STEEL BUILDINGS - PERFORMANCE OF INSULATION
The primary purpose of thermal insulation is to reduce heat exchange between a surface and the environment, or between two surfaces. If you’re an owner of a steel building, Insulation is one of the best investments you can make. Looking at different kinds of insulation materials available, it is very unlikely that you have not come across references to R-Values, K-Values, and U-Values. These terms are measurements of performance of insulation. This article discusses what these terms mean and why they are important for steel building owners.
Thermal Conductivity (K-Value)
The K-Value or thermal conductivity is the measure of the amount of heat, in BTU’s per hour, that will be transmitted through a one inch (1") thick piece of homogenous material that is one square foot (1 ft2) in size, when there is one degree Fahrenheit (1° F) temperature difference between its surfaces. The equation for "K" is
Thermal Resistance Value (R-Value)
The R-Value is a measure of thermal resistance. It measures the ability of an insulating material to resist heat flow. It is of vital importance for building owners to know the R-Value because some states and regions require a roof system have a minimum amount of thermal resistance on commercial, industrial, and institutional buildings. Simply said, the higher the R-Value, the better the insulator.
R-Values are commonly used in the United States and is equal to the reciprocal of the K-Value. R-Values and K-Values are closely related since they are just different representations of the material’s inherent insulating ability.
Thermal Conductance (C-Value)
The C-Value is a measure of the amount of heat that passes through materials of any thickness. The value of "C" is determined only when the thermal conductivity or "K" is known. The equation for "C" is
The C-Value can also be expressed as
Overall Heat Transmission Coefficient (U-Value)
The U-Value is the measure of overall ability of a complete building section, wall or roof or floor, including air films, to prevent heat loss. It is measured in watts per square meter per degree Celsius (Kelvin)
Based on this, the lower the U-Value, the higher the insulation value of the material.
Calculated Thermal Values
In simple terms, it is the reciprocal of the calculated U-Values. However, by definition, it is the summation of all the R-Values for each of the steel building’s components. Take note that this method of calculation does not consider the thermal short circuit effects of structural members, the number of fasteners used or the compression of the insulation material at its structural members. This method of calculation often indicates heat loss values for building envelops that are lower than those actually present in the finished metal structure.
Surface Air Film Coefficient (F)
The factor F is the amount of heat flow, measured in BTU’s per square foot per hour, between an exposed surface of an insulation material and the adjacent air. It pertains to the measurement of the conductance of heat through the air film that clings to all surfaces.
These concepts are better summarized by the following rules:
• The lower its U-Value, the better insulated a system.
• The higher the R-Value and the lower its C-Value, the higher is the performance of a piece of insulation.
• The lower the K-Value of a piece of insulation material, the higher its insulating value for a particular thickness and given set of conditions.
The actual amount of investment for the steel building’s insulation depends on two factors – the cost of the insulation system to achieve a particular insulating level and the cost of installation. Knowledge of the various terms and measurements used in achieving the desired insulating level will give you an edge in preventing over or under insulation for your steel metal building.