THERMAL PERFORMANCE OF THE RASTRA® WALL

 

The TMM (DBMS) values for Rastra walls made of  Thastyron™ per Oak Ridge National Laboratory* computer simulation for the eight representative U.S. climates according to DOE and the resulting dynamic (effective) R-values for Rastra walls of four different wall-thicknesses are shown in the following table:

 

 

 

Notes:

 

      1.   Thermal Mass Multiplier (TMM) represents the influence of thermal mass upon the insulating capacity of a wall. (steady-state R-values were developed for traditional wood frame walls and do not include the Thermal Mass Benefit). Variations per climate zone reflect the influence of temperature and humidity.

      2.   The non-mass steady-state R value for Thastyron™ is 1.73/inch. When the Thermal Mass Benefit is included, the resulting R-value is shown. No TMM is not applied to flat panels with thickness below 4”.

3.      The equivalent thickness of Thastyron™ (the Rastra® insulating material) per Rastra® panel assumes a layer of concrete between two layers of Thastyron™. The combined thickness of the Thastyron™ layer can be approximated as follows:

{ Wall thickness – 3.5” (3”) concrete = number of inches Thastyron }. This simplified calculation matches with the testing and computer simulation conducted. The R-value of the assembly, however, increases slightly exponential with increasing thickness. The TMM decreases with more insulation around  the concrete (mass). This has been considered in the values for 12” and 14” walls.

4.      The 8.5” thick Rastra element has not been tested separately. The values in this column are calculated values, based on the other tests.

5.      Per DOE Prescriptive Table (402.1) Thermal Mass Benefit is not considered in climate zones 7 + 8. The minimum required steady state R-value is 21.

6.      Steady state R-values per testing (see above certificates).

7.      These are prescriptive values which are general. The first number is the steady state R – value prescribed for non mass walls (frame), the second the steady state value required for mass walls unless there is an established, specific TMM higher than the prescriptive multiplier. Values in gray shaded cells do not meet prescriptive values.    

 

*     Computer simulation has been based on a steady state R-value of 7.6 and a 10” thick wall made of 25 lbs/ft³  EPS concrete. Slight variations in DBMS values for other thickness and basic R-value may result.

 

For all building systems the “clear” wall R-value (as measured in hot box or hot plate tests) is higher than for the total house. Some building details  (corner designs, studs) are designed in a way that they interfere with the insulating envelope. That may account for a reduction in the whole house R-value of up to 35%. According to research of Rastra details by ORNL the total house R-value will not  differ more than 3.2%. For wood frame this value is usually >9%. Also other benefits such as tightness of the building or wall surface temperature influence.  These and other factors contribute to the real performance as utility use data supplied by residents of RASTRA® houses show savings in excess of 50% in some instances.