What is a Trombe Wall

A trombe wall is a high-thermal-mass wall typically placed behind south-facing glazing to absorb solar energy and release it into the house. It functions like a thermal battery that stores the radiant heat during sunny days and discharges the energy gradually to the interior space.

Why does it matter?

The trombe wall matters because it is a low-cost, passive energy solution that helps homeowners be less dependent on the grid and reduce energy bills. Because of its passive mechanism, it also reduces CO2 emissions compared to a traditional mechanical heating system.

How does it work?

It works like an indirect-heat-gain system: the sunlight first strikes a collector wall before reaching the interior space. Below is the breakdown of the elements of a Trombe Wall.

1. Massive thermal wall: the major component of a Trombe wall is its dense thermal mass, which is often built from material with high thermal inertia such as concrete, brick, or adobe to store heat.

2. Dark surface: a selective surface is required to maximize the radiant heat absorption. For example, in the custom home in Ann Arbor, Michigan, the homeowner uses a selective thermal envelope called Tinox metal foil to maximize the heat absorption. To maintain its function, the speaker thoroughly applied a smooth skim coat on the masonry wall before attaching the selective surface to ensure complete adhesion and thermal transfer.

3. Glazed surface: the transparent glass serves as a primary heat collector and protective layer of the system. The glass allows short-wavelength solar radiation to pass through and reach the dark high-thermal wall behind it. But the long-wavelength infrared radiation cannot easily pass through the glazing.

4. Air gap: A small air gap is created by positioning the glazing a few inches away from the masonry wall. The property traps heat between the glass and wall, containing warmed-up air that is similar to a greenhouse effect.

5. Vents: The vents are often placed on the top and bottom of the masonry wall to control the airflow and heat distribution. You can see a diagram of how the airflow through the trombe wall in the video features a home near Garrotxa Forest, Catalonia. (starting at 7:36)

Design Consideration

Orientation: In the northern hemisphere, a trombe wall is typically south-facing to maximize winter sun exposure.
Placement: During the planning phase, consider locating the trombe wall in the center area and near the air return location.
Material choice: Dense, high-mass material with a minimum 8-inch thick core.
Surface finish: A black metal surface is preferred to maximize solar gain.
Air-tight seal: Ensure to seal the edge of the trombe wall with a proper product, for example, the Tescon Vana heat tape used in the custom home in Ann Arbor. This can prevent drafts, moisture intrusion, and potential system failure.
Glazing installation: A glass with higher SHGC (solar heat gain coefficient) is ideal. Typically, a 2 to 4-inch air gap is ideal. If the gap is too large, it reduces efficiency; if it is too small, the heat transfer is limited.