Monday, October 22, 2012

Building A Well House #9: Trombe Wall Solar Collector

It was a thrill to finally get to the point in this project 
that I had been most looking forward to 
and that was building the Trombe Wall passive solar heater 
to keep our well house from freezing in the winter.

In the photo above you can see we are pretty solarized with the Trombe wall
 and in the background you can get a glimpse of the attached sunroom on the house
 and the solar batch water heater on the roof, all passive solar use.

To follow along on the well house project:

The photo above was taken as we started prepping for the stucco.

The orange is the surface bonding cement over the 6" cement block
(with all the cores filled with concrete for a solid wall),
and the black is asphalt emulsion for protecting the below grade wall from water infiltration.

The building is set into a bank about 2 1/2' on the south side
 which limits the size of the collector.

Above you can see how we used concrete anchors to attach 
pressure treated 2 x 2's to the block to hold in the 2" XPS rigid foam insulation 
and provide a nailer for the stucco netting,
 as well as create the edge for the Trombe wall.

At the bottom note the below grade XPS insulation.

On the left the insulation has been set in, with 15# roofing felt over that 
and stucco netting and diamond lathe over that;
 while the area on the far right has yet to be done.

To see more on this phase of the project check out the post 

The Trombe wall area has been painted with asphalt emulsion
 to make it more absorptive to the sun's rays.

Now the stucco brown coat has been finished...

...allowing me to finish the collector.

The 3/4" stucco edge stop that is nailed to the 2 x 2's above 
also creates the edge for the 5/8" x 4' x8' twinwall polycarbonite sheet
that will be the glazing for the collector,
allowing for a 2" gap between the glazing and the wall.

This gap is not critical 
and almost any space between 1"+/- and 2"+/- should be adequate.

Although I could find no specs for how much extra room to allow
 around the sheets for expansion and contraction,
 I would think 1/4" in each dimension to be adequate.

I bent a drip pan (above) out of 4" sheet metal to go at the bottom of the glazing
 to keep the framing below the glazing dry.

This is also good for use with thermopane glass windows used in sunrooms.

Above you can see the wood has been painted white, 
everything has been caulked,
the metal flashing has been set in place (it looks better installed),
  the felt weatherstripping has been stapled on 
and we are ready to install the glazing.

The wooden trim has been cut to length, holes drilled for screws, 
soaked with boiled linseed oil, and the felt weatherstripping has been stapled on.

The piece with slots cut across it goes on the bottom
 and the slots allow rain water to move freely through.

I much prefer felt weatherstripping over the foam as it is very sturdy and durable,
but it seems hard to find as the big box stores do not have it;
only our local lumberyard carries one size
 and then I have to cut the 1 1/4" wide strips in half with sturdy scissors. 

And the job is done.

We had to do a bit of searching for the polycarbonite sheet
 but finally found it at Plastic Supply of Albuquerque, NM
 and they were happy to arrange a drop off in Santa Fe.

There are lots of size options and thicknesses available,
but we chose the 5/8" as it more closely matches the 3/4" thickness of the edge stop 
when you factor in the thickness of the felt weatherstripping.

The twinwall  polycarbonite is a series of tubes in the sheet 
 with a third thin film sandwiched in between 
effectively creating triple glazing; amazing stuff.

Before installing, the ends where the tubes are open
 need to be covered with aluminum foil duct tape to keep out insects, dust, etc.;
then I take a sewing needle and make a small prick in the tape at each tube to let moisture
 or condensation escape per the manufacturer's instructions.

The gravel helps to keep rain from splashing up on the glazing.

You can see the slots for rain a bit better (no felt on this bottom board)
and note the trim is screwed in for easy access in the future.

I used pine here which in our high desert area should last a long time
 but other options may be considered for wetter parts of the world.

The whole series for our well house: