F degrees at times in April to mid October.
Based loosely upon a greenhouse, the solar room is not a new concept. An excellent book on greenhouses is Bill Yanda and Rick Fisher's, "The food and Heat Producing Solar Greenhouse", John Muir Publications, 1980.
The room is a useful area for gatherings, as a children's play area, has added value to the home and provides energy savings. My wife Glee and I also find it an enjoyable place for a cup of morning tea and for evening dining. Adapting a design to your particular home is a challenge that should start with a sketch of the south facing side of your home. Make pencil sketches so they can be changed easily. Take your time. Setting plans aside for awhile can help you break through a design block. And remember the sun's heat is free.
Harold L. Sexson
You may obtain additional information on Harold's solar room by sending a stamped, self-addressed envelope to him at 5445 E. Caron Street, Paradise Valley, AZ 85253-1615.
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