Thermal insulation is a natural or manufactured material that retards or slows down the flow of heat. Manufactured insulation materials can slow the transfer of heat to or from walls, pipe or equipment and can be adapted to many shapes and surfaces such as walls, pipe, tanks or equipment. Insulation also is manufactured in rigid or flexible sheets, flexible fiber batts, granular fill, or open or closed cell foam. A variety of finishes are used to protect the insulation from physical and environmental damage, as well as to enhance the appearance of the insulation.
Archaeology has shown that prehistoric humans used various natural materials as insulation. They clothed or covered themselves with animal furs, wool and skins from animals; built homes of wood, stone and earth; and used other natural materials such as straw or other organic materials to protect against the cold in winter and the heat in summer.
In Medieval times, in the colder northern climates, the walls were stuffed with straw. Mud plaster was mixed with straw to try to keep out the cold. Tapestries were hung on the walls of castles or palaces to fight the drafts between stones as large structures could settle and shift from the weight of the walls. Older buildings were likely cold and drafty places without insulation and sealants against drafts.
Insulation evolved very slowly until 1932, when the process to create fiberglass was discovered by accident. The first finely woven glass fibers, called mineral wool, were produced in 1870 by an inventor named John Player. At first, he did not see the mineral wool fibers as an insulation material; he thought it could be a new fabric that could be used to make warm clothes. At the 1893 World's Fair, Player displayed a dress made from mineral wool fiberglass cloth.
It wasn't until 45 years later, in 1938, when Toledo, Ohio-based Owens Corning Co. produced the first fiberglass insulation. This material was made into blankets (called “batts”) and the company began to market it to help make buildings more efficient and comfortable.
Fiberglass insulation quickly dominated the marketplace as the primary method of insulating homes and buildings. Fiberglass batt insulation had to but cut or torn into tiny pieces to pack into odd-shaped wall spaces tight enough to prevent voids or air drafts that would reduce the insulating effect of the material.
Fiberglass also is used with a paper or plastic jacket to insulate pipe. When insulating cold pipe, it is important to use a vapor barrier on the insulation and tape the joints to prevent moisture intrusion and sweating of condensation in the insulation. Wet insulation allows heat to transfer more efficiently.
Understanding Heat Flow/Heat Transfer
To understand how insulation works, it is important to understand the concept of heat flow or heat transfer. In general, heat always flows from warmer to cooler surfaces. This flow does not stop until the temperature in the two surfaces is equal. Heat is “transferred” by three different means: conduction, convection and radiation. Insulation reduces the transference of heat.
1. Conduction heat flow. Conduction is direct heat flow through solids. It results from the physical contact of one object with another. Heat is transmitted by molecular motion. Molecules transmit their energy to adjoining molecules of lesser heat content, whose motion is thereby increased.
2. Convection heat flow. Convection is the flow of heat (forced and natural) within a fluid. A fluid is a substance that may be either a gas or a liquid. The movement of a heat-carrying fluid or air occurs either by natural convection or by forced convection, as in the case of a forced-air furnace.
3. Radiation heat flow. Radiation is the transmission of energy through space using electromagnetic waves. Radiated heat moves at the speed of light through the air without heating the space between the surfaces.
Comparing Insulation Types
Because so much variation exists in the applications and products for pipe insulation, it’s challenging to make general comparisons among different types of insulation. The best pipe insulation for any given job is largely determined by certain application specifics, rather than product benefits.
Here are some application variables to consider for each insulation installation: Process temperature; Compressive resistance or R-Value; Corrosion; pH; Fire performance; and Water vapor permeability.
Insulation is typically used for one or more of the following functions: Reduce heat loss or heat gain to achieve energy conservation; Increase operating efficiency of HVAC, plumbing, steam, process and power systems; Control surface temperatures for personnel and equipment protection; Control the temperature of commercial and industrial processes; Prevent or reduce condensation on surfaces; Prevent or reduce damage to equipment from exposure to fire or corrosive atmospheres; Assist mechanical systems in meeting USDA (FDA) criteria in food and pharmaceutical plants; Reduce noise from mechanical systems; and Protect the environment through the reduction of CO2, NOx and greenhouse gases.
Mechanical pipe and equipment insulation materials can be used to insulate against heat loss or gain and to protect personnel from high-temperature systems that could cause injury (such as burns) if someone were to touch or be exposed to high-temperature pipe. Insulation is used indoors and outdoors on mechanical systems. It is used in the exterior walls of a building to provide a resistance of heat transfer through exterior walls of a building to reduce the energy required to heat or cool a building.
Insulation alone will not prevent freezing; it just slows down the transfer of heat. Therefore, a heat source must be provided within the building insulation envelope to prevent freezing. Heat tracing is sometimes used on piping systems to prevent freezing; however, in most cases, heat tracing of piping requires thicker insulation than normal to minimize the electrical requirements.
If you are using heat tracing in your design, be careful not to let value-engineering reduce the insulation thickness or the heat tracing may not work properly. Check with the heat-tracing system manufacturer for proper insulation type and thicknesses to avoid warranty issues with the installation.
Using more mechanical pipe and equipment insulation is the easiest way to reduce the energy consumption of the buildings' cooling and heating systems, domestic hot water systems and chilled water supply, and refrigerated systems including ducts and housings. At some point, adding more insulation would be cost-prohibitive; however, significant energy or money can be saved over the life of the building by increasing insulation thickness in most applications.
Developer buildings tend to have minimal or no insulation on branch piping because the developers want to construct a building as inexpensive as possible and sell it to someone else who will eventually pay the utility bills. Energy conservation programs should address this with incentive points for good design and installation practices.
For industrial facilities, such as power plants, refineries and paper mills, mechanical thermal insulations are installed to control heat gain or heat loss on process piping and equipment, steam and condensate distribution systems, boilers, smoke stacks, bag houses and precipitators, and storage tanks. These insulations are typically for personnel protection and to maintain a tenable environment within a factory or workspace.
Benefits of Insulation
1. Energy savings. Substantial quantities of heat energy are wasted daily in industrial plants nationwide because of under-insulated, under-maintained or uninsulated heated and cooled surfaces. Properly designed and installed insulation systems will immediately reduce the need for energy. Benefits to industry include enormous cost savings, improved productivity and enhanced environmental quality.
2. Process heat transfer control. By reducing heat loss or gain, insulation can help maintain process temperature to a predetermined value or within a predetermined range. Again, insulation alone will not prevent freezing. Insulation must work with a heat source to maintain freeze protection. The insulation thickness must be enough to limit the heat transfer in a dynamic system or limit the temperature change, with time, in a static system. The need to provide time for owners to take remedial action in emergencies in the event of loss of electrical power or heat sources is a major reason for this action in a static or nonflowing water system to prevent freezing.
3. Condensation control. Specifying enough insulation thickness and an effective vapor barrier system or insulation jacket is the most effective means of controlling condensation on the membrane surface and within the insulation system on cold piping, ducts, chillers and roof drains.
Enough insulation thickness is needed to keep the surface temperature of the membrane above the highest possible design dewpoint temperature of the ambient air within the building so condensation does not form on the surface of the pipe or insulation and drip onto the ceiling or the floor below. An effective vapor retarder or insulation jacket system is needed to restrict moisture migration into the insulation system through the facing, joints, seams, penetrations, hangers and supports.
By controlling condensation, the system designer may control the potential for: Degrading system service life and performance; Mold growth and the potential for health problems resulting from water condensate; and Corrosion of pipe, valves and fittings caused by water collected and contained within the insulation system.
4. Personnel protection. Thermal insulation is one of the most effective means of protecting workers from second- and third-degree burns resulting from skin contact for more than five seconds with surfaces of hot piping and equipment operating at temperatures above 136.4 F (per ASTM C 1055). Insulation reduces the surface temperature of piping or equipment to a safer level as required by OSHA, resulting in increased worker safety and the avoidance of worker downtime due to injury.
5. Fire protection. Used in combination with other heat sources and materials, insulation helps provide fire protection. It is often used in pipe sleeves or cored openings of fire barriers with firestop systems designed to provide an effective barrier against the spread of flame, smoke and gases at penetrations of fire-resistance-rated assemblies by ducts, pipe and electrical or communication cables.
Grease ducts can catch fire and become red-hot until the grease burns away or the fire is extinguished. Insulation materials on grease ducts prevent the spread of fire to adjacent combustible building materials. Insulation often is used in conduit sleeves or openings of fire barriers with firestop systems designed to provide an effective barrier against the spread of flame, smoke and gases for electrical and communications conduit and cable thru penetration protection.
Commercial insulation applications typically have a Fire Hazard Classification Rating of 25/50 for 1-in. thickness and below when tested according to ASTM E-84 (Standard Method of Test for Surface Burning Characteristics of Building Materials). However, insulation surface burning characteristics are considerably different from one product to another and should be a consideration in choosing a product for a particular application.
ASTM cautions users of any of their standards that the test method may not be indicative of actual fire situations. The ASTM E-84 (Steiner Tunnel test) is the most commonly referred to specification in the industrial and commercial construction markets. It is often referred to even when the model building code does not require it.
The Steiner tunnel test is a widely used method of testing building interior wall and ceiling finishes for their ability to support and propagate fire, and for their tendency to emit smoke. The test was developed in 1944 by Al Steiner of Underwriters Laboratories. The test, which measures flame spread and smoke development, has been incorporated as a reference into North American standards for materials testing as tests ASTM E84, NFPA 255, UL 723 and ULC S102. These standards are in widespread use for the regulation and selection of materials for interior building construction throughout North America.
Other small-scale test methods sometimes referred to are ASTM E162 (Radiant Panel Test) and ASTM E-662 (NBS Smoke Density Test). These are more commonly referred to for mass transit and flooring applications. UL 94 can be required for appliance enclosures and equipment applications.
6. Sound attenuation. Insulation materials can be used in the design of an assembly having a high sound transmission loss to be installed between the source and the surrounding area. Sometimes, insulations with high sound absorption characteristics may be used on the source side of an enclosure to help lower the exposure to people to noise in areas immediately around the noise source by absorption, thereby contributing to the reduction of the noise level on the other side of the enclosure.
7. Aesthetics. Most mechanical insulation systems in commercial construction are not generally visible to the occupants of the building. The common exceptions to this are found in mechanical equipment rooms where the heating equipment, cooling equipment and the associated piping is visible to the personnel who work or otherwise must access these areas.
It is common practice to require a finished and neat appearance for insulation surfaces that are visible within the building envelope. These surfaces may also be painted or covered for a more acceptable appearance in the case of hospitals, schools, supermarkets, restaurants and even in industrial facilities in food processing, and computer component manufacturing where visible to the occupants.
8. Greenhouse gas reduction. Thermal insulation for mechanical systems provides reductions in CO2, NOx and greenhouse gas emissions to the outdoor environment in flue or stack emissions by reducing fuel consumption required at the combustion sites because less heat is gained or lost by the system.
Characteristics of Insulation
Insulations have different properties and limitations depending upon the service, location and required longevity of the application. These should be taken into account by engineers or owners when considering the insulation needs of an industrial or commercial application.
1. Thermal resistance (R) (F ft2 h/BTU). The quantity determined by the temperature difference, at steady state, between two defined surfaces of a material or construction that induces a unit heat flow rate through a unit area. A resistance associated with a material shall be specified as a material R. A resistance associated with a system or construction shall be specified as a system R.
2. Apparent thermal conductivity (ka) (BTU in./h ft2 F). A thermal conductivity assigned to a material exhibiting thermal transmission by several modes of heat transfer, resulting in property variation with specimen thickness or surface emittance.
3. Thermal conductivity (k) (BTU in./h ft2 F). The time rate of steady-state heat flow through a unit area of a homogenous material induced by a unit temperature gradient in a direction perpendicular to that unit area. Materials with lower k factors are better insulators.
4. Density (lb./f3) (kg/m3). This is the weight of a specific volume of material measured in pounds per cubic foot (kilograms per cubic meter).
5. Surface burning characteristics. These are comparative measurements of flame spread and smoke development with that of select red oak and inorganic cement board. Results of this test may be used as elements of a fire-risk assessment which considers all the factors which are pertinent to an assessment of the fire hazard or fire risk of a particular end use.
6. Compressive resistance. This is a measure of the material to resist deformation (reduction in thickness) under a compressive load. It is important when external loads are applied to insulation installation.
Two examples are deforming the insulation on a pipe at a Clevis-type hanger due to the combined weight of the pipe and its contents between the hangers, and resistance of insulation to compress on an outdoor rectangular duct due to heavy mechanical loads from external sources such as wind, snow or occasional foot traffic.
7. Thermal expansion/contraction and dimensional stability. Insulation systems are installed under ambient conditions that may differ from service conditions. When the operating conditions are imposed, metal surfaces may expand or contract differently from the insulation and finish applied. This can create openings and parallel heat flow and moisture flow paths that can degrade system performance.
Long-term satisfactory service requires the insulating materials, closure materials, facings, coating and accessories to withstand the rigors of temperature, vibration, abuse and ambient conditions without adverse loss of dimensions.
8. Water vapor permeability. This is the time rate of water vapor transmission through unit area of flat material of unit thickness induced by the unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions. It is important when insulation systems will be operating with service temperatures below the ambient air. Materials and systems with low water vapor permeability are needed in this service.
9. Cleanability. The ability of a material to be washed or otherwise cleaned to maintain its appearance.
10. Temperature resistance. The ability of a material to perform its intended function after being subjected to high and low temperatures that the material might be expected to encounter during normal use. Insulation alone will not prevent freezing. A supplemental heat source must be used with the proper selection of insulation type and thickness to prevent freezing.
11. Weather resistance. The ability of a material to be exposed for prolonged periods to the outdoors without significant loss of mechanical properties. A supplemental heat source must be used with the proper insulation type and selection of insulation to prevent freezing.
12. Abuse resistance. The ability of a material to be exposed for prolonged periods to normal physical abuse without significant deformation or punctures.
13. Ambient temperature. The dry bulb temperature of surrounding air when shielded from any sources of incident radiation.
14. Corrosion resistance. The ability of a material to be exposed for prolonged periods to a corrosive environment without significant onset of corrosion and the consequential loss of mechanical properties.
15. Fire resistance/endurance. The capability of an insulation assembly exposed for a defined period of exposure to heat and flame (fire) with only a limited and measurable loss of mechanical properties. Fire endurance is not a comparative surface burning characteristic for insulation materials.
16. Fungal growth resistance. The ability of a material to be exposed continuously to damp conditions without the growth of mildew or mold.
Insulation Types and Forms
Mass insulation types include Fibrous Insulation. It is composed of air finely divided into interstices by small diameter fibers usually chemically or mechanically bonded and formed into boards, blankets and hollow cylinders: fiberglass or mineral fiber; mineral wool or mineral fiber; refractory ceramic fiber; and cellular insulation.
It is composed of air or some other gas contained within a foam of stable small bubbles and formed into boards, blankets or hollow cylinders: cellular glass; elastomeric foam; phenolic foam; polyethylene; polyisocyanurates; polystyrene; polyurethanes; polyimides; and granular insulation.
It is also composed of air or some other gas in the interstices between small granules and formed into blocks, boards or hollow cylinders: calcium silicate; insulating finishing cement; and perlite.
Rigid or semi-rigid self-supporting insulation is formed into rectangular or curved shapes: calcium silicate; fiberglass or mineral fiber; mineral wool or mineral fiber; polyisocyanurates; polystyrene; and block.
Rigid insulation is formed into rectangular shapes: calcium silicate; cellular glass; mineral wool or mineral fiber; perlite; and sheet. Semi-rigid insulation is formed into rectangular pieces or rolls: fiberglass or mineral fiber; elastomeric foam; mineral wool or mineral fiber; polyurethane; and flexible fibrous blankets.
A flexible insulation is used to wrap different shapes and forms: fiberglass or mineral fiber; mineral wool or mineral fiber; refractory ceramic fiber; and pipe and fitting insulation.
Pre-formed insulation is used to fit piping, tubing and fittings: calcium silicate; cellular glass; elastomeric foam; fiberglass or mineral fiber; mineral wool or mineral fiber; perlite; phenolic foam; polyethylene; polyisocyanurates; polyurethanes; and foam.