Local temperature measurements on full-size systems in the laboratory: insight into the extent of thermal bridges in building envelope components

Techniques that can be applied during hot box measurement of total system thermal performance provide insight into the extent of thermal bridges and the effectiveness of measures taken to eliminate them. The techniques comprise extensive measurements of local temperatures on surfaces near thermal bridges and substitution of simple elements for complicated elements of the test section construction. Three examples present results of local temperature measurements near thermal bridges in terms of dimensionless ratios (T - T_{air out})/(T_{air in} - T_{air out}). Away from the thermal bridges, the ratios approach 1.0 on the inside of the test section and 0.0 on the outside. How far the ratios are from 0.0 or 1.0 is evidence of the strength of the thermal bridges. Conversely, how close they are to the limits shows the effectiveness of measures taken to eliminate the thermal bridges. Good agreement between local temperature measurements and predictions by three-dimensional models of the construction near the thermal bridges allows models to predict local heat transfer through complicated elements. Rate of heat flow through simple elements can be determined by their known geometry, thermal resistance of their construction materials and measurement of temperature differences across them. By measuring the difference between overall system performance with complicated elements and with simple ones, rate of heat flow through the complicated elements can be determined independently of models.