A common myth about to determine the thermal resistance

As an architect, you need to design the structure of the wall, in order to meet the code requirements in international energy saving regulations (value of R Or U factor) 。 Therefore, you need to design wall components of R value and add manufacturer statement. Finished yet? If there is no seam wall, juncture, Windows or doors, so this approach makes sense! Let's think about it.

considering thermal discontinuity

if manufacturers use in accordance with ASHRAE 90. 1 term, the manufacturers specified insulated metal plate ( IMP） Should be a central part of the panel of the value of R R value. However, wall made up of many IMP, and IMP between the joints. We all see infrared image shows the panel - everything Plywood, insulation board. 。 。 。 。 。 The heat loss of joint between and IMP. Each IMP is the joint between thermal discontinuity, often referred to as thermal bridge. The R value is not what you read in the manufacturer's literature. And metal clip and accessories can reduce IMP R value of the wall system. If you are designing a wall system, do not specify a panel of R value, and assuming it is wall system R value!

calculate complete IMP system value of R

building owner shall meet or exceed the requirements of the code minimum or U R value factor. Mechanical engineers need according to the building palisade structure & other True & throughout; Characteristics of the right to determine the size of the building mechanical systems.

let's add some Numbers at the idea behind. Let's consider a 42 inches wide panel, 2 inches thick, R value of 12. The outer surface of the panel is close to the outside temperature - For example 30 degrees. Metal package through joint and reduce the panel on the back part of the temperature of the metal, everywhere, all the connectors. Obviously, this reduces the IMP as total R value of the system. Let's estimate, the hot bridge effect of joint will cut down the panel on the edge of the R value by 5 inches to R - 6. This means that the panel has a R - 30 inches 12, 10 inch panel has a R - 6. Calculate the integral panel R value to an average of 10. 5, which more than 12% of the R value loss. This is why blindly use famous R = 1 / U equation is dangerous.

the U factor test can achieve higher precision obviously, panel joint is thermal bridge, but the damage is, in fact, a kind of educated guesses. But there is a solution! Proactive thinking IMP manufacturers are U factor test and finite element modeling, including the connection between the panels. U factor of thermal resistance measurement of the test is more accurate.

as architect design wall system, if you use the R value, then recognize that the joint, you need to consider the loss of the R value. Or, simply specify manufacturers are determine the U factor of IMP panel!