Precast Concrete Passive Solar Home

Precast Concrete Passive Solar Home

Summary:
The walls of precast concrete passive solar homes are made from concrete panels, cast in a factory and assembled on site, which save time at the construction site and save energy by taking advantage of the sun and wind for heating and cooling. They moderate indoor temperature in the winter by capturing solar energy during the daytime, storing it, and slowly releasing it; they moderate temperature in the summer by blocking sunlight and cooling down at night through ventilation.

The National Renewable Energy Laboratory (NREL) performed energy modeling on a precast concrete home and found the home used less than one-third of the annual heating and cooling energy of a home built to Council of American Building Officials (CABO) Model Energy Code standards in Pueblo, Colorado. Additionally, precast concrete homes cost about the same as homes built using conventional materials and can accommodate various architectural styles.

The home studied by NREL consists of four-inch thick, precast concrete exterior and interior walls situated on an uninsulated slab-on-grade foundation with a conventional wood-frame roof assembly. Reinforced concrete wall panels were produced off-site on a large casting slab. Fabrication proceeds with placement of door and window openings, installation of electrical conduit, and attachment of 2 inches of foam insulation board (R-14) on the exterior surface of perimeter walls, and embedding small steel plates at wall corners.

Wall panels are then welded together at the construction site. The primary source of heat in the winter is sunlight entering south-facing windows that is absorbed by the concrete interior. The concrete stores the heat for release throughout the night and prevents overheating on mild sunny days. During the summer, nighttime ventilation cools the concrete walls and reduces the need for daytime air conditioning.

PATH Attributes (Partnership for Advancing Technology in Housing)
The thermal mass of concrete walls, by storing and releasing energy, moderates indoor temperatures and can reduce mechanical heating and cooling requirements, especially the ‘peak’ energy required. The interaction of the thermal mass with the indoor environment moderates large swings in temperature that can cause heating and cooling equipment to operate inefficiently. In climates with large diurnal swings (daytime to nighttime temperature difference) the energy savings can be increased. In climates where the heating season also has clear sunny days, then the solar energy savings can be significant.

By reducing mechanical heating and cooling needs, passive solar homes eliminate pollution associated with electricity generation and fossil fuel combustion.

Concrete walls are long-lasting and can typically withstand extreme weather conditions well. In addition, concrete walls are more impervious to moisture problems and help to improve the moisture performance of the home.

Ease of Implementation
Builders of passive solar homes are located throughout the United States. One Colorado-based building contractor is willing to license its precast concrete construction method and provide engineering and hardware to builders in other regions. Challenges to use of the technology include the design stage where typical connections applied on site must be specified in the plans. Trade contractors must be trained to work on concrete wall systems, installing utilities using methods more common to commercial installations.

Operational Cost
Depending on climate, heating and cooling costs can be reduced dramatically. In one study, heating and cooling costs were reduced by 73 percent in Pueblo, Colorado.

Initial Cost
A precast concrete home is said to be comparable in price to frame and concrete block construction if the panels can be fabricated fairly close to the building site. One builder offers passive solar concrete homes ranging from $80,000 to $250,000.

U.S. Code Acceptance
Manufacturers of precast concrete systems generally provide engineering and energy performance documentation to builders to facilitate their acceptance by local building departments.

Installation
Panels are transported from the factory to a home site and a crane is used to set concrete panels in place on the foundation. The manufacturer states that it is possible to erect the walls of a 1,200 square foot home in a single day with six workers. Construction of the roof occurs on-site using conventional materials. Many exterior finishes are possible, including stucco, brick, and wood siding. Interior walls can be papered, textured, or painted. Because the electrical conduit is embedded in walls, local code officials may require an electrical inspection prior to casting the walls.

Benefits/Costs
Concrete passive solar homes can be significantly more energy efficient than conventional homes—using up to less than one-third the heating and cooling energy of conventionally-constructed homes in one study. The manufacturer states that its concrete home is more resistant to vermin, fire, and disasters than standard frame homes. Interior wall surfaces are concrete and are more durable than gypsum wallboard.

Availability of passive solar concrete homes is currently limited to regions with qualified builders. Because this method of construction and heating is uncommon, a builder may need to provide supporting documentation to local building departments to gain acceptance. This approach to heating and cooling is most applicable in areas with large variations in temperature between daytime and nighttime, such as the Southwest.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the U.S. Department of Housing and Urban Development (HUD/FHA), The Partnership for Advancing Technology in Housing (PATH), or any PATH-affiliated Federal agency or private company. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.