Wednesday, February 10, 2010

Passive Solar

     I have been interested in the use of passive solar energy since the mid 70's when I lived in northern New Mexico. It is a no brainer to me anywhere that the sun shines. The house that we had in Santa Fe had two trombe walls and one small attached sun room that we added that supplied much of our winter heat.

     (For an updated version of this post please go to: 

     The above photo shows a corner of the greenhouse. The black spine cactus sits in front of the wall separating the house from the greenhouse on a cold winter day. The adobe wall which used to be an exterior wall was plastered a dark color to absorb more of the suns heat. This creates a hot dry environment perfect for cactus.

     To the far left is the bathroom and just behind the fence and under the far left window is a trombe wall. Just to the right of that is the top of the sun room and in the center of the photo is a larger trombe wall that heats the living room.

     A closer view of the living room trombe wall. A trombe wall is basically a solar collector that is put over a masonry wall. The mass of the wall absorbs the heat of the low winter sun during the day and releases that heat slowly to the room behind that wall. The glazing helps to insulate the wall at night keeping the heat in. In the summer the overhang of the roof shades the trombe wall from the high sun. They are very effective at providing low cost heat in the winter, an excellent return on the relatively low investment cost.
     In this case our house was adobe with a cement stucco. We applied the frame for the trombe wall to the stucco leaving about an inch and a half space between the stucco and the glazing of the collector. The stucco wall behind the glazing was painted black to absorb more sun light. Our glazing was a triple wall polycarbonate glazing material.
     We later applied a spray on urethane insulation to the house and once the new stucco covered that the wall was flush with the glazing of the collector giving a nice trim look.
     Notice the window behind the collector with the white frame.

     This is the inside of the wall behind the collector to the right of the post and you can see the window.

     Sorry for the dark photo but a better view of the window. The warm dry conditions are perfect for cactus and yucca. The wide sill indicates the width of the adobe wall. The warm dry conditions are perfect for cactus and yucca. The wall puts out a radiant heat that is much more efficient at warming the body than the convective heat put out by forced air heating systems. Even though this wall has a window that opens into the collector it is not necessary to have any window or vent.

     This shows the sun room on the right and the trombe wall on the bathroom addition on the left.

     A close up of the bathroom trombe wall.

     This is the inside of the trombe wall and it is very suited to heating a bathroom as it helps create a drier environment. Also the windows above the collector never get condensation on them and the sills actually put out a small amount of heat. The toilet is right below the window.

     I stood on the edge of the tub to get this shot. The tub and shower dry much faster with the heat from the collector inhibiting the growth of mold and mildew. The sill is cast in place concrete.

     An outside shot of the sun room. Because of design constraints the only entrance is from the outside. Other than being a great place for putting tender plants in the winter this is too small for much use. When designing a sun room be clear of your objectives. If you want enough space for a breakfast nook it won't be good for heating the house. The most efficient sun rooms for heat are narrow- 3' to 4'.
     And please no skylights. They overheat in the summer and lose heat in the winter. And you need a masonry wall between the sun room and the living space on the other side, in this case adobe.

This window overlooks the greenhouse and is right over the kitchen sink so it is an important place. In the winter it is nice to open the folding window on a cold day with the green plants  and feel the warm air.

     This is the greenhouse side of the same window looking into the kitchen.

     The two small windows are summer vents. The diagonal sticks are used to prop them open. 

     The double pane glass windows have metal drip pans under them to protect the framing.