Building insulation
Building insulation is material used in a building (specifically the building envelope) to reduce the flow of thermal energy. While the majority of insulation in buildings is for thermal purposes, the term also applies to acoustic insulation, fire insulation, and impact insulation (e.g. for vibrations caused by industrial applications). Often an insulation material will be chosen for its ability to perform several of these functions at once.
Since prehistoric times, humans have created thermal insulation with materials such as animal fur and plants. With the agricultural development, earth, stone, and cave shelters arose. In the 19th century, people started to produce insulated panels and other artificial materials. Now, insulation is divided into two main categories: bulk insulation and reflective insulation. Buildings typically use a combination.
Insulation is an important economic and environmental investment for buildings. By installing insulation, buildings use less energy for heating and cooling and occupants experience less thermal variability. Retrofitting buildings with further insulation is an important climate change mitigation tactic,[1][2] especially when buildings are heated by oil, natural gas, or coal-based electricity. Local and national governments and utilities often have a mix of incentives and regulations to encourage insulation efforts on new and renovated buildings as part of efficiency programs in order to reduce grid energy use and its related environmental impacts and infrastructure costs.
Insulation[edit]
The definition of thermal insulation[edit]
Thermal insulation usually refers to the use of appropriate insulation materials and design adaptations for buildings to slow the transfer of heat through the enclosure to reduce heat loss and gain.[3] The transfer of heat is caused by the temperature difference between indoors and outdoors.[3] Heat may be transferred either by conduction, convection, or radiation. The rate of transmission is closely related to the propagating medium.[3] Heat is lost or gained by transmission through the ceilings, walls, floors, windows, and doors. This heat reduction and acquisition are usually unwelcome. It not only increases the load on the HVAC system resulting in more energy wastes but also reduces the thermal comfort of people in the building. Thermal insulation in buildings is an important factor in achieving thermal comfort for its occupants.[4] Insulation reduces unwanted heat loss or gain and can decrease the energy demands of heating and cooling systems. It does not necessarily deal with issues of adequate ventilation and may or may not affect the level of sound insulation. In a narrow sense, insulation can just refer to the insulation materials employed to slow heat loss, such as: cellulose, glass wool, rock wool, polystyrene, polyurethane foam, vermiculite, perlite, wood fiber, plant fiber (cannabis, flax, cotton, cork, etc.), recycled cotton denim, straw, animal fiber (sheep's wool), cement, and earth or soil, reflective insulation (also known as a radiant barrier) but it can also involve a range of designs and techniques to address the main modes of heat transfer - conduction, radiation, and convection materials.
Most of the materials in the above list only retain a large amount of air or other gases between the molecules of the material. The gas conducts heat much less than the solids. These materials can form gas cavities, which can be used to insulate heat with low heat transfer efficiency. This situation also occurs in the fur of animals and birds feathers, animal hair can employ the low thermal conductivity of small pockets of gas, so as to achieve the purpose of reducing heat loss.
The effectiveness of reflective insulation (radiant barrier) is commonly evaluated by the reflectivity (emittance) of the surface with airspace facing to the heat source.
The effectiveness of bulk insulation is commonly evaluated by its R-value, of which there are two – metric (SI) (with unit K⋅W−1⋅m2) and US customary (with unit °F⋅ft2⋅h/BTU), the former being 0.176 times the latter numerically, or the reciprocal quantity the thermal conductivity or U-value W⋅K−1⋅m−2.
For example, in the US the insulation standard for attics, is recommended to be at least R-38 US units, (equivalent to R-6.7 or a U value of 0.15 in SI units).[5] The equivalent standard in the UK are technically comparable, the approved document L would normally require an average U value over the roof area of 0.11 to 0.18 depending on the age of the property and the type of roof construction. Newer buildings have to meet a higher standard than those built under previous versions of the regulations.
It is important to realise a single R-value or U-value does not take into account the quality of construction or local environmental factors for each building. Construction quality issues can include inadequate vapor barriers and problems with draft-proofing. In addition, the properties and density of the insulation material itself are critical. Most countries have some regime of either inspections or certification of approved installers to make sure that good standards are maintained.
History of thermal insulation[edit]
The history of thermal insulation is not so long compared with other materials, but human beings have been aware of the importance of insulation for a long time.[6] In the prehistoric time, human beings began their activity of making shelters against wild animals and heavy weather, human beings started their exploration of thermal insulation.[6][7] Prehistoric peoples built their dwellings by using the materials of animal skins, fur, and plant materials like reed, flax, and straw, these materials were first used as clothing materials, because their dwellings were temporary, they were more likely to use the materials they used in clothing, which were easy to obtain and process.[6] The materials of animal furs and plant products can hold a large amount of air between molecules which can create an air cavity to reduce the heat exchange.
Later, human beings' long life spans and the development of agriculture determined that they needed a fixed place of residence, earth-sheltered houses, stone houses, and cave dwellings began to emerge.[6][7] The high density of these materials can cause a time lag effect in thermal transfer, which can make the inside temperature change slowly. This effect keep inside of the buildings warm in winter and cool in summer, also because of the materials like earth or stone is easy to get, this design is really popular in many places like Russia, Iceland, Greenland.[6]
Organic materials were the first available to build a shelter for people to protect themselves from bad weather conditions and to help keep them warm.[7] But organic materials like animal and plant fiber cannot exist for a long time, so these natural materials cannot satisfy people's long-term need for thermal insulation. So, people began to search for substitutes which are more durable.[7][8] In the 19th century, people were no longer satisfied with using natural materials for thermal insulation, they processed the organic materials and produced the first insulated panels.[7] At the same time, more and more artificial materials start to emerge, and a large range of artificial thermal insulation materials were developed, e.g. rock wool, fiberglass, foam glass, and hollow bricks.[8]
Significance of thermal insulation[edit]
Thermal insulation can play a significant role in buildings, great demands of thermal comfort result in a large amount of energy consumed for full-heating for all rooms.[9] Around 40% of energy consumption can be attributed to the building, mainly consumed by heating or cooling. Sufficient thermal insulation is the fundamental task that ensures a healthy indoor environment and against structure damages. It is also a key factor in dealing with high energy consumption, it can reduce the heat flow through the building envelope. Good thermal insulation can also bring the following benefits to the building: