VARYING INSULATION TYPES
There are many differing forms of insulation currently used in buildings. Table 1 presents data for several of these common insulation types. Thermal conductivity is the ability of material to transfer heat so a lower number is better. N.A. stands for not available. Apart from sheep wool which is cradle to grave (production to disposal), all data is cradle-to-gate (before sent to consumer). A functional unit (f.u.) is defined as mass insulating material required to have a value of 1 (m^2 *K/W) for a one square meter panel [1].
VACUUM INSULATION PANELS
Based solely on thermal resistance, Vacuum Insulation Panels (VIP) have the highest resistance rating. VIPs are made up of a core sealed as a vacuum in several layers designed to keep core undamaged and the vacuum intact [1]. The layers may serve different purposes such as protection of the panel, seal of the core and a radiant heat barrier [1]. These panels boast high resistance but are very costly so they may pose problems being used large scale in a commercial setting. VIPs can have their thermal resistance lowered greatly if the seals are punctured and vacuum within the core is broken [1]. The nature of construction requires panels be made off-site and ordered to size because they cannot be cut without significantly compromising resistance [1]. When room for insulation is narrow, VIPs can be used meet insulation requirements because they have high thermal resistivity with minimal thickness.
FIBERGLASS
Fiberglass, or glass wool, insulation consists of extremely fine glass fibers and is commonly used insulation material [2]. Research has demonstrated the high heat and moisture levels do not greatly affect the insulation ability of fiberglass [1]. Performance remaining constant regardless of heat and moisture make fiberglass a good choice for moist tropical climates. Glass wool is on the high end of environmental impact requiring high energy input to create and releases larger amounts of carbon dioxide in the process. One environmental bonus of fiberglass insulation is the ability to recycle the insulation and create the glass wool initially from recycled glass [1].
STONE WOOL
Stone wool, similar to glass fiber, is made up of fibers of minerals including dolostone, basalt and diabase [1]. Thermal resistance is slightly lower than that of glass wool. Stone wool is a cheaper form of insulation but research has shown that moisture has a negative effect on insulating properties [1]. Stone wool does not require much energy to create and releases low amounts of carbon dioxide during creation. The wool is made-up of seventy-five percent post-industrial recycled content and is naturally resistant to fires. Stone wool can also be recycled [2].
CELLULOSE
Cellulose insulation is created by reducing recycled newspaper into small bits and then treated with borate and other chemicals to add fire, rot and vermin resistance [1,2]. No moisture barrier is required when using cellulose insulation material [2]. Thermal resistance is comparable to fiberglass and stone wool. Insulation properties are hindered when tightly compacted so it is generally blown into place [1]. Energy consumed in creation and carbon dioxide expelled in the process are among the lowest of insulation materials resulting in a low environmental cost. This san be recycled but not composted due to boron salts and chemicals added [1].
COTTON
Cotton insulation is created with recycled cotton fibers treated with borate to achieve fire, rot and vermin resistance [2]. Thermal resistance is lower than fiberglass and cotton generally costs fifteen to twenty percent more [2]. Due to heavy content of recycled material, such as jean trimmings from manufacturing, the energy cost to produce cotton insulation is minimal along with environmental impact [2].
SHEEP WOOL
Wool from sheep is used in insulation and may be freshly harvested or recycled but must be treated with borate similar to cellulose and cotton [1,2]. The thermal resistance of wool is similar to that of cotton and cellulose. Water can get trapped in the wool fibers and thermal resistance will be negatively impacted [1]. Repeated wetting of wool may wash treatment off lowering the lifetime of the insulation. Energy cost is low compared to other insulation materials because little processing is required. The wool can be recycled or reused to reduce negative impact on the environment [1].
POLYSTYRENE
There are two common types of polystyrene used as insulation, expanded and extruded. Expanded polystyrene is created by evaporating pentane added into polystyrene grains [1]. Extruded polystyrene is formed by melting polyester grains into an extruder [1]. The polystyrene insulation mostly takes the form of foam boards. Thermal resistance for both types are nearly identical as seen in Table 1. Polystyrene is easily flammable and releases toxic gases so flame retardants are usually added [1]. Extruded polystyrene absorbs less moisture (.3% vs 2-4%) making it more suitable for wet/humid environments [1]. Despite their similarities, extruded polystyrene costs 10-30% more than expanded [1]. Energy required for production of both is in the middle of the spectrum as well as their carbon dioxide emissions.
POLYISOCYANURATE
Polyisocyanurate is a foam created by a chemical reaction. These foam insulation boards have lower thermal conductivity than polystyrene due to the presence of low conductivity hydrochlorofluorocarbon-free gas in the pores [2]. Gas can slowly leave the pore lowering insulating ability overtime. Material such as foil and plastic can be placed around the panels to keep resistance from dropping [2]. Compared to other foam board insulators, polyisocyanurate has the highest flammability resistance making it a safer choice.
Apart from walls, heat may also be exchanged with the environment through windows. Click the Windows button on the right to learn more.
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Sources:
[1] S.Schiavoni, F. D’Allessandro, F. Bianchi, F. Asdrubali, “Insulation materials for the building sector: A review and comparative analysis,” Renewable and Sustainable Energy Reviews, 62, pp 988-1011. (September 2016). [Online]. http://www.sciencedirect.com/science/article/pii/S1364032116301551
[2] U.S. Department of Energy. "Insulation Materials," [Online], November 22, 2016. Energy Saver. From: http://energy.gov/energysaver/insulation-materials
[1] S.Schiavoni, F. D’Allessandro, F. Bianchi, F. Asdrubali, “Insulation materials for the building sector: A review and comparative analysis,” Renewable and Sustainable Energy Reviews, 62, pp 988-1011. (September 2016). [Online]. http://www.sciencedirect.com/science/article/pii/S1364032116301551
[2] U.S. Department of Energy. "Insulation Materials," [Online], November 22, 2016. Energy Saver. From: http://energy.gov/energysaver/insulation-materials