Real world insulation testing vs laboratory tests
When comparing the overall performance of insulation systems, it is important to consider how the insulation interacts within the whole wall assembly. USDOE supported research(1) lists the important parameters to consider in a whole wall assembly comparison as follows:
2. Thermal Mass
3. Air Tightness
4. Moisture Tolerance
Interestingly enough, standard accepted test protocols used in North America for determining the thermal performance of insulation materials focus only on R-Value achieved in laboratory conditions. In addition to the other parameters above, standard laboratory tests do not consider several real world parameters that also affect insulation performance such as:
* Thermal bridging
* Extreme temperatures
* Installation deficiencies
* Radiative heat losses
* Aging effects on thermal performance
Depending on the type of installation, these parameters may have a significant impact on the real world performance of the insulation system. This translates directly to either an increase or decrease in energy consumption.
To date, a standardized laboratory test has not been developed to measure insulation performance in a whole wall assembly, taking into account many key parameters that affect insulation performance and sustainability.
As a result, innovative insulation systems have been at a great disadvantage in laboratory test situations that only consider conductive (and to some extent convective) resistance in ideal conditions.
In addition to the effects on energy efficiency, failure to consider all key parameters that affect insulation performance may lead to the oversizing of critical heating and cooling mechanical systems in both commercial and residential applications. This may result in premature aging of mechanical equipment from not operating within peak efficiency parameters. In addition innovative insulating systems may be excluded from installations where superior energy efficiency may have been realized.
In the end, are we interested in a building envelope that tests well in a laboratory environment, only to under-deliver after installation….or a building envelope that performs in the real world, reducing energy consumption and enhancing overall thermal comfort?
(1) Home Energy Magazine Online “Wall R-Values That Tell It Like It Is”, Jeffrey Christianson (ORNL) and Jan Kosny (University of Tennessee)