Abstract
Determination of the thermo-physical characteristics of the buildings’ components is crucial to illustrate their thermal behavior and therefore their energy consumption. Along the same line, accurate determination of the thermal resistance of the building walls falls into one the most important targets. Following the difference between in-lab, and on site thermal performance of walls, in-situ measurements have been highly recommended. The most well-known practice for in-situ measurement of walls’ thermal resistance is the Average Method of ISO 9869, using one heat flux meter and two thermocouples. The method, in comparison with other existing methods is quite straight-forward and therefore, is applied widely in large scale. Despite its simplicity, this method usually needs a relatively long time to reach an acceptable result. The current paper deals with a modification to the ISO 9869 method, making it in many situations much quicker than its original state. Through simulation of walls of different typologies, it is shown in which cases the measurement period becomes longer than expected. It is demonstrated how the addition of a heat flux meter to the aforementioned equipment can lead to a much quicker achievement of the thermal resistance, following the rest of the instructions of the standard method.
Highlights
Thermal resistance of the buildings’ exterior walls is a key parameter to determine the thermal behavior of the whole building as well as its energy demand
The specific method being used in large scale campaigns [18, 20] is the “Average Method” by ISO 9869 [12], referred to as “Summation Method” in ASTM [10, 11]
The 3-layered cavity wall has shown a similar behavior to the homogeneous walls where taking the average value of the two Rc-values of indoor and outdoor heat fluxes are of great benefit in terms of time efficiency
Summary
Thermal resistance of the buildings’ exterior walls is a key parameter to determine the thermal behavior of the whole building as well as its energy demand. The method is based on the definition of the long-term average (cumulative) Rc-value In this method, the heat flux at one side (indoor side due to a more stable temperature) and the surface temperature at two sides of a wall are monitored for a relatively long period of time. The index m is the minimum number of time intervals (e.g. one hour) required to fulfill the criteria for reporting the Rc-value The magnitude of this number (duration of the measurement) is a well-known practical obstacle [18] associated with the method. The proposed extension is based on the conservation of energy, and the fact that the sums of the cumulative heat fluxes at two sides of the wall are equal in long term: qt (2). The benefit of using this curve in certain cases is studied
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