Insulation Step by Step
The thermal envelope defines the conditioned or living space in a house. The attic or basement may or may not be included in this area. Reducing airflow from inside to outside can help to reduce convective heat transfer significantly. Ensuring low convective heat transfer also requires attention to building construction (weatherization) and the correct installation of insulative materials.The less natural airflow into a building, the more mechanical ventilation will be required to support human comfort. High humidity can be a significant issue associated with lack of airflow, causingcondensation, rotting construction materials, and encouraging microbial growth such as mould and bacteria. Moisture can also drastically reduce the effectiveness of insulation by creating a thermal bridge (see below). Air exchange systems can be actively or passively incorporated to address these problems.Some of the unwanted continuous air exchange with the outside air, which is an artifact of the inherent hysterisis of thermostat control systems, is inevitable. These thermostats typically require the indoor air temperature to cycle 1 to 2 degrees Fahrenheit (about 1 Celsius) as the heating system cycles on and off. Each of these cycles results in a 0.2% to 0.4% volume exchange with the outside air as conditioned envelope air expands and contracts. Thus a 3000 square foot home with 9 foot ceilings having a volume of 27,000 cubic feet and a heating/cooling system cycling every ten minutes will exchange 7700 to 15400 cubic feet in a 24 hr period. This incoming, unconditioned air places an additional load on heating and cooling systems and results in additional costs to energy consumers. Interestingly, the cycling frequency of the heating/cooling system is at maximum when the heating/cooling load equals half the heating/cooling system capacity.
Thermal bridges are points in the building envelope that allow heat conduction to occur. Since heat flows through the path of least resistance, thermal bridges can contribute to poor energy performance. A thermal bridge is created when materials create a continuous path across a temperature difference, in which the heat flow is not interrupted by thermal insulation. Common building materials that are poor insulators include glass and metal.A building design may have limited capacity for insulation in some areas of the structure. A common construction design is based on stud walls, in which thermal bridges are common in wood or steel studs and joists, which are typically fastened with metal. Notable areas that most commonly lack sufficient insulation are the corners of buildings, and areas where insulation has been removed or displaced to make room for system infrastructure, such as electrical boxes (outlets and light switches), plumbing, fire alarm equipment, etc.Thermal bridges can also be created by uncoordinated construction, for example by closing off parts of external walls before they are fully insulated. The existence of inaccessible voids within the wall cavity which are devoid of insulation can be a source of thermal bridging.Some forms of insulation transfer heat more readily when wet, and can therefore also form a thermal bridge in this state.The heat conduction can be minimized by any of the following: reducing the cross sectional area of the bridges, increasing the bridge length, or decreasing the number of thermal bridges.One method of reducing thermal bridge effects is the installation of an insulation board (e.g. foam board EPS XPS, wood fibre board, etc.) over the exterior outside wall. Another method is using insulated lumber framing for a thermal break inside the wall.
Insulating buildings during construction is much easier than retrofitting, as generally the insulation is hidden, and parts of the building need to be deconstructed to reach them.MaterialsMain article: Building insulation materialssee Thermal insulation This topic is all about Thermal and Bulk InsulationThere are essentially two types of building insulation - Bulk Insulation and Reflective Insulation. Most buildings use a combination of both types to make up a total building insulation system. The type of insulation used is matched to create maximum resistance to each of the three forms of building heat transfer - Conduction, Convection, and Radiation.
Conductive and convective insulators ('Bulk insulation')
Bulk insulators block conductive heat transfer and convective flow either into or out of a building. The denser a material is, the better it will conduct heat. Because air has such low density, air is a very poor conductor and therefore makes a good insulator. Insulation to resist conductive heat transfer uses air spaces between fibers, inside foam or plastic bubbles and in building cavities like the attic. This is beneficial in an actively cooled or heated building, but can be a liability in a passively cooled building; adequate provisions for cooling by ventilation or radiation are needed.
Radiant heat barriers
Radiant barrierRadiant barriers work in conjunction with an air space to reduce radiant heat transfer across the air space. Radiant or reflective insulation reflects heat instead of either absorbing it or letting it pass through. Radiant barriers are often seen used in reducing downward heat flow, because upward heat flow tends to be dominated by convection. This means that for attics, ceilings, and roofs, they are most effective in hot climates. They also have a role in reducing heat losses in cool climates. However, much greater insulation can be achieved through the addition of bulk insulators (see above).Some radiant barriers are spectrally selective and will preferentially reduce the flow of infra-red radiation in comparison to other wavelengths. For instance low-emissivity (low-e) windows will transmit light and short-wave infra-red energy into a building but reflect back the long-wave infra-red radiation generated by interior furnishings. Similarly, special heat-reflective paints are able to reflect more heat than visible light, or vice-versa.Thermal emissivity values probably best reflect the effectiveness of radiant barriers. Some manufacturers quote an 'equivalent' R-value for these products but these figures can be difficult to interpret, or even misleading, since R-value testing measures total heat loss in a laboratory setting and does not control the type of heat loss responsible for the net result (radiation, conduction, convection).A film of dirt or moisture can alter the emissivity and hence the performance of radiant barriers.
Eco-friendly insulation is a term used for insulating material or methods used as an alternative to regular insulating material derived from petroleum. The most common and simplest type is known as the earth sheltering insulation method or earth house and annualized geo solar. It has been around for nearly as long as humans have been constructing their shelters, and involves using earth against building walls for thermal mass insulation. Nanogel is another type, consisting of 95% air in nano-sized pores. Greensulate is a type of insulating material that is made of mixture of agricultural by-product with mushrooms grown into it. Heat pump and refrigeration cycle is an alternative to having insulation in the walls of a home. It is a machine that can be used for heating or cooling a house.Some other types of eco-friendly insulation includes minerals like vermiculite which offer great insulation barriers and help improve energy utilization.