Passive design is any design that uses climate to its advantage and uses it to maintain a comfortable temperature range in a home. Passive design reduces or eliminates all needs for supplementary heating and cooling. Supplementary heating and cooling accounts for around 40% of energy use in the average Australian home. Most passive design revolves around the use of natural sources of heating and cooling, such as the sun or a cool breeze passing by.
It can be achieved by accurately orientating a building or home on its site and carefully designing the building envelope (walls, windows, floors and roofs of a home). A well-designed building or home envelopes minimise all unwanted heat gain or loss. Passive design includes varies form of orientation, shading, passive solar heating, passive cooling, sealing your home, insulation, insulation installation, thermal mass, glazing and skylights. Double glazing refers to windows which have two layers of glass with a space between them, it is designed to reduce loss of heat and exclude noise. Double glazing involves putting an extra layer of glass in front of a window panel. Double glazing can be either installing a sealed glass unit or adding an extra pane, very importantly, the two layers of glass have a very mall air gap between them.
The trapped air in this gap between the two glass layers is an insulator, it does not stop heat from being conducted from the inner pane to the outer pane, it does however, slow heat transfer by conduction considerably. The gap is deliberately too narrow for any air to circulate easily, this reduces the rate of heat transfer by convection. The air which is trapped reduces the rate of heat loss through the window entirely by both conduction and convection, which means that the room in the house will stay warmer for longer. Heat radiates through air and through glass, some of it is reflected and some of it is absorbed, this percentage increases as there is more glass. However, heat transfer overall done by radiation is changed by a double-glazing window slightly. Thermal insulation is the process of forbidding the transfer of thermal energy from one area to another, it can keep an enclosed area warm. Heat is transferred from one material to another by conduction, convection or radiation, as previously stated. Thermal insulators are designed to minimise that transfer of heat energy.
Most insulators are used to prevent he conduction of heat within a home, a good home insulator is a poor conductor. The less dense a material is, the better insulator it will be for a home. This is because the transfer of energy from one atom to the next is more effective, thus gases insulate better than liquids, which insulate better than solids. Since air and water do not conduct heat, they often transfer heat through their motion, this is an example of convection. Insulation from heat transfer by convection is usually completed by either preventing the motion of the fluid or protecting from the convection.
Hot objects radiate infra-red electromagnetic waves, which can heat up objects, insulation against heat transfer by radiation is usually done by using reflective materials. The R-value of a material is its resistance to heat flow and is an indication of its ability to insulate, it has a range from R-10 up to R-30 in homes. Thermal insulation is used to minimise heat transfer in homes, it reduces conduction, convection or radiation effects. All buildings should be designed to use energy efficiently, and to cope with the stresses arising from a changing climate. Passive cooling won’t be enough as climate change advances and cooling loads increase. Designing highly energy efficient buildings is the best way to provide passive sustainability. The source is providing information on the benefits and drawbacks of heat-reflecting low-E light, the author has no intention of selling a product to the viewer.
Along with being up to date, the author uses reliable sources (i.e. NASA) and is a renowned scientific writer and article publisher, as well as an MA in Natural Sciences from Cambridge University. The author provides valid points to someone interested in passive design for a home.
The source uses the electromagnetic spectrum to explain the differences between light and heat, mentioning electromagnetic radiation and waves in the process. The source explains how heat is reflected off the glass panels whilst light passes through the glass. Arguments for and against installing heat reflective windows are present, both sides backed up by scientific theory and research, making the source logical and valid. The source explains the drawback of reflecting heat also means that you lose transmits of light, and the financial differences between low-E glass and regular glass. All the points shown are supported by research and another sources evidence. The source uses two different graphs to express the results of low-E glass (a pie graph and bar graph), the bar graph compares layers of the glass with the heat insulating properties whilst the pie graph compares the percentage of the type of light that reaches the earth, 44% is visible, 3% Ultraviolet, 53% Infrared.
These graphs use scientific evidence, research and results, in order to make them accurate. The graphs accurately shown how the more glazes the low-E glass has, the less heat is transmitted through.
