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Energy  > Residential Energy Model Overview
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Overview
 
These residential energy studies compared the energy use in concrete homes with homes built with lighter, conventional materials. All studies were based on an identical, typical 2,450 square foot single-family house in more than 25 locations in the United States and Canada.
 
The results summarized here are for six cities representative of different climate zones. In each location, the house was modeled with different exterior wall systems including conventional wood frame walls, steel frame walls, autoclaved aerated concrete (AAC) block walls, concrete masonry unit (CMU) walls, insulating concrete form (ICF) walls, and insulated concrete hybrid walls with exterior insulation , interior insulation, or internal insulation.
 
Due to the use of typical construction materials such as fiberglass batt insulation in frame walls and CMU walls, in some locations, these walls were over-insulated as compared to the energy codes. However, because the concrete walls were constructed using identical materials and quantities in all locations, concrete walls were under- or over-insulated, depending on the location.
 
For purposes of comparison, energy use of mass and frame walls were compared to a fictitious code-matching wall that exactly met the energy code requirements of a frame wall. All other assemblies such as the roof, floors, windows, and interior partitions were identical. Indoor temperature set points, occupant habits, and rates of air infiltration were also identical. Analyses showed that houses with concrete walls had lower heating and cooling costs and also required smaller heating and cooling systems than houses with frame and code-matching walls, except for locations where the concrete walls were extremely under-insulated. Read the full report.
 
Summary of Results

In nearly all climates in North America, homes with concrete walls save energy compared with homes with frame walls that have more added insulation—and the savings can be significant. (Concrete walls include those constructed of concrete masonry units (CMU), lightweight CMU, insulating concrete forms (ICF), autoclaved aerated concrete (AAC) blocks, and insulated concrete hybrid walls with exterior insulation or internal insulation.)
 
Homes with exterior mass walls save the most energy in seasons when the outdoor air temperature during the day floats above and below the balance point of the house, about 60° F. Example locations are Phoenix, AZ and Bakersfield, CA. The balance point is the outdoor temperature below which heating will be required in the building because internal heat gains are less than heat loss through envelope and ventilation. The most effective mass wall assembly is with thermal mass (concrete) applied in good contact with the interior of the building. Walls with the insulation material concentrated on the interior side do not perform as well, but still show significant energy savings due to thermal mass.
 
Analyses showed that energy for occupant uses and hot water was essentially identical for all locations, and that heating and cooling energy accounted for 17 to 65% of the total annual energy cost, depending on the exterior wall type and location.
 
Specific findings include:
 
 
  • Due to the thermal mass of the concrete walls, houses with concrete walls had lower heating and cooling costs than houses with frame and code-matching walls, except for locations where the concrete walls were extremely under-insulated (cold climates). In general, percentage savings are greatest for hotter climates.
     
  • In nearly all cases, the best performing walls are concrete walls with the most insulation: ICFs, -, and sandwich panels. In most cases, cast-in-place walls were the next best performing walls.
  • The AAC walls have an inherently lower U-factor than the other walls in the study, and performed better than steel frame walls in climates warmer than Springfield, IL..
     
  • CMU walls performed better than wood and steel frame walls except in some locations where they had no added insulation.
     
  • The orientation of the house has a significant effect on its energy use. An example comparing houses with wood frame and flat-panel ICF walls in Albuquerque showed that if orientations are not identical, heating and cooling costs ranged from 52% more for the wood frame house to 6% more for the ICF house. A comparison of the same houses with orientation effects averaged showed a 20% cost savings for the ICF house.
     
HVAC Sizing
 
Another benefit of housing with mass concrete walls is that they showed additional savings from a reduction in the required heating and cooling system capacity. Homes with concrete mass walls required smaller heating and cooling systems than homes with frame walls, except in locations where the concrete walls have much less insulation than frame walls. (But since cooling units are usually bought in increments of 1/2 ton of cooling capacity, the cost savings for the smaller sizes may not always be realized.)
 
Air Infiltration Effects
 
Concrete homes tend to have significantly less air infiltration than homes build with wood or steel. HVAC systems that bring in supply air from outdoors and circulate air on a regular basis are recommended for these homes to ensure adequate ventilation. These are sometimes referred to as “air handlers” or “air-to-air handlers.” They prevent stale air and odors from accumulating and, more importantly, help prevent the accumulation of moisture on and within walls and other building components. Oversized air conditioning systems can cause additional moisture problems because they do not cycle enough to adequately remove indoor moisture.
 
click to view lower level floor plan
click to view lower level floor plan
click to view upper level floor plan
click to view upper level floor plan
click to view front elevation
click to view front elevation
click to view rear elevation
click to view rear elevation
click to view left elevation
click to view left elevation
click to view right side elevation
click to view right side elevation

Wall Sections Modeled
click to view wood fram wall section
click to view wood frame wall section
click to view steel frame wall
click to view steel frame wall
click to view aerated autoclaved concrete wall
click to view aerated autoclaved concrete wall
click to view concrete masonry unit wall
click to view concrete masonry unit wall
click to view lightweight concrete masonry wall
click to view lightweight concrete masonry wall
click to view waffle grid ICF wall
click to view waffle grid ICF wall
click to view flat panel ICF wall
click to view flat panel ICF wall
click to view cast-in-place with interior insulation wall
click to view cast-in-place with interior insulation wall
click to view cast in place with exterior insulation wall
click to view cast in place with exterior insulation wall
typical sandwich panel wall
typical sandwich panel wall
click to view engineered sandwich panel wall
click to view engineered sandwich panel wall