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2.3 Materials Selection

This section provides guidance on selection of mechanical insulation materials, based on factors including temperature ranges, material characteristics, and system type.

 

1. Insulation Selection

In addition to thermal performance, other considerations are important in selection of insulation material. The following table discusses these considerations for each operating temperature range.
 
 
Table 2.3.1 - Material Selection Considerations by Temperature Range

Temp Range

Selection Considerations

Low

(15º to -75ºC)

The major design problems on low temperature installations are moisture penetration and operating efficiency. For applications below 0°C, the insulation material should have low water adsorption.
 
Vapour retarders are extensively used, but in practice it is difficult to achieve the perfect retarder in extreme applications. The pressure of the vapour flow from the warm outside surface to the cooler inside surface is such that, even with waterproof insulation, vapour may diffuse through the material, enter through unsealed joints or cracks, and condense, then freeze and cause damage.
 
Since the cost of refrigeration is higher than the cost of heating, more insulation is often justified in low temperature applications. Extra thicknesses of insulation, even beyond what would be economically dictated for cold line applications, are sometimes employed to keep the warm surface temperature above the dewpoint, thus preventing condensation from forming.
 
The low temperature range is further divided into application classifications.

Refrigeration (0°C through -75°C)

Water vapour which passes through the vapour-retarder will not only condense, but will freeze. Built up frost and ice will destroy the insulation system.

Cold and chilled water (15°C through 0°C)

Unless properly insulated, water vapour will condense on the metal causing corrosion and failure of the insulation assembly. The permeance of the vapour retarder should be no higher than 0.02 Perms.

Medium

(15º t0 315ºC)

This temperature range includes conditions encountered in most industrial processes and the hot water and steam systems necessary in commercial installations. Selection of material in this range is based more on its thermal values than with low temperature applications. However, other factors such as mechanical and chemical properties, availability of forms, installation time, and costs are also significant.
High

(315ºC to 815ºC)

As the refractory range of insulation is approached, fewer materials and application methods are available. High temperature materials are often a combination of other materials or similar materials manufactured using special binders. Jacketing is generally field applied. Industrial power and process piping and equipment, boilers, breechings, exhausts and incinerators fall within this application range.

 

Condensation control on ducts, chillers, roof drains and cold piping is a basic function of insulation in commercial buildings. Design objectives here are to choose materials and application methods that will achieve the best vapour retarder seal possible, and to calculate the thickness of insulation necessary to prevent condensation.

Insulation chosen for personnel protection and/or fire protection must be able to withstand high temperatures without contributing to a possible fire hazard. Engine exhausts which can reach temperatures of 455°C to 675°C should be insulated sufficiently to reduce surface temperatures exposed to personnel or flammable materials to under 60°C. Kitchen exhaust ducts which are subjected to flammable grease accumulation fall within the same design criteria.

A variety of weather and vapour retarder jackets and mastics is available to aid insulation materials in meeting and designing objectives such as fire safety, appearance and system abuse protection.

All insulation, jacket, adhesives, mastics, sealers, etc., utilized in the fabrication of these systems shall meet NFPA for fire resistant ratings (maximum of 25 flame spread and 50 smoke developed ratings) and shall be approved by the insulation manufacturer for guaranteed performances when incorporated into their insulation system, unless a specific product is specified for a specific application and is stated as an exception to this requirement.

Care should be taken in designing insulation systems to specify the thickness, material and finish. All materials, thicknesses, finishes, securements and design objectives should be carefully communicated to the insulation contractor.

2. General Materials Selection Tables

The following two tables provide general guidance on appropriate materials choices based on system temperature and system type respectively. Note that in some cases there may be exceptions to the temperature ranges shown; consult manufacturer’s product specifications.

For more detailed information on insulation materials descriptions, characteristics and physical properties, refer to Appendix B, Materials Reference Tables.

Table 2.3.2 - Mechanical Insulation Temperature Selection Table

 

Low

(-75ºC to 15ºC)

Medium

(15º to 315ºC)

High

(315ºC to 815ºC)

Polyethylene

X

Polyisocyanurate

X

Elastomeric and Foamed Plastic

X

X*

Fibre Glass

X

X*

X*†

Cellular Glass

X

X

X*

Perlite or Expanded Silica

X

X

X*

Mineral Fibre

X

X

X

Calcium Silicate

X

X

Refractory Fibre

X

* Indicates temperature range exceeds rating for insulation; in this case the material would be suitable only at the lower end of the temperature range.

†There are some fibre glass products available that can service the lower end of this range.

Table ?2.3.3 - Material Recommendations by System Type for Commercial & Institutional Systems

System

Poly-ethylene

Polyiso-cyanurate

Elasto-meric & foamed plastic

Fibre-glass

Cellular Glass

Perlite or Expanded Silica

Mineral Fibre

Calcium Silicate

Refract-ory Fibre

Plumbing

 

X

X

X

X

X

X

Ducts and housings

X

X

X

X

X

X

Steam and condensate

X

X

X

X

X

X

Outdoor air intake

X

X

X

X

X

X

X

Roof drains
 

X

X

X

X

Hot water heating

X

X

X

X

X

Chilled water

X

X

X

X

X

X

X

Engine exhaust

X

X

X

X

Kitchen exhaust ducts

X

X

Refrigerant suction

X

X

X

X

X

X

X

3. Protective Covering Selection

The efficiency and service of insulation is directly dependent upon its protection from moisture entry and mechanical and chemical damage. Choices of jacketing and finish materials are based upon the mechanical, chemical, thermal and moisture conditions of the installation, as well as cost and appearance requirements.

Protective coverings are divided into six functional types.

Table 2.3.4 - Mechanical Insulation Covering Types and Descriptions

Protective Coverings
WEATHER RETARDERS The basic function of the weather-barrier is to prevent the entry of water, ice, snow or atmospheric residue into the insulation. Sunlight and ozone can also damage certain materials. Applications may be either jacketing of metal or plastic, or a coating of weather barrier mastic. Jacketing must be over-lapped sufficiently to shed water. Avoid the use of plastic jacketing materials with low resistance to ultraviolet rays unless protective measures are taken.
VAPOUR RETARDERS Vapour retarders are designed to retard (slow down) the passage of moisture vapour from one side of its surface to the other. Joints and overlaps must be sealed with a vapour tight adhesive or sealer free of pin holes or cracks. Vapour retarders take three forms:

  1. Rigid jacketing – plastic fabricated jackets[19] to the exact dimensions required and sealed vapour retarding.
  2. Membrane jacketing – laminated foils, treated or coated products and plastic films which are field or factory applied to the insulation material. (Additional sealing beyond the factory seal may be necessary depending on temperature/humidity conditions of the installation.)
  3. Mastic applications – solvent types which provide a seamless coating but require time to dry.
MECHANICAL ABUSE COVERINGS The jacket stiffness and compressibility of the insulation need to be considered together, in order to avoid damage or deteriorating appearance that can potentially arise – e.g., a denting of a jacket on a compressible insulation material.
CORROSION AND FIRE RESISTANT COVERINGS Corrosion protection can be applied to the insulation by the use of various jacket materials. The corrosive atmosphere must be determined and a compatible material selected. Mastics may be used in atmospheres that are damaging to jacket materials (see Section 3).
 
Fire resistance can be applied to insulation systems by the use of jacketing and/or mastics. Fire resistant materials are determined by flame spread, smoke developed and combustibility. The total systems should be considered when designing for fire resistance.
APPEARANCE COVERINGS AND FINISHES Various coatings, finishing cements, fitting covers and jackets are chosen primarily for their appearance value in exposed areas.
HYGIENIC COVERINGS Coatings and jackets must present a smooth surface which resists fungal or bacterial growth in all areas. High temperature steam or high pressure water wash down conditions require jackets with high mechanical strength and temperature ranges.
 

Specific materials have not been recommended for protective covering; commonly, the insulation and jacket must work together as a system to achieve the design goals. Manufacturers of these systems are best qualified to make recommendations, in consideration of the conditions.

 


[19] Note that PVC jacketing would not be suitable for “Living Building” certification, as it would fall on the “Red List”; other jacketing and insulation materials may also fall on this list (see section 2.2.3).