A well-insulated home can save energy, keeping your house comfortable year round and reducing the need for artificial heating or cooling. But how does insulation actually work?
It works by inhibiting the movement of thermal energy. To do this it restricts heat flow from three sources; conduction, radiation and convection.
Mechanical Engineering
Mechanical insulation protects people and equipment from contact with hot or cold piping and equipment, as well as reducing acoustic levels. It is also often used to control condensation, maintain temperature and reduce energy costs in buildings, factories, power plants, mines, refineries, paper mills, and other industrial facilities.
The science behind this technology is extensive, with a strong foundation in thermal dynamics, fluid dynamics, wave theory, physics and acoustical dynamics. Understanding the physics of heat transfer and flow is critical to insulating systems effectively.
Electrical engineering is another critical field to understand when it comes to mechanical insulation. Insulators are designed to withstand high voltages without breaking down and conducting electricity. This is accomplished by minimizing the amount of energy transmitted through the material. The amount of energy transferred through an insulator is related to its thermal conductivity. This can be measured by a unit called the k-value, or thermal conductivity.
The insulation material selected for a project is dependent on several factors, including the codes and standards that apply, installation methods, environmental considerations, retail considerations, jacketing materials and more. The mechanical insulation design guide discusses these topics in detail and includes helpful information such as a comprehensive list of relevant codes and standards, an informative table that illustrates time required to cool water to freezing based on nominal pipe size and insulation thickness, and an overview of through-penetration fire stops.
Electrical Engineering
Insulation is essential for homes and businesses, reducing energy costs by slowing heat flow from room to room in the home and reducing the movement of hot and cold air through buildings. It also slows the flow of electricity to protect wiring and electronics from high levels of electric currents. Insulation has many uses, spanning across multiple science disciplines such as thermal and fluid dynamics, convection, wave theory, and acoustical dynamics.
The primary job of insulation is to slow the movement of heat, and it does this by trapping tiny particles of air in the material, which prevents the transfer of heat from one point to another. In the home, this keeps warm air from escaping during the winter and cool air from coming in during the summer. In industrial settings, it prevents the transfer of heat, electricity, and moisture.
Electrical insulators are also a critical component of many mechanical applications, such as preventing the mechanical stresses of launch and reentry of spacecraft from damaging the airframe. In these cases, the insulator must be strong enough to resist physical forces that exceed its thermal transfer retardant properties, such as compressive loads and sudden temperature changes.
For example, the fiberglass and foam insulation found in walls and attics in homes and commercial buildings is a great thermal insulator. However, during reentry to Earth’s atmosphere, re-entry velocity is very high, and the foam and fiberglass must be able to withstand this force without deteriorating or breaking apart.
Chemistry
Several kinds of substances can prevent the flow of electrical or thermal currents. These substances are called insulators. In the case of electrical insulators, such as plastics, they block or retard the flow of electric current by making it difficult for electrons to move through the material. Insulators are generally classified according to their ability to resist the flow of heat or electricity, referred to as thermal conductivity or thermal resistance, respectively. Metals are good thermal conductors, while wood and insulating materials have low conductivities.
The three ways that heat travels are conduction, convection and radiation. Thermal insulators stop conduction by blocking the direct contact of atoms or molecules between hot and cold surfaces. They also block convection by interrupting the flow of hot air and gases, and they slow radiant heat transfer by trapping spaces of air or absorbing it.
The insulating qualities of different materials are measured using the R-value, a figure based on the thickness of the insulation and its thermal conductivity. Students can test the insulating qualities of various materials by timing how long it takes for ice cubes to melt in their presence. As the ice cubes melt, they can compare data on their worksheets and write up their conclusions about the best material for insulating purposes. To maximize accuracy, students should check their ice cubes regularly to ensure that the time taken for melting is consistent.
Mathematics
Though insulation might seem like an old-fashioned technology, it draws on many scientific and mathematical principles. Insulation engineers use their knowledge of these concepts to design a structure or space that is effective in slowing the flow of heat, whether it is a building or a room.
Thermal insulation can be constructed from a variety of materials and designs. While most people think of a down jacket as an example of insulation, all forms of insulation work by slowing the transfer of heat. Generally speaking, the best insulation is made of materials with low thermal conductivity, which are also able to trap air or other substances that help slow down the transfer of heat.
All insulation can be compared in terms of R-value, which describes the thickness of an insulating layer and its resistance to heat flow. The higher the R-value, the greater the resistance of the material to heat flow. However, R-value is only one aspect to consider when selecting insulation for a particular application, and the specific material also matters.
To illustrate the importance of these factors, have students conduct a simple experiment. Have students time how long it takes for ice cubes in different beakers to melt. Then, have students identify which insulating material from the different beakers would be best suited to a house in Florida (using their imagination, of course). They should note that they must be precise when placing the insulating material in each beaker, as air has its own insulating properties.