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"Trombe roof"

buckminster green's picture

A customer came to me today with a curious idea. I quote:

"I have an idea for a passive solar retrofit to my house here in the Italian Market.  I hope you can help me with it.  I refer to the concept as a "trombe roof".  It would be like a rooftop greenhouse, but covering the whole roof, and just a few inches high, not a space to walk around in or grow plants - just glazing over a small airspace above the roof.  The number of btu's from sunlight falling on the roof is twice what we purchase in natural gas.  I'm hoping this will capture a bunch of those."

My thoughts:
"Trombe roof" doesn't fit because there is no significant thermal mass like in a trombe wall. This is more like a storm window, trapping a layer of air as insulation. His idea is to build a frame, cover it somehow (like a greenhouse), trapping air which would heat up in the winter and slow heat loss through the roof. In the summer he wants to take off the cover, exposing the frame, on which he will grow annual vines to shade the roof. It is a flat roof on a rowhouse in Philadelphia. Seems like a lot of work for questionable gain and obvious issues with snow, rain, etc. To me the solution to his problem (heat loss through roof) can be solved with extra insulation and a white roof, but it was interesting thinking about his idea in the shower this morning and I thought someone else might want to take a stab at it.

(post #157568, reply #1 of 18)

Yay buck,


It's part of the fun of thinking about it. Then sometimes they'll actually go out and do it, having a ball in the process.


Beats vinyl on osb for a living:o)



 


 

 

(post #157568, reply #2 of 18)

The trombe wall you mentioned is correct. Without thermal mass, i don't see the benefit.

I had designed a trombe wall for a house project once (not built). From what i'd researched, the exterior of a heavy wall mass has a plate of glass over a reflective sheet, with an air barrier between them. The sunlight hits the reflective sheet, which allows less of the heat to be absorbed. The resulting air trapped between them can get pretty hot, which is what provides the heat.

If he did the glass portion like this i'd be worried that the heat might damage the roof on a sunny day. At best, it seems like a lot of wasted effort.

(post #157568, reply #5 of 18)

I have no idea why, but I find the need to post this, irresistable:


Why not make the thermal mass out of bones? It might be a good use of material that a packing house would otherwise throw away.


And then of course there's the name associated with the roof.......


 


 


Unless you're the lead dog, the view just never changes.

. . . I can't live proud enough to die when I'm gone, So I guess I'll have to do it while I'm here. (Phil Ochs)

(post #157568, reply #6 of 18)

The boner roof!


http://jhausch.blogspot.com
Adventures in Home Building
An online journal covering the preparation and construction of our new home.

(post #157568, reply #8 of 18)

The boner roof!


No, no, no!


It would be a trombe-bone roof!


 


 


Unless you're the lead dog, the view just never changes.

. . . I can't live proud enough to die when I'm gone, So I guess I'll have to do it while I'm here. (Phil Ochs)

(post #157568, reply #9 of 18)

oh, duh.  A little slow to think and too fast to reply.


Cute.



http://jhausch.blogspot.com
Adventures in Home Building
An online journal covering the preparation and construction of our new home.

(post #157568, reply #3 of 18)

I like the idea.  What about working to make it more like a tromb roof and pumping the warm air in, in winter.  I wonder if those four by eight plastic sheets (the light- weight stuff) could be used to construct something that could be easily removed in summer.


Rune

(post #157568, reply #4 of 18)

Why not an inflatable house-cover dome?


 


Treat every person you meet like you will know them the rest of your life - you just might!
Treat every person you meet like you will know them the rest of your life - you just might!

(post #157568, reply #7 of 18)

Instead of the whole roof just do like a 4'X 8' area, like a sky lite. Paint it black under the glass , have an inlet hole say 6" and an outlet hole, the same dim. only with a little fan on it and you got free heat.

(post #157568, reply #10 of 18)

I think the 80 percent solution to this problem is to just
get a bunch of black pipe of some sort that is UV resistant
and just uncoil it across the roof, then connect it up to a heat
storage tank to power an RFH system.

(post #157568, reply #11 of 18)

Hey if it's a flat roof, with access and is structual, why not a nice little rooftop green house you could actually hang out in.

(post #157568, reply #12 of 18)

That's a fantastic idea.

(post #157568, reply #13 of 18)

One thing I like about this idea is a matter of
indoor air quality. You put the air intake for
your HRV in the greenhouse, and that way your
intake air has been oxygenated and scrubbed by
the stuff in the greenhouse (or green Trombe
roof setup)

(post #157568, reply #14 of 18)

Are there any other solar veterans of the 1970s out there whose eyes are glazing over with a sense of deja vu?  All these new ideas, and many variations thereof, were built by the dozens in the 70s.  Many solar attics were built -- gables with glazed south slopes (usually using corrugated plastic roofing) and monster fans that used more electricity than the value of the heat collected.  Moreover, a company in Brentwood, NH (Dawn Solar Systems) sells components to mount PEX tubing under metal roofing, to gather the heat generated on a sunny day.  Now that energy costs are rising, a new generation is trying to reinvent the wheel.

(post #157568, reply #15 of 18)

When the solar panels were removed from the White
House roof in the '80s it wasn't the end of all that
70s stuff, it was just the signal for it to migrate
to friendlier shores.

The Japanese have made a big business out of the whole
trombe roof thing with the OM Solar brand--a very major
national builder.

Another idea from those days that was taken up elsewhere
is the earth cooling tube for HRV air intake, which is now
part of the German Passiv Haus spec.

(post #157568, reply #16 of 18)

Hey, I have a feeling that this next movement towards solar is going to be really big. Passive, active, air , water, electric. Remodel/ retrofits could be the next big wave. Its time to get off the grid and start cooling off this planet. Maybe those guys in Mn., that are faceing slowdowns, could get something going in that direction.

sun elevation at winter (post #157568, reply #17 of 18)

in addition to the low thermal mass of the roof structure, there is another important factor made the use of trombe roof of no use compared with wall structure. it is the sun angle or the angle of incidence it is very low in winter for regions above 45 degree north and south and the incidence angle may below 30 degree, so the direct sun beem strike roof with high inclined angle for flat roofs 

Totally agree. The angle is (post #157568, reply #18 of 18)

Totally agree. The angle is one of the most important, if not the, factors of all.