Given the R-Value and area of a section of a building envelope, it is possible to calculate the rate of heat loss by conduction (in BTUs per hour) through that section at any given temperature difference. The higher the R-Value, the slower the heat flow through the material. R-Value is the inverse of U-Factor (R=1/U). The ability of a material to resist heat flow is measured in R-Value. The higher the U-Factor, the quicker the heat flows. The rate of heat flow through the single pane of glass is more than double that through the double pane. Technically, the U-Factor is the number of BTUs of heat that will flow through one square foot of the material in one hour for each one degree of temperature difference from one side of the material to the other.Ī single pane of glass, for example, has a U-Factor of 1.13. How quickly heat flows through a material is called the material’s U-Factor. A single burning match gives off approximately one BTU of heat. One BTU is equal to the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit. Heat is frequently measured in British Thermal Units (BTU).
Typical insulation materials do not reduce radiation heat loss unless they contain a radiant barrier (such as reflective foil). Even our own bodies radiate a certain amount of heat. The most common example of this is the sun, which radiates heat across space to warm the Earth. Warm objects give off waves of heat, which can travel across an open space and be absorbed by cooler objects. These movements of warm and cold air are known as convection currents, which sometimes move in circles called convective loops. Warm air naturally rises within a space, and colder air falls. The rate at which this heat transfer occurs depends on the temperature difference between the two surfaces and on the thermal When two surfaces at different temperatures are in direct contact, heat will naturally flow from the warmer material to the cooler, until a balance is reached. The principles of applied building science consider how each type of heat flow can affect buildings, equipment, and occupants. Heat flow can occur through three mechanisms: conduction, convection, and radiation. This section examines the basics of heat flow and heat loss, including: A good thermal boundary, which includes insulation, windows, and doors, not only reduces energy waste but greatly increases an occupant’s comfort.
Air leakage and too little or improperly-installed insulation account for a large portion of this. In a typical home, a large portion of all energy consumed is spent on heating and cooling. This introduction defines many of the theories behind the ENERGY STAR New Homes requirements. This introduction focuses on three particular areas:įor each of these issues, the introduction explores causes, control measures, and effects on both buildings and occupants. Many aspects of building design, construction, and operation can affect the health and comfort of the people in the building.