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Technical Information | Energy Efficiency

(Excerpted from Take Credit for a Good Design, published by CMACN)

Desert Block Co., Inc. supplies this information as an educational aid in understanding the benefits of concrete masonry construction and our products. It is the responsibility of the user to obtain engineering or other advisory services from licensed professionals as the basis for incorporating into any project any information, detail, or product offered herein.

We design buildings with masonry for many reasons . . . to be attractive and comfortable, to be durable, to keep out wind, rain and noise. We can also use masonry for energy efficiency.

Thermal Mass Saves Energy

For thousands of years, designers and builders have understood the valuable qualities of masonry, but many have become confused about its role in building energy performance. Because of an emphasis on high insulation levels, the importance of thermal mass has been overlooked.

We've become more sophisticated about energy efficiency, however, and have now quantified and accepted the benefits of thermal mass. The newest energy standards recognize this quality of masonry walls, allowing a reduction in insulation requirements as wall heat capacity increases.

Masonry Walls Offer Thermal Mass

The biggest energy problem in commercial buildings has been to remove unwanted heat. Internal heat gains from lights, equipment and people lead to year-round air conditioning. Outdoor heat gains just add to the problem. But the thermal mass of masonry allows it to absorb much of the heat, reducing the load on the air conditioning system.

Thermal mass in masonry walls moderates the day/night temperature swings and reduces heat flow to the interior, which reduces air conditioning loads inside the building.

Here's how it works: For outside heat to impact the cooling system, it must conduct through the wall by warming up the wall material. If the wall has high thermal mass, it takes a great deal of heat and time to warm it up. When the heat finally makes it through the wall, it is less intense. During cooler nights, this process is reversed; the heat flows out of the wall, and cools it down.

In many climates, this cycle of heat flowing into and out of masonry walls results in substantially lower annual air conditioning loads.

These two wall assemblies are equivalent. One is a stud wall containing insulation with an R-value of R-11. The other is a solid grouted masonry wall with no insulation. Put into otherwise identical buildings in a hot climate, they result in equivalent annual energy performance.

R-Values Are Just Part of the Story

R-values provide a measure of resistance to heat flow in walls or other building elements. They are useful in gaining initial understanding of heat flow in buildings, and for calculating peak heating loads. They are unable to account for heat capacity. Therefore, R-values are of limited usefulness in understanding long-term cooling or heating loads, or for predicting annual energy costs.

Excerpt From California Second Generation Nonresidential Energy Standards
Wall Heat Capacity Required Wall Total R-value Typical Construction
0.0 - 3.99 7.4 Insulated stud wall
4.0 - 9.99 6.3 Masonry veneer/stud wall
10.0 -14.99 3.9 Ungrouted 8" masonry wall
15.0 -19.99 2.6 Grouted 8" masonry wall
20.0 - and more 1.7 Grouted 12" masonry wall
This energy standards excerpt shows that less wall Insulation, or total R-value, is required as the heat capacity of the wall increases. Annual energy performance remains equivalent. (Heat capacity Is the technical term for thermal mass.)

New Energy Standards Recognize Masonry's Benefits

Energy standards are beginning to recognize the benefits of masonry's thermal mass. California's recent energy standards, developed through extensive computer analysis and research, provide a direct credit for thermal mass. Because the benefits are related to changes in daytime temperature and solar heat gain, this credit varies from climate to climate.

Modifying Masonry's Thermal Performance

Masonry walls with solid grouted cores provide maximum thermal mass. Masonry walls can also be insulated, to obtain different thermal performance characteristics or to meet other energy code requirements.

Interior Masonry Walls Save Energy, Too

Interior masonry walls work much like their exterior counterparts, but excess heat is absorbed from inside rather than outside. During the day, the walls absorb heat from inside the building - accumulated heat from the sun, lights, equipment and people. At night the heat is released. This helps cool the building during the day and keep it warm at night. Passive solar heating systems rely on interior thermal mass.

In the summer months, interior masonry can be "precooled" by nighttime ventilation of the building to better absorb heat and cool the building during the day

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