What Are Trombe Walls?
Jan 24, 2022
Most of today’s energy-friendly building techniques come from new technology, like geothermal heating, advanced materials, and solar panels. However, one totally passive heat source has been around since the 1960s: The Trombe wall. Using basic materials, this technique uses solar rays to radiate heat within the home without the use of solar panels, heat exchangers, or any electronics at all.
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What is a Trombe wall?
A Trombe wall is a wall-building design that utilizes basic building techniques and widely-available materials to heat a space using solar radiation. Built on an equator-facing wall, Trombe walls are entirely passive and efficient, so they can be an attractive option for remote homes or off-grid buildings.
The Trombe wall gets its name from its design, French Engineer Felix Trombe. Trombe used the idea of thermal mass walls—which are essentially thick masonry walls heated by the sun (an idea that originated in the 1880s)—and improved upon it. He was able to increase heat gain with a layer of glass in front of the masonry wall, making the new Trombe wall a viable heat source for many buildings.
How does a Trombe wall work?
At its core, a Trombe wall includes a layer of large, fixed-pane glass windows installed on a south-facing wall in the Northern Hemisphere or a north-facing wall in the Southern Hemisphere. On the inside of the glass, the builder constructs a tightly-fitting brick or masonry wall, leaving approximately a ¾-inch air gap between the brick and the glass. The exterior of the brick is typically painted a very dark color to provide better solar absorption.
During the cold winter months, when the leaves are off the trees and the sun’s path is low, the heat from the sun beats directly on the glass. The rays begin warming air caught between the brick and glass. Since heat will travel to colder spaces, the brick wall begins to absorb heat and slowly release it into the space through radiation (just as a steam or hot water radiator would).
As the heat enters the room, it will begin to rise as the cold air within the space drops. As the cold air drops, the Trombe wall will heat it, creating a cycle of convection that will eventually create an even heat (if the space is small enough).
The Trombe wall’s design accounts for summers, as well. First, Trombe walls typically have roof overhangs built at their eaves. Since the sun is higher in the summer, the overhang blocks most of the sun’s rays. For the heat that does collect between the glass and brick, the vents at the top and bottom of the walls allow for air movement, meaning it’s able to escape without allowing for much absorption.
Advantages and disadvantages of Trombe walls
Like any building technique, there are pros and cons of Trombe walls. Between efficiency, ease of use, layout, and energy savings, there is a lot to consider.
Advantages of a Trombe wall
For homes in areas that can utilize them, Trombe walls can significantly reduce a heating bill. While an electric heater might shut off and immediately cease dissipating heat, a Trombe wall captures heat and radiates it for longer periods of time. This means that just because the sun goes down doesn’t mean the Trombe wall stops working. There are still hours of heat energy stored in the wall, and it will release it at night.
Trombe walls also provide comfortable heat. As a source of passive solar heating, the wall radiates heat into the space and creates a cycle of convection. Convection will heat the room from top to bottom, allowing the entire space to heat evenly. And, it does it all without costing extra each month.
Even in spaces too large to heat entirely with a Trombe wall, there are benefits. The Trombe wall can help supplement oil, gas, or electric heating systems. This allows the heater to run less often and heat the space more efficiently, reducing the energy bill and resource consumption.
Disadvantages of a Trombe wall
Trombe walls do have their shortcomings, as well. For instance, spaces that aren’t well insulated to prevent heat loss may never realize the true benefits of the solar radiation. Keep in mind, however, that those spaces will be inefficient regardless of the heat source.
Trombe walls aren’t very attractive. On the inside of the home, they might resemble a typical brick accent wall, but on the outside of the home, they can be unattractive. It’s possible to dress them up a bit, but they will likely never be as attractive as a standard glass wall. Also, consider that a Trombe wall will likely block most homes’ primary source of natural light, which could be a dealbreaker for some designers and homeowners.
Finally, recognize that Trombe walls don’t work everywhere. If the sun’s path is blocked by trees, mountains, or other buildings, it’s unlikely that there will be any benefit. And, for homes that don’t have a wall that faces directly toward the sun, the Trombe wall will be less efficient at the beginning or end of the day (depending on the situation).
Trombe walls can be a big help in reducing a home’s efficiency or dependence on the grid, so they’re definitely worth considering. If a home has a sun-facing wall available and a clear path, this simple and efficient building technique can make a big impact for the residents.
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