Insulation Systems: Is the Sum of the Parts Greater or Less Than the Whole?
There is generally plenty of focus on the type and properties of insulation during the specification and buying process, and insufficient attention to the insulation system as a whole. Whether its roofing, wall, foundation, piping, tank, or equipment insulation, the overall design and optimum application of accessory materials can mean the difference between long term success and failure. Each application has its own peculiarites, but the point can be made by looking at a chill water piping application.
The primary insulation design criteria typically includes thermal conductivity (K-factor and thickness), spread/smoke development, moisture permeability. Other criteria might include compressive strength, thermal expansion properties, and so on. The question posed herein is whether the insulation system components that are integral to the system can be designed to complement these criteria or do they necessarily degrade the attainment of the criteria?
The ASTM E84 fire/smoke criteria offer a good example. It is conventional wisdom that cellular glass insulation has the best E84 rating since glass does not burn. Yet Pittwrap multi-ply bituminous laminate is quite flammable and usually recommended as a vapor retarder over cellular glass, so the fire/smoke rating of the system is degraded.
On the other hand, polyisocyanurate insulation in the same application may have a slightly higher E84 rating but can be designed within a system that improves the overall system fire/smoke characteristics. [Note that building codes generally focus on the E84 rating of the insulation and do not take the overall system characteristics into consideration.]
Another example of how an insulation system can either enhance or degrade the functionality of the insulation involves moisture permeability, which is very important to the performance on an insulating systems that operate below ambient temperatures, and particularly those in humid environments. Again, cellular glass insulation is widely specified when moisture permeability is critical. Yet joints and sealing efficacy override the material’s intrinsic permeability and in many cases can yield an insulation system whose overall permeability is the same or worse than a properly designed polyiso insulating system. This is particularly true in applications where thermal or physical shock, mechanical abuse, or vibration can result in the cellular glass cracking or shattering - - neither of which can happen to polyisocyanurate.
In conclusion, it must be recognizd that there are a number of basic criteria that ultimately determine success of the insulation system: material and installation costs, process functionality (i.e. delivery of chilled water), process efficiency (including energy consumption), insulation system maintenance costs, ease of access to insulated equipment when necessary, avoidance of corrosion, compatibility with the environment (noise, appearance, odors, offgassing, etc.), disaster mitigation (fire spread, failure from shock) and so forth. Insulation systems must be designed and specified to optimize the spectrum of criteria to the extent feasible.
In most circumstances, the overall system can indeed be better than the sum of its parts.