The IL Centre is equipped with sensors inside a wall to demonstrate how insulation works, and how buildings leak and retain heat. The sensor array is located in the third-floor office block. Five thermistors are embedded inside the wall.
The IL Centre also has a cut-away wall demonstration in the Tea Room that shows the wall layers in the building shell. The wall in the cut-away demonstration contains both traditional pink fiberglass batting and brown semi-rigid insulation; the sensor wall only uses semi-rigid insulation.
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The temperature is measured at both the inside and the outside of the slim limestone blocks on the outside facing because the blocks themselves have a thermal mass. It takes them a while to reflect changes in temperature; sometimes in the winter, the outside will be half a degree warmer than the inside, or in the summer it will be the reverse. The thermal mass can hold on to heat energy for hours, sometimes even days.
R-values for the wall materials can then be compared to the wall's actual performance. "R" stands for thermal resistance, and it is calculated based upon the amount of heat that passes through a material over a certain amount of time at a given temperature. R-values are a common construction measurement that is used to describe the efficiency of an insulating material.
The efficiency of any insulation can be seen at extreme temperatures, where the change between inside and outside can vary widely. A thermal mass as large as a building tends to leak heat at a constant rate, so any sharp changes in temperature are smoothed out between each of layer of insulation, as can be seen in the graph on below.
The standard calculation for R-values (in imperial, as are most construction materials) is: R = ( ft2 * °F * h ) / ( BTU ). R-values are additive, so the insulation capability of an entire wall can be calculated if each individual R-value is known.