At the base of the Sangre De Christo Mountains in Taos, N. M., sits a small group of what appear to be traditional adobe pueblo homes. In reality, these are the Sueños del Cañon luxury condominiums, a cutting-edge model of sustainable development in Southwestern disguise.

Living Designs Group (LDG) and Dream-catcher Real Estate & Construction teamed up to create Sueños del Cañon as an affordable, ecological community. LDG is a consulting and design firm where engineers, architects, and ecologists work together to incorporate workable sustainable concepts into each of its design projects. The group's expertise includes water conservation, ecological preservation, and integrating interior and exterior environments to maintain a healthy “living design.” For this particular project, concrete masonry was a key part of LDG's energy conscious plan.

Because of its high thermal mass, masonry stays warm or cool longer than other materials, which reduces the strain on heating and cooling systems by moderating temperature changes inside a building. This feature makes masonry a prime material for projects geared toward energy conservation.

Special concrete block Trombe walls are being added to the wood frame construction of the Sueños del Cañon condo units to allow for passive solar gain. Trombe walls (most often pronounced like ‘trome') are named after a French inventor, Felix Trombe, who popularized the concept in the 1960s, although the design was originally patented in the 1800s.

The Trombe wall is an early version of the double wall, or dual skin, building envelopes which are common today. It is typically a south-facing wall of 8-in. to 16-in. masonry units, with an external pane of single or double layer glass. A ¾ in. to 2 in. space is left between the glass and masonry. The sun shines through the glass and heats the masonry wall, which is coated with dark paint or stucco to better absorb heat.

It takes 8 to 10 hours for heat to pass through an 8-in. Trombe wall, so as the sun goes down, the radiant heat from the wall warms the room. By morning, the wall begins to cool, and the whole process begins again when the sun rises. The denser the wall, the more effective it is for thermal storage. Therefore, to maximize the mass the masonry wall is completely filled with concrete. At Sueños del Cañon, 3000-psi concrete was used to provide additional reinforcement. Although a special mix is not required for Trombe walls, recycled content like fly ash can be used to create density and a more environmentally-friendly finished product.

Nature's heating system

Trombe walls are naturally most effective in sun-filled climates like New Mexico or Arizona where long stretches of overcast days are uncommon. Some design modifications can be made, such as adding vents at the top and bottom of the wall, to take advantage of natural convection. As the air between the glass and masonry wall is heated, it rises and circulates into the room through the top vent. As it cools, air is drawn down through the vent at the bottom of the wall. This action allows for a more direct gain of warm air throughout the day.

One drawback of this design is the potential for too much heat loss at night. Adjustable vent covers can be closed to prevent this backflow of warm air out of the room.

At Sueños del Cañon, windows and Trombe wall panels are used together to take advantage of both direct and indirect passive solar gain. As sunlight shines through the ½-in. thermal pane windows and warms the room, it provides a direct solar gain. When the sun's heat is absorbed into the Trombe wall, an indirect solar gain is created. The window installation is standard, with no special techniques needed. However, for optimal solar gain the glass is usually treated with a low-emittance (low-E) coating, which prevents heat from escaping back out.

The versatility of masonry is an asset to projects like this, where mass is needed but the entire structure is not block or brick. In this case, the 8-ft freestanding Trombe walls are added to wood frame construction. By using masonry, the builder is able to incorporate a solar feature, which will create long-term energy savings and still stay within a tight construction budget.