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Trombe Walls

Posted February 15, 2011 05:20 PM by Alex Wilson
Related Categories: Energy Solutions
A Trombe wall retrofit workshop that I was leading in the late-1970s in New Mexico. To this simple frame, a layer of glazing was added, and sunlight would heat up the dark-painted wall. Photo: Alex Wilson. Click on image to enlarge.

Last week I wrote about sunspaces and how they can be used to deliver passive solar heat to our homes. Another option for passive solar heating is the Trombe wall, or thermal storage wall.

While the sunspace is an "isolated-gain" solar system, a Trombe wall is an "indirect-gain" system. Here's how it works: On the south side of a house you have a high-mass concrete or masonry wall whose exterior surface is painted a dark color. A layer of glass (or some other type of clear or translucent glazing) is held away from the wall surface by a few inches or more. Sunlight shines through the glazing and is absorbed by the dark wall, which heats up. The solar heat conducts into the wall where it is stored, and it gradually moves through the wall to the inner surface, where it radiates its warmth to the room. A short history of Trombe walls

The Trombe wall is named after a French engineer Félix Trombe, who popularized this heating system in the early 1960s. The idea actually goes back a lot further. A thermal-mass wall was patented in 1881 by Edward Morse. In the U.S., interest in Trombe walls emerged in the 1970s, aided by researchers at Los Alamos National Laboratory in New Mexico.

I was fortunate enough to be working in Santa Fe in the late 70s, for the New Mexico Solar Energy Association, and I became particularly interested in Trombe walls. In fact, my first article in a national magazine was on Trombe wall retrofits -- in Solar Age magazine in 1979. I also wrote the obscure Thermal Storage Wall Design Manual in 1979 (see photo), which gained some prominence among the small cadre of passive solar designers around that time.

Trombe walls are particularly well-suited to sunny climates that have high diurnal (day-night) temperature swings, such as the mountain-west. They don't work as well in cloudy climates or where there isn't a large diurnal temperature swing. In New Mexico, where homes have been built out of adobe (dried mud) bricks for hundreds of years, even an unglazed south wall will deliver some heat into the house -- if you add a frame and layer of glazing on the outside of the wall the performance improves dramatically.

We are used to insulating walls, but with Trombe walls there is no insulation. The system works with a material that is both very heavy (high heat capacity) and fairly conductive (low R-value per inch). The trick is to choose the right material and size the wall thickness so that the solar heat makes it through to the inner surface by nighttime. If it's too thick, it won't be as effective at delivering solar heat, and if it's too thin it will result in too much heat loss at night.

I think this was my first technical publication -- more than 30 years ago. Click on image to enlarge.

Tweaking a Trombe wall

An overhang is typically built that extends out over the Trombe wall above it. This will shade the wall from direct sun during the summer (when the sun is high overhead), but allow full solar exposure in the winter (when the sun is lower in the sky).

Top and bottom vents can be installed through the masonry wall to deliver more heat into the house during the daytime hours. Warm air in the space between the glazing and wall surface rises and enters the room, being replaced by air from the house entering through the lower vents in a convective loop. These vents should be closed at night so that the air circulation doesn't reverse, with air next to the glazing cooling off and pulling in warm air from the room through the upper vents and delivering chilled air to the room through lower vents.

Vents through the glazing can also be installed and seasonally opened and closed. In the summer months -- when you don't want the Trombe wall delivering heat into the house -- these vents are left open. Screens on the vents keep out insects and other unwanted visitors.

Like other passive solar heating systems, Trombe walls don't require fans or pumps. Part of the house itself is turned into the solar heating system.

In addition to this Energy Solutions blog, Alex contributes to the weekly blog BuildingGreen's Product of the Week, which profiles an interesting new green building product each week. You can sign up to receive notices of these blogs by e-mail -- enter your e-mail address in the upper right corner of any blog page.

Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News, which is now in its 20th year. To keep up with his latest articles and musings, you can sign up for his Twitter feed.

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Comments

1 Interesting article from a pe posted by Traonvouez on 04/02/2011 at 08:58 am

Interesting article from a person with a rare experience in trombe wall designs. I am interested in the subject, which will probably come back in fashion in the coming years.

Luc

2 Does anyone out there know of posted by Tim Rowse on 10/25/2011 at 12:32 pm

Does anyone out there know of a trombe wall system that's been built as a heat exchanger to supply heat for a radiant floor system?

3 Tim, I think that a trombe wa posted by Derek Roff on 10/26/2011 at 04:32 am

Tim, I think that a trombe wall is not appropriate as a heat exchanger for a hot water radiant floor system. A trombe wall is intended to absorb heat from sunlight during the day, and radiate it into the room's living space day and night. It's thermal mass moderates the temperature swings, and prevents the wall from getting too hot or too cold. If you were able to pull a significant amount of heat out of the wall, and put it into the radiant floor system, then the wall would have insufficient heat left to function as a trombe wall.

On the other side of the equation, the high thermal mass of the wall prevents the temperature from rising as high as would be desired for effective use in a radiant floor system. The two systems have different design parameters, intended to function in different temperature ranges. Therefore, they are incompatible, in the sense of one supplying heat for the other. There is nothing wrong with heating a room with a trombe wall and an independently heated radiant floor system. Having radiant heat coming from two directions can be quite comfortable. But you need separate collectors or a different heat source for the radiant floor system.

4 Derek, great questions. Alex posted by Tristan Roberts on 05/09/2011 at 07:52 pm

Derek, great questions. Alex is on sabbatical for most of the year so unfortunately I don't think he'll be available to answer your questions, though.

I don't think Alex and Quentin are any relation... Alex is up here in Vermont.

5 Derek, just right. Selective posted by Traonvouez on 05/09/2011 at 10:29 pm

Derek, just right. Selective surface and some other products allow completely re-thinking trombe walls, ventilation if any can also be powered by a small PV+battery. I am working on this with the prospect of designing a new equipment that can be industrially produced, and if some company of the construction sector is interested, I can be contacted directly at contact@insula-france.com.

6 As someone still involved wit posted by Derek Roff on 05/09/2011 at 10:53 am

As someone still involved with solar, eco, natural, and adobe building in New Mexico, it's great to see an article on Trombe walls. I'm wondering what design and engineering changes you see as most significant in Trombe walls for residential construction, in the last 15 years, or so. The builders/engineers that I talk to seem to be solidly advocating the superiority of unvented Trombe walls, as opposed to vented. And several of them say that the new selective surface coatings, which radiate almost no heat back out to the outside world, are a real boost to the energy contribution of a Trombe wall.

I would be interested in your views on these and related Trombe wall factors. And it just occurred to me, are you related to the legendary Quentin Wilson, still educating on adobe construction at Northern New Mexico Community College?


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