Energy terms are often confusing and sometimes not suited to the situation they are used in. Terms like “tested R-value,” “performance R-value, and “K-value” need to be better understood in order to appreciate the advantages that ICF construction offers.
In the past there has been much speculation about the high R-values –often 50% or greater compared to conventional construction— associated with ICF buildings. A short review is then in order for the basic course in energy conservation.
Wikipedia.org, the online encyclopedia, defines R-value as “thermal resistance.” In order to give a working definition of thermal resistance it is necessary to understand that there are many factors influencing R-value and that laboratory tests often do not reflect real world performance. For instance, it most certainly it never blows or snows on the lab technicians.
These differences have given rise to the notion of “performance R-values,” which may be accurate, but are difficult to verify. The most recent measurement is K-value, which measures how well an object conducts heat.
In the energy conservation business there are two major problems; heat gain and heat loss from the building envelope—the floors, walls and ceiling of the structure.
The three measurable heat transfer methods are convection, conduction, and radiation. A thermal resistance number, or R-value can be calculated for each of these terms. The higher the R-value, the better the product is a stopping the flow of heat.
Convection is the transfer of heat by the motion of or within a fluid or gas—like central air heating. Convection is the largest form of heat loss from a structure and can be addressed by airtight construction methods like ICF, which limit the amount of air that can get through the building envelope. “Tested R-values,” however, don’t consider the level of airflow through the wall, which is one reason why many claim R-values don’t accurately represent the insulating properties of an ICF wall.
Incidentally, convention is also the most efficient way to heat a structure. Warm air rises off a heated floor; cool air falls to the floor to be warmed.
Conduction
Conduction is the transmission of heat across matter. If you’ve ever burned yourself on the handle of a cast iron skillet, you probably know conduction is the strongest form of energy transfer and the most constant. An un-insulated concrete floor is constantly losing heat to the environment 24 hours a day through conduction, which is why some builders install an underslab thermal barrier.
While convection is the largest form of heat loss, walls, floors and ceilings will also conduct heat to and from the environment unless the conductivity, or K-value, of the materials is very low. K-value, represented in physics by the letter lamda λ, is the ability of a material to conduct heat.
In order to build energy efficient structures, materials of a low thermal conductivity are desirable both above and below grade. The lower the K-value, the better the material is for insulation. Expanded Polystyrene (EPS), which is used to make insulating concrete forms, has a K-value of 0.033. For comparison, fiberglass insulation has a K-value ten times higher (0.33), while wood has a K-Value of 0.76, and marble has a K-Value of 11.0.
"An ICF structure with R-22 walls will outperform any other type of conventional structure with double the R-Value in any side by side comparisons. "
Radiation
Radiation, also called thermal radiation or radiant heat, is electromagnetic radiation from an object. The surface of the sun, for instance, can radiate a significant amount of energy into a home. Radiant barriers exist to keep heat out of a structure, but most of these products are specifically for conventionally built walls and ceiling areas.
In order to use a radiant barrier to bounce heat back into the interior of a structure, there first must be a significant source of energy emitted from the interior. Radiant heat flooring radiates electromagnetic energy into the air, which heats the structure via convection. While radiant heat floors are outstanding in modern terms they rarely get warmer than the human body and certainly cannot compare to the energy emitted from the surface of the sun, this is a very low grade of energy.
In summary, energy efficient structures keep warm air in, radiant energy out and do not conduct energy in or out of the energy envelope.
Thermal Mass
Another consideration in calculating energy efficiency is the thermal mass of the structure. A thermal mass in the most general term refers to anything used to absorb and hold heat. Dense materials like stone, concrete, adobe or water work best. Since the ICF concept couples non-conductive foam with an energy-holding thermal mass, any energy that may bridge the foam is absorbed and held by the concrete –perfect redundancy for the energy envelope.
Finally, the term U-Value is the total amount of energy transfer through convection, radiation and conduction. This is an architectural term used to describe the energy efficiency of a structure, calculated using a formula that considers the materials specified for the building envelope—floors, walls and ceilings.
In summary, the R-Value is a number that has been poorly defined and even less understood. In terms of performance an ICF structure with R-22 walls, SIP (structurally insulated panel) roof, and an foam insulated floor will outperform any other type of conventional structure with double the R-Value (R-40+) in the energy, structural strength and return on investment in most any type of side-by-side comparison. Why? Because ICFs are airtight, non-conductive, have good thermal mass, are very strong and have the advantage of increasing in value purely based on the spiraling cost of energy regardless of location. ICF construction is the way of the future with radiant heat floors and geothermal exchange - the future is now.
This is the first in our newest series: Green Building. Stories submissions about energy efficiency, sustainability, and other topics are welcome at editor@icfmag.com
"In summary, energy efficient structures keep warm air in, radiant energy out and do not conduct energy in or out of the energy envelope."
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